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Evaluation of Dynamic Energy
Consumption of Advanced
Water and Wastewater
Treatment Technologies
Subject Area:
Efficient and Customer-Responsive Organization
Evaluation of Dynamic Energy
Consumption of Advanced
Water and Wastewater
Treatment Technologies
©2008 AwwaRF. ALL RIGHTS RESERVED
About the Awwa Research Foundation
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©2008 AwwaRF. ALL RIGHTS RESERVED
Evaluation of Dynamic Energy
Consumption of Advanced
Water and Wastewater
Treatment Technologies
Prepared by:
YuJung Chang, David J. Reardon, Pierre Kwan, Glen Boyd, and Jonathan Brant
HDR Engineering, Inc.
500 108th Avenue NE, Suite 1200, Bellevue, Washington 98004
Kerwin L. Rakness
Process Applications, Inc.
2627 Redwing Road, Suite 340, Fort Collins, Colorado 80526
and
David Furukawa
Separation Consultants, Inc.
13511 Willow Run Road, Poway, California 96064
Jointly sponsored by:
Awwa Research Foundation
6666 West Quincy Avenue, Denver, CO 80235-3098
and
California Energy Commission
Sacramento, CA
Published by:
Distributed by:
©2008 AwwaRF. ALL RIGHTS RESERVED
DISCLAIMER
This study was jointly funded by the Awwa Research Foundation (AwwaRF) and the California Energy Commission
(Energy Commission) under Cooperative Agreement No. CEC-500-03-025. AwwaRF and Energy Commission
assume no responsibility for the content of the research study reported in this publication or for the opinions or
statements of fact expressed in the report. The mention of trade names for commercial products does not represent
or imply the approval or endorsement of AwwaRF or Energy Commission. This report is presented solely for
information purposes.
Copyright © 2008
by Awwa Research Foundation
ALL RIGHTS RESERVED.
No part of this publication may be copied, reproduced
or otherwise utilized without permission.
ISBN 978-1-60573-033-2
Printed in the U.S.A.
©2008 AwwaRF. ALL RIGHTS RESERVED
CONTENTS
LIST OF TABLES......................................................................................................................... ix
LIST OF FIGURES ..................................................................................................................... xiii
FOREWORD ............................................................................................................................... xxi
ACKNOWLEDGMENTS ......................................................................................................... xxiii
EXECUTIVE SUMMARY .........................................................................................................xxv
CHAPTER 1: INTRODUCTION AND OBJECTIVES..................................................................1
Introduction..........................................................................................................................1
Objectives ............................................................................................................................2
CHAPTER 2: LITERATURE REVIEW .........................................................................................3
Summary of Relevant Existing Publications and Studies....................................................3
Industry Standards for Electrical Energy Efficiency ...........................................................4
Ultraviolet Light Disinfection..............................................................................................4
Energy Consumption ...............................................................................................5
Optimizing Energy Efficiency .................................................................................8
Ozone Disinfection ..............................................................................................................9
Energy Use...............................................................................................................9
Optimizing Energy Efficiency ...............................................................................12
Membrane Filtration ..........................................................................................................15
Low-Pressure Membrane Filtration (Ultrafiltration/Microfiltration) ................................16
Energy Use.............................................................................................................16
Optimizing Energy Efficiency ...............................................................................16
Reverse Osmosis................................................................................................................18
Energy Use.............................................................................................................18
Optimizing Energy Efficiency ...............................................................................19
Membrane Bioreactors.......................................................................................................21
Energy Use.............................................................................................................21
Optimizing Energy Efficiency ...............................................................................21
Electrodialysis Reversal.....................................................................................................22
Energy Use.............................................................................................................22
Optimizing Energy Efficiency ...............................................................................23
Summary of Findings.........................................................................................................23
CHAPTER 3: PROJECT APPROACH .........................................................................................25
Identification of ATTs .......................................................................................................25
Energy Audits ....................................................................................................................27
Collection of Data and Information ...................................................................................29
Data Evaluation..................................................................................................................29
Theoretical EC .......................................................................................................29
EC Measurements ..................................................................................................29
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©2008 AwwaRF. ALL RIGHTS RESERVED
Water Quality Correlation......................................................................................30
EC Audit ............................................................................................................................30
Identification of Optimization Opportunities.....................................................................30
CHAPTER 4: EC OF LOW-PRESSURE MEMBRANE SYSTEMS FOR DRINKING
WATER AND REUSE WATER TREATMENT....................................................................31
Process Description Overview...........................................................................................31
Major EC Components ......................................................................................................32
Descriptions and Findings from Case Studies ...................................................................32
Kamloops Centre for Water Quality ......................................................................32
Anthem Water Campus, Anthem, Ariz..................................................................45
Summary and Conclusions for Low-Pressure Membrane Systems ...................................57
Factors Affecting EC of Low-Pressure Membrane Systems .................................57
Considerations for EC Optimization of Low-Pressure Membrane Systems .........60
CHAPTER 5: REVERSE OSMOSIS SYSTEMS FOR DRINKING WATER AND REUSE
WATER TREATMENT ..........................................................................................................61
Process Description Overview...........................................................................................61
Major EC Components ......................................................................................................62
Descriptions and Findings from Case Studies ...................................................................63
Water Replenishment District of Southern California Robert W. Goldsworthy
Desalter ......................................................................................................63
Seward, Nebraska Corrosion Control Plant ...........................................................69
West Basin Municipal Water District (California) Water Recycling Facility.......84
Summary and Conclusions for Reverse Osmosis Systems................................................92
Factors Affecting EC of Reverse Osmosis Systems ..............................................92
Considerations for EC Optimization of RO Systems ........................................................94
CHAPTER 6: EC OF OZONE SYSTEMS FOR DRINKING WATER TREATMENT .............97
Process Description Overview...........................................................................................97
Major EC Components ......................................................................................................98
Descriptions and Findings from Case Studies ...................................................................98
Southern Nevada Water Authority Alfred Merritt Smith Water Treatment
Plant ...........................................................................................................98
Contra Costa Water District (California) Ralph D. Bollman Water Treatment
Plant .........................................................................................................116
Central Lake County Joint Action Water Agency Paul M. Neal Water
Treatment Plant........................................................................................129
Considerations for EC Optimization of Ozone Systems..................................................141
Factors Affecting EC of Ozonation Systems .......................................................141
Considerations for EC Optimization of Ozonation Systems ...........................................144
CHAPTER 7: EC OF UV SYSTEMS FOR DRINKING WATER AND REUSE WATER
TREATMENT .................................................................................................................145
Process Description Overview.........................................................................................145
Major EC Components ....................................................................................................146
Descriptions and Findings from Case Studies .................................................................146
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©2008 AwwaRF. ALL RIGHTS RESERVED
West Basin Municipal Water District (California) Water Recycling Facility.....146
Central Lake County Joint Action Water Agency ...............................................149
Considerations for EC Optimization of UV Systems ......................................................152
Factors Affection EC of the UV Systems ............................................................152
Considerations for EC Optimization of UV Systems ..........................................152
CHAPTER 8: EC OF MEMBRANE BIO-REACTORS FOR WASTEWATER
TREATMENT .......................................................................................................................153
Process Description Overview.........................................................................................153
Major EC Components ....................................................................................................154
Descriptions and Findings from Case Studies .................................................................154
City of Pooler, Georgia Wastewater Treatment Plant .........................................154
Arizona American Water Company Anthem Water Campus..............................167
Considerations for EC Optimization of MBR Systems ...................................................182
Factors Affecting EC of MBR Systems...............................................................182
Considerations for EC Optimization of MBR Systems .......................................186
CHAPTER 9: ELECTRODIALYSIS REVERSAL ....................................................................187
Process Description Overview.........................................................................................187
Major EC Components ....................................................................................................188
Descriptions and Findings from Case Studies .................................................................188
Sarasota County, Florida T. Marbury Carlton, Jr. WTP......................................188
Considerations for EC Optimization of EDR Systems ....................................................194
Factors Affecting EC of EDR Systems................................................................194
Considerations for EC Optimization of EDR Systems ........................................194
CHAPTER 10: GENERAL GUIDELINES FOR EC ANALYSIS AND OPTIMIZATION......195
CHAPTER 11: CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER
RESEARCH...........................................................................................................................203
Conclusions......................................................................................................................203
Recommendations for Further Research..........................................................................206
APPENDIX A:.............................................................................................................................207
REFERENCES ............................................................................................................................221
ACRONYMS AND ABBREVIATIONS ....................................................................................225
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©2008 AwwaRF. ALL RIGHTS RESERVED
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©2008 AwwaRF. ALL RIGHTS RESERVED
TABLES
2.1
Operating characteristics of UV lamps used to disinfect biologically treated
wastewater................................................................................................................6
2.2
Typical energy requirements for various ozone system components ................................10
2.3
Examples of optimization opportunities for ozone processes............................................14
2.4
Anticipated efficiencies of various energy recovery systems............................................19
2.5
Selected operational statistics for the HERO and RO/electrodeionization process...........20
2.6
Summary of ATTs, major components, typical power usage, and common strategies for
optimizing energy efficiently.................................................................................24
3.1
Project partners and roles...................................................................................................25
3.2
Proposed advanced treatment technologies for energy evaluations ..................................26
3.3
Utility partners ...................................................................................................................27
3.4
Activities for each utility group .........................................................................................28
3.5
Participating utilities and ATT by ATT by group .............................................................28
4.1
Raw water quality parameters for the Kamloops WPT from March 1, 2005
to October 31, 2005................................................................................................33
4.2
Waddell Canal water quality parameters ...........................................................................45
4.3
Summary of membrane trains at AWC WTP ....................................................................47
4.4
Comparison of actual AWC WTP energy consumption, by equipment
categories, between months with lowest and highest energy consumption...........51
5.1
Water characteristics for the raw water feed to the Goldsworthy Desalter
treatment plant .......................................................................................................64
5.2
Breakdown of the specific energy consumption at the Goldsworthy Desalter..................66
5.3
Water quality properties of the raw feedwater and RO product water at the
Seward WTP ..........................................................................................................69
5.4
Average monthly specific energy consumption at the Seward Corrosion
Control Plant ..........................................................................................................75
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©2008 AwwaRF. ALL RIGHTS RESERVED
5.5
Secondary effluent quality to West Basin Water Recycling Facility ................................86
5.6
Performance results for the Phase III RO system ..............................................................90
5.7
WBWRF Phase III MF/RO energy consumption breakdown ...........................................91
5.8
Summary of selected average water quality parameters and RO system specific
energy consumption from the three RO WTPs......................................................94
5.9
Typical energy recovery efficiencies for different energy recovery devices.....................95
6.1
VPSA unit oxygen production and specific energy consumption ...................................103
6.2
Potential energy and cost savings analysis for optimization of ozone concentration
during the winter and summer operating periods at the AMS WTP....................115
6.3
Annual average ozone production rate and specific energy consumption data for the
ozone generator and destruction unit ...................................................................123
6.4
Energy consumption and ozone production for the Bollman WTP.................................128
6.5
Summary of selected data for the Paul M. Neal WTP.....................................................133
6.6
Summary of “other” ozone power at the Paul M. Neal WTP..........................................133
6.7
Summary of ozone-related data for the Paul M. Neal WTP ............................................134
6.8
Summary of ozone concentration and specific energy data.............................................135
7.1
Phase IV UV/peroxide advanced oxidation system design requirement .........................147
8.1
Effluent standards for the Pooler WWTP when discharging to a creek ..........................158
8.2
Average specific energy consumption for specific operational periods ..........................161
8.3
AWC WWTP membrane bioreactor characteristics ........................................................167
8.4
Effluent standards for the Anthem AWC WWTP when discharging to a stream ...........171
8.5
Power loads and associated supplies for the AWC WWTP ............................................174
8.6
Summary analysis of the relationship between the specific energy required for various
process equipment and the total system monthly effluent volume ......................180
9.1
Summary of water treatment system performance and specific energy
consumption at the Carlton WTP.........................................................................193
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©2008 AwwaRF. ALL RIGHTS RESERVED
9.2
Potential Reduction in Pumping Associated with Increased Water Recovery ................194
10.1
General list of data required for EC optimization............................................................196
10.2
List of data required for EC optimization for specific ATTs...........................................196
10.3
Example of electrical equipment inventory sheet............................................................197
10.4
Examples of equipment that should be inventoried for specific treatment
processes ..............................................................................................................198
10.5
Performance benchmarks specific to various treatment systems.....................................199
10.6
Areas of emphasis to be considered for the evaluation of specific treatment
processes ..............................................................................................................200
11.1
Comparison of case studies results and literature values for EC and strategies
for optimizing energy efficiency..........................................................................204
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©2008 AwwaRF. ALL RIGHTS RESERVED
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©2008 AwwaRF. ALL RIGHTS RESERVED
FIGURES
2.1
Impact of operating time on UV lamp efficiency ................................................................7
2.2
Possible lamp configurations inflow-through UV disinfection systems..............................9
2.3
Specific energy consumption for air-fed ozone systems operating at varying degrees of
their ozone production capacity .............................................................................11
2.4
Specific energy data for LOX fed ozone generators in comparing UV to ozone energy
uses, estimated ozone power usage of 0.6kW-hr/kgal at an ozone
dose of 12 mg/L .....................................................................................................12
2.5
Ozone facility evaluation approach for assessing energy efficiency .................................13
2.6
Optimized operating ozone concentration curve for an example LOX oxygen-fed
ozone generator......................................................................................................15
2.7
Specific energy consumption as a function of instantaneous water flux for low-pressure
membranes .............................................................................................................17
2.8
General layout of a seawater reverse osmosis (SWRO) treatment system........................18
2.9
Energy required in SWRO to produce a unit volume of treated water..............................19
2.10
Energy consumption for electrodialysis reversal and other processes as a function of
the feed water total dissolved solids content..........................................................22
4.1
General layout for low-pressure water treatment membrane systems ...............................31
4.2
Kamloops Centre for Water Quality process schematic ....................................................34
4.3
Evolution of membrane permeability overtime for Train 1 at the Kamloops water
treatment facility ....................................................................................................36
4.4
Average daily energy consumption by the membrane, DAF, and ancillary chemical
systems as a function of a) and b) permeate production rate at the Kamloops
water treatment facility ..........................................................................................37
4.5
Specific energy consumption by the membrane, DAF, and ancillary chemical systems
as a function of the daily permeate production rate at the Kamloops water
treatment facility ....................................................................................................38
4.6
Average daily energy consumption by the membrane, DAF, and ancillary chemical
systems at the Kamloops WTP as a function of water temperature ......................40
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©2008 AwwaRF. ALL RIGHTS RESERVED
4.7
Specific energy consumption by the membrane, DAF, and ancillary chemical systems
as a function of the raw water temperature at the Kamloops water treatment
facility ....................................................................................................................40
4.8
Correlation between transmembrane pressure and temperature for Membrane
Train 1 prior to membrane system recalibration at two different flux rates
(x-axis scale reversed to emphasize increasing vacuum).......................................41
4.9
Specific energy consumption and water temperature for the period after system
recalibration ...........................................................................................................41
4.10
Raw water turbidity and specific energy consumption by the membrane, DAF,
and ancillary chemical systems over time for the Kamloops WTP .......................43
4.11
Transmembrane pressure (TMP) for the primary membranes (Train 1) as a function of
the influent raw water turbidity..............................................................................43
4.12
AWC WTP process flow schematic ..................................................................................46
4.13
AWC WTP energy consumption by all equipment at the water treatment plant and
water production ....................................................................................................49
4.14
Breakdown of AWC WTP energy consumption by major equipment ..............................50
4.15
Correlation between AWC WTP membrane energy use by the membrane related
equipment only (permeate pump, air scour, cleaning system) and water
production ..............................................................................................................52
4.16
AWC WTP specific energy consumption by the membrane related equipment only
(permeate pump, air scour, cleaning system).........................................................53
4.17
AWC WTP monthly water production and monthly average raw water temperature.......54
4.18
Correlation between Anthem WTP specific energy consumption by the membrane
related equipment only (permeate pump, air scour, cleaning system) and raw
water temperature...................................................................................................55
4.19
AWC WTP specific energy consumption by the membrane related equipment only
(permeate pump, air scour, cleaning system) and average monthly raw water
turbidity..................................................................................................................56
4.20
Specific energy consumption as a function of daily permeate production at the
Kamloops and Anthem WTPs ...............................................................................58
4.21
Specific energy consumption as a function of water temperature at the Kamloops and
Anthem WTPs........................................................................................................59
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4.22
Specific energy consumption as a function of the raw water turbidity at the Kamloops
and Anthem WTPs.................................................................................................60
5.1
General layout for a RO membrane water treatment system.............................................62
5.2
Process flow diagram for the Goldsworthy Desalter treatment plant ................................65
5.3
Comparison of Goldsworthy energy consumption (influent TDS = 2,393 mg/L).............67
5.4
Theoretical specific energy consumption for several new RO and NF membranes as a
function of raw water TDS ....................................................................................68
5.5
Process flow diagram for the Seward, Nebraska Corrosion Control Plant........................69
5.6
Feed and permeate flowrates as well as the corresponding recovery rate for Seward
Corrosion Plant RO Train A measured over the study period ...............................71
5.7
Permeate flowrate as a function of feed pressure for Seward Corrosion Control Plant
RO Trains A and B taken at two different time periods ........................................71
5.8
Seward Corrosion Control Plant feed water and permeate conductivity as a function of
time ........................................................................................................................72
5.9
Estimated total monthly run time for the booster pumps for RO Trains A and B.............73
5.10
Daily maximum run times for the Seward groundwater wells ..........................................74
5.11
Seward energy consumption by different process equipment as a function of the water
production rate .......................................................................................................75
5.12
Seward energy consumption by different process equipment as a function of time .........76
5.13
Seward well production and energy consumption by the corresponding well pumping
systems...................................................................................................................77
5.14
Seward wellfield specific energy consumption for November 2004 through
November 2005......................................................................................................78
5.15
Specific energy consumption for different process equipment at the Seward Corrosion
Control Plant ..........................................................................................................79
5.16
Average monthly specific energy consumption for the RO booster pumps only as a
function of the feed water conductivity .................................................................80
5.17
Average monthly specific energy consumption for the RO booster pumps only as a
function of the feedwater temperature ...................................................................80
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5.18
Monthly water production for the three different well-field areas in the Seward
system ....................................................................................................................82
5.19
Phase III Low-Pressure Boiler Feed Water (LPBF) Production Train Schematic ............87
5.20
Comparison of WBWRF Phase III MF/RO energy consumption .....................................91
5.21
Specific energy consumption by the RO systems as a function of the operating feed
pressure at West Basin, Goldsworthy, and Seward WTPs ....................................93
5.22
Theoretical energy consumption by a pump operating at different flow rates and feed
pressures.................................................................................................................94
6.1
Typical process layout for an ozonation water treatment system ......................................97
6.2
Schematic of the Alfred Merritt Smith WTP oxygen/ozone generators..........................100
6.3
Detailed schematic of the VPSA system used at the AMS WTP ....................................101
6.4
VPSA specific energy consumption with respect to oxygen production rate..................102
6.5
VPAS specific energy consumption with respect to ozone production rate at 8 percent
(by weight) ozone concentration..........................................................................103
6.6
Ozone generator specific energy consumption as a function of ozone concentration
(by weight) ...........................................................................................................104
6.7
Combined specific energy consumption for the VPSA and ozone generators ................104
6.8
Monthly average specific energy consumption for the ozone generator, VPSA system
and the combined specific energy consumption for both ....................................106
6.9
Specific energy consumption for the ozone generator and the VPSA system as a
function of the average daily flow rate per month to the SNWA treatment
plant......................................................................................................................107
6.10
Hourly raw water flowrate measurements for one week period in January 2006
(winter demand period) and June – July 2006 (summer demand period)............108
6.11
Hourly ozone production and dosage for January 2006 (winter demand period)............109
6.12
Hourly ozone production dosage for June/July 2006 (summer demand period) .............109
6.13
Power demand for the ozone generator and the VPSA system during January 2006
(winter) at the SNWA ..........................................................................................110
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6.14
Power demand for the ozone generator and the VPSA system during June 2006
(summer) at the SNWA .......................................................................................111
6.15
Calculated AMS ozone system specific energy consumption as a function of operating
ozone concentration .............................................................................................112
6.16
Calculated AMS ozone system specific energy consumption as a function of operating
ozone production rate...........................................................................................113
6.17
Calculated AMS ozone system specific energy consumption as a function of water
production ............................................................................................................114
6.18
Process flow diagram for the Ralph D. Bollman drinking water treatment plant............116
6.19
Schematic layout of the ozonation system at the Bollman WTP.....................................117
6.20
Average monthly finished water flowrate and ozone production rate at the
Bollman WTP ......................................................................................................118
6.21
Monthly ozone generator gas flowrate and resulting ozone concentration over the
course of the study period at the Bollman WTP ..................................................119
6.22
Monthly average virus inactivation achieved through ozonation at the Bollman
WTP .....................................................................................................................120
6.23
Influent and effluent concentrations of a) Geosmin and b) MIB following ozonation ...121
6.24
Monthly average ozone dose used at the Bollman WTP .................................................122
6.25
Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) measured from 2004 to 2006 .............................123
6.26
Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the finished water
flowrate ................................................................................................................124
6.27
Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the ozone production rate.........125
6.28
Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the ozone concentration
in the gas stream...................................................................................................125
Unit-mass costs in terms of energy required by the ozone generator and LOX
material costs for producing a pound of ozone at the Bollman WTP..................127
6.29
6.30
Simplified schematic diagram of the unit processes at the Paul M. Neal WTP ..............130
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6.31
Simplified schematic diagram of ozone feed gas and generator unit processes ..............131
6.32
Simplified schematic diagram of ozone destruct units ....................................................131
6.33
Monthly ozone production rate at the Paul M. Neal WTP for the operating year
2006......................................................................................................................132
6.34
Specific energy required for producing a unit mass of ozone as a function of ozone
concentration........................................................................................................135
6.35
Specific energy consumption (kWh/lb O3) for the ozonation system as a function of
the corresponding ozone production rate for the operating year 2006 ................136
6.36
Specific energy consumption by the total water treatment plant as a function of the
ozone dose............................................................................................................137
6.37
Specific energy consumption by the total water treatment plant as a function of raw
water turbidity......................................................................................................138
6.38
Specific energy consumption by the total water treatment plant as a function of the
average monthly temperature...............................................................................139
6.39
Specific energy consumption by the total water treatment plant as a function of the
finished water flowrate ........................................................................................140
6.40
Specific EC for the total ozonation system as a function of ozone concentration for
the Contra Costa, SNWA, and Central Lake County WTPs................................142
6.41
Specific energy consumption for the total ozonation system as a function of the
average daily flowrate at the Contra Costa, SWNA, and Central Lake
County WTPs.......................................................................................................143
6.42
Ozonation system specific energy consumption as a function of ozone production
rate for the Contra Costa, SNWA, and Central Lake County WTPs ...................144
7.1
General layout of a UV disinfection system ....................................................................145
7.2
Estimated range of Phase IV UV/peroxide system electrical load ..................................148
7.3
Estimated range of specific energy consumption of Phase IV UV/peroxide system ......148
7.4
Average daily flowrate and corresponding number of UV reactors in operation at the
Paul M. Neal WTP over the course of this study period .....................................150
7.5
Specific energy consumption by the UV system at the Paul M. Neal WTP as function
of flowrate............................................................................................................151
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8.1
General system layout for a membrane biological reactor (MBR) wastewater
treatment system ..................................................................................................153
8.2
Process schematic for the Pooler WWTP ........................................................................156
8.3
Influent and effluent BOD5 concentrations to the Pooler WWTP...................................158
8.4
Influent and effluent TSS concentrations to the Pooler WWTP......................................159
8.5
Average monthly energy consumption and corresponding effluent flowrates at the
Pooler WWTP......................................................................................................160
8.6
Monthly energy consumption as a function of the effluent flowrate at the Pooler
WWTP .................................................................................................................160
8.7
Specific energy consumption for the total wastewater treatment system at the Pooler
WWTP .................................................................................................................161
8.8
Specific energy plotted as a function of the average monthly flowrate at the Pooler
WWTP .................................................................................................................162
8.9
Monthly specific energy consumption plotted as a function of the average monthly
influent BOD5 concentration to the Pooler WWTP MBR system.......................163
8.10
Monthly specific energy consumption plotted as a function of the average monthly
influent TSS concentration to the Pooler WWTP system....................................163
8.11
Energy consumption by membrane bioreactor relative to the total energy consumption
at the treatment plant............................................................................................165
8.12
Specific energy consumption by the different MBR related equipment during
different months of the study-period....................................................................165
8.13
Process schematic for the AWC Wastewater Treatment Plant........................................168
8.14
Schematic drawings of the bioreactors used at the AWC WWTP...................................169
8.15
Influent and effluent BOD5 concentrations to the MBR system at the AWC WWTP ....172
8.16
Influent and effluent TSS concentrations to the MBR system at the AWC WWTP .......173
8.17
Monthly energy consumption at the AWC WWTP.........................................................175
8.18
Monthly specific energy consumption at the AWC WWTP ...........................................176
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8.19
Monthly effluent flowrate and total treatment system energy consumption for the
AWC WWTP .......................................................................................................177
8.20
Energy consumption by the treatment system as a function of the volume of treated
effluent at the AWC WWTP................................................................................178
8.21
Specific energy consumption for the treatment system as a function of the total
volume of wastewater treated per month .............................................................179
8.22
Specific energy consumption plotted as a function of the average monthly raw water
influent BOD5 concentration................................................................................181
8.23
Specific energy consumption by the treatment system as a function of the monthly
average influent TSS concentration .....................................................................181
8.24
Specific energy consumption for the total MBR systems at the Anthem and Pooler
WWTPs as a function of the effluent flowrate ....................................................183
8.25
Average specific energy consumption by the permeate pumps at the Anthem and
Pooler WWTPs ....................................................................................................184
8.26
Specific energy consumption for the MBR systems at the Anthem and Pooler
WWTPs as a function of the influent a) TSS concentration and b) the BOD5
levels ....................................................................................................................185
9.1
General layout of an EDR membrane stack.....................................................................187
9.2
Sarasota County, Florida Carlton WTP process schematic .............................................189
9.3
Schematic of the EDR stack configuration at the Carlton WTP......................................190
9.4
Historical raw and finished water a) TDS and b) turbidity for the Carlton WTP............191
9.5
Monthly average daily energy consumption for the Carlton WTP..................................192
10.1
General procedure for planning and performing an EC analysis at water and
wastewater treatment plants.................................................................................195
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©2008 AwwaRF. ALL RIGHTS RESERVED
FOREWORD
The Awwa Research Foundation is a nonprofit corporation that is dedicated to the
implementation of a research effort to help utilities respond to regulatory requirements and
traditional high-priority concerns of the industry. The research agenda is developed through a
process of consultation with subscribers and drinking water professionals. Under the umbrella of
a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projects
based upon current and future needs, applicability, and past work; the recommendations are
forwarded to the Board of Trustees for final selection. The foundation also sponsors research
projects through the unsolicited proposal process; the Collaborative Research, Research
Applications, and Tailored Collaboration programs; and various joint research efforts with
organizations such as the U.S. Environmental Protection Agency, the U.S. Bureau of
Reclamation, and the Association of California Water Agencies.
This publication is a result of one of these sponsored studies, and it is hoped that its
findings will be applied in communities throughout the world. The following report serves not
only as a means of communicating the results of the water industry’s centralized research
program but also as a tool to enlist the further support of the nonmember utilities and individuals.
Projects are managed closely from their inception to the final report by the foundation’s
staff and large cadre of volunteers who willingly contribute their time and expertise. The
foundation serves a planning and management function and awards contracts to other institutions
such as water utilities, universities, and engineering firms. The funding for this research effort
comes primarily from the Subscription Program, through which water utilities subscribe to the
research program and make an annual payment proportionate to the volume of water they deliver
and consultants and manufacturers subscribe based on their annual billings. The program offers
a cost-effective and fair method for funding research in the public interest.
A broad spectrum of water supply issues are addressed by the foundation’s research
agenda: resources, treatment and operations, distribution and storage, water quality and analysis,
toxicology, economics, and management. The ultimate purpose of the coordinated effort is to
assist water suppliers in providing the highest possible quality of water economically and
reliably.
David E. Rager
Chair, Board of Trustees
Awwa Research Foundation
Robert C. Renner, P.E.
Executive Director
Awwa Research Foundation
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©2008 AwwaRF. ALL RIGHTS RESERVED
ACKNOWLEDGMENTS
The authors would like to acknowledge the gracious support of the Awwa Research
Foundation (AwwaRF) without whose support, this project would not have been possible.
The authors wish to extend their thanks and appreciation to Linda Reekie AwwaRF
Project Manager and the following AwwaRF Project Advisory Committee members for their
expertise and constructive guidance and contributions throughout the project:
• Paul Roggensack, California Energy Commission
• Joanne Daugherty & Shivaji Deshmukh, Orange County Water District
• Dave Huey, Contra Costa Water District
• Omar Moghaddam, Los Angeles Bureau of Sanitation
• Mike Stenstrom, University of California, Los Angeles
Several utilities, agencies, and companies from across the country provided significant
time, staff, and expertise, as participants in the project’s Expert Workshop. The authors
gratefully acknowledge their efforts:
•
•
•
•
•
•
•
•
•
•
•
West Basin Municipal Water District, CA
Contra Costa Water District, CA
Water Replenish District, CA
Arizona American Water Company, AZ
Southern Nevada Water Authority, NV
City of Pooler, GA
Sarasota County, FL
Central Lake County Joint Action Water Agency, IL
City of Kamloops, British Columbia, Canada
Zenon/GE Water Process and Technologies
Trojan Technologies
The authors would also like to extend a special thanks to California Energy Commission
who provided a financial contribution to the project. Finally, we would like to thank Julie Self
for her efforts in preparing the final report.
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EXECUTIVE SUMMARY
PURPOSE AND OBJECTIVE
The purpose of this study was to evaluate factors that affect energy consumption (EC) by
advanced water/wastewater treatment technologies and to identify energy optimization
opportunities while maintaining treatment performance. While equipment costs have been
decreasing as a result of technological advancements, the cost of energy continues to rise. At
water and wastewater treatment facilities, high EC is typically associated with inefficient
equipment and operations, over design of pumps and processes, and, in many cases, a lack of
understanding of energy conservation measures (ECMs). These problems can be exacerbated for
advanced treatment systems, which tend to be more energy intensive than conventional
technologies.
RESEARCH APPROACH
The research approach for this project consisted of the following major activities:
1) identification of advanced treatment technologies (ATTs) for inclusion in this study;
2) development of a standard framework for evaluating EC and efficiency of ATTs;
3) performance of energy audits of selected ATT installations; 4) analysis of data and
identification of energy optimization opportunities; and 5) development of general guidelines for
EC analysis and optimization.
As part of a project kickoff meeting conducted in December 2005, members of the
Project Partners in consultation with the AwwaRF Project Manager and Project Advisory
Committee identified the following ATTs for inclusion in this study:
• Ultraviolet light disinfection
o Drinking water primary disinfection
o Advanced oxidation with UV/peroxide
• Ozonation
o Vapor/pressure-swing adsorption
o Liquid oxygen
o Ambient air
• Membrane processes
o Microfiltration
o Ultrafiltration
o Reverse osmosis
o Membrane bioreactors
o Electrodialysis reversal
The ATTs listed above were determined to have the greatest impact on EC based on the
following criteria:
• The ATT has broad application potential for meeting water and/or wastewater
treatment requirements.
• The treatment performance of the ATT is proven, well understood, and well
documented based on results from operating installations.
• The ATT is commercially available from more than one manufacturer/supplier.
• The ATT can have a notable energy demand.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Case studies were developed based on the availability of 14 water and wastewater
treatment utilities located throughout the US and Canada that were using one or more of the
selected ATTs listed above. A standard framework was developed for analyzing, evaluating and
comparing EC and efficiency data for the selected ATTs. The framework for this project
consisted of the following activities:
• Grouping of utilities
• Data and information collection
• Analysis and theoretical energy efficiency and correlation of EC with water quality
• EC audit
• Identification of optimization opportunities
Standard units of measurement were also established for quantifying energy data. For the
purpose of comparing the selected ATTs, energy consumption (EC) was expressed in units of
kilowatt hours per 1000 gallons (kWh per 1000 gal).
The specific level of research activities that were conducted at each treatment facility was
determined by the designated “utility group”. Table ES-1 provides a summary of the
participating utilities, the designated group for each utility, definitions for each utility group, and
comments about the selected ATTs.
Table ES-1
Participating utilities, designated utility group, and selected ATTs
Utility
Southern Nevada Water Authority,
NV
Utility
Group*
1
Water Replenishment District of
Southern California, CA
West Basin Municipal Water
District, CA
Sarasota County, FL
City of Seward, NE
1
Arizona American Water
Company, Anthem Water Campus
City of Pooler, GA
City of Kamloops, BC
2
2
2
Contra Costa Water District, CA
2
Central Lake County Joint Action
Water Agency, IL
3
1
1
2
Selected ATTs and Comment
Utility partner with largest ozone installations. Two
different ozone installations; one installation included
in this study.
Brackish water RO desalination facility
Water reuse facility, multiple ATT at site (MF, RO,
UV)
Only utility partner with an EDR facility
Groundwater RO facility that is smaller than Group 1
RO facilities
Smaller than Group 1 MBR and low-pressure facility
Smallest MBR facility
One low-pressure membrane facility already in
Group 1
Two ozone installations; one installation included in
this study.
Potable water treatment facility using UV light
disinfection.
*Activities for each utility group were defined as including the following:
1. Collection of data and information; analysis of historical energy efficiency and correlation of EC with water quality;
performance of EC audit; and identification of optimization measure.
2. Collection of data and information, analysis of historical energy efficiency, and correlation of EC with water quality. If
schedule permitted, optimization measures were identified.
3. If scheduling permitted, activities included one or more of the activities in Group 2.
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FINDINGS AND CONCLUSIONS
Table ES-2 provides a summary of results of the specific EC values that were determined
for the targeted ATTs based on the case studies conducted as part of this study. Also included in
Table ES-2 are summaries of the factors affecting specific EC values. In general, these findings
indicate that UV and ozone disinfection processes exhibited the lowest specific EC values in the
range of 0.02 to 0.16 kWh per 1000 gal whereas pressure-driven processes (ultrafiltration,
reverse osmosis, membrane bioreactors, and electrodialysis reversal) exhibited higher specific
EC values ranging from 0.5 to 7.5 kWh per 1000 gal. For most processes (with the exception of
UV disinfection), case study results indicate a decreasing specific EC with increasing flowrate
and, in nearly all case studies, energy efficiency potentially could be optimized by operating near
design capacity.
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Table ES-2
Results of case studies for EC values and strategies for optimizing energy efficiency
Specific Energy
Consumption
(kWh per 1000
gal)1
ATT
Process or
Component
UV
disinfection
Mediumpressure
lamp system
0.02-0.09
LOX feed
0.02-0.053,6
Ozone
disinfection
Reverse
osmosis
0.06-0.08
Ambient air
feed
0.11-0.165,6
Pumps, air
scour,
cleaning
system
Feed pumps
Membrane
bioreactors
Pumps,
blowers
Electrodialysis
Reversal
Electrified
membrane
plates
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
4
VPSA feed
0.5-1.07
Microfiltration/
Ultrafiltration
2
0.4-0.78
0.5-4.8
9
3.0-7.510
4.3
11
Factors Affecting EC
Optimizing Energy Efficiency
Specific EC decreases with
increasing flow rate (15-40
mgd) and total number of
operating reactors (1-3).
Operate at or near flow capacity.
Ozone concentration
affects all ozone systems
(LOX, VPSA, and ambient
air).
Operate at or near design ozone
concentration.
Production rate
Pretreatment also affects
specific EC. For example,
addition of coag and floc
reduced specific EC related
to pumping whereas
addition of PAC increased
specific EC.
Reconfigure re-circulating lines
and other operational
improvements
Specific EC increases
linearly with feed pressure
Pre-blending, improved pump
operating efficiency, new
membrane materials, and energy
recovery systems.
Air scour blowers represent
approximately 40 percent
of total specific EC
whereas permeate pumps
and aeration blowers
account for 3 to 5 percent.
Specific EC for permeate
pumps depend on
membrane pore size.
Fixed energy consumption
(e.g., building HVAC,
mixers, etc.) is considered
small relative to EDR.
More data would be needed
to determine effects of
TDS or other parameters.
Minimize the frequency of air
scour.
Although insufficient data
available, improved efficiency
potentially could be achieved by
operating near design recovery.
Based on values collected per utility case studies as described in Chapters 4 through 9.
Central Lake County Joint Action Water Agency
Contra Costa Water District, California
Southern Nevada Water Authority
Central Lake County Joint Action Water Agency
Represents EC for ATT only.
Kamloops Centre for Water Quality
Anthem Water Campus, Arizona
Based on operating feed pressures at West Basin, Goldsworthy, and Seward WTPs.
Based on total MBR systems at the Anthem and Pooler WWTPs.
Average based on 3 months of production data at Sarasota County, Florida.
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One notable observation during this study is that despite a high level of interest in
understanding EC by advanced treatment processes, the level of EC monitoring capability varied
greatly amongst the participating utilities. While a few utilities can monitor EC for each major
piece of equipment and log all of the EC data, some utilities have very limited or no monitoring
capability for EC.
The first opportunity for optimizing EC is during the planning and design phase of the
implementation stage. Appropriate engineering design, equipment specification, and operation
strategy can be incorporated into the design. Once the plant is built, any modification in system
operation for the purpose of EC optimization may require collaboration with the equipment
provider so that equipment warranty can be maintained. Also, it should be noted that optimizing
treatment process energy consumption is only one of many system operational objectives. Other
important factors, such as operation flexibility, process reliability, and system redundancy should
also be considered along with the benefits of optimizing treatment energy consumption.
RECOMMENDATIONS FOR FURTHER RESEARCH
Based on the findings of this study, the following topics are suggested for further
research with the goal of optimizing energy efficiency of treatment systems:
• Contrary to conventional expectations, case studies on MBR systems revealed lower
pressure requirements for smaller mean pore size membranes compared to larger
mean pore size. It would therefore be beneficial to assess the effects of other
membrane characteristics (e.g., thickness and hydrophobicity) on pumping
requirements for MBR systems in water and wastewater treatment applications.
• Case studies demonstrated that air scour accounted for roughly 40 percent of the total
specific EC at MBR treatment facilities. Research is needed to determine which
factors (e.g., membrane properties and configuration) could be improved to decrease
the frequency and duration of air scour cycles in MBR facilities. Research could also
be conducted to determine how biofouling can be reduced to optimize energy
consumption.
• Case studies demonstrated that temperature was a minor factor affecting RO
performance whereas TDS had a notable influence on specific EC. More study could
be conducted to assess temperature ranges that have the greatest influence on RO
systems and possible mitigation measures (e.g., heating systems) for improving
energy efficiency.
• Advancements are continuing in the design of membrane configurations (e.g., spiral
wound versus hollow fiber), element design (e.g., 16-inch module versus 8-inch
module), and system design (e.g., 3-Center design concept). It would be valuable to
determine how these design changes affect the energy efficiency of a given
membrane system.
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©2008 AwwaRF. ALL RIGHTS RESERVED
CHAPTER 1
INTRODUCTION AND OBJECTIVES
INTRODUCTION
Water and wastewater systems have been estimated to account for 4 percent of the total
electricity demand in the United States (US) (EPRI 2002). As a particularly extreme example,
water systems in California are estimated to use about 7 percent of the state’s electricity (QEI,
INC. 1992). In 1998, the American Water Works Service Company surveyed 109 drinking
water plants, ranging in size from less than 1 mgd to over 70 mgd. The average power usage per
million gallons of water treated for these plants was 2240 kWh/MG, with the range being 338 to
4500 kWh/MG (Arora and LeChevallier 1998). Many of the systems surveyed in this study used
conventional water treatment technologies. These results may therefore not adequately
characterize future utilities which are increasingly turning to more advanced technologies. This
is because the demand for water from a growing population is rapidly outstripping the available
supply from high quality water sources, so agencies are turning to lower quality sources of
supply. To treat these waters, while at the same time meeting more stringent drinking water
regulations, agencies are implementing more sophisticated and energy intensive advanced
treatment technologies (ATTs). Examples of ATTs being used or considered for both water and
wastewater applications include ozonation, ultra violet (UV) disinfection, and membrane
processes.
Energy consumption (EC) is of particular concern due to the rising cost of electricity.
While equipment costs have been decreasing as a result of technological advancements, the cost
of energy continues to escalate. For example, due to significant reductions in membrane
equipment and material costs over the last 20 years, EC is now the second largest fraction of unit
water cost (capital recovery represents the largest fraction) in RO applications. For example, at a
recently constructed RO plant at Point Lisas, Trinidad, energy represents 23 percent of the total
treatment cost. Given the increasing application of membrane processes, in addition to other
advanced technologies, it is prudent to understand their energy requirements and to determine
applicable optimization strategies.
In general, EC is typically high at water and wastewater treatment plants for a number of
reasons, including: use of inefficient equipment, over design of pumps and processes, operation
of equipment at maximum capacities to maintain predetermined safety factors, and in many cases
a lack of understanding of energy conservation measures (ECMs). These problems are
exasperated for more advanced treatment systems, which tend to be more energy intensive than
conventional technologies. Improving the energy efficiency of both conventional and advanced
treatment systems requires that a comprehensive understanding of the EC by the different
equipment be developed. This understanding may be realized through an energy audit (Reardon,
1995a). In an energy audit the processes are described in detail to identify key sources of EC.
The operating conditions are then characterized to understand how they are influencing process
EC. Based on these results it is possible to develop ECMs in which strategies are outlined for
improving energy efficiency.
Key to improving the energy efficiency of ATTs, is understanding several important
characteristics including: what are the primary energy consuming equipment and what factors
(water quality and operating parameters) are influencing EC? Because the emergence of many
ATTs is relatively recent, particularly with respect to their application in full-scale treatment
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systems, little information is available on their EC characteristics. This effort represents one of
the first to characterize the EC characteristics of a variety of popular ATTs used in both water
and wastewater treatment systems.
OBJECTIVES
This project was conducted to meet three overall objectives: 1) describe the EC
characteristics of different ATTs; 2) evaluate the factors that affect EC by these ATTs; and
3) identify feasible energy optimization measures for each ATT. Selection of the ATTs for study
was based on the degree of application (popularity) in drinking water and wastewater utilities.
Those ATTs that were selected for analysis in this study include:
• Ultraviolet light disinfection
o Drinking water primary disinfection
o Advanced oxidation with UV/peroxide
• Ozonation
o Vapor/pressure-swing adsorption
o Liquid oxygen
o Ambient air
• Membrane processes
o Microfiltration
o Ultrafiltration
o Reverse osmosis
o Membrane bioreactors (MBRs)
o Electrodialysis reversal (EDR)
Case studies were developed based on 14 water and wastewater treatment utilities located
throughout the US and Canada that were using one or more of the ATTs selected for study. A
standard framework was developed for evaluating EC and efficiency data. Energy audits were
also conducted for selected ATT installations. Results were analyzed and energy optimization
opportunities were identified. Based on results of this study, conclusions, recommendations and
general guidelines were developed for performing site-specific EC analysis and optimization
studies.
This project evaluated many different ATTs, but not all ATTs (even those in the same
category) have the same basis of technology, operation criteria, and EC monitoring capability.
Therefore, results from this study do not intend to serve as benchmarks for the types of ATT
evaluated. Those data should be considered as a general spot-check on the actual energy
consumption by the ATTs.
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©2008 AwwaRF. ALL RIGHTS RESERVED
CHAPTER 2
LITERATURE REVIEW
SUMMARY OF RELEVANT EXISTING PUBLICATIONS AND STUDIES
Previous studies on the EC characteristics of water and wastewater treatment industries
have generally focused on a broader assessment of energy management (Reardon et al. 1987a
and 1987b; Reardon, 1995b). There is also a wide range of information on ATTs with respect to
treatment performance, design considerations, and operations and maintenance. However, there
has been little published information that specifically addresses the energy efficiency and
optimization aspects for ATTs. There are however, several published reports from various
research agencies that address the needs for such information. The Public Interest Energy
Research (PIER) Program, managed by the California Energy Commission, Electric Power
Research Institute (EPRI), and Awwa Research Foundation (AwwaRF) have initiated and/or
sponsored recent projects focusing on energy management for water and wastewater treatment
systems and plants.
EPRI published a guidance document entitled “Energy Audit Manual for
Water/Wastewater Facilities” (Reardon, 1994). The purpose of this document was to provide an
overview of the relationship between specific unit processes and energy demands and
conservation. It provides general guidance for conducting energy audits to identify ECMs,
primarily for pumping systems and conventional treatment processes (coagulation,
sedimentation, and granular media filtration). One ATT that is addressed in this report is
ozonation.
A report entitled “Quality Energy Efficiency Retrofits for Wastewater Systems” (EPRI
1998) addressed a wide variety of energy uses within wastewater treatment plants, several of
which (variable-frequency drives (VFDs), energy-efficient motors, and pumping station
modifications) apply indirectly to advanced treatment processes. However, the only advanced
treatment process addressed directly in this report was UV-disinfection. In the discussion on
UV-disinfection the report does not address how system design and operation affect process EC.
Furthermore, little information was provided for energy optimization in UV systems.
AwwaRF and the EPRI Community Environmental Center commissioned a series of
projects to define Energy and Water Quality Management Systems (EWQMS) to help address
energy optimization and energy-cost minimization. As part of this initiative, EPRI published “A
Total Energy and Water Quality Management System,” (EPRI 1999), the objective of which was
to develop a generic model for EWQMS. The purpose of EWQMS is to establish a plan for
operating a utility’s system that delivers the quantities needed to customers, meets the water
quality requirements, and minimizes the net cost of energy consumed. There are many factors
that input into the EWQMS process, only one of which is EC by the treatment processes.
Therefore, while the EWQMS provides a good overall framework for optimization of energy use
in relation to water supply and quality, it was not designed to specifically evaluate energy
efficiencies of specific treatment processes.
The EPRI (2001) report “Summary Report for California Energy Commission Energy
Efficiency Studies,” presented the findings of four energy assessments. The assessments were
performed at two large water treatment plants and two large wastewater treatment plants. The
purpose of these assessments was to identify ECMs and electrotechnologies that can reduce EC
or improve the treatment process efficiency. Five different types of ECMs were identified at the
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©2008 AwwaRF. ALL RIGHTS RESERVED
water plants and eight ECM types were identified at the wastewater plants. The ECMs included
a broad range of measures, including such things as lighting retrofits, load shedding, and
equipment modifications. These assessments appear to have little information that is directly
relevant to energy optimization for advanced treatment processes. However, one interesting
outcome of the assessments is that an overall “unit EC” value was calculated for each plant. For
instance, one of the water plants had a unit EC value of 446 kWh/MG (0.4 kWh/kgal) of water
produced, while one of the wastewater plants had a value of 2,263 kWh/Mgal (2.3 kWh/kgal) of
water treated. Overall unit EC values for a given plant may serve as a good benchmark for
evaluating EC of specific unit treatment processes.
The purpose of the 2003 report “Water and Wastewater Industry Energy Efficiency: A
Research Roadmap,” (Means III 2003) was to provide direction for research and development
activities. The Roadmap identified eight primary research topics where potentially significant
energy savings could occur. These eight research topics included advanced treatment processes,
energy optimization, and total energy management. The suggested research topics included
various aspects and applications of UV disinfection, catalytic advanced oxidation, ozonation, and
membrane filtration.
Because the federal government is the single largest energy consumer in the US, the US
Department of Energy established the Federal Energy Management Program (FEMP) to sponsor
activities and investigations to reduce EC at federal installations. The FEMP has prepared
several publications as part of its New Technology Demonstrations program including some for
advanced water/wastewater treatment processes. For instance, one recent publication focused on
high efficiency RO and is discussed in the RO section below.
INDUSTRY STANDARDS FOR ELECTRICAL ENERGY EFFICIENCY
Currently, there are no accepted energy efficiency standards for ATT systems. However,
one important industry standard for energy efficiency that applies to virtually any treatment
process is the National Electric Manufacturers Association (NEMA) MG1 standards for energyefficient motors (NEMA 2006). The Energy Policy Act of 1992 (EPACT) requires that most
general-purpose motors sold in the US must meet these standards. The EPACT standards
establish minimum full-load nominal efficiencies based on the motor type (open or enclosed),
horsepower (hp), and speed. The Consortium for Energy Efficiency then developed a standard
for premium-efficiency motors that exceeds the EPACT efficiencies by 1 to 4 percent.
ULTRAVIOLET LIGHT DISINFECTION
Disinfection using UV light has received increased attention as an alternative to
chlorination as a result of heightened concerns regarding disinfection by-products associated
with the latter process. UV-disinfection uses UV light to inactivate microorganisms by damaging
their DNA and thus preventing them from reproducing. For disinfection purposes, the optimum
UV wavelengths are from 245 – 285 nm. UV systems typically use low-pressure lamps which
emit maximum energy output at a wavelength of 253.7 nm; medium pressure lamps emit energy
over a broader wavelength spectrum ranging from 180 to 1370 nm. Medium pressure lamps
have a life-expectancy of between 4,000 to 8,000 operating hours. Conversely low-pressure and
low-pressure high-output lamps have longer lifetimes at 8,000-10,000 and 8,000-12,000
operating hours, respectively. Typically, medium pressure lamps are more expensive compared
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©2008 AwwaRF. ALL RIGHTS RESERVED
to low pressure lamps and therefore tend to have higher annual O&M costs as a result of lamp
replacement. Lamp replacement typically accounts for between 35 to 45 percent of the annual
O&M costs for a UV disinfection system in both water and wastewater applications. The UV
lamps are housed in a flow-through reactor in order to expose any pathogens present in the water
to the UV light. Typically, an open channel is used in wastewater applications, while a closed
reactor is used in drinking water treatment.
Energy Consumption
EC is on average greater for UV systems than for chlorination systems. The principle
energy consumers in a UV system are the lamps which generate the UV light. It has been
estimated that UV-disinfection increases EC by 70 to 100 kWh/MG (0.07 to 0.10 kWh/kgal)
relative to that needed by conventional chlorination processes (EPRI, 1997).
For
Cryptosporidium control, Mackey et al. (2001) estimated that UV disinfection will use about
0.05 kWh/kgal to 0.15 kWh/kgal, using low pressure-high intensity and medium pressure lamp
systems, respectively.
There are three types of UV lamps: low pressure-low intensity, low pressure-high
intensity, and medium pressure-high intensity. Pressure refers to the gases inside the lamp, while
intensity refers to the lamp’s energy output. As described earlier, low pressure-low intensity
lamps emit their maximum energy output at approximately 254 nm, while medium pressure
lamps emit UV-light at a wide range of wavelengths. From the perspective of the conversion of
electrical energy to germicidal energy, the low pressure-low intensity lamps are more efficient
than medium-pressure-high intensity lamps. However, because of the higher intensity, fewer
lamps are needed to provide the same dosage emitted by low pressure-low intensity lamps. For
example, in a wastewater pilot study conducted by the New York State Energy Research and
Development Authority (NYSERDA), it was determined that low pressure-low intensity lamps
were not cost-effective at large flow rates due to the number of lamps required (NYSERDA
2004). In order to deliver the necessary disinfectant dose, 2,160 low pressure-low intensity
lamps would be needed whereas 360 low pressure-high intensity lamps, or 176 medium
pressure–high intensity lamps would be required. In a 1990 survey, 98 percent of UV systems
used the low pressure lamps (EPRI 1994).
The operating characteristics of low- and medium- pressure lamps used to disinfect good
quality biologically pre-treated wastewater to comply with an effluent limit of 200 fecal coliform
per 100 mL are summarized in Table 2.1.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 2.1
Operating characteristics of UV lamps used to disinfect biologically treated wastewater
Variable
Emission wavelength
Power draw (W)
Power Conversion to UV (%)
Germicidal output (W/cm of
radiation energy)
Typical Number of lamps in
wastewater application
(Number /mgd)2
Typical Power Use (kWh/mgd)
Minimum lamp life
Typical Cost ($/lamp)
1
2
Low Pressure-Low
Intensity
254 nm
Low Pressure-High
Intensity
Broad Spectrum
Medium PressureHigh Intensity
Broad Spectrum
881
2501
1000 - 150002
20 - 251
15 – 25
0.2 1
131
161
40 – 60
-
2–4
3.2 – 4.8
-
6.8 - 15
13,0001
80001
80001
451
1851
2251
NYSERDA, 2004
EPRI 1994
NYSERDA (2004) investigated the use of three UV technologies for wastewater
treatment: low pressure-low intensity; low pressure-high intensity; and medium pressure-high
intensity. These technologies were investigated at pilot-scale under a variety of UV doses and
flowrates. In order to meet a fecal coliform effluent limit of 200 MPN/100 ml, a fecal log
inactivation of 2.7 – 2.9 was required. This inactivation level required UV doses of
26 mW-s/cm2 (low pressure-low intensity), 30 mW-s/cm2 (low pressure –high intensity), and
32 mW-s/cm2 (medium pressure-high intensity). This study (NYSERDA 2004) then compared
power requirements for the three UV pilot plants with the amount of power needed by a
chlorination/dechlorination facility using hypochlorite and sodium bisulfite to treat the same
quantity of water. The chlorination/dechlorination facility would have a power use of 6 kW,
whereas the UV systems have power uses of 60 kW (low pressure-low intensity), 45 kW (low
pressure-high intensity), and 190 kW (medium pressure-high intensity). The study concluded
that low pressure-low intensity UV lamps would not be cost-effective for an application with
high flow rates.
