advanced biological treatment processes

This chapter covers the above including basic microbiology and kinet-ics, kinetics of activated sludge process, factors affecting the nitrification process, kinetics ofthe nitrification

Handbook of Environmental Engineering Series

Volume 1: Air Pollution Control Engineering L K Wang, N C Pereira, and Y T Hung (eds.) 504 pp (2004)

Volume 2: Advanced Air and Noise Pollution Control L K Wang, N C Pereira, and Y T Hung (eds.)

H ANDBOOK OF E NVIRONMENTAL E NGINEERING

Advanced Biological Treatment Processes

Edited by

Lenox Institute of Water Technology, Lenox, MA

Krofta Engineering Corporation, Lenox, MA

Zorex Corporation, Newtonville, NY

Lenox Institute of Water Technology, Lenox, MA

Krofta Engineering Corporation, Lenox, MA

Department of Civil and Environmental Engineering

Cleveland State University, Cleveland, OH

Lawrence K Wang

Ex-Dean & Director (retired),

Lenox Institute of Water Technology, Lenox, MA, USA

Assistant to the President (retired),

Krofta Engineering Corporation, Lenox, MA, USA

Vice President (retired),

Zorex Corporation, Newtonville, NY, USA

larrykwang@juno.com

lawrencekwang@gmail.com

Nazih K Shammas

Professor and Environmental Engineering Consultant

Ex-Dean & Director,

Lenox Institute of Water Technology, Lenox, MA, USA

Professor, Department of Civil and Environmental Engineering

Cleveland State University

Cleveland, OH, USA

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The past 30 years have seen the emergence of a growing desire worldwide thatpositive actions be taken to restore and protect the environment from the degradingeffects of all forms of pollution—air, water, soil, and noise Because pollution is adirect or indirect consequence of waste, the seemingly idealistic demand for “zerodischarge” can be construed as an unrealistic demand for zero waste However,

as long as waste continues to exist, we can only attempt to abate the subsequentpollution by converting it to a less noxious form Three major questions usuallyarise when a particular type of pollution has been identified: (1) How serious is thepollution? (2) Is the technology to abate it available? and (3) Do the costs of abatementjustify the degree of abatement achieved? This book is one of the volumes of the

Handbook of Environmental Engineering series The principal intention of this series is

to help readers formulate answers to the last two questions above

The traditional approach of applying tried-and-true solutions to specific pollutionproblems has been a major contributing factor to the success of environmental engi-neering, and has accounted in large measure for the establishment of a “methodology

of pollution control.” However, the realization of the ever-increasing complexity andinterrelated nature of current environmental problems renders it imperative thatintelligent planning of pollution abatement systems be undertaken Prerequisite tosuch planning is an understanding of the performance, potential, and limitations ofthe various methods of pollution abatement available for environmental scientistsand engineers In this series of handbooks, we will review at a tutorial level a broadspectrum of engineering systems (processes, operations, and methods) currentlybeing used, or of potential use, for pollution abatement We believe that the unifiedinterdisciplinary approach presented in these handbooks is a logical step in theevolution of environmental engineering

Treatment of the various engineering systems presented will show how an neering formulation of the subject flows naturally from the fundamental principlesand theories of chemistry, microbiology, physics, and mathematics This emphasis onfundamental science recognizes that engineering practice has in recent years becomemore firmly based on scientific principles rather than on its earlier dependency onempirical accumulation of facts It is not intended, though, to neglect empiricismwhere such data lead quickly to the most economic design; certain engineeringsystems are not readily amenable to fundamental scientific analysis, and in theseinstances we have resorted to less science in favor of more art and empiricism.Because an environmental engineer must understand science within the context ofapplication, we first present the development of the scientific basis of a particularsubject, followed by exposition of the pertinent design concepts and operations,

engi-v

and detailed explanations of their applications to environmental quality control orremediation Throughout the series, methods of practical design and calculation areillustrated by numerical examples These examples clearly demonstrate how orga-nized, analytical reasoning leads to the most direct and clear solutions Whereverpossible, pertinent cost data have been provided.

Our treatment of pollution-abatement engineering is offered in the belief that thetrained engineer should more firmly understand fundamental principles, be moreaware of the similarities and/or differences among many of the engineering systems,and exhibit greater flexibility and originality in the definition and innovative solution

of environmental pollution problems In short, the environmental engineer should,

by conviction and practice, be more readily adaptable to change and progress.Coverage of the unusually broad field of environmental engineering hasdemanded an expertise that could only be provided through multiple authorships.Each author (or group of authors) was permitted to employ, within reasonable limits,the customary personal style in organizing and presenting a particular subject area;consequently, it has been difficult to treat all subject material in a homogeneousmanner Moreover, owing to limitations of space, some of the authors’ favored topicscould not be treated in great detail, and many less important topics had to be merelymentioned or commented on briefly All authors have provided an excellent list ofreferences at the end of each chapter for the benefit of interested readers As eachchapter is meant to be self-contained, some mild repetition among the various textswas unavoidable In each case, all omissions or repetitions are the responsibility of theeditors and not the individual authors With the current trend toward metrication, thequestion of using a consistent system of units has been a problem Wherever possible,the authors have used the British system (fps) along with the metric equivalent (mks,cgs, or SIU) or vice versa The editors sincerely hope that this duplicity of units’ usagewill prove to be useful rather than being disruptive to the readers

The goals of the Handbook of Environmental Engineering series are: (1) to cover

entire environmental fields, including air and noise pollution control, solid wasteprocessing and resource recovery, physicochemical treatment processes, biologicaltreatment processes, biosolids management, water resources, natural control pro-cesses, radioactive waste disposal, and thermal pollution control; and (2) to employ amultimedia approach to environmental pollution control because air, water, soil, andenergy are all interrelated

As can be seen from the above handbook coverage, no consideration is given

to pollution by type of industry, or to the abatement of specific pollutants Rather,the organization of the handbook series has been based on the three basic forms inwhich pollutants and waste are manifested: gas, solid, and liquid In addition, noisepollution control is included in the handbook series

This particular book Volume 9, Advanced Biological Treatment Processes, is a sister book to Volume 8 Biological Treatment Processes Both books have been designed

to serve as comprehensive biological treatment textbooks as well as wide-rangingreference books We hope and expect it will prove of equal high value to advanced

undergraduate and graduate students, to designers of water and wastewater ment systems, and to scientists and researchers The editors welcome comments fromreaders in all of these categories.

treat-The editors are pleased to acknowledge the encouragement and support receivedfrom their colleagues and the publisher during the conceptual stages of this endeavor

We wish to thank the contributing authors for their time and effort, and for havingpatiently borne our reviews and numerous queries and comments We are verygrateful to our respective families for their patience and understanding during somerather trying times

Lawrence K Wang, Lenox, MA Nazih K Shammas, Lenox, MA Yung-Tse Hung, Cleveland, OH

