Advanced Physicochemical Treatment Technologies€¦ · The Editors of the Handbook of...

Advanced Physicochemical Treatment Technologies

AdvancedPhysicochemical

Treatment Technologies

Edited by

Lawrence K. Wang, PhD, PE, DEELenox Institute of Water Technology, Lenox, MA

Krofta Engineering Corporation, Lenox, MAZorex Corporation, Newtonville, NY

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 5HANDBOOK OF ENVIRONMENTAL ENGINEERING

DedicationThe Editors of the Handbook of Environmental Engineering series dedicate this volume

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Preface

v

The past thirty years have seen the emergence of a growing desire world-wide that positive actions be taken to restore and protect the environment fromthe degrading effects of all forms of pollution — air, water, soil, and noise.Since pollution is a direct or indirect consequence of waste, the seemingly ide-alistic demand for “zero discharge” can be construed as an unrealistic demandfor zero waste. However, as long as waste continues to exist, we can only at-tempt to abate the subsequent pollution by converting it to a less noxious form.Three major questions usually arise when a particular type of pollution hasbeen identified: (1) How serious is the pollution? (2) Is the technology to abateit available? 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.

Since 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 multimedia approach to environmental pollutioncontrol since air, water, soil and energy are all interrelated.

As can be seen from the above handbook coverage, the organization of thehandbook series has been based on the three basic forms in which pollutantsand waste are manifested: gas, solid, and liquid. In addition, noise pollutioncontrol is included in the handbook series.

This particular book Volume 5 Advanced Physicochemical Treatment Technolo-gies is a sister book to Volume 3 Physicochemical Treatment Processes and Vol-ume 4 Advanced Physicochemical Treatment Processes. Volumes 3 and 4 havealready included the subjects of screening, comminution, equalization, neu-

vi Preface

tralization, mixing, coagulation, flocculation, chemical precipitation, recarbon-ation, softening, oxidation, halogenation, chlorination, disinfection, ozonation,electrolysis, sedimentation, dissolved air flotation, filtration, polymeric adsorp-tion, granular activated carbon adsorption, membrane processes, sludge treat-ment processes, potable water aeration, air stripping, dispersed air flotation,powdered activated carbon adsorption, diatomaceous earth precoat filtration,microscreening, membrane filtration, ion exchange, fluoridation, defluoridation,ultraviolet radiation disinfection, chloramination, dechlorination, advanced oxi-dation processes, chemical reduction/oxidation, oil water separation, evapora-tion and solvent extraction. This book, Volume 5, includes the subjects ofpressurized ozonation, electrochemical processes, irradiation, nonthermalplasma, thermal distillation, electrodialysis, reverse osmosis, biosorption, emerg-ing adsorption, emerging ion exchange, emerging flotation, fine pore aeration,endocrine disruptors, small filtration systems, chemical feeding systems, wet airoxidation, and lime calcination. All three books have been designed to serve ascomprehensive physicochemical treatment textbooks as well as wide-rangingreference books. We hope and expect that the books will prove of equal highvalue to advanced undergraduate and graduate students, to designers of waterand wastewater 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. Wang, Lenox, MAYung-Tse Hung, Cleveland, OHNazih K. Shammas, Lenox, MA

Preface vii

ix

Contents

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

Contributors ............................................................................................................ xvii1 Pressurized Ozonation

Lawrence K. Wang and Nazih K. Shammas..................................................... 1

1. Introduction ................................................................................................................................................... 11.1. Oxyozosynthesis Sludge Management System ................................................................................. 21.2. Oxyozosynthesis Wastewater Reclamation System .......................................................................... 5

2. Description of Processes .............................................................................................................................. 72.1. Ozonation and Oxygenation Process ................................................................................................. 72.2. Flotation Process ................................................................................................................................. 92.3. Filter Belt Press ................................................................................................................................. 132.4. Performance of Oxyozosynthesis Sludge Management System .................................................... 162.5. Performance of Oxyozosynthesis Wastewater Reclamation System ............................................. 18

3. Formation and Generation of Ozone ......................................................................................................... 183.1. Formation of Ozone .......................................................................................................................... 183.2. Generation of Ozone ......................................................................................................................... 19

4. Requirements for Ozonation Equipment ................................................................................................... 224.1. Feed Gas Equipment ......................................................................................................................... 234.2. Ozone Generators .............................................................................................................................. 244.3. Ozone Contactors .............................................................................................................................. 24

5. Properties of Ozone .................................................................................................................................... 266. Disinfection by Ozone ................................................................................................................................ 317. Oxidation by Ozone .................................................................................................................................... 35

7.1. Ozone Reaction with Inorganics ...................................................................................................... 357.2. Ozone Reaction with Organic Material ........................................................................................... 38

8. Oxygenation and Ozonation Systems ........................................................................................................ 438.1. Oxygenation Systems ....................................................................................................................... 438.2. Ozonation Systems ............................................................................................................................ 468.3. Removal of Pollutants from Waste by Ozonation ........................................................................... 48

Nomenclature .................................................................................................................................................... 50Acknowledgments ............................................................................................................................................ 50References ......................................................................................................................................................... 50

2 Electrochemical Wastewater Treatment ProcessesGuohua Chen and Yung-Tse Hung ................................................................ 57

1. Introduction ................................................................................................................................................. 572. Electrochemical Reactors for Metal Recovery ......................................................................................... 58

2.1. Typical Reactors Applied ................................................................................................................. 582.2. Electrode Materials ........................................................................................................................... 642.3. Application Areas ............................................................................................................................. 64

3. Electrocoagulation ...................................................................................................................................... 643.1. Factors Affecting Electrocoagulation .............................................................................................. 663.2. Electrode Materials ........................................................................................................................... 693.3. Typical Design .................................................................................................................................. 693.4. Effluents Treated by EC ................................................................................................................... 70