Mackey et al. (2001) tested four UV technologies for drinking water treatment, including
one medium pressure unit and four low pressure units. In this study, two of the units were low
pressure-high output. The study was conducted in two phases, with one of the low pressure-high
output units receiving a different water quality in the second phase than in the first. The units
had a design UV dose of 40 mJ/cm2. Three of the units had operational flow rates of 200 gpm,
while the fourth had an operational flow rate of 300 gpm. Mackey et al. (2001) found that the
medium pressure unit had the highest power consumption per lamp, while the low-pressure units
had the lowest. In comparing different configurations, these investigators found that the
Spectrotherm Series K 130 low pressure-high output lamps used less than half (2 kWh/day per
lamp) of the energy that the MDW-HO low pressure-high output lamps consumed (5 kW-hr/d
per lamp). The higher power consumption was attributed to the greater length of the MDW-HO
lamps, which was twice that of the Series K 130 lamps.
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The lamp efficiency is shown as a function of the operating time (lamp hours) in
Figure 2.1. All of the units were all evaluated for the same flow rates, even though the units did
not necessarily share the same optimum flow conditions. From the data presented here the
efficiency increased for the Series K130 lamp with operating time, while it decreased for the
remaining lamps. The rate of efficiency loss with operating time varied dramatically amongst
the different lamps. The increased efficiency for the Series K 130 unit, was unexpected and
could not be explained by the project investigators. With regards to the efficiency of dose
delivery per unit, the low pressure – high output lamps were found to be more efficient than both
the low pressure-low intensity lamps and the medium pressure-high output lamps.
Figure 2.1 Impact of operating time on UV lamp efficiency (Source Mackey et al. 2001).
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©2008 AwwaRF. ALL RIGHTS RESERVED
Optimizing Energy Efficiency
Currently there are little published results on the optimization of UV processes in water
and wastewater treatment. This is perhaps due to the relatively recent emergence of this
technology in the field of water treatment. Nevertheless, a dose control strategy is considered to
be the most effective way to reduce EC by UV processes. This type of strategy alters the number
of lamps in use or the lamp power based on the flowrate, level of disinfection required (dose) and
water quality (e.g., UV transmittance) (United States Environmental Protection Agency’s
(USEPA) UV Disinfection Guidance Manual, 2003). EPRI (1994) indicates that two mediumpressure lamps provide settings on the transformer to allow lamps to be dimmed to 60 percent of
the “high” intensity setting to adjust for low flows or good influent water quality.
Temperature will also impact the energy efficiency of the UV-lamps. The NYSERDA
(2004) reported that low pressure-low intensity lamps operate optimally at 40ºC and a variation
from this temperature can reduce lamp intensity by 1 percent to 3 percent per degree. Lamp
energy efficiency will also be affected by fouling of the lamp housing (typically a quartz tube).
Fouling reduces the amount of UV-light which is transmitted to the water, subsequently
requiring that the lamps be operated at a higher intensity to maintain the same dose. The degree
of fouling that is experienced by UV systems has been found to be highly variable and dependent
on a variety of parameters (Job et al., 1995, Mackey et al., 2001, NYSERDA, 2004). Fouling is
a function of the influent water quality, lamp configuration, and system hydraulic characteristics.
Finally, hydraulic conditions and UV lamp configuration could also affect energy efficiency.
Some different possible UV lamp configurations are shown in Figure 2.2. A linear configuration
(configuration #5 in Figure 2.2) is generally considered to be the most energy efficient
configuration for UV lamps so as to avoid UV emission losses due to self-absorption, reflection
or refraction (NYSERDA, 2004).
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Inlet
Outlet
Reflectors
Figure 2.2 Possible lamp configurations inflow-through UV disinfection systems (Source:
Qualls et al. 1989 and Nieuwstad et al. 1991). The solid gray circles represent the UVlamps while the dotted circles represent the water filled areas.
OZONE DISINFECTION
As of 1998, approximately 264 water treatment plants in the US were using ozone for
disinfection purposes. However, most of these facilities were small, with more than half having
treatment capacities that were less than 1 mgd. Ozone is a very strong oxidant that is relatively
unstable, thus, the ozone must be generated on-site in order to be useful. The ozonation process
includes four steps: feed-gas preparation, ozone generation, ozone contacting, and off-gas
treatment.
Energy Use
Implementation of ozonation can significantly increase the energy demand by a treatment
system. EPRI (1997) estimates that implementation of ozonation to meet new or proposed
drinking water regulations will increase power consumption by 170 kWh/MG. Although EC will
increase when implementing ozone processes, the magnitude of this increase is variable (100 to
200 kWh) and is dependent on the system design and other variables (DeMers et al., 1996). The
energy requirements of different components in an ozone system are summarized in Table 2.2.
9
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 2.2
Typical energy requirements for various ozone system components
(Source: DeMers et al. 1996)
System Component
Electrical Energy Usage
Air Compressors
Liquid ring compressors
20 – 25 bhp per 100 scfm @ 30 psig
Rotary screw compressors
13 – 17 bhp per 100 scfm @35 psig
Rotary lobe compressors
27 – 33 bhp per 100 scfm @ 100 psig
Refrigerant Dryers
1 – 3 kW per 100 scfm
Desiccant Dryers
Heat reactivated
2 – 3 kW per scfm
Heatless
Minimal
Liquid Oxygen Feed Systems
Minimal
Pressure Swing Adsorption Feed Systems
15 – 18 kW per ton of oxygen
Ozone Generators
Air feed (low and medium frequency)
6 – 9 kWh per lb ozone
Oxygen feed (medium frequency)
3.5 – 6 kWh per lb ozone
Chillers
0.7 – 1.4 kW per ton cooling
Off-gas Treatment (destruct & blowers)
1 – 3 kW per 100 scfm
The energy required by an ozonation system is determined by the plant capacity,
operating flowrate, ozone dosage, and type of feed gas system (i.e., ambient air, LOX or on-site
generated oxygen). The energy efficiency for ozonation systems may be assessed in terms of the
amount of energy required to produce one pound of ozone (kWh/lb O3), or the specific EC by the
system. Evaluating the EC in this manner allows for a baseline comparison to be drawn between
different ozonation systems. The specific energy requirements for several ambient air-fed
ozonation systems operating at varying fractions of their design ozone production capacities are
shown in Figure 2.3. From the data shown in Figure 2.3 the following are general optimization
considerations for EC associated with air-fed ozone systems:
• Air-fed ozone systems tend to have the lowest specific energy requirements at or near
design production.
• Systems became less efficient (i.e., higher specific energy) when operating at or near
30 percent to 50 percent of their respective design capacities.
• Two air-fed ozone systems maintained efficiency, even below 10 percent to
15 percent of their design capacity.
EC for liquid oxygen (LOX)-fed ozone systems is largely (i.e., > 90 percent) from the
ozone generator. The specific EC by several different ozone generators using an LOX feed gas
system is reported in Figure 2.4. Ozone generators have a characteristic energy efficiency curve
that is a function of ozone concentration, water temperature and type of generator.
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28
26
24
22
Specific Energy, kWh/lb
20
Plant 'D'
Plant 'G'
Plant 'H'
Plant 'F'
Plant 'B'
Charles-J. Des Baillets-OFE
Charles-J. Des Baillets-Optimized
Canal Road- Optimized
18
16
14
12
10
8
6
4
2
0
0
10
20
30
40
50
60
70
80
90
Percent of Design Production
Figure 2.3 Specific energy consumption for air-fed ozone systems operating at varying
degrees of their ozone production capacity (Rakness and DeMers 1998).
11
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100
6.0
Equation for solid line is:
Y = 4.655 – 0.518x + 0.0487x2
Specific Energy, kWh/lb
5.0
4.0
3.0
Plant 10 Supplier A @ 95F
Plant 10 Supplier A @ 70F
2.0
Plant 11 Supplier B @ 70F
Plant 12 Supplier B @ 84F
1.0
Plant 13 Suppler C @ 66F
+/- 10%
0.0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Ozone Concentration, %wt
Figure 2.4 Specific energy data for LOX-fed ozone generators (Rakness and Hunter 2002
Mackey et al. (2001), in comparing UV to ozone energy uses, estimated ozone power usage
of 0.6 kWh/kgal at an ozone dose of 12 mg/L.
Optimizing Energy Efficiency
In 1996, the City of Ann Arbor, Michigan replaced chlorine with ozone as its primary
disinfectant and observed a 45 percent increase in electrical costs as a result (Steglitz and Alford,
2001). In response, the utility implemented a strategy to reduce energy costs (not necessarily
energy usage) through improving their understanding the electricity rate structure; installing
energy monitoring devices; analyzing loads and energy consumption; and assessing process
modifications. As a result of this strategy, Ann Arbor implemented strategies to reduce energy
use by replacing old equipment with energy-efficient equipment, evaluating motors for operating
efficiency, and regularly inspecting and maintaining capacitors in the electrical system. Ann
Arbor also planned to evaluate the operation of the ozonation process. For instance, the
treatment plant had routinely been providing more than the required CT, by about 50 percent,
alluding to the possibility that the system may be suffering from over design. This was planned
to be addressed in the future through better monitoring.
DeMers et al. (1996) developed a standard approach for evaluating opportunities for
energy optimization of ozone facilities, which was termed an Ozone Facility Evaluation. This
approach develops optimization opportunities and assesses the result of implementing some of
these opportunities as an Ozone Facility Technical Assistance project (Figure 2.5). DeMers et al.
(1996) determined that energy optimization opportunities for ozonation facilities could be
separated into three different categories: Type 1 – operations and maintenance (O&M)
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activities; Type 2 – involves an O&M evaluation prior to implementing process changes; and
Type 3 - involves a design change or system modifications. Table 2.3 presents examples of the
three types of opportunities. DeMers et al. (1996) estimated that implementing all of these
opportunities could result in a reduction of energy use by 5 to 15 percent.
Figure 2.5 Ozone facility evaluation approach for assessing energy efficiency
(Source DeMers et al 1996).
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Table 2.3
Examples of optimization opportunities for ozone processes
Type
Examples
Type 1 Opportunity involving
equipment maintenance or a change
in system operation
Type 2 Opportunity involving
further O&M evaluation before
implementing change in operating
parameter
Type 3 Opportunity involving
design change and system
modifications
•
•
•
Establish performance targets for operation of ozone system.
Calibrate gas flow meters, ozone residual monitors, and power
meters.
Inspect and clean ozone generator dielectrics/check fuses.
Adjust ozone dosage to match diurnal changes in ozone
demand.
Extend desiccant dryer cycle.
•
Decrease system operating pressure.
•
Utilize existing refrigerant dryer bypass.
•
Install small compressor(s).
•
•
Bypass/modify refrigerant dryer or chiller.
Modify ozone residual sampling and monitoring to accurately
detect residual inside contactor.
•
•
Source: DeMers et al. 1996.
In their study, DeMers et al. (1996) presented two specific examples of possible energy
savings. In one example, the investigators looked at reducing desiccant dryer time from 30 hours
to 12, finding that this reduced EC for this step by more than 50 percent. A second example
involves providing two post-ozone contact basins, but no energy savings is calculated.
Many ozone systems operate at less than 30 percent design production rate due to
(a) lower than design water flow rate, especially during late fall, winter and spring and (b) lower
than design ozone dose due to the fact that the usual water quality is better than the “worst-case”
water quality condition that established the design production value. One consideration for
reducing EC at air-fed ozone plants is to focus on ways to modify operating practices for lowproduction operation (i.e., if identified as a need) that is different from design-production
operation, or to implement minor design or equipment changes, such as installing a small
capacity air compressor in place of the large compressors needed to achieve design production
value.
Energy optimization considerations associated with LOX-ozone-fed generators include
the following:
• Ozone generators might become inefficient over time. Current operating specific
energy value can be compared to the characteristic energy efficiency curve to assess
degree of inefficiency. Generators can return to like-new efficiency when
maintenance activities are completed, such as cleaning.
• Knowing the specific energy versus ozone concentration characteristic curve, the
optimum operating ozone concentration can be identified, as shown in Figure 2.6.
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©2008 AwwaRF. ALL RIGHTS RESERVED
1.00
Chart developed at prices
LOX
= $0.035 / lbO2
Energy = $0.08 / kWh
0.90
Unit Mass Ozone Cost, $/lb
0.80
LOX Cost
Energy Cost
0.70
Energy + LOX Cost
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0
1
2
3
4
5
6
7
8
9
10
11
12
Ozone Concentration, %wt
Figure 2.6 Optimized operating ozone concentration curve for an example LOX oxygenfed ozone generator.
On-site oxygen systems vary according to the size of the plant at which they are
operating. Large plants (Q > 600 mgd) typically use Vacuum/Pressure Swing Adsorption
(VPSA) systems. Conversely, small plants (Q < 5 mgd) use Pressure Swing Adsorption (PSA)
units. These systems are differentiated by the amount of oxygen that each can produce. For
instance, VPSA systems can generate between 10,000 and 200,000 ft3/hr of oxygen, while the
production rate for PSA systems is substantially less. Thus, PSA systems are better suited and
more economical for smaller systems, which have lower ozone generation requirements. Energy
optimization considerations for both VPSA and PSA systems should be based on the fact that
both are most energy efficient (lowest specific EC) when they are operated at or near their
respective design oxygen production values. One consideration for reducing EC might be to
install a smaller-sized unit in a plant that operates at low ozone (i.e., low oxygen) production
rates for much of the time.
MEMBRANE FILTRATION
Membrane filtration is an energy intensive process where most of the energy is being
used to provide necessary operating pressure. In order to reduce the capital, operating and
maintenance costs for a membrane system – membrane selection plays a critical role. This
section discusses the energy requirements for a variety of membrane processes, including MF,
UF, and RO (the systems examined in this study). If available, methods of increasing energy
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efficiency have been described as well. In general, most of the information on improving energy
efficiency is related to RO systems since it is the most energy intensive of all membrane systems.
LOW-PRESSURE MEMBRANE FILTRATION (MICROFILTRATION/
ULTRAFILTRATION)
Energy Use
On average, low-pressure membranes have lower energy requirements compared to highpressure membranes. This is due to the lower operating pressures and hence pumping
requirements of the former category. Mackey et al. (2001) estimated that the specific EC for UF
membrane systems is around 0.5 kWh/kgal of water treated. EPRI (1997) estimated that the
average specific EC of MF membrane systems is approximately 0.1 kWh/kgal. The values
referenced here are only general estimates and will vary based on the specific membrane and
feedwater characteristics. Operational parameters such as backwashing frequency and air
scouring will also affect the EC by both UF and MF processes.
Optimizing Energy Efficiency
The energy efficiency of low-pressure membrane systems is determined largely by the
membrane permeability and the backwash frequency that is used. Backwash frequency affects
the system energy efficiency due to the associated pumping of the backwash water and the loss
of product water during the process. Thus, more frequent backwashing decreases the energy
efficiency of the membrane system. Backwashing frequency and duration are optimized through
careful selection of pretreatment practices and proper membrane selection (Jacangelo et al. 1992;
Crozes et al. 2003). The latter is important because some membranes are more susceptible to
fouling under a given set of conditions than others. This is due to differences in membrane
surface chemistry and physical structure. Thus, some membranes will perform better than others
under a given set of conditions and require less cleaning and other maintenance (air scouring and
backwashing) as is shown in Figure 2.7.
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Figure 2.7 Specific energy consumption as a function of instantaneous water flux for lowpressure membranes (Source: Jacangelo et al. 1992).
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REVERSE OSMOSIS
Energy Use
RO processes (Figure 2.8) utilize electric motors for 1) low pressure forwarding pumps,
2) the pretreatment step, 3) the high pressure process driver, and 4) product water delivery. The
efficiency of the electric motors and the pumps vary greatly depending upon the size of the plant,
and more specifically for large plants, the size of the repeating train.
Pretreatment/
Chemical Addition
Membrane
Bank
Post Treatment/
Chemical Addition
Raw
Feedwater
Cartridge
Filter
Energy
Recovery
Finished
Water
Concentrate
Figure 2.8 General layout of a seawater reverse osmosis (SWRO) treatment system.
Since seawater must be desalted at pressures exceeding 800 psi, and sometimes as high as
1200 psi, the seawater RO process is still the most expensive of the membrane applications. For
brackish water, the most recently developed membranes for low pressure are very effective and
have reduced the overall cost of the process significantly. Some of these brackish water plants
operate at 100 to 150 psi.
For many years, seawater reverse osmosis (SWRO) suffered from very high EC.
However, development of more efficient energy recovery equipment, particularly during the past
10 years, has greatly reduced EC. Table 2.4 summarizes the energy-saving features that are
commonly used in RO applications and Figure 2.9 illustrates how EC by SWRO processes have
changed with time. In 1979, SWRO systems consumed more than 30 kWh/m3 water produced
(114 kWh/kg). This high EC was partly due to the relatively small size of systems at that time.
Today, SWRO systems consume on average only 3.5 kwh/m3 (13 kWh/kg). Of the devices listed
in Table 2.4 the flow-work exchanger and pressure exchanger are the most recent developments.
These devices have demonstrated the ability to reduce SWRO EC by roughly 2.0 kWh/m3
(7.6 kWh/kg).
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Table 2.4
Anticipated efficiencies of various energy recovery systems
Equipment
Efficiency (%)
Reverse running pump
75 – 82
Pelton turbine (ERT)
80 – 86
Turbocharger
70
Flow-work exchanger
90 – 95
Pressure exchanger
~95
35
Energy Consumption, kwh/m3
30
25
Mubeen compiled
Andrews (DWEER)
20
Childs (Vari-Ro)
ERI @Pt. Hueneme
15
10
5
0
1975
1980
1985
1990
1995
2000
2005
Year
Figure 2.9 Energy required in SWRO to produce a unit volume of treated water. This
trend illustrates how the energy requirements of SWRO have decreased with time.
Optimizing Energy Efficiency
One manner of optimizing energy use in RO is pressure reduction. A pilot-treatment
process was used to investigate RO for desalination of Colorado River water (California Energy
Commission 1999). Typically, this untreated water can contain 600 – 800 mg/L of total
dissolved solids (TDS). In comparing two different pre-treatment processes, the RO unit was
operated at two different pressure levels: 113 psi (in conjunction with ozone and biofiltered
water) and 125 psi (in conjunction with conventional pre-treatment). The higher pressure
operation used 1.66 kWh/kgal, while the lower pressure process used 1.37 kWh/kgal. However,
membrane fouling increased significantly with lower operating pressure.
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Other important issues related to EC are:
• Process design. EC can be minimized with good process design. As product water
recovery increases, the total volume that must be pretreated decreases, as does the
energy requirement. Several plants have been constructed using a two-pass, high
pressure system. One company that installed such a system has developed a
membrane that operates satisfactorily at up to 1,400 psi.
• Equipment selection. For smaller plants, positive displacement pumps, which greatly
reduce EC, can be used. For large plants multi-stage or split-case centrifugal pumps
are the current pumps of choice. As described above, the selection of the proper
energy recovery device is critical. Since most desalination plants must be operated
with somewhat variable outputs, the use of VFDs has improved energy efficiency.
• Feedwater temperature. One obvious technique is to use once through cooling water
as it leaves the power plant for a co-located desalination plant. The increase in
temperature for the RO feedwater reduces energy costs since the output for
membranes increases approximately 2.5 percent for each oC of temperature increase.
This was done at Tampa Bay and has been proposed for a few of the plants proposed
in California. However, elevated influent temperature may also promote biological
fouling in the RO membrane system. Appropriate anti-fouling measures should be
considered for this approach.
There are other optimization techniques for improving desalination EC, although some
are limited by the water chemistry and desired water recovery. A particularly interesting
possibility is to reduce the number of elements in a pressure vessel from the conventional six or
seven, to just three. It is well known that the membranes beyond the third in series produce very
little product and contribute additional pressure drop. With the imminent introduction of 16-inch
diameter membrane elements, a short design begins to make much more sense. A 15.5-inch
(nominal 16-inch) membrane system (Koch Membranes, MegaMagnum) was successfully pilot
tested in Perth, Australia, and operated up to a feed pressure of 60 bar (980 psi).
Sandia National Laboratories (Department of Energy, undated) investigated two RO
technologies for its water purification systems: high efficiency reverse osmosis (HERO) and RO
in conjunction with electrodeionization. HERO is a proprietary process developed for the
microelectronics industry. HERO uses pre-treatment to reduce hardness and increase the water’s
pH prior to RO. In the second process, water was treated with RO and then underwent
electrodeionization. Table 2.5 compares operational statistics for both processes. The
information in this table was developed to describe operation of 250 gpm systems. As Table 2.5
demonstrates, the HERO process uses 65 percent of the power required by the other process.
The investigators note, however, that the power efficiency of the RO/electrodeionization process
could be increased if the system is designed to have a larger membrane, reducing the power and
membrane maintenance requirements.
Table 2.5
Selected operational statistics for the HERO and RO/electrodeionization processes
Annual Statistic
Power Use (kWh)
Feed water use (kgal)
Wastewater production (kgal)
HERO
1,849,760
160,421
44,781
Source: US Department of Energy, 2004
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RO/electrodeionization
2,838,667
116,817
7,767
Green energy has often been examined to power RO. For example, photovoltaics
coupled with wind energy have been used at a small plant in Israel. Wave energy is touted by a
Nova Scotia company that has coupled their wave energy device directly to a small RO
membrane. Solar devices generally require large surface areas. At this writing, none of these
sources appear practical for desalination, particularly in large sized plants. Green power is
available today, but at ~ 50 percent premium over grid prices.
Although the reduction in actual consumption is important, the cost of energy is a
significant factor. Most recently-proposed SWRO plants in California have assumed an energy
cost of about $0.05/kWh. This is based on the ability to negotiate “inside the fence” pricing with
a co-located power plant. If grid prices must be paid, SWRO may still be too expensive.
MEMBRANE BIOREACTORS
MBRs are specialized applications of low-pressure membranes modified for municipal
wastewater treatment. With regards to EC, the principal difference is that MBRs require aeration
during the filtration process to reduce the amount of fouling caused by the high concentration of
suspended solids typical in municipal wastewaters.
Energy Use
EC by MBRs is largely determined by the pressure required to transport water across the
membrane, which is typically done using vacuum pumps, and the aeration systems. Energy is
also consumed by support processes, such as the backwashing and clean-in-place (CIP) systems.
Zhang et al. (2003) estimated that the specific EC by MBRs is roughly 22 – 30 kWh/kgal of
permeate. Notably, this is significantly higher than that consumed by traditional wastewater
treatment processes (1.0 – 1.5 kWh/kgal of treated water).
Optimizing Energy Efficiency
Energy efficient MBRs have been configured and tested. However, this literature review
did not find many numerical comparisons between the power consumption of traditionally
configured MBRs versus more energy efficient types. In general, the literature indicates that
submerged membranes reduce EC as well as vacuum pressure. The NYSERDA (2004) reported
on an MBR system piloted for installation at a wastewater treatment plant that used a vacuum
instead of positive pressure to reduce the energy associated with pumping permeate through the
immersed membranes. The unit was operated at negative 1 to negative 10 psi. In this study,
assuming average flow capacity of 0.3 mgd and a daily peak capacity of 0.6 mgd, investigators
calculated EC at 327,500 kWh/yr (NYSERDA, 2004). While the authors indicated that this
would be a more energy efficient operation than positive pressure MBRs, there was no
comparison of power consumption between the different types of plants.
Zhang et al. (2003) conducted a laboratory experiment using an MBR configuration that
relied on transverse flow of water instead of the cross-flowing mode usually used to enhance
filtration capacity and reduce fouling. Additionally, the MBR had a two-loop connection
between the bioreactor and membrane module to allow for low recirculating flow between the
membrane and the membrane and bioreactor. Additionally, this design required no cooling
device. The investigators differentiated the energy consumed by the separate systems in the
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©2008 AwwaRF. ALL RIGHTS RESERVED
MBR process as the pump, pipe system, aeration, membrane module, and return sludge velocity.
On average, this design used 7.46 kWh/kgal of permeate produced, which compares to
9.10 kWh/kgal of permeate for submerged MBRs. The investigators found that the membrane
module consumed the majority of the energy.
ELECTRODIALYSIS REVERSAL
EDR is a self-cleaning electrodialysis in which the polarity of the voltage is reversed
several times per hour. DC voltage is applied across a pair of electrodes, causing positive ions to
move toward the cathode and negatively charged ions to move to the anode. Membranes are
placed between the electrodes, forming compartments. Water flows across the surface of the
membranes instead of through the membranes. The ions travel through the membranes due to an
applied voltage. The US Army Corps of Engineers (USACE, 1986) indicates that while EDR
has been used to treat ocean water, the upper, economical limit is 4,000 mg/L of TDS for potable
water needs.
Energy Use
EC by EDR processes is proportional to the TDS content of the water being treated, as
shown in Figure 2.10.
Figure 2.10 Energy consumption for electrodialysis reversal and other processes as a
function of the feed water total dissolved solids content (USACE 1986).
22
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Optimizing Energy Efficiency
Stack configuration for EDR units can be optimized to allow for greater energy
efficiency. Von Gotteberg (1998) found that configuration of the EDR system can be improved
to promote more turbulent flow in an electrodialysis stack. The spacer configuration is such that
each stack contains 38 percent more usable membrane area than a conventional electrodialysis
stack. This results in a higher mineral concentration per stack and, thus, fewer stacks re required
to treat a given volume of water.
SUMMARY OF FINDINGS
The EC of ATTs to be investigated at 14 different water and wastewater treatment
facilities located in the US and Canada was reviewed in the literature. The ATTs that were
studied included : UV light disinfection, ozonation, RO, UF, MF, MBRs, and EDR. These
treatment systems represented a wide range of raw water qualities and treatment strategies.
The major components, typical power consumption, and common strategies for
optimizing the energy efficiency of each of the targeted ATTs are summarized in Table 2.6. In
general, the ATT with the greatest EC is membrane filtration. Greater power usage is typically
associated with greater pressure requirements of specific membrane processes. Based on
information currently available in the literature, MBRs consume the greatest amount of energy.
Typical power uses of MBRs are reportedly in the range of 23-30 kWh/kgal whereas lowpressure membranes (MF and UF) typically consume energy in the range of 0.1-0.5 kWh/kgal.
EC requirements for ozone disinfection (0.6 kWh/kgal) are considered comparable to EC
requirements for low-pressure membrane systems. EC requirements for UV disinfection (0.050.15 kWh/kgal) were identified as the lowest of the ATTs included in this study. EC
requirements for EDR reportedly range from 6 to 13 kWh/kgal, which is generally comparable to
EC requirements for RO.
In general, findings from this review of the literature indicate that energy efficiency can
be optimized by evaluating the process design, equipment performance, and routine system
operation and maintenance. For example, a process or component could potentially be optimized
by ensuring that operations occur with optimal flow rates and/or water quality conditions. This
review of the literature yielded general information regarding expected (or theoretical) power
usage requirements for each ATT and typical strategies for optimizing energy efficiency. More
data and information are needed regarding true energy costs associated with these ATTs. This
research therefore was devoted to the evaluation of EC of existing ATTs and subsequent
optimization practices that have been adopted by utilities to improve energy efficiency. The
project approach, findings, conclusions, and recommendations for further research are discussed
in the following chapters of this report.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 2.6
Summary of ATTs, major components, typical power usage, and common strategies for
optimizing energy efficiency
ATT
Process or
Component
Typical Power
Use (kWh per
1000 gal)
UV disinfection
Lamps (lowpressure high
intensity and
medium pressure
lamp systems
Ozone
disinfection
Process includes
feed-gas
preparation,
ozone generation,
ozone contacting,
and off-gas
treatment.
0.05-0.15 (a)
Typical power use
is based on
Cryptosporidium
control.
0.6 (b)
Equipment maintenance
or change in operation
Design change and
system modifications
Typical power
based on ozone
dose of 12 mg/L.
Careful selection of
pretreatment processes
Minimize backwash
frequency/duration
Air-scour
consumes large
fraction of total
energy consumed
in MF/UF systems
Pumps
0.1-0.5 (a)
Reverse
Osmosis
Feed pumps
7.6-13 (c)
Membrane
bioreactors
Pumps, blowers
23 – 30 (d)
(a)
(b)
(c)
(d)
(e)
(f)
Electrified
membrane plates
Comments
Dose control (i.e., alter
the number of lamps in
use or the lamp power
based on flow, water
quality, or UV
absorbance)
Microfiltration/
Ultrafiltration
Electro- dialysis
Reversal
Optimizing Energy
Efficiency
6-13 (e)
Process design
Equipment selection
Feedwater temperature
Design including
configuration and
operating pressure
Design such as stack
configuration (f).
Mackey et al. (2001)
EPRI (1997)
Ventresque et al. (2001) for high pressure pumps.
van Dijk and Roweken (1997)
USACE (1986)
Von Gotteberg (1998)
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©2008 AwwaRF. ALL RIGHTS RESERVED
Power use depends
on TDS. Upper
limit reflects
economic limit of
4,000 mg/L TDS.
CHAPTER 3
PROJECT APPROACH
The objective of this study was to quantify the actual and theoretical EC of selected water
and wastewater advanced treatment unit operations for the purpose of evaluating factors that
affect EC and to identify energy optimization opportunities while maintaining treatment
performance. The Project Team was led by HDR Engineering, Inc. and consisted of engineering
firms and manufacturers as summarized in Table 3.1.
Table 3.1
Project partners and roles
Project Partner
Engineering Firms
HDR Engineering, Inc.
Separation Consultants, Inc.
Process Applications, Inc.
Manufacturers
ZENON Environmental
Trojan Technologies
Location
Project Role
Bellevue, WA
Poway, CA
Fort Collins, CO
Project lead
RO specialist
Ozone specialist
Oakville, ON
London, ON
Membrane technology
UV technology
The project approach consisted of the following activities, which are described in the
sections to follow:
• Select ATT’s for inclusion in this study and conduct a literature review to identify
the most feasible energy optimization measures for each selected ATT.
• Develop a standard framework for evaluating and presenting EC and efficiency data
for selected ATT.
• Conduct energy audits of selected ATT installations and compare to their theoretical
EC rates.
• Analyze data and identify energy optimization opportunities.
IDENTIFICATION OF ATTS
This research focused on evaluating EC of ATT that can be characterized as having high
energy demand and a wide range of potential applications. Selected ATTs were determined to
have the most significant impact on overall EC within the operations of a water and/or
wastewater treatment plant.
Eight ATTs were proposed by the Project Team for consideration by the Project
Advisory Committee as summarized in Table 3.2. For each ATT, typical water/wastewater
applications and its primary EC components are listed in Table 3.2.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 3.2
Proposed advanced treatment technologies for energy evaluations
ATT
UV Irradiation –
Water
UV Irradiation –
Wastewater
Advanced Oxidation
Process
Ozone
Low-Pressure
Membranes
High-Pressure
Membranes
Electro- dialysis
Reversal
Typical Applications for Water /
Wastewater Treatment
• Disinfection / inactivation of
microorganisms
• Disinfection / inactivation of
microorganisms
• Destruction of taste and odor
compounds
• Destruction of trace organic
contaminants (NDMA,
endocrine disruptors, etc.)
• Destructive oxidation of organic
matter
• Oxidation of dissolved metals
• Primary disinfection /
inactivation of microorganisms
•
Microbial and particulates
removal
•
•
Desalination
Removal of trace inorganic
contaminants
Desalination
•
•
Membrane Bioreactor (MBR)
Secondary/tertiary treatment of
wastewater including solids
separation / clarification, BOD
reduction, and sometimes
nitrogen reduction
Primary Energy Consumption
Components
• UV lamps and ballasts
•
UV lamps and ballasts
•
UV lamps and ballasts
•
•
Ozone generator
Air compressor (if air is
oxygen source)
•
•
•
•
•
Feed and backwash pumps
Air compressors
Blowers and heaters
Feed pumps
Heaters
•
•
•
•
•
Electrodes
Pumps
Feed and backwash pumps
Air compressors
Blowers and heaters
The final selection of ATTs and list of participating utilities were determined at a meeting
of the Project Partners with the AwwaRF Project Manager and Project Advisory Committee at
the West Basin Municipal Water District in El Segundo, California on December 7, 2005. The
selected ATTs were determined to have the greatest impact on EC based on the following
criteria.
• The ATT has broad application potential for meeting water and/or wastewater
treatment requirements.
• The treatment performance of the ATT is proven, well understood, and welldocumented based on results from operating installations.
• The ATT is commercially available from more than one manufacturer/supplier.
• The ATT can have a significant energy demand.
The name of location of participating utilities, a description of the facility type, and
identification of the specific processes that were evaluated for this study are summarized in
Table 3.3.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 3.3
Utility Partners
Utility
Arizona American Water
Company
Central Lake County Joint
Action Water Agency
Contra Costa Water
District
City of Kamloops, BC
Location
Anthem, AZ
City of Pooler, GA
Sarasota County
Environmental Services
City of Seward, NE
Pooler, GA
Venice, FL
Southern Nevada Water
Authority
Water Replenishment
District of So. CA
West Basin Municipal
Water District
Rock Bluff, IL
Contra Costa, CA
Kamloops, BC
Seward, NE
Henderson, NV
Torrance, CA
El Segundo, CA
Facility Type
Drinking water (surface
water) and wastewater
Drinking water (surface
water)
Drinking water (surface
water)
Drinking water (surface
water)
Wastewater
Drinking water
(groundwater)
Drinking water
(groundwater)
Drinking water (surface
water)
Drinking water
(groundwater)
Municipal and industrial
water reuse
Process Analyzed
3 mgd MBR and 8 mgd
UF
50 mgd ozone and UV
80 mgd ozone plants
42 mgd UF
2.5 mgd MBR
12 mgd EDR
1.15 mgd RO for nitrate
removal
600 mgd ozone plant
2.75 mgd brackish water
RO
5.4 mgd MF, 4.6 mgd RO,
and 12.5 mgd UV
ENERGY AUDITS
A standard framework was developed for analyzing, evaluating and comparing EC and
efficiency data for the selected ATTs. Standard units of measurement were also established for
quantifying energy data. The framework for this project consisted of the following activities:
• Grouping of utilities
• Data and information collection
• Analysis of theoretical energy efficiency and correlation of EC with water quality
• EC audit
• Identification of optimization opportunities
After identifying possible ATTs, participating utilities were divided into one of three
groupings based on the following criteria:
• Group 1 – These utilities have the largest installation of a specific ATT or have
multiple ATTs.
• Group 2 – These utilities have ATT installations that are already included at least
once in Group 1 and/or are generally smaller in capacity.
• Group 3 – Due to scheduling conflicts that could impact the project schedule, utilities
in this group may potentially not be analyzed as part of this project. These utilities
have ATTs that have already been included in Group 1 so omitting these utilities
would not reduce the breadth of the project.
For those utilities included in Group 1, data and information were collected (Step 1),
theoretical energy efficiency was analyzed and EC was correlated with water quality (Step 2),
EC audits were performed (Step 3), and optimization measures were identified (Step 4). For
those utilities included in Group 2, Steps 1 and 2 were performed, with Step 3 conducted if
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©2008 AwwaRF. ALL RIGHTS RESERVED
project schedule permitted. For Group 3, Steps 1 and 2 were performed to the extent possible
based on available scheduling. The activities that were carried out for each Utility Group as part
of this study are summarized in Table 3.4.
Table 3.4
Activities for each utility group
Step
Description
1
Collect data and information
2
3
Analyze theoretical energy efficiency and
correlate EC with water quality
Conduct EC audit
4
Identify optimization measures
1
Utility Group
2
3
3
3
3
3
3
3
3
3
3
3
Preliminary site visits were conducted at some participating utilities during October to
November 2005 to assess the selected ATT systems and to identify challenges associated with
conducting energy audits for this project at the selected facilities. Findings of the preliminary
site visits were discussed with the AwwaRF Project Manager and Project Advisory Committee
as summarized in Appendix A. The utilities and selected ATT systems assigned to each
Grouping as a result of this evaluation are identified in Table 3.5.
Table 3.5
Participating utilities and ATT by ATT group
Utility
Southern Nevada Water Authority,
NV
Utility
Group
1
Water Replenishment District of
Southern California, CA
West Basin Municipal Water
District, CA
Sarasota County, FL
City of Seward, NE
1
Arizona American Water
Company, Anthem Water Campus
City of Pooler, GA
City of Kamloops, BC
2
2
2
Contra Costa Water District, CA
2
Central Lake County Joint Action
Water Agency, IL
3
1
1
2
Comment
Utility partner with largest ozone installations. Two
different ozone installations; one installation included
in this study.
Brackish water RO desalination facility
Water reuse facility, multiple ATT at site (MF, RO,
UV)
Only utility partner with an EDR facility
Groundwater RO facility that is smaller than Group 1
RO facilities
Smaller than Group 1 MBR and low-pressure facility
Smallest MBR facility
One low-pressure membrane facility already in
Group 1
Two ozone installations; one installation included in
this study.
UV facility.
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COLLECTION OF DATA AND INFORMATION
Data and information pertaining to general operating conditions and water quality
parameters were collected from the participating utilities. Requested information included a
general description of the facility plus the following (Reardon, 1995b):
• Plant flows (average and yearly total for one year);
• One year of electric utility bills;
• Pumping records and pump performance curves;
• Hour per day the plant is attended and hour per day it is operated;
• Design summary, drawings and specifications;
• Normal operating time for intermittently operated processes such as filter backwash
and solids handling;
• Utility bill schedule and possible alternative schedules;
• One year of water quality data either from standard monthly reports submitted to
local regulatory agencies or from a data dump from the utility supervisory control and
data acquisition (SCADA) and laboratory information management system (LIMS).
Data typically included flow, turbidity, pH and UV transmittance.
DATA EVALUATION
Data and information collected from participating utilities were evaluated by determining
the theoretical EC of the selected ATT systems, measuring EC, and correlating EC with water
quality. These activities were conducted for all participating utilities. In addition, an EC audit
was conducted for Group 1 utilities. These data evaluation activities are described below.
For this report, the energy data will be presented in the standardized units of kilowatthours per 1,000 gallons treated (kWh/kgal).
Theoretical EC
Theoretical EC rates were determined for each ATT based on data and information
provided by the manufacturer such as rated sizes of components, nameplate data, and observed
operational parameters such as equipment run times and set points. The theoretical EC
information derived from this project represents the same type of EC estimates that are often
prepared as part of engineering evaluations, design development, and O&M cost estimates.
EC Measurements
EC was measured by monitoring true power (in units of kWh) versus apparent power
using existing EC monitoring equipment. Findings from the preliminary site visits indicated that
most sites already had kWh displayed on electric panels, major blowers had their own Watt-hour
meters on the equipment, and that monitoring of specific equipment would require installation of
additional monitoring equipment. Some facilities, such as SNWA, Kamloops, and CLCJAWA,
had the SCADA systems that were already configured to continuously monitor and record the
EC of specific equipment. For facilities where either the SCADA system did not have EC
monitoring and logging capabilities, either monthly utility bills were used or the plant staff
manually collected EC data. The requested amount of data to be collected manually was set to
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be four individual 1-week periods interspersed throughout the project duration in order to cover
various seasonal impacts on water quality. The actual amount of data collected varied by utility.
Water Quality Correlation
Changes in water quality and observed impacts on EC were analyzed to identify potential
energy saving opportunities. For example, correlations were developed for EC as a function of
turbidity or TDS. Statistical parameters such as R2 were used to asses the quality of the
correlations.
EC AUDIT
Data and information collected from selected ATT systems were summarized in an
equipment energy inventory as part of the EC audit (Reardon and Culp, 1987a; 1987b). For each
process or equipment unit, the inventory included available information regarding power, load
factor, hours of operation and EC per year, and the estimated distribution of power expressed as
a percentage of total plant power consumed by the specific process or equipment. Based on data
and information collected from each selected ATT, the big picture parameter was determined
expressed as energy consumed per thousand gallons of water treated.
IDENTIFICATION OF OPTIMIZATION OPPORTUNITIES
After analyzing the collected EC data and correlating EC with general plant operation
and water quality parameters, the research team identified opportunities where the operation of
an ATT could be adjusted to maximize the energy efficiency. When considering a particular
ATT or system component, potential ECMs were evaluated by posing “what if” questions such
as the following (EPRI, 1994; Reardon, 1995a; 1995b):
• Does the equipment really need to run at all?
• Will the process perform satisfactorily if the flow or capacity (thus energy) is
reduced?
• If the flow or loading is variable, will an adjustable-speed drive lower EC?
• Can energy be reduced if the process/equipment can be controlled to match process
loading (e.g., dissolved-oxygen control of activated sludge)?
• Is more efficient equipment or technology available to do the same function?
• Can equipment operation be shifted from on-peak hours to partial of off-peak hours to
reduce energy costs?
• Can another energy source be used to power the equipment (engine-driven prime
movers versus electric motors)?
• Is the equipment using a premium efficiency motor?
Optimization opportunities were identified for all participating utilities as part of this
study. The research team identified those options that were most promising for achieving
favorable changes in energy efficiencies and could be more easily measured and documented.
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CHAPTER 4
EC OF LOW-PRESSURE MEMBRANE SYSTEMS FOR DRINKING
WATER AND REUSE WATER TREATMENT
This chapter focuses on EC by utilities that use low-pressure membrane systems for
drinking water and reuse water treatment applications. This chapter begins with an overview
description of low-membrane processes and identification of major system components that
typically consume the greatest fraction of energy. Two case studies are provided: the Kamloops,
BC Centre for Water Quality and Arizona American Water Company Anthem Water Campus.
For the purpose of this study, each of these utilities was designated as a member of Group 2
(Table 3-4) and the EC analysis therefore included a system description, analysis of EC and
correlation of EC with water quality. Additional information was included as available with
regard to EC audits and identification of potential optimization opportunities. A summary of the
EC analysis for these two case studies is included at the end of this chapter.
PROCESS DESCRIPTION OVERVIEW
Low pressure membrane systems generally employ either MF or UF membranes. MF
membranes have pore sizes in the range of 0.1 to 10 μm, while UF membranes have slightly
smaller pores ranging from 0.002 to 0.1 μm. Pressure (5 to 35 psi) or vacuum (-3 to -12 psi) may
be used as the driving force to transport water across the membrane. MF and UF membranes
may be used in either a spiral wound, tubular, or hollow fiber element design, with the hollow
fiber being the most prevalent for municipal applications. The permeate water flux for lowpressure membranes is typically greater than 0.4 gfd/psi (> 10 L/m2-hr/bar), with the actual value
dependent on site specific water turbidity, pump sizing, and acceptable levels of trans-membrane
pressure (TMP). The process schematic shown in Figure 4.1 is characteristics of most lowpressure membrane systems.
Backwash
Prescreen
Membrane
Bank
Finished
Water
Recirculation Loop
Air Scour
Backwash
To Waste
Figure 4.1 General layout for low-pressure water treatment membrane systems.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Raw water to the low-pressure membrane system is first passed through a pre-screen to
remove large materials that may damage the membrane fibers or the pumps. Depending on the
system configuration there is either a feed pump sends the water to the membrane bank and
supplies the driving pressure through the membrane or there is a vacuum pump that draws the
water through membranes that are submerged in a tank. For small systems, a single feed pump
may be used for the entire membrane bank, while larger systems may have individual pumps
dedicated to each one. The permeate is stored in a finished water storage tank, where it may be
disinfected or go through pH adjustment. Alternatively, the permeate may be sent to additional
treatment processes in water reuse applications. A portion of the permeate is retained for the
periodic membrane backwash cleanings. Air scouring may also be employed during the
backwash to further clean the membranes. Some systems operated in a cross-flow mode, in
which the feed water that crosses over the membranes is recirculated to the beginning of the
membrane system.
MAJOR EC COMPONENTS
Components of low-pressure membrane systems that consume the largest fraction of
energy include the feed/vacuum pump(s), backwash pump, air scour blower, and the
recirculation pump (if used). Heaters that are sometimes used in some applications for heating
the chemical cleaning solution could also consume significant amount of energy in colder
climate. Membrane permeability and the desired permeate flux will dictate the system pressure
requirements. Membrane fouling is thus a significant determinant of the energy consumption in
MF/UF processes as membrane permeability decreases with increased fouling. This reduction in
membrane permeability increases the pressure that must be applied to the membrane to achieve a
desired flux, thus increasing the energy consumption on behalf of the pumps. Energy
consumption by the backwash and air scour system will depend on the frequency of
backwash/air scouring and the volume of backwash water that is used.
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
Kamloops Centre for Water Quality
System Description
The Kamloops, British Columbia Centre for Water Quality (Centre) consists of a
drinking water filtration plant operated by city staff and an associated onsite education and
training facility led by Thompson Rivers University (Kamloops, B.C.), with support from the
City and the membrane manufacturer. The Centre began operations in February 2005 and is
operated and staffed continuously. Raw water is drawn from the South Thompson River, where
turbidity has routinely exceeded 100 NTU during spring runoff, with historical maximum
turbidities exceeding 500 NTU. The raw water quality for the Kamloops WTP is summarized in
Table 4.1 and a schematic of the treatment facility is presented in Figure 4.2.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 4.1
Raw water quality parameters for the Kamloops WTP from
March 1, 2005 to October 31, 2005
Units
pH
Temperature
Alkalinity
Hardness
Turbidity (24-hour avg.)
Total suspended solids
Total dissolved solids
Conductivity
Apparent color
True color
Total coliform
E. Coli
°C
mg/L as CaCO3
mg/L as CaCO3
NTU
mg/L
mg/L
µS/cm
PCU
PCU
MPN/100 mL
MPN/100 mL
Average
7.81
13.5
37.8
37.8
2.36
4.75
27.5
52.7
22
4
110.1
8.5
Raw Water
Minimum
6.96
4.0
32.0
32.0
1.04
<0.01
25.4
48.7
6
<1
<0.01
<0.1
Maximum
8.12
20.9
42.0
40.0
8.30
30.00
33.9
64.7
100
32
1,299.7
53.7
The river intakes have 3 mm screens to remove bulk materials. A low lift pump station
sends water to six rapid-mix flocculation basins where aluminum chlorohydrate is added via
chemical metering pumps. The aluminum chlorohydrate coagulant forms pinhead flocs in the
flocculation basins and removes dissolved organics and color from the water. Each flocculation
basin is operated continuously; the plant does not have the normal operational ability to shut
down individual basins during low demand. A list of the mechanical process equipment in the
Centre is listed in Appendix A.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Figure 4.2 Kamloops Centre for Water Quality process schematic.
The flocculated water gravity flows to the membrane system. The membrane system
consists of primary and secondary UF membrane filters. The primary membrane filters consist
of 12 parallel trains, with each train consisting of six membrane cassettes and additional space
for two future cassettes. The current and ultimate capacity of the primary membrane filters is
160 ML/d and 200 ML/d (42 mgd and 52.5 mgd), respectively. Each membrane train is
cyclically aerated at 10-second intervals and backpulsed for 30 seconds every 15 minutes to
remove any solids which have accumulated on the membrane surface. Permeate water from the
primary membrane filters is chlorinated prior to entering the distribution system.
Backwash water from the primary membrane filters is sent to the secondary membrane
filters. The purpose of the secondary membranes is to reduce the amount of water that must be
withdrawn from the river and the amount of reject water that must be discharged to the sewer.
This design reduces the raw water pumping requirements for the system. The secondary stage
consists of six parallel membrane trains. Each train consists of three UF membrane cassettes
identical to the primary stage cassettes. The total treatment capacity of the secondary stage is
12.5 ML/d (3.3 mgd). The secondary membranes are aerated and backpulsed on the same cycle
as the primary membranes. Permeate from the secondary stage is recycled back to the raw water
34
©2008 AwwaRF. ALL RIGHTS RESERVED
channel prior to the flocculation basins. Backwash water from the secondary membrane filters is
pumped to a holding tank containing a dissolved air flotation (DAF) system. The DAF system
operates intermittently based on the level in the holding tank. The treated water is sent to a pond
adjacent to the plant and is used for irrigation. The skimmed solids are currently sent to a tank
for disposal. The Centre has a centrifuge to dewater the solids but the system is currently not in
use.
Power Supply
Power is supplied to the Kamloops WTP by B.C. Hydro. The Centre’s billing schedule is
based on a tiered rate energy schedule with no time-of-day charges. The Centre power is
supplied by two fully redundant power feeds from the same local substation. The power feeds
are monitored using two buses before being distributed among four master control centers
(MCCs) in the plant. Due to the configuration of the Centre’s electrical system, power to the
plant buses supplies only the membrane, DAF, and ancillary chemical systems. The river intake
and distribution system pump stations are not supplied by these buses and are therefore not
included in the energy analysis presented in this report. Power consumption data was obtained
from daily readouts of the total energy of the two plant buses from April 1, 2005 to October 31,
2005. The power data measured apparent power in units of kilovolt-amps-hours (kVAh). The
daily apparent power data was converted to true energy data (with units of megawatt-hours
[MWh]) using an assumed constant power factor of 0.95.
Energy Consumption
The initial analysis of the data found that the membrane permeability changed
approximately halfway through the study period. Membrane permeability for Primary
Membrane Train 1 is reported in Figure 4.3. From April 1 to July 4, 2005, the membrane
permeability varied between 2.2 – 2.3 Lmh/kPa (8.9 – 9.3 gfd/psi). The permeability rapidly
decreased to 1.8 Lmh/kPa (7.3 gfd/psi) between July 5 to July 13, 2005, with a gradual decrease
in permeability afterwards. The rapid degradation in permeability shown for Primary Membrane
Train 1 also occurred for the other eleven primary membrane trains but not for any of the six
secondary membrane trains. After investigation, it was found that the permeability change was a
result of engineers from the membrane manufacturer recalibrating various on-line instruments
and reprogramming some of the mathematical functions in the plant SCADA system. No
conversion factor was provided to the Project Team to reconcile the data difference between the
periods before and after the equipment recalibration. However, although the lack of this
conversion factor affects the presentation of membrane permeability, the energy consumption
information will not be affected. Kamloops and membrane manufacturer staff confirmed that the
change in membrane permeability was not due to any membrane degradation or operational
changes. However, for some of the subsequent results discussed in this section, there appears to
be a difference in the results before and after the change. Data that were affected by the
equipment recalibration are noted accordingly in the associated figures to follow. Nonetheless,
Figure 4.3 shows that the permeability did not change much within the two distinctive sections
(representing before and after programming changes). This result suggests that membrane
fouling was well controlled during the monitoring period.
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©2008 AwwaRF. ALL RIGHTS RESERVED
2.50
Permeability (Lmh/kPa)
2.25
2.00
1.75
1.50
Apr-05
May-05
May-05
Jun-05
Jul-05
Aug-05
Sep-05
Oct-05
Figure 4.3 Evolution of membrane permeability overtime for Train 1 at the Kamloops
water treatment facility. The change in permeability was associated with the recalibration
of membrane control and data logging equipment.
Water Production
Figure 4.4 shows both the daily permeate production and the average daily power
consumption at the Kamloops facility. Daily permeate production varied between approximately
10 to 30 mgd; daily EC ranged from approximately 200,000 to 325,000 kWh. Permeate
production and EC varied seasonally with both peaking in August. EC correlated linearly with
permeate production (Figure 4.4b). Following recalibration of the control and data acquisition
equipment the R2 value increased from 0.7 to 0.9. The reason that the data prior to the
recalibration is to the left of the data after the recalibration is that the pre-recalibration period
was in the spring and early summer when the raw water temperature is cooler than the late
summer and early fall post-recalibration period.
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©2008 AwwaRF. ALL RIGHTS RESERVED
400,000
60
Permeate
300,000
40
250,000
200,000
30
150,000
20
100,000
10
Energy Consumption (kWh/day)
Permeate Production (mgd)
350,000
Energy
50
50,000
0
0
Apr-05
May-05
May-05
Jun-05
Jul-05
Aug-05
Sep-05
Oct-05
Energy Consumption (MWh/day)
15
After Recalibration
2
R = 0.92
10
Before
Recalibration
R2 = 0.71
5
Before Recalibration
After Recalibration
0
0
5
10
15
20
25
30
Permeate Production (mgd)
Figure 4.4 Average daily energy consumption by the membrane, DAF, and ancillary
chemical systems as a function of a) and b) permeate production rate at the Kamloops
water treatment facility.
