Advanced Physicochemical Treatment Processes

AdvancedPhysicochemical

Treatment Processes

Edited by

Lawrence K. Wang, PhD, PE, DEEZorex Corporation, Newtonville, NY

Lenox Institute of Water Technology, Lenox, MAKrofta Engineering Corporation, Lenox, MA

Yung-Tse Hung, PhD, PE, DEEDepartment of Civil and Environmental Engineering

Cleveland State University, Cleveland, OH

Nazih K. Shammas, PhDLenox Institute of Water Technology, Lenox, MA

Krofta Engineering Corporation, Lenox, MA

VOLUME 4HANDBOOK OF ENVIRONMENTAL ENGINEERING

© 2006 Humana Press Inc.999 Riverview Drive, Suite 208Totowa, New Jersey 07512

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Library of Congress Cataloging-in-Publication DataAdvanced physicochemical treatment processes / edited by Lawrence K. Wang, Yung-Tse Hung, NazihK. Shammas.

p. cm. — (Handbook of environmental engineering ; v. 4)Includes bibliographical references and index.ISBN 1-58829-361-0 (alk. paper)1. Water—Purification. 2. Sewage—Purification. I. Wang, Lawrence K. II. Hung, Yung-Tse. III. Shammas,Nazih K. IV. Series: Handbook of environmental engineering (2004) ; v. 4.TD170 .H37 2004 vol. 4[TD430]628 s—dc22[628.1/ 2005016683

Preface

v

The past thirty years have witnessed a growing worldwide desire that posi-tive actions be taken to restore and protect the environment from the degrad-ing effects of all forms of pollution—air, water, soil, and noise. Becausepollution is a direct or indirect consequence of waste, the seemingly idealisticdemand for “zero discharge” can be construed as an unrealistic demand forzero waste. However, as long as waste continues to exist, we can only attemptto abate the subsequent pollution by converting it to a less noxious form. Threemajor questions usually arise when a particular type of pollution has been iden-tified: (1) How serious is the pollution? (2) Is the technology to abate it avail-able? and (3) Do the costs of abatement justify the degree of abatementachieved? This book is one of the volumes of the Handbook of EnvironmentalEngineering series. The principal intention of this series is to help readers for-mulate answers to the last two questions above.

The traditional approach of applying tried-and-true solutions to specificpollution problems has been a major contributing factor to the success of envi-ronmental engineering, and has accounted in large measure for the establish-ment of a “methodology of pollution control.” However, the realization of theever-increasing complexity and interrelated nature of current environmentalproblems renders it imperative that intelligent planning of pollution abatementsystems be undertaken. Prerequisite to such planning is an understanding ofthe performance, potential, and limitations of the various methods of pollutionabatement available for environmental scientists and engineers. In this seriesof handbooks, we will review at a tutorial level a broad spectrum of engineer-ing systems (processes, operations, and methods) currently being utilized, orof potential utility, for pollution abatement. We believe that the unified inter-disciplinary approach presented in these handbooks is a logical step in the evo-lution of environmental engineering.

Treatment of the various engineering systems presented will show how anengineering formulation of the subject flows naturally from the fundamentalprinciples and theories of chemistry, microbiology, physics, and mathematics.This emphasis on fundamental science recognizes that engineering practice hasin recent years become more firmly based on scientific principles rather thanon its earlier dependency on empirical accumulation of facts. It is not intended,though, to neglect empiricism where such data lead quickly to the most eco-nomic design; certain engineering systems are not readily amenable to funda-mental scientific analysis, and in these instances we have resorted to less sciencein favor of more art and empiricism.

Because an environmental engineer must understand science within the con-text of application, we first present the development of the scientific basis of aparticular subject, followed by exposition of the pertinent design concepts and

operations, and detailed explanations of their applications to environmentalquality control or remediation. Throughout the series, methods of practicaldesign and calculation are illustrated by numerical examples. These examplesclearly demonstrate how organized, analytical reasoning leads to the most di-rect and clear solutions. Wherever possible, pertinent cost data have been pro-vided.

Our treatment of pollution-abatement engineering is offered in the belief thatthe trained engineer should more firmly understand fundamental principles,be more aware of the similarities and/or differences among many of the engi-neering systems, and exhibit greater flexibility and originality in the definitionand innovative solution of environmental pollution problems. In short, the en-vironmental engineer should by conviction and practice be more readily adapt-able to change and progress.

Coverage of the unusually broad field of environmental engineering hasdemanded an expertise that could only be provided through multiple author-ships. Each author (or group of authors) was permitted to employ, within rea-sonable limits, the customary personal style in organizing and presenting aparticular subject area; consequently, it has been difficult to treat all subjectmaterial in a homogeneous manner. Moreover, owing to limitations of space,some of the authors’ favored topics could not be treated in great detail, andmany less important topics had to be merely mentioned or commented onbriefly. All authors have provided an excellent list of references at the end ofeach chapter for the benefit of interested readers. As each chapter is meant tobe self-contained, some mild repetition among the various texts was unavoid-able. In each case, all omissions or repetitions are the responsibility of the edi-tors and not the individual authors. With the current trend toward metrication,the question of using a consistent system of units has been a problem. Wher-ever possible, the authors have used the British system (fps) along with themetric equivalent (mks, cgs, or SIU) or vice versa. The editors sincerely hopethat this duplicity of units’ usage will prove to be useful rather than being dis-ruptive to the readers.

The goals of the Handbook of Environmental Engineering series are: (1) tocover entire environmental fields, including air and noise pollution control,solid waste processing and resource recovery, physicochemical treatment pro-cesses, biological treatment processes, biosolids management, water resources,natural control processes, radioactive waste disposal, and thermal pollutioncontrol; and (2) to employ a multithematic approach to environmental pollu-tion control because air, water, soil and energy are all interrelated.

As can be seen from the above handbook coverage, no consideration is givento pollution by type of industry or to the abatement of specific pollutants.Rather, the organization of the handbook series has been based on the threebasic forms in which pollutants and waste are manifested: gas, solid, and liq-uid. In addition, noise pollution control is included in the handbook series.

vi Preface

This particular book Volume 4, Advanced Physicochemical Treatment Pro-cesses, is a sister book to Volume 3 Physicochemical Treatment Processes, whichhas already included the subjects of screening, comminution, equalization,neutralization, mixing, coagulation, flocculation, chemical precipitation, re-carbonation, softening, oxidation, halogenation, chlorination, disinfection,ozonation, electrolysis, sedimentation, dissolved air flotation, filtration, poly-meric adsorption, granular activated carbon adsorption, membrane pro-cesses, and sludge treatment processes. Both books have been designed toserve as comprehensive physicochemical treatment textbooks as well as wide-ranging reference books. We hope and expect it will prove of equal high valueto advanced undergraduate and graduate students, to designers of water andwastewater treatment systems, and to scientists and researchers. The editorswelcome comments from readers in all of these categories.

The editors are pleased to acknowledge the encouragement and support re-ceived from their colleagues and the publisher during the conceptual stages ofthis endeavor. We wish to thank the contributing authors for their time andeffort, and for having patiently borne our reviews and numerous queries andcomments. We are very grateful to our respective families for their patienceand understanding during some rather trying times.

Lawrence K. WangYung-Tse Hung

Nazih K. Shammas

Preface vii

ix

Contents

Preface ...........................................................................................................................v

Contributors ................................................................................................................xi

1. Potable Water AerationJerry R. Taricska, Lawrence K. Wang, Yung-Tse Hung,

and Kathleen Hung Li ................................................................................... 1

1. Introduction ................................................................................................................................................... 11.1. Types of Aeration Process .................................................................................................................. 1

2. Applications .................................................................................................................................................. 22.1. Taste and Odor Removal .................................................................................................................... 22.2. Iron and Manganese Oxidation .......................................................................................................... 22.3. Hydrogen Sulfide and Carbon Dioxide Removal .............................................................................. 32.4. Ammonia Removal ............................................................................................................................. 42.5. Aesthetic or Decorative Aeration ....................................................................................................... 42.6. Reservoir De-stratification and Oxygenation of Water .................................................................... 42.7. Dissolved Air Flotation for Flocculation/Flotation ........................................................................... 52.8. Trihalomethanes Removal .................................................................................................................. 52.9. Volatile Organics Removal ................................................................................................................ 52.10. Hazardous Waste Cleanup .................................................................................................................. 52.11. Radionuclides Removal ...................................................................................................................... 6

3. Unit Processes for Organic Contaminant Removal .................................................................................... 63.1. Packed Column Aeration .................................................................................................................. 103.2. System Design Considerations ......................................................................................................... 203.3. Additional System Design Considerations ...................................................................................... 243.4. PTA Pilot Testing for VOC Removal .............................................................................................. 263.5. Other Types of Tower ....................................................................................................................... 29

4. Diffused Aeration ....................................................................................................................................... 334.1. Design Criteria .................................................................................................................................. 34

