Clarifier Design: WEF Manual of Practice No. FD-8

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ISBN: 9780071464161 | 0071464166
Cover: Hardcover
Copyright: 11/16/2005

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Clarification is the final step in wastewater treatment. Once the water has been thoroughly cleansed, clarifiers remove both any remaining pollutants and the chemicals added by the treatment process (such as chlorine), so water can be safely released back into the local environment.

Preface

xxxix

Introduction

Approach

(2)

Traditional and Vendor Approaches

(1)

A Word about Thickening

(1)

Chapter Descriptions

(1)

References

(3)

Primary Clarifier Design Concepts and Considerations

Introduction

(2)

Performance

(13)

Process Objective

(1)

Factors Affecting Performance

(6)

Case Studies

(6)

Chemically Enhanced Primary Treatment

(6)

Design Concepts and Considerations

(10)

Wastewater Characterization

(1)

Configuration and Depth

(3)

Flow Splitting

(1)

Inlet Design

(1)

Sludge Collection and Withdrawal

(1)

Scum Collection and Withdrawal

(1)

Effluent Discharge

(1)

Research Needs

(1)

References

(4)

High-Rate and Wet Weather Clarifier Design Concepts and Considerations

Introduction

(9)

Background

(1)

Current Practice

(1)

Regulatory Considerations

(1)

Role of Clarification

(3)

Role of Storage

(1)

Methodology

(3)

Basics---The Science of Design

(17)

Wastewater Characteristics

(1)

First Flush

(2)

Settling Velocities

(2)

Measurement of Settling Velocity

(2)

Estimation of Settling Theory

(1)

Coagulation/Flocculation

(3)

Plates and Tubes (Lamella®)

(3)

Example 3.1

(2)

Changes in Suspended Solids Concentration

(1)

Changes in Temperature

(1)

Types

(29)

Conventional Primary Treatment

(1)

Rerated Conventional Primary Clarification

(1)

Chemically Enhanced Primary Treatment

(2)

Retention Treatment Basins

(1)

Lamella (Plate or Tube) Clarifiers

(5)

High-Rate Clarification Process

(5)

Dense Sludge Process

(3)

Ballasted Flocculation

(3)

Aeration Tank Settling

(2)

Step-Feed

(2)

Vortex Separators

(5)

Case Studies

(27)

Ballasted Flocculation

(2)

Combined Storage/Settling Tanks

101

(7)

Pilot Testing of High-Rate Clarification

108

(5)

Aeration Tank Settling

113

(4)

Vortex Separators

117

(9)

Process Selection

126

(2)

References

128

(16)

Secondary Clarifier Design Concepts and Considerations

Introduction

144

(1)

Functions of a Final Clarifier

145

(2)

Clarifier Configurations

147

(1)

Basics---The Science of Design

148

(44)

Sedimentation Process

148

(1)

Type I Settling (Discrete Settling)

149

(1)

Type II Settling (Flocculent Settling)

150

(3)

Type III Settling (Hindered Settling or Zone Settling)

153

(10)

Type IV Settling (Compression Settling)

163

(1)

Factors Affecting Sludge Settleability

164

(1)

Microbial Makeup

165

(3)

Nonsettleable Solids

168

(2)

Effect of Temperature

170

(1)

Measurement of Sludge Settleability

171

(1)

Sludge Volume Index

171

(1)

Dilute Sludge Volume Index

172

(1)

Stirred Specific Volume Index at 3.5g MLSS/L

172

(1)

Clarifier Analysis

173

(1)

Flux Theory

173

(1)

State Point Analysis

174

(4)

Other Approaches

178

(1)

The Daigger Approach

178

(2)

The Keinath Approach

180

(2)

The Wilson Approach

182

(1)

The Ekama--Marais Approach

182

(1)

Design Parameters of Importance

183

(1)

Solids Loading Rate

183

(1)

Overflow Rate

184

(1)

Side Water Depth

185

(1)

Weir Loading

186

(1)

Hydraulic Considerations

187

(1)

Internal and External Factors

187

(1)

Effect of Flow Variation

187

(1)

Flow Regimes

188

(3)

Flow Control

191

(1)