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©2008 AwwaRF. ALL RIGHTS RESERVED
35
The specific EC for the Kamloops water treatment facility is plotted as a function of the
total permeate volume produced per day in Figure 4.5. This data principally reflects the energy
use of the membrane pumps and blowers. The high-energy low and high service pumps are not
included in this analysis. The data was fit using a power law function and showed a relatively
strong correlation after the equipment was recalibrated (R2 = 0.96). The difference between the
specific EC before and after the equipment recalibration was roughly 0.023 kWh/kgal (3 to 5
percent difference). One hypothesis to explain the difference is that the recalibration, which
suddenly reduced the membrane permeability in a manner similar to sudden irreversible fouling,
resulted in the vacuum pumps operating at higher speeds, thereby reducing the energy efficiency.
As previously noted, Kamloops operates the flocculation basins and primary and secondary
membrane trains on a continuous basis. Though many of the pumps have VFDs to improve
energy efficiency, overall efficiency will increase as the pumps operate at higher flowrates. In
comparison, there is a lower limit at which the VFDs can operate before efficiency significantly
degrades. During the low demand periods, each of the membrane pumps operate at or below this
lower limit and energy efficiency is reduced. Therefore, as permeate production increases the
membrane system begins to operate at higher efficiencies and thus at lower specific EC values.
1.2
Specific Energy Consumption (kWh/kgal)
Before recalibration
After recalibration
R2 = 0.96
1.0
After recalibration
0.8
0.6
0.4
Before
recalibration
R2 = 0.91
0.2
0.0
0
10
20
30
Permeate Production (mgd)
Figure 4.5 Specific energy consumption by the membrane, DAF, and ancillary chemical
systems as a function of the daily permeate production rate at the Kamloops water
treatment facility. The data are each fit with a power law function.
38
©2008 AwwaRF. ALL RIGHTS RESERVED
40
Water Temperature
The relationship between EC at the entire plant and influent water temperature is
illustrated in Figure 4.6. Specific EC by the membrane related equipment only is plotted as a
function of the influent water temperature in Figure 4.7. As temperature increased EC at the
plant also increased, both before and after recalibration of the equipment. The increase in EC is
a result of increased water production during warmer summer months. Conversely, specific EC
by the membrane equipment decreased in a linear fashion with increasing water temperature.
Following recalibration of the equipment, the specific EC correlated rather linearly (R2 = 0.88)
with water temperature.
The trend observed in Figure 4.7 is due to two factors: changes in water viscosity with
temperature and the higher permeate production rates, and associated increases in pumping
efficiencies, which occur during warmer periods (Figure 4.4). This latter issue has been
addressed previously. Water viscosity decreases as temperature increases. In membrane
processes, as water viscosity decreases it is more easily transported across the membrane and in
this case, the permeate pumps are able to work at lower absolute transmembrane pressure
(TMPs) while achieving the desired permeate flux. The effect of water temperature on the
required TMP is evidenced in Figure 4.8. The impact of changing water viscosity (μ) on the
permeate flux (J) may be observed using the well-known Darcy equation:
J =
ΔP
μRm
(4.1)
which is commonly used to describe membrane performance. Holding the membrane resistance
and TMP constant, the theoretical permeate flux would increase by nearly 40 percent over the
observed temperature range of 5 to 25°C. Operating at lower TMPs results in lower EC by the
pumps. The impacts of higher production rates and changes in water viscosity on EC cannot be
individually analyzed from this set of data as both factors tended to occur at the same time.
Breaking down the data by water production, as shown in Figure 4.8, found that the
correlation between energy use and temperature was due primarily to permeate production.
However, for a specific flux rate, the energy efficiency increases (lower specific EC) at higher
water temperature. The permeate pump was required to operate at higher vacuums (greater TMP
values) to compensate for the lower water viscosity at the colder temperatures. This temperature
effect is more profound at lower water production rates. In comparison, the data after the
recalibration shows a strong inverse relationship between temperature and specific energy use.
Breaking down the data by water production found that the correlation between energy use and
temperature was due entirely to permeate production (see Figure 4.9). Nonetheless, the
temperature effect is not as prominent as the production capacity to EC. In other words, the
impact of temperature is only a secondary factor on specific energy use, with the main
relationship as follows: increasing water temperature → higher water production → increased
energy efficiency due to better pump efficiency and lower water viscosity.
39
©2008 AwwaRF. ALL RIGHTS RESERVED
14
Energy Consumption (MWh/day)
12
10
Before
recalibration
R2 = 0.19
8
After recalibration
R2 = 0.73
6
4
Before recalibration
2
After recalibration
0
0
2
4
6
8
10
12
14
16
18
20
o
Temperature ( C)
Figure 4.6 Average daily energy consumption by the membrane, DAF, and ancillary
chemical systems at the Kamloops WTP as a function of water temperature.
Specific Energy Consumption (kWh/kgal)
1.2
After
recalibration
R2 = 0.88
1.0
Before recalibration
After recalibration
0.8
0.6
Before
recalibration
R2 = 0.08
0.4
0.2
0.0
0
2
4
6
8
10
12
14
16
18
20
o
Temperature ( C)
Figure 4.7 Specific energy consumption by the membrane, DAF, and ancillary chemical
systems as a function of the raw water temperature at the Kamloops water treatment
facility.
40
©2008 AwwaRF. ALL RIGHTS RESERVED
-30
Flux = 33 - 35 Lmh
Transmembrane Pressure (kPa)
Flux = 39 - 41 Lmh
-25
R2 = 0.70
-20
R2 = 0.95
-15
4
6
8
10
12
14
16
18
o
Temperature ( C)
Figure 4.8 Correlation between transmembrane pressure and temperature for Membrane
Train 1 prior to membrane system recalibration at two different flux rates (x-axis scale
reversed to emphasis increasing vacuum).
0.30
Q = 30-44 ML/day
Specific Energy Consumption (kWh/kL)
0.28
Q = 45-59 ML/day
0.26
Q = 60-74 ML/day
0.24
Q = 75-89 ML/day
0.22
Q = 90-104 ML/day
0.20
Q = 105-120 ML/day
0.18
0.16
0.14
0.12
0.10
0
2
4
6
8
10
12
14
16
18
20
o
Temperature ( C)
Figure 4.9 Specific energy consumption and water temperature for the period after system
recalibration.
41
©2008 AwwaRF. ALL RIGHTS RESERVED
Turbidity
Raw water turbidity and specific EC are reported as a function of time in Figure 4.10 for
the Kamloops facility. Spikes in turbidity were observed during April and May 2005, which
corresponded to the spring run-off period for that area. Raw water turbidity was less variable
from June to November, during which time it averaged roughly 2 NTU. Spikes in raw water
turbidity did not necessarily result in increased specific EC. Indeed, higher specific EC values
were measured during periods of lower average turbidity (August – November). Instead, the
specific EC increased during periods of lower permeate production (winter months) as was
previously discussed.
Specific EC would typically be expected to increase with raw water turbidity. The
reasoning for this expected relationship is that more frequent backwashes would be required as
the membranes should foul at faster rates during periods of higher turbidity. Since energy is
consumed during the backwash process, and no product water is produced, the overall specific
energy use is typically expected to increase as the membranes are backwashed more often.
However, a number of factors may account for the lack of influence by turbidity on the specific
EC. One factor is the two-stage design of the membrane system that is used at Kamloops. The
secondary membrane filters continually treat backwash water from the primary membrane filters
and permeate from the secondary membranes, having a turbidity less than 0.0 NTU, is blended
with the raw water prior to the primary membranes. This design reduces the volume of water
that must be disposed of or wasted and also reduces the influent turbidity to the primary
membrane filters. By blending permeate from the secondary membrane filters with influent to
the primary ones, the spikes and variability in the influent turbidity is reduced. A second factor
is the cyclic backwash cycle that is employed at Kamloops. Because the backwash frequency is
set (every 15 minutes for 30 seconds) and not initiated based on the TMP, then its frequency is
not affected by varying fouling rates. Indeed, the TMP for the primary membrane filters was
found to be relatively constant (-20 kPa) regardless of the influent turbidity (Figure 4.11). A
third factor to be considered is that the higher turbidity values occurred during periods of
increasing permeate production corresponding to increased pumping efficiencies as previously
noted. This increase in efficiency would likely mitigate any impact of turbidity, over the
turbidity range observed here, on the specific EC. It should also be noted that the turbidity of
this membrane influent is relatively low. Most of the newer membranes, especially the
submerged membranes, are designed to handle turbidity excursion exceeding 50 NTU or higher.
Therefore the turbidity observed in this study period (< 10 NTU) would not post a significant
challenge to the membrane system.
42
©2008 AwwaRF. ALL RIGHTS RESERVED
1.0
Turbidity (NTU)
8
0.8
6
0.6
4
0.4
2
0.2
0
Specific Energy Consumption (kWh/kgal)
1.2
10
0.0
Apr-05
May-05
Jun-05
Jul-05
Aug-05
Turbidity
Sep-05
Oct-05
Nov-05
Energy
Figure 4.10 Raw water turbidity and specific energy consumption by the membrane, DAF,
and ancillary chemical systems over time for the Kamloops WTP.
0
-5
TMP (kPa)
-10
-15
-20
-25
-30
0
1
2
3
4
5
6
7
8
9
10
Turbidity (NTU)
Figure 4.11 Transmembrane pressure (TMP) for the primary membranes (Train 1) as a
function of the influent raw water turbidity. More negative TMP values correspond to
greater vacuum pressures.
43
©2008 AwwaRF. ALL RIGHTS RESERVED
Potential Energy Conservation Improvements
Analysis of the Kamloops facility did not differentiate between the energy consumed by
the permeate pumps and the air scour blowers. Furthermore, energy data was only collected for
these pieces of equipment and none other at the plant. Therefore, discussion of the specific EC
by the membrane process relative to the entire treatment plant is limited. Nevertheless, there are
two operational changes that could be implemented that may result in a significant reduction in
EC. The first change is to reroute the secondary permeate from being recycled to the beginning
of the headworks to the clearwell. The plant records indicate that secondary permeate has the
same water quality as the primary permeate. However, the secondary permeate is recycled to the
front of the plant while the primary permeate is sent to the clearwell. In essence, the secondary
permeate is treated a second time though it does not need to be. Rerouting the secondary
permeate to the clearwell will eliminate passing the same volume of water through the primary
permeate pumps a second time, thereby reducing the EC of the primary trains. This change
would also result in increasing the total capacity of the plant. An ancillary benefit is that
chemical consumption will decrease since the secondary permeate would not be chemically
treated again.
Such a change would require coordination with provincial and local health agencies to
address any potential risks that could occur when fibers in the secondary membrane trains break.
The feed water to the secondary trains is the backwash from the primary trains. The primary
trains concentrate all particulate and larger microbiological contaminants in the coagulated river
water into the backwash water. As such, a fiber break in the secondary membranes has the
potential of leaking more contaminants into the clearwell when compared a break in the primary
membranes. The City would need to work with health agencies to address this potential risk.
The second area that could potentially reduce the EC of the plant is to shut down primary
and secondary membrane trains during low flow conditions. Kamloops staff indicated that all
trains operate regardless of water demand. The pumps are inefficient when operating at lower
flowrates which occur during periods of low demand (such as during the winter months) despite
the fact that the primary and secondary permeate pumps have VFDs in order to maintain high
energy efficiencies for a wide range of operating conditions. Shutting down one or more primary
and secondary membrane trains, during periods of low demand would allow the remaining
operational trains to operate closer to their optimal energy efficiency point on their respective
pump curves. In order to periodically shut down some of the membrane trains would require
reprogramming the membrane control system. It should be kept in mind that changing system
operation protocol after the plant is commissioned may require membrane manufacturers’
consent so that the membrane warranty can be maintained.
A minor improvement in energy efficiency may also be realized by shutting down some
of the flocculant mixer trains at the same time as the primary and secondary membrane trains.
The benefits of this operational change would be minor because the mixer motor is only 3-hp,
compared to the 75-hp and 10-hp motors for the primary and secondary membrane trains,
respectively.
44
©2008 AwwaRF. ALL RIGHTS RESERVED
Anthem Water Campus, Anthem, Ariz.
System Description
The Anthem Water Campus (AWC) drinking water system uses UF membranes to treat
surface water from the Central Arizona Project (CAP) Canal to meet base drinking water demand
for the new community of Anthem, Arizona (Arizona American Water Company 2003). The
plant is owned by the Arizona American Water Company and was constructed in 1999. Since
start-up, the facility has since been expanded three times, the last expansion being in 2002. The
plant is currently rated for 8.0 mgd. The AWC WTP uses groundwater wells and an intertie with
the City of Phoenix, Arizona distribution system to meet Anthem’s peak day demands. The
facility is operated 24-hours a day and is staffed eight hours a day.
The source water for the AWC WTP is from the CAP Waddell Canal. Table 4.2 lists the
canal water quality, which is a blend of water from the Colorado River and Lake Pleasant. TOC
data were not available. The CAP transfers the canal water to two raw water reservoirs located
on-site. It is from these two reservoirs that the AWC draws the CAP water. AWC has a raw
water pump station at each reservoir, with each station consisting of one 50-hp pump and one 40hp pump. Figure 4.12 is a schematic of the water intake and treatment process.
Table 4.2
Waddell Canal water quality parameters
Raw Water
Parameter
Units
s.u.
Average
8.1
Minimum
7.2
Maximum
8.6
°C
17.4
8.5
28.5
Alkalinity
mg/L as CaCO3
133
81
160
Hardness
mg/L as CaCO3
311
157
382
Turbidity (24-hour avg.)
NTU
3.3
0
149
Total dissolved solids
mg/L
620
521
674
µmhos/cm
810
428
1166
Odor
TON
4.3
1.2
8
Iron
µg/L
66
0.1
780
Fluoride
mg/L
0.62
0.27
0.85
Sulfate
mg/L
262
160
300
Lead
mg/L
-
0.004
<0.1
Manganese
µg/L
30
0.1
360
Copper
mg/L
0.005
0.005
0.005
Calcium
mg/L
66
52
72
Chloride
mg/L
81
75
300
pH
Temperature
Conductivity
Source: Damon S. Williams and Associates 2001.
45
©2008 AwwaRF. ALL RIGHTS RESERVED
Prior to membrane treatment, the water is prefiltered through 2-mm strainers to remove
large particulates and then dosed with powered activated carbon for taste and odor control.
Potassium permanganate addition is also available though not typically used. After the
pretreatment step, the water is pumped to a header pipe that supplies four parallel membrane
trains.
The AWC WTP uses a submerged UF membrane system. As noted earlier, the AWC has
been expanded four times, during each of which a membrane train added. The same membrane
vendor supplied the most current membrane at the time of each expansion. Because different
membranes were installed during each expansion, each of the four trains has different membrane
types and total membrane surface area (Table 4.3). The historical data that will be used later in
this report represents a period with the different membranes. At the time of writing, the AWC is
retrofitting the trains to standardize the entire membrane system around one particular membrane
type.
Figure 4.12 AWC WTP process flow schematic. Source: Arizona American Water
Company 2003.
46
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 4.3
Summary of membrane trains at AWC WTP
Parameter
Installed membrane type
Total membrane Area (ft2)
Design flux (gfd)
Treatment capacity (mgd)
Train 1
Train 2
Train 3
Train 4
C
55,000
35.5
1.95
B
52,000
35.5
1.85
B and C
54,080
35.5
1.92
C
57,200
35.5
2.03
Note: Membrane type designation is based on manufacturer’s equipment code
The membrane system SCADA system determines how many trains operate at any given
particular water production requirement. One train is used at low flow rates while at peak
capacity all four trains operate. The train operation is rotated so that each train runs for
approximately the same number of hours in order to balance equipment wear. Filtrate is pumped
from each operating membrane train under a vacuum of -2 to -9 psi, depending on level of
fouling. There is one dedicated filtrate pump for Membrane Train 1 and another for Train 2. For
Trains 3 and 4, there are three filtrate pumps (two duty and one standby) connected to a common
header.
Each train includes a separate pumping system to remove the solids accumulating in the
membrane basins. Each basin has two submersible reject pumps (one duty, one standby).
Depending on the system recovery setpoint, the reject pumps continuously extract a small
portion of the water flow at the basin bottom to waste accumulated solids. The system design
recovery setpoint is 85 percent to 95 percent, which means that 5 percent to 15 percent of the
total raw influent flow will be removed by the reject pumps. The reject flow is discharged to the
adjacent wastewater treatment plant.
The membrane filtration system includes an air scour system, an air/water separation
system, and a compressed air system. Air scour is used to agitate the membrane fibers in the
membrane modules to limit the particulate matter accumulation and fouling on the membranes.
The air scour also mixes the membrane basin contents to limit solids settling at the bottom of the
basins. There are three air scour blowers (2 duty and 1 standby). The blowers normally operate
in a cyclic operation. In this cyclic operation, two blowers operate continuously, one for Trains
1 and 2 and one for Trains 3 and 4. The full output of a blower is used to scour one basin for
30 seconds. Afterwards, the blower air is transferred (“cycled”) to the second basin for
30 seconds while the first basin receives no air scour. At the end of the next 30 seconds, the air
scour is cycled back to the first basin while the second receives no air. The output from the
blower is fixed by the manufacturer.
An air/water separation system is provided for each unit to remove the air from the
individual filtrate lines. As filtrate flows through the air/water separation system, any air that is
pulled through the membranes is off gassed and is removed by vacuum pumps.
The treatment system also includes backpulse and clean-in-place (CIP) systems. The
backpulse system uses a dedicated pump to push flow back through the membrane system for
removing particle accumulation on the membranes. The CIP system pumps and recirculates
either sodium hypochlorite or citric acid into the basins to remove any accumulated material not
removed by the regular backpulsing. The filtered water is disinfected using sodium hypochlorite
and then discharged to a finished water reservoir and into the distribution system.
47
©2008 AwwaRF. ALL RIGHTS RESERVED
Power Supply
Power is supplied to the AWC by the Arizona Public Service power feed from a
substation located onsite. The substation feed is split between four Service Entrance Sections
(SES). SES 1 solely serves the drinking water plant. SES 2 primarily feeds the drinking water
plant but also serves on-site irrigation pumps and the wastewater treatment plant headworks.
SES 3 and SES 4 feed are dedicated for the wastewater plant.
The plant SCADA system records a daily power measurement from each SES. These
data are used in the analysis of EC at the plant. Since this report specifically deals with the
drinking water system, the data for SES 1 and SES 2 were analyzed, with the SES 2 data
corrected to remove the irrigation and wastewater system components. The specific equipment
served by SES 1 and SES 2 are listed in Appendix A.
The AWC has three on-site backup generators which can supply a total of 4.5 MW power
to both the drinking water and wastewater treatment plants. Two smaller generators, with a total
capacity of 2.5 MW, supply additional dedicated power to the drinking water treatment plant.
These generators were not operating for any duration long enough to have a significant impact
on the AWC’s EC during the period studied for this analysis.
Energy Consumption
The EC analysis for the Anthem WTP concentrated on comparing the overall EC of the
WTP and determining what correlations exist between water quality, quantity, and energy use.
Daily power consumption data was acquired from SES 1 and SES 2 from January 1, 2004 to
July 31, 2006 and used for the analysis discussed in this report. These daily data values were
compared with monthly EC noted in the facility’s monthly electricity bills.
Figure 4.13 shows both the monthly EC of AWC WTP and the monthly water
production. Energy use ranged between 169,000 and 382,000 kWh/month while water
production varied between 47 MG/month to 138 MG/month.
48
©2008 AwwaRF. ALL RIGHTS RESERVED
500,000
150
Energy Use (kWh/month)
100
300,000
75
200,000
50
100,000
Water Production (MG/month)
125
400,000
25
Energy
Water Production
0
Jan-04
0
Jun-04
Dec-04
Jun-05
Dec-05
Jun-06
Figure 4.13 AWC WTP energy consumption by all equipment at the water treatment plant
and water production.
EC at the AWC WTP was classified into six major categories. These categories are:
1. The CAP pumps used to transfer surface water from the Waddell Canal to the raw
water storage reservoirs.
2. Raw water pumps used to pump the water from the reservoirs to the membrane
basins.
3. The UF membrane filtrate pumps.
4. The dedicated air-scour blowers for the UF membrane system.
5. Other equipment for the UF membrane system, including air compressors, air dryers,
vacuum pumps, reject pumps, backpulse pumps, and CIP equipment.
6. Finish water pumps used to transfer the treated water to the distribution system.
Figure 4.14 shows the breakdown of the overall AWC WTP EC by these major
categories. The EC for each category was estimated by dividing the daily recorded total EC by
the estimated consumption of each specific equipment (i.e. individual pump or blower). The EC
of each specific equipment was based on the size of the equipment motor and the estimated daily
use.
49
©2008 AwwaRF. ALL RIGHTS RESERVED
Monthly Energy Consumption (kWh/month)
500,000
CAP Pumps
UF Filtrate Pumps
Other UF Equipment
400,000
Raw Water Pumps
UF Air Scour Blower
Finished Water Pumps
300,000
200,000
100,000
Ja
n
-0
4
M
ar
-0
4
M
ay
-0
4
Ju
l-0
4
Se
p04
N
ov
-0
4
Ja
n05
M
ar
-0
5
M
ay
-0
5
Ju
l-0
5
Se
p05
N
ov
-0
5
Ja
n06
M
ar
-0
6
M
ay
-0
6
Ju
l-0
6
0
Figure 4.14 Breakdown of AWC WTP energy consumption by major equipment.
The highest EC at the AWC WTP that was observed during the two and a half year data
period is attributed to the CAP pumps, raw water pumps, and finished water pumps. These two
categories account for 81 percent to 86 percent of all EC at the WTP, depending on the month.
The remaining 14 percent to 19 percent was associated with the membrane system. The range is
due to the fixed or mostly constant speed equipment that is part of the membrane system,
primarily the air systems (air scour blower, compressor, and vacuum pumps). Table 4.4
compares the EC of these equipment categories between March 2005, the month with the lowest
EC, and July 2006, the month with the highest EC. In March, the constant speed blowers
accounted for more than half of the energy used for the membrane system since the blower
operations are fixed while the pumps are variable speed. However, during the peak EC month
(July), the energy consumed by the blowers accounts for approximately 25 percent of the
membrane system EC. This percentage decrease of EC occurs because the blowers are still in
operation at a constant rate, while the variable speed pumps are operating more and using more
energy to meet higher water production requirements.
50
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 4.4
Comparison of actual AWC WTP energy consumption, by equipment categories, between
months with lowest and highest energy consumption
Data for March 2005
Equipment
Data for July 2006
Energy
Used (kWh)
% of Total
Energy
Used (kWh)
% of Total
CAP Pumps
43,393
26%
111,479
29%
Raw Water Pumps
7,811
5%
20,066
5%
Finished Water Pumps
86,038
51%
197,436
52%
137,242
81%
328,981
86%
Filtrate Pumps
11,716
7%
30,099
8%
Air Scour Blowers
16,722
10%
16,722
4%
Other Membrane Equipment
3,700
2%
6,540
2%
Membrane Subtotal
32,138
19%
53,361
14%
Total
169,380
100%
382,342
100%
Pumping Subtotal
This report further analyzes how the EC of the membrane portion of the AWC WTP was
impacted by various water quality parameters. Specifically, this analysis consisted of correlating
the major parameters that could affect membranes with the energy use of the membranes. The
parameters analyzed (water production, temperature, and turbidity) were obtained from AWC
WTP monthly reports.
Water Production
The monthly water production fluctuates with demand through the year. Total EC
follows the same fluctuation pattern. However, when compared directly to each other, as in
Figure 4.15, the best-fit linear trend of increasing EC with increasing water production is
confirmed with a strong correlation (as defined by a R2 value of 0.85).
51
©2008 AwwaRF. ALL RIGHTS RESERVED
Membrane Energy Use (kWh/month)
60,000
50,000
40,000
R2 = 0.85
30,000
20,000
10,000
0
0
20
40
60
80
100
120
140
160
Water Production (MG/month)
Figure 4.15 Correlation between AWC WTP energy use by the membrane related
equipment only (permeate pump, air scour, cleaning system) and water production.
The specific EC is a value which normalizes the EC to account for the amount of water
production per month, which is defined as energy usage per 1,000 gallon treated. This value is
calculated by dividing the monthly energy use by the monthly water production. Figure 4.16
shows the specific EC over the two and a half years of operational data received. The figure
shows a strong logarithmic correlation between specific EC and monthly water production. The
trend observed from the graph shows the decreasing contribution of fixed energy users, such as
the air scour blowers, as water production increases. Conversely, at low water production, the
energy used for the fixed portions of the membrane system becomes incrementally larger
fractions of the total energy used.
52
©2008 AwwaRF. ALL RIGHTS RESERVED
Specific Energy Consumption (kWh/kgal)
1.0
0.8
R2 = 0.87
0.6
0.4
0.2
0.0
0
20
40
60
80
100
120
140
160
Water Production (MG/month)
Figure 4.16 AWC WTP specific energy consumption by the membrane related equipment
only (permeate pump, air scour, cleaning system). The data is fit using a logarithmic
function.
Water Temperature
Water viscosity decreases as temperature increases. For membrane treatment facilities,
decreased viscosity results in the filtrate pumps working at lower negative pressures (less
vacuum) to draw a unit volume of water through the membrane pores. In turn, less vacuum
results in reduced EC by the system. As a result, there exists a potential linkage in water
temperature and EC.
Figure 4.17 shows a comparison of the AWC WTP monthly water production and the
average water temperature. Except for two outliers, the water temperature entering the AWC is
between 15 and 25 °C. From August 2004 to March 2005 and August 2005 to March 2006, the
raw water temperature corresponds to a general trend of water production. As the water
temperature cooled, which also corresponds to cooler air temperatures, water production
decreased due to reduced demand. Between April and July, raw water temperatures actually
decrease though air temperatures in the region reach the hottest levels for the year. The cause of
this summer-time cooling is due to CAP’s management of the two source waters, the Colorado
River and Lake Pleasant, into the Waddell Canal.
The correlation between specific energy and water temperature for the entire two and a
half years of data is shown in Figure 4.18. This figure shows a weak correlation between the two
variables. This weakness is due to two different behaviors of water temperature and water
production, i.e. summer time water production is high while the water is cooler. However, an
53
©2008 AwwaRF. ALL RIGHTS RESERVED
analysis of just the August to March timeframes found no significantly stronger correlations for
August 2004 to March 2005 (R2 = 0.35). For August 2005 to March 2006, the correlation was a
stronger R2 = 0.68. This strong correlation was for a single six-month period in the entire two
and a half years of data analyzed and not replicated during the prior period the year before. As a
result, this correlation may be potentially anomalous. In summary, this investigation into the
AWC WTP could not quantifiably state that water temperature had any measurable impact on the
EC of the AWC WTP membrane system.
Water Production (MG/month)
125
40
100
30
75
20
50
25
10
Water Production
Temperature
0
Jan-04
0
Jun-04
Dec-04
Jun-05
Dec-05
Jun-06
Figure 4.17 AWC WTP monthly water production and monthly average raw water
temperature.
54
©2008 AwwaRF. ALL RIGHTS RESERVED
Average Monthly Raw Water Temperature (oC)
50
150
Specific Energy Consumption (kWh/kgal)
1.0
0.8
R2 = 0.22
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
o
Average Monthly Raw Water Temperature ( C)
Figure 4.18 Correlation between Anthem WTP specific energy consumption by the
membrane related equipment only (permeate pump, air scour, cleaning system) and raw
water temperature.
Turbidity
Specific EC is expected to increase as the raw water becomes more turbid. The reason is
that the membrane trains will backpulse more frequently during higher turbidity episodes. Since
energy is consumed during the backpulse process, though no water is being produced, the overall
specific energy use is expected to increase as the membranes are backpulsed more often.
Figure 4.19 shows the recorded raw water turbidity and specific EC at the AWC WTP.
The raw water turbidity was relatively low (less than 5 NTU) and fairly constant for the majority
of the time throughout the two and half years of operation, and thus has little to no correlation
with the specific energy. The spike on turbidity during the winter of 2005-2006 did not show
any discernable impact to the specific EC to the membrane system.
Part of the issue with the lack of correlation is due to the lack of variability in the feed
water turbidity. While the energy data, both raw and specific, was found to vary throughout the
year, turbidity was generally between 1 and 2 NTU. There is no other data to compare the winter
2005-2006 increase in turbidity with EC.
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40
1.0
35
Turbidity
30
0.8
25
20
0.5
15
0.3
10
5
0.0
Jan-04
Average Monthly Raw Water Turbidity (NTU)
Specific Energy Consumption (kWh/kgal)
Specific Energy
0
Jun-04
Dec-04
Jun-05
Dec-05
Jun-06
Figure 4.19 AWC WTP specific energy consumption by the membrane related equipment
only (permeate pump, air scour, cleaning system) and average monthly raw water
turbidity.
In summary, the analysis of the AWC WTP found that the CAP, raw water, and finished
water pumps are the most energy intensive equipment at the AWC WTP. These three pump
systems account for 81 to 86 percent of the total energy used at the facility. The EC by the
membrane system accounted for the remaining 14 to 19 percent. Of the membrane system
equipment, the variable speed filtrate pumps and the constant speed air scour blowers are the
largest energy users. At low flowrates, the constant speed blowers consume the most energy. At
higher flowrates, the filtrate pumps are the most energy intensive equipment in the membrane
system. Water production was determined to be the single largest factor in determining the
specific EC of the membrane plant. No discernable relationship could be determined between
EC and temperature or turbidity, which are normally important factors for the design and
operation of membrane systems.
Potential Energy Conservation Improvements
The primary energy consuming equipment in the AWC membrane system are the
permeate pumps and the air scour blowers. Here, the permeate pumps accounted for 7.5 percent
of the total specific EC at the plant, while the air scour blower account for 6.6 percent of the
total. Overall then, equipment directly linked to the membrane process accounted for roughly 15
percent of the total specific EC. The filtrate pumps are the correct types for the application and
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already on VFDs to improve the motor efficiency. As a result, there is little required to further
optimize the pumps.
The blowers are constant speed rotary-lobe units. The speed is set by the equipment
vendor for the specific basin and application. One potential opportunity for energy conservation
that could be explored would be to change the amount of air scour required from a constant
output to a variable output that is controlled by the feed water turbidity. In low turbidity waters,
less cyclical air scour is required since the solids loading on the filters is reduced. When the feed
water turbidimeter detects high turbidity, the output from the blowers would correspondingly
increase to limit the fouling on the membranes. This potential opportunity would require
collaboration with the equipment vendor to ensure that the conditions of the equipment warranty
are not violated. In addition, a separate analysis should be conducted to determine the costs of
additional SCADA programming and blower VFDs relative to the amount of energy saved.
Another option would be to consider changing the operation of the air scour blowers from
one blower for every two trains to one blower for four trains in periods of low turbidity. This
option would save on the expense of purchasing and installing VFDs but at the expense of less
operational flexibility.
Finally, this analysis focused specifically on the membrane system. However, as noted
earlier, the membrane system accounts for a small fraction of the energy costs of the WTP.
More emphasis should be put into investigating and potentially optimizing the operation of the
CAP pumps, raw water pumps and finished water pumps as these three pump systems are
considerably larger than the membrane system and therefore can be potential areas of larger
energy savings.
SUMMARY AND CONCLUSIONS FOR LOW-PRESSURE MEMBRANE SYSTEMS
The principal factors expected to affect the EC of low-pressure membrane systems are
production rates, water temperature, and turbidity. Considerations for EC optimization are
generally associated with design and operational improvements. These issues are discussed
below.
Factors Affecting EC of Low-Pressure Membrane Systems
Production Rates
Results of the overall specific energy use as a function of daily permeate production are
shown in Figure 4.20. Results are shown for both the Kamloops Centre and the AWC. Results
generally indicate that the specific energy use is greatest at low permeate production rates and it
declines with increased water production rates in a power law fashion. In other words, energy
efficiency increases as the plants approach their respective design treatment capacities. It is
worth noting that Arizona American reported production rates (2.5-6.5 mgd) lower than
Kamloops (10–32 mgd) and correspondingly reported specific energy use that was up to 10 times
greater than Kamloops. It is also worth noting that the average TDS was more than 20 times
greater in the raw water supply of Arizona American (620 mg/L) compared to Kamloops
(27.5 mg/L), though the waters had similar turbidities (≤ 5 NTU). With regard to pretreatment,
the AWC adds powered activated carbon directly to the process flow stream (direct filtration)
whereas Kamloops adds aluminum chlorohydrate and performs rapid mixing and flocculation
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prior to UF treatment. It is not known to what extent these different pretreatment processes
affected backwash operations and EC at each of the two sites. It is possible that the membranes
may foul to a greater extent and at a faster rate during direct filtration, resulting in higher
operating TMPs. The difference between theoretical and measured EC was not evaluated
because measured EC consumption data were not available for the Anthem and Kamloops water
treatment plants.
Specific Energy Consumption (kWh/kgal)
5
Anthem
4
3
2
Kamloops
1
R2 = 0.9643
0
0
5
10
15
20
25
30
35
Permeate Production (mgd)
Figure 4.20 Specific energy consumption as a function of daily permeate production at the
Kamloops and Anthem WTPs. All equipment is considered at the Anthem WTP while only
the membrane, DAF, and ancillary chemical systems are considered at the Kamloops WTP.
The data is fit using a power law function.
Temperature
Impacts of water temperature on overall EC were evaluated for Kamloops and Arizona
American (Figure 4.21). Results generally indicate no clear correlation regarding temperature
impacts on EC because of the overriding effects of production. At low temperatures, EC was
expected to increase because water viscosity is greater and pumping requirements would thus be
expected to be greater. However, greater EC at Kamloops also coincided with lower production
rates (Figure 4.4). Energy efficiency was therefore determined to be driven primarily by
production rates instead of water temperature. Similar results were observed for Arizona
American.
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Specific Energy Consumption (kWh/kgal)
5
Anthem
4
3
Kamloop
2
1
0
0
5
10
15
20
25
30
Temperature (oC)
Figure 4.21 Specific energy consumption as a function of water temperature at the
Kamloops and Anthem WTPs. All equipment is considered at the Anthem WTP while only
the membrane, DAF, and ancillary chemical systems are considered at the Kamloops WTP.
Turbidity
Data and information collected at Kamloops and the AWC indicate no clear correlation
regarding the effects of turbidity (Figure 4.22). EC was expected to increase with increased
water turbidity because backwashing occurs more frequently. However, no clear correlation
between EC and turbidity was realized for either facility.
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Specific Energy Consumption (kWh/kgal)
5
4
Anthem
3
2
Kamloops
1
0
0
5
10
15
20
25
30
35
40
Turbidity (NTU)
Figure 4.22 Specific energy consumption as a function of the raw water turbidity at the
Kamloops and Anthem WTPs. All equipment is considered at the Anthem WTP while only
the membrane, DAF, and ancillary chemical systems are considered at the Kamloops WTP.
Considerations for EC Optimization of Low-Pressure Membrane Systems
Potential design and operational improvements were identified for the Kamloops and
Arizona American low-pressure membrane filtration systems. For Kamloops, the secondary
permeate flow line could be rerouted directly to the clearwell and thus reduce the total volume of
water passing through the primary permeate pumps. EC could also be reduced by shutting down
one or more primary and secondary membrane trains during low flows and thus allows the
remaining trains to operate near the optimal energy efficiency point. For Arizona American,
several specific improvements were identified for the air scour blowers. These improvements
include tying the operation of the air scour blowers to the influent water quality and increasing
the number of membrane trains that are serviced by a single blower.
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CHAPTER 5
EC OF REVERSE OSMOSIS SYSTEMS FOR DRINKING WATER AND
REUSE WATER TREATMENT
This chapter focuses on EC by utilities that use RO membrane systems for drinking water
and reuse water treatment applications. An overview process description and identification of
major EC components is provided followed by three case studies: the Water Replenishment
District of Southern California (WRD) Robert Goldsworthy Desalter; the City of Seward,
Nebraska Corrosion Control Plant; and the West Basin Municipal Water District (California)
Water Recycling Facility (WBWRF). Each of these case studies includes a description of the
system and analysis of EC, and identification of potential optimization opportunities. Seward
and WRD facilities are for groundwater application, and WBWRF is for water reclamation. In
addition, two of these case studies (WRD and WBWRF) include the results of EC audits.
Finally, a summary of the EC analysis for these three case studies is included at the end of the
chapter.
PROCESS DESCRIPTION OVERVIEW
RO is a separation process that uses semi-permeable membranes to separate dissolved
and colloidal materials from water. RO is considered a high-pressure membrane process as it
typically requires feed pressures in the range of 200 to 1000 psi. RO systems almost universally
consist of three major components: a pretreatment system to condition the water, a high-pressure
pumping system, and a membrane module containing the membrane elements. Other RO system
components that may be present include a chemical cleaning system [i.e., clean in place (CIP)
system] and some form of post RO stabilization process. Because RO membranes remove nearly
all of the minerals from the feedwater the permeate water is aggressive and may require
conditioning prior to the distribution system. A general layout for an RO system is shown in
Figure 5.1.
Two process streams are produced in the RO process, a clean permeate water and a
concentrated reject stream. To increase system recovery, reject or concentrate from an RO
system (Stage 1) may serve as the feedwater for a second system (Stage 2) in a process known as
staging. When staging is employed, a booster pump may be required to increase the feed
pressure for the subsequent stage. Permeate is sent to a storage vessel where a portion of it may
serve as the make-up solution for the CIP system. The CIP system chemically cleans the
membranes once their efficiency drops to a specific target value. The CIP system is composed
of a pump and a storage tank. A booster pump may be required for the permeate to provide
sufficient pressure to move the permeate into storage or to the subsequent treatment process.
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CIP System
Chemical
Pretreatment
Membrane
Module
Permeate
Boost Pump
Feed Pump
Prefiltration
Reject
Figure 5.1 General layout for a RO membrane water treatment system.
Membrane elements and trains of elements are designed to have minimum and maximum
ranges of operational variables such as feed and permeate flowrates, recoveries, and pressures.
In order to fall within the specified ranges, which vary depending on the membrane used,
membrane systems are typically operated in an on/off basis. During on/off operation, the
membrane system is operated for a specified time period and the product water (permeate) is
stored. In most cases, the membrane system is designed to meet the maximum daily flowrate
that is required by the system (max daily flow). Once the designated storage volume is reached,
the membrane system is turned off until additional product water is required. Systems are
designed to operate to minimize the length of these idle periods in order to prevent
fouling/scaling of the membranes in the absence of crossflow.
MAJOR EC COMPONENTS
The high-pressure feed pump is the largest energy consumer in RO membrane processes.
Secondary sources of EC include the concentrate and permeate booster pumps (if required).
Peak periods of EC occur during events such as cleaning, flushing, and maintenance events.
RO energy consumption is directly related to the TDS concentration in the feed water.
Salts impart an osmotic back-pressure that must be overcome in order to transport water across
the membrane. Thus, greater feed pressures, and in turn pumping requirements, are needed for
higher salinity waters. Other important factors include the membrane permeability/resistance
and the development of membrane fouling. Fouling reduces the membrane permeability and
necessitates higher feed pressures in order to maintain a desired permeate flux.
The importance of fouling points to the significance of implementing an effective
pretreatment scheme in order to minimize energy costs. Membrane age and feed solution
chemistry also affect the energy required by the pumps to achieve a desired flux, though to a less
substantial degree than the aforementioned factors. Over time, polymeric membranes become
compacted (i.e., less permeable) as a result of the high operating pressure. As a result, older, less
permeable membranes require higher operating feed pressures to produce the same volume of
permeate as less used membranes. Other operational parameters of importance include the
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system recovery ratio (permeate flowrate/feed flowrate), system feed pressure, raw water
temperature, and feed flowrate.
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
Water Replenishment District of Southern California Robert W. Goldsworthy Desalter
System Description
In the Los Angeles area, seawater intrusion into the groundwater aquifers has occurred
over time as a result of over pumping in the West Coast Basin. A groundwater injection system
was constructed to form a barrier to prevent further intrusion, and protect the remaining
uncontaminated groundwater supplies. In 2001, the WRD began operation of the Robert W.
Goldsworthy Desalter, located in Torrance, California, to withdraw a plume of saline water that
was trapped in the aquifer as a result of the intrusion barrier. The treated effluent from WRD is
sold to the City of Torrance for use as drinking water.
The Desalter consists of a groundwater well pump and an RO membrane plant that is
contract operated and maintained by Eco Resources, Inc. The facility has operated nearly
continuously since it was constructed in 2001. The raw water source for the Goldsworthy
Desalter is a brackish groundwater plume that has been impacted by seawater intrusion into the
aquifer and was subsequently trapped behind the WRD’s intrusion barrier. The well is 450 ft
deep, and is cased to a depth of 445 ft. Water quality parameters for the raw well water are
summarized in Table 5.1. The groundwater has a TDS of 2,580 mg/L and a pH of 7.7. The
groundwater permit for the Desalter plant requires that the water quality equals or exceeds
1,000 mg/L chloride so as to minimize withdraw of fresh groundwater and prevent further
seawater intrusion. The well pump is operated by a variable speed motor so that the groundwater
withdraw rate is more easily controlled. Aquifer testing suggested a withdraw rate of 2,200 gpm
(3.2 mgd). The WRD initially anticipated that upon continuous pumping, well operation would
cause migration of more saline water from the basin to the extraction zone. However,
continuous operation of the Goldsworthy Desalter plant from 2005 to 2006 has been at 2.06 mgd
to maintain the chloride levels above 1,000 mg/L. Higher pumping rates resulted in lower
chloride levels in the raw water, indicating that some fresher groundwater was being
incorporated into the brackish water plume.
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Table 5.1
Water characteristics for the raw water feed to the Goldsworthy Desalter treatment plant
Parameter
Calcium
Magnesium
Sodium
Potassium
Carbonate
Bicarbonate
Sulfate
Chloride
Nitrate
Silica
Fluoride
Total Dissolved Solids
pH
1
Unit
January 20051
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L as HCO3
mg/L
mg/L
mg/L as NO3
mg/L as SiO2
mg/L
mg/L
units
320
94
340
15
0.6
211
334
1,050
0
29
0.17
2,580
7.7
Analyzed by MWH Laboratories
A schematic of the Goldsworthy Desalter treatment system is shown in Figure 5.2. The
Goldsworthy Desalter pretreatment process includes acidification, using sulfuric acid, antiscalant
addition, and prefiltration through 20-μm cartridge filters. The RO treatment system is
comprised of 462, 8-in diameter spiral wound ESPA2 membrane elements (Hydranautics,
Oceanside, California). The membranes are housed in 66 pressure vessels, each containing
seven membrane elements in series. It is a two-stage system with 42 pressure vessels in the first
stage and 24 pressure vessels in the second stage. A single vertical turbine pump with variable
frequency drive feeds water to the RO system. Product water leaving the RO system is passed
through a decarbonator to remove any dissolved carbon dioxide. Carbon dioxide removal is
required to raise the pH and to stabilize the water with respect to the Langelier Saturation Index
(corrosion control). Afterwards, sodium hydroxide is added for additional pH adjustment,
followed by sodium hypochlorite and ammonia to provide a chloramine residual. A portion of
the untreated groundwater water bypasses the RO and decarbonation steps and is blended with
the RO product water prior to chemical addition. The ability to by pass a portion of the
feedwater around the RO system reduces pumping requirements and increases the overall water
recovery at the treatment plant.
The CIP system is used to chemically clean the membranes once they have become
sufficiently fouled. For groundwater fed systems, chemical cleans are typically required once or
twice a year. The Goldsworthy Desalter CIP system is capable of cleaning either of the
membrane stages by physically connecting to the respective plumbing.
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Acid & Antiscalant
Pumps
NaOH/NaOCl/ Ammonia
Pumps
High-Pressure
2 Stage RO
Pump
Decarbonator
Well
Pump
Return
Immersion
Heater
Product
Forwarding Pump
NaOH
Pump
CIP
Recirculation
Pump
Figure 5.2 Process flow diagram for the Goldsworthy Desalter treatment plant.
Power Supply
The Southern California Edison Company (SCE) supplies power to the Goldsworthy
Desalter treatment plant using one power feed. SCE monitors power consumption through a
single watt-hour meter on the power feed and bills WRD on a monthly basis. The plant’s
SCADA system has the ability to monitor, but not log, instantaneous EC by the large pumps, but
not for the smaller equipment. EC is primarily tracked by Eco Resources using the monthly SCE
electricity bills.
Energy Consumption
The pieces of equipment associated with the treatment system which consume significant
quantities of electricity on a daily basis include the raw water well pump, chemical injection
pumps, RO booster pump, decarbonator blower, and product forwarding pump. Power
consuming equipment associated with the CIP system are the immersion heater and the cleaning
solution recirculation pump. Because the CIP system is used infrequently (once or twice a year)
it does not contribute significantly to the daily power consumption at the plant. Each piece of
equipment is shown in the process flow diagram in Figure 5.2. Other power consuming
equipment not directly linked to the treatment system includes equipment instrumentation and
controls and HVAC.
The principle consumers of electricity are the high-pressure pump, followed by the well
pump and the product forwarding pump. The high-pressure pump is driven by a variable
frequency motor, allowing the pump to deliver the desired volume while minimizing EC. The
well pump is operated by a constant speed motor. There are two product forwarding pumps (one
active and one stand-by), both of which have variable frequency motors. The decarbonator
blower is driven by a 7.5-hp motor.
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From June 7 to July 7, 2005, the entire treatment facility consumed 241,718 kWh of
electricity while producing 61,821,000 gallons of treated water. This corresponds to a specific
EC of 3.91 kWh/kgal, which is comparable to that for other RO treatment systems using low
salinity brackish waters as a raw water source. These values represent typical monthly
performance values for the Goldsworthy Desalter treatment plant. A breakdown of the specific
EC by the different process equipment at the plant is given in Table 5.2. The high pressure RO
pumps accounted for approximately half of the specific EC, followed by the product forwarding
pump (25 percent) and then the raw water well pumps (15 percent). The EC of the decarbonator
blower was accounted for a considerably lower fraction of the specific EC compared to the
pumps. The unaccounted energy is attributed to the HVAC and other support systems. The
energy consumed by these systems was however, substantial and considered to be higher than
normal when compared to other similar treatment systems. The total process EC of
3.36 kWh/kgal represents approximately 91 percent of the actual measured energy at the plant,
with the remainder attributed to support equipment and HVAC.
Table 5.2
Breakdown of the specific energy consumption at the Goldsworthy Desalter
Treatment Equipment
Well pump
High pressure RO pump
Product forwarding pump
Decarbonator blower
Major Equipment Total
Unaccounted Energy
Total
Specific Energy Consumption
(kWh/kgal)
0.55
1.83
0.92
0.06
3.36
0.32
3.68
Percent of Total
14.9
49.7
25.0
1.6
91.3
8.7
100.0
The total specific EC measured at the Goldsworthy Desalter plant is compared to
theoretical values in Figure 5.3. The specific EC as a function of influent TDS for a typical
brackish water RO application is also plotted for comparison. The theoretical specific EC for the
Goldsworthy Desalter plant is similar to that expected for typical brackish water RO systems. At
an influent TDS of 1000 mg/L the specific EC is estimated to be 1.6 kWh/kgal and increase
linearly with TDS. At a TDS concentration of 2400 mg/L the specific EC for the plant is
predicted to be approximately 2.2 kWh/kgal. The specific EC by the RO system fell below the
estimated value, and was equal to 1.63 kWh/kgal at an influent TDS of 2400 mg/L. The specific
EC for the entire plant was higher and equal to 3.7 kWh/kgal. Specific EC was calculated based
on average flows as reported in the annual report for the plant. During design it was assumed
that the membranes would experience a 7 percent flux decline on an annual basis, and up to an
annual 10 percent reduction in salt rejection. However, the membranes are performing better
than predicted values. The manufacturer’s modeling software predicted a specific EC of
2.2 kWh/kgal, compared to the actual specific energy value of 1.6 kWh/kgal. This better than
expected actual specific energy value is an indication that the well water at this location does not
foul the membrane at the 7 percent per year assumed at design, but is actually performing with a
fouling factor of less than 2 percent per year.
Differences in theoretical expectations and actual measured values may be attributed to a
number of factors. One possibility is the impact of water temperature on membrane
performance. Unfortunately, as data could only be collected under one set of water quality
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conditions membrane performance could not be evaluated as a function of TDS and temperature,
which are known to affect RO performance. Of note however, is the fact that design
performance values were based on a water temperature of approximately 23°C. Indeed, actual
water temperature on those days that EC was measured was 21.7°C. Thus, temperature does not
appear to be the differentiating factor here, with respect to the design and actual performance
values. The original system design was for an influent TDS that was approximately 4,800 mg/L,
which is approximately double the current operating value. The original design also assumed
larger flowrates than are currently being realized. However, the membrane system is operating
at better than expected EC. The pumps are operating at less than peak efficiencies due to lower
pressure and flowrate requirements. Finally, the current average membrane flux is below that of
the original design values indicating that the better than expected specific EC is occurring despite
less than optimal membrane characteristics.
4
Specific Energy Consumption (kWh/kgal)
Calculated typical RO system
Total Goldsworthy Facility
Calculated Goldsworthy RO
3
Actual Goldsworthy RO
2
1
0
0
500
1,000
1,500
2,000
2,500
3,000
3,500
Influent TDS (mg/L)
Figure 5.3 Comparison of Goldsworthy energy consumption (influent TDS = 2,393 mg/L).
Potential Energy Conservation Improvements
There are several areas in which the energy efficiency could be improved at the
Goldsworthy Desalter facility. The RO, product forwarding, and well pumps account for
roughly 90 percent of the total specific EC at the plant. Therefore, efforts to improve plant
energy efficiency should focus on these three key areas. For the RO feed pumps, energy savings
may be realized by optimizing the raw and product water blending ratio. While blending
improves water recovery and reduces the volume of concentrate that must be disposed of, it also
results in the RO feed pumps operating farther down on their respective pump curves making
them less efficient. Therefore, increasing the blending ratio may have unexpected consequences.
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Determination of the optimal blending ratio, with regards to chemical consumption, concentrate
disposal and RO pump efficiency, may result in improved specific EC.
The energy efficiency for each of the pumps (well, RO, and product forwarding) could be
improved through continuous operation at their optimal point on their respective pump curves.
Currently, the system is required to operate at variable flowrates (the plant can only pump water
with a TDS > 1,000 mg/L) so it is not possible to always operate at the maximum pump
efficiency. Alleviating this constraint through RO product storage or some other design change
may improve the efficiency of all three pump systems.
Operation at lower feed pressures could also improve energy efficiency. Lower pressure
operation may be realized through replacement of the older membrane elements with newer high
rejection, low-pressure RO membranes. This alternative would require that a cost benefit
analysis be done that accounts for the costs associated with membrane replacement versus the
potential energy savings costs. Figure 5.4 shows the expected specific EC for several newer RO
membranes treating water that approximates that of the Goldsworthy raw feedwater. From these
projections none of the selected new membranes will improve on the current specific EC. Only
the NF90 (a NF membrane) could provide a lower specific EC based on the modeling software.
However, it must be noted that actual performance testing would be needed to determine the
performance of each membrane when treating the Goldsworthy raw feedwater. This is illustrated
by the fact that the current membranes were expected to have a specific EC that was greater than
its actual value (see Figure 5.3).
Specific Energy Consumption (kWh/kgal)
10
8
6
4
2
Current Specific
Energy Consumption
Typical
BW30
ESPA3
Marco Is.
CPA3
BW30wER
NF90
Series8
0
0
3,000
6,000
9,000
12,000
15,000
Influent Total Dissolved Solids (mg/L)
Figure 5.4 Theoretical specific energy consumption for several new RO and NF
membranes as a function of raw water TDS. The actual specific energy consumption value
for the RO process at the Goldsworthy Desalter treatment plant is also shown for
comparison.
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Seward, Nebraska Corrosion Control Plant
System Description
The Seward, Nebraska Corrosion Control Plant is a 3.2 mgd groundwater treatment plant
that was commissioned in June 2004. A process flow diagram of the Seward facility is given in
Figure 5.5, and water quality characteristics for the raw and finished water are summarized in
Table 5.3. The primary treatment processes at the plant are a two-stage RO process for nitrate
removal, and a degasification step for pH adjustment and carbon dioxide removal. The plant is
remotely operated and is inspected on a daily basis. The groundwater has a relatively low
conductivity of around 800 μS/cm (~512 mg/L TDS) but contains elevated levels of nitrate.