5. Mechanical Aeration .................................................................................................................................. 356. System Performance ................................................................................................................................... 357. System Costs ............................................................................................................................................... 368. Case Study of Packed Tower Aeration ...................................................................................................... 40

8.1. Scottsdale, AZ ................................................................................................................................... 408.2. Naples, FL ......................................................................................................................................... 40Nomenclature .............................................................................................................................................. 44References ................................................................................................................................................... 44

2. Air StrippingJu-Chang Huang and Chii Shang .................................................................. 47

1. Introduction ................................................................................................................................................. 472. Henry’s Law and the Mass-Transfer Coefficient ..................................................................................... 483. Analytical Requirements for an Air-Stripping Program .......................................................................... 494. Features and Designs .................................................................................................................................. 50

4.1. Features of the Countercurrent Air Stripper .................................................................................... 504.2. Air-Stripper Design Parameters ....................................................................................................... 504.3. Packing Material ............................................................................................................................... 54

5. Pilot Studies ................................................................................................................................................ 556. Ammonia Stripping .................................................................................................................................... 587. Water Quality Problems ............................................................................................................................. 69

8. Off-Gas Emissions ..................................................................................................................................... 709. Capital and Operational Cost Analysis ..................................................................................................... 71

9.1. Minimizing Power Costs .................................................................................................................. 719.2. Comparisons of Capital and Operational Costs .............................................................................. 72

10. Recent Advancements ................................................................................................................................ 7411. Conclusions ................................................................................................................................................. 75

Nomenclature .............................................................................................................................................. 77References ................................................................................................................................................... 78

3. Adsorptive Bubble Separationand Dispersed Air Flotation

Lawrence K. Wang ........................................................................................... 81

1. Introduction ................................................................................................................................................. 811.1. General Description .......................................................................................................................... 811.2. Adsorptive Bubble Separation ......................................................................................................... 82

2. Bubble Separation Process Descriptions and Definitions Based on the TechniquesUsed for Bubble Generation ................................................................................................................... 85

2.1. Dissolved Air Flotation .................................................................................................................... 852.2. Dispersed Air Flotation .................................................................................................................... 852.3. Vacuum Flotation .............................................................................................................................. 852.4. Electrolytic Flotation ........................................................................................................................ 872.5. Biological Flotation .......................................................................................................................... 872.6. Deep-Shaft Flotation ......................................................................................................................... 88

3. Bubble Separation Process Descriptions and Definitions According to the TechniquesUsed for Solids Separation ..................................................................................................................... 88

3.1. Foam Separation ............................................................................................................................... 883.2. Nonfoaming Adsorptive Bubble Separation .................................................................................... 91

4. Bubble Separation Process Descriptions and Definitions According to the Operational Modes .......... 934.1. Continuous Adsorption Bubble Separation ..................................................................................... 934.2. Sequencing Batch Reactor Adsoprive Bubble Separation .............................................................. 93

5. Surface Adsorption ..................................................................................................................................... 936. Bubble Phenomena ..................................................................................................................................... 967. Multiphase Flow ......................................................................................................................................... 978. Material Balances ....................................................................................................................................... 989. Foam Separation by Dispersed Air Flotation Cell .................................................................................. 10010. Chemical Reagents for Adsorptive Bubble Separation .......................................................................... 10511. Laboratory Foam Separation Tests .......................................................................................................... 106

11.1. Sequencing Batch Reactor Foam Separation ................................................................................. 10611.2. Continuous Foam Separation ......................................................................................................... 106

12. Engineering Applications ......................................................................................................................... 10712.1. De-inking Process for Waste Paper Purification and Recycle ..................................................... 10712.2. Flotation Process for Calcium Carbonate Recovery from Water Treatment Sludges ................. 110

13. Analytical Methods Available for Process Monitoring .......................................................................... 11214. Glossary .................................................................................................................................................... 112

Nomenclature ............................................................................................................................................ 114References ................................................................................................................................................. 116

4. Powdered Activated Carbon AdsorptionYung-Tse Hung, Howard H. Lo, Lawrence K. Wang,

Jerry R. Taricska, and Kathleen Hung Li ................................................ 123

1. Introduction ............................................................................................................................................... 1232. Properties of Activated Carbon ............................................................................................................... 1253. Adsorption Isotherm Models ................................................................................................................... 1274. Design Consideration of PAC Systems ................................................................................................... 131

4.1. Design Considerations .................................................................................................................... 1314.2. Laboratory Procedures for Batch Adsorption Study ..................................................................... 133

5. Regeneration ............................................................................................................................................. 133

x Contents

6. Factors Affecting Performance ................................................................................................................ 1346.1. Variables for the Combined Activated Carbon–Activated Sludge Process ................................. 1346.2. Factors Affecting Adsorption ......................................................................................................... 135

7. Performance and Case Studies ................................................................................................................. 1368. Economics of Powdered Activated Carbon System ............................................................................... 1389. Design Examples ...................................................................................................................................... 138

9.1. Example 1 (Langmuir and Freundlich Isotherms Constants) ....................................................... 1389.2. Example 2 (Powdered Activated Carbon Adsorption Tests) ........................................................ 1429.3. Example 3 (Design and Applications of Physicochemical PAC Process Systems) .................... 1469.4. Example 4 (Design and Applications of Combined Biological

and Physicochemical PAC Process Systems) .......................................................................... 148Nomenclature ............................................................................................................................................ 150References ................................................................................................................................................. 151

5. Diatomaceous Earth Precoat FiltrationLawrence K. Wang ......................................................................................... 155

1. Introduction ............................................................................................................................................... 1552. Process Description .................................................................................................................................. 156

2.1. Diatomaceous Earth ........................................................................................................................ 1562.2. Diatomaceous Earth Filtration and Filter Aid ............................................................................... 156

3. Diatomaceous Earth Filtration System Design ....................................................................................... 1634. Diatomaceous Earth Filtration System Operation .................................................................................. 163

4.1. Precoating Operation ...................................................................................................................... 1634.2 Filtration Operation ........................................................................................................................ 1644.3. Filter Cake Removal ....................................................................................................................... 167

5. Diatomaceous Earth Filtration System Maintenance ............................................................................. 1686. Types of Precoat Filter ............................................................................................................................. 169

6.1. Plate and Frame Filters ................................................................................................................... 1696.2. Tubular Filters ................................................................................................................................. 1706.3. Vertical Tank–Vertical Leaf Filters ............................................................................................... 1706.4. Horizontal Tank–Vertical Leaf (“H” Style) Filters ....................................................................... 1716.5. Rotating Leaf Filters ....................................................................................................................... 1716.6. Horizontal Leaf Filters .................................................................................................................... 1736.7. Specialty Filters .............................................................................................................................. 1736.8. Vacuum Leaf Filters ....................................................................................................................... 1736.9. Rotary Vacuum Precoat Filters ...................................................................................................... 174

7. Auxiliary Parts and Equipment ................................................................................................................ 1767.1. Precoat Filter Leaves ...................................................................................................................... 1767.2. Filter Feed Pumps ........................................................................................................................... 1777.3. Precoat and Body Feed Tanks ........................................................................................................ 1777.4. Body Feed Systems ......................................................................................................................... 1777.5. Automation Equipment ................................................................................................................... 178

8. Bulk Filter Aid Handling ......................................................................................................................... 1789. Precoat Filtration Applications, Advantages, and Disadvantages ......................................................... 179

9.1. Municipal and Military Applications ............................................................................................. 1799.2. Industrial Applications ................................................................................................................... 1809.3. Advantages and Disadvantages ...................................................................................................... 182

10. Summary ................................................................................................................................................... 18311. Glossary of Diatomaceous Earth Filtration (Precoat Filtration) ............................................................ 184

Acknowledgments .................................................................................................................................... 187References ................................................................................................................................................. 188

6. Tertiary MicroscreeningNazih K. Shammas, Chein-Chi Chang, and Lawrence K. Wang ............... 191

1. Introduction ............................................................................................................................................... 1912. Microscreening Process ........................................................................................................................... 192

Contents xi

3. Design Criteria .......................................................................................................................................... 1924. Backwashing ............................................................................................................................................. 1955. Design of Microscreens ............................................................................................................................ 196

5.1. Input Data ........................................................................................................................................ 1965.2. Design Parameters .......................................................................................................................... 1965.3. Design Procedure ............................................................................................................................ 1965.4. Output Data ..................................................................................................................................... 197

6. Energy and Costs ...................................................................................................................................... 1977. Design Example ........................................................................................................................................ 197

Nomenclature ............................................................................................................................................ 200References ................................................................................................................................................. 200Appendix ................................................................................................................................................... 202

7. Membrane FiltrationJ. Paul Chen, Honghui Mou, Lawrence K. Wang,

and Takeshi Matsuura ............................................................................... 203

1. Introduction ............................................................................................................................................... 2032. Membrane and Membrane-Separation Processes for Water Treatment ................................................ 204

2.1. Basics of Membrane and Membrane-Separation Systems ............................................................ 2042.2. Membrane-Separation Processes for Water Treatment ................................................................ 2052.3. Case Studies on Membrane Applications in Water Treatment ..................................................... 213