4. Electroflotation ........................................................................................................................................... 704.1. Factors Affecting EF ......................................................................................................................... 714.2. Comparison with Other Flotation Technologies ............................................................................. 764.3. Oxygen Evolution Electrodes ........................................................................................................... 76

4..4 Typical Designs ................................................................................................................................. 774.5. Wastewaters Treated by EF .............................................................................................................. 80

5. Electro-oxidation ........................................................................................................................................ 805.1. Indirect EO Processes ....................................................................................................................... 825.2. Direct Anodic Oxidation .................................................................................................................. 825.3. Typical Designs ................................................................................................................................. 93

6. Summary ..................................................................................................................................................... 93Nomenclature .................................................................................................................................................... 95References ......................................................................................................................................................... 95

3 IrradiationLawrence K. Wang, J. Paul Chen, and Robert C. Ziegler .......................... 107

1. Introduction ............................................................................................................................................... 1071.1. Disinfection and Irradiation ........................................................................................................... 1071.2. Pathogenic Organisms .................................................................................................................... 1081.3. Pathogen Occurrence in the United States .................................................................................... 1081.4. Potential Human Exposure to Pathogens ....................................................................................... 108

2. Pathogens and Thier Characteristics ....................................................................................................... 1092.1. Viruses ............................................................................................................................................. 1092.2. Bacteria ............................................................................................................................................ 1102.3. Parasites ........................................................................................................................................... 1102.4. Fungi ................................................................................................................................................ 112

3. Solid Substances Disinfection ................................................................................................................. 1123.1. Long-Term Storage ......................................................................................................................... 1123.2. Chemical Disinfection .................................................................................................................... 1123.3. Low-Temperature Thermal Processes for Disinfection ................................................................ 1133.4. High-Temperature Thermal Processes for Disinfection ............................................................... 1143.5. Composting ..................................................................................................................................... 1143.6. High-Energy Radiation ................................................................................................................... 115

4. Disinfection with Electron Irradiation .................................................................................................... 1154.1. Electron Irradiation Systems and Process Description ................................................................. 1154.2. Electron Irradiation Design Considerations .................................................................................. 1174.3. Electron Irradiation Operational Considerations .......................................................................... 1184.4. Electron Irradiation Performance ................................................................................................... 118

5. Disinfection with -Irradiation ................................................................................................................ 1195.1. -Irradiation Systems and Process Description ............................................................................. 1195.2. -Irradiation Design Considerations .............................................................................................. 1225.3. -Irradiation Operational Considerations ...................................................................................... 124

6. X-Ray Facilities ........................................................................................................................................ 1267. New Applications ..................................................................................................................................... 126

7.1. Food Disinfection by Irradiation .................................................................................................... 1267.2. Hospital Waste Treatment by Irradiation ...................................................................................... 1287.3. Mail Irradiation ............................................................................................................................... 130

8. Glossary .................................................................................................................................................... 131References ....................................................................................................................................................... 132

4 Nonthermal Plasma TechnologyToshiaki Yamamoto and Masaaki Okubo .................................................... 135

1. Fundamental Characteristics of Nonthermal Plasma .............................................................................. 1351.1. Definition and Characteristics of Plasma ...................................................................................... 1351.2. Generation of Plasma ...................................................................................................................... 1451.3. Analysis and Diagnosis of Nonthermal Plasma ............................................................................ 165

2. Environmental Improvement ................................................................................................................... 1732.1. Electrostatic Precipitator ................................................................................................................ 1732.2. Combustion Flue Gas Treatment from Power Plant ..................................................................... 1832.3. Nonthermal Plasma Application for Detoxification ..................................................................... 1962.4. Air Cleaner for Odor Control ......................................................................................................... 199

x Contents

2.5. Ozone Synthesis and Applications ................................................................................................. 2062.6. Decomposition of Freon and VOC ................................................................................................ 2122.7. Diesel Engine Exhaust Gas Treatment .......................................................................................... 2152.8. Gas Concentration Using Nonthermal Plasma Desorption ........................................................... 2392.9. Emission Gas Decomposition in Semiconductor Manufacturing Process ................................... 248

3. Surface Modification ................................................................................................................................ 2563.1. RF Plasma CVD .............................................................................................................................. 2563.2. Surface Modification for Substrate ................................................................................................ 2573.3. Surface Modification for Glass ...................................................................................................... 2613.4. Surface Modification for Polymer or Cloth ................................................................................... 2663.5. Surface Modification for Metal ...................................................................................................... 271

Nomenclature .................................................................................................................................................. 277References ....................................................................................................................................................... 280

5 Thermal Distillation and Electrodialysis Technologies for DesalinationJ. Paul Chen, Lawrence K. Wang, and Lei Yang ........................................ 295

1. Introduction ............................................................................................................................................... 2952. Thermal Distillation ................................................................................................................................. 301

2.1. Introduction ..................................................................................................................................... 3012.2 Working Mechanisms ..................................................................................................................... 3022.3. Multistage Flash Distillation .......................................................................................................... 3042.4. Multieffect Distillation ................................................................................................................... 3042.5. Vapor Compression ........................................................................................................................ 3072.6. Solar Desalination ........................................................................................................................... 3072.7. Important Issues in Design (O&M) ............................................................................................... 311

3. Electrodialysis .......................................................................................................................................... 3123.1. Introduction ..................................................................................................................................... 3123.2. Mechanisms ..................................................................................................................................... 3123.3. Important Issues in Design ............................................................................................................. 3143.4. Electrodialysis Reversal ................................................................................................................. 3173.5. Electrodeionization ......................................................................................................................... 319

4. Reverse Osmosis ...................................................................................................................................... 3215. Energy ....................................................................................................................................................... 3226. Environmental Aspect of Desalination ................................................................................................... 324Nomenclature .................................................................................................................................................. 325References ....................................................................................................................................................... 326