Preface v

Contributors xxi

1 Principles and Kinetics of Biological Processes Nazih K Shammas, Yu Liu, and Lawrence K Wang 1

1 Introduction 1

2 Basic Microbiology and Kinetics 2

2.1 Microbial Growth Requirements 2

2.2 Kinetics of Microbial Growth in an Ideal Medium 4

2.3 Kinetics of Biological Growth in an Inhibitory Medium 5

2.4 Minimum Substrate Concentration 6

2.5 Mathematical Approximation for Wastewater Treatment 7

3 Kinetics of Activated Sludge Processes 8

3.1 Brief Description of Activated Sludge Processes 8

3.2 Kinetics of Completely Mixed Activated Sludge Process 9

3.3 Oxygen Requirements 15

3.4 Biosolids Production 15

4 Factors Affecting the Nitrification Process 17

4.1 Factors Affecting the Half-Velocity Coefficient, Ks 18

4.2 Factors Affecting the Maximum Rate Constant, k 20

4.3 Design Criteria of Nitrification Systems 27

5 Kinetics of the Nitrification Process 32

5.1 Analysis of Nitrification Data 32

5.2 Allosteric Kinetic Model 33

5.3 Application of M–W–C Model to Nitrification 36

5.4 Determination of Kinetic Parameters 37

6 Denitrification by Suspended Growth Systems 44

6.1 Effect of pH 45

6.2 MLSS and MLVSS 45

6.3 Effect of Temperature 46

6.4 Size of Denitrification Tank 46

6.5 Carbonaceous Matter 46

6.6 Other Requirements 47

7 Design Examples 49

7.1 Example 1 49

7.2 Example 2 50

7.3 Example 3 51

7.4 Example 4 52

Nomenclature 52

References 54

2 Vertical Shaft Bioreactors Nazih K Shammas, Lawrence K Wang, Jeffrey Guild, and David Pollock 59

1 Process Description 60

2 Technical Development 63

ix

3 Vertreat Bioreactor 67

3.1 Key Process Features and Advantages 68

3.2 Process Applications 68

3.3 Reactor Features 69

4 Process Theory and Design Basis 70

4.1 Process Fundamentals 70

4.2 Biological Properties 72

4.3 Oxygen Transfer 72

4.4 Organic Loading 76

4.5 Solids Separation 78

5 Variations of the Basic VSB 79

5.1 Single Zone Vertical Shaft Bioreactors 79

5.2 Multi-Zone Vertical Shaft Bioreactors 80

5.3 Multi-channel Vertical Shaft Bioreactors 80

5.4 Multi-Stage Vertical Shaft Bioreactors 81

5.5 Thermophilic Vertical Shaft Bioreactors 81

6 Process Design Considerations 81

7 Operation and Maintenance Considerations 84

8 Comparison with Equivalent Technology 85

8.1 Equivalent Conventional Concept 85

8.2 Land Area 86

8.3 Cost 86

8.4 Energy 88

9 Case Studies 89

9.1 Dairy Plant Wastewater Treatment 89

9.2 Refinery Wastewater Treatment 94

9.3 Municipal Wastewater Treatment 100

Nomenclature 105

References 105

Appendix 108

3 Aerobic Granulation Technology Joo-Hwa Tay, Yu Liu, Stephen Tiong-Lee Tay, and Yung-Tse Hung 109

1 Introduction 109

2 Aerobic Granulation as a Gradual Process 110

3 Factors Affecting Aerobic Granulation 112

3.1 Substrate Composition 112

3.2 Organic Loading Rate 113

3.3 Hydrodynamic Shear Force 113

3.4 Presence of Calcium Ion in Feed 116

3.5 Reactor Configuration 116

3.6 Dissolved Oxygen 117

4 Microbial Structure and Diversity 117

4.1 Characteristics of Aerobic Granule 117

4.2 Layered Structure of Aerobic Granules 119

4.3 Microbial Diversity of Aerobic Granules 119

5 Mechanism of Aerobic Granulation 120

6 Applications of Aerobic Granulation Technology 121

6.1 High-Strength Organic Wastewater Treatment 121

6.2 Phenolic Wastewater Treatment 122

6.3 Biosorption of Heavy Metals by Aerobic Granules 123

Nomenclature 124

References 124

4 Membrane Bioreactors

Lawrence K Wang and Ravinder Menon 129

1 Introduction 130

1.1 General Introduction 130

1.2 Historical Development 130

1.3 Membrane Bioreactors Research and Engineering Applications 134

2 MBR Process Description 137

2.1 Membrane Bioreactor with Membrane Module Submerged in the Bioreactor 137

2.2 Membrane Bioreactor with Membrane Module Situated Outside the Bioreactor 138

2.3 MBR System Features 139

2.4 Membrane Module Design Considerations 141

3 Process Comparison 142

3.1 Similarity 142

3.2 Dissimilarity 144

4 Process Applications 146

4.1 Industrial Wastewater Treatment 146

4.2 Municipal Wastewater and Leachate Treatments 146

5 Practical Examples 147

5.1 Example 1 Dairy Industry 147

5.2 Example 2 Landfill Leachate Treatment 148

5.3 Example 3 Coffee Industry 150

6 Automatic Control System 151

6.1 Example 4 Cosmetics Industry 152

7 Conclusions 153

7.1 Industrial Applications 153

7.2 Municipal Applications 153

Acknowledgement 153

Commercial Availability 154

References 154

5 SBR Systems for Biological Nutrient Removal Nazih K Shammas and Lawrence K Wang 157

1 Background and Process Description 157

2 Proprietary SBR Processes 159

2.1 Aqua SBR 160

2.2 Omniflo 161

2.3 Fluidyne 162

2.4 CASS 162

2.5 ICEAS 163

3 Description of a Treatment Plant Using SBR 164

4 Applicability 165

5 Advantages and Disadvantages 165

6 Design Criteria 166

6.1 Design Parameters 166

6.2 Construction 171

6.3 Tank and Equipment Description 172

6.4 Health and Safety 173

7 Process Performance 173

8 Operation and Maintenance 175

9 Cost 175

10 Packaged SBR for Onsite Systems 177

10.1 Typical Applications 178

10.2 Design Assumptions 178

10.3 Performance 179

10.4 Management Needs 179

10.5 Risk Management Issues 180

10.6 Costs 180

References 180

Appendix 183

6 Simultaneous Nitrification and Denitrification (SymBio R Process) Hiren K Trivedi 185

1 Introduction 186

2 Biological Nitrogen Removal 186

2.1 Nitrification 187

2.2 Denitrification 187

2.3 Simultaneous Nitrification and Denitrification 188

3 NADH in Cell Metabolism 189

4 The Symbio  Process for Simultaneous NitrificationR and Denitrification 192

4.1 NADH Proportional Control Strategy 193

4.2 NADH Jump Control Strategy 195

4.3 Process Design 198

5 Case Studies 201

5.1 Big Bear, CA 201

5.2 Perris, CA 204

5.3 Rochelle, IL 205

6 Conclusion 206

Nomenclature 206

References 207

7 Single-Sludge Biological Systems for Nutrients Removal Lawrence K Wang and Nazih K Shammas 209

1 Introduction 210

2 Classification of Single-Sludge Processes 211

3 Stoichiometric and Kinetic Considerations 213

3.1 Routes of Nitrogen Removal in Single-Sludge Systems 213

3.2 Stoichiometric and Metabolic Principles 214

3.3 Endogenous Nitrate Respiration (ENR) 215

3.4 Nitrogen Removal by ENR and Aerobic Sludge Synthesis 217

3.5 Nitrogen Removal by Substrate Nitrate Respiration and Anoxic Biosolids Synthesis 219

3.6 Design Alternatives for Compartmentalized Aeration Tanks 221

4 Multistage Single Anoxic Zone 222

4.1 Background and Process Description 222

4.2 Typical Design Criteria 225

4.3 Process Performance 226

4.4 Process Design Features 228

5 Multistage Multiple Anoxic Zones 229

5.1 Background and Process Description 229

5.2 Typical Design Criteria 232

5.3 Process Performance 233

5.4 Process Design Features 236

6 Multiphase Cyclycal Aeration 236

6.1 Background and Process Description 236

6.2 Typical Design Criteria 238

6.3 Process Performance 239

6.4 Process Design Features 240

7 Phosphorus Removal by Biological and Physicochemical Technologies 240

7.1 Phosphate Biological Uptake at Acid pH 240

7.2 Emerging Phosphorus Removal Technologies 240

8 Coxsackie Wastewater Treatment Plant—A Single-Sludge Activated Sludge Plant for Carbonaceous Oxidation, Nitrification, Denitrification, and Phosphorus Removal 242