3. Membrane Materials: Preparation and Modification .............................................................................. 2163.1. Membrane Materials ....................................................................................................................... 2163.2. Types of Membrane and Their Formation ..................................................................................... 216

4. Membrane Characterization ..................................................................................................................... 2204.1. Porous Membrane ........................................................................................................................... 2204.2. Nonporous Membrane .................................................................................................................... 220

5. Mass Transport in Membranes ................................................................................................................ 2215.1. The Solution–Diffusion Model ...................................................................................................... 2225.2. The Pore Model ............................................................................................................................... 226

6. Membrane Module and Process Design .................................................................................................. 2286.1. Introduction ..................................................................................................................................... 2286.2. Typical Membrane Modules ........................................................................................................... 2286.3. Design Considerations .................................................................................................................... 2326.4. Engineering Design ......................................................................................................................... 2366.5. Membrane Testing .......................................................................................................................... 2406.6. Economics of Membrane Processes ............................................................................................... 241

7. Membrane Fouling and Prevention ......................................................................................................... 2427.1. Mechanisms ..................................................................................................................................... 2427.2. Feed Pretreatment ........................................................................................................................... 244

8. Membrane Cleaning and Flux Restoration ............................................................................................. 2488.1. Chemical Cleaning Methods .......................................................................................................... 2488.2. Physical Cleaning Methods ............................................................................................................ 251

9. Summary ................................................................................................................................................... 252Acknowledgment ...................................................................................................................................... 252Abbreviations ............................................................................................................................................ 252Nomenclature ............................................................................................................................................ 253References ................................................................................................................................................. 255

8. Ion ExchangeJ. Paul Chen, Lei Yang, Wun-Jern Ng, Lawrence K. Wang,

and Sook-Leng Thong ............................................................................... 261

1. Introduction ............................................................................................................................................... 2612. Characterization of Ion Exchangers ........................................................................................................ 263

2.1. Physical Properties .......................................................................................................................... 2632.2. Chemical Properties ........................................................................................................................ 265

xii Contents

Contents xiii

3. Ion-Exchange Calculations ...................................................................................................................... 2713.1. Equilibrium ...................................................................................................................................... 2723.2. Kinetics ............................................................................................................................................ 2773.3. Fixed-Bed Operation ....................................................................................................................... 278

4. Applications .............................................................................................................................................. 2794.1. Water Softening .............................................................................................................................. 2804.2. Deionization nd High-Quality Water Supply ................................................................................ 2814.3. Removal and Recovery of Heavy Metals ...................................................................................... 2834.4. Removal of Nitrogen ...................................................................................................................... 2844.5. Removal of Phosphorous ................................................................................................................ 2854.6. Organic-Chemical Removal ........................................................................................................... 286

5. Operations ................................................................................................................................................. 289Nomenclature ............................................................................................................................................ 289References ................................................................................................................................................. 290

9. Fluoridation and DefluoridationJerry R. Taricska, Lawrence K. Wang, Yung-Tse Hung,

and Kathleen Hung Li ............................................................................... 293

1. Introduction ............................................................................................................................................... 2932. Natural Fluoridation ................................................................................................................................. 2963. Controlled Fluoridation ............................................................................................................................ 2984. Dry Feeders ............................................................................................................................................... 299

4.1. Example of Dry Feeders ................................................................................................................. 3004.2. Checking Particle Size .................................................................................................................... 3004.3. Example of Sieve Analysis ............................................................................................................. 3014.4. Feeding System ............................................................................................................................... 3014.5. Meters .............................................................................................................................................. 3024.6. Auxiliary Equipment ....................................................................................................................... 302

5. Saturators .................................................................................................................................................. 3055.1. Downflow Saturators ...................................................................................................................... 3065.2. Upflow Saturators ........................................................................................................................... 309

6. Common Operational Problems in Preparation of Fluoride Solution ................................................... 3107. Calculations Involving Solutions ............................................................................................................ 311

7.1. Example 1 ........................................................................................................................................ 3117.2. Example 2 ........................................................................................................................................ 3117.3. Example 3 ........................................................................................................................................ 3127.4. Example 4 ........................................................................................................................................ 313

8. Defluoridation ........................................................................................................................................... 314References ................................................................................................................................................. 314

10. Ultraviolet Radiation for DisinfectionJ. Paul Chen, Lei Yang, Lawrence K. Wang, and Beiping Zhang ............. 317

1. Introduction ............................................................................................................................................... 3171.1. Historical Background and Technology Development ................................................................. 3171.2. UV Radiation Process Description ................................................................................................ 320

2. Pathogens in the Environment ................................................................................................................. 3213. Disinfection Mechanisms ......................................................................................................................... 322

3.1. Chemistry of DNA and RNA ......................................................................................................... 3233.2. Physical Properties of UV Light .................................................................................................... 3243.3. Inactivation of Pathogens ............................................................................................................... 3253.4. Reactivation of Pathogens .............................................................................................................. 327

4. Mathematical Description of UV Disinfection Process ......................................................................... 3284.1. UV Dose .......................................................................................................................................... 3284.2. Effect of UV Dose on Pathogen Inactivation ................................................................................ 330

5. Collimated Beam Test .............................................................................................................................. 3326. Design of UV Unit for Aqueous-Phase Disinfection ............................................................................. 336

xiv Contents

6.1. Empirical Design Approach ........................................................................................................... 3366.2. Probabilistic Design Approach ...................................................................................................... 3396.3. Model-Based Design Approach ..................................................................................................... 3396.4. Professional Engineering Design Approach .................................................................................. 340

7. Applications of UV Unit for Aqueous-Phase Disinfection .................................................................... 3417.1. Water Treatment ............................................................................................................................. 3437.2 Wastewater Treatment .................................................................................................................... 3477.3. Environmental Protection ............................................................................................................... 348

8. Operation and Maintenance of UV System in Aqueous Environments ................................................ 3488.1. UV Lamps ....................................................................................................................................... 3488.2. Operational Factors ......................................................................................................................... 3528.3. Maintenance Factors ....................................................................................................................... 353

9. UV Disinfection By-Products and UV Lamp Disposal .......................................................................... 35410. UV Disinfection of Air Emissions .......................................................................................................... 35511. UV Engineering Case History and Applications .................................................................................... 357

11.1. Engineering Case History ............................................................................................................... 35711.2. UV Engineering Applications ........................................................................................................ 358Nomenclature ............................................................................................................................................ 361References ................................................................................................................................................. 362

11. Water Chloridation and ChloraminationLawrence K. Wang ......................................................................................... 367

1. Introduction ............................................................................................................................................... 3671.1. Chlorine ........................................................................................................................................... 3681.2. Monochloramine ............................................................................................................................. 368

2. Potable Water Chlorination ..................................................................................................................... 3692.1. Surface Water Treatment Rules ..................................................................................................... 3692.2. Potable Water Chlorination Process Description .......................................................................... 3702.3. Design and Operation Considerations ........................................................................................... 3732.4. Process Equipment and Control ..................................................................................................... 3742.5. Design Example .............................................................................................................................. 379

3. Potable Water Chloramination ................................................................................................................ 3833.1. Potable Water Chloramination Process Description ..................................................................... 3833.2. Design and Operation Considerations ........................................................................................... 3843.3. Process Equipment and Control ..................................................................................................... 3853.4. Application Examples ..................................................................................................................... 386

4. Controlling Disinfection By-Products in Drinking Water ..................................................................... 3874.1. Strategies for Controlling Disinfection By-Products .................................................................... 3874.2. Using Alternative Disinfectants ..................................................................................................... 3884.3. Minimizing Precursor Concentrations ........................................................................................... 390References ................................................................................................................................................. 390Appendix A: Summary of Corrosion Indices ......................................................................................... 393Appendix B1–B6: CT Values for Inactivation of Giardia and Viruses by Free Chlorine ................... 394Appendix C: CT Values for Inactivation of Viruses by Free Chlorine ................................................. 400Appendix D: CT Values for Inactivation of Giardia Cysts by Chloramine, pH 6–9 ........................... 400Appendix E: CT Values for Inactivation of Viruses by Chloramine ..................................................... 400Appendix F: On-Site Sodium Hypochlorite Generation System ........................................................... 401

12. Waste Chlorination and StabilizationLawrence K. Wang ......................................................................................... 403

1. Introduction ............................................................................................................................................... 4031.1. Process Introduction ....................................................................................................................... 4031.2. Glossary ........................................................................................................................................... 404

2. Wastewater Chlorination .......................................................................................................................... 4052.1. Process Description ......................................................................................................................... 4052.2. Design and Operation Considerations ........................................................................................... 406

Contents xv

2.3. Process Equipment and Control ..................................................................................................... 4092.4. Design Example—Design of a Wastewater Chlorine Contact Chamber ..................................... 4152.5. Application Example—Coxsackie Sewage Treatment Plant, Coxsackie, NY, USA .................. 416