Clarifier Performance Enhancements

192

(7)

Process Configuration

192

(1)

Selectors

193

(3)

Foam Control

196

(1)

Dissolved Oxygen and Food-to-Microorganism Ratio

196

(1)

Chemical Addition

196

(2)

Hydraulic Improvements

198

(1)

Aeration Tank Settling

199

(1)

Miscellaneous Items

199

(3)

Special Considerations with Nutrient Removal Sludges

199

(1)

Clarifiers Following Fixed-Film Processes

200

(1)

Interaction with Other Processes

201

(1)

Cost Optimization

202

(1)

References

202

(7)

Suggested Readings

488

(2)

Rectangular Clarifiers

Introduction

490

(2)

Typical Hydraulic Flow Patterns

492

(3)

Longitudinal Flow Tanks

492

(1)

Cocurrent, Countercurrent, and Crosscurrent Sludge Removal

492

(2)

Transverse Flow Tanks

494

(1)

Vertical Flow Tanks

495

(1)

Stacked Clarifiers

495

(1)

Dimensions of Rectangular Clarifiers

495

(4)

Surface Area and Relative Dimensions

495

(2)

Length

497

(1)

Width

497

(1)

Depth

498

(1)

Flow Distribution to Multiple Clarifier Units

499

(2)

Inlet Conditions and Designs

501

(7)

General Inlet Conditions

501

(1)

Flow Distribution within the Clarifier

502

(2)

Inlet Design

504

(1)

Inlet Baffles and Flocculation Zones

504

(4)

Location of the Sludge Hopper

508

(6)

Influent End Hoppers

511

(2)

Effluent End Hoppers

513

(1)

Midlength Hoppers

513

(1)

Multiple Hopper Locations

514

(1)

Sludge Removal Systems

514

(8)

Chain-and-Flight Collectors

515

(2)

Traveling Bridge Collectors

517

(1)

Traveling Bridge Scraper Systems

518

(1)

Traveling Bridge Suction Systems

518

(1)

Discussion of Other Considerations in Designing Sludge Removal Systems

519

(3)

Outlet Conditions and Effluent Removal

522

(10)

Surface Launders

523

(1)

End Wall Effect

523

(4)

Weir Loading Rates

527

(3)

Submerged Launders

530

(2)

Removal of Floatables

532

(3)

Internal Tank Baffles

535

(7)

Solid Baffles

535

(3)

Perforated Baffles

538

(1)

Single Perforated Baffles

538

(1)

Multiple Perforated Baffles

539

(1)

Sludge Removal with Internal Baffles

540

(2)

Stacked Clarifiers

542

(5)

Materials of Construction and Equipment Selection

547

(4)

Materials of Construction

547

(3)

Equipment Selection

550

(1)

Drives

550

(1)

Chain and Flights

551

(1)

Valves

551

(1)

Case Histories

551

(19)

Increase in Length of Rectangular Clarifiers

551

(1)

Retrofit of Midlength Hopper Crosscollector to Manifold Suction Header

552

(4)

Comparison of Shallow Rectangular Clarifier with Deep Circular Tanks

556

(6)

Depth Requirement Study for High-Purity-Oxygen Activated Sludge Clarifiers

562

(6)

Conversion of Longitudinal Flow Rectangular Clarifiers to Transverse Flow

568

(2)

Summary, Conclusions, and Recommended Research

570

(5)

References

575

(9)

Clarifier Performance Monitoring and Control

Introduction

584

(1)

Key Parameters

585

(4)

Primary Clarifiers

585

(2)

Secondary Clarifiers

587

(1)

Monitoring of Activated Sludge Solids Inventory

587

(2)

Monitoring of Sludge Settleability

589

(1)

Plant Influent Flow and Load Monitoring

589

(1)

Monitoring and Control Equipment and Instrumentation

589

(22)

Introduction

589

(1)

Monitoring of Clarifier Drive Unit Operation

590

(1)

Clarifier Drive Torque Monitoring

590

(1)

Clarifier Drive Power Monitoring and Sludge Pump Withdrawal Rate Control

591

(1)

Clarifier Drive Motion Monitoring

592

(1)