Table 5.3
Water quality properties of the raw feedwater and RO product water at the Seward WTP
pH
Hardness (mg/L as CaCO3)
Nitrate (mg/L)
Temperature (°C)
Conductivity (μS/cm)
Raw Water
6.7
410
13
9 – 13
800
RO Permeate
5.5
0
3
Not available
50
Blended Water
7.67 – 7.76
137 – 205
5.9 – 8.6
11
-
The feed water to the treatment plant comes from nine groundwater wells, which are
located in three different wellfields (South Nos. 1, 2, and 3; Southwest Nos. 1 and 2; and West
Nos. 7, 8, 9, and 10). A minimum of two wells are required to provide sufficient influent
flowrate to the plant. At least three wells are in operation during the winter, and more are used
during the summer months, as demand increases. The wellfields are located at different
distances from the plant and have different yields, water qualities, and allocated water rights.
The Southwest wellfield is located approximately 6 miles from the plant, while the South and
West wellfields are located 4 and 2.5 miles away, respectively.
Figure 5.5 Process flow diagram for the Seward, Nebraska Corrosion Control Plant.
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Raw water is passed through cartridge filters with a pore size of 5-μm prior to the twostage RO units. The well pumps provide sufficient pressure to pass the water through the
cartridge filters. Following cartridge filtration, 50 percent of the influent water bypasses the RO
units and is blended with the RO product water. Each RO unit consists of one booster pump and
a two-stage RO array. The first stage consists of 24 pressure vessels, with each pressure vessel
containing two Hydranautics ESP-2 elements and four ESP-4 elements. The second stage is
made up of 12 pressure vessels with each containing 6 ESP-4 elements. The membrane elements
have not been replaced or cleaned since plant start up in 2004.
After RO treatment, the permeate water and the bypass water are blended together and
passed through a degasifier for CO2 removal and pH adjustment. The pH of the finished water is
7.7. The degasifier blower is driven by a constant speed motor, whose operation is linked to that
of the RO units. Liquid caustic soda injection is also available for supplemental pH adjustment
if needed. The finished water is piped to the clearwell following degasification. Three high
service pumps, each with a constant-speed motor, deliver the finished water from the clearwell to
the distribution system. One high service pump is half the size of the other two and is used for
base load demands. The two larger pumps are for peak demand and fire flow. High-service
pump operation is based on the water level in the clearwell.
The RO trains, designated as A and B, operate in a lead/lag configuration, with the RO
train in the lead position switched once daily. Operation of the RO units is based on the water
level in the plant clearwell. During low demand periods such as in the colder winter months, the
lead unit tends to operate for short durations, while the lag unit sits idle for most of the time. The
lead unit runs nearly continuously during high demand periods (i.e., during the summer), with
the lag unit running for several hours per day. Performance data for the RO trains is summarized
in Figures 5.6 through 5.8. The RO system was designed to operate at a recovery rate of 85
percent. However, except for a 10-day period in August, 2005 each RO train has operated at a
75 percent recovery rate (Figure 5.6). This translates to a permeate production rate of roughly
570 gpm (0.8 mgd). The plant operated at a lower recovery rate than its design value due to a
performance issue related to inadequate nitrate removal. The RO concentrate is disposed of
through a NPDES-permitted discharge to the adjacent Blue River. The facility may also
discharge to the sanitary sewer if necessary.
The feed pressure for Trains A and B are reported as a function of permeate flowrate in
Figure 5.7. From the data presented here, the feed pressure required to reach the desired
permeate flowrate of roughly 570 gpm increased during the first year of operation. For instance,
in November 2004, the average feed pressure was 116 psig to achieve the desired permeate
flowrate (~570 gpm). By November 2005, the feed pressure had increased to 126 psig to achieve
the same production rate; this is an increase of 8.8 percent (Figure 5.7). This increase is
attributed to membrane fouling. As the membranes become fouled, the resistance to mass
transport across the membrane increases, resulting in the observed increased pressure
requirements to reach the target production rate.
The feedwater and permeate conductivities are shown in Figure 5.8 as a function of time.
The raw water conductivity varied between 700 to 900 μS/cm, with a brief drop to 200 μS/cm in
October 2005. The relatively low variability in the raw water TDS (as indicated by the
conductivity values) suggests that the osmotic back-pressure, and thus the necessary driving
pressure, will not vary substantially for the RO system, outside of fouling effects. The permeate
conductivity was generally constant and varied between 40 to 50 μS/cm, owing to the relatively
constant rejection properties that are characteristic of RO membranes.
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900
100%
800
75%
700
50%
600
25%
500
Nov-04
Recovery Ratio
Flow (gpm)
Feed flow
Permeate flow
Recovery rate
0%
Feb-05
May-05
Aug-05
Nov-05
Figure 5.6 Feed and permeate flowrates as well as the corresponding recovery rate for
Seward Corrosion Control Plant RO Train A measured over the study period.
590
Permeate Flowrate (gpm)
580
570
560
550
RO-A Nov-04
540
RO-A Nov-05
RO-B Nov-04
530
RO-B Nov-05
520
100
110
120
130
140
Feed Pressure (psig)
Figure 5.7 Permeate flowrate as a function of feed pressure for Seward Corrosion Control
RO Trains A and B taken at two different time periods.
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1,000
Conductivity (mS/cm)
Feedwater
100
Permeate
10
Nov-04
Feb-05
May-05
Aug-05
Nov-05
Figure 5.8 Seward Corrosion Control Plant feed water and permeate conductivity as a
function of time.
Energy Supply
Electricity is supplied to the Seward facility by the City of Seward. Each of the three
wellfields has electrical meters that monitor their respective EC. There is an electrical meter at
the treatment plant that records the total EC for the RO trains, degasifier, high service pumps,
and the ancillary treatment and building equipment. The City tracks the EC of the wellfields and
treatment plant based on monthly energy bills. There is no data available for individual
treatment processes, such as the RO process or the high service pumping.
Power is supplied by one power feed, with standby power supplied by an on-site 500 kW
diesel generator. The standby generator is exercised weekly without a load, and once a month
with a load. There was no correction to the energy data to account for the use of the standby
generator in the subsequent data analysis. A summary of all the major electrical equipment in
the plant is listed in Appendix A.
Analysis of the Seward treatment plant EC consisted of two phases. The first was to
identify the major areas of EC. The second was to determine how the system EC could be
correlated to water production. The initial evaluation concentrated on comparing the overall EC
of the plant and determining what correlations exist between water quality and quantity versus
energy use. Power consumption was obtained from monthly electrical bills, from November
2004 to November 2005. The power data was recorded as true energy, in units of kWh.
Although EC by individual processes could not be directly measured, it was possible to calculate
these values according to the procedures outlined in the following paragraphs.
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The three groundwater wellfields are metered in different ways. The three South Wells
draw power through a single meter, while the two Southwest Wells each have their own
electrical meter. The West Wellfield has four electrical meters, one for the well pumps and three
for ancillary equipment and a building associated with the wells. To account for this metering
variability, the energy analysis was based on the average EC for all of the wellfields, with the
meter readings of the two Southwest Wells and the four readings for the West Wellfield merged
into one value for each respective wellfield.
The monthly RO booster pump EC was calculated based on records for pump operation
and using Equation 5.1:
EC =
QDP
×T × C
3960 E P E M
(5.1)
where EC is the EC in kilowatt-hours, Q is the pump flow rate in gpm, DP is the pump discharge
pressure in feet of water, EP is the pump efficiency, EM is the motor efficiency, T is the estimated
monthly operating time in hours, and C is a conversion factor for converting horsepower to
kilowatt-hours. The calculation was based on the daily recorded pump flow rate, elapsed time,
and discharge pressure for the RO booster pumps. Pump efficiency was based on a review of the
manufacturer’s pump curve. The monthly water production was divided by the average pumping
rate for the particular month to determine the number of hours the RO booster pumps were
operated (Figure 5.9). With this methodology, the number of RO trains operating at any given
time is not required.
Estimated Total Booster Pump Run Time (hrs/month)
600
500
400
300
200
100
0
Nov-04
Feb-05
May-05
Aug-05
Nov-05
Figure 5.9 Estimated total monthly run time for the booster pumps for RO Trains A
and B.
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EC by the degasifier blower was calculated in a similar method to the RO booster pumps.
Here, the operating horsepower of the fan motor is multiplied by the operating time. Since the
blower operates at a constant speed, and there were no daily recorded values for blower output,
the operating horsepower was assumed to be the rated motor horsepower. The blower’s
operational time was calculated differently from that for the operational RO booster pumps since
it operates when either one or both RO trains are operating. Since the blower operates whenever
water is pumped to the treatment plant, the operational time was assumed to be equal to the
longest time that any one well was operating on a given day. Well run times are shown in
Figure 5.10. Discussions with plant operators indicated that well operations are not staged (i.e.,
one well turns on after another is turned off) so the assumption on longest run time seems valid.
Daily Maximum Well Run Time (hrs)
30
25
20
15
10
5
0
Nov-04
Feb-05
May-05
Aug-05
Nov-05
Figure 5.10 Daily maximum run times for the Seward groundwater wells.
The energy consumed by the high service pumps, and the ancillary treatment and
building equipment was calculated by subtracting the calculated energy use of the RO booster
pumps and the degasifier blower from the monthly EC for the entire treatment plant. For the
subsequent analysis, the amount of energy consumed by the ancillary equipment was considered
to be negligible when compared to the high-service pumps. This assumption was made since the
ancillary equipment’s power demand is considerably smaller than that of the high service pumps,
and/or it is used less than the high service pumps.
Energy Consumption
EC at the Seward facility was divided into five major equipment categories: the
groundwater well pumps, RO booster pumps, degasifier blower, high service pumps, and the
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ancillary equipment for the water treatment process (such as the chemical feed pumps, on-site
hypochlorite generator, process instrumentation, and valves) and the building functions (HVAC,
bridge crane, computers, lighting). A breakdown of the average monthly specific EC by each of
these different systems is reported in Table 5.4.
Table 5.4
Average monthly specific energy consumption at the Seward Corrosion Control Plant
Specific Energy Consumption
(kWh/kgal)
4.71
0.57
0.14
1.47
6.89
Treatment Equipment
Well pumps
High pressure RO pump
Degasifier
High Service Pumps*
Total
Percent of Total
68.3
8.3
2.0
21.4
100.0
*energy consumption by the ancillary equipment is included with the high service pumps
Figure 5.11 shows the cumulative EC for the major process equipment over the study
period. The corresponding water production rates are also included in Figure 5.11 for reference.
The same data is shown in a non-cumulative manner in Figure 5.12. Pumping the groundwater
to the treatment plant and pumping the finished water from the plant to the distribution system
were found to be the most energy-intensive portions of the entire Seward drinking water system.
This pumping accounted for 65 to 85 percent of the total system EC. The degasifier was the
least energy-intensive step, accounting for approximately 4 percent of the total system EC, due to
the relatively small motor size needed in comparison to the various water pumps. The remainder
of the EC was attributed to the RO booster pumps.
200,000
100
High Service Pumping & Ancillary Equip.
Degassifier
Energy Use (kWh/Month)
75
Wellfield
Water Production
100,000
50
50,000
25
0
Nov-04
Water Production (MG/Month)
Reverse Osmosis
150,000
0
Feb-05
May-05
Aug-05
Nov-05
Figure 5.11 Seward energy consumption by different process equipment as a function of
the water production rate.
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Monthly Energy Consumption (kWh)
80,000
60,000
40,000
20,000
0
Nov-04
Feb-05
May-05
Aug-05
Nov-05
High Service Pumping and Ancillary Equipment
Degassifier
Reverse Osmosis
Figure 5.12 Seward energy consumption by different process equipment as a function of
time.
The average monthly water production rate for each of the wellfields is plotted as a
function of EC in Figure 5.13. EC increased at each of the wellfields with increasing water
production (i.e., as more water is pumped to the treatment plant). EC at the South and West
wellfields are relatively equal over the different water production rates seen in Figure 5.13.
However, for the Southwest wellfield the EC tends to be lower that that for the other two
wellfields, particularly when the production rate exceeds 10 MG/month. Recalling that the
Southwest wellfield is located the farthest distance from the plant and must therefore pump the
water over the greatest distance, this result is somewhat surprising. This observation is further
highlighted through inspection of the specific EC as a function of water production for the three
well-field areas (Figure 5.14).
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Energy Consumption (kWh/month)
25,000
20,000
15,000
10,000
South Wellfield
5,000
Southwest Wellfield
West Wellfield
0
0
5
10
15
20
25
Water Production (MG/month)
Figure 5.13 Seward well production and energy consumption by the corresponding well
pumping systems.
Figure 5.14 shows that for the full period studied, each of the wellfields was found to be
more efficient as more water was pumped out of the ground to the treatment plant. Furthermore,
the calculated specific EC trend lines of the South and Southwest Wellfields were found to be
nearly the same where the respective ranges of water production overlap, with the West
Wellfield having a higher specific EC at approximately 8 MG/month. However, this analysis
was found to be sensitive to the single outlier data point (November 2005) for the Southwest
Wellfield. The overall results changed significantly when the November 2005 data was removed
from all three wellfields. While the South and West Wellfield changed very little, removing the
data outlier for the Southwest Wellfield resulted in a calculated specific EC trend line that is
lower than the other two wellfields. The difference between the Southwest and South Wellfields
was approximately 0.04 kWh/kgal, indicating that the Southwest Wellfield was the most energyefficient one in the Seward system.
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5
South Wellfield
Specific Energy Consumption (kWh/kgal)
Outlier Data Point
Southwest Wellfield
4
West Wellfield
3
South Wellfield
R2 = 0.72
West Wellfield
R2 = 0.60
Southwest Wellfield
R2 = 0.86
2
1
0
0
5
10
15
20
25
Water Production (MG/month)
Figure 5.14 Seward wellfield specific energy consumption for November 2004 through
November 2005.
Since the RO booster pumps operated at constant feed and permeate flowrates and
recovery rate for the time period studied, no correlation could be made between water production
and EC. The specific EC for the RO process, which accounts for 50 percent of the total water
produced at the plant (50 percent is bypassed around the RO system), ranged from 0.55 to
0.60 kWh/kgal. Specific EC increased from November 2004 to November 2005 as the feed
pressure required to meet the desired permeate production rate increased. This increased pressure
requirement was again due to membrane fouling (Figure 5.7).
As with the RO booster pumps, the degasifier operated at a constant speed and output.
Since the degasifier EC was constant regardless of the water delivered to the treatment plant, the
specific EC of the degasifier decreased as more water was treated. The calculated specific EC
was 0.15 kWh/kgal, and decreased to 0.12 kWh/kgal when treating water at higher flows
(> 50 MG/month). The estimated portion of the plant specific EC for the degasifier was roughly
2 percent of the total plant’s value (Table 5.4).
The specific EC as a function of the monthly water production rate is reported for each of
the major processes in Figure 5.15. Note that these values do not include the specific energy
consumed by the well pumps. The high service pumps consumed the largest portion of the
plant’s (not including the well pumps) specific EC for nearly the entire range of water production
rates. Only as water production increases above 48 MG/month does the RO process become the
largest fraction of the plant’s total specific EC and over 50 percent of the total consumption at
over 52 MG/month. Specific EC by all of the processes in the plant decreased in a logarithmic
fashion with increasing water production. Its value is largely controlled by the energy consumed
by the high service pumps, which constitute the largest fraction of the specific EC outside of the
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well pumps. However, as the monthly production volume increased the specific energy
consumed by the high service pumps decreased and began to approximate that of the RO booster
pumps once a water production rate of roughly 50 MG/month was reached.
4
Specific Energy Consumption (kWh/kgal)
Plant
RO
Plant Total
Degassifier
3
High Service Pumps
High Service
Pumps
2
1
0
0
10
20
30
40
50
60
Water Production (MG/month)
Figure 5.15 Specific energy consumption for different process equipment at the Seward
Corrosion Control Plant.
The average monthly specific EC for the RO system is reported as a function of
feedwater conductivity and temperature in Figures 5.16 and 5.17, respectively. From
Figure 5.16, as the conductivity increases, which is a surrogate for TDS increases, there appears
to be little to no corresponding correlation in the specific EC. The reason for lack of correlation
is because the data range is small. The Seward RO system is removing nitrate from a relatively
clean groundwater source. Assuming a conversion factor of TDS (mg/L) = 0.67*Conductivity
(μS/cm), the Seward groundwater contains approximately only 450-600 mg/L TDS. In
comparison, Figure 5.4 shows a comparison between TDS and specific EC that spans
15,000 mg/L TDS. This data suggests that in cases where the overall range of conductivities was
narrow, the RO specific EC is more greatly affected by the water production rate.
From Figure 5.17 the specific EC is fairly insensitive to the minor fluctuations in the
groundwater temperature. As a result, no correlation between specific EC and temperature could
be determined at Seward.
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Specific Energy Consumption (kWh/kgal)
1.0
0.8
0.5
0.3
0.0
0
100
200
300
400
500
600
700
800
900
1000
Feedwater Conductivity (μS/cm)
Figure 5.16 Average monthly specific energy consumption for the RO booster pumps only
as a function of the feedwater conductivity.
Specific Energy Consumption (kWh/kgal)
1.0
0.8
0.5
0.3
0.0
0
2
4
6
8
10
12
14
Feedwater Temperature (oC)
Figure 5.17 Average monthly specific energy consumption for the RO booster pumps only
as a function of the feedwater temperature.
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Potential Energy Conservation Improvements
The Seward Corrosion Control Plant is billed under the City’s Municipal Uses rate
schedule, where users are billed at a single unit energy cost (1¢/kWh). It is not billed for peak
demands or power factors. However, the City does pay the regional electricity provider,
Nebraska Public Power District (NPPD), for peak power demands. The power demand charges
are paid through increased unit energy rates. There are no available alternate billing rate
schedules to the Corrosion Control Plant that allows the plant to be billed directly for peak power
demands. The City’s Electric Department manages the power demand on a citywide basis but
does not use the Corrosion Control Plant’s standby generator to shed loads during peak
conditions.
Each of the major equipment categories were analyzed for potential improvements in EC
and efficiency. Cost savings estimates are based on the November 2005 unit energy cost of
7.1¢/kWh. In addition to category-specific recommendations, a general energy optimization
recommendation for the City would be to install energy monitoring equipment at the wellfields
and at the other large pumps in the Seward WTP. The signals from the equipment would be
routed back to the plant SCADA system for storage and trending analysis. Currently, the only
readily available tool for City staff to track overall energy data from specific facilities is through
the monthly electric bills. Installing energy monitoring equipment would provide both a more
refined timescale for analysis as well as the opportunity to track individual equipment. With this
data, the City staff will have the tools to identify energy (and cost) saving measures and operate
the overall system in the most efficient manner possible.
Groundwater Wellfields
The Southwest Wellfield was found to have the lowest specific EC. Figure 5.18 shows
the breakdown of groundwater pumping by wellfield. With the exception of November 2005,
the South, Southwest, and West Wellfields contributed 25 percent, 40 percent, and 35 percent,
respectively, of the total water production. Increasing use of the Southwest Wellfield, and
reducing the use of the West Wellfield could result in significant energy savings. Assuming a
calculated specific EC differential of 0.4 kWh/kgal, increasing the use of the Southwest
Wellfield could result in a cost savings of 2.8 ¢/kgal pumped ($28.40/MG pumped). However,
this cost estimate does not include any potential hindrances to increasing the Southwest
Wellfield use, such as adverse impacts on water quality, water right limitations, or declining
yields associated with increased pumping.
An alternative suggestion is to further investigate the differences as to why the South and
West Wellfields are not as efficient as the Southwest Wellfield. It is possible that the well
pumps and motors at the other wellfields are being operated in a less efficient manner compared
to those at the Southwest Wellfield. The less efficient well operations could have offset any
potential energy savings by these two wellfields being closer to the treatment plant.
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60
South Wellfield
Water Production (MG/month)
50
Southwest Wellfield
West Wellfield
40
30
20
10
0
Nov-04
Feb-05
May-05
Aug-05
Nov-05
Figure 5.18 Monthly water production for the three different well-field areas in the
Seward system.
Reverse Osmosis
Beyond water production rate, membrane fouling was determined to have the greatest
impact on the RO specific EC. Cleaning the membranes would improve the energy efficiency by
lowering the process operating pressure. Assuming that the cleaning process removes 85 percent
of the materials accumulated on the surface and pores of the membranes (and thus lowers the
resistance to mass transport across the membranes), the energy needed to treat the water would
be reduced by 0.1 kWh/kgal, an 8 percent reduction from the November 2005 specific EC. Since
only half the water is treated by the RO process, the cost savings would be 0.4¢/kgal
($3.55/MG). Continuing to operate the system without cleaning would likely result in increased
feed pressures and higher specific EC values.
Increasing the ratio of bypassed water to RO-treated water would easily increase both the
energy and cost efficiencies of the treatment plant. However, such a change would most likely
result in a failure to meet drinking water standards for nitrate. For that reason, this report does
not recommend this action be considered without more extensive testing.
As noted previously, the RO system is designed for 85 percent recovery while currently
being operated at 75 percent due to issues related to inadequate nitrate removal. Though a higher
recovery requires that the RO booster pumps operate at higher pressures, and therefore require
more power, less groundwater is required to be pumped to produce a given volume of drinking
water. Since groundwater pumping has significantly higher specific EC than RO pumping, any
reduction in groundwater pumping energy would more than offset the increased RO EC. As a
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result, there will be a net energy savings to the overall system by operating the RO system at
higher recoveries.
No information is currently available on what the required RO booster pressure would be
to obtain 85 percent recovery. However, the overall EC by the plant would increase by an
estimated 0.05 kWh/kgal (or $0.04/kgal assuming $0.071 per kWh) for every 10 psi increase by
the RO booster pumps. In comparison, 0.60 – 2.4 kWh ($0.042 – $0.168) can be saved for every
1,000 gallons of groundwater that is not pumped.
Typical capital improvement measures that can be implemented to improve the energy
efficiency of RO systems are to heat the feed water and to install energy-recovery devices.
Theoretically increasing the feed water temperature should decrease the required RO feed
pressure. Only a small number of drinking water RO treatment plants heat the water due to the
cost of installing, maintaining, and powering the necessary heaters needed; the few that do are
often located next to a steam or power plant to take advantage of excess heat from the adjacent
facility. Due to the high costs, this improvement is not recommended for the Seward plant.
Degasifier
There are no recommendations for increasing the energy efficiency of the degasifier
system. The most common option is to install a VFD to vary the speed of the motor so as to
reduce over-aeration. This is a common alternative for wastewater applications due to daily and
seasonal variations in aeration demands. Such installations for drinking water systems are rare
because the aeration demands do not vary substantially. In the case of Seward, the variation in
groundwater pH is relatively small, and there is very little variability in the RO-treated water
quality. Therefore, there is little need to have a blower with a varying output. Any potential
energy and cost savings from using a VFD would either be completely offset by the need to
install the equipment or result in long payback periods.
High Service Pumping
Based on the data available, adding VFDs to the 100 and 200-hp pumps would reduce the
plant power demand. Though the treatment plant is not directly billed for peak power demand,
the City does pay for peak power demand through increased unit energy rates. Adding the VFDs
would allow for ramping-up and ramping-down, which would subsequently reduce energy
demand associated with starting the large high service pumps. In addition, adding the VFDs
would provide the following benefits that are outside the scope of this report:
• Increased mechanical life. The ability to ramp-up and ramp-down would lessen the
high mechanical torque and stress associated with starting the pumps. With reduced
stress the pumps would last longer and maintenance requirements would be reduced.
• Improved distribution system conditions. The VFDs could improve operational
conditions in the downstream distribution system, such as pressure and water age, by
providing greater control of the high service pumps flow and discharge.
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West Basin Municipal Water District (California) Water Recycling Facility
System Description
The West Basin Municipal Water District (“West Basin”) serves 17 cities and 9
unincorporated areas in the greater Los Angeles metropolitan area. West Basin serves a
population of approximately 900,000 over an area of 185 square miles. Prior to 1992, West
Basin supplied its municipal and industrial customers with a combination of local groundwater
wells and surface water purchased from the regional wholesaler, the Metropolitan Water District
of Southern California.
To improve their water supply portfolio, West Basin began the development of a water
reuse program. Federal funding was received in 1992 to construct a water recycling plant at a
site adjacent to the City of Los Angeles Hyperion Wastewater Treatment Plant. The West Basin
Water Recycling Facility (WBWRF) is currently one of the largest water reuse treatment
facilities in the United States. The facility is owned by West Basin and is contract operated and
maintained by United Water.
The WBWRF processes secondary wastewater effluent from the Hyperion Wastewater
Treatment Plant using differing combinations of conventional coagulation/filtration, MF, RO,
and UV disinfection to produce six different water qualities tailor-made to meet varying
requirements for non-potable municipal, commercial and industrial applications. The six
different product waters are:
1. Disinfected Tertiary Water (Title 22 water): The secondary treated effluent is
treated using conventional sand filtration and chlorine disinfection to produce water
meeting California Title 22 requirements. The Title 22 water is used for a variety of
industrial and irrigation applications.
2. Amended Tertiary Water: The Title 22 water is further chemically conditioned to
produce a water specifically for sports turf irrigation.
3. Nitrified Water: A portion of the Title 22 water is nitrified to remove ammonia, and
is provided to nearby industries as cooling tower supply.
4. Softened RO Water: Secondary treated wastewater is treated with MF. The water is
then pumped to an RO system for further improve the water quality. RO permeate is
disinfected with a new combination of UV and peroxide for NDMA destruction. The
highly treated water is then injected into the West Basin aquifer as groundwater
recharge.
5. Low-Pressure Boiler Feed (LPBF) Water: Secondary treated wastewater is treated
with a MF system and then a single-pass of RO membranes for use as LPBF water a
nearby ChevronTexaco facility.
6. High Pressure Boiler Feed Water: This water is produced by passing the LPBF
water through a second RO stage.
Since the WBWRF became fully operational in 1992, the plant has been expanded twice
(Phases II and III) to increase the production capacities for each of the waters described above.
At the time of this analysis, Phase IV is currently underway to further expand the MF and RO
capacities of plant and to add a new UV/peroxide system to begin NDMA destruction. The
emphasis of this report on advanced treatment processes will be on the Phase III MF and RO
systems used to produce the West Basin-designated “Pure RO Water” for low-pressure boiler
feed water. The MF/RO systems used to produce Pure RO Water was selected for this analysis
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since it is the one process train that would be most comparable to trains that would normally be
installed for the municipal water industry.
The newest MF and RO system installed as part of the current Phase IV expansion would
also be used to produce the Pure RO Water but was not included in this analysis because these
systems had not been fully commissioned at the time of this analysis. However, the Phase IV
UV/peroxide advanced oxidation system will be examined even though this system was also not
fully commissioned at the time of analysis. The UV/peroxide advanced oxidation system was
included in this analysis because this technology is new and the installation at the WBWRF is
one of first for the municipal water industry (drinking water, wastewater, and reuse water).
The raw water for the plant is secondary effluent from the City of Los Angeles Hyperion
Wastewater Treatment Plant, which is pumped directly to the WBWRF. Water quality
parameters used for the design of the Phase III expansion, as well as values measured for a
sample collected during this study, are reported in Table 5.5. The raw water varied from 5 to 13
NTU from January to March 2006. During this same period, the effluent turbidity from the MF
system ranged from 0.03 to 0.21 NTU. The two orders-of-magnitude reduction in turbidity by
the MF system indicates that the MF process functioned adequately as pretreatment for the RO
system. As will be discussed later in this report, this performance was despite the individual
membrane elements in the MF system approaching the end of their service life.
Although the concentration of the TDS of the secondary effluent continually varies, the
concentration in the March 24, 2006 sample was nearly the same as the projected effluent
quality. There was a slight difference in the ion composition. The March analysis found sulfate
concentrations to be higher than the design quality (228 mg/L versus 149 mg/L) and lower in
chlorides (114 mg/L versus 146 mg/L). MF systems alone have little to no impacts on these
water quality parameters so removal would be with the RO system. Since RO membranes reject
divalent ions more readily than monovalent ions, the water quality of the MF filtrate going to the
RO system can be considered better than the design values.
This analysis considers two treatment processes. The first is the Phase III MF and RO
treatment systems to produce water for use in low-pressure boilers at a nearby Chevron
petrochemical refinery. This process is most comparable to typical MF/RO installations for the
municipal water industry. The second treatment process is the Phase IV UV/peroxide advanced
oxidation system used to treat Phase IV RO permeate prior to aquifer recharge injection. There
are no normal interconnections between the Phase III MF/RO and Phase IV UV/peroxide
systems, so this analysis will consider each separately. The Phase IV UV/peroxide system is
discussed in Chapter 7 with the other UV systems.
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Table 5.5
Secondary effluent quality to West Basin Water Recycling Facility
Value:
Parameter
Temperature
pH
Conductivity
Total Dissolved Solids
Bicarbonate
Chloride
Sulfate
Boron
Sodium
Calcium
Magnesium
Potassium
Iron
Manganese
Fluoride
Residual Chlorine
Silica
Ammonia
Nitrate
Nitrite
Suspended Solids
Biological Oxygen Demand
Total Organic Carbon
Langelier Index
Turbidity
Units
°F
specific units
μS/cm
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L as N
mg/L as N
mg/L as N
mg/L
mg/L
mg/L
specific units
NTU
Design Quality1
77
7.1
1,145
733
293
146
149
0.65
153
48
20
16
0.1
0.04
0.8
0
26.5
24.4
1.8
2.3
11
28
11
-0.27
23
March 24, 20062
75
6.2
1,240
736
160
114
228
Not analyzed
113
37.3
16.7
15
Not analyzed
Not analyzed
Not analyzed
Not analyzed
22
30
Not analyzed
Not analyzed
Not analyzed
Not analyzed
13
Not analyzed
See text
Sources:
1. CDM, Inc., July 2003.
2. West Basin Municipal Water District Water Quality Laboratory.
Figure 5.19 is a schematic of the Phase III MF/RO treatment process used to produce
low-pressure boiler feed (abbreviated LPBF in the figure). Secondary effluent is first being
pumped by the MF feed pumps through 500-μm automatic strainers to remove large particles
and then through the MF system. The MF system is based on the USFilter/Memcor pressurized
CMF membrane module. Each module consists of bundles of hundreds of hollow polypropylene
hollow fibers with nominal 0.2-μm pore sizes. The Phase III MF system consists of ten parallel
membrane trains, each 90 membrane modules installed.
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Figure 5.19 Phase III Low-Pressure Boiler Feed Water (LPBF) Production Train Schematic (Source: West Basin
Municipal Water District, 2001).
Nine units are operating at one time with one unit in standby. Each CMF unit contains
90 membrane modules with fibers in a vertical position. Each membrane module is rated at
440 gpm. In normal operation, the backwash cycle interval is 20 minutes, with each backwash
cycle lasting 2.5 minutes. The system operates at minimum 86.8 percent recovery. A
compressed air system is installed as part of the MF system to periodically scour and backwash
the membranes.
The installed membranes are five years old and approaching the end of their usable
service life, with United Water estimating that each module had approximately 20 fiber breaks.
(The membranes were replaced shortly after the data reported here was obtained.) As a result,
the membranes can no longer sustain pressure during a routine pressure decay test. Each unit is
backwashed with air and water every 20 minutes for 2.5 minutes. The backwashing is no longer
as efficient as when the membranes were first installed due to the numerous fiber breaks. The
system is cleaned in place (CIP) with chemicals on a frequency of 150 to 200 hours. The CIP
frequency is relatively short due to inefficient backwashing. Despite the number of broken
fibers, the Phase III MF system was still produced filtrate with a silt density index (SDI)
consistently about 0.1, which is within the acceptable water quality limits for the downstream
RO units.
Filtrate from the Phase II MF system and the Phase III MF system flow to the MF filtrate
clearwell, located underneath the MF facilities. The combined filtrate is pumped to the RO
system after additional filtration with 20 μm cartridge filters. These final filters provide a
precautionary measure to ensure that particulates do not enter the RO membrane system.
Permeate from Stages One and Two are combined and delivered to the decarbonator. The
product is then sent to Chevron for low pressure boiler feed and to Phase IV RO system for
production of high purity water for high pressure boiler feed.
The first pass RO system is comprised of two trains, labeled Train 4 and 5. Each is a two
stage unit where the first stage concentrate is fed to the second stage for further water removal.
There are 48 pressure vessels in the 1st stage and 24 in the second stage. Each pressure vessel
contains seven 8-in x 40-in Hydranautics ESPA2 RO membranes. Each train was originally
designed to produce 2.3 mgd, for a total of 4.6 mgd from Phase III. Permeate from the first pass
is partially delivered to Chevron for low-pressure boiler feed and the balance to the second pass
for further purification. This represents the flow scheme that would be used in most wastewater
recycling plants. Further treatment at West Basin is not considered in this analysis.
Power Supply
The Southern California Edison Company (SCE) supplies power to the WBWRF using a
single 66kV power feed through an 11.2/14MVA, 66kV-16kV transformer substation. The
WBWRF then runs a 16kV loop system inside the plant. For this analysis, the individual
electrical equipment draws 120V or 480V power off of the loop through several transformers
located around the facility. SCE charges West Basin electricity costs for the WBWRF based on
a single watt-hour meter at the substation. The SCE bill is sent directly to West Basin; the
United Water staff does not routinely receive a copy of the bill. The United Water operating and
maintenance contract has requirements for water production and quality but not for EC or
conservation.
Power draw and EC for 480V equipment is monitored on individual control panels but
there is no output signal to the facility SCADA system to track power or energy. United Water
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staff routinely monitors the individual control panels only during maintenance or repair
activities. As a result, there are no electrical records for individual equipment. However, the EC
for major pumps can be manually estimated based on pressure and flow measurements, which
are continually monitored and logged by the SCADA.
Energy Consumption
The EC of the Phase III MF/RO system is covered in this section. This analysis included
a comparison of the theoretical EC for the total system and RO system only with measured
values. EC for the various pieces of equipment was calculated from the measured total value
using pressure and flowrate measurements. Data was only available for one set of water quality
and operating conditions. Therefore, an analysis of the impact of different variables (e.g., TDS,
temperature, flowrates, etc.) could not be performed for this case study.
The energy consuming equipment included in this analysis of the Phase III MF/RO
systems are listed in Appendix A. The analysis of the Phase III MF and RO systems were
complicated due to the interconnections with the Phase II systems. Filtrate from the Phase II MF
membranes is sent to the same clearwell as the Phase III filtrate and the combined flow is then
delivered to the Phase III RO system. As a result, this analysis, which is limited to Phase III of
the WBWRF, does not include MF energy for the Phase II filtrate. Part of the Phase III product
water is delivered to Chevron and the balance to a second pass RO to produce high purity water
for high pressure boiler feed.
The RO system has consistently produced a high quality permeate. The pressure is much
higher than would be expected for the ESPA2 membrane used in both trains. The manufacture’s
modeling program estimated that the ESPA2 membrane would operate at a feed pressure of less
than 100 psi at startup (Table 5.6). However, the membranes undergo a non-recoverable
permeability loss with the Phase III MF effluent. The initial permeability loss resulted in
increased RO operating pressures of 150-180 psi by about the eighth month after startup, after
which performance stabilized.
Fouling of the RO membranes was evidenced by decreasing RO membrane permeability
over the past 5 years of operation. The source of the RO fouling was not established as the SDI
and turbidity levels in the RO feedwater were in the acceptable ranges for these parameters. The
plant staff hypothesize that the fouling resulted from scale formation on the RO membranes,
and/or through the accumulation of materials that are not rejected by the MF membranes.
Despite the fouling, plant staff indicated that the RO system performance was stable for the past
three years. By February 2006, the feed pressure was 237 psi for Train 4 and 255 psi for Train 5.
The high feed pressures indicated that the Phase III RO system would soon require that a
chemical cleaning be initiated. Except for the feed pressure, all other operating and performance
values for the ESPA2 membranes were comparable to the design values.
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Table 5.6
Performance results for the Phase III RO System
Parameter
Feed conductivity
Temperature
Concentrate flow
Permeate flow
Feed flow
Recovery
Feed pressure
Pressure drop
Permeate conductivity
Unit
μS/cm
°C
gpm
gpm
gpm
%
psi
psi
μS/cm
Design Value
1,200
25
281
1,597
1,878
85
99
40
None
February 2006 Values
Train #4
Train #5
1,375
1,375
24.1
24.1
225
223
1,302
1,240
1,527
1,463
85.2
84.8
237
255
37.3
35
40.6
44
Figure 5.20 shows a comparison between the theoretical and measured EC of the Phase
III MF and RO systems. Here, the MF system is composed of the MF feed pumps and the MF
air compressor. The RO system is composed of the RO transfer pump, RO feed pumps,
decarbonator blower, and the product forwarding pumps. The measured total EC of all process
components is within 5 percent of the calculated theoretical value. Note that the figure shows
the expected EC by the RO feed pumps at startup, which did not reflect the one time nonrecoverable flux decline which caused a near doubling of the EC by the RO feed pumps. The
projected EC by the feed pumps at various TDS values was estimated with the membrane
manufacturer’s modeling program and assuming a fouling factor of 20 percent per year. The 20
percent fouling factor is a common value used by design engineers for RO membrane treatment
of secondary effluent and does reflect the current operating conditions of the Phase III RO
system. Nevertheless, the projected EC by the RO feed pumps was relatively equal to the
measured value at a TDS of 736 mg/L.
Table 5.7 is a breakdown of the energy consumed by the different components of the
Phase III MF/RO system. The specific EC for the total system is 6.31 kWh/kgal. The MF
portion of the Phase III system used 0.70 kwh/kgal, or 11.1 percent of the total, while the RO
feed pumps and decarbonator blowers used 4.35 kWh/kgal or 68.9 percent of the total. The
remaining 1.26 kWh/kgal (20.0 percent) is used for the transfer pumps between the MF system
to the RO system and the product forward pumps sending the decarbonated RO permeate to the
Chevron facility.
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Specific Energy Consumption (kWh/kgal)
7
6
5
4
Initial Design: RO feed pumps
3
Projected RO, 20% FF
Actual: RO feed pumps
2
Calculated: MF+RO
Measured: MF+RO
1
Measured RO System
0
0
200
400
600
800
1000
1200
TDS (mg/L)
Figure 5.20 Comparison of WBWRF Phase III MF/RO energy consumption. The
projected specific energy consumption for the RO system only (gray square) was calculated
assuming a fouling factor of 20 percent over a 5-year operating period.
Table 5.7
WBWRF Phase III MF/RO energy consumption breakdown
Treatment Equipment
MF feed pumps
MF air compressors
RO transfer pump
Train #4 RO feed pump
Train #5 RO feed pump
RO decarbonator blowers
Product forwarding pump
Total
Calculated Energy
Consumption (kWh/kgal)
0.50
0.20
0.90
2.07
2.23
0.05
0.36
6.31
Percent of Total
7.9
3.2
14.3
32.8
35.3
0.8
5.7
100.0
Note: Phase II MF filtrate also goes to the Phase III RO system. Phase II MF system was not included as part of this analysis.
There were slight differences in the operating conditions for membrane Trains 4 and 5
(Table 5.6). Train 5 operated at a higher feed pressure but at a lower feedwater flowrate
compared to Train 4. The specific EC was higher for the feed pumps for Train 5
(2.23 kWh/kgal) compared to that for Train 4 (2.07 kWh/kgal). The improved specific EC for
Train 4 is likely due to the higher feedwater flowrate and higher water recovery of Train 4.
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Potential Energy Conservation Improvements
In the Phase III MF/RO treatment system the RO feed pumps accounted for roughly onethird of the total EC. Therefore, energy conservation efforts should focus on optimizing the
performance of the feed pumps. One avenue for reducing the EC of the RO feed pumps is to
reduce the system operating pressure. Currently, the operating pressure is greater than that
expected during design as a result of membrane fouling. Identification and minimization of this
fouling should allow for the system to operate at a lower pressure, thus reducing the EC by the
RO feed pumps. Recalling that the EC by the various process equipment which make up the
Phase III system was projected based on the measured total system EC, it is recommended that a
monthly energy audit be performed in order to develop improved baseline EC values for the
different process equipment. This would require that monitoring equipment be installed on the
selected process equipment to determine monthly EC. This would allow for a more complete
picture to be developed for pinpointing system energy inefficiencies. Following the energy
audit, areas may be identified for reducing EC and improving plant efficiency. As noted in this
analysis, the current equipment control panels display the instantaneous power and energy usage
but the information is not monitored or logged on a regular basis. While modifying the current
SCADA system to include continuous power and energy monitoring and logging would be quite
expensive, performing a monthly audit of the major equipment would provide adequate data to
begin an energy analysis of the entire plant.
SUMMARY AND CONCLUSIONS FOR REVERSE OSMOSIS SYSTEMS
As discussed previously, RO systems typically are operated on an on/off basis at the
required flow rate. Accordingly, the principal factors affecting the EC by RO systems are the
feed pressure that is needed to achieve a set permeate flux and the water quality conditions that
affect the membrane permeability. Considerations for EC optimization are generally associated
with design and operational improvements. These issues are summarized below.
Factors Affecting EC of Reverse Osmosis Systems
Two of the three RO plants only reported data under a single set of water quality
conditions, which provides little data to develop good statistical correlations between the specific
EC of the RO equipment and different water quality parameters. Nevertheless, some general
conclusions may be drawn based on the data that is available for the systems studied here. Of all
the parameters studied, specific EC was only found to correlate strongly with feed pressure
(Figure 5.21). Specific EC was found to increase rather linearly with increasing feed pressure.
This relationship is in agreement with expectations from the pump energy equation
(Figure 5.22). As evidenced in Figure 5.22, pump EC increases in a linear fashion with
increasing feed pressure and with increasing flowrate.
Both temperature and TDS are known to be significant parameters for determining the
feed pressure required to achieve a set permeate flux. Increasing temperature results in a
lowering of water viscosity allowing it to more easily pass through the membrane. The TDS
determines the osmotic back pressure which must be overcome by the feed pumps. However,
with RO membrane systems, the resistance imposed by the membrane and the impact of
membrane fouling must also be accounted. Therefore, the relationship between water quality
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parameters and specific EC by the feed pump may not in fact be a straightforward relationship.
For instance, while the Goldsworthy Desalter had the highest influent TDS, it operated at a feed
pressure that was roughly half that of the WBWRF (Table 5.8). Consequently, the specific EC
was almost four times greater at the West Basin plant compared to that at the Water
Replenishment District. The difference in feed pressure may be attributed to a variety of
operating guidelines, but fouling of the WBWRF RO membranes was cited as the source for
decreases in the membrane permeability and thus required higher feed pressures in order to
achieve the desired permeate flux. These higher than expected EC observations were attributed
primarily to the failing integrity of the MF system, thus degrading the quality of influent water
delivered to the RO system and consequently reducing the Phase III MF/RO performance
efficiency. Thus, because feed pressure is influenced by many factors (e.g., membrane
permeability, TDS, temperature, etc.) it must be carefully scrutinized to determine what factors
are ultimately affecting specific EC. Regardless, this data suggests that feed pressure is the
principle factor affecting the energy efficiency of RO membrane systems.
5.0
Specific Energy Consumption (kWh/kgal)
R2 = 0.9969
4.0
3.0
2.0
1.0
0.0
0
50
100
150
200
250
300
350
Feed Pressure (psi)
Figure 5.21 Specific energy consumption by the RO systems as a function of the operating
feed pressure at West Basin, Goldsworthy, and Seward WTPs. The data is fit using linear
regression analysis.
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25
Energy Consumption (kWh/gal)
Q = 20 gpm
Q = 50 gpm
20
Q = 100 gpm
15
10
5
0
0
50
100
150
200
250
300
350
400
Feed Pressure (psi)
Figure 5.22 Theoretical energy consumption by a pump operating at different flow rates
and feed pressures. The pump efficiency is assumed to be 80 percent and the motor
efficiency is assumed to be 95 percent.
Table 5.8
Summary of selected average water quality parameters and RO system specific energy
consumption from the three RO WTPs
Facility
WBWRF
Goldsworthy
Desalter
Seward Corrosion
Control Plant
Feed
Water
TDS
(mg/L)
736
Feed
Pressure
(psi)
Temperature
(°C)
Qavg
(MG/month)
Specific Energy
Consumption
(kWh/kgal)
246
24.1
102.5
4.70
2393
165
21.7
53.2
1.63
529
121
12.0
29.8
0.57
CONSIDERATIONS FOR EC OPTIMIZATION OF RO SYSTEMS
Potential design and operational improvements were identified for the three participating
RO systems. For the WRD Goldsworthy Desalter, EC potentially could be reduced by
considering additional blending of product water, improvements in pumping efficiencies, lower
operating pressure using new membrane materials, and installation of energy recovery systems
(see Chapter 2). For the Seward Corrosion Control Plant, EC potentially could be reduced by
cleaning the membranes, adding VFD to the high service pumps, and possibly re-allocating
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production from specific wellfields. The WBWRF EC could potentially be reduced by
considering replacement of the Phase III MF membranes to improve MF filtrate quality,
replacement of the RO membranes for reduced operating pressure, and implementation of
monthly energy audits.
Energy-recovery devices for RO systems transfer excess pressure from the RO effluent to
the feed water and thereby reduce the booster pumping pressure. These devices are commonly
installed for high-pressure RO seawater desalination operations. Typical efficiencies of several
different types of energy recovery devices are listed in Table 5.9. However, because the capital
costs associated with these devices is often quite large, a cost benefit analysis would be required
to determine their economic feasibility. Of the currently available energy recovery systems, the
Pelton turbine and turbocharger are most widely used. The flow-work exchanger (Direct Work
Exchange Energy Recovery – DWEER) system was recently installed on two of the largest RO
seawater systems (Ashkelon, Israel and Tuas, Singapore). It is possible that more widespread
use will lead to development of economic models for brackish water. The Energy Recovery
Incorporated pressure exchanger (ERI) has recently been tested for seawater service at Dhekelia,
Cyprus and the Affordable Desalination Cooperative. An acceptable energy recovery device for
brackish water could potentially reduce consumption by 10 percent for a facility treating a feed
water with 5,000 mg/L TDS to up to 30 percent for 10,000 mg/L TDS feed water.
Table 5.9
Typical energy recovery efficiencies for different energy recovery devices
System
Typical Energy Recovery Efficiency (%)
Reverse running pump
75 – 82
Pelton turbine (ERT)
80 – 86
Turbocharger
70
Flow-work exchanger
90 – 95
Pressure exchanger
~95
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96
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CHAPTER 6
EC OF OZONE SYSTEMS FOR DRINKING WATER TREATMENT
This chapter discusses EC of utilities that use ozone systems for drinking water treatment.
The chapter includes an overview of the process and description of major components that
typically require the greatest energy usage. Three case studies (Southern Nevada Water
Authority; Contra Costa Water District, California; and Central Lake County Joint Action Water
Agency, Illinois) are described. Each case study includes a system description, analysis of EC,
and identification of potential optimization opportunities. A summary of the EC analysis based
on these three case studies is included at the end of the chapter.
PROCESS DESCRIPTION OVERVIEW
Principle components of ozonation systems include the feed gas (air or high-purity
oxygen), ozone generator, ozone contact basin, and the ozone destruction unit. A general
schematic for an ozonation system is shown in Figure 6.1. All feed gas supplies have minimum
moisture content. This is often achieved by passing the feed gas through a dessicator to reduce
the gas water content and into the ozone generator. Ozone is produced by applying a high
voltage alternating current (6 to 20 kVAC) across a dielectric discharge gap that contains the
feed gas. On-site generation is required because the ozone is highly unstable. The gas stream
now contains approximately 0.5 to 3 percent weight ozone. Air feed-gas systems are designed to
operate at ozone concentrations between 1.0 to 2.5 percent weight ozone, conversely, high-purity
oxygen feed-gas systems are designed to operate at ozone concentrations between 8 to 12 percent
weight ozone. The ozone gas stream is diffused into the feedwater using a down flow contact
basin. The contact basin may take a variety of designs, including a diffused bubbler, mechanical
agitation, packed tower, or venture mixer. Off-gas in the contactor is collected and sent to a heat
catalyst unit which reduces the ozone to oxygen and discharges it to the atmosphere.
Ozone Destruction
Off-Gas
Feed Gas Preparation
• O2 Production
• O2 Storage
• Air/O2 Treatment
Ozone Generator
Ozone Contact
Basin
Feed Water
Figure 6.1 Typical process layout for an ozonation water treatment system.
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MAJOR EC COMPONENTS
Ozonation systems are typically comprised of four energy consuming devices:
• Feed-gas treatment.
• Ozone generator.
• Cooling water pumps for the ozone generator.
• Ozone destruction unit.
The ozone generator represents the primary energy consumer for the ozonation system.
Auxiliary systems include the feed-gas treatment, ozone diffuser in the contact basin, generator
cooling water pumps, and the ozone destruction unit. The ozone generator consumes energy via
two routes including production of the voltage across the dielectric and pumping of the cooling
water through the generator. The ozone diffuser requires energy for pumping the ozone rich gas
into the contact basin.
EC associated with the ozone generator tends to increase with increasing ozone
generation rate. However, the energy required for the auxiliary systems remains relatively fixed
regardless of the ozone generation rate. Process efficiency is therefore lowest at low ozone
production rates.
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
This section includes case studies for three utilities that operate ozone systems. Each
system uses a different oxygen feed system, which appears to impact EC and process efficiency.
Southern Nevada Water Authority uses the vacuum/pressure-swing adsorption equipment,
Contra Costa Water District uses the vaporized liquid oxygen system, and Central Lake County
Joint Action Water Agency uses an ambient air feed system. These three utilities are described
as case studies for ozone systems in the sections below.
Southern Nevada Water Authority Alfred Merritt Smith Water Treatment Plant
System Description
The Southern Nevada Water Authority (SNWA) operates two drinking water treatment
plants in the Las Vegas valley. One of these is the Alfred Merritt Smith (AMS) WTP which was
originally constructed in 1971 and has a maximum production capacity of 600 mgd. The AMS
WTP is located on the shores of Lake Mead, and is approximately 30 miles away from the Las
Vegas valley. The treatment system is composed of conventional coagulation followed by direct
filtration through dual media filters. Chlorine gas is used as the primary disinfectant and fluoride
and zinc orthophosphate are added during post-treatment. Preozonation, coming before the
coagulation step, is practiced here primarily for achieving a minimum 1-log Giardia disinfection
credit and may also be used for Cryptosporidium inactivation and taste and odor control if
needed in the future.
The plant has three major energy consuming components, including low-lift pumping
from the lake (installed power demand of 14.9 MW), oxygen and ozone generation equipment
(installed power demand of 4.8 MW), and high-lift pumping from the plant to the Las Vegas
valley (installed power demand of 132 MW). The total installed power demand for pumping and
oxygen/ozone production is 151.7 MW. Oxygen/ozone production installed power demand is
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small, at only 3.2 percent of the total. Each of the twenty 1000 hp low-lift pumps delivers
between 20 to 34 mgd of water flow, depending on the lake elevation, which varies from 1100 ft
MSL to 1150 ft MSL. Each of the five 600 kW ozone generators delivers 4,000 lb/day of ozone
at a concentration of 8 percent weight. Each of the two 900 kW VPSA units delivers 50 tons/day
of high purity oxygen (92 percent by volume O2) to the ozone generators. The 65 high-lift
pumps (14 at 2500 hp, 29 at 3000 hp and 22 at 4000 hp) each deliver between 32 and 37 mgd of
treated water up and over the 1,200 ft high River Mountains through about 30 miles of pipe from
Lake Mead to the Las Vegas valley.
Equipment and process components of the AMS oxygen/ozone system are shown
schematically in Figure 6.2. The oxygen feed-gas supply is high purity oxygen that is derived
from VPSA oxygen generation equipment that is located on site. LOX serves as a backup in
case of operating problems with the VPSA units. On-site VPSA oxygen production facilities
were installed mostly because of the plant’s remote location and long distance (200 miles) from
commercial LOX suppliers that are located in southern California. In addition, ozone generation
cost savings occur, but these savings are somewhat mitigated by the increased maintenance that
is required of the VPSA equipment (i.e., mostly valve and valve actuator maintenance activities).
There are eight ozone contactors each having a hydraulic detention time of 24 minutes. Residual
ozone is quenched at the end of the contactors. The off-gas ozone destruction is carried out
using a vacuumed heater at 30oC with a MnO2 catalyst.
The AMS facility has watt-hour meters installed on MCCs that serve different parts of the
ozone facility. The “ozone” system has watt-hour meters installed on MCCs at selected
locations. Cumulative watt-hour meter readings are collected on SCADA. SCADA readings for
energy usage were automatically input into an Excel spreadsheet for further evaluation. The
primary (90 percent) energy-consuming components of the oxygen/ozone system are the VPSA
unit and the ozone generators. The remaining 10 percent process-related energy-consuming
components include off-gas ozone destruct equipment and closed-loop cooling water pumps.
The building’s HVAC system is considered non-process related energy-consuming equipment.