3. Sludge Chlorination and Stabilization ..................................................................................................... 4183.1. Process Description ......................................................................................................................... 4183.2. Design and Operation Considerations ........................................................................................... 4193.3. Process Equipment and Control ..................................................................................................... 4213.4. Application Example—Coxsackie Sewage Treatment Plant, Coxsackie, NY, USA .................. 425

4. Septic Chlorination and Stabilization ...................................................................................................... 4334.1. Process Description ......................................................................................................................... 4334.2. Design and Operation Considerations ........................................................................................... 4344.3. Process Equipment and Control ..................................................................................................... 4354.4. Design Criteria ................................................................................................................................ 436

5. Safety Considerations of Chlorination Processes ................................................................................... 436Nomenclature ............................................................................................................................................ 438Acknowledgments .................................................................................................................................... 438References ................................................................................................................................................. 438

13. DechlorinationRajagopalan Ganesh, Lawrence Y. C. Leong,

Maria W. Tikkanen, and Gregory J. Peterka........................................... 441

1. Background ............................................................................................................................................... 4411.1. Chlorination of Potable Waters ...................................................................................................... 4411.2. Release of Chlorinated Water and Concerns ................................................................................. 442

2. Dechlorination of Water Releases ........................................................................................................... 4422.1. Non-chemical Methods for Chlorine Dissipation ......................................................................... 4432.2. Dechlorination Using Chemicals ................................................................................................... 446

3. Field Dechlorination Studies ................................................................................................................... 4543.1. Background ..................................................................................................................................... 4543.2. Field Dechlorination Tests at Tacoma Waters .............................................................................. 4543.3. Field Dechlorination Studies at Bureau of Water Works, Portland ............................................. 4573.4. Dechlorination Field Studies at EBMUD ...................................................................................... 4583.5. Summary of Field Dechlorination Studies .................................................................................... 460Acknowledgments .................................................................................................................................... 461References ................................................................................................................................................. 461

14. Advanced Oxidation ProcessesM. B. Ray, J. Paul Chen, Lawrence K. Wang,

and Simo Olavi Pehkonen ......................................................................... 463

1. Introduction ............................................................................................................................................... 4632. Mechanisms and Theory .......................................................................................................................... 464

2.1. Chemical Oxidation ........................................................................................................................ 4642.2. Radiation Methods .......................................................................................................................... 4652.3. Combination Processes ................................................................................................................... 467

3. Reaction Kinetics ..................................................................................................................................... 4684. Intermediates and By-Products ................................................................................................................ 4695. Process Parameters ................................................................................................................................... 469

5.1. Characteristics of Wastewater ........................................................................................................ 4695.2. Operating Conditions ...................................................................................................................... 470

6. Reactor Design ......................................................................................................................................... 4716.1. Reactor Models ............................................................................................................................... 4716.2. Light Source .................................................................................................................................... 4736.3. Reactor Configurations ................................................................................................................... 4736.4. Commercial Applications ............................................................................................................... 4756.5. Cost and Energy Efficiency of AOP .............................................................................................. 475

7. Limitations and Challenges of AOP ........................................................................................................ 476

xvi Contents

8. Recent R&D .............................................................................................................................................. 4769. Summary ................................................................................................................................................... 477

Nomenclature ............................................................................................................................................ 478References ................................................................................................................................................. 479

15. Chemical Reduction/OxidationLawrence K. Wang and Yan Li ..................................................................... 483

1. Chemical Reduction ................................................................................................................................. 4831.1. Process Description ......................................................................................................................... 4831.2. Chemical Reduction Process Chemistry ........................................................................................ 4841.3. Process Applications ....................................................................................................................... 4861.4. Chemical Reduction Design Considerations ................................................................................. 4871.5. Design and Application Examples ................................................................................................. 488

2. Chemical Oxidation .................................................................................................................................. 4902.1. Process Description ......................................................................................................................... 4902.2. Process Chemicals .......................................................................................................................... 4912.3. Process Applications ....................................................................................................................... 4932.4. Chemical Oxidation Design Considerations ................................................................................. 4942.5. Design and Application Examples ................................................................................................. 495

3. Recent Developments ............................................................................................................................... 5013.1. Liquid-Phase Chemical/Reduction System for Site Remediation ................................................ 5013.2. Gas-Phase Chemical Reduction Process for Site Remediation .................................................... 502References ................................................................................................................................................. 505Appendices

Appendix A1: Chemical Reduction and Clarification Used in Metal Finishing Industry ............... 509Appendix A2: Chemical Reduction and Filtration Used in Metal Finishing Industry .................... 510Appendix B: Chemical Reduction and Clarification Used in Aluminum Forming Industry ........... 511Appendix C: Chemical Reduction and Filtration Used in Inorganic Chemical Industry ................ 512Appendix D1: Chemical Oxidation (Chlorination) Used in Inorganic Chemical Industry

(Sodium Bisulfite Manufacturing Industry) ................................................................................. 513Appendix D2: Chemical Oxidation (Chlorination) Used in Inorganic Chemical Industry

(Hydrogen Cyanide Manufacturing Industry) .............................................................................. 514Appendix E1: Chemical Oxidation (Chlorination) Used in Ore Mining and Dressing Industry

(Lead/Zinc Industry) ...................................................................................................................... 515Appendix E2: Chemical Oxidation (Chlorination) Used in Ore Mining and Dressing Industry

(Ferroalloy Industry) ...................................................................................................................... 516Appendix F: Chemical Oxidation (Chlorination) Used in Organic and Inorganic Wastes ............. 517Appendix G: Chemical Oxidation (Ozonation) Used in Textile Mills

(Woven Fabric Finishing) .............................................................................................................. 518Appendix H: Chemical Oxidation (Ozonation) Used in Adhesive and Sealants Industry .............. 519

16. Oil Water SeparationPuangrat Kajitvichyanukul, Yung-Tse Hung,

and Lawrence K. Wang ............................................................................. 521

1. Introduction ............................................................................................................................................... 5212. Oil Properties ............................................................................................................................................ 5233. Treatment Technology ............................................................................................................................. 524

3.1. Process Selection ............................................................................................................................ 5243.2. Primary Treatment System ............................................................................................................. 5253.3. Secondary Treatment System ......................................................................................................... 530

4. Engineering Design .................................................................................................................................. 5374.1. Gravity Flotation ............................................................................................................................. 5374.2. Coalescing Plate Interceptor (CPI) ................................................................................................ 5394.3. Dissolved Air Flotation (DAF) ...................................................................................................... 5404.4. Ultrafiltration Membrane ................................................................................................................ 541

5. Design Examples and Questions ............................................................................................................. 543

Contents xvii

5.1. Example 1 ........................................................................................................................................ 5435.2. Example 2 ........................................................................................................................................ 5435.3. Example 3 ........................................................................................................................................ 544Nomenclature ............................................................................................................................................ 545References ................................................................................................................................................. 546

17. Evaporation ProcessesLawrence K. Wang, Nazih K. Shammas, Clint Williford,

Wei-Yin Chen, and Georgios P. Sakellaropoulos .................................... 549

1. Introduction ............................................................................................................................................... 5491.1. Drying and Evaporation Processes ................................................................................................ 5491.2. Natural Sludge Evaporation Lagoons and Evaporation Process Reactor .................................... 550

2. Sludge Evaporation Lagoons (Sludge Drying Lagoons) ........................................................................ 5512.1. Process Description ......................................................................................................................... 5512.2. Process Applications and Limitations ............................................................................................ 5522.3. Design Considerations .................................................................................................................... 5532.4. Costs ................................................................................................................................................ 555

3. Evaporators ............................................................................................................................................... 5563.1. Process Description ......................................................................................................................... 5563.2. Process Applications and Limitations ............................................................................................ 5593.3. Design Considerations .................................................................................................................... 559

4. Design Examples ...................................................................................................................................... 5634.1. Example 1 ........................................................................................................................................ 5634.2. Example 2 ........................................................................................................................................ 5644.3. Example 3 ........................................................................................................................................ 5654.4. Example 4 ........................................................................................................................................ 5664.5. Example 5 ........................................................................................................................................ 5664.6. Example 6 ........................................................................................................................................ 5674.7. Example 7 ........................................................................................................................................ 5674.8. Example 8 ........................................................................................................................................ 5674.9. Example 9 ........................................................................................................................................ 5704.10. Example 10 ...................................................................................................................................... 570Nomenclature ............................................................................................................................................ 575References ................................................................................................................................................. 576Appendix ................................................................................................................................................... 579

18. Solvent Extraction, Leaching,and Supercritical Extraction

Paul Scovazzo, Wei-Yin Chen, Lawrence K. Wang,and Nazih K. Shammas ............................................................................. 581

1. Introduction ............................................................................................................................................... 5812. General Applications ................................................................................................................................ 5823. Process Description .................................................................................................................................. 582

3.1. The Extractor or Extraction Step ................................................................................................... 5823.2. Solvent Recovery ............................................................................................................................ 582