Sludge Concentration and Density Measurement

592

(1)

Light Emitting (Optical) Analyzers

593

(1)

Principle of Operation

593

(1)

Typical Areas of Application

594

(1)

Key Advantages

595

(1)

Key Technology Limitations

595

(1)

Ultrasonic Analyzers

596

(1)

Principle of Operation

596

(1)

Typical Areas of Application

597

(1)

Key Advantages

597

(1)

Key Technology Limitations

597

(1)

Nuclear Density Analyzers

597

(1)

Principle of Operation

597

(1)

Typical Areas of Application

598

(1)

Key Advantages

598

(1)

Key Technology Limitations

598

(1)

Installation of Solids Analyzers

599

(2)

Sludge Blanket Depth Measurement

601

(1)

Manual Sludge Blanket Measurement

602

(1)

Automated Sludge Blanket Measurement

602

(1)

Sludge Blanket Level Detectors

603

(1)

Ultrasonic Sludge Blanket Level Detector

603

(1)

Optical Sludge Blanket Level Detectors

604

(2)

Typical Areas of Application

606

(1)

Key Technology Limitations

606

(2)

Installation of Sludge Blanket Level Detectors

608

(1)

Selection of Monitoring Equipment

609

(2)

Case Studies

611

(5)

Case Study for Activated Sludge Solids Inventory Monitoring---San Jose/Santa Clara Water Pollution Control Plant, California

611

(2)

Case Study for Sludge Control Monitoring---Clark County Sanitation District, Las Vegas, Nevada

613

(2)

Case Study for Sludge Blanket Depth Monitoring---Lumberton, Texas

615

(1)

Case Study for Sludge Blanket Depth Monitoring---Ashbridges Bay Wastewater Treatment Plant, Toronto, Canada

615

(1)

References

616

(5)

International Approaches

Introduction

621

(4)

United Kingdom History and Development of Clarifiers

621

(1)

Water Industry Trends and their Effect on Design Practice

622

(1)

Changes in Design Practice

622

(1)

Current European Focus

622

(1)

Staffing Levels

622

(1)

Planning Issues

622

(1)

Legislation

623

(1)

Consents

623

(1)

Conditions

623

(1)

Site Conditions

624

(1)

Effect of Collection Systems on Settling Tank Design

624

(1)

Process Design

625

(1)

Types of Settling Tanks

625

(1)

Functions of the Settling Tank

625

(1)

Settling Tank Configurations

625

(1)

Primary Tank Design

626

(3)

Typical United Kingdom Design Parameters

626

(1)

Retention Period

626

(1)

Surface Loading

626

(1)

Upward Velocity

626

(1)

Weir Overflow Rate

626

(1)

Horizontal Velocity

626

(1)

Horizontal Flow Tanks

627

(1)

Radial Flow Tanks

627

(1)

Desludging

628

(1)

Cosettlement

628

(1)

Odor Control

629

(1)

Humus Tank Design

629

(1)

Typical United Kingdom Design Criteria

629

(1)

Surface Loading

629

(1)

Horizontal Flow Tanks

630

(1)

Upward Flow Tanks

630

(1)

Final Tank Design

630

(6)

Typical United Kingdom Design Parameters

630

(1)

Retention Period

630

(1)

Mass Flux Theory

630

(1)

Settleability Parameters

631

(1)

Settlement Curve

631

(1)

Initial Settling Velocity

631

(1)

Sludge Volume Index

631

(1)

Stirred Specific Sludge Volume Index

632

(1)

Sludge Density Index

632

(1)

Stirred Sludge Density Index

633

(1)

Diluted Sludge Volume Index

633

(1)

Differences between the Two Design Approaches

633

(1)

Design of Sludge Scrapers

634

(1)

Desludging Settling Tanks

634

(1)

Scum Removal

635

(1)

Deep Sidewall Depths

635

(1)

Parabolic Floors

635

(1)

Alternatives

636

(15)

Tertiary Treatment

636

(1)

Septic Tanks

636

(1)

Alternatives to Conventional Clarifiers

636

(1)

Spiral Lamella Separators

637

(1)

Theory of the Spiral Separator

637

(2)