As indicated above, pumping is the significant energy cost for the SNWA. Because of
this cost, the SNWA negotiates energy-pricing contracts that yield significant cost savings when
EC is minimized during on-peak hours of the day. As such, at times, the AMS plant might
operate at a design flow of 600 mgd during off-peak hours and 126 mgd during on-peak hours.
The ozone system control strategy was designed and operated to maintain disinfection
performance during these fluctuations in plant flow. The result is optimized (i.e., minimized)
energy cost for plant and pumping operation as a whole, but somewhat non-optimized energy
usage for the ozone system alone.
Figure 6.3 shows the process schematic for each of the two 100,000-lb/day (50-ton/day or
775 scfm0C) VPSA systems. The total gas capacity delivered from two units is 200,000-lb/day,
or 1,550 scfm0C. At the design ozone concentration of 8 percent weight, the design ozone
production capacity is 16,000 lb/day (i.e., 4 of 5 generators operating at 4,000 lb/day each, with
one standby unit).
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Vaporizer
Vaporizer
LOX Storage Tank
To Flash
Mix
Preheater/ O3
Destruction
LOX Fill
Station
Vaporizer
LOX Storage Tank
Vent Gas
Blower
Vaporizer
Preheater/ O3
Destruction
To Flash
Mix
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To Flash
Mix
Process
Vent
Recovery
Tank
Product Tank
Inline
Silencer
To Flash
Mix
Vent Gas
Blower
Preheater/ O3
Destruction
Vent Gas
Blower
Absorbent
Vessel
Baseload Oxygen
Compressor
To Flash
Mix
Air Unload/
Waste Vent
Air Inlet
Filter
Preheater/ O3
Destruction
Vent Gas
Blower
North VPSA Room
To Flash
Mix
Product Tank
Recovery
Tank
Preheater/ O3
Destruction
North Generator Room
Vent Gas
Blower
Absorbent
Vessel
Baseload Oxygen
Compressor
To Flash
Mix
Air Unload/
Waste Vent
Air Inlet
Filter
Rotary
Blower
Discharge
Silencer
To Flash
Mix
Figure 6.2 Schematic of the Alfred Merritt Smith WTP oxygen/ozone generators (Source: SNWA 2003).
Ozone Destruct Room
Figure 6.3 Detailed schematic of the VPSA system used at the AMS WTP (Source: SNWA
2003).
Each VPSA unit has one 1,000 hp air compressor and one 200 hp oxygen-pressurebooster compressor (called a Base Load Oxygen Compressor, or BLOC). Figure 6.4 shows the
specific energy value, with respect to oxygen production, at variable oxygen production rates.
These data were collected during the on-site installation performance tests that were conducted
in November 2003. As shown, the specific energy value is higher at turndown operating
conditions. In other words, at 50 percent turndown in production there is only a 20 percent
101
©2008 AwwaRF. ALL RIGHTS RESERVED
Atmospheric
Air
Atmospheric
Air
Air Inlet Feed
Air Feed & Vacuum
Blower System
Rotary
Blower 1
Discharge Silencer 1
Waste Vent
Absorbent
Vessel
1
Inline Silencer
No. 1
Discharge Silencer 2
Waste Vent
Absorbent
Vessel
2
Inline Silencer
No. 2
Rotary Blower 2
Air Separation System
Recovery
Tank 1
Air Inlet Feed
Air Feed & Vacuum
Blower System
Air Separation System
Recovery
Tank 2
Waste
Vent
Product Tank 1
Waste
Vent
Product Tank 2
Oxygen
Monitoring
System
Oxygen
Analyzer
Instrument Air
Supply System
Baseload
Oxygen Compressor
Oxygen Compression
System
Oxygen
Monitoring
System
Oxygen
Analyzer
Instrument Air
Supply System
Baseload
Oxygen Compressor
Oxygen Compression
System
Oxygen
Vent
Oxygen
Vent
To Ozone
Generators
Backup
Oxygen
Source from
LOX System
Analyzer
turndown in power. The air compressor has limited turndown capability, and the BLOC always
operates with the same power demand.
0.25
Specific Energy Consumption (kWh/lb O2)
R2 = 0.98
0.20
0.15
0.10
0.05
0.00
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
VPSA Oxygen Flow (lb/day)
Figure 6.4 VPSA specific energy consumption with respect to oxygen production rate.
Each VPSA unit provides oxygen feed-gas for 8,000 lb/day of ozone production capacity
when the ozone generators operate at their design ozone concentration of 8 percent weight.
Figure 6.5 shows the specific EC by the VPSA system relative to the ozone production rate (i.e.,
at 8 percent weight ozone). Table 6.1 displays the data that was used to develop the charts.
Later, these values are coupled with the ozone generator’s specific EC to determine total specific
energy value for generator plus VPSA unit operation.
Specific EC of each ozone generator depends upon the operating ozone concentration, as
shown in Figure 6.6. Specific energy value increases as ozone concentration increases. The
design ozone concentration used at AMS is 8 percent weight.
Using the best-fit equations from Figures 6.4 and 6.5, the combined generator plus VPSA
specific energy values were developed for variable ozone production rates, as shown in
Figure 6.7. Measured data from the performance test conducted in November 2003 are also
shown in Figure 6.7. The performance data shows that total system (i.e., VPSA plus ozone
generator) specific energy is between 5.0 and 5.5 kWh/lbO3 when production exceeds
7,000 lb/day.
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3.0
R2 = 0.98
Specific Energy (kWh/lb O3)
2.5
2.0
1.5
1.0
0.5
0.0
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
Ozone Production (lb/day)
Figure 6.5 VPSA specific energy consumption with respect to ozone production rate at
8 percent (by weight) ozone concentration.
Table 6.1
VPSA unit oxygen production and specific energy consumption
Test
1
2
3
4
5
6
7
8
1.
VPSA O2
Flowrate
(lb/day)
48,425
62,042
62,605
96,054
96,063
96,756
97,332
97,536
Unit Mass
Energy
(kWh/lb O2)
0.211
0.181
0.167
0.139
0.137
0.133
0.134
0.133
Ozone Flowrate1
% Ozone Flow
(lb/day)
3,874
4,963
5,008
7,684
7,685
7,741
7,787
7,803
Based on an ozone concentration of 8 percent weight.
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50
64
64
98
98
99
100
100
Unit Mass
Energy
(kWh/lb O3)
2.639
2.257
2.089
1.733
1.709
1.659
1.674
1.661
6
Specific Energy Consumption (kWh/lb O3)
Generator 1
Generator 2
5
Generator 3
R2 = 0.94
Generator 4
4
Generator 5
3
2
1
0
0
2
4
6
8
10
12
14
O3 Concentration (% wt)
Figure 6.6 Ozone generator specific energy consumption as a function of ozone
concentration (by weight).
9
Specific Energy Consumption (kWh/lb)
8
7
6
5
4
3
2
VPSA + Generator From Curves @ 8% wt
1
Performance Test Measurements
0
0
4,000
8,000
12,000
16,000
Ozone Production (lb/day)
Figure 6.7 Combined specific energy consumption for the VPSA and ozone generators.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Energy Consumption
The AMS plant uses power monitoring equipment that continuously monitors and logs
power demand and energy watt-hour usage data. These data are available on SCADA, along
with other ozone system operating data such as gas flow, ozone concentration, water flow, ozone
residual, etc. An Excel spreadsheet was developed and used to evaluate ozone system operating
information. Data was input into the spreadsheet from the server that “housed” the SCADA
database. The spreadsheet was set up to automatically (i.e., Excel macro command) bring in data
for the day that was being evaluated. Upon activation by press of a macro button, the
spreadsheet input table would display the data that was received from SCADA for each hour on
the hour. The data was the discrete value that occurred at that instant; it was not an hourly
average.
Energy assessment information collected for this project included ozone production from
the ozone generators; oxygen production from the VPSA units; and energy consumed by both the
ozone generators and VPSA units. EC was measured by subtraction of totalized watt-hour
readings for selected periods (e.g., month). Ozone and oxygen production information was
obtained by averaging the hourly-reported gas flow and ozone concentration values over the
selected period (e.g., average of values for the month).
Averaged data for each month from November 2005 through September 2006 is shown in
Appendix A. At the AMS plant, enhanced disinfection by ozone is practiced. The monthly
average CT value ranged between 3.5 and 5.7 mg-min/L. These values are more than ten-times
greater than CT-required by regulation to meet the minimum 1-log Giardia inactivation at the
AMS direct-filtration facility. Voluntarily, the AMS plant-operating disinfection target
approaches 1 log inactivation of Cryptosporidium. The applied ozone dose is between 1.0 and
1.2 mg/L, with monthly average water flow rates ranging between 225 and 390 mgd.
The ozone system operating strategy is to keep the oxygen gas flow steady and vary
ozone production by varying generator power, which changes the operating ozone concentration.
This control philosophy was selected in lieu of “constant-concentration” control, which would
involve change in gas flow in response to change in required ozone production. With constantconcentration control the gas flow adjustment response was too slow, which caused variation in
ozone dose. Alternatively, generator power adjustments can be quickly implemented in direct
response to water flow, thus maintaining ozone dose during water flow adjustments. Keeping
oxygen feed-gas flow steady maintains performance during water flow changes, but creates
slightly non-optimized energy usage during portions of the day. More information is discussed
later in this report concerning operation with significant water flow fluctuation.
Monthly average specific energy values are shown for the generator and VPSA unit in
Figure 6.8, along with operating ozone concentration. The ozone concentration varied between
3 percent weight and 5 percent weight, depending on required ozone production. The combined
generator and VPSA unit specific energy value was indirectly proportional to ozone
concentration, and was about 8 kWh/lbO3 at 3 percent weight concentration and 6 kWh/lbO3 at
5 percent weight concentration. The ozone generator specific energy was fairly steady at
3.3 kWh/lbO3. The VPSA specific energy value varied between 2.7 and 4.7 kWh/lbO3.
However, VPSA specific energy was steady with respect to oxygen production, at 0.13 to
0.14 kWh/lbO2.
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©2008 AwwaRF. ALL RIGHTS RESERVED
9
6
5
7
6
4
5
4
3
3
2
Generator
O3 Concentration (%wt)
Specific Energy Consumption (kWh/lb O3)
8
2
VPSA
1
Generator + VPSA
O3 Concentration
0
1
N
5
-0
ov
D
e
05
c-
J
6
-0
an
Fe
06
b-
M
a
6
r-0
p
A
6
r-0
a
M
06
y-
06
nu
J
lJu
06
A
6
-0
ug
Se
06
p-
Figure 6.8 Monthly average specific energy consumption for the ozone generator, VPSA
system and the combined specific energy consumption for both. The corresponding ozone
concentration is plotted on the secondary y-axis.
Figure 6.9 shows measured generator plus VPSA unit-flow EC as a function of the
monthly average water flow rate. The relationship is predictable, since minimal variation
occurred in ozone dose (i.e., ozone dose ranged between 1.0 and 1.2 mg/L). EC for ozone
generation was 0.08 kWh/kgal at a monthly average flow rate of 225 mgd and 0.06 kWh/kgal at
a monthly average flow rate above 350 mgd. It appears that EC levels off at 0.06 kWh/kgal for
the operating applied ozone dose of 1.0 to 1.2 mg/L.
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©2008 AwwaRF. ALL RIGHTS RESERVED
0.09
Specific Energy Consumption (kWh/kgal)
0.08
0.07
R2 = 0.91
0.06
0.05
0.04
0.03
0.02
0.01
0.00
200
220
240
260
280
300
320
340
360
380
400
Average Monthly Flowrate (mgd)
Figure 6.9 Specific energy consumption for the ozone generator and the VPSA system as a
function of the average daily flowrate per month to the SNWA treatment plant. The data
is fit with a power law function.
The installed power demand of the ozone generators and VPSA units is 4.8 MW, or
3.2 percent of the total installed power demand for low-lift pumping, oxygen/ozone production and
high-lift pumping. Energy price at the AMS plant is a function time of day usage, with higher
price during the day and lower price during the nighttime hours. The AMS plant staff minimizes
overall pumping plus plant-operating energy cost by maximizing water pumping and treatment
during the nighttime (off-peak power cost) hours and minimizing the daytime operations. The
AMS pumps are equipped with VFDs to accommodate the large daily variations in flowrates while
maintaining high-energy efficiencies.
The degree of water-flow fluctuation is different during winter and summer. Figure 6.10
shows the operating data for representative one-week periods in January and June/July 2006. The
winter flowrate was generally between 160 mgd and 250 mgd, but reached 320 mgdD for one of
the days. In comparison, the minimum summer flowrate was also about 160 mgd, but high flow
was 550 mgd, which just below the facility’s rated capacity of 600 mgd. Again, the daily lows
correspond to periods of high power and energy pricing for the AMS plant while the daily water
production peak is during the lower off-peak power and energy prices.
The target ozone dosages were nearly the same between the two periods, 1.25 mg/L in the
winter versus 1.10 mg/L in the summer, and the gas flow was a constant 650 scfm0C (Figures 6.11
and 6.12). However, since water production differed greatly between the two seasons, the ozone
production was also correspondingly different. The winter low production was about 2,000 lb/day
and high production was usually 3,000 lb/day, but reached 3,600 lb/day for one of the days. In
comparison, the range of summer ozone production was between 1,500 lb/day and 5,500 lb/day.
107
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600
Hourly Water Flowrate (mgd)
500
400
300
200
100
January 8 to 15, 2006
June 25 to July 2, 2006
0
0
1
2
3
4
5
6
Study Period Days
Figure 6.10 Hourly raw water flowrate measurements for one week period in January
2006 (winter demand period) and June-July 2006 (summer demand period).
108
©2008 AwwaRF. ALL RIGHTS RESERVED
7
6,000
3.00
Ozone
Production
Ozone Dosage
2.50
4,000
2.00
3,000
1.50
2,000
1.00
1,000
Ozone Dosage (mg/L)
Ozone Production (lb/day)
5,000
0.50
Hourly total gas flowrate was a constant
650 scfm during this period.
0
0.00
8-Jan
9-Jan
10-Jan
11-Jan
12-Jan
13-Jan
14-Jan
15-Jan
6,000
3.0
5,000
2.5
4,000
2.0
3,000
1.5
2,000
1.0
1,000
Ozone Dosage (mg/L)
Ozone Production (lb/day)
Figure 6.11 Hourly ozone production and dosage for January 2006 (winter demand
period).
0.5
Ozone Production
Ozone Dosage
Hourly total gas flowrate was a constant
650 scfm during this period.
0
25-Jun
0.0
26-Jun
27-Jun
28-Jun
29-Jun
30-Jun
1-Jul
2-Jul
Figure 6.12 Hourly ozone production and dosage for June/July 2006 (summer demand
period).
109
©2008 AwwaRF. ALL RIGHTS RESERVED
1,200
6,000
1,000
5,000
800
4,000
600
3,000
400
2,000
Total Ozone Generator
200
Total VPSA
Ozone Production (lb/day)
Power Demand (kW)
Figures 6.13 and 6.14 show the measured power demand of the ozone facilities during
January and June 2006, respectively. Since the AMS was using a constant 650 scfm (15,600
scfm) of oxygen, the VPSA power demand was essentially constant at 420 kW, and all the
variability in the total system power demand was associated with the ozone generators. The
range of ozone generator power demand was approximately 250 to 450 kW during the winter
and 200 to 750 kW during summer. The daily maximum total demand during the summer was
approximately 1.15 MW (1,150 kW), which is 23 percent of the maximum installed demand of
4.8 MW. The principal reason for the lower-than-design operating power demand is that the
AMS was treating the water with 1.1 mg/L O3, which approximately one-third of the design dose
of 3.0 mg/L.
1,000
Ozone Production
15
-J
an
14
-J
an
13
-J
an
12
-J
an
11
-J
an
10
-J
an
0
9Ja
n
8Ja
n
0
Figure 6.13 Power demand for the ozone generator and the VPSA system during January
2006 (winter) at the SNWA. The corresponding ozone production rate is shown on the
secondary y-axis.
110
©2008 AwwaRF. ALL RIGHTS RESERVED
6,000
1,000
5,000
800
4,000
600
3,000
400
2,000
200
1,000
Total Ozone Generator
Total VPSA
Ozone Production
l
2Ju
l
1Ju
30
-J
un
29
-J
un
28
-J
un
27
-J
un
0
26
-J
un
0
25
-J
un
Ozone Production (lb/day)
Power Demand (kW)
1,200
Figure 6.14 Power demand for the ozone generator and the VPSA system during June
2006 (summer) at the SNWA. The corresponding ozone production rate is shown on the
secondary y-axis.
The high variability in ozone concentration, due to the great hourly changes in generator
power at a constant gas flow, resulted in variations in the process specific EC. Figure 6.15
shows the calculated specific EC of the AMS ozone system as a function of the hourly ozone
concentration for both one-week winter and summer periods analyzed. The winter specific EC
was between 6 kWh/lb O3 produced and 9 kWh/lbO3 produced while the summer specific EC
was between 5 kWh/lbO3 produced and 15 kWh/lbO3 produced; the larger summer range
corresponds to the wider range of summer water treatment. At ozone concentrations between
5 percent and 7 percent weight, the specific EC was lowest at about 5 kWh/lbO3. When
operating at ozone concentrations less than 5 percent weight, the specific energy was higher. As
an example, the specific energy doubled to 10 kWh/lbO3 when AMS was operating at an ozone
concentration of 2 percent weight.
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©2008 AwwaRF. ALL RIGHTS RESERVED
15
Summer
Winter
Specific Energy (kWh/lb O3)
12
9
6
3
0
0
1
2
3
4
5
Ozone Concentration (%wt)
6
7
8
Figure 6.15 Calculated AMS ozone system specific energy consumption as a function of
operating ozone concentration.
Figure 6.16 shows the specific EC for both weeks in winter and summer plotted against
ozone production rate. Also shown are the monthly average values for said parameters and
projected values if the system operated at the design 8 percent weight ozone concentration. At
an ozone production rate below 3,500 lb/day, the operating specific EC was higher than indicated
by the design-based condition. This inefficiency is the result of maintaining a constant gas flow
rate of 650 scfm0C despite varying ozone demand. As will be noted later, the AMS plant staff
maintained the constant gas flow because of other operational issues. When the AMS plant
operated at above 3,500 lb/day of ozone production, the specific EC was slightly less than the
design-based condition. The more efficient operation was because the operating ozone
concentrations were below the 8 percent weight design condition, which in turn means that less
energy was required. When analyzed on a monthly average basis, the AMS ozone system EC
was higher than the design conditions, with the additional inefficiency being smallest at ozone
production rates greater than 3,500 lbs/day.
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15
Specific Energy Consumption (kWh/lb O3)
Constant Gas Flow & Variable O3 Conc
12
Monthly Average
R2 = 0.97
9
6
3
0
0
1,000
2,000
3,000
4,000
Ozone Production (lb/day)
5,000
6,000
Figure 6.16 Calculated AMS ozone system specific energy consumption as a function of
operating ozone production rate. The data is fit using a power function.
The specific EC for the ozonation system is reported for both January and June 2006
(winter and summer conditions) as a function of the daily water production in Figure 6.17. The
data follows the same trend for both time periods in which the specific EC decreases with
increasing water flow. In both cases the relationship between specific EC and water production
is best described by a power function (R2 = 0.95), which is similar to the relation observed
between specific EC and ozone concentration (Figure 6.16).
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©2008 AwwaRF. ALL RIGHTS RESERVED
0.15
Specific Energy Consumption (kWh/kgal)
Summer
Winter
0.12
0.09
R2 = 0.9481
0.06
0.03
0.00
0
100
200
300
400
500
600
700
Water Production (mgd)
Figure 6.17 Calculated AMS ozone system specific energy consumption as a function of
water production. For the data reported here the feed gas flowrate was held constant at
650 scfm.
Potential System Improvements
The preceding discussion indicates that EC potentially can be reduced by operating the
AMS plant consistently at the design ozone concentration of 8 percent weight. Potential energy
and cost savings resulting from operating the AMS ozonation facilities at the design ozone
concentration of 8 percent weight are detailed in Table 6-1. This analysis was done for both the
winter and summer operating periods during which the average water flowrates were 226 and
379 mgd, respectively. The average operating ozone concentration in winter and summer was
3.08 and 4.44 percent weight, respectively, which are below the design operating value.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Table 6.2
Potential energy and cost savings analysis for optimization of ozone concentration during
the winter and summer operating periods at the AMS WTP
Parameter
Water Flow Rate
Units
mgd
Operating Results
kW
kW
kW
%wt
Generator Power Demand
VPSA Unit Power Demand
Generator + VPSA Unit Power Demand
Operating Ozone Concentration
Design-based Conditions
Generator + VPSA Unit Power Demand
kW
Ozone Concentration
%wt
Energy Optimization Assessment
Operating Results
Unit-flow Energy Consumption
kW/kgal
Daily average energy cost @$0.07/kWh
$/day
Unit-flow Energy Cost
$/kgal
Design-based Assessment
Unit-flow Energy Consumption
kW/kgal
Daily average energy cost @$0.07/kWh
$/day
Unit-flow Energy Cost
$/kgal
Potential Savings with Optimization
Unit-flow Energy Consumption
kW/kgal
Daily average energy cost @$0.07/kWh
$/day
Unit-flow Energy Cost
$/kgal
Percent savings
%
Winter
Operation
226
Summer
Operation
379
345
422
767
3.08
485
429
914
4.44
709
8.00
900
8.00
0.081
1,289
0.0057
0.058
1,536
0.0041
0.075
1,192
0.0053
0.057
1,513
0.0040
0.006
97
0.0004
7.5%
0.001
23
0.0001
1.5%
From Table 6.2, the potential energy and cost savings during the summer was 1.5 percent,
while that in the winter was 7.5 percent over what is now incurred under the current operating
values. At the time of this study the average energy price is $0.07/kWh at the AMS plant.
Therefore, operating the ozone system at the design concentration of 8 percent weight would
result in potential cost savings of about $97/day in the winter and $23/day in the summer. These
savings could be achieved by gas flow adjustment, provided disinfection performance is
maintained by consistency in ozone dosage during changes in plant water flow rate.
The AMS plant has eight ozone contactors (shown in Figure 6.2), each with a gas flow
control valve and valve actuator. The plant also has a gas flow control valve on the main header
to all ozone contactors. In automatic operation, the valve on the main header is adjusted
automatically to control total gas flow to the system. The plant operators manually adjust the
individual contactor control valves to equalize disinfection performance from parallel contactors.
The primary reason that gas flow is unchanged is reduced operator involvement for manual valve
adjustment. Automatic gas flow control at the contactors was attempted, but was unsuccessful
due to mechanical limitations with the installed valve actuators.
Plant staff has identified that the installed valve actuators on the individual contactors
lack adequate sensitivity for good gas flow control. The installed actuators are alternating
current-control devices. Staff has replaced one analog unit with a direct current actuator, and gas
115
©2008 AwwaRF. ALL RIGHTS RESERVED
flow control improved. The staff is considering replacing all the remaining analog actuators with
digital actuators. The primary purpose of this improvement is to reduce the time required by
operators in making manual valve adjustments to balance disinfection performance among the
parallel contactors. This replacement might also provide an opportunity to relocate the gas flow
control point from the main header to each ozone contactor. This control approach would
maximize automatic control (i.e., eliminate the need for manual valve adjustments) and
potentially, provide an opportunity to optimize gas flow rate and lower EC.
Contra Costa Water District (California) Ralph D. Bollman Water Treatment Plant
System Description
The 80 mgd Ralph D. Bollman WTP is operated by the Contra Costa Water District in
Concord, California and has a service population of roughly 230,000. The plant was originally
constructed in 1968 and has undergone two major upgrades. A process flow diagram for the
Bollman WTP is given in Figure 6.18. Raw water is drawn from the Mallard Reservoir and
pumped to the WTP. Following coagulant addition the water undergoes flocculation and
sedimentation. The clarified water enters the ozone contact basins prior to filtration. Any
residual ozone is collected and destroyed in the ozone destruction unit. The filters are composed
of granular activated carbon (GAC) and sand. Prior to entering the distribution system the
treated water undergoes pH adjustment and is chloraminated to provide residual disinfection.
Flocculation/
Sedimentation
Ozone
Contact Basin
Filtration
Chemical
Addition
Clearwell
Storage
Chemical
Addition
LOX
Ozone Generators
Figure 6.18 Process flow diagram for the Ralph D. Bollman drinking water treatment
plant.
The addition of ozonation facilities in 1999 as a disinfection process was the most recent
of the two major upgrades at the WTP. Equipment and process components of the Bollman
ozonation system, including the oxygen feed gas system, are shown schematically in Figure 6.19.
The ozone system feed-gas is vaporized LOX. The ozone generator feed-gas supply also
contains a small amount (1 to 2 percent) of nitrogen, which is obtained from the dried air. There
are two 11,000-gal LOX storage tanks that supply LOX to the vaporizers. The LOX enters the
ozone generator, where it passes through a dielectric and electrical charge to produce ozone.
Vaporized LOX is under sufficient pressure so that the ozone does not need to be pressurized
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©2008 AwwaRF. ALL RIGHTS RESERVED
prior to the ozone diffusers. In fact, the ozone line pressure is lowered via a pressure-reducing
valve to control the bubbling rate through the diffusers. EC by the LOX vaporizer and the
delivery system is minimal. Residual ozone is off-gassed from the ozone contactor and directed
into the ozone destruction unit, where it is converted back into oxygen by catalytic reaction.
Electrical components of the ozone destruction system include a heating element and vent-gas
blower.
Figure 6.19 Schematic layout of the ozonation system at the Bollman WTP.
There are three ozone generators at the Bollman plant, each having a design ozone
production capacity of 1,020-lb/day at a concentration of 10 percent weight ozone. This yields a
firm design capacity of 2,040-lb/day with one generator serving as a standby unit. The power
supply unit (PSU) for each generator is rated at 210 kW. Monthly average ozone production and
water flow rate is shown in Figure 6.20. The actual operating ozone production rate is
significantly below the design value, due primarily to the lower ozone dosages used at this plant.
Average ozone production was 270-lb/day, and ranged between 110 and 565 lb/day. The ozone
production rate varied as a function of the raw water flowrate. Higher flowrates required
increased ozone production rates in order to maintain the desired ozone residual in the treated
water. Because the actual ozone demand is significantly less than the design demand, the
Bollman WTP operates only one generator most of the time, with the other two in standby.
117
©2008 AwwaRF. ALL RIGHTS RESERVED
2500
80
Ozone Production
70
Water Flow
60
50
1500
40
1000
30
Water Flowrate (mgd)
Ozone Production Rate (lb/day)
2000
20
500
10
0
Jan04
0
Apr- Jul-04 Oct-04 Jan04
05
Apr- Jul-05 Oct-05 Jan05
06
Apr- Jul-06 Sep06
06
Dec06
Figure 6.20 Average monthly finished water flowrate and ozone production rate at the
Bollman WTP. The design ozone production capacity is 2,040 lb O3/day.
The monthly ozone generator gas flowrate and the resulting ozone concentration at the
treatment plant are reported in Figure 6.21. Ozone gas is delivered to one or two bubble-diffuser
ozone contactors. Both contactors are in service most of the time. At low ozone production
rates, the operating ozone gas flowrate is less than the design value (85 scfm) though it exceeds
the minimum required gas flowrate (15 scfm) for the ozone generator and/ ozone contactor
diffusers. The average gas flowrate was 34-scfm, and ranged between 23 and 57 scfm. The
average ozone concentration was 6.5 percent weight, and ranged between 4.2 and 9.3 percent
weight. From Figure 6.21, the gas flowrate increases with increasing ozone concentration.
However, there appears to be a maximum achievable ozone concentration of around 9 percent
weight. Here, further increases in the gas flowrate to the ozone generator do not result in
increased ozone concentration. This would suggest that it is unnecessary and perhaps inefficient
to operate at gas flowrates greater than around 35 scfm as it does not result in an increased ozone
concentration. This conclusion is based however, on the assumption that the elevated flowrates
were not initiated to overcome other inefficiencies in the ozone generator during July 2005 and
June through August 2006. If the latter scenario is true then it would be worthwhile to identify
the sources of these inefficiencies and minimize them. The ozone contactors themselves
consume a minimal amount of energy.
118
©2008 AwwaRF. ALL RIGHTS RESERVED
10
70
9
60
50
7
6
40
5
30
4
3
20
10
Ozone Concentration (%wt)
Ozone Generator Gas Flow (scfm)
8
2
Flowrate
1
Concentration
0
0
Jan-04 Apr-04 Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Apr-06 Jul-06 Sep-06 Dec-06
Figure 6.21 Monthly ozone generator gas flowrate and resulting ozone concentration over
the course of the study period at the Bollman WTP.
The primary purpose of ozonation is to achieve a minimum 2-log inactivation of viruses
(Figure 6.22). These disinfection credits may be combined with the 2-log removal credit from
the sedimentation/filtration processes to meet the plant’s required overall 4-log regulation. In
meeting the 2-log virus inactivation regulation via ozonation, the 0.5-log Giardia inactivation
regulation is also met. Secondary objectives of the ozonation process include reduced formation
of disinfection by-products such as THM and HAA5, elimination of taste and odor complaints,
improved particle removal via micro flocculation and color removal. Here, the virus inactivation
ranged between 15-log and 20-log, which is considerably higher than the requirements. From
December 2004 to January 2005 the measured virus inactivation dropped to roughly 12-log.
This time period corresponds to when the ozone dosage at the WTP was lowest (0.6 mg/L)
relative to the average ozone dosage (1 mg/L).
119
©2008 AwwaRF. ALL RIGHTS RESERVED
30
Virus Inactivation (log)
25
20
15
10
5
2-log required inactivation
0
Jan-04 Apr-04 Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Apr-06 Jul-06 Sep-06 Dec-06
Figure 6.22 Monthly average virus inactivation achieved through ozonation at the Bollman
WTP.
The removal of taste and odor compounds such as Geosmin and 2-methylisoborneol
(MIB) through ozonation at the Bollman WTP is shown in Figures 6.23a and b, respectively. No
data is reported for either Geosmin or MIB during the fall and winter months, where it is
expected to be minimal. The Geosmin concentrations in the raw water varied considerably over
the study period. Significant spikes in the Geosmin concentration were recorded in April 2005,
June 2005, and June – August 2006; without these concentration spikes the average influent
Geosmin concentration was roughly 10 ng/L. Overall, Geosmin was present in the feedwater at
higher concentrations than the MIB. The influent MIB concentration was less variable than that
observed for the Geosmin and averaged around 3 ng/L over the study period. However, the
concentrations of both compounds were reduced in the effluent as a result of ozonation. Indeed,
nearly 100 percent of the MIB was removed during the year 2006. Based on these results
ozonation provides an effective process for inactivating viruses and removing (through
oxidation) taste and odor compounds.
120
©2008 AwwaRF. ALL RIGHTS RESERVED
1,000,000
a
100,000
Influent
Effluent
Concentration (ng/L)
10,000
1,000
100
10
D
ec
-0
6
N
ov
-0
6
p06
Se
6
l-0
Ju
06
M
ay
-
6
M
ar
-0
Ja
n06
N
ov
-0
5
Se
p05
5
Ju
l-0
M
ay
-
M
ar
-0
5
05
1
100
b
Concentration (ng/L)
Influent
Effluent
10
D
ec
-0
6
6
O
ct
-0
A
ug
-0
6
n06
Ju
A
pr
-0
6
Fe
b06
D
ec
-0
5
5
O
ct
-0
A
ug
-0
5
n05
Ju
M
ay
-0
5
M
ar
-0
5
Ja
n-
05
1
Figure 6.23 Influent and effluent concentrations of a) Geosmin and b) MIB following
ozonation.
121
©2008 AwwaRF. ALL RIGHTS RESERVED
The operating ozone dose ranged between 0.7 and 1.3 mg/L, as shown in Figure 6.24,
with an average dose of 0.94 mg/L. The highest ozone dose occurred during the May/June 2005
time period when Geosmin and MIB concentrations were highest. In the event that taste and
odor problems become severe, the maximum design ozone dosage is 3 mg/L. Periods of lower
than average ozone dosages (December 2004 – January 2005) were found to correspond to
reduced levels of virus inactivation (Figure 6.22) signifying the important relationship between
these two parameters.
2.0
Ozone Dose (mg/L)
1.5
Avg. Ozone Dose
1.0
0.5
A
pr
-0
6
Ju
l-0
6
Se
p06
N
ov
-0
6
Fe
b06
Se
p05
N
ov
-0
5
A
pr
-0
5
Ju
n05
05
nJa
Ja
n-
04
M
ar
-0
4
Ju
n04
A
ug
-0
4
N
ov
-0
4
0.0
Figure 6.24 Monthly average ozone dose used at the Bollman WTP.
Energy Consumption
Operating data for the ozone system was recorded by the plant operators six times per
day. The annual average ozone performance statistics are reported in Table 6.3 for 2004 to 2006.
Statistics are provided for the two principle pieces of equipment in the ozonation system, the
ozone generator and the ozone destruction unit. The average monthly specific EC for the
ozonation system is plotted as a function of time in Figure 6.25. Power demand by the ozone
generators averaged 46 kW, and ranged between 18 and 87 kW. Power demand by the ozone
destruct unit averaged 1.2 kW, and ranged between 0.9 and 1.8 kW. The average ozone
production rate for each month was roughly 272 lb O3/day. The specific EC for producing a unit
weight of ozone was substantially higher for the ozone generator compared to the ozone
destruction unit. Overall, it took approximately 4.2 kWh to produce 1 lb of ozone. Furthermore,
0.03 kWh were consumed when producing 1,000 gal of ozonated water. The specific EC is
highest during high demand periods (summer months) and decreases during low-demand periods
(winter months).
122
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 6.3
Annual average ozone production rate and specific energy consumption data for the ozone
generator and destruction unit
O3 Production
Rate
Process
O3 Generator
(lb/day)
271.8
O3 Destruction Unit
Total
271.8
Specific Energy Consumption
Fraction of Total
(kWh/kgal)
0.031
(kWh/lb O3)
4.063
(%)
99
0.001
0.105
1
0.032
4.168
100
Specific Energy Consumption (kWh/kgal)
0.05
0.04
0.03
0.02
0.01
0.00
Jun-03
Jan-04
Aug-04
Feb-05
Sep-05
Mar-06
Oct-06
Apr-07
Figure 6.25 Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) measured from 2004 to 2006.
The specific EC for the ozonation system is reported in Figure 6.26 as a function of the
average monthly finished water flowrate. While the correlation between the two parameters is
poor (R2 < 0.5) the specific EC (kWh/kgal) shows an overall trend of increasing with increasing
finished water flowrate. In other words, the ozonation system does not become more energy
efficient with increasing liquid flowrates. This is in contrast to what is observed for systems that
contain pumps, which do become more efficient as they operate farther up on their respective
pump curves. Because the ozonation system does not contain any pumps the energy efficiency
decreases as it is simply using more energy to produce more ozone. This point is further
illustrated through inspection of Figure 6.27.
123
©2008 AwwaRF. ALL RIGHTS RESERVED
Specific Energy Consumption (kWh/kgal)
0.05
0.04
R2 = 0.162
0.03
0.02
0.01
0.00
0
20
40
60
80
Finished Water Flowrate (MG/month)
Figure 6.26 Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the finished water flowrate.
As was observed for the finished water flowrate, the correlation between specific EC
(kWh/lb O3) and ozone production rate is poor (Figure 6.27). As the ozone production rate
increases the specific EC by the ozonation system also increases, signifying a decrease in energy
efficiency. This observation is supported by the data presented in Figure 6.28. Here the specific
EC for the ozonation system is plotted as a function of the resulting ozone concentration (percent
weight) in the gas stream. The correlation between these two parameters is relatively good with
a correlation coefficient of 0.68. As was seen for the other performance parameters the
ozonation energy efficiency degrades with increasing ozone production, measured here as ozone
concentration.
124
©2008 AwwaRF. ALL RIGHTS RESERVED
Specific Energy Consumption (kWh/lb O3)
5
4
R2 = 0.3423
3
2
1
0
0
100
200
300
400
500
600
Ozone Production Rate (lb/day)
Figure 6.27 Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the ozone production rate.
Specific Energy Consumption (kWh/lb O3)
5.0
4.0
R2 = 0.6798
3.0
2.0
1.0
0.0
0
1
2
3
4
5
6
7
8
9
10
Ozone Concentration (%wt)
Figure 6.28 Average monthly specific energy consumption by the ozonation system (ozone
generator and destruction unit) as a function of the ozone concentration in the gas stream.
125
©2008 AwwaRF. ALL RIGHTS RESERVED
For LOX-fed ozone systems, the total energy cost is determined from both the energy
required to produce the ozone and that required by the LOX system itself. While relevant to
determining the EC of an LOX fed ozone system, the EC of LOX production was outside the
scope of this project. From 2004 to 2006 the average unit-volume EC for producing ozone was
0.031 kWh/kgal, and ranged between 0.021 and 0.047 kWh/kgal. The associated average unitmass cost for energy was $0.21/lb O3, and ranged between $0.18/lb O3 and $0.24/lb O3.
However, the combined LOX material costs plus energy costs associated with operation of the
ozone generator was three times higher, at an average value of $0.67/lbO3, and ranged between
$0.53/lbO3 and $0.86/lbO3.
The unit costs associated with producing ozone are plotted as a function of ozone
concentration in Figure 6.29. As the ozone concentration increases the associated unit cost for
the LOX decreases. Conversely, the unit mass energy costs increase slightly with increasing
ozone concentration. This increase in the energy costs likely results from the increased voltage
requirements on behalf of the ozone generator to convert more oxygen to ozone. Taking into
account both the costs for the LOX and the energy costs, the total unit mass costs for the
ozonation system decrease (in a logarithmic fashion) with increasing ozone concentration,
eventually reaching a rather stable value of $0.55/lb O3 at a ozone concentration between 9 and
10 percent weight. At ozone concentrations greater than 10 percent weight, the unit mass costs
begin to increase and the savings are lost. The optimum ozone concentration will ultimately be
determined by site specific conditions and may in fact be higher than the 9 percent weight value
found for the Bollman WTP. In summary, the unit mass cost savings associated with the LOX
system when operating it at higher ozone concentrations outweigh the marginal increase in the
energy costs. This suggests that operation of the ozonation system is most efficient when
targeting an ozone concentration of roughly 9 percent weight. Furthermore, these findings
illustrate the importance of considering both the ozone generator and the feed gas system when
assessing the unit costs for operating an ozonation system.
126
©2008 AwwaRF. ALL RIGHTS RESERVED
1.0
Energy
Unit-mass Cost ($/lb O3)
0.8
LOX material
Energy plus LOX
0.6
0.4
0.2
0.0
0
1
2
3
4
5
6
7
8
9
10
Ozone Concentration (%wt)
Figure 6.29 Unit-mass costs in terms of energy required by the ozone generator and LOX
material costs for producing a pound of ozone at the Bollman WTP.
Potential Energy Conservation Improvements
The monthly average ozone production rate and monthly average cost of ozone, including
energy and LOX are shown in Table 6.4. At an average operating ozone concentration of
6.5 percent weight the average energy costs per month plus the costs associated with the LOX
system is $5,188. If the Bollman plant were able to operate at an average ozone concentration of
roughly 9 percent weight, the unit-mass cost of ozone would be about $0.53 /lbO3 and the
average monthly cost for energy plus LOX would be $4,400. This represents savings in
operating cost of about 18 percent. However, it must be emphasized that the Bollman plant
might be unable to operate at the gas flowrates necessary to maintain this optimum operating
ozone concentration (9 percent weight). If the gas flow rate falls below this minimum value,
then gas distribution to the generator dielectrics (i.e., uneven cooling) or gas distribution to the
diffusers (i.e., uneven ozone contact with water) might be negatively affected. Nevertheless, any
possible reduction gas flow that could occur to maintain the ozone concentration near 9 percent
weight would minimize the total unit cost for producing ozone.
127
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 6.4
Energy consumption and ozone production for the Bollman WTP
Jan-04
Feb-04
Mar-04
Apr-04
May-04
Jun-04
Jul-04
Aug-04
Sep-04
Oct-04
Nov-04
Dec-04
Jan-05
Feb-05
Mar-05
Apr-05
May-05
Jun-05
Jul-05
Aug-05
Sep-05
Oct-05
Nov-05
Dec-05
Jan-06
Feb-06
Mar-06
Apr-06
May-06
Jun-06
Jul-06
Aug-06
Sep-06
Oct-06
Nov-06
Dec-06
Total
Ozone
Conc.
%wt
4.34
4.74
5.42
6.53
8.54
8.96
9.26
9.02
9.02
7.74
4.43
4.22
4.17
4.27
5.09
6.37
7.93
7.36
8.57
8.69
7.97
6.67
5.50
5.36
4.54
5.11
4.71
4.93
7.24
8.30
8.19
8.76
7.15
5.60
4.81
4.24
Monthly
Ozone
Production
lbO3/month
4,464
4,439
7,226
7,588
9,487
10,554
12,669
11,719
11,674
7,641
4,135
3,543
3,723
4,317
6,457
8,345
10,650
9,957
14,594
12,683
9,732
7,556
5,814
5,641
5,342
5,343
5,457
5,558
10,621
13,853
17,211
13,727
10,211
7,325
4,855
4,270
Monthly
Ozone
Cost
$/month
3,772
3,523
5,122
4,822
5,277
5,765
6,839
6,376
6,349
4,438
3,449
3,044
3,206
3,674
4,839
5,375
6,096
5,906
8,084
6,998
5,571
4,755
4,118
4,078
4,253
3,917
4,273
4,202
6,314
7,354
9,288
7,331
5,960
5,066
3,726
3,598
Minimum
Monthly
Cost
$/month
2,370
2,357
3,836
4,028
5,037
5,603
6,726
6,222
6,198
4,056
2,195
1,881
1,977
2,292
3,428
4,430
5,654
5,286
7,748
6,733
5,167
4,012
3,087
2,995
2,836
2,836
2,897
2,951
5,639
7,354
9,137
7,288
5,421
3,889
2,577
2,267
Savings
$/month
1,402
1,166
1,286
793
240
162
113
154
151
382
1,254
1,164
1,229
1,382
1,411
944
442
620
336
265
404
743
1,031
1,083
1,416
1,081
1,376
1,251
676
0
151
43
539
1,178
1,148
1,331
Minimum
Average
Maximum
4.17
6.49
9.26
3,543
8,288
17,211
3,044
5,188
9,288
1,881
4,400
9,137
0
788
1,416
Month-Year
128
©2008 AwwaRF. ALL RIGHTS RESERVED
Central Lake County Joint Action Water Agency Paul M. Neal Water Treatment Plant
System Description
The Paul M. Neal WTP was placed into operation in 1992. The plant is owned and
operated by the Central Lake County Joint Action Water Agency (CLCJAWA), which is
composed of nine members representing 12 communities in Lake County, IL. Source water is
obtained from Lake Michigan, which is locally turbid in the winter due to cold north/northeast
winds. Summer supply is least turbid due to the formation of an insular epilimnion and less
intense, warm south/southeastern winds, but has potential for taste and odor issues due to
2-methylisoborneol (MIB) and Geosmin. Ozonation has mitigated the occurrence of taste and
odor complaints (Nerenberg et al, 2000) at the same time as other area Lake Michigan water
treatment facilities have reported customer complaints about earthy/musty tastes and odors.
Plant unit processes are shown in Figure 6.30, and include raw water pumping (off-site),
pre-ozonation, rapid mix (chemical addition), three-stage flocculation, inclined-plate
sedimentation, BAC filtration, UV-disinfection, chlorination, clearwell storage, and high-service
pumping. Water is drawn from Lake Michigan into a raw water pumping station through a
54-inch steel intake pipe. The raw water is chemically treated with potassium permanganate and
screened for algae and debris. Four 500 hp raw water pumps, with a maximum capacity of
13 mgd, pump the raw water 2 miles to the Paul M. Neal WTP. The WTP has four treatment
trains, each consisting of an ozone contactor, coagulation and sedimentation basin, and three
filters that together are capable of treating 12.5 mgd of raw water.
From Figure 6.30 the first treatment process that the water undergoes is ozonation.
Ozone is produced on site and is diffused into the raw water in vacuum-sealed chambers, where
it disinfects and oxidizes compounds in the water. The ozonation process is powered by three
ozone generators, each with a 500 lb/day capacity. The ozone contact basins were designed to
ensure a minimum contact time of 8 minutes. The ozone system has a production capacity of
1,000 lb/day, which provides a maximum dosage of 4.0 mg/L at the design flow rate of 30 mgd.
Following ozonation, the water enters a two-stage rapid mix process, where polyaluminum
chloride is added to promote coagulation of suspended solids. The rapid mix system was
designed to have a minimum mixing time of 26 seconds. Following rapid mix, the water is
gently stirred in a three-stage flocculation process to facilitate floc formation. The flocculation
basins are equipped with pitched blade turbine mixers and the basins are designed to have a
minimum detention time of 27 minutes. After flocculation, the water is directed to the inclined
plate sedimentation basins. Then, the water is sent to BAC filters, where the remaining solids
are trapped and dissolved organic compounds are removed. Each treatment train is equipped
with three filters that are designed to filter at a rate of 5 gpm/ft2. To maintain filtering efficiency
the system has two 200 hp filter pumps that periodically backwash the filter beds. After
filtration, the water is through UV reactors to destroy any remaining pathogens. Finally,
chlorine, fluoride and phosphoric acid are added to the filtered water, which is stored in two
2.5-MG clearwells. Six 500 hp finished water pumps draw the water from the clearwell to
service the CLCJAWA communities.
129
©2008 AwwaRF. ALL RIGHTS RESERVED
O3 Contactor Rapid Mix
1
A
2
A
1
B
2
B
3
A
3
B
4
A
Flocculation/
Sedimentation
Basin
Filters
4
B
Lake
Michigan
Train #1
Pump
Station
Train #2
Train #3
Train #4
High-Service
Pumps
UV
Disinfection
Treated Water
to Distribution
System
Clearwell
Figure 6.30 Simplified schematic diagram of the unit processes at the Paul M. Neal WTP.
A schematic of the ozone generator and off-gas treatment systems are shown in Figures
6.31 and 6.32, respectively. Four liquid-ring air compressors (one standby) supply air, which
serves as the feed gas to the ozone system. The ambient air, which has a water content
≥10,000 ppm, must be dried to <6 ppm water content (i.e., dew point temperature <–60oC)
before delivery to the ozone generators. The ambient air is dried in three steps: by pressurization
(operating pressure is 20 psig) in the four air compressors (one standby), by cooling in three
refrigerant dryers (one standby) and by adsorption within three desiccant dryers (one standby).
Dried air is directed to three medium frequency ozone generators (one standby). The design
ozone concentration is 1.5 percent weight. Ozone demand was very low during 2006, and only
one air compressor, one refrigerant dryer, one desiccant dryer, and one ozone generator were in
operation at any given time during this period. Three pumps (one standby) provide filtered water
for cooling the ozone generators’ shells and two power supply cooling water pumps (one
standby) recirculate demineralized water through a heat exchanger and the power supply unit
(PSU).
130
©2008 AwwaRF. ALL RIGHTS RESERVED
Desiccant Dryers
Refrigerant
Dryers
Filters
Filters
Air
Compressors
Ozone Generators
To Four Ozone
Contact Basins
Figure 6.31 Simplified schematic diagram of ozone feed gas and generator unit processes
Off-gas from each
contact basin
Heat catalyst
destruct units
Vacuum
blowers
Figure 6.32 Simplified schematic diagram of ozone destruct units.
Four parallel 8-chamber over/under baffled contact basins are used for ozone dissolution
(chamber 1 only) and reaction (chambers 2 through 8) in the raw water. Ozone gas is introduced
into the water via dome-shaped fine bubble diffusers. An ozone residual sample can be obtained
from the effluent of each chamber using a gravity-fed piping system. Ozone residual monitors
are installed to monitor disinfection performance and control ozone dose. The ozone dose is
131
©2008 AwwaRF. ALL RIGHTS RESERVED
adjusted to achieve a residual value of 0.04 mg/L at the end of the ozone contactor. This control
strategy was established to provide a controlled amount of ozone exposure to the raw water for
inactivation of bacteria and oxidation of potential taste and odor compounds. An off-gas destruct
system maintains each contact basin under vacuum conditions and converts the remaining ozone
in the off-gas to oxygen before being vented to the atmosphere.
The operating ozone production rate is significantly below the design dose, mostly due to
lower ozone dose requirements for controlling taste and odor, rather than for Giardia inactivation
as anticipated during plant design in the late 1980’s. Monthly average ozone production rates are
shown in Figure 6.33. Average ozone production was 145-lb/day, and ranged between 90 and
250 lb/day. During the study period one generator was in operation most of the time, with two
generators in standby. Ozone production was highest during the summer months (June –
September) compared to the colder months. The increased ozone production corresponds to the
increased raw water flowrates and the associated demand that occurs during this time period.
500
Ozone Production (lb/day)
400
300
Average Ozone
Production
200
100
0
Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 Jul-06 Aug-06 Sep-06 Oct-06 Nov-06 Dec-06
Figure 6.33 Monthly ozone production rate at the Paul M. Neal WTP for the operating
year 2006. The average ozone production rate is shown as a solid line.
Energy Consumption
Averaged data for selected water quality parameters for 2006 and ozone generation
parameters are given in Table 6.5. For 2006 the average ozone dose was 0.81 mg/L and the
average water flow rate was 21.4 mgd.
132
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 6.5
Summary of selected data for the Paul M. Neal WTP
Raw Water
Month
January
February
March
April
May
June
July
August
September
October
November
December
Average
Flowrate
mgd
19.3
19.3
19.1
20.3
21.6
24.7
27.8
26.4
20.8
19.2
18.7
19.0
21.4
Turbidity Temperature
NTU
°C
12.3
2.3
18.3
1.3
18.11
2.8
12.11
7.8
3.3
10.2
2.54
15.7
1.53
17.6
3.03
20.3
6.16
19.6
3.88
12.1
12.6
7.7
6.71
3.5
8.38
10.1
Ozone
pH
8.27
8.30
8.25
8.25
8.18
8.29
8.34
8.28
8.19
8.17
8.17
8.22
TOC
mg/L
2.1
2.1
2.1
1.8
1.9
2.3
2.1
2.2
2.3
2.1
2.4
2.1
Dose
mg/L
0.56
0.70
0.66
0.76
0.69
0.85
0.99
1.14
1.33
0.78
0.75
0.56
Production
lb/day
90
113
105
129
124
175
230
251
231
125
117
89
8.24
2.1
0.81
148
Power consuming devices for the ozone system consists of the ozone generator and the
support equipment, which includes the air compressor, refrigerant dryer, desiccant dryer, off-gas
destruct heater, off-gas destruct blower, PSU cooling water pump and ozone generator cooling
water pump. The power demand for each piece of equipment component is summarized in
Table 6.6. The data reported in Table 6.6 was obtained during a jointly sponsored ozone
research study by the Electric Power Research Institute (EPRI) and the Awwa Research
Foundation (AwwaRF) (Rakness and Hunter, 2000). The power demand for the various support
equipment remains constant over the course of the year. The sub-total power demand is 59.6 kW
for the ozone support equipment. The air compressor consumes the largest fraction (51 percent)
of energy dedicated to the support equipment followed by the cooling water pump for the
generator (21 percent).
Table 6.6
Summary of “other” ozone power at the Paul M. Neal WTP
Air
Refrigerant Desiccant
Compressor
Dryer
Dryer
kW
kW
kW
30.3
5.7
4.8
Off-gas
Destruct
Heater
kW
1.1
Off-gas
Destruct
Blower
kW
2.3
PSU
Cooling
Water
Pump
kW
2.9
Generator
Cooling
Water
Pump
kW
12.5
Sub-total
Other
Power
kW
59.6
EC by the ozone generators is monitored continuously by watt-hour meters installed on
each generator. Ozone generator EC and power demand is summarized on a daily basis, and the
monthly averages are shown in Table 6.7. During 2006, the average unit-volume EC value was
0.124 kWh/kgal and ranged between 0.114 and 0.163 kWh/kgal. Unlike the power demand by
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the support equipment, that for the ozone generator varied throughout the year. Power
consumption is greatest during the summer months (June – September), when water demand is
typically highest. Thus, as the amount of water being treated increases, power consumption by
the ozone generators also increases. This same relationship was observed for the Bollman WTP
discussed in Section 6.3.2.