4. Technology Status and Reliability ........................................................................................................... 5835. Equipment Types and Modifications ....................................................................................................... 5846. Chemicals Required ................................................................................................................................. 5847. Residuals Generated ................................................................................................................................. 5848. Applications .............................................................................................................................................. 5849. Advantages and Limitations .................................................................................................................... 585

10. Cost ........................................................................................................................................................... 58511. Design Criteria .......................................................................................................................................... 586

11.1. Part 1—Equilibrium Conditions .................................................................................................... 58611.2. Estimating Korg/w Values .................................................................................................................. 587

xviii Contents

11.3. Environmental Factors Affecting Organic Liquid/Water Distribution Coefficients ................... 59111.4. Part 2—Governing Equations and Relationships .......................................................................... 59111.5. Type 2 Liquid/Liquid Extraction ................................................................................................... 594

12. Leaching .................................................................................................................................................... 59512.1. Solubility and Mass-Transfer Factors ............................................................................................ 59512.2. Equipment and Applications .......................................................................................................... 597

13. Extraction and Destruction of Hazardous Materials by Supercritical Fluids ........................................ 59813.1 Principles ......................................................................................................................................... 59913.2. Applications .................................................................................................................................... 601

14. Example Problems .................................................................................................................................... 60214.1. Example 1—Preliminary Design of the Minimum Solvent Flow Rate

and Number of Extraction Stages ............................................................................................. 60214.2. Example 2—Extraction of Phenol with Caustic Water Recovery ................................................ 60314.3. Example 3—Selecting an Extraction Solvent ............................................................................... 60914.4. Example 4—Performance of Solvent Extraction .......................................................................... 610Nomenclature ............................................................................................................................................ 611References ................................................................................................................................................. 613

Appendix: Conversion Factors for Environmental EngineersLawrence K. Wang ......................................................................................... 615

Constants and Conversion Factors .......................................................................................................... 617Basic and Supplementary Units ............................................................................................................... 673Derived Units and Quantities ................................................................................................................... 674Physical Constants .................................................................................................................................... 676Properties of Water ................................................................................................................................... 677Periodic Table of the Elements ................................................................................................................ 678

Index .......................................................................................................................... 679

Contributors

CHEIN-CHI CHANG, PhD, PE • Senior Engineer, District of Columbia Water and SewerAuthority, Washington, DC

GHOHUA CHEN, PhD • Associate Professor, Department of Chemical Engineering, HongKong University of Science & Technology, Hong Kong, China

J. PAUL CHEN, PhD • Assistant Professor, Department of Chemical and BiomolecularEngineering, National University of Singapore, Singapore

WEI-YIN CHEN, PhD • Professor, Department of Chemical Engineering, University ofMississippi, University, MS

RAJAGOPALAN GANESH, PhD • Kennedy/Jenks Consultants, Irvine, CAJU-CHANG HUANG, PhD • Chair Professor, Department of Civil Engineering, Hong

Kong University of Science and Technology, Hong Kong, ChinaKATHLEEN HUNG LI, MS • Senior Technical Writer, NEC Unified Solutions, Irving, TXYUNG-TSE HUNG, PhD, PE, DEE • Professor, Department of Civil and Environmental

Engineering, Cleveland State University, Cleveland, OHPUANGRAT KAJITVICHYANUKUL, PhD • Assistant Professor, Department of Environmental

Engineering, King Mongkut’s University of Technology, Thonburi, Bangkok, ThailandLAWRENCE Y. C. LEONG, PhD, QEP • Kennedy/Jenks Consultants, Irvine, CAYAN LI, MS, PE • Environmental Engineer, Rhode Island Department of Environment

Management, Providence, RIHOWARD LO, PhD • Professor, Department of Biological, Geological and Environmental

Sciences, Cleveland State University, Cleveland, OHTAKESHI MATSUURA, PhD • Emeritus Professor, Department of Chemical Engineering,

University of Ottawa, Ottawa, Ontario, CanadaHONGHUI MOU, MEng • Research Scholar, Department of Chemical and Biomolecular

Engineering, National University of Singapore, SingaporeWUN-JERN NG, PhD • Professor, Division of Environmental Science and Engineering

and Department of Civil Engineering, National University of Singapore, SingaporeMASAAKI OKUBO, PhD • Associate Professor, Department of Mechanical Engineering,

Osaka Prefecture University, Osaka, JapanGREGORY J. PETERKA, PE • Public Utility District 1 of Skagit County Washington,

Mount Vernon, WAM. B. RAY, PhD • Associate Professor, Department of Chemical and Biochemical Engineering,

The University of Western Ontario, London, Ontario, CanadaPAUL SCOVAZZO, PhD, PE • Assistant Professor, Department of Chemical Engineering,

University of Mississippi, University, MS

xix

GEORGE P. SAKELLAROPOULOS, PhD • Professor, Department of Chemical Engineering, Aristotle University of Thessaloniki, Thessaloniki, GreeceNAZIH K. SHAMMAS, PhD • Professor and Environmental Engineering Consultant,

Lenox Institute of Water Technology, Lenox, MACHII SHANG, PhD • Assistant Professor, Department of Civil Engineering, Hong Kong

University of Science and Technology, Hong Kong, ChinaJERRY R. TARICSKA, PhD, PE, DEE • Senior Environmental Engineer/Associate, Hole

Montes, Inc., Naples, FLSOOK-LENG THONG, MSc • Research Scholar, Department of Chemical and Biomolecular

Engineering, National University of Singapore, SingaporeMARIA W. TIKKANEN, PhD • Kennedy/Jenks Consultants, Sacramento, CALAWRENCE K. WANG, PhD, PE, DEE • Dean & Director (Retired), Lenox Institute of

Water Technology, Lenox, MA; Krofta Engineering Corporation, Lenox, MA; ZorexCorporation, Newtonville, NY

CLINT WILLIFORD, PhD • Associate Professor, Department of Chemical Engineering,University of Mississippi, University, MS

TOSHIYAKI YAMAMOTO, PhD • Professor, Department of Mechanical Engineering, OsakaPrefecture University, Osaka, Japan

LEI YANG, MSc • Research Scholar, Department of Chemical and Biomolecular Engineering,National University of Singapore, Singapore

BEIPING ZHANG, PhD • Professor, School of Environmental Engineering and Science,Hua Zhong University of Science and Technology, Wuhan, China

ROBERT C. ZIEGLER, PhD • Section Head (Retired), Environmental Systems Section,Arvin-Calspan, Inc., Buffalo, NY

xx Contributors

1Potable Water Aeration

Jerry R. Taricska, Lawrence K. Wang, Yung-Tse Hung,and Kathleen Hung Li

CONTENTS

INTRODUCTION

APPLICATIONS

UNIT PROCESSES FOR ORGANIC CONTAMINANT REMOVAL

DIFFUSED AERATION

MECHANICAL AERATION

SYSTEM PERFORMANCE

SYSTEM COSTS

CASE STUDY OF PACKEDPP TOWER AERATION

NOMENCLATURE

REFERENCES

1. INTRODUCTION

Water aeration has been long used in water treatment for the removal of odor andWWtaste-causing compounds, the oxidation of iron and manganese, as well as corrosioncontrol and aesthetics. Since the mid-1970s, however, the process has been used toremove carcinogenic and hazardous chemicals from water. These chemicals includevolatile organics such as trihalomethanes, radon, trichloroethylene, tetrachloroethylene,1,1,1-trichloroethane, chloroform, and toluene. As a result, water aeration may be thesingle most important water treatment process used in the 21st century.

1.1. Types of Aeration Process

Aeration may be accomplished in a variety of ways using different types of equip-ment including surface aeration, submerged aeration, and falling water unit (1–6). Theequipment types are listed below:

• Falling Water Units (commonly used in water treatment)1. Spray aerators—water sprayed into the air. Problems include evaporation and freezing.2. Cascade aerators and hydraulic jumps—these operate using waterfalls over a structure.3. Fountain aerators or spray—water cascaded or sprayed over rocks or other types of

material.

1

From: Handbook of Environmental Engineering, Volume 4: Advanced Physicochemical Treatment ProcessesEdited by: L. K. Wang, Y.-T. Hung, and N. K. Shammas © The Humana Press Inc., Totowa, NJ

4. Multiple tray aerators with and without coke (often used for iron and manganeseremoval)—water cascaded over manufactured tray constructed from slats and coke.

5. Packed column aeration—air flows up, water is sprayed down (these are efficient and themost common type).

• Surface Aerators (commonly used in the wastewater industry)1. Mechanical surface aerators—water surface is mechanically mixed to increase water to

air interface.a. Brush: a series of circular brushes partially submerged are rotated through the water

surface to cause turbulence. A support structure is required to suspend the brushesover the water.

b. Floating: Floating aerator pumps the water from beneath it up through a draft tube tothe surface,which disperses water into the air.

• Submerged Aerators (commonly used in the wastewater and water industries)1. Injection of air with blowers by static tube or diffuser (fine bubble and coarse bubble).2. Jet aeration (the injection of air into pumped water).