6 Reverse Osmosis Technology for DesalinationEdward S.K. Chian, J. Paul Chen, Ping-Xin Sheng,

Yen-Peng Ting, and Lawrence K. Wang .................................................. 329

1. Introduction ............................................................................................................................................... 3292. Membrane Filtration Theory .................................................................................................................... 330

2.1. Osmosis and RO .............................................................................................................................. 3302.2 Membranes ...................................................................................................................................... 3322.3. Membrane Filtration Theory .......................................................................................................... 3342.4. Concentration Polarization ............................................................................................................. 3382.5. Compaction ..................................................................................................................................... 339

3. Membrane Modules and Plant Configuration ......................................................................................... 3403.1. Membrane Modules ........................................................................................................................ 3403.2. Plant Configuration of Membrane Modules .................................................................................. 343

4. Pretreatment and Cleaning of Membrane ................................................................................................ 3464.1. Mechanisms of Membrane Fouling ............................................................................................... 3464.2. Feed Pretreatment ........................................................................................................................... 3494.3. Membrane Cleaning and Regeneration .......................................................................................... 354

5. Case Study ................................................................................................................................................ 3595.1. Acidification and Scale Prevention for Pretreatment .................................................................... 3595.2. Cartridge Filters for Prefiltration ................................................................................................... 3595.3. Reverse Osmosis ............................................................................................................................. 359

Contents xi

5.4 Neutralization and Posttreatment ................................................................................................... 3615.5. Total Water Production Cost and Grand Total Costs ................................................................... 362


7 Emerging Biosorption, Adsorption, Ion Exchange,and Membrane Technologies

J. Paul Chen, Lawrence K. Wang, Lei Yang, and Soh-Fong Lim.............. 367

1. Introduction ............................................................................................................................................... 3672. Emerging Biosorption for Heavy Metals ................................................................................................ 367

2.1. Biosorption Chemistry .................................................................................................................... 3682.2 Biosorption Process ........................................................................................................................ 3692.3. Biosorption Mathematical Modeling ............................................................................................. 372

3. Magnetic Ion Exchange Process .............................................................................................................. 3744. Liquid Membrane Process ....................................................................................................................... 377

4.1. Introduction ..................................................................................................................................... 3774.2. Mechanism ...................................................................................................................................... 3774.3. Applications .................................................................................................................................... 378

5. Emerging Technologies for Arsenic Removal ........................................................................................ 3805.1. Precipitation–Coagulation, Sedimentation, and Flotation ............................................................ 3805.2. Electrocoagulation .......................................................................................................................... 3815.3. Adsorption ....................................................................................................................................... 3825.4. Ion Exchange ................................................................................................................................... 3865.5. Membrane Filtration ....................................................................................................................... 386


8 Fine Pore Aeration of Water and WastewaterNazih K. Shammas ......................................................................................... 391

1. Introduction ............................................................................................................................................... 3912. Description ................................................................................................................................................ 3923. Types of Fine Pore Media ........................................................................................................................ 393

3.1. Ceramics .......................................................................................................................................... 3943.2. Porous Plastics ................................................................................................................................ 3953.3. Perforated Membranes .................................................................................................................... 396

4. Types of Fine Pore Diffusers ................................................................................................................... 3984.1. Plate Diffusers ................................................................................................................................. 3984.2. Tube Diffusers ................................................................................................................................. 4004.3. Dome Diffusers ............................................................................................................................... 4024.4. Disc Diffusers ................................................................................................................................. 403

5. Diffuser Layout ........................................................................................................................................ 4075.1. Plate Diffusers ................................................................................................................................. 4085.2. Tube Diffusers ................................................................................................................................. 4095.3. Disc and Dome Diffusers ............................................................................................................... 410

6. Characteristics of Fine Pore Media ......................................................................................................... 4116.1. Physical Description ....................................................................................................................... 4116.2. Dimensions ...................................................................................................................................... 4116.3. Weight and Specific Weight ........................................................................................................... 4126.4. Permeability .................................................................................................................................... 4126.5. Perforation Pattern .......................................................................................................................... 4136.6. Strength ............................................................................................................................................ 4136.7. Hardness .......................................................................................................................................... 4146.8. Environmental Resistance .............................................................................................................. 4146.9. Miscellaneous Physical Properties ................................................................................................. 4156.10. Oxygen Transfer Efficiency ........................................................................................................... 415

xii Contents

Contents xiii

6.11. Dynamic Wet Pressure ................................................................................................................... 4166.12. Bubble Release Vacuum ................................................................................................................. 4196.13. Uniformmity .................................................................................................................................... 420

7. Performance in Clean Water .................................................................................................................... 4227.1. Steady-State DO Saturation Concentration (C ) ........................................................................... 4237.2. Oxygen Transfer ............................................................................................................................. 424

8. Performance in Process Water ................................................................................................................. 4328.1. Performance .................................................................................................................................... 4328.2. Factors Affecting Performance ...................................................................................................... 4398.3. Operation and Maintenance ............................................................................................................ 441


9 Emerging Flotation TechnologiesLawrence K. Wang ......................................................................................... 449

1. Modern Flotation Technologies ............................................................................................................... 4502. Groundwater Decontamination Using DAF ............................................................................................ 4523. Textile Mills Effluent Treatment Using DAF ......................................................................................... 4594. Petroleum Refinery Wastewater Treatment Using DAF ........................................................................ 4595. Auto and Laundry Wasterwater Using DAF ........................................................................................... 4606. Seafood Processing Wastewater Treatment Using DAF ........................................................................ 4627. Storm Runoff Treatment Usng DAF ....................................................................................................... 4648. Industrial Effluent Treatment by Biological Process Using DAF

for Secondary Flotation Clarification ................................................................................................... 4659. Industrial Resource Recovery Using DAF for Primary Flotation Clarification ................................... 46710. First American Flotation–Filtration Plant for Water Purification—Lenox

