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Is reverse osmosis water treatment really worth the expense?
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Introduction to UC Davis
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UC Davis Boiler Plant & Steam System

Reverse Osmosis Technology

Project Description

Project Benefits
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Opened in 1909 as University of CA Farm School

Ranked 8th greenest college in the US by Sierra Club

32,000 students, 33,000 employees

5,300 acres (largest of UC campuses)

Over 950 buildings
Building Age
Under 25 yrs
25 to 50 yrs
Over 50 yrs
Percentage
40%
42%
18%

Over 23 mi of underground
steam & condensate piping
serving 90 buildings

Served by 4 steam boilers
at the Central Heating and
Cooling Plant
Boiler
No.
Boiler Make & Type
Year
Installed
Primary
Fuel
NOx Level
(ppm)
Capacity
(lb/hr)
1
Babcock & Wilcox water-tube
1967
Nat Gas
<30
100,000
2
Babcock & Wilcox water-tube
1967
Nat Gas
<30
100,000
3
English water-tube
2000
Nat Gas
<30
75,000
4
Rentech water-tube
2009
Nat Gas
<5
150,000
TOTAL MAIN CAMPUS STEAM PRODUCTION CAPACITY (lb/hr)
400,000*
*Maximum capacity determined by 400,000 lb/hr deaerator tank, boiler design operating pressure is 150 psig

2009: Steam Plant Expansion
project replaced an aging
dealkalizer/ softener system with
RO system

Change prompted by new wastewater limits for EC
(Electrical Conductivity) in discharge

Installed two RO units, each sized for 90 GPM and
70% recovery

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Campus Wastewater Treatment Plant constructed in 2000.
Tertiary treatment process meets strict limits for
conventional pollutants, bacteria, and metals, but does not
reduce salts.
State Water Quality Control Board, concerned about
potential impacts to agriculture and domestic water
supplies, added new Electrical Conductivity (EC) limit.
Campus didn’t agree with the underlying science or basis
for limit, but committed to actions that would reduce salt
discharges to comply with EC limits.
If this failed, campus would have been compelled to pursue
other water supply options.

Amount of salt present in a liter of water:
http://www.waterontheweb.org/under/waterquality/conductivity.html
10
97
92
110
316
850
43k
158k
Electrical Conductivity of Sources Above (μS/cm)

http://en.wikipedia.org/wiki/File:Water_salinity_diagram.png
Our source water quality:
Davis Well Water
Typical Value
Conductivity (μS/cm)
550
Silica Content (ppm)
30
Hardness (ppm)
100
Alkalinity (ppm)
220
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Pre-RO System - One Month’s Supply of Salt for
the Plant (33,000 lbs):
Images courtesy of FILMTEC Membranes by Dow Water Solutions

RO is a type of filtration
but there is a waste
stream (concentrate)
that carries away the
contaminants
Images courtesy of FILMTEC Membranes by Dow Water Solutions
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Siemens M280 Series
Highlights:
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25 – 150 GPM of high-purity
water
Membrane salt rejection 99%
nominal
Up to 98% of dissolved
inorganics
Over 95% of total dissolved
organics
All colloidal and suspended
matter >0.05 micron
Fully automatic

Unit Cost:
 $54,000

Installation Cost:
 $20,000 (including design, electrical, controls
integration, and start-up)

Total Initial Cost:
 ($54,000 + $20,000) * 2 units = $148,000

Pre-treatment Chemistry
 Chlorine Reduction
▪ Bisulfite (Sodium Metabisulfite)
 Dispersant/anti-scalant
▪ High-performance polymeric additives and sequestrates
which inhibit silica scales, carbonate scales, and
disperse colloidal particles at threshold levels


Daily Sampling and Data Logging/Trending
Membrane Maintenance/Replacement
 Approximately $3k/year for our system

EC Reduction in Plant Discharge Water

Make-up Water Reduction Results in
Significant Cost Savings:
 Water Cost Savings
 Treatment Cost Savings
 Fuel Cost Savings

Total EC reduction of 13% at WWTP influent
after installing the RO system
WWTP Influent Conductivity
1400
1350
1300
1250
µS/cm
1200
1150
1100
1050
2007
2008
2009

Higher Purity Water Means Higher Cycles
(Less Blowdown)

Less Blowdown = Less Makeup Water

Makeup Water Savings Drive Other Savings
Condensate
Makeup
Feedwater
Steam
Header
Boiler Water
Blowdown
DEAERATOR TANK
BOILER
Condensate
System Losses
CONDENSATE TANK
Steam
Distribution
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Less Blowdown = Less Makeup Water
 Makeup Water Savings Outweigh Concentrate (Reject)
Water Losses
Comparison
Blowdown
%
Before RO
20%
With RO System
2%
MU Water
Savings
(lb/hr)
RO System
Reject Rate
(lb/hr)
Annual Water
Cost Savings
($/year)
Baseline
17,137
3,672
$66,190
Annual avg boiler steam prod. rate of 75k lb/hr, 9% steam system losses, water rate of $1.00/CCF & sewer rate of $2.50/CCF
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Less Blowdown = Less Makeup Water
 Reduced Alkalinity Requires Less Amines

Less Blowdown = Less Chemicals Going Down Drain
 O2 Scavenger, Corrosion & Scale Inhibitors Costs Drop
Comparison
Blowdown %
Before RO
20%
With RO System
2%
Makeup Water
Savings (lb/hr)
Annual Treatment
Cost Savings
Baseline
17,137
$102,126
Annual average boiler steam production rate of 75k lb/hr, water treatment rate reduced from approx $0.25/klb stm to
$0.08/klb stm, annual savings include cost of RO membrane cleaning/replacement
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Less Blowdown = Less Makeup Water

Less Makeup Water = Less Heating Energy
 OR Less Blowdown = Less Energy Going Down the Drain
 RO System Pump Power Becomes Insignificant
Comparison
Blowdown
%
Before RO
20%
With RO System
2%
MU Water RO Pump Power
Savings
Consumption
(lb/hr)
($/year)
Annual Fuel
Cost Savings
($/year)
Baseline
17,137
$726
$396,692
Annual average boiler steam production rate of 75k lb/hr, gas rate of $0.70/therm, and elec rate of $0.10/kWh
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Total Annual Potential Savings Summary

Reject Water and Pump Power Losses – insignificant at high cycles
Comparison
Blowdown
%
Before RO
20%
With RO System
2%
MU Water
Savings
(lb/hr)
Total Annual
Savings
($/year)
Annual GHG
Savings
(tons CO2/year)
Baseline
17,137
$564,283
2,834
Annual average boiler steam production rate of 75k lb/hr, GHG conversion of 0.005 metric tons CO2/therm of natural gas
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Cost savings dependent on current boiler cycles:
Blowdown Level
MU Water
Estimated Total
Reduction
Savings (lb/hr) Savings ($/yr)
Simple Payback
(Years)
20% to 2%
17,000
$565,000
0.25
15% to 2%
11,700
$375,000
0.4
10% to 2%
6,800
$208,000
0.75
Assuming boiler annual average steam production rate of 75,000 lb/hr,
steam system losses of 10%, costs of $0.10/kWh Elect, $0.70/therm NG,
$1/CCF Water, $2.50/CCF Sewer
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Condensing Economizer Boiler Flue Gas Heat
Recovery Project