8.1 Background Information 242

8.2 Plant Operation and Parameters 242

8.3 Performance Results 255

8.4 Solids Management 261

8.5 Sludge Chlorination Treatment 261

Acknowledgment 263

Nomenclature 264

References 264

8 Selection and Design of Nitrogen Removal Processes Nazih K Shammas and Lawrence K Wang 271

1 Factors that Affect Process Selection 271

1.1 Wastewater Characteristics 271

1.2 Site Constraints 272

1.3 Existing Facilities 273

2 Costs 274

2.1 Capital Cost 274

2.2 Operational Cost 275

3 Design Considerations 275

3.1 Primary Settling 275

3.2 Aeration Systems 276

3.3 Mixers 277

3.4 Recycle Pumping 277

3.5 Reactor Design 277

3.6 Secondary Settling 278

3.7 Selectors 278

4 Process Design 279

4.1 Introduction 279

4.2 Summary of Design Procedures 280

5 Design Examples 281

5.1 Introduction 281

5.2 Design Example 1: Plant B with Less Stringent Limits 282

5.3 Design Example 2: Plant B with more Stringent Limits 290

5.4 Design Example 3—Plant A with Less Stringent Limits 294

5.5 Design Example 4—Plant A with More Stringent Limits 298

Nomenclature 298

References 300

List of Appendixes 303

9 Column Bioreactor Clarifier Process (CBCP) Anatoliy I Sverdlikov, Gennadij P Shcherbina, Michail M Zemljak, Alexander A Sverdlikov, Donald H Haycock, Andrew Lugowski, George Nakhla, Lawrence K Wang and Yung-Tse Hung 313

1 Background 314

2 Introduction 314

3 Description of Novel Treatment Technology 315

3.1 Concepts of Biological Processes 315

3.2 Distinction of Biosorption and Oxidation Processes in the Pseudoliquified Activated Sludge Bioreactor 316

3.3 Process Configuration 318

3.4 Operating Process Parameters 323

4 Development and Implementation of Model Pilot Plant 334

4.1 System Capabilities and Need for Technology Refinement 334

4.2 Project Objectives 335

4.3 Methodology 336

4.4 Conceptual and Detailed Design of Mobile Pilot Plant 336

4.5 Manufacturing, Installation, and Testing of the Mobile Pilot Plant 338

4.6 Development of Sampling and Monitoring Program 338

4.7 Testing of the Pilot Plant at Municipal Wastewater Facilities 339

4.8 Detailed Analysis of Pilot Plant Testing Data 340

4.9 Overall System Performance 350

4.10 Municipal and Industrial Wastewater Treatment—Process Applicability 351

5 Computer Modeling 351

5.1 Model Descriptions 351

5.2 Wastewater Characterization 352

5.3 Determination of Model Stoichiometric Coefficients 353

5.4 Process Modeling 353

6 Summary and Recommendations 360

Nomenclature 361

References 361

10 Upflow Sludge Blanket Filtration Svatopluk Mackrle, Vladimír Mackrle, and Oldˇrich Draˇcka 365

1 Introduction 366

2 Theoretical Principles of Fluidized Bed Filtration 366

2.1 Hydrodynamic Similarity and Dimensionless Numbers 366

2.2 Characteristics of Granular Porous Medium 367

2.3 Flow Through Fixed Porous Medium 368

2.4 Filtration 369

2.5 Single Particle Sedimentation 370

2.6 Turbulent Flow 372

2.7 Coagulation 372

2.8 Hydrodynamic Disintegration of Aggregates 373

2.9 Fluidization in Cylindrical Column 373

2.10 Fluidization in Diffuser 376

2.11 Upflow Sludge Blanket Filtration 378

3 Principles of Integrated USBF Reactors Design 380

3.1 Types of Sludge Blanket 380

3.2 Water Treatment Systems with USBF 382

4 Examples of USBF Integrated Treatment Reactors Implementation 385

4.1 Chemical USBF Integrated Reactors 386

4.2 First Generation of Biological USBF Integrated Reactors 388

4.3 Second Generation of Biological USBF Integrated Reactor 394

5 Advanced Wastewater Treatment Systems 396

5.1 Upgrading of Conventional Municipal WWTP 397

5.2 Decentralized Sewerage Systems 401

5.3 Wastewater Reclamation and Reuse 403

6 Design Example of Advanced Treatment Systems 406

6.1 Upgrading of Classical Municipal WWTP 406

Nomenclature 408

References 410

11 Anaerobic Lagoons and Storage Ponds

Lawrence K Wang, Yung-Tse Hung, and J Paul Chen 411

1 Introduction 411

2 Process Description 412

3 Applications and Limitations 413

4 Expected Process Performance and Reliability 413

5 Process Design 413

5.1 Minimum Treatment Volume 413

5.2 Waste Volume for Treatment Period 416

5.3 Sludge Volume 416

5.4 Lagoon Volume Requirement 417

5.5 Anaerobic Lagoon Design Criteria 419

5.6 Data Gathering and Compilation for Design 420

6 Energy Consumption and Costs of Anaerobic Lagoons 420

7 Waste Storage Ponds 422

7.1 Process Description 422

7.2 Process Design 422

8 Design and Application Examples 424

8.1 Example 1 424

8.2 Example 2 424

8.3 Example 3 425

8.4 Example 4 427

8.5 Example 5 429

8.6 Example 6 430

8.7 Example 7 430

Nomenclature 431

References 432

12 Vertical Shaft Digestion, Flotation, and Biofiltration Lawrence K Wang, Nazih K Shammas, Jeffrey Guild, and David Pollock 433