Water Treatment Plant, MA, USA ....................................................................................................... 46911. Once the World’s Largest Potable Flotation–Filtration Plant—Pittsfield

Water Treatment Plant, MA, USA ....................................................................................................... 47112. The Largest Potable Flotation–Filtration Plant in the Continent of North

America—Table Rock and North Saluda Water Treatment Plant, SC, USA .................................... 47313. Emerging DAF Plants—AquaDAF™ ..................................................................................................... 47414. Emerging Full-Scale Anaerobic Biological Flotation—Kassel, Germany ............................................ 47615. Emerging Dissolved Gas Flotation and Sequencing Batch Reactor (DGF-SBR) ................................. 47816. Application of Combined Primary Flotation Clarification and Secondary Flotation Clarification

for Treatment of Dairy Effluents—A UK Case History ..................................................................... 47917. Recent DAF Developments ..................................................................................................................... 480References ....................................................................................................................................................... 481

10 Endocrine Disruptors: Properties, Effects, and Removal ProcessesNazih K. Shammas ......................................................................................... 485

1. Introduction ............................................................................................................................................... 4852. Endocrine System and Endocrine Disruptors ......................................................................................... 487

2.1. The Endocrine System .................................................................................................................... 4872.2. Endocrine Disruptors ...................................................................................................................... 487

3. Descriptions of Specific EDCs ................................................................................................................ 4883.1. Pesticide Residues ........................................................................................................................... 4883.2. Highly Chlorinated Compounds ..................................................................................................... 4913.3. Alkylphenols and Alkylphenol Ethoxylates .................................................................................. 4943.4. Plastic Additives ............................................................................................................................. 495

4. Water Treatments for EDC Removal ...................................................................................................... 4964.1. Granular Activated Carbon ............................................................................................................. 4964.2. Powdered Activated Carbon ........................................................................................................... 4984.3. Coagulation/Filtration ..................................................................................................................... 4984.4. Lime Softening ................................................................................................................................ 498

5. Point-of-Use/Point-of-Entry Treatments ................................................................................................. 4996. Water Treatment Techniques for Specific EDC Removal ..................................................................... 499

6.1. Methoxychlor .................................................................................................................................. 499

xiv Contents

6.2. Endosulfan ....................................................................................................................................... 5006.3. DDT ................................................................................................................................................. 5006.4. Diethyl Phthalate ............................................................................................................................. 5006.5. Di-(2ethylhexyl) Phthalate ............................................................................................................. 5006.6. Polychlorinated Biphenyls ............................................................................................................. 5006.7. Dioxin .............................................................................................................................................. 5006.8. Alkylphenols and Alkylphenol Ethoxylates .................................................................................. 501


11 Filtration Systems for Small CommunitiesYung-Tse Hung, Ruth Yu-Li Yeh, and Lawrence K. Wang ....................... 505

1. Introduction ............................................................................................................................................... 5052. Operating Characteristics ......................................................................................................................... 5053. SDWA Implementation ............................................................................................................................ 5064. Filtration Treatment Technology Overview ........................................................................................... 5065. Common Types of Water Filtration Processes for Small Communities ............................................... 507

5.1. Process Description ......................................................................................................................... 5085.2. Operation and Maintenance Requirements .................................................................................... 5125.3. Technology Limitations .................................................................................................................. 5125.4. Financial Considerations ................................................................................................................ 513

6. Other Filtration Processes ........................................................................................................................ 5146.1. Direct Filtration ............................................................................................................................... 5146.2. Membrane Processes ....................................................................................................................... 5146.3. Bag and Cartridge Type Filtration ................................................................................................. 5166.4. Summary of Compliance Technologies for the SWTR ................................................................ 519

7. Case Studies of Small Water Systems ..................................................................................................... 5197.1. Case Study of Westfir, OR ............................................................................................................. 5197.2. Mockingbird Hill, Arkansas, Case Study ...................................................................................... 524

8. Intermittent Sand Filters for Wastewater Treatment .............................................................................. 5278.1. Technology Applications ................................................................................................................ 5278.2. Process Descriptions ....................................................................................................................... 5278.3. Operation and Maintenance (O&M) Requirements ...................................................................... 5298.4. Technology Limitations .................................................................................................................. 5298.5. Financial Considerations ................................................................................................................ 5298.6. Case Studies .................................................................................................................................... 530

References ....................................................................................................................................................... 539

12 Chemical Feeding SystemPuangrat Kajitvichyanukul, Yung-Tse Hung,

and Jirapat Ananpattarachai .................................................................... 543

1. Introduction ............................................................................................................................................... 5432. Chemicals Used in Water Treatment ....................................................................................................... 545

2.1. Aluminum Sulfate or Alum ............................................................................................................ 5462.2. Ammonia ......................................................................................................................................... 5462.3. Calcium Hydroxide and Calcium Oxide ........................................................................................ 5462.4. Carbon Dioxide ............................................................................................................................... 5462.5. Ferric Chloride ................................................................................................................................ 5472.6. Ferric Sulfate ................................................................................................................................... 5472.7. Ferrous Sulfate ................................................................................................................................ 5472.8. Phosphate Compounds .................................................................................................................... 5472.9. Polymers .......................................................................................................................................... 5482.10. Potassium Permanganate ................................................................................................................ 5482.11. Sodium Carbonate ........................................................................................................................... 5482.12. Sodium Chlorite .............................................................................................................................. 5492.13. Sodium Hydroxide .......................................................................................................................... 5492.14. Sodium Hypochlorite ...................................................................................................................... 550

Contents xv

2.15. Sulfuric Acid ................................................................................................................................... 5503. Chemical Storage ...................................................................................................................................... 550

3.1. Storage of Powder Chemicals ........................................................................................................ 5503.2. Storage of Liquid Chemicals .......................................................................................................... 5553.3. Storage of Gaseous Chemicals ....................................................................................................... 5553.4. Storage Facility Requirements ....................................................................................................... 557

