Water Residuals Management

October 2014

Presented byMichael F. Graves, PE – CP&Y

Co-AuthorsLarry L. Hare, PE – Oklahoma City

J. Dustin Segraves – Oklahoma City

• Project Background• Thickening and Dewatering• Hefner WTP Evaluation

– Develop Your Goals– Know Your Residuals– Review Your Process– Consider Operating Options

Discussion Topics

Hefner WTP Residuals Study

Hefner WTP Residuals Study

• Hefner WTP located in Oklahoma City• Currently rated for 100 MGD• Future expansion to 200 MGD• Lime Softening Process

Hefner Residual Handling Layout

• Five Clarifiers• Pump Station • Two backwash ponds• Five Sludge Lagoons

• Gravity Thickeners;– Smaller Circular Concrete Tanks– Mechanical Rake Mechanism– Overflow Weirs– Thickened Sludge Trench

Gravity Thickening

• Gravity Belt Thickeners;– Polymer added before process– Conditioned sludge moves on belt– Water drains through the belt– Thickened sludge discharged at end

Gravity Belt Thickeners

• Belt Filter Presses– Polymer added to condition sludge– Sludge moves across a series of belts– Rollers increase pressure– Water drains through belt– Sludge is discharged at end of belt

Mechanical Dewatering

• Centrifuge– Polymer Added to condition sludge– Sludge is added to high speed scroll– Bowl and Scroll offer high differential Speed– Water flows through openings in bowl– Sludge is discharged at the end

Mechanical Dewatering

• 100% mechanical dewatering during all treatment conditions up to 200 MGD

• High level of redundancy• Recovery Pump Station: 15-20% recycle at 150 MGD• Sludge Pump Station: Dry pit to reduce maintenance

Project Design Goals

Mass Balance – Lime Usage

Mass Balance – Hardness Removal

Mass Balance – Solids Production

Raw/recovery water solids: 24,236 lb/d (5.6%)Ferric precipitates: 7,074 lb/d (1.6%)Lime precipitates: 400,628 lb/d (92.8%) PredominatedTotal solids: 431 938 lb/d

Review Process Changes• Based on Historical Chemical Usage

• Impact of PolymerParameter Unit Capacity

75 mgd 100 mgd 150 mgd 200 mgdSolids Handling Capacity (Optimized Lime Dose)

lb/d dry solids

140,000 190,000 280,000 370,000

Wet Solids Volume (4% Solids Content)Solids Handling mgd 0.4 0.6 0.8 1.1

Parameter Unit Capacity75 mgd 100 mgd 150 mgd 200 mgd

Solids Handling Capacity (Historical Lime Dose)

lb/d dry solids

215,000 287,000 430,000 575,000

Wet Solids Volume (1% Solids Content)Solids Handling mgd 2.5 3.5 5 7

Consider Constructibility

Solids Pump Station

Force Main

Solids Handling Facility Site

Proposed Process

Clarifiers Flow / Solids Meters Solids Pump Station

ThickenersBalancing Tanks

Mechanical Dewatering

Solids Storage Hauling and Disposal

Consider How You Want to Load the TrucksDirect Loading Advantages Stacking Pad Advantages

Minimize stacking of product. Allows for Operational Flexibility. More storageavailable.

Reduces storage of the product on-site. Single story building.

Eliminates handling the product multiple times.

Less dependent on truck hauling schedules.

Small Footprint

Belt Filter Press 24/7 with Stacking Pad

Centrifuge 24/7 with Direct Loading

1. Base Scenario2. High Lime - Historical Lime Dosages

– 190 mg/L of Lime– Mechanical Dewatering to 200 MGD

3. Low Lime – Considers Polymer Usage– 110 mg/L of Lime– Mechanical Dewatering to 200 MGD

4. Hybrid – Partial Use of Lagoons to Save Capital– 110 mg/L of Lime– Partial Mechanical Dewatering to 80 MGD. – Over 80 MGD, solids flow to lagoons.

Scenarios

Base Scenario

ItemOperation with Polymer

(Lime Dosage = 110 mg/L)Operation without Polymer(Lime Dosage = 190 mg/L)

Capital Cost $14,570,000 $14,570,00030-year

Dewatering, Hauling, and

Disposal

$118,090,000 $136,480,000

Total 30-Year Cumulative Value

$132,660,000 $151,050,000

30-Year Net Present Value

$72,900,000 $82,200,000

Base Scenario Costs

Mechanical Dewatering ScenariosItem Scenario 1 - High Lime Scenario 2 – Low Lime

Capital Cost $27,670,000 $23,390,000Maintenance Costs $5,020,000 $4,280,000

Operations Cost $52,820,000 $49,320,000Hauling, and Disposal $30,330,000 $26,250,000

Total 30-Year Cumulative Value $115,840,000 $103,240,00030-Year Net Present Value $70,000,000 $61,800,000

ItemHybrid – Partial

Mechanical DewateringCapital Cost $12,030,000

Maintenance Costs $5,320,000Operations Cost $47,900,000

Hauling, and Disposal $36,700,000Total 30-Year Cumulative Value $101,950,000

30-Year Net Present Value $56,400,000

• Consider the entire plant treatment process in evaluating residuals

• Design Goals - The cheapest solution may not be the best for a utility

Take Aways

Questions & Answers