water residuals management - weat

Water Residuals Management

May 8, 2014

Presented by;

Michael Graves, P.E.

• Comparison of Wastewater & Water Residuals

• Residuals Management Basics

• Hefner WTP Evaluation

– Develop Your Goals

– Know Your Residuals

– Review Your Process

– Consider Operating Options

Discussion Topics

History of Residuals Management

Increasing Complexity over Time

Water Treatment Residuals Wastewater Sludge

1980s 2014

Time

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1980s 2014

Time

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Sources of Residuals

Identified Sources

Water Treatment Residuals Wastewater Sludge

• Bulk Screenings

• Inorganic Particulate (Grit )

• Primary Sludge

• WAS Activated Sludge

• Combined Primary & WAS

• Bulk Screenings

• Pre-Sed Sediment

• Chemical Sludge

• Filter Backwash

Municipal WTP

Municipal WWTP

Characteristics of Residuals

Characteristics

Water Treatment Residuals Wastewater Sludge

• Bulk Screenings / (Grit)

•Inorganic Solids

• Primary Sludge

•Inorganic / Organic Solids

• WAS Activated Sludge

•Organic / Volatile Solids

• Pre-Sed Sediment

• Inorganic Particulates

• Chemical Sludge

• Coagulated Colloids

• Filter Backwash

• Sheared Chemical Flocs

Municipal WTP

Municipal WWTP

Fate of Residuals

Typical Disposal Options

Water Treatment Residuals Wastewater Sludge

• Bulk Screenings / (Grit);

• Typically Landfilled

• Primary Sludge;

• Inorganic / Organic Solids

• Further Stabilization

• Landfilled

• Energy Recovery

• WAS Activated Sludge;

• Further Stabilized

• Landfilled

• Beneficially Reused

• Energy Recovery

• Incinerated

• Pre-Sed. Sediment;

• Landfilled

• Land Application

• Chemical Sludge;

• Landfilled

• Land Application

• Building Materials

• AgLime

• Filter Backwash;

• Recovered Water Ponds

• Land Fill Solids

• Land Application

Residual Management Operations

Typical Disposal Options

Water Treatment Residuals Wastewater Sludge

• Thickening;

• Gravity Thickening

• Mechanical Thickening

• Sludge Stabilization;

• Aerated Digestion

• Anaerobic Digestion

• Dewatering

• Evaporation

• Mechanical Dewatering

• Disposal

• Thickening;

• Gravity Thickening

• Mechanical Thickening

• Dewatering;

• Gravity / Evaporation

• Mechanical Dewatering

• Disposal

• Thickening;

– Gravity Thickening

– Mechanical Thickening

• Dewatering;

– Gravity & Evaporation

– Mechanical Dewatering

Water vs. Wastewater Residuals

• Stabilization;

– Digestion

– Energy Recovery

• Disposal;

– Regulated Landfilling

– Regulated Land Application

– Incineration

• Regulatory Constraints

Difference in Residuals Properties

Differences in Residuals

Water Treatment Residuals Wastewater Sludge

• Primary Sludge;

• Water held within floc

•Biological Sludge;

•Water Held Inside Floc

•Water held inside Cells

•Harder to remove water

• Sediment;

• Water drains by gravity

• Chemical Sludge;

• Water Held within floc

• Gravity Thickening;

– Thickening in Sedimentation Basin

– Gravity Thickeners

Thickening Water Treatment Residuals

• Mechanical Thickening

– Gravity Belt Thickeners

– Rotary Drum Thickeners

Sedimentation Basin

Gravity Thickener

• Belt Filter Presses

• Centrifuges

Mechanical Dewatering

Hefner WTP Residuals Study

• 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

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%) Predominated

Total solids: 431,938 lb/d

Review Process Changes

• Based on Historical Chemical Usage

• Impact of Polymer

Parameter Unit Capacity

75 mgd 100 mgd 150 mgd 200 mgd

Solids 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 Capacity

75 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

Thickeners Balancing

Tanks Mechanical Dewatering

Solids Storage Hauling and Disposal

Consider How You Want to Load the Trucks

Direct Loading Advantages Stacking Pad Advantages

Minimize stacking of product. Allows for Operational Flexibility. More storage available.

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 Scenario

2. 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

Item Operation with Polymer

(Lime Dosage = 110 mg/L)

Operation without Polymer

(Lime Dosage = 190 mg/L)

Capital Cost $14,570,000 $14,570,000

Annual Dewatering,

Hauling, and

Disposal

$2,920,000 $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 Scenarios

Item Scenario 1 - High Lime Scenario 2 – Low Lime

Capital Cost $27,670,000 $23,390,000

Maintenance Costs $5,020,000 $4,280,000

Operations Cost $52,820,000 $49,320,000

Hauling, and Disposal $30,330,000 $26,250,000

Total 30-Year Cumulative Value $115,840,000 $103,240,000

30-Year Net Present Value $70,000,000 $61,800,000

Item Hybrid – Partial

Mechanical Dewatering

Capital Cost $12,030,000

Maintenance Costs $5,320,000

Operations Cost $47,900,000

Hauling, and Disposal $36,700,000

Total 30-Year Cumulative Value $101,950,000

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

• Dewatering water and wastewater solids is similar

but different

• Consider the entire process in making changes

• Design Goals - The cheapest solution may not be the

best for a utility

Take Aways

Questions & Answers