Table 6.7
Summary of ozone-related data for the Paul M. Neal WTP
Generator
Power
Jan-06
Feb-06
Mar-06
Apr-06
May-06
Jun-06
Jul-06
Aug-06
Sep-06
Oct-06
Nov-06
Dec-06
kW
30.5
35.2
36.1
41.7
41.5
58.1
73.9
84.0
78.8
39.4
37.5
29.5
Average
48.8
Subtotal Total
Power Gas Flow
Other
Power Demand
kW
kW
scfm
59.6
90.1
191
59.6
94.7
184
59.6
95.6
187
59.6
101.2
184
59.6
101.1
187
59.6
117.6
178
59.6
133.5
184
59.6
143.5
181
59.6
138.4
172
59.6
99.0
194
59.6
97.1
185
59.6
89.1
186
59.6
108.4
184.4
Ozone
Dose
mg/L
0.56
0.70
0.66
0.76
0.69
0.85
0.99
1.14
1.33
0.78
0.75
0.56
0.81
Influent
Ozone
Energy
Water
Production Usage
Flow
mgd
lb/day
kWh/kgal
19.3
90
0.112
19.3
113
0.118
19.1
105
0.120
20.3
129
0.120
21.6
124
0.112
24.7
175
0.114
27.8
230
0.115
26.4
251
0.130
20.8
231
0.160
19.2
125
0.124
18.7
117
0.125
19
89
0.113
21.4
148
0.122
Table 6.8 summarizes the specific energy (kWh/lbO3) data for the ozone generator only,
support equipment only and total of ozone generator and support equipment. This data is also
displayed graphically in Figure 6.34. Specific energy changes as a function of the operating
ozone concentration. The specific EC by the ozone generator remains relatively stable regardless
of the ozone concentration needed, with a value of about 8 kWh/lbO3. The specific energy
required by the support equipment however, was highly variable, and ranged from 6 to
16 kWh/lbO3 for ozone concentrations ranging from 0.4 to >1.1 percent weight. The specific
energy consumed by the support equipment decreased with, and seemed to reach a stead value, at
an ozone concentration of around 1 percent weight. Notably, this is a far lower ozone
concentration than was observed for steady-state conditions at the LOX fed system (i.e., the
Bollman WTP). This variability of specific energy for the support equipment translates into
variability in the specific energy consumed by the total ozone system, which ranged from 14 to
24 kWh/lbO3. The gas flow rate is constant from the constant-speed air compressor. As such,
ozone concentration varies in response to ozone production changes. The generator power is
adjusted to change the ozone concentration, and, in addition, change the ozone production rate.
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Table 6.8
Summary of ozone concentration and specific energy data
Ozone
Concentration
Ozone Generator
Specific Energy
%wt
0.44
0.57
0.52
0.65
0.61
0.91
1.15
1.28
1.24
0.59
0.58
0.44
0.75
kWh/lb O3
8.1
7.5
8.2
7.8
8.0
8.0
7.7
8.0
8.2
7.6
7.7
8.0
7.9
Jan-06
Feb-06
Mar-06
Apr-06
May-06
Jun-06
Jul-06
Aug-06
Sep-06
Oct-06
Nov-06
Dec-06
Average
Other
Equipment
Specific Energy
kWh/lb O3
15.9
12.7
13.6
11.1
11.5
8.2
6.2
5.7
6.2
11.4
12.2
16.1
10.9
Total
Specific Energy
kWh/lb O3
24.0
20.2
21.8
18.9
19.5
16.1
14.0
13.7
14.4
19.0
19.9
24.1
18.8
Specific Energy Consumption (kWh/lb O3)
30
Total System
25
Ozone Generator
Support Equipment
20
15
10
5
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Ozone Concentration (%wt)
Figure 6.34 Specific energy required for producing a unit mass of ozone as a function of
ozone concentration.
The variability in specific EC is consistent with design expectations, as indicated in
Figure 6.35. Here, the specific EC data from the 2006 operating year is plotted along with that
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expected based on the initial installation performance test data. Finally, the specific EC expected
based on pump upgrades is also shown. At low ozone production rates, the specific energy value
is expected to be much higher than at elevated ozone production rates. The monthly average
data points for 2006 are shown for ozone production rates ranging between 87 and 250 lb/day.
The total system specific energy value ranged from 24 to 14 kWh/lb at ozone production rates of
90 and 250 lb/day. When the ozone production rate exceeds 300 lb/day, then the specific energy
value is expected to be fairly consistent at about 11 to 12 kWh/lb. It is evident that the measured
specific EC for 2006 closely followed the trend expected based on the pump improvements. The
upgrade involved modifications and additions to the cooling water pumping system to utilize
non-chlorinated filtered water for cooling instead of chlorinated water.
Specific Energy Consumption (kWh/lb O3)
30
From 2006 Energy Data
25
Installation Performance Test
20
Performance Test + 'New' Pumping
15
10
5
0
0
100
200
300
400
500
600
700
800
Ozone Production (lb/day)
Figure 6.35 Specific energy consumption (kWh/lb O3) for the ozonation system as a
function of the corresponding ozone production rate for the operating year 2006. Data is
also reported for the installation performance test before and after new pumping was
installed.
Specific energy consumption by the ozonation system is plotted as a function of ozone
dose in Figure 6.36. Over this time period the ozone dose varied from 0.6 to 1.1 mg/L. Despite
changes in the ozone dose there was relatively no change in specific energy consumption. This
finding supports the observation from Figure 6.34 where the specific energy required by the
ozone generator did not vary as a function of the ozone concentration (percent weight) that was
produced, for reasons noted previously. Again, however, as the ozone dose increased the
specific energy consumed by the supporting equipment decreases indicating an increase in the
ozonation system efficiency.
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Specific Energy Consumption (kWh/kgal)
3.0
2.5
R2 = 0.01
2.0
1.5
1.0
0.5
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
O3 Dose (mg/L)
Figure 6.36 Specific energy consumption by the total water treatment plant as a function
of ozone dose.
At CLCJAWA, ozone dose is driven by the residual measured in the final cell of the
ozone contactor. This scheme requires that the ozone dose is adjusted to changes in water quality
(i.e., if ozone demand increases, ozone dose is increased). It also requires that ozone dose is
adjusted with changes in flow (i.e., as flow increases through the reactor the contact time
decreases and thus causes an apparent increase in the ozone residual). Ozone dose would thus be
decreased in this scenario. Because ozone dose is adjusted as a result of flow and water quality
changes, factors directly correlated with ozone demand are difficult to ascertain. Nevertheless, it
is worthwhile here to explore the possible impact of several key water quality parameters and
flow on ozone dose and EC.
Ozone dose and in turn specific EC may be impacted by water quality parameters such as
TOC, turbidity and temperature. TOC data are shown in Table 6.5. The 2006 annual average
TOC concentration was 2.1 mg/L, with a standard deviation of 0.2 mg/L. Therefore, in the
absence of specific upsets in the feedwater quality, ozone dose should not be greatly affected
(through changes in oxidant demand) by TOC in this case. Additionally, pH was also consistent
with a 2006 annual average raw water pH of 8.24 with a standard deviation of 0.11.
Examination of Figure 6.37 finds that the ozone dose decreased overall with increasing raw
water turbidity. However, this decrease in ozone dose did not correspond to a change in specific
EC. Because ozonation occurs at the beginning of the treatment head works it would “see” the
raw water turbidity and potentially be affected by it. This is because the presence of organics
and metals like iron and manganese, which would likely make up a sizable fraction of the
turbidity measured here, affect the transfer efficiency of ozone into the water. Nevertheless, no
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correlation between raw water turbidity and specific EC was observed here, which is attributed
to the lack of dependence here of specific energy on the ozone dose.
1.2
1.0
2.0
0.8
1.5
0.6
1.0
0.4
Specific Energy
0.5
Ozone Dose (mg/L)
Specific Energy Consumption (kWh/kgal)
2.5
0.2
Ozone Dose
0.0
0.0
0
3
5
8
10
13
15
18
20
Raw Water Turbidity (NTU)
Figure 6.37 Specific energy consumption by the total water treatment plant as a function
of the raw water turbidity.
Water temperature may also affect the ozone transfer efficiency and degradation rate.
Temperature may therefore be expected to affect the system’s energy efficiency. Here, the
temperature of concern is that of the raw water. Both the specific EC and the corresponding
ozone dose are plotted as a function of the average monthly temperature in Figure 6.38.
Temperature varied from 1 to 21°C over this time period (Table 6.5). The relationship between
ozone dose and water temperature is relatively strong (R2 = 0.69), warmer water requiring more
ozone to maintain the target ozone residual concentration. Correspondingly the specific EC
decreased slightly (3 percent). This suggests that seasonal variations in water temperature do not
significantly affect the energy efficiency of the ozone system. This may also be attributed to the
fact that water demand, required ozone dose and thus ozone production rate is seasonally
affected. Each of these factors do impact the EC of the ozone system (see Figure 6.35).
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1.4
2.5
1.2
1.0
2.3
0.8
R2 = 0.21
2.1
O3 Dose (mg/L)
Specific Energy Consumption (kWh/kgal)
R2 = 0.69
0.6
Specific Energy
Dose
)Linear (Dose
)Linear (Specific Energy
0.4
0.2
1.9
0
5
10
15
20
25
Temperature (oC)
Figure 6.38 Specific energy consumption by the total water treatment plant as a function
of the average monthly temperature. The corresponding ozone dose is plotted on the
secondary y-axis.
Both EC and finished water demand are higher during warmer months (Figure 6.39).
From Figure 6.39, as the water demand increases the specific EC decreases in a somewhat linear
fashion (R2 = 0.67). Taking an average of the specific energy consumed from October through
March (colder months) and then again from June through September (warmer months) there is 3
percent higher specific EC during the cooler months. Therefore, while demand and equipment
stress increase during high demand periods the operating specific EC decreases.
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2.30
Specific Energy Consumption (kWh/kgal)
October - March
2.25
R2 = 0.66
2.20
June - August
2.15
2.10
2.05
2.00
400
500
600
700
800
900
1000
Finished Water Flowrate (MG/month)
Figure 6.39 Specific energy consumption by the total water treatment plant as a function
of the finished water flowrate.
Potential Energy Conservation Improvements
There are several changes, that if implemented could result in some improvement in the
specific EC by the ozonation system. The first operational change is to operate at a higher
average ozone concentration of approximately 1.2 percent. As the operating ozone concentration
approaches that of the design value (1.5 percent weight ozone) the specific EC (kWh/lb O3) by
the total ozonation system is lowered and will then result in cost savings. For example, the
specific EC (kWh/lb O3) for the total ozonation system was roughly 43 percent greater when it
was operating at the lowest ozone concentration compared to that measured at the highest ozone
concentration. These savings result from improvements in the efficiency of the ozone generator
support equipment such as the air compressor, refrigerant dryer, desiccant dryer, cooling water
pumps, and ozone destruction unit.
The support equipment consumes the largest fraction of energy dedicated to the total
ozonation system. Of the support equipment the air compressor and the cooling water pump
consume nearly 72 percent of the total energy consumed by the support systems. Thus, the
greatest potential energy savings may be realized from improvements in these two pieces of
equipment. Such improvements can include replacing the existing equipment with units that are
either more energy efficient and/or whose peak output more closely corresponds to the current
operating demands. If it is found to be cost efficient, it may be beneficial to consider switching
from an ambient air fed system, requiring the air compressor and desiccator support systems, to
an alternative system such as LOX.
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CONSIDERATIONS FOR EC OPTIMIZATION OF OZONE SYSTEMS
The ozone generator represents the primary energy consumer for ozonation systems that
use LOX feed systems. In cases where oxygen is produced on-site (i.e., the VPSA unit) or
ambient air is used as the feed gas, then the ozone generator EC is secondary. For the ambient
air and VSPA feed gas systems considered, process efficiency is typically lowest at low ozone
production rates and increases with higher production. For the LOX fed system, energy
efficiency actually decreased with increasing ozone concentration, however the loss in energy
efficiency was more than offset by increases in material (i.e., LOX) savings with increases in the
operating ozone concentration. EC optimization of ozone systems generally is associated with
operational improvements aimed at producing ozone at the design concentration of
approximately 8 to 9 percent weight. These issues are summarized below.
Factors Affecting EC of Ozonation Systems
Considering data from all three ozonation facilities, each unique in terms of their design
and operation, the specific EC commonly correlated only with the operating ozone concentration
(Figure 6.40). The correlation coefficient was reasonably strong (R2 = 0.87) when the dataset
was fit with a logarithmic function. As the operating ozone concentration increased, the energy
required to produce a unit weight of ozone decreased. Savings in specific EC with increasing
ozone concentration are attributed to increases in efficiency of the support equipment (feed gas
system) and less to that of the ozone generator itself. The data shown in Figure 6.40 suggests
that based solely on ozone concentration by weight, an ambient air fed system is the more
efficient system at ozone concentrations somewhere lower than 3 percent, VPSA is better
between 3 percent and 4 percent, and LOX is the most appropriate for above 4 percent. The
results also generally indicate that the site-specific optimal energy efficiency is achieved when
systems are operated at conditions that generate ozone near design concentrations. For the
SNWA AMS and Contra Costa Bollman systems, optimal ozone concentration is 8 to 9 percent
weight. For the CLCJAWA system, optimal ozone concentration is approximately 1.2 percent
weight. However, this analysis is assumes that all other conditions are equal. In the case studies
shown here, the SNWA unique diurnal swings to optimize on pumping energy costs, which has
been shown repeatedly in this study to be a substantially larger power demand than treatment,
results in some inefficiency for the ozone system.
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Specific Energy Consumption (kWh/lb O3)
30
R2 = 0.87
25
Central Lake:
Ambient Air Fed
20
15
SNWA:
VPSA Fed
10
Contra Costa:
LOX Fed
5
0
0
1
2
3
4
5
6
7
8
9
10
Ozone Concentration (%wt)
Figure 6.40 Specific EC for the total ozonation system as a function of ozone concentration
for the Contra Costa, SNWA, and Central Lake County WTPs. The dataset was fit using a
logarithmic function.
Operation at higher ozone concentrations is also desirable as a result of cost savings (i.e.,
lower material costs) associated with the feed gas system with increasing ozone concentration
(Figure 6.29). This result is particularly significant for those systems (i.e., LOX fed systems) in
which the feed gas represents a substantially greater part of the total operating costs than the EC
by the ozone generator. Figure 6.40 also demonstrates that the specific type of oxygen feed-gas
supply influences the level of EC per lb of ozone generated. For example, the SNWA ozone
system uses the VPSA equipment located on site, which consumes the greatest amount of energy
at approximately 9 kWh/lb O3 generated with a concentration of 5 percent by weight. In
comparison, the Contra Costa system uses LOX for ozone generation and consumes
approximately 4 kWh/lb O3 with a concentration of 5 percent by weight. For the CLCJAWA
system that uses ambient air for ozone generation, the EC is substantially higher while operating
at much lower ozone concentrations.
Contrary to what has been observed for pump intensive systems (e.g., membrane
systems) ozonation system specific EC did not commonly correlate with water production rate
(Figure 6.41). In other words, specific EC did not decrease with increasing flowrates. One
exception to this trend is the Southern Nevada Water Authority facility where the specific EC by
the ozonation system showed a decreasing trend with increasing flowrate. This trend is realized
for the SNWA facility as a result of energy savings associated with the VPSA oxygen production
unit. Specific EC decreases with increasing oxygen, and thus ozone production rate resulting in
the observed energy savings with increasing water flows. The relationship between specific EC
and flowrate is related to the specific EC and the ozone production rate (Figure 6.42). The same
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©2008 AwwaRF. ALL RIGHTS RESERVED
trends are observed for ozone production rate and liquid flowrate (i.e., more ozone must be
produced in order to treat more water). It is possible that if the Bollman and CLCJAWA plants
were larger, that a stronger relationship between the specific EC and this parameter may become
evident. If this were to occur it may in fact illustrate that for ozonation systems the relationship
between specific EC and flowrate exists only when a critical minimum finished water flowrate
value is reached.
Specific Energy Consumption (kWh/kgal)
0.18
0.16
Central Lake:
Ambient Air Fed
0.14
0.12
0.10
SNWA:
VPSA Fed
0.08
Contra Costa:
LOX Fed
0.06
0.04
0.02
0.00
0
50
100
150
200
250
300
350
400
450
Average Daily Flowrate (mgd)
Figure 6.41 Specific energy consumption for the total ozonation system as a function of the
average daily flowrate at the Contra Costa, SNWA, and Central Lake County WTPs.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Specific Energy Consumption (kWh/lb O3)
30
25
Central Lake:
Ambient Air Fed
20
SNWA:
VPSA Fed
15
10
Contra Costa:
LOX Fed
5
0
0
500
1000
1500
2000
2500
3000
3500
4000
Ozone Production (lb/day)
Figure 6.42 Ozonation system specific energy consumption as a function of ozone
production rate for the Contra Costa, SNWA, and Central Lake County WTPs.
Considerations for EC Optimization of Ozonation Systems
EC optimization of ozone systems generally is associated with operational improvements
aimed at producing ozone at or near the design concentration. For SNWA, EC potentially could
be reduced by operating the AMS plant consistently at the design ozone concentration of
8 percent weight. For the Contra Costa Water District, EC potentially could be reduced by
increasing the average ozone concentration generated at the Bollman plant from 6.5 percent
weight to the design concentration of approximately 9 percent weight. For CLCLJAWA, which
uses ambient air for ozone generation, EC improvements may result from using an ozone
concentration that approximates the design value of 1.5 percent weight. From the analysis
performed in this study, further improvements in energy efficiency may also be realized (pending
further study) if the operating ozone concentration is increased beyond the design operating
ozone concentration of 1.5 percent weight. However, operating beyond the design ozone
concentration would have to carefully consider other costs, such as maintenance issues.
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CHAPTER 7
EC OF UV SYSTEMS FOR DRINKING WATER AND REUSE WATER
TREATMENT
Chapter 7 focuses on EC by utilities that use UV systems for drinking water and reuse
water treatment. This chapter includes an overview of the process and description of major
components that typically require the greatest energy usage. Two case studies (West Basin
Municipal Water District, California and Central Lake County Joint Action Water Agency,
Illinois) are included in this chapter. Each case study includes a system description, analysis of
EC, and identification of potential optimization opportunities. A summary of the EC analysis
based on these two case studies is included at the end of the chapter.
PROCESS DESCRIPTION OVERVIEW
UV light disinfection systems disinfect water by altering the genetic material of target
organisms through exposure to UV radiation. UV disinfection systems are relatively simple in
design and are comprised of a flow-through reactor, mercury arc lamps, and a control box or
ballast. The general process layout for a UV disinfection system for water treatment applications
is shown in Figure 7.1. The reactor is designed to allow for sufficient contact time between the
UV radiation and the feed stream. Contact time will vary according to the feed stream
characteristics, lamp strength and number, and the organisms being targeted. The UV dosage is
generally measured as millijoule per square centimeter (mJ/cm2). UV light is generated by
passing an electrical current through mercury vapor (mercury arc lamp). The mercury arc lamps
UV systems use low to medium pressure mercury lamps to generate the short-wave (λ = 250 to
270 nm) UV radiation. UV-lamps are available in two different sizes: low-pressure and medium
pressure. Low-pressure lamps are commonly used in small systems, while medium pressure
lamps are used in larger systems. Medium pressure lamps operate at higher temperatures and
consume more energy than their low-pressure counterparts. The UV-lamps may be housed in a
protective sleeve, typically quartz, for protection. The ballast provides the starting voltage for
the UV-lamps and maintains a constant current for the system.
UV-lamp
Effluent
Feed Water
Reactor
Control
Box
Figure 7.1 General layout of a UV disinfection system.
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MAJOR EC COMPONENTS
EC in UV-disinfection systems is dictated by the energy required by the mercury arc
lamps. EC increases with increasing voltage applied to the lamps and is determined by the
required UV dosage. The UV lamps require a high voltage of roughly 440 V. The required UV
intensity, and thus the EC by the UV system, is affected by the following parameters:
• Feed water transmittance
• Dosage requirements
• Lamp fouling
• Lamp configuration and placement in the reactor
The feed water transmittance is determined by the water’s turbidity and the presence of
natural organic matter (NOM) and dissolved metals which may adsorb the UV light at the given
wavelength. Turbidity is determined by the presence of colloidal and suspended solids in the
water. Transmittance then is largely controlled by implementing effective pretreatment
strategies (i.e., filtration).
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
West Basin Municipal Water District (California) Water Recycling Facility
System Description
The WBWRF facility has been expanded twice (Phases II and III) to increase production
capacity since it became fully operational in 1992. At the time of this analysis, Phase IV
development was underway to further expand the MF and RO capacities and to add a new
UV/peroxide system to begin NDMA destruction. The Phase III MF and RO systems were
discussed previously in section 5.3.3 of this report. This section focuses on the new
UV/peroxide system.
The Phase IV UV/peroxide advanced oxidation system treats water that is separate from
the Phase III MF and RO systems. Up to 12.5 mgd of permeate from the new Phase IV RO
Train 9 is dosed with up to 3 mg/L hydrogen peroxide and pumped directly to three Phase IV UV
trains for disinfection and N-nitrosodimethylamine (NDMA) destruction prior to aquifer
recharge injection. The Phase IV RO Train 9 feed pumps provide all the pressure required to
pass the water through both the RO array and UV trains before discharging to the Phase IV
decarbonators. The EC of the Phase IV RO Train 9 feed pumps is outside the scope of this
analysis.
There are site provisions for the installation of a fourth UV train. Each train consists of
four Trojan Technologies UV reactors in parallel; each reactor is filled with 72 high-intensity,
low-pressure amalgam UV lamps. Each reactor is designed to continuously maintain a minimum
UV intensity of 50 mJ/cm2 at a wavelength of 254 nm. The system requirements are listed in
Table 7.1.
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Table 7.1
Phase IV UV/peroxide advanced oxidation system design requirements
Design Parameter
Minimum system flow rate
Maximum system flow rate
Maximum flow rate through train
Maximum NDMA influent concentration
Minimum NDMA removal with all trains in service
Minimum NDMA removal with one train in service
Maximum NDMA effluent concentration
Minimum MS2 bacteriophage or poliovirus inactivation
Maximum 7-day mean total coliform
Units
mgd
mgd
mgd
ng/L
log10
log10
ng/L
log10
MPN/100 mL
Required Value
2.3
12.5
4.16
100
1.3
1.0
5
3
2.2
Source: West Basin, 2003
One UV/peroxide train is operating all the time. A second train is started when flow rates
to the UV/peroxide system reaches 4.2 mgd. The third train starts at 8.3 mgd. The water is
divided equally between the trains when multiple trains are operating.
Energy Consumption
The EC of the Phase IV UV/peroxide advanced oxidation system is included in this
section. The analysis is based on manufacturer’s data since the system has not been
commissioned yet at the time of this report.
The UV/peroxide has three types of equipment that use electricity: the low-pressure
lamps in each reactor, three 0.75-hp peroxide feed pumps, and three 104 W heat exchangers for
each train electrical cabinet to cool the lamp ballasts. Of the three equipment types, the lamps
are estimated to account for 74 to 82 percent of the total EC. The peroxide pumps are estimated
to account for 15 to 22 percent, with the remainder to be consumed by the heat exchangers.
Each of the reactors draws 18.5 kW at 100 percent power draw. For a train, which
consists of four reactors in series, the maximum lamp power draw is 74.0 kW. The lamps can be
turned down as low as 60 percent of maximum power, which would mean that the lowest power
draw for each train is 44.4 kW. A 60 percent turndown is the limit before the lamps have
difficulty staying lit. For less than maximum power, all the lamps in the train are uniformly
turned down. Individual reactors in a train are not normally shutdown nor are individual lamps
in a reactor turned off. Figure 7.2 shows the estimated range of electrical loads for the
UV/peroxide system over the range of treatment flowrates. The minimum estimated electrical
load would be for new lamps treating RO permeate with high UV transmittance. The maximum
estimated electrical load would occur when the lamps are near the end of the service life and/or
there is a system upset in the upstream RO system that results in water with lower UV
transmittance. The lamps are rated for 12,000 hours each and the UV light output is projected to
decrease 20 percent for the same energy input over the course of the service life.
The specific EC of the UV/peroxide system is shown in Figure 7.3. In general, at all
flowrates above the design minimum of 2.3 mgd, the specific EC of the UV/peroxide system is
0.3 to 1 kWh/kgal. The difference between the Phase IV UV/peroxide system and the
substantially higher consumption for the Phase III MF/RO is the lack of pumps for the UV
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system to move water. The Phase IV RO permeate has adequate pressure to push water through
the Phase IV UV/peroxide system without additional pumping.
300
1 UV/peroxide
train
operating
Electrical Load (kW)
250
2 UV/peroxide
trains
operating
3 UV/peroxide
trains
operating
200
2.3 mgd
minimum
design
flowrate
150
100
Maximum estimated
electrical load
50
Minimum estimated
electrical load
0
0
1
2
3
4
5
6
7
Flow Rate (mgd)
8
9
10
11
12
Figure 7.2 Estimated range of Phase IV UV/peroxide system electrical load.
Specific Energy Consumption (kWh/kgal)
5.0
1 UV/peroxide
train
operating
4.0
3 UV/peroxide
trains
operating
2 UV/peroxide
trains
operating
3.0
2.3 mgd
minimum
design
flowrate
2.0
Maximum estimated
energy consumption
Minimum estimated
energy consumption
1.0
0.0
0
1
2
3
4
5
6
7
8
9
10
11
12
Flow Rate (mgd)
Figure 7.3 Estimated range of specific energy consumption of Phase IV UV/peroxide
system.
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Potential Energy Conservation Improvements
Because the Phase IV UV/peroxide system has not been fully commissioned at the time
of this report, no design recommendations can be made at this time. The one operating
recommendation is to ensure that the system flowrate is maintained above the 2.3 mgd design
minimum. As noted in Figure 7.3, the specific EC of the system increases at an exponential rate
as flowrates decrease. Below 2.3 mgd, the specific EC increases to above 1.0 kWh/kgal.
Central Lake County Joint Action Water Agency
System Description
Details on the Paul M. Neal WTP were previously provided in Chapter 6 of this report.
Therefore, the system will only be briefly described here, with attention being primarily focused
on the design and operation of the UV disinfection system. The Paul M. Neil WTP is a 50 mgd
facility that is owned and operated by the Central Lake County Joint Action Water Agency, Lake
County, Illinois. Raw water is obtained from Lake Michigan. The plant is composed of four
parallel 12.5 mgd processing trains. A schematic of the plant unit processes is given in
Figure 6.30. The treatment scheme is composed of raw water pumping (off-site), pre-ozonation,
rapid mix (chemical addition), three-stage flocculation, inclined-plate sedimentation, GAC
filtration, UV-disinfection, chlorination, clearwell storage, and high-service pumping.
The UV-disinfection system consists of three medium-pressure in-line UV reactors
(Model #4L30, Trojan Technologies, Ontario, Canada) in parallel, each rated to provide a UV
dose of 40 mJ/cm2 at a peak hydraulic capacity of 25 mgd/reactor. Each reactor contains four
medium pressure UV lamps. During normal operation one or two of the reactors are on-line,
depending on the flow rate, with the third reactor serving as a back-up.
Energy Consumption
The EC analysis for the UV system at the Paul M. Neal WTP consisted of examining the
daily recorded energy and production values for the UV system from Jan. 1, 2006 to Dec. 31,
2006. During this period, the operations staff had set up the UV system to continuously operate
at 60 percent output, which is the lowest turndown available while still keeping the UV lamps lit.
Each reactor has a calculated power draw of 22.6 kW at this operational setting.
The daily flowrate and maximum number of operating reactors for this study period is
shown in Figure 7.4. In general, the UV system was operated based on hydraulic requirements.
For water flowrates of less than 22.5 mgd, one reactor operated. Above this value, which is
90 percent of the maximum hydraulic capacity of the individual reactors, a second reactor was
turned on and the water flowed through each reactor equally. The plant SCADA system
recorded which reactor was operating on a given day. The duration that each reactor operated on
any given day was not provided, though in general, each operating reactor was continuously online for several days in a row.
All three reactors operated on four separate occasions spanning a total of five days during
the 2006 calendar year. Each occasion corresponded to when the reactor quartz sleeve cleaning
mechanisms were activated; the reactor has to be on-line with water moving past the bulb sleeves
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during cleaning events. In this case, the SCADA system records the use of all three reactors,
though the actual duration of all three is on the order of minutes instead of days.
The specific EC of the UV system is shown in Figure 7.5 as function of flowrate. Since
each reactor has a constant power demand, the specific energy use of the UV system at the Paul
M. Neal WTP is a function of flowrate and the number of reactors that are operating at that time.
When a single reactor was operating, the specific EC varied between 0.02 kWh/kgal to
0.04 kWh/ kgal. When two reactors were operating, the specific EC varied between 0.03 kWh/
kgal and 0.06 kWh/kgal. Therefore, as the number of reactors in operation increased, the
specific EC by the UV system also increased. When two reactors were in operation and at
flowrates less than 22.5 mgd, the specific EC was roughly twice that of a single operating
reactor. This result is due to the fact that each reactor is using the same amount of power
(22.6 kWh) while the flowrate is halved between the two reactors.
50
4
Daily Average Q
Average Daily Flowrate (mgd)
3
30
2
20
1
10
0
Jan-2006
Daily Max. Number of UV Units in Use
Number of Reactors in Use
40
0
Apr-2006
Jul-2006
Oct-2006
Jan-2007
Figure 7.4 Average daily flowrate and corresponding number of UV reactors in operation
at the Paul M. Neal WTP over the course of this study period.
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Specific Energy Consumption (kWh/kgal.)
0.10
Three reactors
operating (theoretical)
0.08
Two reactors
operating
0.06
One reactor
operating
0.04
0.02
0.00
0
5
10
15
20
25
30
35
40
45
Average Daily Flowrate (mgd)
Figure 7.5 Specific energy consumption by the UV system at the Paul M. Neal WTP as
function of flowrate.
Above 22.5 mgd two reactors must be used due to the hydraulic limit of individual
reactors is exceeded. However, the specific EC is still higher than that of a single reactor. The
specific EC for two reactors begins matching the range of a single reactor when treated flowrates
exceed 30 mgd. For the available 2006 data, the best EC was 0.03 kWh/kgal at 39 mgd.
Extrapolating the dataset forward (not shown in figure) would indicate that 0.02 kWh/kgal
specific EC could be achieved by operating near 50 mgd, which is the rated capacity of the
treatment plant.
The data for operating all three reactors for a full day was also plotted in Figure 7.5. The
UV system is highly energy inefficient at the flowrates used since the EC has increased again
while the treated water is now divided between three reactors instead of two. These calculated
values are for theoretical comparison as all three reactors would only operate for substantially
less than a full day during the automatic cleanings.
Potential Energy Conservation Improvements
EC by the UV system studied here is determined by the number of lamps that are on and
the flowrate that must be divided between separate UV reactors. For this reason, it is critical that
the system not be over designed such that when divided, the flowrate is not so low in the reactors
as to dramatically increase the specific EC. This may be achieved through accurate flow
forecasting to determine the critical times at which two or three reactors must come on line. Due
to the age (approximately 1 year old) of this system there is little data to support other areas for
improvement in the EC. Furthermore, as the lamps are currently operating at their lowest
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intensity (60 percent) energy efficiency cannot likely be improved through reductions in the
lamp intensity.
CONSIDERATIONS FOR EC OPTIMIZATION OF UV SYSTEMS
Factors Affecting EC of the UV Systems
Based on the analyses presented here, EC of UV systems is directly proportional to the
number of lamps that are in operation. Energy efficiency, measured in terms of the specific EC,
is determined by the number of lamps that are on and the corresponding flowrate through the UV
reactor.
Considerations for EC Optimization of UV Systems
Optimizing the energy efficiency of UV systems is based on operating the UV reactors as
close to their maximum flow capacity as possible when they are in operation. This is best
achieved during the design process during which time it is critical that the system not be over
designed. The critical parameter here is the maximum daily flowrate and its duration.
Minimizing the time at which the reactors must operate at less than maximum capacity should
result in the greatest improvements in specific EC (i.e., energy efficiency).
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CHAPTER 8
EC OF MEMBRANE BIO-REACTORS FOR WASTEWATER
TREATMENT
Chapter 8 focuses on EC by utilities that use MBRs for wastewater treatment. This
chapter includes an overview of the process and description of major components that typically
require the greatest energy usage. Two case studies (City of Pooler, Georgia and Arizona
American Water Company) are included in this chapter. Each case study includes a system
description, analysis of EC, and identification of potential optimization opportunities. A
summary of the EC analysis based on these two case studies is included at the end of the chapter.
PROCESS DESCRIPTION OVERVIEW
MBRs are a membrane process that may be used in conjunction with biological processes
to treat municipal wastewater. MBR systems combine the conventional treatment processes of
clarification, aeration, and filtration steps (activated sludge) into a single treatment step. MBRs
most commonly use hollow fiber UF membranes (pore size 0.04 to 0.4 μm). Typical system
configurations submerge the membranes into the biological reactor, however, a pressurized side
stream configuration may also be used. Submerged systems are preferred as their energy
demand is roughly two orders of magnitude less than that required by pressurized side-stream
designs. For submerged systems, a vacuum is applied to the UF membranes operating in an
outside-in (i.e., wastewater going from the outside of the fiber to the inside cavity) setup.
A typical MBR process layout is shown in Figure 8.1. Influent wastewater is first passed
through a screening device that separates out coarse materials. The wastewater then enters the
biological treatment step, which may be comprised of aerobic, anaerobic, and/or anoxic zones
depending on the treatment configuration. Following biological treatment the water, now
containing a high concentration of bio-solids, enters the membrane basin. The water is then
filtered through the UF membranes and discharged from the treatment system. In the aerobic
zone air/oxygen is supplied to maintain a specified dissolved oxygen concentration. Aeration
also serves to suspend the solids in the mixing basin. Air scouring is used to minimize fouling of
the UF membranes.
Aeration
Air Scour
Prescree
Effluent
Sludge Recycle
Waste
Figure 8.1 General system layout for a membrane biological reactor (MBR) wastewater
treatment system.
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MAJOR EC COMPONENTS
The principle components of an MBR system that exert a sizable energy demand include
the process air blowers, mixers, recirculation pumps, air scour blowers, and process pumps. The
process air blowers and air scour blowers consume the largest fraction of the total MBR energy
requirement. The process pumps are comprised of the vacuum pumps, backflushing pumps, and
the foam pumping system (if required).
The aeration sequence used may dramatically impact the MBR energy usage. For
continuous aeration systems, aeration may make up to 50 percent of the MBRs total energy
demand. Conversely, cyclic aeration may reduce the aeration power requirement by up to
75 percent. Membrane fouling is an issue with MBRs and may increase power consumption by
increasing the membrane hydraulic resistance. Fouling is determined by the feed water
characteristics (MLSS concentration, etc.) and system operation variables (air scouring, aeration
rate).
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
City of Pooler, Georgia Wastewater Treatment Plant
System Description
The Pooler WWTP was commissioned in December 2004 to replace an aging aerated
lagoon that is adjacent to the site. The facility treats flows from the Cities of Pooler and
Bloomingdale and discharges to Hardin Canal, a tributary of the Ogeechee River. The new plant
is based on a submerged ultrafiltration MBR system. It is rated to treat 2.5 mgd maximum daily
flow (MDF) with an instantaneous peak flow of 4.0 mgd, with an ultimate capacity of 6.0 mgd
MDF. During this study period (from Jan 01, 2005 to June 30, 2006) the WWTP was treating
between 0.394 mgd and 2.41 mgd, with an average of 1.08 mgd, from a separated collection
system. Discussions with operators indicate the collection system experiences high storm-related
inflow and infiltration, though no data was provided. Flows exceeding the peak capacity are
diverted into lagoons for emergency storage. The stored wastewater is pumped back to the plant
after peak flows subside.
The plant is staffed 8 hours a day with a crew of three during weekdays, excluding public
holidays. For the remainder of the time, the plant is controlled by the plant SCADA system.
Figure 8.2 is a simplified process flow schematic for the Pooler WWTP. An influent pump
station first conveys wastewater into a one million gallon equalization tank at the front of the
plant. The equalization tank is typically half full during normal operating condition.
Afterwards, the wastewater passes through the course and fine screens (0.02-inch slot size)
before entering a splitter box that directs wastewater into two parallel biological treatment trains.
Each train consists of two sequential anoxic zones (34.5 feet wide x 36 feet long x 21 feet deep
per basin per train) followed by two sequential aerobic zones (34.5 feet wide x 51.5 feet long x
21 feet deep per basin per train). Denitrification, carbonaceous BOD removal and nitrification
take place in these basins. The anoxic basins are mixed continuously by means of mixers to keep
solids in suspension (4 hp mixers in each anoxic zone). The aeration basins include fine bubble
diffusers that provide aeration to the biomass through 3 blowers (100 hp each), the air flow rate
depending on actual loading to the bioreactors and on the bioreactor temperature. There are 341
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9-inch fine bubble diffuser elements per tank. Blowers are equipped with VFDs to adjust the
blower output based on dissolved oxygen (DO) concentrations in the aeration zones.
Following the biological treatment trains, wastewater is combined and gravity fed to a
second splitter box (called a membrane flow distribution channel) that directs it to two MBR
subtrains. Each subtrain consists of two basins (10 feet wide x 37 feet long x 11 feet deep per
tank), each containing three cassettes of submerged UF membranes. Each cassette has 48
modules with 340 ft2 of membrane surface area per module. The membrane tanks have the
ability to fit an additional two cassettes per tank. Five (four duty and one standby) 60 hp
aeration blowers provides coarse air scour to the membrane units. While the air scour provides
some dissolved oxygen (DO) to the wastewater, the main purpose is to prevent solids deposition
and accumulation on the membrane surface area and within each membrane cassette. The air
flow is either cyclic or continuous. Normally, cyclic aeration is used. The valves cycle the air
within a train in 10 second interval. When the system is shutdown, the blowers must be
manually cycled for 30 minutes every 24 hours according to the system Operation and
Maintenance Manual. Filtrate is drawn from each membrane unit through a dedicated 30 hp
vacuum pump, which transfers the filtrate into an inline CIP/backpulse holding tank. Filtrate
overflows from the CIP/backpulse tank and goes into a UV disinfection chamber and through a
turbidimeter prior to creek discharge. Filtrate from the membrane subtrains can also be
discharged to a nearby drain or fed into a secondary membrane unit, (known as ‘Staging Tank’)
for further treatment and re-circulate it to the membrane flow distribution channel for further
treatment through membranes.
The filtrate pump speed is controlled by the programmable logic controller (PLC) which
calculates a plant flow demand based on the raw water feed flow and the aerobic tank levels.
This demand is divided among the trains in operation. The supervisor can elect to manually
enter a production flow rate which overrides the PLC calculated value. The system maintains the
entered production flowrate or PLC calculated production flow rate up to a maximum transmembrane pressure (TMP) or a minimum tank level. As the speed of the pump increases, TMP
increases. To protect the integrity of the membrane, there is a limit beyond which the TMP is
not allowed to increase. At this point, the speed of the pump is controlled to maintain this value
for TMP, rather than to maintain a permeate flow rate.
Mixed liquor from each of the membrane subtrains is recirculated to the beginning of the
biological treatment train in the influent splitter box. A portion of the recirculated mixed liquor
is wasted to the sludge digesters. The recirculation pumps prevent solids accumulation in the
membrane tanks. This recirculation also aids denitrification in the anoxic tanks. These pumps
operate at a constant rate during production, relaxation, backpulse and standby mode.
The ancillary equipment at the Pooler WWTP includes sodium hypochlorite, citric acid
systems, sodium hydroxide (caustic soda) for membrane maintenance and recovery cleanings,
and a sodium bisulfite system for dechlorination. One additional piece of equipment used to
operate the MBR plant are air compressors. Compressed air is used to operate the pneumatic
valves for the membrane system and the air diaphragm chemical metering pumps.
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Influent
Split Box
Raw Influent
Wastewater from EQ
tank via Fine Screens
Membranes
Anoxic
Anoxic
Anoxic
Aeration
Aeration
Aeration
Aeration
Membrane Distribution Channel
Anoxic
Membranes
UV
Membranes
Membranes
Figure 8.2 Process schematic for the Pooler WWTP.
Membrane fouling slowly occurred over the course of the year and the control valve was
adjusted to maintain a specific permeate production rate. Different cleaning methods are
consequently implemented, which influence the operation of the permeate pumps, air scour
blowers and recirculation pumps, and hence affect the energy usage at the plant.
• Relaxation: Here the operator can select to either automatically relax or backpulse
the membranes. The system typically operates in relaxation mode. During
relaxation, pressure is removed from the membranes for a specified duration before
resuming production. During this time the air scour removes solids that have
accumulated on the membranes
• Backpulse: Here the permeate flow is reversed through the membranes. Backpulsing
slightly expands the membrane pores and dislodges any particles that may be trapped
or that have adhered to the membrane surface. It occurs automatically at an operator
selected interval (every 12 minutes) and duration (30 seconds). The relaxation
duration is equal to the backpulse duration.
• Maintenance clean: This is automatically initiated by the operator. The cleaning
solution is either citric acid or sodium hypochlorite. The membrane tank can either
be full or empty during the maintenance clean. The chemicals are backpulsed
through the membranes via the permeate pumps and then the membrane is relaxed.
The membranes are not aerated during the backpulse and relax steps.
• Recovery clean: It is required when the TMP control limit is reached. The TMP
control limit has priority over the flow control. Once the TMP reaches the limiting
value, the control valve will maintain the pressure, even if the flow setpoint has not
been achieved. There are two types of recovery clean regiments: chlorine clean and
acid clean. A chlorine recovery clean removes organic materials, while an acid
recovery clean removes inorganic materials. Both are semi automatic and operator
driven procedures. During a recovery clean, the permeate pumps backpulse and relax
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the cassettes with chemicals. At the end of the backpulse/relax cycles the membrane
tank is refilled. Then the membranes are soaked in the chemicals for 5 hours, after
which the cleaning solution is pumped out by the recirculation pump. During
draining, the membranes are backpulsed with clean permeate water to remove any
residual cleaning chemicals. The spent cleaning solution is manually neutralized with
either sodium hydroxide for acid cleans or sodium bisulfite for chlorine cleans.
The facility has the ability to re-pump the high-quality filtrate from the plant to adjacent
properties as reclaimed water. However, an analysis of the water reuse system is outside the
scope of this project.
At the Pooler WWTP, each membrane sub-train has two aeration headers with cyclic
valves that allow the air flow to be cycled between the two air headers. In this configuration, air
alternates between the two headers within one train, and between two trains. Each cassette has
10 seconds on, 10 seconds off aeration pattern, with the location of the air injection alternating
between the cassettes. The pattern alternates within each membrane cassette so that at any given
moment, only half of the modules are being aerated. This can reduce the energy cost by half
compared to constantly aerating the membranes.
During low flow or average flow condition, the amount of time that a membrane module
operates without air can be extended from 10 seconds to 30 seconds. While maintaining
membrane performance, this can reduce the energy usage by air scour blowers. Membrane
aeration requirements are increased to 10/10 sequential during peak flow periods to reduce
membrane fouling. The aerators within a given membrane train operate on an interval of
10 seconds on and 30 seconds off during average daily flows when the membranes require less
air. The plant control system can monitor membrane performance and automatically determine
the modes of operation.
In this configuration, a single blower sized to aerate one train is used to aerate two trains,
resulting in 50 percent reduction in air required. According to vendor literature, such an
operation could result in substantial energy and cost savings due to reduced usage of large
equipment. This study could not substantiate this claim since the study group contained only one
other similarly configured MBR system (the Arizona-American AWC) and no different MBR
systems.
Water Quality and Treatment Performance.
The Pooler WWTP discharge requirements for the treated effluent are listed in Table 8.1.
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Table 8.1
Effluent standards for the Pooler WWTP when discharging to a creek
Parameter
Units
BOD5
mg/L
Dissolved oxygen
pH
Total suspended
solids
mg/L
s.u.
mg/L
Nitrate-N
mg/L
Fecal coliform
CFU/100 mL
Value(s)
Comment
4.0
6.0
6.0
6.0 – 9.0
10
15
0.8
1.2
1.6
2.4
200
400
Max. monthly average limit
Max. weekly average limit
Instantaneous minimum
Permitted instantaneous range
Max. monthly average limit
Max. weekly average limit
Max. monthly average limit (May to October)
Max. weekly average limit (May to October)
Max. monthly average limit (Nov. to April)
Max. weekly average limit (Nov. to April)
Max. monthly geometric mean average
Max. weekly geometric mean average
The influent BOD5 ranged between 103 to 396 mg/L for the duration of this study, while
the effluent BOD5 concentration typically ranges between 1 to 4 mg/L, with an average of
2 mg/L (Figure 8.3). Influent TSS concentrations were between 130 to 390 mg/L while effluent
TSS concentrations were around 1.0 mg/L (Figure 8.4). All other discharge parameters were
well within the discharge limits for the period studied.
1,000
BOD5 (mg/L)
100
10
1
Influent
Effluent
Figure 8.3 Influent and effluent BOD5 concentrations to the Pooler WWTP.
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ec
-0
5
19
-D
ov
-0
5
9N
ep
-0
5
30
-S
ug
-0
5
21
-A
12
-J
ul
-0
5
-0
5
2Ju
n
pr
-0
5
23
-A
5
ar
-0
5
14
-M
2Fe
b0
24
-D
ec
-0
4
0
1,000
TSS (mg/L)
100
10
1
Influent
Effluent
ec
-0
5
19
-D
ov
-0
5
9N
ep
-0
5
30
-S
ug
-0
5
21
-A
12
-J
ul
-0
5
-0
5
2Ju
n
pr
-0
5
23
-A
ar
-0
5
5
14
-M
2Fe
b0
24
-D
ec
-0
4
0
Figure 8.4 Influent and effluent TSS concentrations to the Pooler WWTP.
Power Supply
The power supply to the plant is from a single supply line from Georgia Southern Energy
(GSE), with backup power supplied by an on-site generator. Plant staff manually records the
electrical data such as voltage, current, and power reading from the different panels in the
electrical room once a day since plant start-up. The plant also tracks EC based on monthly
energy bills. There is no other data available for individual treatment process power
consumption. The influent pump station has a GSE account separate from the rest of the
WWTP. Since this analysis deals only with the treatment processes, the EC for the pump station
has been excluded from the subsequent analysis.
Energy Consumption
At the Pooler WWTP EC is tracked based on the monthly electric bills obtained for
January 2005 to May 2006. The volume of treated effluent produced by the plant per month
since the operation began in January 2005 is shown in Figure 8.5, along with the corresponding
monthly EC plotted on the secondary y-axis. Over the study period the effluent volume ranged
from 28 to 36 MG/month, with generally larger flows being experienced during summer months.
Monthly EC ranged from 181,500 to 246,300 kWh/month. No clear trend could be found
between EC and the volume of water that was treated based on the data shown in Figure 8.6.
Indeed, during the second year of operation (Dec 2006-May 2006), it could be noted that
although the amount of treated wastewater increased, the energy requirements showed a decrease
during corresponding months (Figure 8.5).
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300,000
Energy
Consumption
Effluent Flowrate
250,000
40
200,000
30
150,000
20
100,000
10
50,000
06
M
ay
-
M
ar
-0
6
Ja
n06
05
N
ov
-
Se
p05
Ju
l-0
5
05
M
ay
-
M
ar
-0
5
0
Ja
n05
0
Monthly Energy Consumption (kWh/month)
Average Effluent Flowrate (MG/month)
50
Figure 8.5 Average monthly energy consumption and corresponding effluent flowrates at
the Pooler WWTP.
Energy Consumption (kWh/month)
300,000
250,000
R2 = 0.02
200,000
150,000
Outlier Data
Point
100,000
50,000
0
0
10
20
30
40
Effluent Flowrate (MG/month)
Figure 8.6 Monthly energy consumption as a function of the effluent flowrate at the Pooler
WWTP.
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The specific EC for the entire WWTP is shown in Figure 8.7 for the fifteen months of
operation. A decrease in specific energy is observed in the second year of operation, indicating
the process is being optimized to minimize EC. The plant has implemented energy optimization
strategy through intermittent operation of air scour blower to the membranes to minimize the EC
by the membrane units. According to the plant operators, two of the four trains of membrane
modules implemented such optimization in July 2005, while the remaining two trains were
optimized in March 2006. The average monthly specific ECs during these three periods are
compared to study the effect on the total EC and data are shown in Table 8.2. The total EC
shows a gradual decrease correlating the periods of implementing energy optimization of the air
scour blower, as evident in Table 8.2. It is also worth noting that the air scour blowers contribute
20-35 percent of the total EC in the plant. The details of air blower energy optimization
mechanism and contribution of specific equipment in the plant are further discussed later in this
report.
Specific Energy Consumption (kWh/kgal)
10
8
6
4
2
Ja
n05
Fe
b05
M
ar
-0
5
A
pr
-0
5
M
ay
-0
5
Ju
n05
Ju
l-0
5
A
ug
-0
5
Se
p05
O
ct
-0
5
N
ov
-0
5
D
ec
-0
5
Ja
n06
Fe
b06
M
ar
-0
6
A
pr
-0
6
0
Figure 8.7 Specific energy consumption for the total wastewater treatment system at the
Pooler WWTP.
Table 8.2
Average specific energy consumption for specific operational periods
Period
Duration
Jan 2005- Jun 2005
Jul 2005- Feb 2006
Mar 2006 – May 2006
6 months
8 months
3 months
Average Specific
Energy
(KWh/kgal)
7.01
6.14
5.62
Range of Average Specific
Energy Consumption During
Respective Periods
6.4 to 7.27
5.10 to 7.48
5.5 to 5.9
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The specific EC during these fifteen months of operation is also plotted against treated
wastewater per month and is shown in Figure 8.8. The specific EC decreases from roughly
7 kWh/k gal at a flowrate of 28 MG/month to around 5 kWh/kgal at a flowrate of 38 MG/month.
Overall then, the specific EC decreases with increasing monthly effluent volume. The decrease
would mean that as flows increase, some equipment is operating further along their respective
pump curves with increasing mechanical efficiencies. It also indicates that the membranes are
operating at their design flow. The decrease in specific EC occurs despite the fact that the largest
set of process equipment, the air scour blowers, operates at a constant output regardless of the
flow through the plant.
Specific Energy Consumption (kWh/ kgal)
10
R2 = 0.52
8
6
4
2
0
0
5
10
15
20
25
30
35
40
Effluent Flowrate (MG/month)
Figure 8.8 Specific energy plotted as a function of the average monthly effluent flowrate at
the Pooler WWTP.
Intuitively, the energy usage is thought to depend on influent BOD5 concentrations, since
higher BOD5 levels would exert a higher oxygen demand on the aeration blowers. Figure 8.9
shows specific EC against the average influent BOD5 concentration for the months of operation
since January 2005. The average influent BOD5 concentration ranged from 190 mg/L to
285 mg/L over the study period. The corresponding specific EC for the entire facility showed a
decreasing trend of EC. This may be due to the decrease of monthly specific EC in the second
year of operation, as the biological treatment process may be optimized to minimize aeration
needs. The decrease in specific EC at the higher BOD5 concentrations is attributed to the
reduced specific EC which occurred as a result of the previously noted steps that were taken to
optimize the efficiency of the aeration process. If the data from 2005 and 2006 are considered
separately then there is a negligible change in specific EC with changing influent BOD5
concentrations.
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Specific Energy Consumption (kWh/kgal)
10
8
R2 = 0.16
6
4
2
0
0
50
100
150
200
Monthly Average Influent BOD5 (mg/L)
250
300
Figure 8.9 Monthly specific energy consumption plotted as a function of the average
monthly influent BOD5 concentration to the Pooler WWTP MBR system.
Specific Energy Consumption (kWh/kgal)
10
8
R2 = 0.06
6
4
2
0
0
50
100
150
200
250
Influent TSS (mg/L)
Figure 8.10 Monthly specific energy consumption plotted as a function of the average
monthly influent TSS concentration to the Pooler WWTP MBR system.
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300
Figure 8.10 shows specific EC as a function of the average influent TSS concentration for
the months of operation since January 2005. As TSS increases, the membranes would foul
faster, which in turn requires greater vacuum draw from the permeate pumps for a given volume
of permeate. As the average influent TSS concentration ranged from 125 to 252 mg/L over the
study period, the specific EC shows a marginal increase in specific energy with increasing
influent TSS concentrations. However, the correlation is too poor (R2 < 0.5) to draw any
definitive conclusions with respect to the impact of TSS concentrations on the specific EC by the
MBR.
The EC at the treatment plant is primarily associated with the following major equipment
categories:
1. The aeration blowers used to deliver the fine bubble air in the aeration basins for
biological treatment.
2. The aeration blowers used to provide air scour to the membrane units.
3. The process pumps used to pump out permeate from the membrane units.
4. The recirculation pumps used to recycle return activated sludge (RAS) to the front of
the biological treatment train and waste activated sludge (WAS) sludge digesters.
5. The power required for UV disinfection.
6. The power required for sludge digesters.
7. The ancillary equipment for the wastewater treatment process (such as the chemical
feed pumps, metering facilities and process instrumentation and valves, compressors
and screens).