This discussion will be limited to equipment used for water treatment, specifically thefalling-water-type equipment and submerged-aeration equipment. The critical factorsthat determine aeration efficiency include (a) time of aeration, (b) ratio of surface area ofair to volume of water, and (c) ventilation. Normally, two approaches are used: (a) expo-sure of water films to air and (b) introduction of small bubbles. The rate of gas transferwith aeration depends on the concentration of contaminants in the water or air as well astemperature, pH, and the degree of agitation. Production of a large water–air surface isdesired. Technically, aeration refers to the addition of air while air stripping refers to theuse of air to remove dissolved gases. As a practical matter, the terms are interchangeable.

2. APPLICATIONS

2.1. Taste and Odor Removal

It is sometimes difficult to identify the actual cause of odor and taste problems inffwater. Some of common odor- and taste-causing compounds include hydrogen sulfide(H2S), methane, algae, oils, phenols, cresols, and volatile compounds. Removal of tasteand odor problems is a common application for the water aeration process. The processis suitable for H2S, methane, and volatiles, but not for algae and oils, phenols, andcresols. The compounds must be volatile for aeration to be effective. Aeration is appro-priate for many industrial compounds. A classic installation is at Nitro, WV, which uti-lizes aeration and granular activated carbon (GAC). The raw water had threshold odornumbers (T.O.N.) of 5000–6000 from industrial contamination. The process was effec-tive for reducing the taste and odor down to levels of 10–12 T.O.N. Although taste andodor applications are most common, there are many other tastes and odors that simplycannot be removed by aeration alone, which may explain why so many early plantswere abandoned (1–10).

2.2. Iron and Manganese Oxidation

When the total concentration of iron in water is 0.3 mg/L or greater, the iron willcause the water to have an unpleasant taste and redden in color—this may result in thestaining of plumbing fixtures and clothes, and accumulations of iron deposits in the

2 Jerry R. Taricska et al.

water mains. The aeration process is an excellent and common pretreatment applicationfor the removal of iron. First, the process oxides iron by changing the iron from the fer-rous state (Fe2+) to the ferric state (Feff 3+), which converts the iron from a soluble form(Fe2+) to a non-soluble form (Fe3+) that precipitates from the water. This precipitationprocess occurs rapidly when the pH is around 7+. The removal of iron is accomplishedthrough sedimentation and filtration of the precipitated iron. Theoretically, 1 mg/L of O2will oxidize about 7 mg/L of Fe2+.

Manganese concentrations greater than 0.3 mg/L in water will result in dark brownstaining. Oxidation will convert the manganese from Mn2+ to Mn4+ when the pH isabove 9. Below a pH of 9, the process is negligibly slow. When tray aerators are utilizedfor aeration and trays become coated with manganese oxides, the removal is accom-plished first by adsorption on accumulated oxidation products (Fe2O3 or MnO2) fol-lowed by slow oxidation (2).

2.2.1. Air Injection into Groundwater for Iron Control

In order to lower the iron concentration in groundwater prior to pumping raw waterto the municipal water treatment plant, air is injected into the groundwater source. Theinjected air oxides the iron in the groundwater. This process involves the periodicalinjection of air into groundwater via a series of wells that surrounds a production well.This application was implemented in a groundwater supply system in Pembroke, MA.

2.3. Hydrogen Sulfide and Carbon Dioxide Removal

Hydrogen sulfide and carbon dioxide (as carbonic acid and free carbon dioxide) arecommonly found in well water. Even a low concentration of hydrogen sulfide can causeodor and taste problems. Hydrogen sulfide is a colorless gas which has a foul odor sim-ilar to rotten eggs and is slightly heavier than air (SG = 1.192). In water, molecularhydrogen sulfide is formed from the reduction, dissolves and disassociates in accor-dance with the reversible ionization reactions:

H2S ↔ HS– + H+

HS– ↔ S2– + H+

The equilibrium of sulfide in water, the percentages of H2S, HS–, and S2– species, isdependent on the pH. Figure 1 shows the distribution of each species at various pH. Ata pH of approx 5.7, the sulfide species in water would be near 100% H2S and at approxpH 7, 50% of the sulfide species in water would be H2S and the other 50% would beHS– species. The H2S species are volatile; as a result, the aeration process effectivelyremoves it from the water. Therefore, the removal efficiency of sulfide depends on pH.As the pH increases, aeration becomes less effective because there are fewer sulfides inthe form of H2S, which is readily removed by aeration. This process is utilized by bothmunicipalities and chemical industries. In water treatment, the process is called degasi-fication, and is effectively used to remove both H2S and carbon dioxide from well waterand product water from the reverse osmosis process.

Dissolved carbon dioxide (CO2) is commonly found in well water. CO2 gas is solublein water (1700 mg/L @20°C) and is volatile. When CO2 gas is dissolved in water, itforms carbonic acid (H2CO3) and aqueous carbon dioxide (CO2(aq)). Aqueous carbon

Potable Water Aeration 3WW

dioxide is sometimes identified as free CO2. Using analytical procedures (titration), it isdifficult to distinguish between H2CO3 and CO2(aq); therefore, a hypothetical species(H2CO3*) is used to identify combination of both H2CO3 and CO2(aq) in water.

H2CO3 is a weak acid. As the water CO2 concentration is increased, then both theH2CO3 concentration and corrosion potential increase. Aeration drives off CO2 and lowersthe H2CO3 levels, which reduces the corrosion potential of the water. When both H2Sand CO2 are present in water, aeration will remove both. As water is aerated, both CO2and H2S are removed, but as the pH of the water increases due to the removal of CO2,the removal efficiency of H2S decreases (10).

2.4. Ammonia Removal

This is a limited application in the water industry, but is more commonly used inwastewater treatment. One of the processes utilized in the wastewater industry is theaerated suspended growth process, which utilizes nitrifying bacteria and aeration toconvert ammonia to nitrites and nitrates.

2.5. Aesthetic or Decorative Aeration

Fountains are an attractive way to display product water. They can also be functionalparticularly for taste and odor improvement. Also, they conjure positive associations formany onlookers.

2.6. Reservoir De-stratification and Oxygenation of Water

In small reservoirs and ponds that have trouble maintaining dissolved oxygen levelsin water near the bottom of the reservoir (stratification of dissolved oxygen level—highlevel near the surface and low level near the bottom), aeration can accomplish the fol-lowing: it mixes the water, reduces stratification, and increases the dissolved oxygenlevel in the water. This is accomplished by placing diffusers on the reservoir floor andbubbling air into the water or by using floating aerators. In some cases, this has provedvery beneficial, but in other cases it has not been effective; results cannot be determined

4 Jerry R. Taricska et al.

Fig. 1. Effect of pH on hydrogen sulfide equilibrium (US EPA) (10).ff

until the process is implemented. Aeration restores oxygen to water, making the watertaste better but it also increases corrosiveness, by increasing the CO2 in the water(resulting from the oxidation of organic matter to CO2). Therefore, there is often a tradeoff between benefit and detriment (11–20).

2.7. Dissolved Air Flotation for Flocculation/Flotation

Aeration has been used rarely for air flotation for flocculation. The purpose of thisapplication is to increase flocculation size by inducing particle-to-particle contact.However, air bubbles attached to the flocculation particles often cause them to floatrather than to settle. A newer, promising approach is flotation, which injects oxygen-saturated water at the bottom of shallow basins, resulting in flocculation forming ascum layer at the water surface, which is then removed (21).

2.8. Trihalomethanes Removal

The aeration process is rated as good to excellent for the removal of trihalomethanes(THM) because they are fairly volatile. This is an increasing application because THMsare not effectively removed by other processes such as granular activated carbon (GAC),although GAC is suitable for organic precursors that react with chlorine to form tri-halomethanes. Aeration is a poor choice for THM precursors removal but suitable forremoving trihalomethanes.

2.9. Volatile Organics Removal

The US EPA has identified many types of organic compounds in our water supplies.Some of the organic compounds are volatile, and, as a result, aeration would be a goodprocess selection for removing them from water. For compounds that are non-volatile,adsorption would be a better process selection than aeration for their removal from thewater. Some common volatiles include trihalomethanes, which have already been dis-cussed: chlorobenzene, 1,1,1-trichloroethane, tetrachloroethylene, and trichloroethylene.Aeration can achieve up to 95% removal of these compounds.

Non-volatile organic compounds also create problems in water supplies. Adsorptionis an excellent removal method for non-volatiles such as styrenes, benzene, phthalates,and fluorine. Therefore, it is often logical to couple air stripping with carbon adsorption,particularly when both volatile and non-volatile compounds are present. Air stripping isparticularly suitable for volatile organics because (a) all volatile organics have an affinityfor the vapor phase, (b) most organics are hydrophobic—they don’t like water—and(c) air is readily available and inexpensive. Nearly 1000 types of organics have beenidentified in drinking water and we shall see more applications of air stripping. This willbe true particularly in areas of gross contamination.

