1. No category

Presented by:
Brent Bode, P.E., Tetra Tech, Inc.
Low Energy, Non Shear WAS Thickening
Alternatives and Design
for Grand Rapids, MI WWTP
PRESENTATION AGENDA
• Project Background and Goals for GR
WWTP WAS Thickening
• Preliminary Design Evaluation, Technology
Selection
• Pilot Testing and Performance Expectation
• Design Features
• Construction
City’s Clean Water Management
• Secondary Treatment with UV Disinfection
• Two Parallel Processes Referred to as North
and South Plants
• Secondary Treatment Capacity of 90 MGD
• South Secondary Upgraded in 2005
• North Secondary Upgrade Almost Complete
• Recent Improvements Include Aeration, Bio-P
removal, Clarifier Upgrades
• WAS Thickening Improvement the Next
Secondary System Upgrade
Biosolids Management Program
• Un-thickened WAS
Co-settled with
Primary
• Primary/Secondary
Pumped to Holding
Tank at GVRBA
Facility
• Combined Biosolids
to Dewatering
• Dewatered Cake to
Landfill
Grand Rapids WAS Handling History
• Existing Thickening was
done by Centrifuges
• Centrifuge Technology
from Mid-90’s
• 2 units w/ 200 hp Drives
and 40 hp Back Drives
• Abandoned Operation to
Save Energy
• Co-settled WAS in
Primary Tanks
Program Goals
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Replace Existing 200 HP Centrifuge Thickeners
Utilize Low Energy Technology
Minimize O&M Requirements
Unattended Operation
Improve Pumping Hydraulics of TWAS
Capitalize on Process Benefits for WAS
Thickening
Benefits of WAS Thickening
• Reduced Volume of Biosolids to Dewatering
• Eliminate WAS Solids Load to Primary
Treatment
• Improved Dewatering with Thicker Feed Sludge
• Reduced Polymer Use for Dewatering
• Reduce Odor Potential for Primary Treatment
• Energy Reduction for Sludge Pumping
Why No/Low Shear Technology?
• City Mandate Based on Experience
• Thickened WAS Characteristics Concern
• Better Integration with Subsequent Dewatering
Process
• Synergy with Polymer Use Between Thickening
and Dewatering
• TWAS Pumping Concerns
Existing Facility Challenges
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Compact Building Footprint
Proximity of WAS Building to Dewatering Facility
Transfer Pumping Distance for TWAS
Existing Piping System for TWAS Pumping
Transfer of Centrifuge TWAS was Difficult
Existing Transfer Pump Capability Limited
Thickened WAS Transfer Route
PRELIMINARY DESIGN
EVALUATION
Basis of Design for WAS Thickening
Improvements
Design Condition
Current Day
Design Average Day
Design Max Day
Flow (gpm)
Solids
(Dry lbs/day)
Solids
(Dry lbs/hr)
800
43,160
1,800
1,000
54,040
2,250
1,200
64,550
2,690
WAS Thickening Performance
Requirements
• Installed Capacity to
Process 1,200 GPM
• Raw WAS at 0.5%
Solids
• Thickened WAS
Range of 4% to 6%
Max
• Multiple Thickener
Units for Process
Redundancy
Design
Parameter
Design
Average
Design Max
Day
Influent WAS
Solids (0.5%)
0.5
0.5
Influent WAS
Flow (GPM)
800
1,200
Thickened
WAS Flow
(GPM)
80
150
City’s Preferred Approach
• Fit New Equipment to Existing Building
• Installed Capacity to Match Peak WAS Design
Production
• Achieve Substantial Energy Reduction for WAS
Thickening
• Improve Transfer Pumping Capability
• Minimize O&M
• Examine Technology Options for Low EnergyLow Shear
• Select Technology with Best Fit for Goals
Low Energy, Low Shear Technology
Options
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•
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•
•
Gravity Belt Thickener
Rotary Fan Press
Rotary Screen
Disk Thickener
Rotary Drum
Thickener
• Volute/Screw
Thickener
Gravity Belt Thickener
Rotary Fan Press
Rotary Screen
Disk Thickener
Rotary Drum Thickener
Volute/Screw Thickener
Workshop to Select Preferred
Technology
• City Experience and Research
• Engineering Team Experience
• Vendor Community and Site Specific
Proposals
• Developed Consensus Regarding Two(2)
Competing Technologies
• Rotary Drum (RDT) and Volute/Screw
Thickener (VT)
• Testing, Evaluation, Research Followed
Rotary Drum Technology
Standard Unit Configuration