4. Chemical Preparation of Solutions and Suspensions ............................................................................. 5584.1. Preparation of Dilute Solutions from Concentrated Solutions ..................................................... 5584.2. Preparation of Dilute Solutions from Solid Products ................................................................... 5594.3. Preparation of Suspensions ............................................................................................................ 560

5. Chemical Feeding System ........................................................................................................................ 5605.1. Dry Feeders ..................................................................................................................................... 5615.2. Solution Feeders .............................................................................................................................. 5665.3. Gas Feeders ..................................................................................................................................... 567

6. Design Examples ...................................................................................................................................... 567References ....................................................................................................................................................... 572

13 Wet Air Oxidation for Waste Treatment Linda Y. Zou, Yuncang Li, and Yung-Tse Hung ........................................ 575

1. Introduction ............................................................................................................................................... 5751.1. Process Description ......................................................................................................................... 5761.2. Mechanisms and Kinetics ............................................................................................................... 5781.3. Design .............................................................................................................................................. 5801.4. Issues and Considerations of Using Wet Air Oxidation ............................................................... 580

2. Catalytic WAO Processes ........................................................................................................................ 5812.1. Process Description ......................................................................................................................... 5812.2. Process Application and Limitation ............................................................................................... 5822.3. Design Considerations .................................................................................................................... 586

3. Emerging Technologies in Advanced Oxidation .................................................................................... 5873.1. Photocatalytic Oxidation (PCO) Process ....................................................................................... 5873.2. Supercritical Water Oxidation ........................................................................................................ 592

4. Application Examples .............................................................................................................................. 5984.1. Case 1: WAO of Refinery Spent Caustic: A Refinery Case Study .............................................. 5984.2. Case 2: CWAO for the Treatment of H-Acid Manufacturing Process Wastewater .................... 6014.3. Case 3: Photocatlytic Decolorization of Lanasol Blue CE Dye Solution

in Flat-Plate Reactor .................................................................................................................. 6024.4. Case 4: Oxidation of Industrial Waste Waters in the Pipe Reactor (100) ................................... 604

References ....................................................................................................................................................... 605

14 Lime CalcinationGupta Sudhir Kumar, Anushuya Ramakrishnan, and Yung-Tse Hung .... 611

1. Introduction ............................................................................................................................................... 6112. The Chemical Reactions .......................................................................................................................... 612

2.1. Calcium Carbonate .......................................................................................................................... 6122.2. Magnesium Carbonate .................................................................................................................... 6122.3. Dolomite and Magnesian/Dolomitic Limestone ........................................................................... 613

3. Kinetics of Calcination ............................................................................................................................. 6133.1. Stages of Calcinations .................................................................................................................... 6133.2. Dissociation of High Calcium Limestone ...................................................................................... 6143.3. Calorific Requirements for Dissociation of Calcium and Dolomitic Quick Lime ...................... 6173.4. Dissociation of Magnesian/Dolomitic Limestones and Dolomite ............................................... 6183.5. Sintering of High Calcium Quickllime .......................................................................................... 6183.6. Sintering of Calcined Dolomite ..................................................................................................... 6203.7. Steam Injection ............................................................................................................................... 6213.8. Recarbonation ................................................................................................................................. 6213.9. Calcination of Finely Divided Limestones .................................................................................... 622

4. Properties of Limestones and Their Calcines ......................................................................................... 6225. Factors Affecting Lime Calcination ........................................................................................................ 623

xvi Contents

5.1. Effect of Stone Size ........................................................................................................................ 6235.2. Effect of Crystal Ion Spacing ......................................................................................................... 6245.3. Effect of Salts .................................................................................................................................. 6245.4. Influence of Stone Imurities ........................................................................................................... 6245.5. Effect of Steam ................................................................................................................................ 6255.6. Effect of Storage and Production ................................................................................................... 6255.7. Effect of Calcination Temperature ................................................................................................. 626

6. Calcination of Industrial Solid Wastes .................................................................................................... 6277. Carbon Dioxide Emissions from Lime Calcination ................................................................................ 6288. Solar Lime Calcination ............................................................................................................................ 6289. Conclusions ............................................................................................................................................... 631Nomenclature .................................................................................................................................................. 631References ....................................................................................................................................................... 632

Appendix: Conversion Factors for Environmental EngineersLawrence K. Wang ......................................................................................... 635

Index ................................................................................................................ 699

Contributors

JIRAPAT ANANPATTARACHAI, PhD CANDIDATE • Research Assistant, Department of Envi-ronmental Engineering, King Mongkut’s University of Technology Thonburi,Bangkok, Thailand

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

J. PAUL CHEN, PhD • Associate Professor, Division of Environmental Science andEngineering, National University of Singapore, Singapore

EDWARD S.K. CHAIN, PhD • Retired Professor, School of Civil and EnvironmentalEngineering, Georgia Institute of Technology, Atlanta, GA

YUNG-TSE HUNG, PhD, PE, DEE • Professor, Department of Civil and EnvironmentalEngineering, Cleveland State University, Cleveland, OH

PUANGRAT KAJITVICHYANUKUL, PhD • Assistant Professor, Department of EnvironmentalEngineering, King Mongkut’s University of Technology, Thonburi, Bangkok, Thailand

GUPTA SUDHIR KUMAR, PhD • Professor, Centre for Environmental Science and Engineering,Indian Institute of Technology, Bombay, Powai, Mumbai, Maharashtra, India

YUNCANG LI, PhD • Research Fellow, School of Engineering and Technology, Faculty ofScience and Technology, Deakin University, Geelong, Victoria, Australia

SOH-FONG LIM, MEng • Research Scholar, Department of Chemical and EnvironmentalEngineering, National University of Singapore, Singapore