2.10. Hazardous Waste Cleanup

An increasing amount of contamination results from landfills, leaking containers, andaccidental spills. Many of the contaminants are volatile and amenable to aeration. Atwofold approach can be used: either clean the water supply or clean the contaminationsource. When a highly concentrated contaminant is aerated through a packed tower,then air pollution from the aeration process becomes a concern. Air discharge from thepacked tower must be collected and treated.

Potable Water Aeration 5WW

2.11. Radionuclides Removal

Radionuclides are radioactive atoms. The number of protons and neutrons in theirnucleus and their energy content are used to characterize the radioactivity of the atoms.The number following the chemical abbreviation describes the radionuclide composi-tion. In drinking water, the most commonly found radionuclides are radium, uranium,and radon. Radioactive atoms emit three types of nuclear radiation: alpha, beta, andgamma radiation. Various methods are used to measure the level of radionuclides indrinking water, including counters (internal proportional, end-window, thin window,low-background beta counter, gamma spectrometer, alpha spectrometer, alpha scintilla-tion counter, and liquid beta scintillation counter). The average estimated costs foranalyzing these radiation types ranges from $25 to $100 per sample.

In the early 1970s, the inhalation of a radioactive gas such as radon gas (Rn-222) andits daughter progenies (Po-213 and Po-214) were linked to lung carcinogenesis and alsoassociated with development of acute myeloid, acute lymphoblastic leukemia, and othercancers. Regions with granite areas that have relatively high uranium content and arefractured have been found to have a high radon emanation rate. The unit Becquerel (Bq)is used to express radioactivity as disintegrations per second. A more commonly usedunit the Curie (Ci) is equal to 3.7 × 1010 Bq.

US EPA surveys of well drinking water sources showed that 74% of the sources hadradon concentrations below 100 Bq/L and only 5% had concentrations above 400 Bq/L.The high levels were linked to deep wells. A concentration of 400 Bq/L will increase theindoor air radon concentration by about 0.04 Bq/L. Other sources of radon are:

1. Soil around buildings.2. Cracks in floors and walls.3. Construction joints.4. Gaps in suspended floors and around pipes.5. Cavities inside walls.

When the above sources are available, then the radon level in air could reach the USEPA action level of 150 Bq/m3 (0.15 Bq/L). Because radon is highly volatile, the radonlevels in groundwater may be lowered by using an aeration process, such as a packedtower. This aeration process increases the rate of desorption of radon by increasing thesurface area for mass transport across the water–air interface. In Table 1, aeration iscompared to other treatment technologies for effectiveness in removing radionuclidesfrom water. Depending on the aeration process, aeration can achieve a removal effi-ciency ranging from 20% to 96% for radon (Rn), but is not used for radium (Ra) or ura-nium (U) removal. Aeration processes such as PTA [packed tower (column) aeration],which provides a large water–air interface, can achieve high removal efficiency.

3. UNIT PROCESSES FOR ORGANIC CONTAMINANT REMOVAL

The Safe Drinking Water Act (SDWA) through the 1986 Amendments requires theestablishment of new maximum contaminant levels (MCLs) for many organic contam-inants, including disinfection by-products (such as THMs). As a result, regulationspassed in 1987 designated best available technologies (BATs) as well as MCLs fororganic contaminants. Table 2 lists final regulations for eight volatile organic compounds(VOCs) that include the maximum contaminant level goal (MCLG) and the MCL (4,6).

6 Jerry R. Taricska et al.

Potable Water Aeration 7WW

Table 1TTTreatment Technologies for Removing Radionuclides (US EPA) (4)

Reportedapproximate

process Treatment efficiency Technology Radionuclide (percent) Comments

Conventional Ra <25 High pH and Mg requiredtreatment with U 18–98 High pH (10+) and high dosages of ferriccoagulation- chloride or alum only accomplished infiltration laboratory studies with diatomaceous

earth filtrationLime softening Ra 75–96 Best choice for large plants

43–92 Plant-scale resultsU 80 Plant-scale results

85–90 pH 10.6–11.599 High pH, high Mg

Ion exchange Ra 95+ Best choice for small plants; cationexchangers

99 Brine disposal problemU 99 Anion exchangers; largely experimental

but some full-scale plants on lineAdsorption Ra 90+ Adsorption on any solids; experimental

85–90 Sand adsorption; experimentalRn 62–99 GAC adsorption

Aeration Rn 20–96 Depends on process93+ Depends on process

Reverse osmosis Ra 87–96 Plant-scale data87–98 Based on eight plants95+ High-volume brine solution for disposal

U 95+ High-volume brine solution for disposal

Table 2TTFinal MCLGs and MCLs for VOCs (US EPA) (4)

Final MCLGa (mg/L) Final MCL (mg/L)

Trichloroethylene zero 0.005Carbon tetrachloride zero 0.005Vinyl chloride zero 0.0021,2-Dichloroethane zero 0.005Benzene zero 0.005para-Dichlorobenzene 0.075 0.0751,1-Dichloroethylene 0.007 0.0071,1,1-Trichloroethane 0.2 0.2

aFinal MCLGs were published Nov. 13, 1985. The MCLG and MCL for p-dichlorobenzene werereproposed at zero and 0.005 mg/L on April 17, 1987; comment was requested on levels of 0.075 mg/Land 0.075 mg/L, respectively.

Tab

le 3

TT Trea

tmen

t Te

chn

olog

y R

emov

al E

ffec

tive

nes

s R

epor

ted

for

Org

anic

Con

tam

inan

ts i

n P

erce

nt

(US

EPA

) (4

)

Coa

gula

tion/

Dif

fuse

d R

ever

seC

onta

min

ant

filtr

atio

nG

AC

PCA

PAC

aera

tion

Oxi

datio

nos

mos

is

Acr

ylam

ide

5 N

A

0–29

13

N

A

NA

0–

97

Ala

chlo

r 0–

49

70–1

00

70–1

00

36–1

00

NA

70

–100

70

–100

Ald

icar

b N

A

NA

0–

29

NA

N

A

NA

94

–99

Ben

zene

0–

29

70–1

00

70–1

00

NA

N

A

70–1

00

0–29

C

arbo

fura

n 54

–79

70–1

00

0–29

45

–75

11–2

0 70

–100

70

–100

Car

bon

tetr

achl

orid

e 0–

29

70–1

00

70–1

00

0–25

N

A

0–29

70

–100

C

hlor

dane

N

A

70–1

00

0–29

N

A

NA

N

A

NA

Chl

orob

enze

ne

0–29

70

–100

70

–100

N

A

NA

30

–69

70–1

002,

4-D

0–

29

70–1

00

70–1

00

69–1

00

NA

W

0–

65

1,2-

Dic

hlor

oeth

ane

0–29

70

–100

70

–100

N

A

42–7

7 0–

29

15–7

01,

2-D

ichl

orop

ropa

ne0–

29

70–1

00

70–1

00

NA

12

–79

0–29

10

–100

Dib

rom

ochl

orop

ropa

ne

0–29

70

–100

30

–69

NA

N

A

0–29

N

A

Dic

hlor

oben

zene

N

A

70–1

00

NA

N

A

NA

N

A

NA

o-

Dic

hlor

oben

zene

0–

29

70–1

00

70–1

00

38–9

5 14

–72

30–8

8 30

–69

p-D

ichl

orob

enze

ne

0–29

70

–100

70

–100

N

A

NA

30

–69

0–10

1,1-

Dic

hlor

oeth

ylen

e 0–

29

70–1

00

70–1

00

NA

97

70

–100

N

A

cis-

1,2-

Dic

hlor

oeth

ylen

e 0–

29

70–1

00

70–1

00

NA

32

–85

70–1

00

0–30

Tran

s-TT

1,2-

Dic

hlor

oeth

ylen

e0–

29

70–1

00

70–1

00

NA

37

–96

70–1

00

0–30

E

pich

loro

hydr

in

NA

N

A

0–29

N

A

NA

0–

29

NA

Eth

ylbe

nzen

e 0–

29

70–1

00

70–1

00

33–9

9 24

–89

70–1

00

0–30

Eth

ylen

e di

brom

ide

0–29

70

–100

70

–100

N

A

NA

0–

29

37–1

00H

epta

chlo

r 64

70–1

0070

–100

53–9

7N

A70

–100

N

AH

epta

chlo

r ep

oxid

eN

AN

AN

AN

AN

A26

NA

Hig

h-m

olec

ular

-wei

ght

NA

WN

AN

AN

AN

AN

AH

ydro

carb

ons

(gas

olin

e,dy

es,a

min

es,h

umic

s)