8. The building functions (HVAC, bridge crane, computers, and lighting).
The direct EC by the membrane bioreactor is associated with the process/permeate pumps
and aeration blowers to provide air scour for the membranes. Figure 8.11 shows the EC at the
plant during this study period from January 2005 to May 2006. EC by specific equipment, such
as air scour blowers, permeate pumps, RAS pumps and supplemental aeration blowers are also
shown in this graph. Equipment specific EC data are estimated based on their operational data
such as amperage, voltage, operating hours etc. that were logged for those months.
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300,000
Only Total Energy Data Available
Energy Usage (kWh/month)
250,000
200,000
150,000
100,000
50,000
0
Jan-05
Mar-05
May-05
Air Scour
Jul-05
Sep-05
Permeate Pumps
Nov-05
RAS Pumps
Jan-06
Mar-06
Aeration Blowers
May-06
Others
Figure 8.11 Energy consumption by membrane bioreactor relative to the total energy
consumption at the treatment plant.
8
Specific Energy Consumption (kWh/kgal)
7
6
5
4
3
2
1
0
Oct-05
Air Scour
Nov-05
Dec-05
Permeate Pumps
Jan-06
RAS Pumps
Feb-06
Mar-06
Aeration Blowers
Apr-06
May-06
Others
Figure 8.12 Specific energy consumption by the different MBR related equipment during
different months of the study-period. The specific energy consumption is shown as a
fraction of the total value for the WWTP.
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Figure 8.12 shows a comparison of specific EC by the various process equipment in the
plant. As shown in Figures 8.11 and 8.12, membrane air scour blowers account for 20 percent to
35 percent of the total EC at the plant. Permeate pumps only account for 1-2 percent of the
entire EC. Therefore, for MBRs, the main EC is by the air scour blowers. Often the membrane
modules are designed such that it minimizes the energy requirement to provide the air scour to
the membrane units. The Pooler WWTP implemented 10/10 sequential aeration and 10/30 ‘ecoaeration’ strategy, as described in earlier sections, to minimize the EC by the membrane units.
Recirculation pumps, which recycle mixed liquor RAS from the membrane tanks to the
beginning of the biological treatment train in the influent splitter box, is shown to account for
23 percent to 42 percent of the total EC at the plant. RAS pumps account for the highest amount
of EC in this plant, followed by membrane air scour blowers. These pumps operate at a constant
rate during production, relaxation, backpulse and standby mode. Among other major equipment,
supplemental aeration blowers account for 7 percent to 13 percent of the total EC, as found from
the data obtained for this study.
Potential Energy Conservation Improvements
For most wastewater treatment plants, aeration has the second-highest EC (the highest
being pumping). Aeration tends to be the highest area of EC at the Pooler WWTP due to the use
of blowers for the aeration tanks for DO addition and air scour blowers for the MBR tanks. The
air scour blowers have especially high consumption since they usually operate on a continuous
basis or in cyclic mode at a fixed capacity. The ZeeWeed system installed at the Pooler WWTP
was programmed with a relatively new aeration control strategy to reduce the energy usage.
Considering each system on an individual basis, the RAS pumps accounted for the largest
fraction (33 percent on average) of the specific EC, followed by the air scour blowers
(27 percent). The permeate pumps and aeration blowers accounted for much smaller fractions at
1 and 9 percent, respectively. If the air scour and permeate pumps are considered to be the only
equipment that consume energy in the MBR system, then the MBR technology only accounts for
about one third of the total EC at the Pooler WWTP. Energy optimization efforts should focus
on the RAS pumps and the air scour system. Less significant benefits will be realized through
optimization of the permeate pumps.
Options for energy optimization may include changing the RAS pump motor to a VFD to
optimize its operation at different flowrates. Because the permeate pumps represent a relatively
small fraction of the total amount of energy consumed by the MBR system it may be beneficial
to reduce the air scour frequency. This would increase the demand on the permeate pumps while
at the same time reducing the energy demand by the air scour system. A field study would be
required to determine the feasibility of this potential operational change. If the membrane
fouling rate could be reduced, perhaps through the use of better fouling resistant membranes,
then the air scour frequency could be further reduced. Strategies to minimize operation of
membrane air scour blowers have been implemented to reduce EC; however, the degree of
effectiveness could not be substantiated in this study. Finally, operating only the number of
membrane tanks that are needed based on the influent flowrate may result in savings from the
permeate pumps and air scour system. This would require some sort of automated system that
can switch the membranes tanks on and off as a result of measured flows. This option would
need to consider the wear and tear of on and off operation on the associated equipment.
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Arizona American Water Company Anthem Water Campus
System Description
The AWC Wastewater Treatment Plant (WWTP) is a tertiary wastewater treatment plant
that currently uses an advanced activated sludge system. The activated sludge system at the
WWTP incorporates a membrane bioreactor (MBR) to remove organic and suspended material
from the waste stream to meet ADEQ (Arizona Department of Environmental Quality)
requirements for unrestricted reuse. The wastewater plant has an average daily flowrate of
3.0 mgd and a peak hour flowrate of 8 mgd. Half of the influent is municipal wastewater, while
the other half is the concentrate waste stream from the membrane processes at the drinking water
portion of the AWC.
A process layout schematic for the AWC WWTP is shown in Figure 8.13. Raw
wastewater flows from the collection system to the influent pump station, where it is pumped
into the plant. There are four influent pumps capable of pumping up to 8.0 mgd into the plant.
The flow from the influent pumps is redistributed to two screening channels. A mechanicallycleaned auger screen removes debris greater than 2 mm in diameter from the process stream.
The flow is gravity fed into the vortex grit-removal tank, which primarily removes inorganic
materials larger than roughly 0.2 mm.
Effluent from the grit-removal tank flows to two 250,000 gal equalization tanks before
being treated in the MBR. The bioreactor is divided into anoxic and aerobic zones as shown in
Figure 8.14. The wastewater first enters the anoxic zone where it is mixed with recycled mixed
liquor (mixed liquor suspended solids or MLSS) retuned from the downstream MBR. The
MLSS then enters the aerobic zone where it is aerated by submerged air diffusers. Organics in
the wastewater are biologically degraded to reduce the BOD5 and dissolved organics content of
the wastewater.
Table 8.3
AWC WWTP membrane bioreactor characteristics
1
Train
Membrane Type1
1
2
A
C
Membrane Surface Area
(ft2)
500
250
– designation by the membrane vendor
Effluent from the aerobic zone then enters the membrane basin, which consists of two
submerged UF membrane trains (see Table 8.3). The UF membranes have a mean pore size of
0.035 μm through which water is drawn and the solids are removed and remain in the membrane
tank. Water is transported through the membranes by applying a vacuum, essentially sucking the
water through the membrane. The thickened slurry is pumped back to the bioreactor by the
75 hp mixed liquor return (MLR) pumps. A portion of the MLR flow is pumped by a 3 hp WAS
pump to the sludge storage tank. The treated water has a low BOD5 and low suspended solids
content. The membranes allow the activated sludge process to operate at higher loading rates as
it is no longer constrained by the sludge settleability and associated clarification requirements.
167
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168
©2008 AwwaRF. ALL RIGHTS RESERVED
Figure 8.13 Process schematic for the AWC wastewater treatment plant.
AERATION DIFFUSERS
OXIC
ANOXIC
Figure 8.14 Schematic drawings of the bioreactors used at the AWC WWTP.
Normal MBR operation will result in an accumulation of solid organic and inorganic
materials on the feed side of the hollow fiber UF membranes, a process commonly known as
membrane fouling. Fouling results in a reduction of membrane permeability (the membrane
pores becomes clogged) and thus reduced specific permeate flux (flux/trans-membrane pressure).
To compensate for this decrease in permeability, the TMP must be increased to maintain a
specified flux, before the system is eventually shut-down for cleaning. Air scouring is a process
in which air is vigorously bubbled over the membrane surface, and is typically used to minimize
169
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membrane fouling in MBR systems. The air scour system has an operating discharge pressure of
5 to 7 psig and has a cyclic delivery schedule (i.e., 10 seconds on then 10 seconds off). The air
scour blowers are driven by 250 hp motors and a blower speed of 3550 rpm. The instantaneous
air flowrate per membrane module is 30 scfm. The net air scour flowrates for membrane Trains
1 and 2, and Trains 3 and 4 are 1800 and 2625 scfm, respectively.
Air scouring cannot prevent fouling from occurring and therefore cannot wholly replace
more intensive cleaning processes. A CIP system removes foulants from the membrane surface
by utilizing a number of different cleaning techniques. These different techniques are described
in detail in the following sections:
• Relaxation: Some solids accumulate on, but are not adsorbed to, the membrane
surfaces as a result of permeate drag or fluid flow through the membrane pores.
These materials may be removed by stopping the permeate pumps for a short time,
while maintaining the air scour. This allows the solids to be dislodged or simply
allowed to diffuse back into the bulk water. This cleaning process is termed
relaxation, as the permeate pressure, and hence attachment mechanism, is relaxed or
removed.
• Backpulsing/Backflushing: Backpulsing or backflushing is generally operated on a
set time interval (operator adjustable) where the permeate flow is reversed for a short
period of time. This process removes materials that have become lodged in the
membrane pores and cannot be removed through air scouring alone. A backpulse
interval is 30 seconds of backpulse every 15 minutes of operation. Backpulsing is
conducted with the air scour in operation, to assist in the agitation and removal of
solids from the membrane surface. Backpulsing is done by altering the path through
the permeate pumps using pneumatic valve actuators to pull from a Backpulse CIP
Tank (permeate storage tank).
• Maintenance Clean: Maintenance cleaning is performed daily on each membrane
train and uses a dilute solution of sodium hypochlorite or citric acid. The system is
backflushed for approximately 15 minutes with the cleaning solution.
• Chemical Clean: Once the membranes become so fouled as to reach an alarm point
or point to which only a small portion of the original membrane flux is recovered
following the aforementioned cleaning methods, a chemical clean is performed.
Influent water is first diverted to the other membrane basins, while the unit to be
cleaned is stopped, drained, flushed and filled with clean permeate water. Cleaning
chemicals are then added to the membrane basin and recirculated. The membranes
soak in this solution for 10 to 12 hours, before the cleaning solution is neutralized and
drained. The unit is then filled with mixed liquor, and a normal maintenance clean is
performed prior to normal operation.
The AWC WWTP discharge requirements are summarized in Table 8.4. For each
parameter the 7-day median, 30-day average, and single sample maximum values are listed.
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Table 8.4
Effluent standards for the Anthem AWC WWTP when discharging to a stream
Parameter
BOD5, mg/L
CBOD5, mg/L
TSS, mg/L
Turbidity, NTU
Fecal Coliform Organisms,
CFU/100 mL
7-day
Median
45
40
45
--
30-day
Average
< 30
< 25
< 30
2
Single-sample
Maximum
Non Detect
--
23
5
Discharge Limit
Sampling
Frequency
1.5
Daily
1
Quarterly
10
Quarterly
Nitrate + Nitrite, mg/L as N
10
Monthly
Total Kjeldahl Nitrogen, mg/L
as N
10
Monthly
Total Nitrogen, mg/L as N
10
Monthly (5-month
geometric mean)
4
Quarterly
6-9
Non-Detect
Non-Detect
Non-Detect
Daily
Monthly
Semi-Annually
Semi-Annually
Parameter
Average Monthly Flow, mgd
Nitrite, mg/L as N
(as measured in groundwater)
Nitrate, mg/L as N
(as measured in groundwater)
Fluoride, mg/L
(as measured in groundwater)
pH
Enteric Viruses
Ascaris lumbricoides
Giardia lamblia
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1,000
Influent
Effluent
BOD5 (mg/L)
100
10
6
-0
6
A
ug
n0
Ju
ar
-0
6
M
Ja
n06
-0
5
ct
O
l-0
5
Ju
5
M
ay
-0
Fe
b05
4
N
ov
-0
p04
Se
Ju
n0
4
4
A
pr
-0
Ja
n04
1
Figure 8.15 Influent and effluent BOD5 concentrations to the MBR system at the AWC
WWTP.
Figure 8.15 shows the influent and effluent BOD5 for the AWC WWTP over the two and
a half year study period. The influent BOD5 ranged from 44 to 700 mg/L over the duration of
this study. Conversely, the effluent BOD5 concentration ranged from 1 to 323 mg/L, with a
95-percentile value of 42 mg/L over this time period. Thus, for more than 95 percent of the time
the plant effluent BOD5 was below the 7-day median discharge limit of 45 mg/L. Figure 8.16
shows the influent and effluent TSS concentration for the same study period. The influent TSS
concentrations are observed to range from 22 mg/L to 832 mg/L. The effluent TSS concentration
ranged between 1 to 20 mg/L with a 95-percentile value of 8 mg/L, as compared to the 7-day
median limit of 45 mg/L.
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1,000
Influent
Effluent
TSS (mg/L)
100
10
A
ug
-0
6
Ju
n06
-0
6
M
ar
-0
6
Ja
n
ct
-0
5
O
5
Ju
l-0
Fe
b05
M
ay
-0
5
04
N
ov
-
p04
Se
Ju
n04
A
pr
-0
4
Ja
n
-0
4
1
Figure 8.16 Influent and effluent TSS concentrations to the MBR system at the AWC
WWTP.
Power Supply
Electricity is provided to the AWC WWTP from the Arizona Public Service system via
an on-site substation. The substation feed is split between four different SES. SES 1 is
dedicated entirely to the drinking water plant. SES 2 is primarily dedicated to the drinking water
plant, but also serves the irrigation pumps, wastewater headworks, and drinking water reject
water pump. SES 3 and SES 4 are dedicated solely to the wastewater treatment plant. A list of
the load centers SES-2, SES-3, SES-4 with the power source for each equipment component is
provided in Appendix A. The main power loads in the plant and their respective power sources
are detailed in Table 8.5.
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Table 8.5
Power loads and associated supplies for the AWC WWTP
MCC/Power Panel
MCC-2-1
Loads Served
Location
Blower Building
MF Process Equipment
Building
MCC-2-4
WAS Pump, Permeate Pump, Air Scour
Blower
Air Compressor
MCC-4
Aeration Blowers, MF Filtrate Pump
Panel G
Generator Appurtenances
Panel SHF
Belt Filter Press, Washwater Pumps, BFP
Feed Pumps
Solids Handling Facility
PP3
Influent Pumps
Influent Pump Station
MCC-2-3
PP4
PP6
Screening Equipment, Conveyors, Odor
Control Scrubbers
Equalization Basin Pump, Anoxic Mixer,
MLR Pumps
MF Process Equipment
Building
Generator
Headworks Building
PP7
Equalization Pumps, Anoxic Mixers at
Bioreactors, Mixed Liquor Return Pumps,
Drain Pump
Bioreactor #2
PP8
UV Disinfection Units
Headworks Building
Energy Consumption
EC at the AWC WWTP is primarily associated with the following equipment categories:
1. Influent feed pumps transport the water from the intake to the beginning of the
treatment works.
2. Aeration blowers used to aerate the biological reactors, facilitating bacteria growth
and solids mixing within the biological reactor.
3. Permeate pumps provide the vacuum to draw water through the membranes to filter
out suspended solids from the effluent.
4. Air scour blowers bubble air across the membranes to minimize membrane fouling
and dislodge accumulated solids.
5. MLR pumps continuously withdraw mixed liquor from the membrane basins and
return it to the anoxic and aerobic zones in the bioreactor.
6. Reclaimed water pumps transport reuse water (a portion of the treated effluent) from
the AWC WWTP to the Anthem community.
7. Ancillary equipment for the wastewater treatment processes includes chemical feed
pumps, metering facilities and process instrumentation and valves, air compressors
and screening equipment.
8. The building functions (heating/ventilation/air conditioning [HVAC], bridge crane,
computers and lighting).
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EC by the membrane bioreactor system is attributed to the permeate pumps, MLR pumps,
and air scour blowers. Figure 8.17 shows the total EC at the AWC WWTP from January 2004 to
July 2006. The total EC is subdivided according to the energy consumed by specific equipment,
such as the air scour blowers, permeate pumps, MLR pumps and supplemental aeration blowers.
Process support equipment such as mixers, headworks equipment, grit pumps, WAS pumps, air
compressors, and CIP pumps are included in the category labeled as ‘Other’ in Figure 8.1. The
EC data reported in Figure 8.17 were obtained from daily records for the SES load centers.
Equipment specific EC data was estimated using a power factor. The power factor is calculated
as the power required by each piece of equipment over the total power contributed to each SES
load center.
From the data presented in Figure 8.17 it appears that the total EC increased from January
2004 to July 2006, going from approximately 125,000 kWh to around 160,000 kWh over this
time period. As noted previously in this report, the total volume of wastewater being treated at
the WWTP steadily increased over this time period. Therefore, the increase in the total EC is
attributed to the increase in the volume of wastewater being treated at the plant. The largest total
energy consumer are the air scour blowers, followed by the reclaimed water pumps. EC was
most variable for the aeration system. There were some EC variability for the other systems but
the overall impact is limited because either the variability was small for a large piece for
equipment or the variability was large but the equipment used relatively little energy.
Energy Consumption (kWh/month)
175,000
150,000
125,000
100,000
75,000
50,000
25,000
MLR Pumps
Permeate Pumps
Air Scour
Influent Pumps
Reclaimed Water
Other
Figure 8.17 Monthly energy consumption at the AWC WWTP.
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Ju
l-0
6
-0
6
A
pr
06
Ja
n-
ct
-0
5
O
Ju
l-0
5
-0
5
A
pr
05
Ja
n-
ct
-0
4
O
Ju
l-0
4
-0
4
A
pr
Ja
n-
04
0
Aeration Air Blowers
Specific Energy Consumption (kWh/kgal)
5
4
3
2
1
MLR Pumps
Influent Pump Station
Permeate Pumps
Reclaimed Water
Air Scour
Other
Ju
l-0
6
-0
6
A
pr
6
Ja
n0
5
ct
-0
O
Ju
l -0
5
5
A
pr
-0
5
Ja
n0
4
O
ct
-0
Ju
l-0
4
-0
4
A
pr
Ja
n0
4
0
Aeration Air Blowers
Figure 8.18 Monthly specific energy consumption at the AWC WWTP.
The specific EC, broken down according to equipment type, over the study period is
shown in Figure 8.18. Conversely to the data presented in Figure 8.17, the trend evidenced in
Figure 8.18 shows a general decrease in specific EC over the study period. These results suggest
that while the volume of wastewater being treated by the plant increased the associated processes
operated more efficiently. This in turn, resulted in a reduction in the energy required to produce
a unit volume of treated water. These findings support the notion that pumps operate more
efficiently as they approach their full capacity.
From Figure 8.18, the air scour blowers account for 30 to 47 percent of the total specific
EC, while the permeate pumps account for only 3 to 4 percent of the total specific EC. The
MLR pumps account for 7 to 9 percent of the total specific EC. The reclaimed water pumps that
discharge non-potable reuse water from the treatment plant out to the Anthem community
account for 23 to 42 percent of the total specific EC. As with the total EC data, the air scour
blowers used the greatest amount of energy for producing a unit volume of treated water and
exhibited the greatest variability. Variability in the specific EC for the remaining equipment was
similar.
In the following discussion the monthly EC and the specific EC data are reported for the
total treatment system. Here, the treatment system refers to the following equipment: influent
pump station, MLR pumps, membrane permeate pumps, air scour pumps/blowers, aeration
pumps/blowers, and the reclaimed water pumps. Power consumption by smaller support systems
such as mechanical mixers, headworks equipment, grit pumps, WAS pumps, air compressors,
and the CIP pumps are also accounted for here.
The volume of treated effluent per month and the monthly average EC at the AWC
WWTP are reported in Figure 8.19. These two variables are also plotted as a function of one
another in Figure 8.20. From Figures 8.19 and 8.20 it appears that EC is generally correlated
176
©2008 AwwaRF. ALL RIGHTS RESERVED
with the volume of wastewater treated per month. In other words, as the volume of wastewater
being treated increases so does EC. However, there are instances (see August 2004) where there
is a substantial spike in EC which does not correspond to spikes in the effluent volume at the
WWTP. This anomaly hints at the probable importance of non-process related equipment in
determining the WWTP power consumption. Additionally, the slope characterizing the rise in
effluent volume is higher compared to that for the corresponding rise in EC. This suggests that
plant is operating at a higher efficiency as the volume of wastewater being treated increases.
180,000
60
Energy Consumption
Effluent Volume
Effluent Volume (MG/month)
140,000
120,000
40
100,000
30
80,000
60,000
20
40,000
10
Energy Consumption (kWh/month)
160,000
50
20,000
0
Ja
n0
M 4
ar
-0
M 4
ay
-0
4
Ju
l-0
4
Se
p0
N 4
ov
-0
4
Ja
n0
M 5
ar
-0
M 5
ay
-0
5
Ju
l-0
5
Se
p0
N 5
ov
-0
5
Ja
n0
M 6
ar
-0
M 6
ay
-0
6
Ju
l-0
6
0
Figure 8.19 Monthly effluent flowrate and total treatment system energy consumption for
the AWC WWTP.
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200,000
Energy Consumption (kWh/month)
180,000
160,000
140,000
R2 = 0.43
120,000
100,000
80,000
60,000
40,000
20,000
0
0
10
20
30
40
50
60
Average Effluent Volume (MG/month)
Figure 8.20 Energy consumption by the treatment system as a function of the volume of
treated effluent at the AWC WWTP.
Specific EC is plotted as a function of the average monthly flowrate to the plant in
Figure 8.21. The R2 correlation in Figure 8.21 is only 0.59 because the largest set of process
equipment operates at a constant output regardless of the flow through the plant. In other words,
as the total volume of treated wastewater increased the specific EC decreased. This trend
indicates that as flow rate increases, some components are operating further along their
respective pump curves with increasing mechanical efficiencies.
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Specific Energy Consumption (kWh/kgal)
6.0
5.0
R2 = 0.59
4.0
3.0
2.0
1.0
0.0
0
10
20
30
40
50
60
Effluent Volume (MG/month)
Figure 8.21 Specific energy consumption for the treatment system as a function of the total
volume of wastewater treated per month.
A summary analysis of the relationship between the specific energy consumed by the
principal equipment systems and the volume of wastewater treated per month is given in
Table 8.6. For each system the specific energy decreased (as indicated by a negative slope) with
increasing volumetric flowrate. One exception to this trend was the air scour system, which had
a slightly positive slope. However, the magnitude of the slope in this case, and the lack of a
good correlation (R2 < 0.5) suggests that the specific energy consumed by the air scour system is
independent of the volumetric flowrate. The greatest increase in efficiency (i.e., decrease in
specific EC) was observed for the reuse water pumps, suggesting that they were operating the
farthest below their optimal capacity. The strongest correlation between specific EC and
volumetric flowrate was for the influent and reuse water pumps (R2 = 0.66). For all other
systems the correlation was weak to non-existent (e.g., as that measured for the air scour
system). The lack of a correlation for the air scour system is likely due to the fact that operation
of this system is not dictated by the system flowrate as is the case for the influent and reuse water
pumps. Therefore, operating these two pumping systems at higher flowrates (the influent and
reuse water pumps) should result in increased system energy efficiency.
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Table 8.6
Summary of the relationship between the specific energy required for various process
equipment and the total system monthly effluent volume
Process
Influent Pump(s)
Permeate Pump(s)
Aeration
Air Scour
MLR Pump(s)
Reuse Pump(s)
Slope*
(kWh/kgal)/(MG/month)
-0.005
-0.002
-0.006
0.001
-0.001
-0.040
R2
0.66
0.33
0.31
0.001
0.03
0.66
*A negative slope indicates that the specific energy is decreasing with increasing effluent volume. The R2 value is an indicator of
the linearity of the correlation between the two variables (R2 = 1.0 is indicative of a perfectly linear relationship
Impact of BOD5 – Figure 8.22 shows the specific EC by the treatment system as a
function of the average influent BOD5 concentration for the months of operation following
January 2004. Additionally, the average monthly power consumption by the aeration blowers is
reported on the secondary y-axis. The average influent BOD5 concentration ranged from 186
mg/L to 484 mg/L over the 31-month study period. Intuitively, the EC by the aeration system
specifically should be a function of the influent BOD5 concentration, since higher BOD5
concentrations should require greater aeration rates by the blowers. However, the data presented
for the AWC WWTP show that there is no such correlation. The lack of correlation may the
result of the time scale analyzed used, i.e., monthly BOD5 averages and energy summations are
hiding correlations on a daily basis. No correlation could be found between BOD5 concentration
and the energy consumed by other process equipment (air scour, permeate pumps, and MLR
pump). This suggests that over the BOD5 concentration range observed, it does not significantly
affect the overall energy efficiency of the WWTP.
Impact of Total Suspended Solids – Generally, as TSS concentration increases,
membranes are fouled at a faster rate, which in turn requires greater vacuum filtration for a given
volume of permeate. However, such a relationship would not be appropriate for MBR systems
since solids concentrations are deliberately maintained at a high concentration using a controlled
MLR flowrate. As a result, TSS variability in the influent would have little to no impact with
specific EC. Figure 8.23 confirms that the specific EC for the treatment system has no
correlation with the average monthly influent TSS concentration.
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8,000
6
R2 = 0.15
6,000
4
R2 = 0.11
3
4,000
2
2,000
1
Aerator Energy Consumption (kWh/month)
Specific Energy Consumption (kWh/kgal)
5
Specific Energy
Aerator Energy
0
0
50
100
150
200
250
300
350
400
450
500
0
550
Average Influent BOD5 (mg/L)
Figure 8.22 Specific energy consumption plotted as a function of the average monthly raw
water influent BOD5 concentration.
Specific Energy Consumption (kWh/kgal)
6
5
4
R2 = 0.02
3
2
1
0
0
50
100
150
200
250
300
350
400
450
Influent TSS (mg/L)
Figure 8.23 Specific energy consumption by the treatment system as a function of the
monthly average influent TSS concentration.
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Potential Energy Conservation Improvements
There are several changes that can be implemented that may result in reduced EC at the
AWC WWTP. The air scour blowers are the most energy intensive equipment at the Anthem
WWTP with an average specific energy requirement of 1.46 kWh/kgal. The reclaimed water
pumps are the second most energy intensive, with an average specific energy requirement of
1.22 kWh/kgal. Combining the aeration systems (aeration and air scour) into one single system
may result in increased energy efficiency and reduce costs associated with redundant equipment
(air compressors, etc). However, this will also increases costs associated with drying the air
stream (dessicator regeneration). The strongest correlation between specific EC and influent
volumetric flowrate was for the water reuse pump and the influent pump station (R2 = 0.66). The
efficiency of the water reuse pumps increased more substantially with increasing flowrate than
for any other system. Operating these two pump systems at or near their respective capacities
will result in the greatest improvement in the energy efficiency of the overall system.
The membrane permeate pumps require the least amount of energy (3 to 4 percent of the
total) and have a specific energy requirement of 0.14 kWh/kgal, which is just below that for the
influent pump station (0.15 kWh/kgal). Considering the air scour and permeate pumps then the
MBR system accounts for about one half of the total EC at the AWC WWTP. The greatest
portion (> 90 percent) of the MBR EC was dedicated to cleaning purposes only (i.e., air scour).
Reducing scouring rate and/or frequency would therefore reduce the energy requirements of the
MBR system. To optimize system efficiency it would be beneficial to determine the optimal
balance between the permeate draw (related to membrane fouling and thus the air scour) and the
scouring rate/frequency.
CONSIDERATIONS FOR EC OPTIMIZATION OF MBR SYSTEMS
Factors Affecting EC of MBR Systems
On average, air scour blowers account for roughly 40 percent of the total specific EC at
MBR treatment plants. The permeate pumps and aeration blowers account for substantially less
EC, at about 3 and 5 percent, respectively of the total specific EC. Operation and design of the
air scour system is most likely to affect the overall EC by the MBR system outside of operating
associated pumping systems at their most efficient point on their respective pump curves.
Overall, specific EC by the total MBR plant decreased with increasing water production rate in a
somewhat linear fashion (R2 = 0.57) (Figure 8.24). This improvement in specific EC with
increasing effluent flowrate is attributed to more efficient operation of pumping systems, such as
raw water pumps and reclaimed water pumps (at Anthem). The specific energy consumed by the
permeate pumps does not change substantially with increasing production rates.
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Specific Energy Consumption (kWh/kgal)
8
7
R2 = 0.57
6
5
4
3
2
1
0
0
10
20
30
40
50
60
Effluent Flowrate (MG/Month)
Figure 8.24 Specific energy consumption for the total MBR systems at the Anthem and
Pooler WWTPs as a function of the effluent flowrate. The data is fit using a linear
function.
Specific EC by the permeate pumps was found to be dependent on membrane pore size
(Figure 8.25). For example, specific EC by the permeate pumps was approximately one order of
magnitude higher at the AWC WWTP compared to that measured for the Pooler plant, which
used membranes having a smaller mean pore size (0.035 μm compared to 0.1 μm). The
differences in specific EC cannot be attributed to more efficient pump operation with increased
flowrates as the two parameters were found to be independent of each other. While membrane
selection, and the pore size thereof, is based on a number of design requirements consideration of
its impact on the EC and efficiency of the MBR system is obvious. However, EC by the
permeate pumps accounts for a small fraction (~3 percent) of the total energy required by the
MBR system. Thus, the costs and benefits of membrane replacement must be carefully weighed.
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Permeate Pump Specific Energy Consumption (kWh/kgal)
0.20
Membrane Pore Size
0.035 μm
0.15
0.10
Membrane Pore Size
0.1 μm
0.05
0.00
Avg Anthem
Avg Pooler
Figure 8.25 Average specific energy consumption by the permeate pumps at the Anthem
and Pooler WWTPs. The error bars represent the standard deviation of the reported
averages. The mean pore size of the UF membranes used at the respective facilities is
reported in the plots for reference.
Considering data from the two WWTPs studied here (Figure 8.26a and b), the MBR
specific EC was relatively independent of the raw water quality (TSS and BOD5) owing to the
relative independence of the air scour and aeration EC from these two parameters. In other
words, the air scour did not consume more energy despite increases in fouling conditions (i.e.,
higher TSS concentrations). The independence of the air scour system from the influent TSS
concentration is attributed to the fact that the air scour is set by the TSS concentration in the
reactor itself, which remains relatively stable during MBR operation. Similarly, EC by the
aeration system did not increase despite increased influent BOD5 levels. As with TSS, this is
attributed to the fact that the aeration requirements are rather stable as the BOD5 within the
reactor changes very little during operation. While these relationships are not suggested to be
without limit it may be possible at either of these facilities to optimize either of the air scour
and/or aeration system while maintaining current performance standards.
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Specific Energy Consumption (kWh/kgal)
8
7
6
5
4
3
2
1
0
0
50
100
150
200
250
300
350
400
450
Influent TSS (mg/L)
Specific Energy Consumption (kWh/kgal)
8
7
6
5
4
3
2
1
0
0
50
100
150
200
250
300
350
400
450
500
550
Influent BOD5 (mg/L)
Figure 8.26 Specific energy consumption for the MBR systems at the Anthem and Pooler
WWTPs as a function of the influent a) TSS concentration and b) the BOD5 levels.
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Considerations for EC Optimization of MBR Systems
The energy efficiency of MBR systems may be optimized primarily through efforts
focusing on the air scour system and secondarily on the feed pressure. The air scour system is
the most energy intensive part of the MBR. Therefore, optimization of its application should
result in the most dramatic energy savings. Efforts should focus on minimizing the frequency of
the air scour and also possibly combing certain operating systems with the aeration units.
Minimizing air scour frequency may be realized through the application of more fouling resistant
membranes, allowing the MBR to work at slightly higher operating pressures (as permeate
pumps consume less energy), implement cyclic air scour, and allowing single air scour blowers
to treat multiple membrane trains. Utilizing membranes with larger pore sizes, and thus lower
feed pressure requirements, should result in lower specific energy requirements by the vacuum
pump. The larger pore size will allow the membrane to operate at lower feed pressures while
obtaining higher permeate fluxes and thus the lower specific energy requirements.
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CHAPTER 9
ELECTRODIALYSIS REVERSAL
Chapter 9 focuses on the EC of an EDR treatment system used for producing drinking
water treatment. This chapter includes an overview of the process and description of major
components that typically require the greatest energy usage. The Sarasota County (Florida)
T. Marbury Carlton, Jr. WTP is analyzed as the case study for analyzing the EC of this ATT.
This case study includes a description of the EDR system, analysis of EC, and identification of
potential optimization opportunities. A summary of the EC analysis based on this case study is
included at the end of the chapter.
PROCESS DESCRIPTION OVERVIEW
EDR is an alternative ATT to RO for treating high TDS source waters (up to 5,000
mg/L). The fundamental difference between the ATTs, is that RO uses high feed water pressures
as the force to desalinate water while EDR uses electricity. The fundamental unit of an EDR
system is the membrane stack, which is analogous to an RO membrane element. The membrane
stack is a vertical multi-compartment tank filled with alternating plates of cationic and anionic
membranes. Water flows between the membrane plates. The electrodes located at each end of
the membrane stack supply a DC voltage across each electrical stage of the stack. When
electrified, cations (i.e. sodium and calcium) in the water move towards the cathode and anions
(i.e. chloride, sulfate, nitrate) move towards the anode. The cationic membranes allow the
positively charged ions to pass through to the anode and the concentrate stream and reject the
negatively charged ions; the opposite scenario holds true for the anionic membranes (Figure 9.1).
C = Cation Permeable Membrane
A = Anion Permeable Membrane
Feed Water In
A
C
To Negative Pole
of Electrical
Supply
A
C
A
C
Na+
Na+
Na+
Cl-
Cl-
Cl-
To Positive
Pole of Electrical
Supply
Anode
Cathode
Na+
Na+
Cl-
Cl-
Concentrated Brine Water
Fresh Product Water
Figure 9.1 General layout of an EDR membrane stack.
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With each plate, a fraction of all the ions are removed from the feed water, creating a
demineralized product water and a concentrated wastewater stream. Approximately 50 percent
of the feed TDS is removed in a stack. EDR systems stage several stacks in series, in order to
achieve higher TDS removals. Generally, a single feed pump provides all the pressure to push
the water through a single series of stacks. Concentrate is removed from each stack through an
adjustable waste valve, similar to the reject flow control valve on RO systems.
As with RO systems, scale formation is controlled on the membranes with the addition of
antiscalant to the feed water. Additionally, for EDR systems antiscalant is commonly added to
the concentrate stream as it must be recycled through the membrane stacks. The DC voltage
polarity is reversed two to four times per hour to further minimize mineral scaling on the
membranes. The other similarity to RO systems is that the EDR permeate is sent through a
degasifier as a final treatment step. Unlike RO degasifiers, which strip dissolved carbon dioxide
from permeate, an EDR degasifier is used to remove the gasses formed by the water contacting
the electrified membranes, such as oxygen and hydrogen (from water disassociation), and
chlorine (formed by oxidizing chloride anions).
MAJOR EC COMPONENTS
The primary power demand in EDR systems are the rectifiers used to electrify the
electrodes within the membrane stacks and the feed pumps required to circulate the feed water,
concentrate stream, and product water through the membrane stacks. The amount of salt
removed by an EDR system corresponds to the extent of polarization in the stacks. As a result,
the EC by the EDR system is directly proportional to the desired TDS reduction sought by the
system.
Secondary power demands are chemical pumps used to adjust water pH prior to or after
the EDR system, antiscalants chemical feed pumps used to control membrane fouling, and the
degasifier used to remove formed catalytic gasses from the permeate.
DESCRIPTIONS AND FINDINGS FROM CASE STUDIES
Sarasota County, Florida T. Marbury Carlton, Jr. WTP
System Description
The Carlton WTP was constructed in 1994 to treat brackish groundwater from an aquifer
400 to 700 feet below the ground. The EDR system is used to desalinate the water for drinking
water purposes. The plant has a rated capacity of 12 mgd, making it the world’s largest EDR
facility, with a peak capacity of 14 mgd.
A process schematic of the Carlton WTP is provided in Figure 9.2. The plant draws
groundwater from 16 production wells. A degasifier is used to remove dissolved hydrogen
sulfide and carbon dioxide from the groundwater as it enters the plant. Afterwards, the water
goes to a sedimentation basin for sand and grit removal prior to the dual media pressure filters.
Further filtration is carried out using 10-μm cartridge prefilters prior to the EDR system.
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Wellfield
HCl
5 MG
Storage Tank
Degasifier
Distribution
System
NaOH
Chlorine
Contact
Wash Water
Tank
HCl
Settling
Basin
Chlorine
EDR
Stacks
Deep
Well
Storage
Tank
AntiScalant
High Service
Pumps
Prefilter
Dual-Media
Filters
Basin
Figure 9.2 Sarasota County, Florida Carlton WTP process schematic.
The EDR process at the Carlton WTP consists for 10 separate parallel units (Figure 9.3).
Each unit has eight parallel lines, each composed of four membrane stacks. Therefore, each
EDR unit has a total of 32 membrane stacks (8 lines × 4 stacks/line). With 10 EDR units
running in parallel, there are a total of 320 membrane stacks in operation. The designed overall
water recovery for the EDR system is 85 percent.
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Line 1
Line 2
UNIT 1
Line 3
Line 4
Qin
Line 7
Line 8
UNIT 2
UNIT 3
UNIT 10
Figure 9.3 Schematic of the EDR stack configuration at the Carlton WTP.
A chemical enhanced backwash is regularly used to clean the EDR electrodes. In
addition, a centralized CIP system is used to remove mineral scale and other foulants that
accumulate within the EDR stacks and on the membranes. The CIP system is semi-automated
and is performed on one unit at a time. The unit to be cleaned is taken off line, while the other
EDR units continue with normal operation. A centralized antiscalant system is also used to
retard scale accumulation on the membranes using hydrochloric acid.
The product water is chlorinated and is pH adjusted for distribution system corrosion
control. The finished water is pumped into the distribution system using two high service
pumps, one 2 mgd and one 9 mgd. The EDR reject water is disposed of via deep well injection.
To maximize water efficiency, a portion of the reject stream is re-circulated to the front of the
EDR system for retreatment.
Historical data for the raw and finished water TDS and turbidity is shown in Figure 9.4a
and b, respectively. The raw water TDS is approximately 1,900 mg/L, while the EDR permeate
TDS is approximately 800 mg/L. The finished water turbidity was generally <0.5 NTU.
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2500
Total Dissolved Solids (mg/L)
2000
1500
1000
500
Raw Water
Product Water
0
24-Jun-06
8-Jul-06
22-Jul-06
5-Aug-06
19-Aug-06
2.5
Raw Water
Product Water
Turbidity (NTU)
2.0
1.5
1.0
0.5
0.0
24-Jun-06
08-Jul-06
22-Jul-06
05-Aug-06
19-Aug-06
Figure 9.4 Historical raw and finished water a) TDS and b) turbidity for the Carlton WTP.
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Power Supply
Florida Power & Light (FP&L) provides the power to the Carlton WTP through a single
watt-hour meter. Power within the plant is distributed through three motor control centers
(MCCs). Power to the EDR system is routed from one of the MCCs to one of 20 rectifiers.
There are two rectifiers for each EDR unit, each powering four of the eight lines of the
membrane stacks for an EDR unit.
One of the rectifiers for each EDR unit is equipped with an output monitor. The power
demand and energy consumption for the EDR unit are displayed on the output monitor, but the
data is not recorded by the plant SCADA system or by the plant staff. The plant SCADA system
is not configured to record any power or energy data for the treatment plant equipment.
Energy Consumption
Given the plant SCADA configuration, plant energy data used for this analysis was taken
from FP&L energy bills for the Carlton WTP for the period from May 2005 to April 2007.
However, finished water production data was only available for January through March 2007.
Figure 9.5 shows that the monthly average daily EC ranged from a maximum of
36,980 kWh/day in May 2006 to a minimum of 22,675 kWh/day in September 2005. The
average EC over this time period was 28,249 kWh/day. Daily EC tended to be highest during
winter and spring months, and lower during summer months.
Energy Consumption (kWh/day)
40,000
30,000
20,000
10,000
0
Feb-05
May-05
Sep-05
Dec-05
Mar-06
Jul-06
Oct-06
Jan-07
Apr-07
Aug-07
Figure 9.5 Monthly average daily energy consumption for the Carlton WTP. The energy
consumption is for the entire treatment plant and all associated processes.
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Energy and water quality data during three months of plant operation is summarized in
Table 9.1. The average finished water flowrate was 6.83 mgd from January to March 2007. The
feed water recovery was between 75 and 78 percent for this period, which is below the design
recovery of 85 percent. TDS removal was approximately 55 percent for each of the three
months. Specific EC did not follow a clear trend with either finished water flowrate or influent
TDS concentration. The data suggests that there may be an inverse correlation between specific
EC with the finished water flowrate. Based on the results shown for the previous ATTs in the
report, higher production rates corresponded to lower ECs for two reasons:
1. Pumps were operating closer to their design optimum efficiency points on their
respective pump curves, and
2. The fraction of fixed energy consumption, such as building HVAC, constant speed
mixers, air compressors, becomes smaller to the overall facility specific EC.
Additional analysis is warranted to bring more definition to this potential correlation.
Interestingly, there was no large change in specific EC between the first two months when the
feed water TDS was approximately 1,700 mg/L and in March when TDS concentrations
decreased by 35 percent, though the water recovery rate was relatively constant. Again, further
analysis is suggested to determine if the March data is anomalous or if there is little to no
correlation between specific EC and TDS.
Table 9.1
Summary of water treatment system performance and specific energy consumption for all
equipment at the Carlton WTP
Month
Jan-07
Feb-07
Mar-07
Average
Feed Water
Q
(mgd)
8.8
8.6
9.4
8.9
Finished
Water Q
(mgd)
6.57
6.55
7.36
6.83
Feed Water
TDS
(mg/L)
1,732
1,759
1,128
1,540
Monthly Average
Daily EC
(kWh/month)
895,600
836,400
980,800
904,267
Specific
Energy
Consumption
(kWh/kgal)
4.26
4.41
4.20
4.29
Potential Energy Conservation Improvements
Given the data used in this analysis, there is little opportunity to identify energy
conservation areas specific to the EDR system. However, an associated area of improvement for
the entire facility would be to further analyze the potential to increase the current operating water
recovery of 75 – 78 percent to the 85 percent design recovery. This increase should result in
requiring less groundwater to be pumped through the plant to provide the same given volume of
finished water. As shown in Table 9.2, increasing the recovery to 85 percent to meet a
hypothetical demand of 7.5 mgd would result in the need to pump 1.2 mgd less groundwater to
the plant and 1.2 mgd reject brine from the plant into the deep well for disposal. To phrase it
differently, the cost of operating at a lower water recovery is to pump untreated groundwater out
of the ground, through the treatment plant, and back into the ground as brine. An additional
analysis would be required to determine the precise balance between increased EDR EC due to
the higher recovery versus the decreased pumping EC for groundwater and reject brine.
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Table 9.2
Potential Reduction in Pumping Associated with Increased Water Recovery
Water
Recovery
75%
85%
Difference
Finished Water Q (mgd)
7.5
7.5
0
Required Groundwater Q
(mgd)
10.0
8.8
1.2
Reject Brine
Q (mgd)
2.5
1.3
1.2
Another area that could be potentially studied is to have the operating water recovery
vary as a function of the feed water TDS. In the case of the Carlton WTP, the water recovery
could potentially exceed 85 percent during the periods when the feed water TDS decreases, as it
did in March 2007.
CONSIDERATIONS FOR EC OPTIMIZATION OF EDR SYSTEMS
Factors Affecting EC of EDR Systems
Specific EC at the Carlton WTP did not correlate with any operational parameters for the
duration provided. The data suggests that energy efficiency may improve somewhat with
increasing influent flowrate. Additional analysis would be required to establish better
comparisons between EC with operational or water chemistry parameters.
Considerations for EC Optimization of EDR Systems
Operating the EDR system at or as close to the design water recovery has the potential to
significantly reduce the overall facility EC since less water needs to be pumped to and from the
facility. Aside from this one consideration, additional analysis of the Carlton WTP and other
EDR systems would be required to identify more areas where EC could be optimized.
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CHAPTER 10
GENERAL GUIDELINES FOR EC ANALYSES AND OPTIMIZATION
Optimizing the EC of a water or wastewater treatment plant is one the easiest ways to
reduce the operating costs of such facilities. This section outlines some general guidelines for
performing such optimization studies. The steps and procedures discussed here are based on
work performed previously by Reardon (1994). A flowchart showing the general process for
conducting and implementing the results from an energy analysis at a water or wastewater
treatment system is given in Figure 10.1.
Obtain Detailed
Knowledge of
System
Conduct Inventory,
Determine Distribution of
Power
Benchmark to
Similar Facilities if
Possible
Electric Utility Info
Determine
Pump/Equipment
Efficiencies
(% or kWh/mg)
Quantify
Promising ECMs
Detailed Process
Analysis
Develop Implementation
Program
Create ECMs
Implement
Figure 10.1 General procedure for planning and performing an EC analysis at water and
wastewater treatment plants.
Each of the steps shown in the Figure 10.1 are discussed in the following sections.
Step 1: Obtain detailed knowledge of the treatment system - Information needs to be
collected on the types of processes and equipment being used at the treatment plant. In addition,
the power demand and energy consumption data for the large (greater than 5 HP) equipment that
is used often will need to collected. To compare the energy analysis with treatment plant
performance, relevant water quality and quantity data from the same period as the power/energy
data should also be collected.
The type of data to be collected will generally vary according to the types of processes
being employed (e.g., RO versus ozonation). The general information that should be collected
during this step are listed in Table 10.1. Table 10.2 is the data that should be collected for
specific ATTs.
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Table 10.1
General list of data required for EC optimization
Operational Data
Water Quality Data
•
•
•
Historical EC monitoring
data for the process
equipment (one year
minimum, preferably
daily, monthly power bill
acceptable)
Daily/hourly/weekly/
monthly hours of
operation
•
Historical raw and
finished water
quality/quantity data for
the process equipment
(one year minimum,
preferably daily)
•
•
•
•
Other
Manufacturer’s pump
curves and motor
efficiencies.
SCADA energy/power
data logging capabilities
Treatment plant
electrical utility rate
schedule
Plant process flow
diagram
Plant equipment design
and operating criteria
Table 10.2
List of data required for EC optimization for specific ATTs
Technology
Ozone
Operational Data
Daily oxygen consumption (lb/day)
Daily production rates (lb/day)
UV
Average lamp age
Microfiltration/
ultra-filtration
Average membrane age and condition
Flowrate and pressure for feed (if
pressure-driven) or permeate (if vacuumdriven).
Transmembrane pressure
Blower use and discharge flowrate and
pressure
Backwash schedule and setpoints
CIP frequency
Time since last CIP
Feed chemical type and dosage (if any)
Average membrane age and condition
Flowrate and pressure for permeate
Transmembrane pressure
Blower use and discharge flowrate and
pressure
Backwash schedule and setpoints
CIP frequency
Time since last CIP
Membrane
Bioreactor
Water Quality Data
Total organic carbon
MIB/geosmin feed and treated
concentrations (if used for T&O control)
Virus, Giardia inactivation rates
Output dosage (mJ/cm2)
Water transmissivity
Feed and permeate turbidity
Feed temperature
Feed and permeate turbidity
Feed temperature
Feed TSS
Feed and permeate BOD5
(Continued)
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Table 10.2 (Continued)
Technology
Reverse
Osmosis
Electrodialysis
removal
Operational Data
Average membrane age
Bypass rate (if any)
Flowrate and pressure for feed, permeate,
and concentrate streams.
Antiscalant use (type and dosage) (if used)
CIP frequency
Time since last CIP
Average membrane age
Bypass rate (if any)
Flowrate and pressure for feed, permeate,
and concentrate streams.
Antiscalant use (type and dosage) (if used)
Cell voltage, amperage
Polarity reversal frequency
CIP frequency
Time since last CIP
Water Quality Data
Feed, permeate, and concentrate TDS.
Blended water TDS if bypass is used.
Feed pH
Feed temperature
Feed, permeate, and concentrate TDS.
Blended water TDS if bypass is used.
Feed pH
Feed temperature
Step 2: Conduct an inventory of the energy consuming equipment and power
distribution - It is necessary to log what equipment and processes consume energy and if it is
possible to determine how much energy is being consumed by each. This step may entail
installing new meters or performing calculations based on known operating variables and
manufacture’s data. An example electrical equipment inventory sheet is provided in Table 10.3
(Reardon and Culp, 1987a).
Table 10.3
Example electrical equipment inventory sheet (Source Reardon and Culp, 1987a). Example
values are shown in the table for illustrative purposes only
Process
Equipment
HP
Motor Nameplate Data
Full
Speed
Volts
Load
Phases
rpm
Amps
CAP Pump Station
CAP Water
300
460
Pump
Raw Water Pump Station
Raw Water
50
230
Pump 1
Membrane System
Permeate
60
230
Pump
3
200
Reject Pump
Field Measurements1
Amps
Volts
kW
Power
Factor
hrs
/yr
kW
/yr
480
1800
3
385
400
58
0.95
7.8
452
75
800
3
63
200
77
0.87
8.0
616
85
800
3
78
200
35
0.86
8.0
280
10
250
3
6
180
42
0.80
8.0
336
1 – The values for hrs/yr and kW/yr are in thousands (value = x 1,000)
197
©2008 AwwaRF. ALL RIGHTS RESERVED
Equipment that has been determined to consume measurable quantities of energy at all
water and wastewater treatment plants include the raw water pumps, finished water pumps, and
aeration equipment. These three equipment categories should therefore be inventoried at all
treatment plants. Conversely, some equipment is specific to the types of treatment processes that
are being used at a given facility and must therefore not always be inventoried. Examples of
equipment that is specific to several varieties of treatment processes are listed in Table 10.4.
Table 10.4
Examples of equipment that should be inventoried for specific treatment processes
Treatment System
Equipment to be Inventoried
Feed or permeate pumps
Microfiltration/ultrafiltration
Backwash blower
Permeate pumps
Membrane bioreactors
Air scour blowers
Recycle pumps
Rectifier
Electrodialysis reversal
Feed pump
Degasifier blower
Booster pump
Reverse osmosis
Degasifier blower (if present)
Support equipment (dessicator, cooling water
pump, etc)
Feed gas system (LOX, ambient air, VSPA)
Ozonation
UV disinfection
Ballast
Step 3: Benchmark results to similar facilities - Benchmarking provides for a baseline
comparison between two utilities that employ similar treatment systems and operate under
comparable water quality conditions. Through benchmarking, it is possible to determine the
energy efficiency of the treatment plant relative to other systems. The principle benchmark for
comparison purposes is specific energy consumption, due to the overriding importance of
finished water production rate in determining energy consumption at water and wastewater
treatment plants. For ease of comparison, specific energy should be calculated in terms of
kilowatt hours per thousand gallons of water treated (kWh/kgal). This will aid in comparing to
both historical and future EC studies. It is important to ensure that the analogous systems are
using similar treatment processes and are operating under similar influent and effluent water
quality parameters. Water quality and operational benchmarks that are used to specifically
compare two treatment systems that are employing the same type of primary treatment processes
are outlined in Table 10.5. Examples of general benchmarks, which may be used to compare
treatment systems of any type include:
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©2008 AwwaRF. ALL RIGHTS RESERVED
•
•
•
Finished water production rate
Specific energy consumption
Raw and finished water qualities
Table 10.5
Performance benchmarks specific to various treatment systems
Treatment System
Microfiltration/
ultrafiltration
Water Quality Benchmark
Turbidity
Temperature
Membrane bioreactor
Total suspended solids
Temperature
Turbidity
Reverse osmosis
Feed, permeate TDS
Electrodialysis
reversal
Feed, permeate TDS
Ozonation
Total organic carbon
Temperature
Giardia, virus inactivation
MIB/geosmin (if used for taste and
odor removal)
UV dosage
Transmissivity
UV disinfection
Operational Benchmark
System configuration
CIP frequency
Specific EC
Flowrate
Membrane age
System configuration
CIP frequency
Specific EC
Flowrate
Membrane age
System configuration
Specific EC
Feed pressure
Bypass rate
Membrane age
System configuration
Specific EC
Feed pressure
Bypass rate
Membrane age
System configuration
Ozone dose
Specific EC
System configuration
Specific EC
Step 4: Determine the energy efficiencies of pumps, blowers, and other process
related equipment - The efficiencies of all pumps and blowers that are determined to be
substantial consumers of energy should be determined based on their respective pump curves.
The operating efficiency will be based on the pump and blower operating data (flowrate and
pressure) collected in Step 1. Pump and blower efficiencies are generally determined using the
pump or blower curve for that equipment and the measured pump performance. Pump curves are
supplied by the manufacturer. Alternatively, the overall wire-to-water efficiency may be
determined using Equation 10. 1.