MASAAKI OKUBO, PhD • Associate Professor, Department of Mechanical Engineering,Osaka Prefecture University, Osaka, Japan

ANUSHUYA RAMAKRISHNAN, MSc • Research Scholar, Centre for Environmental Scienceand Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai,Maharashtra, India

NAZIH K. SHAMMAS, PhD • Professor and Environmental Engineering Consultant,Ex-Dean and Director, Lenox Institute of Water Technology, Lenox, MA, KroftaEngineering Corporation, Lenox, MA

PING-XIN SHENG, PhD • Research Fellow, Division of Environmental Science andEngineering, National University of Singapore, Singapore

YEN-PENG TING, PhD • Associate Professor, Department of Chemical and BiomolecularEngineering, National University of Singapore, Singapore

LAWRENCE K. WANG, PhD, PE, DEE • Dean & Director (Retired), Lenox Institute of WaterTechnology, Lenox, MA; Assistant to the President, Krofta Engineering Corporation,Lenox, MA; Vice President, Zorex Corporation, Newtonville, NY

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

LEI YANG, PhD • Research Fellow, Department of Chemical and Biomolecular Engineering,National University of Singapore, Singapore

xvii

RUTH YU-LI YEH, PhD • Professor, Department of Chemical Engineering, Ming HsinUniversity of Science and Technology, Hsin-Chu, Taiwan

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

LINDA ZOU, PhD • Associate Professor, Institute of Sustainability and Innovation,Werribe Campus, Victoria University, Melbourne, Australia

xviii Contributors

1Pressurized Ozonation

Lawrence K. Wang and Nazih K. Shammas

CONTENTS

INTRODUCTION

DESCRIPTION OF PROCESSES

FORMATION AND GENERATION OF OZONE

REQUIREMENTS FOR OZONATION EQUIPMENT

PROPERTIES OF OZONE

DISINFECTION BY OZONE

OXIDATION BY OZONE

OXYGENATION AND OZONATION SYSTEMS

NOMENCLATURE

ACKNOWLEDGMENTS

REFERENCES

1. INTRODUCTION

Increasing population and improving standards of living are placing increasing bur-dens on water resources. The preservation of the limited natural water supplies and, inthe near future, the necessity for direct recycling of water in some parts of the world willrequire improved technologies for the removal of contaminants from wastewater.

There are many contaminants in wastewater, which vary from time to time, and theyare not well characterized with respect to chemical species. Commonly, the level oforganic contamination is expressed by biochemical oxygen demand (BOD), chemicaloxygen demand (COD), or total organic carbon (TOC). Ozone and oxygen are power-ful oxidants, which can oxidize many contaminants in wastewater and sludge biosolids.Ozone is more powerful than oxygen, but it must be generated at the point of usebecause it is an unstable material.

For many years in European countries, ozone has been used for disinfecting drinkingwater. It has also been used for treating some special industrial wastes, notably forremoving cyanides and phenols. Since 1980, ozone has been used for wastewater, indus-trial wastes, and sludge treatment on a large scale (1–6). Oxidative purification and

1

From: Handbook of Environmental Engineering, Volume 5: Advanced Physicochemical Treatment TechnologiesEdited by: L. K. Wang, Y. -T. Hung, and N. K. Shammas © The Humana Press Inc., Totowa, NJ

disinfection with ozone as a tertiary wastewater treatment or sludge treatment has anumber of inherent advantages:

a. Reduction in BOD and COD.b. Reduction of odor, color, turbidity, and surfactants.c. Pathogenic organisms are destroyed.d. The treatment products are beneficial.e. The effluent water has a high dissolved oxygen (DO) concentration.

The relatively high cost of ozone generation requires a high ozone-utilization effi-ciency if ozone treatment is to be economically competitive. A principal disadvantageto the use of ozone in waste treatment is its cost. However, recent advances in ozonegeneration have rendered the ozonation process more competitive.

This chapter deals with two newly developed oxygenation–ozonation (Oxyozosynthesis®)systems for wastewater and sludge treatment. Each treatment scheme consists of a wetwell for flow equalization and pH adjustment, a hyperbaric reactor for oxygenation andozonation, a flotation clarifier for degasification and solid–water separation, and a filterbelt press for final sludge dewatering. Special emphasis is placed on theory, kinetics, anddisinfection effect of ozonation and oxygenation (7–12).

1.1. Oxyozosynthesis Sludge Management System

As shown in Figs. 1 and 2, the new sludge management system consists of the fol-lowing unit operations and processes: sludge production from clarifiers, flow equaliza-tion and pH adjustment in a wet well, oxygenation–ozonation in a hyperbaric reactorvessel (Fig. 3), flotation, dewatering in a belt press, and resource recovery of final prod-uct as fuel or for land application.

A full-scale Oxyozosynthesis sludge management system was installed at the WestNew York Sewage Treatment Plant (WNYSTP), West New York, NJ. The plant treatsdomestic wastewater flow of 10 MGD and produces 22,000 gpd of primary sludge.Primary raw sludge is pumped from sumps located at the bottom of the primary sedi-mentation clarifiers by means of two positive-displacement pumps to a sludge grinder,then to the wet well. As the wet well is being filled with ground sludge, a chemical meter-ing pump is used to add a 10% sulfuric acid solution to adjust the pH value to between3.5 and 4.0. A mechanical mixer and a pH meter are mounted in the wet well for propermixing and pH monitoring, respectively. Following acidification, the sludge is pumpedby a progressive cavity pump to one of the two batch-operated hyperbaric reactor ves-sels, each capable of treating 1500 gal of sludge in 90 min by oxygenation and ozona-tion. To start each reactor vessel, the pressure in the reactor is increased to 40 psig withliquid oxygen first and then up to 60 psig with ozone. There are two operational modes:

a. Continuous oxygenation–ozonation. After the startup with oxygen and ozone, ozone iscontinuously fed into the reactor for a total of 90 min. The pressure is maintained at 60 psigby bleeding off (or recycling) the excess gas.

b. Noncontinuous oxygenation–ozonation. After the startup with oxygen and ozone, ozoneis then shut off, to isolate the reactor and maintain the conditions for 90 min.