1 Introduction 433

1.1 Biosolids Treatment 433

1.2 Vertical Shaft Bioreactor and Vertical Shaft Digestion 434

1.3 Vertical Shaft Flotation Thickening Process 436

1.4 Gas-Phase Biofiltration 436

1.5 Biosolids Digestion and Stabilization 437

2 Principles of VSD and Optional Anaerobic Digestion 438

2.1 Theory and Principles of Aerobic Digestion 438

2.2 Theory and Principles of Optional Anaerobic Digestion 440

2.3 Combined Vertical Shaft Digestion and Anaerobic Digestion 440

3 Description, Operation, and Applications of VSD System 441

3.1 Process Description 441

3.2 Process Operation 441

3.3 Process Applications 442

4 Design Considerations of a Complete VSD System 443

4.1 Autothermal Thermophilic Aerobic Digestion Using Air 443

4.2 Autothermal Thermophilic Digestion Using Pure Oxygen 444

4.3 Flotation Thickening after Vertical Shaft Digestion 445

4.4 Optional Dual Digestion System 447

4.5 Biosolids Dewatering Processes 449

4.6 Gas-Phase Biofiltration for Air Emission Control 449

4.7 Operational Controls of Biofiltration 453

5 Case Study 454

5.1 Facility Design and Construction 454

5.2 Vertical Shaft Digestion Demonstration Plan 457

5.3 Design Criteria Development for Vertical Shaft Digestion 458

5.4 Capital Costs 472

6 Conclusions 473

References 474

Appendix 477

13 Land Application of Biosolids Nazih K Shammas and Lawrence K Wang 479

1 Introduction 480

2 Recycling of Biosolids Through Land Application 480

3 Description 481

4 Advantages and Disadvantages 482

5 Design Criteria 484

6 Performance 485

7 Costs of Recycling Through Land Application 486

8 Biosolids Disposal on Land (Landfill) 487

9 Biosolids Landfill Methods 487

9.1 Biosolids-Only Trench Fill 487

9.2 Biosolids-Only Area Fill 489

9.3 Co-Disposal with Refuse 491

9.4 Landfilling of Screenings, Grit, and Ash 493

10 Preliminary Planning 493

10.1 Biosolids Characterization 493

10.2 Selection of a Landfilling Method 494

10.3 Site Selection 494

11 Facility Design 497

11.1 Regulations and Standards 497

11.2 Site Characteristics 498

11.3 Landfill Type and Design 499

11.4 Ancillary Facilities 499

11.5 Landfill Equipment 502

11.6 Flexibility, Performance, and Environmental Impacts 502

12 Operation and Maintenance 502

12.1 Operations Plan 504

12.2 Operating Schedule 504

12.3 Equipment Selection and Maintenance 504

12.4 Management and Reporting 506

12.5 Safety 506

12.6 Environmental Controls 506

13 Site Closure 507

13.1 Ultimate Use 508

13.2 Grading at Completion of Filling 508

13.3 Landscaping 508

13.4 Continued Leachate and Gas Control 508

14 Costs of Biosolids Disposal on Land (Landfill) 508

14.1 General 508

14.2 Hauling of Biosolids 509

14.3 Energy Requirements 511

14.4 Costs 512

15 Examples 512

15.1 Example 1 Typical Biosolids Application Rate Scenario 512

15.2 Example 2 Hauling of Biosolids 515

References 516

Appendix 520

14 Deep-Well Injection for Waste Management Nazih K Shammas, Charles W Sever, and Lawrence K Wang 521

1 Introduction 522

2 Regulations for Managing Injection Wells 523

3 Basic Well Designs 526

4 Evaluation of a Proposed Injection Well Site 532

4.1 Confinement Conditions 533

4.2 Potential Receptor Zones 534

4.3 Subsurface Hydrodynamics 535

5 Potential Hazards-Ways to Prevent, Detect, and Correct Them 537

5.1 Fluid Movement during Construction, Testing, and Operation of the System 537

5.2 Failure of the Aquifer to Receive and Transmit the Injected Fluids 538

5.3 Failure of the Confining Layer 538

5.4 Failure of an Individual Well 540

5.5 Failures Because of Human Error 540

6 Economic Evaluation of a Proposed Injection Well System 541

7 Use of Injection Wells in Wastewater Management 541

7.1 Reuse for Engineering Purposes 542

7.2 Injection Wells as a Part of the Treatment System 542

7.3 Storage of Municipal Wastewaters for Reuse 543

7.4 Storage of Industrial Wastewaters 543

7.5 Disposal of Municipal and Industrial Sludges 544

8 Use of Injection Wells for Hazardous Wastes Management 544

8.1 Identification of Hazardous Wastes 545

8.2 Sources, Amounts and Composition of Injected Wastes 546

8.3 Geographic Distribution of Wells 549

8.4 Design and Construction of Wells 549

8.5 Disposal of Radioactive Wastes 551

9 Protection of Usable Aquifers 553

9.1 Pathway 1: Migration of Fluids through a Faulty Injection Well Casing 553

9.2 Pathway 2: Migration of Fluids Upward Through the Annulus between the Casing and the Well Bore 554

9.3 Pathway 3: Migration of Fluids from an Injection Zone through the Confining Strata 555

9.4 Pathway 4: Vertical Migration of Fluids through Improperly Abandoned or Improperly Completed Wells 557

9.5 Pathway 5: Lateral Migration of Fluids from Within an Injection Zone into a Protected Portion of Those Strata 560

9.6 Pathway 6: Direct Injection of Fluids into or Above an Underground Source of Drinking Water 562

10 Case Studies of Deep Well Injection 563

10.1 Case Study 1: Pensacola, FL (Monsanto) 564

10.2 Case Study 2: Belle Glade, FL 567

10.3 Case Study 3: Wilmington, NC 569

11 Practical Examples 571

11.1 Example 1 571

11.2 Example 2 573

11.3 Example 3 573

11.4 Example 4 574

11.5 Example 5 575

11.6 Example 6 575

References 576

Appendix 582

15 Natural Biological Treatment Processes Nazih K Shammas and Lawrence K Wang 583

1 Aquaculture Treatment: Water Hyacinth System 583

1.1 Description 583

1.2 Applications 584

1.3 Limitations 585

1.4 Design Criteria 585

1.5 Performance 585

2 Aquaculture Treatment: Wetland System 586

2.1 Description 586

2.2 Constructed Wetlands 587

2.3 Applications 588

2.4 Limitations 589

2.5 Design Criteria 589

2.6 Performance 589

3 Evapotranspiration System 590

3.1 Description 590

3.2 Applications 592

3.3 Limitations 593

3.4 Design Criteria 593

3.5 Performance 593

3.6 Costs 593

4 Land Treatment: Rapid Rate System 594

4.1 Description 595

4.2 Applications 596

4.3 Limitations 596

4.4 Design Criteria 596

4.5 Performance 597

4.6 Costs 598

5 Land Treatment: Slow Rate System 599

5.1 Description 599

5.2 Applications 600

5.3 Limitations 601

5.4 Design Criteria 602

5.5 Performance 602

5.6 Costs 603

6 Land Treatment: Overland Flow System 605

6.1 Description 605

6.2 Application 606

6.3 Limitations 606

6.4 Design Criteria 606

6.5 Performance 607

6.6 Costs 607

7 Subsurface Infiltration 609

7.1 Description 609

7.2 Applications 612

7.3 Limitations 612

7.4 Design Criteria 612

7.5 Performance 613

References 613

Appendix 617

16 Emerging Suspended-Growth Biological Processes

Nazih K Shammas and Lawrence K Wang 619

1 Powdered Activated Carbon Treatment (PACT) 619

1.1 Types of PACT Systems 619

1.2 Applications and Performance 620

1.3 Process Equipment 623

1.4 Process Limitations 623

2 Carrier-Activated Sludge Processes (CAPTOR and CAST Systems) 623

2.1 Advantages of Biomass Carrier Systems 623

2.2 The CAPTOR Process 624

2.3 Development of CAPTOR Process 624

2.4 Pilot-Plant Study 624

2.5 Full-Scale Study of CAPTOR and CAST 624

3 Activated Bio-Filter (ABF) 632

3.1 Description 632

3.2 Applications 633

3.3 Design Criteria 634

3.4 Performance 634

4 Vertical Loop Reactor (VLR) 634

4.1 Description 634

4.2 Applications 635

4.3 Design Criteria 636

4.4 Performance 636

4.5 EPA Evaluation of VLR 637

4.6 Energy Requirements 638

4.7 Costs 638

5 Phostrip Process 638

5.1 Description 638

5.2 Applications 640

5.3 Design Criteria 641

5.4 Performance 641

5.5 Cost 641

Nomenclature 643

References 644

Appendix 648

17 Emerging Attached-Growth Biological Processes Nazih K Shammas and Lawrence K Wang 649

1 Fluidized Bed Reactors (FBR) 649

1.1 FBR Process Description 650

1.2 Process Design 651

1.3 Applications 651

1.4 Design Considerations 653

1.5 Case Study: Reno-Sparks WWTP 653

2 Packed Bed Reactor (PBR) 654

2.1 Aerobic PBR 654

2.2 Anaerobic Denitrification PBR 656

2.3 Applications 658

2.4 Design Criteria 658

2.5 Performance 660

2.6 Case Study: Hookers Point WWTP (Tampa Florida) 661

2.7 Energy Requirement 663

2.8 Costs 664

3 Biological Aerated Filter (BAF) 665

3.1 BAF Process Description 665

3.2 Applications 667

3.3 BAF Media 667

3.4 Process Design and Performance 668

3.5 Solids Production 671

4 Hybrid Biological-Activated Carbon Systems 672

4.1 General Introduction 672

4.2 Downflow Conventional Biological GAC Systems 672

4.3 Upflow Fluidized Bed Biological GAC System (FBB-GAC) 675

References 676

Appendix 681

Appendix: Conversion Factors for Environmental Engineers Lawrence K Wang 683

Index 729

J PAUL CHEN,Ph.D. • Associate Professor, Division of Environmental Science and neering, National University of Singapore, Singapore