199
©2008 AwwaRF. ALL RIGHTS RESERVED
η pump =
QH
3960hp
(10.1)
where ηpump = pump efficiency, %
Q = fluid flowrate, gpm
H = differential head across the pump, ft
hp = horsepower
The efficiency of process related equipment should focus on how the equipment is
operating respective to its design parameters, such as volume of water treated, dosing rates (e.g.,
ozone), and product production (e.g., ozone, oxygen). This is important as over design is
commonly cited as a principle reason for inefficient equipment operation.
For equipment other than pumps, such as EDR rectifiers and UV ballasts, the energy
efficiency would be determined by dividing the energy consumption data shown on the local
PLC or recorded in the SCADA with the measured treated water flowrate. As mention earlier in
this section, the final value should be in a standardized unit, such as kWh/kgal treated, for easy
comparison with other data.
Step 5: Prepare a detailed process analysis - A detailed analysis examining the water
quality, operating parameters, and EC is prepared. This analysis should consider all parameters
that are thought to be significant determinants of the EC by the relevant treatment processes.
This analysis should consider the effects of external factors on EC, such as water demand,
seasonal variations, water quality effects, process requirements, and any other factor thought to
be relevant. EC should be determined through inspection of all available monitoring data and
through energy bill statements from the respective utility. Emphasis in the process analysis will
vary according to the types of treatment systems being analyzed. Example areas of emphasis in
the process analysis are outlined in Table 10.6 for different types of treatment processes.
Table 10.6
Areas of emphasis to be considered for the evaluation of specific treatment processes
Treatment System
Emphasis Area for Process Analysis
Membrane processes
Booster/vacuum pump operation
Membrane cleaning requirements
Membrane characteristics
Ozonation
Comparison to design ozone dose
Support system analysis
UV
Variation of lamp intensity
200
©2008 AwwaRF. ALL RIGHTS RESERVED
Step 6: Create energy conservation measures (ECMs) - ECMs should be developed
based on the analysis prepared in Step 5. ECMs are cost-effective steps or measures that may be
taken in order to reduce the EC at a given treatment plant. ECMs may encompass both changes
in operational strategies and process equipment. Examples of ECMs may include the following:
• Installing premium efficiency motors.
• Operating at or near design capacities for existing pumps.
• Minimizing over design for the process related equipment.
• Performing routine maintenance on pumps to ensure efficient pump operation.
• Installing VFDs on pumps that experience variable flow demands.
• Utilizing off-peak demand energy consumption.
• Reducing or eliminating non-essential building lighting.
ECMs may be developed for the plant as a whole or in the more likely scenario for an
individual piece of equipment. For individual process equipment ECMs may be developed by
performing a “what if scenario” by asking the following questions:
• Is the process equipment needed to achieve the desired treatment result?
• Can the process equipment achieve the same results at lower flow or capacity?
• Can the running time be reduced for the process equipment?
• Can the operation shift from on-peak to off-peak hours?
• Is the process efficient at the existing loading conditions or does it need to be
modified or replaced?
Step 7: Quantify the potential benefits of ECMs - The potential benefits of
implementing the ECMs should be considered with regards to costs associated with
improvements in energy efficiency, changes in operation strategies, and those associated with
purchasing and installing new equipment.
Step 8: Develop an implementation program - A strategy and plan for implementing
the ECMs that are deemed economically feasible.
Step 9: Implement ECMs - Implementation of the ECMs deemed most feasible must be
based on several factors including costs associated with the measure and training requirements.
It is critical that follow-up studies be done to determine the energy savings that are realized from
the ECMs that are implemented at the treatment plant. Follow-up studies will also aid in
identifying future ECMs that may be needed as the conditions at the treatment plant change and
as newer technologies become available.
201
©2008 AwwaRF. ALL RIGHTS RESERVED
202
©2008 AwwaRF. ALL RIGHTS RESERVED
CHAPTER 11
CONCLUSIONS AND RECOMMENDATIONS
FOR FURTHER RESEARCH
CONCLUSIONS
Table 11.1 provides a summary of the specific EC for the targeted ATTs based on case
studies described in this report. Also shown for comparison are typical EC values that have been
reported in the literature, as discussed previously in Chapter 2. As a general conclusion,
treatment plants using ATTs are characterized by a relatively wide range of energy consumption
0.4 to 6.89 kWh/kgal. This range is similar to that reported for conventional water treatment
plants which may range from 0.338 to 4.5 kWh/kgal as referenced in Arora (1998). This wide
range attests to many variables that have been identified throughout this study which determine
the energy consumption for the overall system. As with conventional systems, energy
consumption by ATTs is not inherently high and is in fact a function of many design and
operating parameters.
Considering the EC specifically by those ATTs (i.e., EC by ATT related equipment only)
examined in this study and comparing it to the literature values reported in Table 11.1 some
similarities and discrepancies emerge. For UV disinfection and UF systems, findings from the
case studies revealed EC values that were near and within the range of typical values reported in
the literature. For the other targeted ATTs (ozone disinfection, RO, MBRs, and EDR), the
findings from the case studies were lower than those values reported in the literature. These
differences may be explained by considering two issues: (1) technological advancements in
ATTs that were applied at the case studies but not incorporated in literature reports or (2) the
dependence of RO performance on influent water quality.
Taking for example the literature value for the EC for RO, the rather large difference is
due to the fact that the case studies discussed in this report were treating brackish water. The
literature value reflects the EC of RO treating seawater, for which RO is most commonly
applied. The lower EC for the case studies results from the lower operating pressures required to
treat brackish water, which is characterized by lower TDS compared to seawater. For the MBR
case studies, the typical EC cited in the literature is for MBRs that employ tubular membranes
operated in a cross-flow configuration, which is now considered to be the least efficient MBR
configuration. Conversely, those MBRs studied here used submerged hollow fiber membranes
and vacuum filtration. These results demonstrate how the EC of MBRs may be improved
through improvements in module configuration and operation.
More specific conclusions based on the case studies presented in this report are
summarized as follows:
• Of those ATTs studied here, UV systems have the lowest specific energy
consumption on average. RO systems have the highest specific energy consumption
on average out of those ATTs studied here.
• The energy consumption by RO systems is directly correlated with the feed pressure
requirements. Therefore, EC for RO systems will most greatly be reduced through
lowering of the pressure requirements. This EC reduction can realistically be
achieved through improvements in membrane characteristics (i.e., permeability).
• Energy consumption by the feed pumps for RO systems can vary considerably
depending on the quality (i.e., TDS) of the RO feedwater.
203
©2008 AwwaRF. ALL RIGHTS RESERVED
•
•
•
Energy consumption by UF membrane processes is largely a function of the air scour
and backwash design and operation (frequency, duration). For this reason, water
quality and pretreatment process selection will impact the energy consumption by UF
systems.
Energy consumption by ozonation systems is dictated by the EC of the feed gas
systems. Ambient air-fed systems consume the most amount of energy, while LOX
fed systems consume the least. However, LOX systems are more cost efficient when
operated at higher ozone concentration as material costs (i.e., the cost for the LOX)
decrease with increasing ozone concentration.
Membrane cleaning and maintenance, in the form of air scour, consumes the largest
fraction of the EC for MBR systems. Permeate pumping actually consumes the least
amount of energy. Therefore, from a design and operation stand-point, EC for MBR
systems will be most greatly improved through changes in membrane module design,
which affects air scour efficiency, and air scour duration and frequency.
Table 11.1
Comparison of case studies results and literature values for EC and strategies for
optimizing energy efficiency
ATT
Process or
Component
Case Studies7
Specific
Energy
Consumption
Comments
(kWh per
1000 gal)
Literature Review1
Optimizing
Energy
Efficiency
Typical
Power Use
(kWh per
1000 gal)
UV
disinfection
Mediumpressure lamp
system
0.02-0.092
Specific EC is a
function of flow
rate (15-40 mgd)
and total number
of operating
reactors (1-3).
Operate at or
near flow
capacity.
0.05-0.15
Ozone
disinfection
LOX feed
0.02-0.053,6
0.06-0.084
Ambient air
feed
0.11-0.165,6
Operate at or
near design
ozone
concentration.
0.6
VPSA feed
EC is dictated
by feed gas
system.
0.5-1.08
Add coag and
floc prior to UF.
0.5
0.4-0.79
High TDS and
add PAC prior
to UF.
Reconfigure
re-circulating
lines and
other
operational
improvements
Ultrafiltration
Pumps, air
scour, cleaning
systems
Optimizing
Energy
Efficiency
Dose control (i.e.,
alter the number of
lamps in use or the
lamp power based
on flow, water
quality, or UV
absorbance)
• Equipment
maintenance or
change in
operation;
• Design change
and system
modifications
• Operations (e.g.,
backwash
frequency)
• Water quality
(Continued)
204
©2008 AwwaRF. ALL RIGHTS RESERVED
Table 11.1 (Continued)
ATT
Reverse
osmosis
Membrane
bioreactors
Process or
Component
Feed pumps
Pumps, blowers
Case Studies7
Specific
Energy
Consumption
Comments
(kWh per
1000 gal)
0.5-4.810
Specific EC
increases
linearly with
feed pressure
3.0-7.511
Literature Review1
Optimizing
Energy
Efficiency
Pre-blending,
improved
pump
operating
efficiency,
new
membrane
materials, and
energy
recovery
systems.
Minimize the
frequency of
air scour.
Typical
Power Use
(kWh per
1000 gal)
7.6-13
Air scour
23 – 30
blowers
represent
approximately
40 percent of
total specific EC
whereas
permeate pumps
and aeration
blowers account
for 3 to 5
percent. Specific
EC for permeate
pumps depend
on membrane
pore size.
ElectroElectrified
4.312
Fixed energy
Although
6-13
dialysis
membrane
consumption
insufficient
Reversal
plates
(e.g., building
data available,
HVAC, mixers,
improved
etc.) is
efficiency
considered small potentially
relative to EDR. could be
More data
achieved by
would be needed operating near
to determine
design
effects of TDS
recovery.
or other
parameters.
1. Based on values reported in the literature review in Chapter 2 and summarized in Table 2.6.
2. Central Lake County Joint Action Water Agency
3. Contra Costa Water District, California
4. Southern Nevada Water Authority
5. Central Lake County Joint Action Water Agency
6. Represents EC for ATT only.
7. Based on values collected per utility case studies as described in Chapters 4 through 9.
8. Kamloops Centre for Water Quality
9. Anthem Water Campus, Arizona
10. Based on operating feed pressures at West Basin, Goldsworthy, and Seward WTPs.
11. Based on total MBR systems at the Anthem and Pooler WWTPs.
12. Average based on 3 months of production data at Sarasota County, Florida.
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©2008 AwwaRF. ALL RIGHTS RESERVED
Optimizing
Energy
Efficiency
•
•
•
Process design
Equipment
selection
Feedwater
temperature
Design including
configuration and
operating pressure
Design such as stack
configuration.
RECOMMENDATIONS FOR FURTHER RESEARCH
Based on the experience and insight gained from this endeavor the following topics are
suggested for further research and study with the goal of optimizing the energy efficiency of
water treatment systems:
• When evaluating the EC of MBR systems it was found that the pressure requirements
were lower for the system employing UF membranes having a smaller mean pore
size, compared to the utility using membranes with a larger mean pore size. This
finding contradicts conventional wisdom where pressure requirements should
increase with decreasing pore size for MF and UF membranes. Therefore, it would
be valuable to assess the roles played by other membrane characteristics, such as
thickness and hydrophobicity in determining their pressure and subsequently their
pumping requirements. Optimization of these parameters may result in lower energy
consumption by MF and UF permeate pumps.
• Air scour accounted for roughly 40 percent of the total specific energy consumption
at MBR treatment plants. Significant energy savings could be realized through
improvements in the design and operation of air scour systems. Research is needed to
determine which factors (e.g., membrane properties and configuration) could be
improved to decrease the air scour frequency and duration.
Furthermore,
improvements in the design of air scour systems which minimize the number of
blowers needed per membrane train and maximize the effectiveness of the scour in
removing accumulated solids are also needed and may be realized through further
research.
• Membrane biofouling is determined by both the properties of the membrane and that
of the biological composition in the bioreactors that precede the MBR. Understanding
how or if biofouling varies according to the characteristics of the microorganisms and
their biological debris may aid in optimizing the energy consumption of air scour
systems used in MBR systems.
• Theory states that temperature should play a more substantial role in determining the
pressure requirements for RO systems. However, it was found to play only a minor,
or no role at all in the systems studied here. Instead, TDS was identified as the major
water quality factor affecting EC by RO systems. Research is therefore needed to
assess what ranges of temperature increases are required to significantly improve
membrane flux under actual operating conditions. Once these ranges are established
then an economical and energy evaluation may be instituted that examines the cost
effectiveness of incorporating heating systems (e.g., solar ponds, heating elements,
waste heat sources, etc) into RO systems.
• Advancements are continuing in the design of membrane configurations (spiral
wound versus hollow fiber) and element design. It would be valuable to determine
how these design changes affect the energy efficiency of a given membrane system.
An example would be investigating whether spiral wound membranes have a lower
overall specific energy consumption when compared to spiral wound membrane
elements.
206
©2008 AwwaRF. ALL RIGHTS RESERVED
APPENDIX A
207
©2008 AwwaRF. ALL RIGHTS RESERVED
Alfred Merritt Smith Water Treatment Facility Ozone Monthly Report
OZONE GENERATION SYSTEM ENERGY CONSUMPTION
Row
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
Year
2005
2005
2006
2006
Units
November
December
January
February
days
30
31
31
28
lb
76,296
67,665
76,059
65,056
lb/day
2,543
2,183
2,454
2,323
MG
8,890
6,966
7,452
6,453
MGD
296
225
240
230
mg/L
1.03
1.16
1.22
1.21
mg-min-L
4.11
4.04
4.74
5.26
C
15.53
15.69
14.60
13.83
Ozone Generator Energy Consumption
Generator 1
Total kWh
44,820
58,206
47,642
Generator 2
Total kWh
86,122
53,428
45,729
58,606
Generator 3
Total kWh
57,092
46,731
32,212
Generator 4
Total kWh
40,257
39,891
40,723
58,094
Generator 5
Total kWh
69,478
52,504
84,083
59,614
Total Generator
Total kWh
252,949
237,373
260,955
223,957
Operating Ozone Concentration
%wt
3.34
2.88
3.26
3.25
Generator
kWh/lb
3.32
3.51
3.43
3.44
VPSA
VPSA 1
Total kWh
200,402
98,650
205,921
84,981
VPSA 2
Total kWh
102,354
219,539
108,561
192,583
Total VPSA
Total kWh
302,756
318,189
314,483
277,564
VPSA
kWh/kg
3.97
4.70
4.13
4.27
Total System Energy Consumption by Two Totalizer Switchgear Measurements
Switchgear 1
Total kWh
466,983
425,058
514,192
344,117
Switchgear 2
Total kWh
427,567
552,133
474,592
502,492
Total System - Switchgear
kWh
894,550
977,192
988,783
846,608
Total System Energy Consumption by Components
Total Generator
Total kWh
252,949
237,373
260,955
223,957
Total VPSA
Total kWh
302,756
318,189
314,483
277,564
Switchboard 1 MA
Total kWh
39,074
61,529
37,976
54,621
Switchboard 1 MB
Total kWh
178,053
172,903
197,063
149,164
Switchboard 2 MA
Total kWh
51,226
113,543
105,103
76,338
Switchboard 2 MB
Total kWh
49,821
54,864
55,713
47,143
Sum of Component Values
kWh
873,879
958,401
971,293
828,787
Delta from Totalizer Switchgear
kWh
20,671
18,791
17,490
17,821
Discrepancy
%
2.3%
1.9%
1.8%
2.1%
Generator Plus VPSA
Generator
Total kWh
252,949
237,373
260,955
223,957
VPSA
Total kWh
302,756
318,189
314,483
277,564
Generator Plus VPSA
Total kWh
555,706
555,562
575,437
501,521
Total System Energy Consumption
Total kWh
894,550
977,192
988,783
846,608
Percent Generator +VPSA
% total
62%
57%
58%
59%
Generator +VPSA
kWh/lb
7.28
8.21
7.57
7.71
Ozone System Unit Energy Consumption
Total System Energy - Switchgear
kWh
894,550
977,192
988,783
846,608
Total Ozone Production
lb
76,296
67,665
76,059
65,056
Total System Specific Energy
kWh/lb
11.72
14.44
13.00
13.01
Average Daily Ozone Production
lb/day
2,543
2,183
2,454
2,323
Average Daily Water Flow Rate
MGD
296
225
240
230
Average Daily Energy Consumption
kWh/day
29,818
31,522
31,896
30,236
Unit-flow Energy Consumption
kWh/MG
101
140
133
131
Parameter
Days in the Month
Total Ozone Production
Daily Average Ozone Production
Total Raw Water Flow
Daily Average Water Flow
Average Ozone Dose
Disinfectin CT value
Water Temperatue
208
©2008 AwwaRF. ALL RIGHTS RESERVED
2006
March
7
15,456
2,208
1,613
230
1.15
5.65
13.91
24,090
8,214
620
2,077
17,697
52,698
3.41
3.41
64,726
64,726
4.19
102,242
91,525
193,767
52,698
64,726
2,914
45,160
12,538
11,680
189,714
4,052
2.1%
52,698
64,726
117,423
193,767
61%
7.60
193,767
15,456
12.54
2,208
230
27,681
120
ENERGY CONSUMPTION AND OZONE PRODUCTION AT THE BOLLMAN WTP
MonthYear
Jan-04
Feb-04
Mar-04
Apr-04
May-04
Jun-04
Jul-04
Aug-04
Sep-04
Oct-04
Nov-04
Dec-04
Jan-05
Feb-05
Mar-05
Apr-05
May-05
Jun-05
Jul-05
Aug-05
Sep-05
Oct-05
Nov-05
Dec-05
Jan-06
Feb-06
Mar-06
Apr-06
May-06
Jun-06
Jul-06
Aug-06
Sep-06
Oct-06
Nov-06
Dec-06
Wate Ozone
Total
System
r
Flow Gas
Ozone Gener Destruct Ozone System Energy
Total Flow Prod. Power Power Conc. SE
Consu
mption
MG scfm lb/day kW
kW
%wt
kWh/lb kWh/k
D
gal
22.4 27.8
144
33
1.0
4.34
5.71
0.037
20.9 28.1
159
25
1.0
4.74
3.94
0.030
28.2 35.3
233
38
1.2
5.42
3.99
0.033
34.4 32.4
253
42
1.1
6.53
4.09
0.030
42.7 29.9
306
57
1.1
8.54
4.52
0.032
46.7 32.8
352
66
1.2
8.96
4.61
0.035
54.2 36.8
409
79
1.3
9.26
4.71
0.035
52.1 35.0
378
72
1.2
9.02
4.63
0.034
47.8 36.0
389
74
1.2
9.02
4.63
0.038
33.0 26.3
246
44
1.0
7.74
4.42
0.033
21.0 26.2
138
22
1.0
4.43
3.92
0.026
21.7 22.6
114
18
0.9
4.22
3.92
0.021
20.7 23.8
120
19
0.9
4.17
3.93
0.023
21.6 30.1
154
24
1.1
4.27
3.91
0.028
23.7 34.2
208
33
1.2
5.09
3.94
0.035
27.6 36.3
278
46
1.3
6.37
4.10
0.041
32.1 36.1
344
61
1.3
7.93
4.35
0.047
44.6 37.4
332
58
1.3
7.36
4.26
0.032
53.8 45.7
471
87
1.5
8.57
4.52
0.040
56.2 39.2
409
76
1.3
8.69
4.55
0.033
46.7 33.9
324
58
1.2
7.97
4.38
0.030
40.2 30.6
244
41
1.1
6.67
4.13
0.025
31.5 29.3
194
31
1.1
5.50
3.98
0.024
23.1 28.4
182
29
1.0
5.36
3.97
0.031
23.1 31.6
172
25
1.1
4.54
3.59
0.027
23.3 31.1
191
28
1.1
5.11
3.70
0.030
22.0 31.2
176
26
1.1
4.71
3.74
0.030
22.9 31.4
185
28
1.1
4.93
3.75
0.030
43.3 39.6
343
57
1.3
7.24
4.10
0.032
52.6 46.2
462
73
1.5
8.30
3.88
0.034
59.8 57.3
555
87
1.8
8.19
3.83
0.036
63.3 42.1
443
77
1.4
8.76
4.25
0.030
49.4 39.4
340
53
1.3
7.15
3.87
0.027
36.8 35.3
236
36
1.2
5.60
3.78
0.024
23.7 28.0
162
24
1.0
4.81
3.73
0.025
22.0 27.0
138
20
1.0
4.24
3.68
0.023
Minimum 21
Average
36
Maximum 63
23
34
57
114
272
555
18
46
87
0.9
1.2
1.8
4.17
6.49
9.26
3.59
4.09
4.71
Energy Energy LOX
Price Cost
Price
LOX
Cost
Unit
Unit
Mass
Cost
Volume
Cost
$/kWh $/lb
$/Cft3 $/lb
$/lb
$/MG
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.0508
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.65
0.59
0.51
0.43
0.33
0.31
0.30
0.31
0.31
0.36
0.63
0.66
0.66
0.65
0.55
0.44
0.35
0.38
0.32
0.32
0.35
0.42
0.51
0.52
0.61
0.55
0.59
0.57
0.39
0.33
0.35
0.32
0.39
0.50
0.58
0.66
0.94
0.79
0.71
0.64
0.56
0.55
0.54
0.54
0.54
0.58
0.83
0.86
0.86
0.85
0.75
0.64
0.57
0.59
0.55
0.55
0.57
0.63
0.71
0.72
0.80
0.73
0.78
0.76
0.59
0.53
0.54
0.53
0.58
0.69
0.77
0.84
6.01
6.03
5.86
4.67
3.99
4.12
4.07
3.95
4.42
4.33
5.48
4.52
5.00
6.07
6.59
6.49
6.13
4.41
4.85
4.01
3.98
3.82
4.36
5.69
5.93
6.01
6.26
6.13
4.70
4.66
5.01
3.73
4.02
4.44
5.24
5.27
0.30
0.46
0.66
0.53
0.67
0.86
3.73
4.99
6.59
0.021
0.031
0.047
209
©2008 AwwaRF. ALL RIGHTS RESERVED
0.29
0.20
0.20
0.21
0.23
0.23
0.24
0.24
0.24
0.22
0.20
0.20
0.20
0.20
0.20
0.21
0.22
0.22
0.23
0.23
0.22
0.21
0.20
0.20
0.18
0.19
0.19
0.19
0.21
0.20
0.19
0.22
0.20
0.19
0.19
0.19
0.18
0.21
0.24
Kamloops, BC Centre For Water Quality
List Of Major Electrical Equipment
Treatment Equipment
Raw Water Pumping
Pump ID
VFD?
Motor Size
(hp)
Comment
Outside of plant, not included in
analysis
Low Lift Pumps
Chemical Feed/Flocculation
Side Stream Pump
P56A
25
Side Stream Pump
P56B
25
Side Stream Pump
P56C
25
ACH Dosing System
Flocculant Mixer
Flocculant Mixer
Flocculant Mixer
Flocculant Mixer
Flocculant Mixer
Flocculant Mixer
Primary Membrane System
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Primary Permeate Pump
Temporary
Peristaltic Pump
MX7005-1
MX7005-2
MX7005-3
MX7005-4
MX7005-5
MX7005-6
P35-1
P35-2
P35-3
P35-4
P35-5
P35-6
P35-7
P35-8
P35-9
P35-10
P35-11
P35-12
2 duty + 1 standby. Pump curves
required to estimated energy
consumption.
Too small for analysis
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
3
3
3
3
3
3
All duty, no provision to shut
down individual trains during
low flows. Energy consumption
will be estimated without pump
curves.
75
75
75
75
75
75
75
75
75
75
75
75
All duty, no provision to shut
down individual trains during
low flows. Pump curves
required to estimated energy
consumption.
Primary Blower
B85C
200
Primary Blower
B85D
200
Primary Backpulse Pump
P88A
Yes
150
Primary Backpulse Pump
P88B
Yes
150
Secondary Membrane System
Secondary Permeate Pump
P37-1
Yes
10
Secondary Permeate Pump
P37-2
Yes
10
Secondary Permeate Pump
P37-3
Yes
10
Secondary Permeate Pump
P37-4
Yes
10
Secondary Permeate Pump
P37-5
Yes
10
Secondary Permeate Pump
P37-6
Yes
10
210
©2008 AwwaRF. ALL RIGHTS RESERVED
1 duty + 1 standby. Blower
curves required to estimated
energy consumption. Blower
use fixed by warranty
requirements.
1 duty + 1 standby. Pump curves
required to estimated energy
consumption.
All duty, no provision to shut
down individual trains during
low flows... Pump curves
required to estimated energy
consumption.
(Continued)
Kamloops (Continued)
Treatment Equipment
Secondary Blower
Pump ID
VFD?
Motor Size
(hp)
B84A
125
Secondary Blower
B84B
125
Secondary Blower
B84C
125
Secondary Backpulse Pump
P89A
Yes
25
Secondary Backpulse Pump
P89B
Yes
25
Comment
2 duty + 1 standby. Blower
curves required to estimated
energy consumption. Blower
use fixed by warranty
requirements.
1 duty + 1 standby. Blower
curves required to estimated
energy consumption.
Ancillary Membrane Equipment
Vacuum Pump
P-92A
20
Vacuum Pump
P-92B
20
Vacuum Pump
P-92C
20
CIP Backwash Pump
P-81A
7.5
CIP Backwash Pump
P-81B
7.5
CIP Transfer/Drain Pump
P97A
20
CIP Transfer/Drain Pump
P97B
20
CIP Tank Heater
H81
35kW
Air Compressor
AC-91A
30
Air Compressor
AC-91B
30
Air Compressor
AC-95
75
Air Compressor
AC-95A
7.5
Air Compressor
AC-95B
7.5
Chlorination System
Chlorine System Rectifier
TR59A
80 kVA
Chlorine System Rectifier
TR59B
160 kVA
DAF System
DAF Feed Pump
DAF Feed Pump
DAF Recycle Pump
DAF Recycle Pump
DAF Recycle Pump
DAF Flocculator
DAF Flocculator
DAF Scraper
DAF Scraper
P-20A
P-20B
P22A
P22B
P22C
FLC20A
FLC20B
SCR20A
SCR20B
Yes
Yes
5
5
10
10
10
10
10
3
3
211
©2008 AwwaRF. ALL RIGHTS RESERVED
2 duty + 1 standby. Intermittent
use, estimate energy use based
on 4 hours of operation per day.
1 duty + 1 standby. Use too
infrequent to include in analysis.
1 duty + 1 standby. Use too
infrequent to include in analysis.
Use too infrequent to include in
analysis.
1 duty + 1 standby. Use too
infrequent to include in analysis.
Use too infrequent to include in
analysis.
Intermittent use, estimate energy
use based on 4 hours of
operation per day.
Intermittent use, estimate energy
use based on 4 hours of
operation per day.
1 duty + 1 standby. Estimate
each rectifier used 2 hours per
day.
Intermittent use, estimate energy
use based on 4 hours of
operation per day.
(Continued)
Kamloops (Continued)
Treatment Equipment
DAF Bleed Tank Mixer
Centrifuge
Centrifuge Balance Tank Mixer
Centrifuge Feed Pump
Centrifuge Feed Pump
Centrifuge
Miscellaneous Pumps
Pump ID
MX-20
VFD?
Yes
MX-21
P21A
P21B
CF21
Motor Size
(hp)
2
3
2
2
Sewage/Sump Pump
10
Sewage/Sump Pump
10
Irrigation Pump #1
Irrigation Pump #2
P23A
P23B
Yes
Yes
100
100
212
©2008 AwwaRF. ALL RIGHTS RESERVED
Comment
The centrifuge system has not
been used yet.
1 duty + 1 standby. Intermittent
use, estimate energy use based
on 4 hours of operation per day
during the summer and 12 hours
of use during winter.
The irrigation system has not
been used yet
West Basin Plant
List of Major Electrical Equipment
ID1
Treatment
Equipment
1
MF Feed
2
3
4
5
6
Sodium
hypochlorite
pump
MF CIP
cleaning pump3
MF CIP
immersion
heater3
Compressed air
system5
RO transfer
pump
Pump Type
Capacity
(gpm)
TDH
(psi)
Motor
Size
(hp)
Split case
3,529
28
200
Hydraulic
diaphragm
0.18
60
0.5
Centrifugal
1,600
26
40
n.a.4
n.a.
n.a.
52 kW
233 cfm
150
60
1,870
52
75
Rotary screw
compressor
Vertical
turbine
Drive
System
Variable
speed
SCR2 w/
tach
feedback
Constant
Speed
Constant
speed
Constant
speed
Constant
speed
SCR w/
tach
feedback
SCR w/
tach
feedback
Variable
speed
Comment
Two duty,
one standby
One duty,
one standby
One duty
One installed
Two duty,
one standby
Three duty,
one standby
7
Acid addition
pump
Hydraulic
diaphragm
0.12
40
0.5
8
Threshold
inhibitor pump
Hydraulic
diaphragm
0.18
45
0.5
9
Sodium
bisulfite pump
0.18
45
0.5
10
High pressure
RO feed pump
Hydraulic
diaphragm
5-stage
vertical
turbine
1,800
301
75
Variable
speed
Two duty
Centrifugal
1,700
100
150
Constant
speed
One duty
Forced draft
5,205 scfm
n.a.
5
Vertical
turbine
600
50
25
11
12
13
RO CIP
cleaning
pumps6
Decarbonator
blower
Product
transfer pump
Notes:
1. ID refers to equipment label on Error! Reference source not found..
2. SCR = Silicon controlled rectifier
3. Used every 150 to 200 hours.
4. n.a. = not applicable.
5. Used at 20 minute intervals for each membrane backwash cycle.
6. Used every three to six months or when RO flux declines by 15%.
213
©2008 AwwaRF. ALL RIGHTS RESERVED
Constant
speed
Variable
speed
One duty,
one standby
One duty,
one standby
One duty,
one standby
Two duty
Two duty,
one standby
Energy Consuming Equipment for Goldsworthy Desalter
Capacity
(gpm)
TDH
(psi)
Motor
Size
(hp)
2,200
100
200
ID1
Treatment
Equipment
1
Well pump
Pump Type
Vertical
turbine
2
Sulfuric acid
pump
Hydraulic
diaphragm
0.18
60
0.5
SCR2 w/ tach
feedback
3
Threshold
inhibitor pump
Hydraulic
diaphragm
0.05
60
0.5
SCR w/ tach
feedback
High pressure
RO feed pump
Decarbonator
motor
Sodium
hydroxide
pump
Sodium
hypochlorite
pump
Vertical
turbine
1,970
275
450
n.a.3
3,120
n.a.
7.5
Hydraulic
diaphragm
0.12
40
0.5
SCR w/ tach
feedback
Hydraulic
diaphragm
0.18
45
0.5
SCR w/ tach
feedback
Ammonia feed
pump
Hydraulic
diaphragm
0.05
45
0.5
SCR w/ tach
feedback
Vertical
turbine
1,700
101
150
Variable
speed
Horizontal
centrifugal
1,680
60
100
Constant
speed
One duty
n.a.
n.a.
n.a.
175
kW
n.a.
Two duty
Diaphragm
0.33
60
0.5
Constant
speed
One duty
4
5
6
7
8
9
10
11
12
Product
forwarding
pumps
CIP
recirculating
pump4
Immersion
heater4
Caustic dose
pump
Notes:
1. ID refers to equipment label on Error! Reference source not found..
2. SCR = Silicon controlled rectifier
3. n.a. = not applicable
4. Equipment used only during membrane CIP.
214
©2008 AwwaRF. ALL RIGHTS RESERVED
Drive
System
Constant
speed
Variable
speed
Constant
speed
Comment
One duty
One duty,
one
standby
One duty,
one
standby
One duty
One duty
One duty,
one
standby
One duty,
one
standby
One duty,
one
standby
One duty,
one
standby
Seward, Nebraska Corrosion Control Plant
List Of Major Electrical Equipment
Treatment Equipment
Groundwater Wells
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Groundwater Pump
Reverse Osmosis System
Feed Pump for RO Train A
Feed Pump for RO Train B
Degasifier
Degasifier Fan
Ancillary Reverse Osmosis Systems
Cleaning Pump
Cleaning Pump
Cleaning Tank Heater
Chemical Feed Systems
Scale Inhibitor Drum Transfer Pump
Scale Inhibitor Metering Pump 1
Scale Inhibitor Metering Pump 2
Onsite Hypochlorite Generator
Caustic Soda Metering Pump 1
Caustic Soda Metering Pump 2
Hypochlorite Metering Pump 1
Hypochlorite Metering Pump 2
High Service Pumping
Base Demand High Service Pump
High Demand High Service Pump
High Demand High Service Pump
Pump ID
VFD?
S-01
S-02
S-03
SW-01
SW-02
W-07
W-09
W-11
W-10
Motor
Size (hp)
Comment
40
40
30
50
50
40
40
40
40
10FP-1
10FP-2
VFD
VFD
50
50
15DG-1
15
20CP-1
20CP-2
20T-1
30
30
15 kW
Infrequently used.
25DTP-1
25MP-1
25MP-2
<5
<5
<5
Motor too small for
analysis.
35MP-1
35MP-2
45MP-1
45MP-2
<5
<5
<5
<5
PP-1
PP-2
PP-3
100
200
200
215
©2008 AwwaRF. ALL RIGHTS RESERVED
No data available.
Motor too small for
analysis.
Motor too small for
analysis.
City of Pooler, Georgia Wastewater treatment plant
List of Major Electrical Equipment
Treatment Equipment
Raw Water Pumping
Pump ID
VFD
Motor
Size (hp)
Comment
Outside of plant, not
included in analysis
Low Lift Pumps
Biological Treatment
Anoxic Mixer 1
MX-74A-1
4
Anoxic Mixer 2
MX-74A-2
4
Anoxic Mixer 3
MX-74B-1
4
Anoxic Mixer 4
MX-74B-2
4
Supplement Aeration Blowers 1
B-87A
Yes
100
Supplement Aeration Blowers 2
B-87B
Yes
100
Supplement Aeration Blowers 3
B-87C
Yes
100
Primary Membrane System
Membrane Air Scour Blower 1
Membrane Air Scour Blower 2
Membrane Air Scour Blower 3
Membrane Air Scour Blower 4
Membrane Air Scour Blower 5
Primary Permeate Pump 1
Primary Permeate Pump 2
Primary Permeate Pump 3
Primary Permeate Pump 4
Recirculation Pump 1
Recirculation Pump 2
Recirculation Pump 3
Recirculation Pump 4
Air Compressor 1
Air Compressor 2
B-85A
B-85B
B-85C
B-85D
B-85A
P-35-1
P-35-2
P-35-3
P-35-4
P-34-1
P-34-2
P-34-3
P-34-4
AC-91A
AC-91B
60
60
60
60
60
30
30
30
30
40
40
40
40
7.5
7.5
Staging Tank Recirculation Pump
P-81
3
216
©2008 AwwaRF. ALL RIGHTS RESERVED
Two mixer per biological
train.
2 duty + 1 standby, All piped
to provide aeration to both
biological trains.
Typically one operational.
3 duty + 2 standby, All piped
to provide aeration to both
membrane subtrains.
All duty, one pump with
each membrane tank
All duty, one pump with
each membrane tank.
1 duty + 1 standby
Not operational during the
study period.
VPSA Unit Oxygen Production and Specific Energy Values
Nov
2005
Parameter
Units
Days in the
days
30
Evaluation
Total Ozone
lb
75,801
Production
Average Ozone
Lb/day
2,527
Production
Average Oxygen
lb/day
75,580
Production
Total Raw Water
MG
9,133
Flow
Average Water
MGD
304
Flow
Average Ozone
mg/L
1.03
Dose
Disinfection CT mg-min/L 4.21
value
Water
C
15.5
Temperature
Generator 1
Generator 2
Generator 3
Generator 4
Generator 5
Total Generator
Ozone
Concentration
Generator
Specific Energy
VPSA 1
VPSA 2
Total VPSA
VPSA Specific
Energy
VPSA Specific
Energy
Generator Plus
VPSA
Generator +
VPSA Specific
Energy
Total
kWh
Total
kWh
Total
kWh
Total
kWh
Total
kWh
Total
kWh
%wt
kWh/lbO3
Dec
2005
31
Jan
2006
31
Feb
2006
28
Mar
2006
31
Apr
2006
30
May
2006
31
Jun
2006
30
Jul
2006
31
Aug
2006
31
Sep
2006
24
67,756 76,781
69,221
82,412 91,597 115,410 106,900 98,896 92,819 78,872
2,186
2,477
2,472
2,658
75,900 75,874
75,977
72,417 78,831 76,239 76,141 74,260 77,081 85,216
6,975
7,523
6,891
8,129
9,147
225
243
246
262
305
388
375
350
345
375
1.16
1.22
1.21
1.22
1.20
1.15
1.14
1.10
1.07
1.05
4.02
4.71
5.21
5.67
4.44
4.03
4.05
3.77
3.63
3.46
15.7
14.6
13.8
13.6
13.1
13.2
13.5
13.9
14.0
14.1
3,053
3,723
3,563
3,190
2,994
12,027 11,251 10,858 10,696
3,286
8,999
Ozone Generator Energy Consumption
Not
44,820 58,206 47,642 69,652 71,054 83,050 126,988 69,706 94,015 32,635
available
86,122 53,428 45,729 58,606 50,642 58,807 22,165 90,155 145,402 46,957 32,291
57,092
46,731 32,212
40,257
Not
51,974 68,888 44,877 46,107 88,860 57,905 55,503
available
39,891 40,723 58,094 60,099 46,483 97,375 25,473 12,504 32,012 96,057
69,478
52,504 84,083
59,614
41,546 64,367 137,671 68,976 14,084 81,524 47,807
252,949 237,373 260,955 223,957 273,912 309,599 385,139 357,699 330,555 312,413 264,293
3.34
2.88
3.26
3.25
3.67
3.87
4.88
4.68
4.30
3.88
3.86
3.34
3.50
3.40
3.24
3.32
3.38
3.34
3.35
3.34
3.37
3.35
VPSA
Total 200,402 98,650 205,921 84,981 252,921 113,310 93,015 253,693 178,752 132,791 172,776
kWh
Total 102,354 219,539 108,561 192,583 50,293 198,646 221,064 59,638 140,857 184,931 105,957
kWh
Total 302,756 318,189 314,483 277,564 303,214 311,956 314,079 313,331 319,609 317,722 278,733
kWh
kWh/lbO3 3.99
4.70
4.10
4.01
3.68
3.41
2.72
2.93
3.23
3.42
3.53
kWh/lbO2
0.134
0.135
0.134
0.130
0.135
0.132
0.133
0.137
0.139
0.133
0.136
Generator Plus VPSA
Total 555,706 555,562 575,437 501,521 577,127 621,555 699,218 671,030 650,165 630,135 543,026
kWh
kWh/lbO3 7.33
8.20
7.49
7.25
7.00
6.79
6.06
6.28
6.57
6.79
6.88
(Continued)
217
©2008 AwwaRF. ALL RIGHTS RESERVED
VPSA (Continued)
Parameter
Total Ozone
Production
Average Ozone
Production
Average Water
Flow Rate
Average Gen &
VPSA Energy
Units
Nov
2005
lb
75,801
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
2005
2006
2006
2006
2006
2006
2006
2006
2006
2006
Ozone System Unit Energy Consumption
67,756 76,781 69,221 82,412 91,597 115,410 106,900 98,896 92,819 78,872
lb/day
2,527
2,186
2,477
2,472
2,658
3,053
3,723
3,563
3,190
2,994
3,286
MGD
304
225
243
246
262
305
388
375
350
345
375
kWh/day 18,524
17,921 18,562
17,911
18,617 20,719 22,555 22,368 20,973 20,327 22,626
218
©2008 AwwaRF. ALL RIGHTS RESERVED
Arizona-American Water Company
Anthem Water Campus (WTP)
List of Major Electrical Equipment
Equipment
CAP Pump Station
CAP Water Pump
CAP Water Pump
CAP Water Pump
CAP Water Pump
Air Compressor
Raw Water Pump Station
Raw Water Pump 1
Raw Water Pump 2
Raw Water Pump 3
Raw Water Pump 4
Membrane System
Permeate Pump
Permeate Pump
Permeate Pump
Permeate Pump
Permeate Pump (Spare)
Reject Pump
Reject Pump
Reject Pump
Reject Pump
Reject Pump
Reject Pump
Reject Pump
Reject Pump
Scour Air Blower
Scour Air Blower
Scour Air Blower
Air Compressor
Air Compressor
Air Dryer
Air Dryer
Vacuum Pumps
Vacuum Pumps
Vacuum Pumps
Vacuum Pumps
Backpulse Pump
Backpulse Pump
CIP Pump
CIP Pump
Finished Water
Pump Station 1
Zone 1 Pump
Zone 2 Pump
Zone 2 Pump (spare)
VFD?
I.D
hp
Yes
Yes
Yes
Yes
CAP1
CAP2
CAP3
CAP4
300
300
200
200
5
Yes
Yes
Yes
Yes
P-1010
P-1020
P-1030
P-1040
Yes
Yes
Yes
Yes
Yes
P-35-1
P-35-2
P-35-3
P-35-4
P-35-5
P-38-1A
P-38-1B
P-38-2A
P-38-2B
P-38-3A
P-38-3B
P-38-4A
P-38-4B
BWR-85-1
BWR-85-2
BWR-85-3
M-95-1
M-95-2
Yes
Yes
Yes
Yes
Yes
Power Source
Load Center
50
50
40
40
MCC-1
MCC-1
SWBD-1
SWBD-1
SES-1
SES-1
SES-1
SES-1
P-92-1
P-92-2
P-92-3
P-92-4
P-88-1
P-88-2
P-35-1
P-35-2
60
60
50
50
50
3
3
3
3
3
3
3
3
50
50
50
15
15
15
15
3
3
3
3
30
30
15
15
MCC1-2
MCC1-2
MCC1-3
MCC1-3
MCC1-3
MCC1-1
MCC1-1
MCC1-2
MCC1-2
MCC1-3
MCC1-3
MCC1-3
MCC1-3
MCC1-2
MCC1-2
MCC1-3
MCC1-2
MCC1-2
MCC1-2
MCC1-2
MCC1-2
MCC1-2
MCC1-3
MCC1-3
SWBD-1
SWBD-1
MCC1-2
MCC1-2
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
SES-1
P-1910
P-1920
P-1930
150
450
450
SWBD-1
SWBD-1
SWBD-1
SES-1
SES-1
SES-1
(Continued)
219
©2008 AwwaRF. ALL RIGHTS RESERVED
Arizona American (Continued)
Pump Station 2
Zone 1 Pump
Zone 1 Pump
Zone 2 Pump
Zone 2 Pump
Yes
Yes
Yes
Yes
P-1940
P-1950
P-1960
P-1970
150
150
350
350
220
©2008 AwwaRF. ALL RIGHTS RESERVED
SWBD-1
SWBD-2
SWBD-1
SWBD-2
SES-1
SES-2
SES-1
SES-2
REFERENCES
Arizona American Water Company. 2003. Anthem Water Campus O&M Manuals. ArizonaAmerican Water Company Internal Report.
Arora, H.; M.W. LeChevallier. 1998. Energy management opportunities Journal of the
American Water Works Association; Vol. 90; Issue: 2; PBD: Feb 1998.
California Energy Commission. 1999. Water and wastewater technology demonstration
projects. California Energy Commission.
CDM, Inc. 2003. West Basin Water Recycling Facility Phase III Preliminary Design Report.
West Basin Municipal Water District Internal Report.
Crozes, G.; D. Hugaboom, V. Roquebert, S. Sethi. Selecting the right membrane for the right
application by taking advantage of recent trends in the industry. Water Quality
Technology Conference: Stewardship of Drinking Water Quality; Philadelphia, PA;
USA; 2-6 Nov. 2003.
Damon S. Williams and Associates. 2001. Anthem Water Campus Water Treatment Plant
Buildout Expansion Basis of Design Report. Arizona-American Water Company Internal
Report.
DeMers, L. D.; K. L. Rakness, and B. D. Blank. 1996. Ozone system energy optimization
handbook. AwwaRF: Denver CO.
Energy Policy Act. 1992. Energy Policy Act of 1992. Pub L. 102-486, 106 Stat. 2776.
EPRI (Electric Power Research Institute). 1994. UV system plant survey.
EPRI. 1997. Quality Energy Efficiency Retrofits for Water Systems: A Guide to Implementing
Energy Efficiency Upgrades in Water Supply Facilities (2). Report CR-107838. Palo
Alto, California: EPRI.
EPRI. 1998. Quality Energy Efficiency Retrofits for Wastewater Systems. Report CR-109081,
Palo Alto, Calif.: EPRI.
EPRI. 1999. A Total Energy and Water Quality Management System. Report TR-113528, Palo
Alto, Calif.: EPRI.
EPRI. 2001. Summary Report for California Energy Commission Energy Efficiency Studies,
Report WO-6710, Palo Alto, Calif.: EPRI.
EPRI. 2002. Water and Sustainability (Volume 4): U.S. Electricity Consumption for Water
Supply and Treatment – The Next Half Century. EPRI Report #000000000001006787,
Palo Alto, Calif.: EPRI.
Jacangelo, J.G.; N.L. Patania, J.-M. Laîne, W. Booe, and J. Mallevialle. 1992. Low Pressure
Membrane Filtration for Particle Removal, AWWA Research Foundation, Denver,
Colorado.
Job, G.D.; R. Trengove, and G.J. Realey. 1995. Trials using a mobile ultraviolet disinfection
system in South West Water, J. CIWEM, Vol. 9, No. 6, pp. 257-263.
Mackey, E. D., R. S. Cushing, and G. F. Crozes. 2001. Practical aspects of UV disinfection.
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Means III, E. 2003. Water and Wastewater Industry Energy Efficiency: A Research Roadmap.
Denver, Colo.: AwwaRF and the California Energy Commission.
NEMA (National Electric Manufacturers Association). 2006. NEMA Standards MG 1-2006:
Motors and Generators. Rosslyn, Va.: NACE. Approved 2006.
Nerenberg, R., Rittmann, B. E., and Soucie, W. J. 2000. Ozone/biofiltration for removing MIB
and geosmin. Journal American Water Works Association, Vol. 92 No. 12: pp 85.
221
©2008 AwwaRF. ALL RIGHTS RESERVED
Nieuwstad, T.J., A.H. Havelaar, and M. van Olphen. 1991. Hydraulic and Microbiological
Characterization of Reactors for Ultraviolet Disinfection of Secondary Wastewater
Effluent. Water Research 25(7): 775-783.
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of ultraviolet (UV) radiation disinfection technologies for wastewater treatment plant
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Foundation, Report CR-110229, February 1998.
Rakness, K.L. and G.F. Hunter. 2000. Advancing Ozone Optimization During Pre-Design,
Design and Operation, EPRI, Palo Alto, California and AWWA Research Foundation,
Denver, Colo.
Rakness, K.L. and G.F. Hunter. 2002. “Ozone Equipment Performance Testing Experiences
and Results”, Paper presented at the International Ozone Association Conference in
Raleigh, North Carolina, May 2002.
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Reardon, David J. 1995b. Energy conservation at water and wastewater facilities: a panacea for
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478.
van Dijk, L. and G.C.G. Roweken, 1997. Membrane bioreactors for wastewater treatment: the
state-of-the art and new developments. 35 (10): 35-41.
Ventresque, C.; V. Gisclon, G. Bablon, and G. Chagneau. 2001. First year operation of the
Mery-sur-Oise membrane facility. In Proceedings of the AWWA membrane conference.
AWWA: Denver CO.
Von Gottberg, A. 1998. New high-performance spacers in eletrodialysis reversal (EDR)
systems. In Proceedings of the AWWA annual conference. AWWA: Denver CO.
222
©2008 AwwaRF. ALL RIGHTS RESERVED
West Basin Municipal Water District. 2001. Operations & Maintenance Manual: West Basin
Water Recycling Plant – Phase III Expansion. West Basin Municipal Water District
Internal Report.
West Basin Municipal Water District. 2003. West Basin Water Recycling Plant Phase IV
Expansion – Volume II: Preliminary Design Report, Part 1 of 2. West Basin Municipal
Water District Internal Report.
Zhang, S., a, b, Renze van Houtenb, Dick H. Eikelboomb, Hans Doddemab, Zhaochun Jianga,
Yaobo Fana and Jusi Wanga. 2003. Sewage treatment by a low energy membrane
bioreactor Bioresource Technology Vol 90, Issue 2, November 2003, pp. 185-192
223
©2008 AwwaRF. ALL RIGHTS RESERVED
224
©2008 AwwaRF. ALL RIGHTS RESERVED
ACRONYMS AND ABBREVIATIONS
bhp
°C
$
kW
kPa
kWh/MG
kWh/kgal
kWh/day
kWh/m3
kWh/lb O3
kWh/lb O2
ft
ft3/hr
gpm
hp
mgd
mg/L
mg-min/L
mm
μm
mJ/cm2
mW-s/cm2
nm
ppm
psi
psig
scfm
scfm/day
scfm/hour
%wt
Brake horsepower
Degrees Celsius
US dollar
Kilowatts
Kilopascals
Kilowatt hours per million gallons
Kilowatt hours per thousand gallons
Kilowatt hours per day
Kilowatt hours per cubic meter
Kilowatt hours per pound of ozone produced
Kilowatt hours per pound of oxygen produced
Feet
Cubic feet per hour
Gallons per minute
Horsepower
Million gallons per day
Milligrams per liter
Milligram-minute per liter
Millimeter
Micron
Millijoules per square centimeter
Milliwatts-seconds per square centimeter
Nanometer
Parts per million
Pounds per square inch
Pounds per square inch gauge
Standard cubic feet per minute
Standard cubic feet per minute per day
Standard cubic feet per minute per hour
Percent weight
ADEQ
AMS
AOP
APS
ATTs
AWC
AwwaRF
BAC
BLOC
BOD5
Arizona Department of Environmental Quality
Alfred Merritt Smith
Advanced Oxidation Process
Arizona Public Services
Advanced treatment technologies
Anthem Water Campus
Awwa Research Foundation
Biologically Active Carbon
Base Load Oxygen Compressor
Biological oxygen demand after five days
225
©2008 AwwaRF. ALL RIGHTS RESERVED
CAP
CIP
CLCJAWA
CT
DAF
DBPs
DC
DNA
DO
DWEER
EC
ECMs
EDR
EPRI
ERI
EWQMS
FEMP
GAC
GSE
HERO
LOX
LPBF
MBRs
MCCs
MDF
MF
MIB
MLR
MLSS
MPN
MSL
NDMA
NEMA
NOM
NPDES
NPPD
NYSERDA
PIER
PLC
PSA
PSU
RAS
RO
SCADA
SCE
SDI
Central Arizona Project
Clean-in-place
Central Lake County Joint Action Water Agency
Contact time
Dissolved air flotation
Disinfection by-products
Direct current
Deoxyribonucleic acid
Dissolved oxygen
Direct Work Exchange Energy Recovery
Energy consumption
Energy conservation measures
Electrodialysis reversal
Energy Power Research Institute
Energy Recovery Incorporated
Energy and Water Quality Management Systems
Federal Energy Management Program
Granular activated carbon
Georgia Southern Energy
High efficiency reverse osmosis
Liquid oxygen
Low-Pressure Boiler Feed
Membrane bioreactors
Master control centers
Maximum daily flowrate
Microfiltration
2-methylisoborneol
Mixed liquor return
Mixed liquor suspended solids
Most Probable Number
Mean sea level
N-nitrodoimethylamine
National Electric Manufacturers Association
Natural organic matter
National Pollutant Discharge and Elimination System
Nebraska Public Power District
New York State Energy Research and Development Authority
Public Interest Energy Research
Programmable logic controller
Pressure swing adsorption
Power supply unit
Return activated sludge
Reverse osmosis
Supervisory control and data acquisition
Southern California Edison Company
Silt dense index
226
©2008 AwwaRF. ALL RIGHTS RESERVED
SES
SES
SNWA
SWRO
TDS
TMP
TSS
UF
US
USEPA
UV
VFDs
VPSA
WAS
WBWRF
WRD
WTP
WWTP
Service entrance sections
Service entrance sections
Southern Nevada Water Authority
Seawater reverse osmosis
Total dissolved solids
Trans-membrane pressure
Total suspended solids
Ultrafiltration
United States
United States Environmental Protection Agency
Ultraviolet
Variable frequency drives
Vacuum/pressure swing adsorption
Waste activated sludge
West Basin Water Recycling Facility
Water replenishment district
Water treatment plant
Wastewater treatment plant
227
©2008 AwwaRF. ALL RIGHTS RESERVED
228
©2008 AwwaRF. ALL RIGHTS RESERVED
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