During the first 90 min contact time in the oxygenation–ozonation reactor,pathogenic bacteria, viruses, total suspended solids, and volatile suspended solids in the

2 Lawrence K. Wang and Nazih K. Shammas

sludge are all significantly reduced. The reactor effluent is then released (at a flow rateof about 1500 gal/90 min) into an open flotation unit where DO, ozone, and carbondioxide gases are released out of the solution to form tiny bubbles, which adhere to theresidual suspended solids causing them to float and thickened at the top of the unit. Theflotation unit is equipped with revolving paddles (or scoops) that transport these float-ing solids onto a filter belt press for sludge dewatering. The subnatant liquor is recycled

Pressurized Ozonation 3

Fig. 1. General view of oxygenation–ozonation (Oxyozosynthesis™) system.

4

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to the head of the sewage treatment plant for further treatment with the incomingwastewater flow.

The filter belt press produces a dry high-nutrient sludge cake with low metal contentand high BTU value. The sludge cake can be recycled by spreading on agricultural land,reused as a fuel source, or disposed off in a landfill. The dry sludge can also be reusedas secondary fiber in paper manufacturing or as raw material for building blocks.

1.2. Oxyozosynthesis Wastewater Reclamation System

As shown in Fig. 4, the new wastewater reclamation system consists of the followingunit operations and processes: wastewater collection and preliminary treatment (barscreens and grit chambers), flow equalization and pH adjustment in a wet well, oxy-genation–ozonation in a hyperbaric reactor vessel, dissolved gas flotation (DGF), andfiltration.

A pilot-scale Oxyozosynthesis wastewater reclamation system was installed at theLenox Institute of Water Technology, Lenox, MA. The pilot plant treats a wastewaterflow of 6 gpm and produces small amount of sludge. Raw wastewater is pumped fromsumps located at the bottom of the grit chambers by means of positive-displacementpumps to a wet well. As the wet well is being filled with the raw wastewater, a chemi-cal metering pump is used to add a 10% sulfuric acid solution to adjust the pH value tobetween 3.5 and 4.0 by a chemical metering pump. A mechanical mixer and a pH meterare mounted in the wet well for proper mixing and pH monitoring, respectively.

From the wet well, a progressive cavity pump delivers the acidified wastewater to abatch-operated hyperbaric reactor vessel capable of treating 100 gal of wastewater in


Fig. 3. The hyperbaric reactor vessel.

6

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30–60 min depending on the characteristics of the wastewater. To start the reactor vessel, the pressure in the reactor is increased to 40 psig with liquid oxygen first, andthen to 60 psig with ozone. There are two operational modes:

a. Continuous oxygenation–ozonation. After the startup with oxygen and ozone, ozone iscontinuously fed into the reactor for a total of 30–60 min. The pressure is maintained at 60 psig by bleeding off (or recycling) the excess gas.

b. Noncontinuous oxygenation–ozonation. After the startup with oxygen and ozone, ozoneis then shut off, to isolate the reactor and maintain the conditions for 30–60 min.

During the first 30–60 min contact time in the oxygenation–ozonation reactor,pathogenic bacteria, viruses, total suspended and volatile suspended solids, phenols,cyanides, manganese, and so on, in wastewater are all significantly reduced. The reac-tor effluent is released into a DGF unit, where flocculant(s) can be added and the dis-solved gases come out of aqueous phase forming tiny bubbles, which adhere to the flocsand residual suspended solids causing them to float to the top of the unit. Heavy metals,iron, phosphate, humic acids, hardness, toxic volatile organics, and so on, will all reactwith the flocculant(s) to form insoluble flocs that are floated. The flotation unit isequipped with revolving paddles (or scoops) that transport these floating solids onto asubsequent filter belt press for final sludge dewatering. A dual-media filter further polishes the subnatant clarified water.

The filter effluent quality is close to that of potable water, having extremely lowcolor, turbidity, suspended solids, hardness, iron, manganese, trihalomethane precursor(humic acid), heavy metal, volatile organics, phenol, cyanide, and so on. The productwater is suitable for reuse for industrial and agricultural purposes. Further treatment ofthe final filter effluent by adsorption on activated carbon is optional.

2. DESCRIPTION OF PROCESSES

2.1. Ozonation and Oxygenation Process

Ozone gas is sparingly soluble in water. The solubility of ozone in water increaseswith its increasing partial pressure, decreasing water pH, and decreasing temperature.However, oxidation rate increases with increasing temperature. For economic operationof the hyperbaric oxygenation–ozonation reactor, it is operated at room temperature anda pressure in the range of 40–60 psig, the influent liquid sludge pH is reduced with sul-furic acid to a value in the 3.5–4.0 range.

The addition of oxygen at 40 psig and ozone at 60 psig ensure proper partial pres-sures for solubilizing both oxygen and ozone gases in the sludge. Both DO and ozoneact to oxidize chemically the reducing pollutants found in the liquid sludge, thusdecreasing BOD and COD, which results in the formation of oxygenated organic inter-mediates and end products. Ozonation–oxygenation treatment also reduces color andodor in waste sludge.

Because there is a wide range of ozone reactivity with the diverse organic content ofwastewater, both the required ozone dose and reaction time are dependent on the qualityof the influent to the ozonation process. Generally, higher doses and longer contact timesare required for ozone oxidation reactions than are required for wastewater disinfectionusing ozone. Ozone tertiary treatment may eliminate the need for a final disinfection


step. Ozone breaks down to elemental oxygen in a relatively short period of time (itshalf-life is about 20 min). Consequently, it must be generated on-site using either air oroxygen as the feed gas. Ozone generation utilizes a silent electric arc or corona throughwhich air or oxygen passes, and yields ozone in the air/oxygen mixture, the percentageof ozone being a function of voltage, frequency, gas flow rate, and moisture. Automaticdevices are commonly applied to control and adjust the ozone generation rate.