Czech Republic

Ltd, Vancouver, BC, Canada

YUNG-TSE HUNG, Ph.D., P.E., DEE • Professor, Department of Civil and Environmental Engineering, Cleveland State University, Cleveland, OH, USA

JOO-HWATAY,Ph.D.,P.E. • Professor and Division Head, School of Civil and tal Engineering, Nanyang Technological University, Singapore

Engineering, Nanyang Technological University, Singapore

YU LIU, Ph.D. • Assistant Professor, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore

ONDEO Degremont Inc., Richmond, VA, USA

of Western Ontario, London, Ontario, Canada

NORAM Engineering and Constructors, Ltd, Vancouver, BC, Canada

DC, USA

Ex-Dean and Director, Lenox Institute of Water Technology, Lenox, MA, USA; and Advisor, Krofta Engineering Corporation, Lenox, MA, USA

Municipal Facilities and Services, Kiev, Ukraine

Research and Development Institute for Municipal Facilities and Services, Kiev, Ukraine

xxi

ANATOLIY I SVERDLIKOV • Senior Manager, Wastewater Treatment Department, Research and Development Institute for Municipal Facilities and Services, Kiev, Ukraine

GL & V India Pvt., Ltd., Bombay, India

Technology, Lenox, MA, USA; Assistant to the President (retired), Krofta ing Corporation, Lenox, MA, USA; and Vice President (retired), Zorex Corporation, Newtonville, NY, USA

Institute for Municipal Facilities and Services, Kiev, Ukraine

Principles and Kinetics of Biological Processes

Nazih K Shammas, Yu Liu, and Lawrence K Wang

C ONTENTS

of wastewater, a sound understanding of the fundamentals of microbial growth and substrateuse kinetics is essential This chapter covers the above including basic microbiology and kinet-ics, kinetics of activated sludge process, factors affecting the nitrification process, kinetics ofthe nitrification process, denitrification by suspended growth systems and design examples.Key Words Activated sludge rbiological treatment rdenitrification rkineticsrmathematical

modelingrallosteric kinetic modelrnitrification.

1 INTRODUCTION

Microorganisms are found nearly everywhere in the biosphere and thus are a force in theenvironment In the past decades, bacteria have been intensively exploited in wastewatertreatment processes It is therefore the task of the environmental engineer and scientist tounderstand the role of microorganisms first and then use them to beneficially transform the

From: Handbook of Environmental Engineering, Volume 9: Advanced Biological Treatment Processes

1

particular environment, such as water or soil Theoretically, biological technologies can beused to treat a vast majority of organic wastewaters because all organics could be biologicallydegraded if the proper microbial communities are established, maintained, and controlled.

In this regard, many environmental engineering principles have been developed for biologicalwastewater treatment Before environmental engineers design and operate biological treatmentsystems that create the environment necessary for the effective treatment of wastewater, asound understanding of the fundamentals of microbial growth and substrate utilization kinetics

is essential

2 BASIC MICROBIOLOGY AND KINETICS

Microorganisms are powerful and cheap bioagents of biological wastewater treatment Theperformance and stability of a biological treatment system relies on the interaction of differentspecies of living organisms, typically including bacteria, fungi, algae, and protozoa (1)

2.1 Microbial Growth Requirements

Biological processes designed for wastewater treatment must maintain rich microbialpopulations and enough biomass to metabolize the soluble and colloidal organic wastes.For a successful operation of the biological treatment process, several conditions must befulfilled, such as the type and concentration of organic waste (as electron donor), electronacceptors, moisture, temperature, necessary nutrients, and the absence of toxic and inhibitorycompounds A sound understanding of these microbial growth requirements is essential forenvironmental engineers and scientists to design and manage biological wastewater treatmentsystems

2.1.1 Electron Acceptors

Aerobic and anaerobic processes are the two main biological technologies used for ater treatment Bacterial respirations for aerobic and anaerobic bacteria need different electronacceptors The choice of electron acceptors depends on which treatment process is desirablefor a specific wastewater (2) For aerobic biodegradation, dissolved oxygen (DO) serves asthe terminal electron acceptor However, under anaerobic conditions, a variety of inorganiccompounds can be used as terminal electron acceptors, e.g., NO3 −, SO

wastew-4 −,and so on.

In aerobic systems, the theoretical oxygen demand of an organic compound can be lated from stoichiometry or determined by laboratory test The theoretical oxygen demand isthe amount of oxygen required to completely oxidize the organic carbon to carbon dioxide and

calcu-water As an example, for the complete oxidation of phenol (C6H6O) the balanced equation is

written as follows:

C6H6O94

2.1.2 Moisture

Because about 75% of cellular mass is water, and water is a good medium for nutrient portation, adequate moisture concentration is strongly required in biodegradation of organicchemicals, especially in bioremediation of contaminated soil (3) It is generally accepted thatthe minimum moisture content necessary for bioremediation of contaminated soil is around40% of saturation (4) In fact, there is no moisture-associated problem in biological wastewatertreatment processes

trans-2.1.3 Temperature

The performance and response of a biological system depends on temperature variation.The effect of process temperature on microbial activity or the rate of biodegradation can beroughly described by the following simple equation:

For most of biological treatment systems, α values are in the range of 1.0 to 1.14 (5).

Different groups of bacteria have various temperature optimums For example, methanogenicbacteria are slow-growing bacteria with a generation time of 3 days at 35◦C and 50days at 10◦C, indicating that methane-producing bacteria are very sensitive to changes intemperature (1)

2.1.4 pH

Most bacteria can optimally function only at a relatively narrow pH range of 6 to 8 Inbiological treatment system, once the reactor pH falls outside the optimal range, the activity

of microbial population would drop significantly, and such a decline of activity in turn causes

a serious operation problem and may result in the failure of the system (1) Consequently,

it is recommended that on-site operators need to regularly monitor the system pH and payattention to its changes

2.1.5 Nutrients

Typical elementary composition of bacterial cells based on dry weight is 50% carbon, 20%

oxygen, 15% nitrogen, 8% hydrogen, 3% phosphorus and <1% each of sulfur, potassium,

sodium, calcium, iron, and magnesium (6) Microbial metabolism requires these elements

as nutrients for synthesis and energy generation The most commonly accepted empiricalforms of activated sludge biomass are expressed as C5H7NO2 and C42H100N11O13P (7).The empirical formulae of bacterial cells provide a basis for calculation of the N and Prequirements for synthesis of biomass from organic waste

2.2 Kinetics of Microbial Growth in an Ideal Medium

Bacteria can grow at high rates under suitable conditions because of their relatively ple structures and growth requirements However, a particular environment will favor somespecies more than others

sim-2.2.1 Kinetics of Microbial Growth

The growth of bacteria in an ideal medium can be described by the best-known Monodequation:

μ= specific growth rate

μmax= maximum specific growth rate

X= biomass concentration in the system

In the environmental engineering field, it is accepted that the conversion coefficient oforganic waste to new synthesized cells is constant, thus the ratio of the increase in biomass to

the decrease in organic substrate is defined as the growth yield coefficient Y ,

qmax= maximum specific substrate utilization rate = μmax/Y

q = specific substrate utilization rate defined as follows:

Equation (7) is one of the most commonly used design equations for biological treatment

systems In addition, it can be deduced from above equations that Y can also be defined as the μ/q ratio.