Thickened WAS Discharge
Volute/Screw Technology
• Screw Press Type Process
• Unique Dewatering Drum Design
• Dewatering Drum Comprised of Fixed and
Moving Rings Around a Screw Conveyor
• Conveyor can Achieve Either Thickening
or Dewatering
• Introduced by PWTech to US Market in
2008
Dewatering Drum Components
• Fixed Rings Held with
Rods to Form
Cylinder
• Internal Screw
Conveyor
• Moving Rings
Between Each Fixed
Ring
• Water Drains
Between Gaps
Drum Assembly
Multiple Drum Assembly Sections
Dewatering Drum End Plate
Sludge Conditioning Configuration
2-stage flocculation tanks
– Adjustable mixing
energy
– Independent of
flow
– Visual flocculation
performance
– Adjustable VFD
driven mixers
Preventative Maintenance
• Weekly - Check unit performance
• Monthly - Inspection of motors, pumps, sensors
• For Dewatering Applications - Replace moving rings in
the dewatering section of the dewatering drum casing
every 10,000 - 15,000 hours
• For Thickener Applications- No required maintenance for
30,000 - 50,000 hours
PILOT TESTING FOR SITE
PERFORMANCE VALIDATION
Testing Considerations
• Representative WAS
Source for Testing
• Utilize RAS Active
Channel
• Secondary Influent
Channel
• Return TWAS, Filtrate
Rotary Drum Thickener Site Test
Volute/Screw Site Test
Thickener Performance Expectation
Type of Thickener
Rotary Drum
Volute Screw
400 gpm
450 gpm
1,000
1,125
4
6.6
60 gpm
30 gal/hr
Solids Capture Rate
93%
99%
Max Thickening
5%
7%
Polymer Usage
18 lbs/dry ton
18 lbs/dry ton
Unit Dimensions
6'x22'-9"
6'x13'-9"
Cost per Unit
$275,000
$280,000
Unit Capacity – Full Scale
Model
Solids Loading Rate
(lbs/hr)
Hp per Unit
Flush Water Rate
Present Worth Analysis
Cost Item
Rotary Drum
Thickener
Volute Thickener
Equipment
$ 885,000
$ 834,300
Installation
Mechanical and Electrical
(20%)
$ 32,750
$125,145
$ 203,550
$191,890
General Overhead (8%)
$ 97,700
$ 92,110
Contingencies (15%)
$ 197,850
$ 186,520
Total Capital
Total Present Worth of
Annual O&M
Total Present Worth of
Thickener
$1,517,000
$ 1,430,000
$6,200,932
$5,463,009
$7,717,932
$6,893,010
Equipment Layout
ROTARY DRUM THICKENER
LAYOUT
VOLUTE THICKENER LAYOUT
Preferred Technology Selection
• Capital Cost Similar for Competing
Technologies
• Polymer/Power Costs Similar
• No Major Maintenance Difference
• Water Consumption Big Difference
• Operational Cost Edge for Volute/Screw
• City Team Consensus for Volute Technology
Smaller Footprint, Much Lower Water Use
• Validate Choice with Site Visits
Field Visit Validation
• Journey to New York
• Three Facility
Locations
• Unattended
Operations
• Very Clean and
Reliable Performance
Observed
• Team Consensus
Validated
DESIGN
Volute/Screw Thickener Design
Basis
Parameter
Design Basis
Number of Units
3
Peak Feed Rate per Unit
450 GPM
Influent Solids Concentration
0.5%
Maximum Discharge Concentration
5.0%
Solids Loading Capacity
1,125 lbs/hr
Polymer Range
15 – 25 lbs/dry ton solids
Solids Capture Efficiency
98%
Thickened WAS Pumping Considerations
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Transfer Distance 1,500 Feet
Existing Piping System, Not Direct Line
Previously Experienced Pumping Difficulty at 5%
Increased Pump Discharge Pressure
Design Pressure to Pipe Rating of 125 PSI
5% TWAS Transfer Max, 4% Average
Rotary Lobe Pumps Selected
Polymer Feed System
• Emulsion Polymer
• Planned as Same for
Dewatering
• Dedicated Feed for
Each Thickener
• Supply/Integration by
Thickener
Manufacturer
Process Schematic
Floor Plan Layout
Section Layout Drawing
WAS Building Under Construction
Main Thickener Process
Lower Level Pump Room
New Volute/Screw Thickener Unit
Three Stage Screw Configuration, Ready to Ship
Performance of New System
• How does it perform?
• Manufacturer
Responsible for
Process Performance
• System Responsibility
for Component
Integration
Summary
• Eliminated Co-Settling WAS with Primary
• Selected Volute/Screw Thickener
Technology
• Low Energy Solution
• Low O&M
• Consistent Thickened Product
• Process Will Provide Return on
Investment
Questions?