8

Lin

dane

0–29

70

–100

0–

29

82–9

7 N

A

0–10

0 50

–75

Met

hoxy

chlo

r N

A

70–1

00

NA

N

A

NA

N

A

>90

Mon

ochl

orob

enze

ne

NA

N

A

NA

14

–99

14–8

5 86

–98

50–1

00

Nat

ural

org

anic

mat

eria

lP

P N

A

P N

A

W

P PC

Bs

NA

70

–100

70

–100

N

A

NA

N

A

95Ph

enol

and

chl

orop

heno

lsN

AW

NA

NA

NA

WN

APe

ntac

hlor

ophe

nol

NA

70–1

000

NA

NA

70–1

00N

ASt

yren

e0–

29N

AN

AN

AN

A70

–100

NA

Tetr

achl

oroe

thyl

ene

NA

70–1

00N

AN

A73

–95

W70

–90

Tri

chlo

roet

hyle

ne0–

2970

–100

70–1

00N

A53

–95

30–6

90–

100

Tri

chlo

roet

hane

NA

70–1

00N

AN

AN

AN

AN

A1,

1,1-

Tri

chlo

roet

hane

0–29

70–1

0070

–100

40–6

558

–90

0–29

15–1

00To

luen

e0–

2970

–100

70–1

000–

6722

–89

70–1

00N

A2,

4,5-

TP

6370

–100

NA

82–9

9N

A30

–69

NA

Toxa

phen

e0–

2970

–100

70–1

0040

–99

NA

NA

NA

Vin

yl c

hlor

ide

0–29

70–1

0070

–100

NA

NA

70–1

00N

AX

ylen

es0–

2970

–100

70–1

0060

–99

18–8

970

–100

10–8

5

W =

wel

l rem

oved

.P

=po

orly

rem

oved

.N

A=

not a

vaila

ble.

Not

e:L

ittle

or

no s

peci

fic

perf

orm

ance

dat

a w

ere

avai

labl

e fo

r:1.

Mul

tiple

-tra

y ae

ratio

n2.

Cat

enar

y ae

ratio

n3.

Hig

ee a

erat

ion

4. R

esin

s5.

Ultr

afilt

ratio

n6.

Mec

hani

cal a

erat

ion

9

US regulations require water utilities with these contaminants to provide removals atleast equivalent to those achieved by the designated BATs. Table 3 lists the typical tech-nologies used in the water treatment industry with their removal capabilities for organiccontaminants, including both VOCs and synthetic organic compounds (SOCs). As shownin this table, the packed column aeration (PCA) and granular activated carbon (GAC) pro-vide 70–100% removal for many of the listed organic contaminants, which includes theeight VOCs for which the US EPA has established the MCL. Other technologies [coagu-lation/filtration, powdered activated carbon (PAC), diffused aeration, oxidation, andreverse osmosis (RO)] can be effective in removing selective organics. GAC and PCA,also referred to as packed tower aeration (PTA), are classified as BAT technologies for theremoval of VOCs under the US EPA regulations promulgated in July 1987.

The removal efficiencies of GAC and PTA are different for each organic compound.GAC can also be effective for the removal of inorganics, whereas PTA is only effectivefor VOC removal. Sometimes selection of treatment technology is based on potentialremoval efficiencies for a specific organic contaminant. However, the best decision con-siders both removal efficiency and cost. As a result, PTA is often chosen for VOCsbecause it has a lower cost and high removal efficiency. Occasionally, both technologiesare necessary to remove a particular combination of organic compounds or organic andinorganic compounds. In these instances, the resulting total costs are not always the sumof costs for each system, because the installation of both systems may result in somecost savings. The upstream system may reduce loading on the downstream system.Other types of aeration technologies are emerging from the laboratory and pilot-levelstages, and provide promising alternatives for the near future. These technologiesinclude catenary grid aeration, Higee aeration, and diffused/mechanical aeration.

3.1. Packed Column Aeration

Packed column aeration (2,4,6–9,11–13,22), also called PTA or air-stripping, mixeswater with air to volatilize contaminants. The volatilized contaminants are eitherreleased directly to the atmosphere or are treated and then released. PCA is used pri-marily to remove VOCs, but is commonly used to remove hydrogen sulfide and CO2. Inthis application, the aeration unit is described as degasifier.

The Henry’s law constant indicates a contaminant’s volatility and its affinity for theaeration process. Substances with high Henry’s law constants are easily aerated, whilethose with low constants are difficult to remove with aeration. Table 4 presents Henry’slaw constants for several compounds. As the table indicates, vinyl chloride has anextremely large Henry’s law constant relative to any other VOC.

If the solubility, vapor pressure, and molecular weight of a compound are known,Henry’s law constant can be calculated using the Eq. (1). Table 5 presents the vaporpressures and solubilities and Henry’s law constants for priority pollutants:

(1)

where HunitlessH = Henry’s law constant, dimensionless; VP = the vapor pressureexpressed, mm; M = the molecular weight of the solute; T = the temperature, K; and S =the solubility, mg/L.

Hunitless

16.04VP MT S

10 Jerry R. Taricska et al.

ExampleDetermine the unitless form of Henry’s law constant for benzene at 20°C using Eq. (1).

SolutionBenzene has chemical formula of C6H6; therefore, the molecular weight is determined asfollows:

C6: 12 × 6 = 72

H6: 1 × 6 = 6

MW = M = 78

VP = 95.2 mm Hg (from Table 5)

S = 1780 mg/L (from Table 5)

T = (273.15 K + 20°C ) = 293.15 K

Substituting into Eq. (1) yields the following:

Henry’s law constant is commonly expressed in units of atm m3/mole for atmosphericconditions. Table 6 lists some of US EPA’s priority pollutants with their Henry’s law con-stants expressed as atm m3/mole. To convert this form of the constant to the unitless form,use the following equation:

(2)

where H = Henry’s law constant, atm m3/mole; R = universal gas constant, 0.000082057atm m3/mole-K; and T = temperature, K (K = 273.15 + °C).

HHRTunitless

Hunitless

16 04 95 2 78

293 15 17800

. .

...228

Hunitless

16.04VP MT S

Potable Water Aeration 11WW

Table 4TTHenry’s Law Constants for Nine Organic Chemicals (US EPA) (4)

Type of organic chemical Henry’s law constantTT a (dimensionless units)

VOCsVinyl chloride 265.00a

Trichloroethylene 0.41TT a

Tetrachloroethylene 0.82TT a

cis-1,2-Dichloroethylene 0.32b

PesticidesAldicarb 0.00000017b

Chlordane 0.004b

Dibromochloropropane 0.01b

Chlorinated AromaticsPolychlorinated biphenols 0.059b

Dichlorobenzene 0.081b

Note: Constants estimated at about 20°C.aAWWA Research Foundation and KIWA (1983).AAbUS EPA (1998).PP

12 Jerry R. Taricska et al.

Table 5TTChemical Characteristics of the Priority Pollutants with Henry’s Law Constant(Unitless) Listed (US EPA) (6)

VP(2) Solubility(3)

H(1) (mmHg) (mg/L)

1. *Acenaphthene 0.009 (c) 3.0 × 10–2 3.882. *Acrolein 0.0046 (b) 300 200,0003. *Acrylonitrile 0.0030 (b) 100 93,0004. *Benzene 0.22 (b) 95.2 17805. *Benzidine6. *Carbon tetrachloride (tetrachloromethane) 1.2 (c) 91.3 800

*Chlorinated benzenes (other thandichlorobenzenes)

7. Chlorobenzene 0.19 (d) 15 4488. 1,2,4-Trichlorobenzene9. Hexachlorobenzene

*Chlorinated ethanes (including 1,2-dichloroethane, 1,1,1-trichloroethaneand hexachloroethane)

10. 1,2-Dichloroethane 0.050 (c) 82 870011. 1,1,1-Trichloroethane 0.17 (b) 100 440012. Hexachloroethane 0.05 (c) 0.33 813. 1,1-Dichloroethane 0.24 (c) 226 510014. 1,1,2-Trichloroethane 0.037 (c) 25 442015. 1,1,2,2-Tetrachloroethane 0.020 (c) 6.5 300016. Chloroethane 0.73 (c) 1200 5700

*Chloroalkyl ethers (chloromethyl,chloroethyl and mixed ethers)

17. bis (Chloromethyl) ether18. bis (2-Chloroethyl) ether19. 2-Chloroethyl vinyl ether (mixed)

*Chlorinated naphthalene20. 2-Chloronaphthalene

*Chlorinated phenols (other than thoselisted elsewhere; includes trichlorophenolsand chlorinated cresols)

21. 2,4,6-Trichlorophenol22. Parachlorometa cresol23. *Chloroform (trichloromethane) 0.16 (c) 192 784024. *2-Chlorophenol 0.001 (b) 5.0 28,000

*Dichlorobenzenes25. 1,2-Dichlorobenzene 0.081 (b) 1.0 10026. 1,3-Dichlorobenzene 0.13 (c) 2.0 12327. 1,4-Dichlorobenzene 0.10 (c) 1.0 79

*Dichlorobenzidine28. 3,3′-Dichlorobenzidine

*Dichloroethylenes (1,1-dichloroethyleneand 1,2-dichloroethylene)

29. 1,1-Dichloroethylene 7.80 598 400

(Continued)