2.2.2 Microbial Decay and Endogenous Respiration

According to Pirt (8), part of the energy source would be used for maintaining the livingfunctions of microorganisms, which is so-called maintenance metabolism This includes theenergy for turnover of cell materials, active transport, motility, and so on The importance

of maintenance metabolism is that the maintenance-associated substrate consumption is notsynthesized to new cellular mass Thus, the biosolids production should be inversely related tothe activity of maintenance metabolism (9, 10) On the other hand, to account for the decrease

in biomass production that is usually observed when the specific growth rate decreases,Herbert et al (11) postulated that the maintenance energy requirement could be satisfiedthrough endogenous metabolism In this case, part of cellular biomass is oxidized to producethe energy for maintenance functions It is generally assumed that microbial decay occursfollowing a first-order pattern as follows:

where,

Kd= constant decay coefficient

Endogenous respiration has profound effect on the production of excessive biosolids It hasbeen suggested that the aim of both design and operation is to foster as much of this biologicaldecay as possible Including the decay in Eq (6) yields an expression for the net growth ofbiomass in biological system:

Equations(3) to (10)provide the basis for detailed kinetic analysis and basic design guidelines

of biological treatment systems

2.3 Kinetics of Biological Growth in an Inhibitory Medium

Some substrates may inhibit their own degradation at increased concentrations Whendesigning and running a biological system for inhibitory waste treatment, environmentalengineers must seriously account for the toxicity and inhibition of waste to bacterial growth

It is obvious that the Monod equation does not include the toxic or inhibitory effect, thusthey must be modified for biological treatment of inhibitory waste.Figure 1.1shows typicalgrowth patterns of bacteria in noninhibitory and inhibitory media It seems that when theconcentration of inhibitory substrate is higher than a critical value, a sharp decline in microbialgrowth is observed, on the other hand, if the concentration of inhibitory substrate is lowenough, the inhibitory effect would not be significant

INHIBITORY SUBSTRATE

NO INHIBITORY SUBSTRATE

SUBSTRATE CONCENTRATION RATE

Fig 1.1 Schematic presentation of inhibitory effect on bacterial growth.

So far, the Haldane equation has been most frequently used to describe the inhibitory effect

of a substrate on bacterial growth:

Current practice shows that for a target inhibitory substrate, its concentration is criticalfor biological treatment If the threshold of substrate concentration that bacteria can bear

is exceeded, inhibition, and die-off of bacteria in the reactor will start on a continuing andirreversible basis, leading to serious loss or even failure of the system’s purification efficiencyand capability Predetermination of inhibitory threshold of substrate concentration is essentialfor the design of a biological treatment system for inhibitory wastes In industrial practice,where inhibitory wastes are more common, there are some technical measures that can help tomitigate inhibition, such as acclimation of bacteria, introduction of robust species, or dilution

of the waste stream

2.4 Minimum Substrate Concentration

In many cases, the characteristics of soluble wastes found in soil and wastewater have dualeffects on biological treatment processes; one, when the concentrations of waste constituentsare generally low and two, when their toxicity to microbial activity is relatively high A low

waste concentration may be risky in case it could not support a sustainable and viablebiomass needed for biological treatment As Eq (3) indicates, the specific growth rate ofmicroorganisms is proportionally related to substrate concentration Microbial growth couldcease as the substrate concentration diminishes to a certain low unsustainable concentration.For a biological treatment system, a minimum substrate concentration is required to sustain aviable biomass In the environmental engineering field, the minimum substrate concentration

(Smin) is defined as the substrate concentration at which formation of new biomass equals

its loss by endogenous respiration (3) When the minimum substrate concentration occurs,

Eq.(10)shows that

Smin= KsKd

Y qmax− Kd

(14)

2.5 Mathematical Approximation for Wastewater Treatment

In many situations of wastewater treatment, a simple first-order approximation has beenused with reasonable accuracy to describe the biodegradation of organic wastewater Thisapproximation is based on two main assumptions (4):

1 The target substrate or waste is at a relatively low concentration.

2 The biomass concentration in the system is at a steady state, consequently it changes little with operation time and can be regarded as a constant.

Thus, Eq.(6)reduces to:

k1= Xqmax/Ks = first-order biodegradation rate constant

Integrating both sides of Eq.(16)yields

t = reaction time

S o = initial substrate concentration at t = 0

S = substrate concentration at any time t

In case the substrate concentration is relatively higher than Ksand X is considered constant,

Eq.(6)can be simplified to

ko= Xqmax= zero-order rate constant

Reported examples of zero-order biodegradation kinetics include substances such as cose, phenol, phthalic acid, aspartic acid, ethanol, and acetate (5)

glu-3 KINETICS OF ACTIVATED SLUDGE PROCESSES

3.1 Brief Description of Activated Sludge Processes

The activated sludge process is the most widely used biological process for treatment of avariety of wastewaters In the past century many modifications of the basic activated sludgeprocess have evolved for various purposes (2):

1 Complete-mix activated sludge process: A completely mixed system can allow a more uniform aeration of the wastewater in the aeration tank This process has been applied to handle a variety of wastewaters with great success, especially because the process can sustain shock and toxic loads.

2 Step-aeration activated sludge process: In this modified system, influent wastewater is distributed through several points in the aeration tank This leads to a relatively homogenous load distribution along the length of the aeration tank resulting in a more efficient use of dissolved oxygen.

3 Contact-stabilization activated sludge: The influent contacts with a high concentration of biomass

in a small contact tank for a short period of time (20 to 40 min) The mixture then flows to the secondary clarifier where it gets settled and the resulting biosolids are returned to a stabilization tank with a hydraulic retention time of 4 to 8 h In this contact tank, a rapid biosorption of organic compounds is expected followed by the oxidation of the organics This system would need smaller tankage and produce smaller amounts of biosolids.

4 Tapered aeration process: In the basic activated sludge process, organic influent is one-point loaded to the head of aeration tank, thus the oxygen demand is extremely high at the head of the aeration tank, but very low at the exit end To overcome this problem, in tapered aeration process, the air supply tapers off with distance along the aeration tank so that supply and demand can be balanced throughout the tank.

5 Pure oxygen activated sludge process: The pure oxygen activated sludge process is based on such a simple idea that the rate of oxygen transfer in water is proportional to the partial pressure

of oxygen, that is, the rate of oxygen transfer is higher for pure oxygen than for atmospheric

Similarly, the mass balance on substrate yields:

V dS

dt = Q o S o − (QeSe+ QwSw) − rsV (22)

It should be pointed out that Eqs.(21) and (22)are derived on the basis of a mass balance onbiomass and substrate, respectively, thus can be used to describe the operation of the systemunder nonsteady or steady-state conditions In practice, activated sludge processes are rununder steady-state conditions At steady state, the changes in accumulation of both biomassand substrate are zero, that is,

Mean cell retention time or solids retention time (θ x ):

θ x = biomass in the aeration tank

Equation(28)is an important design relationship for the completely mixed activated sludge

process It can be applied whatever the form of rs may be; a Monod equation, a first-orderapproximation for dilute wastewater or the Haldane equation for high-concentration inhibitoryorganics If we assume that for a wastewater the Monod equation is applicable, then