Process Design Parameters

639

(1)

Design Constraints

640

(1)

Upstream Requirements

641

(1)

Desludge Requirements

641

(1)

Maintenance and Inspection

641

(1)

Dissolved Air Flotation

641

(2)

Single Tank React/Settle

643

(1)

Sequencing Batch Reactors

643

(1)

Advantages and Disadvantages of Sequencing Batch Reactors

644

(1)

Triple Ditches

644

(1)

Operational Basics

644

(2)

Triple Ditch Design Parameters

646

(2)

Predicting Sludge Blanket Depth

648

(1)

Design of Decanting Weirs

649

(1)

Performance of Weirs

649

(1)

Migration of Mixed Liquor Suspended Solids

650

(1)

Summary of Performance

650

(1)

Operational Problems

651

(1)

Microbial Considerations

651

(1)

Diagnosis

651

(1)

Common United Kingdom Problems

651

(1)

Primary Tanks

651

(1)

Humus Tanks

651

(1)

Final Clarifiers

651

(1)

References

652

(4)

Interaction of Clarifiers with Other Facilities

Introduction

656

(1)

Clarifiers and Wastewater Collection Systems

657

(10)

Effect of Wastewater Collection Systems on Clarifier Design

657

(1)

Mitigation of Transient Flow Effect on Clarifier Performance

658

(1)

Transient Flow Reduction Measures in the Wastewater Collection System

658

(1)

Reduction of Transient Flow Effect by Equalization

659

(1)

Transient Flow Handling Using High-Rate Solids Separation

659

(1)

Transient Flow Handling by Increasing Clarifier Depth

660

(1)

Mitigation of Transient Flow Effect by Reducing Overall Solids Inventory

661

(2)

Transient Flow Control by Increase of Return and Waste Activated Sludge Rates

663

(1)

Handling of Transient Flows by Activated Sludge Contact Stabilization

664

(1)

Handling of Transient Flows by Step-Feed Aeration

665

(1)

Mitigation of Transient Flow Effects by Aeration Basin Adjustable Effluent Weirs

666

(1)

Mitigation of Transient Flows by Temporary Shutdown of Aeration

666

(1)

Clarifiers and Pretreatment Facilities

667

(3)

Effect of Plant Influent Pumping Station Design on Clarifier Performance

667

(1)

Effect of Screening Facilities on Clarifier Performance

667

(1)

Effect of Grit Removal System Type and Design on Clarifier Performance

668

(2)

Clarifiers and Biological Wastewater Treatment

670

(8)

Effect of Primary Clarification on Nutrient Removal in Conventional Activated Sludge Systems

670

(1)

Use of Primary Clarifiers for Chemical Phosphorus Removal

671

(1)

Use of Primary Clarifiers for Solids Prefermentation

672

(2)

Secondary Clarifier Design for Enhanced Nutrient Removal

674

(3)

Optimization of Clarifiers---Aeration Basin System

677

(1)

Interaction with Solids-Handling Facilities

678

(7)

Clarifiers and Sludge Thickening

678

(1)

Thickening in Primary Clarifiers

679

(1)

Thickening in Secondary Clarifiers

679

(1)

Cothickening of Primary and Secondary Sludge in Primary Clarifiers

679

(1)

Sludge Thickening Facilities

680

(1)

Clarifiers and Anaerobic Digestion

680

(1)

Effect of Clarifier Performance on Digester Operation

680

(1)

Digester Hydrogen Sulfide Control by Chemical Addition to Primary Clarifiers

681

(1)

Effect of Enhanced Primary Clarification on Digester Capacity

682

(1)

Clarifier and Aerobic Sludge Digestion

682

(1)

Effect of Plant Sidestreams on Clarifier Performance

683

(2)

Case Studies

685

(5)

Use of Primary Clarifiers for Solids Fermentation and Enhanced Phosphorus Removal

685

(1)

Optimization of Clarifiers---Aeration Basin Design

685

(5)

References

690

(5)

Appendix A Settling Test Procedure

695

(2)

Index

697

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Clarifier Design: WEF Manual of Practice No. FD-8

Summary

Author Biography

Table of Contents

Supplemental Materials