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?