Equation(30)is one of the recognized design equations originally derived by Lawrence andMcCarty (12) This equation shows that the efficiency of substrate removal is proportional

to the sludge age Thus, environmental engineers can expect to need a relatively large θ x toobtain high treatment efficiency; while at the same time have a short hydraulic retention time,which means a small reactor volume

Similarly, at steady state, Eq.(22)can be rearranged to give rsas a function of S:

rs= Q o S o − QeSe− QwSw

The substrate concentration in the aeration tank, S, is equal to the concentration in the effluent

Seas well as in the waste sludge line, Swbecause no biological reaction occurs in the settlingtank Also from the continuity equation of fluid flows one can state that:

Equation (34) indicates that the biomass concentration in the aeration tank depends on the

ratio of solids retention time to the hydraulic retention time, θ x /θ This equation is one of the

most commonly recognized design formulas (7, 12)

3.2.2 Process Control Parameters

Equations (30) and (34) can be useful in predicting the effects of various changes insystem parameters, but they are difficult to use from a design standpoint because of themany kinetic constants involved Environmental engineers and scientists have developed moreusable process design relationships enthatough are widely used in process design practice

These include the specific removal rate of soluble waste (q), mean solid retention time (θ x ),

and the food-to-microorganisms, F/M, ratio (7) The following discussion is based on materialfrom Metcalf and Eddy (7)

The specific removal rate of soluble waste, q: The specific removal rate of soluble wastes is

To determine q, the liquid waste flow and the biomass effective in substrate utilized must

be known The substrate utilized can be quantified by the difference between the influent

and effluent waste concentrations (S o − S e ) However, the evaluation of the active biomass

of microorganisms, X, is not an easy task, which in practice can be roughly quantified by

measuring the mixed liquor volatile suspended solids (MLVSS) in the aeration tank

Solid retention time or sludge age (θ x ): θ x is defined by the expression in Eq (25) In thecompletely mixed activated sludge process with sludge recycle, as shown inFig 1.2, excessivesludge wastage can be accomplished by directly discharging from the aeration tank or wastingfrom the mixed-liquor return line In practice, to obtain a thicker sludge, wasting is preferred

by drawing off sludge from the recycle line (2) If the system is operated correctly, Xr(which

is equal to Xw) is much larger than Xe, thus Eq (26) can be simplified to

XrQw

(36)

Equation (36) shows that to control sludge age the biomass concentrations in both aeration

tank and return sludge line must be known The biomass concentration in the return line (Xr)

can be roughly estimated in the following way:

Xr= 106

where

Xr= biomass concentration in the return line (mg/L)

SVI= sludge volume index

The sludge volume index (SVI) is a measure of the ability of sludge to settle and compact,which can be easily determined from a laboratory column settling test (13) SVI is defined asthe volume in ML occupied by 1 g of activated sludge mixed liquor solids, dry weight, aftersettling for 30 min in a 1-L graduated cylinder (16)

θ xindeed describes the residence time of the sludge in the aeration tank The sludge requires

a certain time to assimilate the liquid waste and reproduce itself If the sludge is not able

to reproduce itself before being washed out of the aeration tank, the operation will fail Onthe other hand, higher sludge age may cause the sludge to undergo more endogenous decay

leading to poorer settleability of the sludge and effluent quality The control of θ x means thecontrol of the sludge growth rate, and hence the degree of waste stabilization (2) To maintain

a desirable sludge age, a specific percentage of the biomass in the system must be wasteddaily Substituting Eq (35) into (28) gives

1

Equation (38) reveals a direct relationship between the net specific growth rate, 1/θ x, and the

specific removal rate of liquid waste, q In addition, when the effect of endogenous respiration

on the true growth yield (Y ) is taken into account, the observed growth yield (Yobs) of biomass

is lower than Y and can be expressed as

1+ Kdθ x

(39)

F/M

Fig 1.3. Effect of F/M ratio on SVI of biosolids (Source: Adapted from (6)).

Food to microorganisms’ ratio (F/M ratio): In the environmental engineering field, food to

microorganisms’ ratio (F/M) is defined as

F/M= S o

The physical meaning of this parameter indeed describes the degree of starvation of the sludge

or the potential food availability to the sludge in the system It is known that the F/M ratioinfluences the ability of the sludge to swttle and compact A typical plot of SVI against F/Mratio is presented inFig 1.3

3.2.3 Process Management

For a completely mixed activated sludge process, the performance and stability of thesystem is highly dependent on the system sludge age For a target waste, a given biologicalcommunity and the known environmental conditions, the kinetic constants in Eq (30), Y,

qmax, Ks, and Kdare fixed In this case, Eq (26) clearly shows that the target waste

concentra-tion in effluent (Se) is a function of the sludge age (θ x ) A schematic presentation of Eq (26)

plotted as Seversus θ xis shown inFig 1.4 The figure reveals that there exists a critical value

of the sludge age below which waste biodegradation does not occur This critical value of

θ x is then defined as the minimum sludge age or minimum solid retention time (θ x )min The

physical meaning of this parameter is that (θ x )minreflects the retention time of sludge at whichthe biomass is washed out or wasted from the system faster than it can be reproduced (7) Itseems fromFig 1.4that when washout occurs, the influent waste concentration (S o ) should equal the waste concentration in effluent (S), hence the minimum sludge retention time (SRT)

or sludge age can be calculated using Eq (29), that is,

(θx)min θx

Fig 1.4. Relationship between effluent concentration and biosolids age (Source: Adapted from (14)).

It must be stressed that a biological treatment system requiring a certain target

efflu-ent concefflu-entration must be designed with θ x greater than its minimum value According toEckenfelder and Argaman (14), in real system design, a safety factor of 2 to 20 is usuallyconsidered Hence,

where,

SF= safety factor

(θ x )min= minimum value of sludge age or sludge retention time (SRT)

For a given wastewater, many factors may affect the selection of SF Such factors includefluctuations in operation temperature, in wastewater flow rate and in wastewater strengthand characteristics: desired treatment efficiency; required reliability in operation; reactorconfiguration and nutrient removal

In addition, microorganisms are the main agents for the bio-oxidation of organics, thusbiomass concentration in the aeration tank is another key factor for maintaining the stability

of the system The maintenance of suspended solids is dependent, to a great extent, upon thesettleability and recycling extent of the sludge The recycle ratio of sludge from the secondaryclarifier is defined as

is particularly true for diffused aeration although mechanical aeration provides good mixingwithout relying on the diffused air in the wastewater It is believed also that turbulent mixing

by diffused air facilitates mass transfer of oxygen into the biological flocs and transfer ofcarbon dioxide and other waste products out of the flocs In the activated sludge process,the oxygen requirement consists of the amount of oxygen needed for both synthesis andrespiration Consequently one needs to know the ultimate BOD of the wastewater that can becalculated from BOD5using an appropriate conversion factor The respiration oxygen demand

is 1.42 g O2/g MLVSS (15) Because part of the MLVSS produced is wasted in the process

operation for the control of sludge retention time, the respiration oxygen demand is reduced

by an amount proportional to the amount of wasted sludge According to Wang (16), thetheoretical oxygen requirement for an activated sludge process therefore is:

Daily theoretical O2requirement= BOD removed daily −1.42 (VSS wasted daily) (47)

in which all terms are expressed in mass per day In practice, air is supplied to the aerationtank mixed liquid to maintain a minimum dissolved oxygen concentration of 1 to 2 mg/L.The objective is to maintain a dissolved oxygen gradient across the liquid–floc interface toensure an effective oxygen transfer into the biological flocs The critical oxygen tension forthe biological floc is believed to be in the neighborhood of 0.1 mg DO/L Equation (47) can

be used for the calculation of theoretical oxygen requirements of an activated sludge system

In practice, oxygen uptake rate (OUR) is a useful process control parameter Any changes inOUR reflects the need for a change in operation (6, 17)

3.4 Biosolids Production

The activated sludge process has been applied worldwide in municipal and industrialwastewater treatment practice Removal of organic materials by biological oxidation is acore technology in wastewater treatment processes New biomass, carbon dioxide, solublemicrobial products, and water are the end products for this process The daily production ofexcess biosolids from a conventional activated sludge process is around 15 to 100 L/kg ofBOD5removed, out of which more than 98% is water (18) For an activated sludge processcontrol, it is important to know the quantity of excess biosolids to be produced daily, as itwill affect the design of the biosolids treatment facilities As discussed earlier, the rate of

change of biomass concentration in a reactor, V (dX/dt), is equal to the net rate of microbial growth in the reactor, V (Y Xqmax− KdX), minus the rate of biomass outflow from the system.

