Low Energy, Non-Shear WAS Thickening for Grand Rapids, MI WWTP · Low Energy, Non Shear WAS...
Transcript of Low Energy, Non-Shear WAS Thickening for Grand Rapids, MI WWTP · Low Energy, Non Shear WAS...
Low Energy, Non Shear WAS Thickening
Alternatives and Design
for Grand Rapids, MI WWTP
Presented by:
Brent Bode, P.E., Tetra Tech, Inc.
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
• 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
• 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 Flow (gpm)
Solids (Dry lbs/day)
Solids (Dry lbs/hr)
Current Day 800 43,160 1,800
Design Average Day 1,000 54,040 2,250
Design Max Day 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 Energy-Low Shear
• Select Technology with Best Fit for Goals
Low Energy, Low Shear Technology
Options
• 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
– Adjustable mixing
energy
– Independent of flow
– Visual flocculation performance
– Adjustable VFD driven mixers
2-stage flocculation tanks
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
Unit Capacity – Full Scale Model
400 gpm 450 gpm
Solids Loading Rate (lbs/hr)
1,000 1,125
Hp per Unit 4 6.6
Flush Water Rate 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
Present Worth Analysis
Cost Item Rotary Drum Thickener
Volute Thickener
Equipment $ 885,000 $ 834,300
Installation $ 32,750 $125,145 Mechanical and Electrical
(20%) $ 203,550 $191,890
General Overhead (8%) $ 97,700 $ 92,110
Contingencies (15%) $ 197,850 $ 186,520
Total Capital $1,517,000 $ 1,430,000 Total Present Worth of
Annual O&M $6,200,932 $5,463,009 Total Present Worth of
Thickener $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
• 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?