Therefore, to maintain a constant biomass concentration in the aeration tank, the excess

biosolids production rate on a mass basis must be equal to V (Y Xqmax− KdX) The following

equation describes the above situation (19):

V (dX/dt)excess = QwXw = V (Y qmaxX − KdX) = V X/θ x (48)where,

V (dX/dt)excess = excess biosolids production rate

Xw= wasted biosolids concentration

Qw = wasted biosolids flow rate

Many operating parameters can affect the production of excess biosolids from a logical treatment process These include sludge age, temperature, and dissolved oxygenconcentration

bio-Different opinions can be found in the literature with regard to the effect of dissolvedoxygen concentration on biosolids production (7, 20–22) It is generally recognized that in

an activated sludge process, supply of dissolved oxygen plays a limiting role on any futureincrease in the loading rate on the treatment facility Results from purified oxygenationactivated sludge process show that the growth yield can be lowered by up to 54% as comparedwith conventional air-activated sludge system even at high biosolids loading rate (20) Boonand Burgess (23) compared the biosolids production in oxygen and air-activated sludgesystems They found that for similar biosolids retention time, the observed biosolids yield inthe pure oxygen system was only 60% of that in the air system Abbassi et al (22) also reportedthat the excess biosolids production decreased from 0.28 mg MLSS/mg BOD5 to 0.20 mgMLSS/mg BOD5as the reactor DO was increased from 1.8 to 6.0 mg/L in a laboratory-scaleconventional activated sludge reactor

In the current activated sludge theory, sludge age (θ x ) is defined as the average time a unit

of biomass remains in the treatment system Much research has shown that θ x is the mostimportant operational parameter in the activated sludge process For a steady state system, the

θ xis inversely related to the specific growth rate It has been demonstrated that the relationship

between the observed sludge yield (Yobs) and sludge age can be described by the following

Ymaxis the maximum growth yield

Equation (49) shows that the observed growth yield is inversely proportional to sludgeretention time and endogenous decay rate in a steady state activated sludge process Thisequation also provides a theoretical basis for in-plant engineers to control the total biosolids

production by adjusting θcduring the wastewater biological treatment Stall and Sherrard (24)

reported that excess biosolids production was reduced by 60% when the θ xwas increased from

2 to 18 days, while no effect on COD removal efficiency was observed On the other hand,

Wunderlich et al (25) showed that in a high-purify oxygen activated sludge system, biosolids

production was reduced from 0.38 to 0.28 mg MLVSS/mg COD removed as the θ x increasedfrom 3.7 to 8.7 days It seems from these results that the pure oxygen aeration process operated

at a relatively long θ x would be much more beneficial to the reduction of excessive biosolidsproduction

The general purpose of the activated sludge process is the removal of organic pollutantsrather than the cultivation of excess biosolids With increase of population and expansion inindustrialization, the management of the increased excess in biosolids production is generating

a real challenge in the field of environmental engineering So far the regulations in biosolidsmanagement in most countries are becoming more and more stringent in relation to theapplication of biosolids on agricultural land, dumping into sea, or disposal in landfill Wasteactivated sludge production is an important economic factor because the generated biosolidshave to be treated before reuse or disposal in an environmentally sound and cost-effectivemanner The treatment of excess biosolids may account for 25% up to 65% of a total plantoperation cost (26, 27) Also it is necessary to look for appropriate ways to recycle theexcess biosolids production for beneficial uses Hence, an ideal way to solve the biosolids-associated problems is to reduce their production in first place rather than spending valuableresources in post-treatment of the generated product (27) Strategy for minimization of excessbiosolids production from biological treatment processes has become a very practical andurgent issue (28)

4 FACTORS AFFECTING THE NITRIFICATION PROCESS

The Michigan studies on the significance of nitrogenous oxidation in creating oxygen sag

in receiving streams and other studies showing the role of ammonia and nitrate nitrogen instimulating algal blooms have demonstrated the need for information on how wastewater-treatment plants can be designed to optimize nitrification and denitrification processes.Nitrogen removal from wastewater can be accomplished through a variety of alternativeprocesses The popular approach is by biological nitrification-denitrification (29–37), whichhas the additional advantage of returning nitrogen to the atmosphere in its natural form Inthis regard, it has been shown that the efficiency of nitrogen removal is strictly correlatedwith the degree of nitrification achieved (31) Moreover, the process of denitrification isquite effective and the nitrification phase is the limiting step in determining the efficiency ofnitrogen extraction It can be concluded that further perfection of the overall process depends

on the improvement of the nitrification phase, which is the less reliable phase in the processsequence In simple terms, nitrification in treatment plants can be maintained only when therate of growth of nitrifying bacteria is rapid enough to replace organisms lost through biosolidswasting When these bacteria can no longer keep pace, the ability to nitrify decreases and maybecome extinct

To be able to evaluate accurately the effect of the environmental factors and to present aconsistent and valuable basis for application, it is clear that a kinetic description of the process

is essential Several equations have been proposed to describe the nitrification process (38)

The kinetic expression most extensively used to describe biological systems is the one lated and experimentally sustained by Monod (39–43) Eqs (6) and (7) discussed in a previoussection can be expressed in the following form:

v = (qX) = rate of substrate (NH3-N) utilization, mg/L/d

S= substrate ammonia nitrogen concentration, mg/L

t = time, day

dS/dt = rate of substrate (NH3-N) utilization, mg/L/day

k = (qmax)= rate of NH3-N utilization per unit weight of microorganisms, mg/L N/mg/L MLVSS/day

The first step for evaluating the kinetic parameters Vm, Ks, and k is to determine the fication rate, v, as a function of substrate concentration From plots of ammonia-nitrogen

nitri-concentration versus time (0 to 8 h) for all 45 experiments, values of v were determined from

the slopes of the tangents at different substrate concentrations Ks and Vm (hence k) were determined from the reciprocal plots of 1/v against 1/S, taking advantage of the linearity of the plots at high values of v The intercepts on the 1/v axis yield the values of Vm(hence k); the values of Ksare obtained from the slopes (44)

4.1 Factors Affecting the Half-Velocity Coefficient, Ks

The variation of this parameter with temperature and pH at different MLVSS concentrations

is shown inTable 1.1 At low (430 mg/L) MLVSS, Ksdecreases with increasing temperature(4◦C to 33◦C) and pH (7.0 to 8.3) While the Ksvalues for higher MLVSS concentrations alsotend to decrease with increasing pH and temperatures to 10◦C and 17◦C, the trend reversesitself at higher temperatures This reversal seems to begin at 10◦C to 20◦C, with a small

variation in Ksafter 25◦C (44)

An interesting feature of this change in behavior created by the increase in microbial mass

is that it altered both the pH and temperature effects on K (44) The shift is much more