For sludge treatment or wastewater reclamation, it is a developing technology.Recent developments and cost reduction in ozone generation and ozone dissolutiontechnology make the process very competitive. A full-scale application is currently inthe demonstration stage at the WNYSTP, West New York, NJ. If oxygen-activatedsludge is employed in the system, ozone treatment may be even more economicallyattractive, because a source of pure oxygen is available facilitating ozone production.

For poor-quality wastewater or sludge with extremely high COD, BOD, and/or TOCcontents (>300 mg/L), ozone treatment can be economical only if there is adequate pre-treatment. The process will not produce any halogenated hydrocarbons. Table 1 shows thereduction of overall COD, BOD, and TOC, achieved in the US Environmental ProtectionAgency (EPA) controlled tests after a 90 min contact time with ozone oxidation. Beyondthe 70% COD removal level, the oxidation rate is significantly slowed. In laboratory tests,COD removal never reaches 100% even at a high ozone dose of 300 mg/L.

As a disinfectant with common dosages of 3–10 mg/L, ozone is an effective agent fordeactivating common forms of bacteria, bacterial spores, and vegetative microorgan-isms found in wastewater, as well as eliminating harmful viruses. Additionally, ozoneacts to chemically oxidize materials found in the wastewater and sludge, forming oxy-genated organic intermediates and end products. Furthermore, ozone treatment reduceswastewater color and odor. Ozone disinfection is applicable in cases, where chlorine(Cl2) disinfection might produce potentially harmful chlorinated organic compounds. Ifoxygen-activated sludge is employed in the system, ozone disinfection is economicallyattractive, because a source of pure oxygen is available for facilitating ozone produc-tion. However, ozone disinfection does not form a residual that will persist and can beeasily measured to ensure adequate dosage. Ozonation may not be economically com-petitive with chlorination under nonrestrictive local conditions.


Table 1Effectiveness of Ozone as an Oxidant

Ozone dosageCOD (mg/L) BOD5 (mg/L) TOC (mg/L)

(mg/L) Influent Effluent Influent Effluent Influent Effluent

50 318 262 142 110 93 80100 318 245 142 100 93 77200 318 200 142 95 93 80325 318 159 142 60 93 5050 45 27 13 7 20.5 15.5

100 45 11 13 3 20.5 9200 45 5.5 13 1.5 20.5 5

Source: US EPA.

Easily oxidizable wastewater organic materials consume ozone at a faster rate thandisinfection, therefore, the effectiveness of disinfection is inversely correlated witheffluent quality but directly proportional to ozone dosage. When sufficient concentra-tion is introduced, ozone is a more complete disinfectant than chlorine. Results of dis-infection by ozonation have been reported by various sources, which are summarized inTable 2.

2.2. Flotation Process

DGF is mainly used to remove suspended and colloidal solids by flotation resultingfrom the decrease in their apparent density. The influent feed liquid can be raw water,wastewater, or liquid sludge. The flotation system consists of four major components: gassupply, pressurizing pump, retention tank, and flotation chamber. According to Henry’sLaw, the solubility of gas in aqueous solution increases with increasing pressure. A pres-surizing pump is used to saturate the feed stream with gas at pressures several times theatmospheric pressure (25–70 psig). The pressurized feed stream is held at this high pres-sure for about 0.5–3 min in a retention tank (hyperbaric vessel) designed to provide therequired time for dissolution of gas into the treatment stream. Following the retention ves-sel, the stream is released back to atmospheric pressure in the flotation chamber. Most ofthe pressure drop occurs downstream from a pressure-reducing valve and in the transferline between the retention vessel and the flotation chamber, so that the turbulent effect ofdepressurization is minimized. The sudden reduction in pressure in the flotation chamberresults in the release of microscopic gas bubbles (average diameter 80 μm or smaller) thatattach themselves to the suspended and colloidal particles present in water. This results inan agglomeration, due to entrained gas giving a net combined specific gravity less thanthat of water thereby resulting in flotation. The vertical rising rate of gas bubbles rangesbetween 0.5 and 2 ft/min. The floated materials rise to the surface of the flotation cham-ber, where they are continuously scooped by specially designed flight scrapers or otherskimming devices. The surface sludge layer or float can in certain cases attain a thickness


Table 2 Effectiveness of Ozone as a Disinfectant

Dose Contact Effluent Source Influent (mg/L) time (min) residual

US EPA Secondary 5.5–6 ≤1 <2 fecal coliforms/100 mLeffluent

US EPA Secondary 10 3 99% inactivation effluent of fecal coliform

US EPA Secondary 1.75–3.5 13.5 <200 fecal coliforms/effluent 100 mL

US EPA Drinking water 4 8 Sterilization of virusWNYSTP Primary sludge NA 60 >99% inactivation

of fecal coliformSIT/LI Secondary NA 60 >99% inactivation

sludge of fecal coliform

Source: US EPA.

of several inches and be relatively stable. The layer thickens with time, but undue longdelays in removal will cause release of particulates back to the liquid. The clarified efflu-ent is usually drawn off from the bottom of the flotation chamber, which can be recoveredfor reuse or for final disposal. Figures 5 and 6 illustrate up-to-date DGF systems using sin-gle cell and double cell, respectively. The flotation system is known as dissolved air flota-tion (DAF) only when air is used. In the Oxyozosynthesis system, the dissolved gasesinclude oxygen, ozone, carbon dioxide, and air.

The retention time in the flotation chamber is usually short, about 3–5 min depend-ing on the characteristics of process water and the performance of the flotation unit.DGF units with such short retention times can treat water, wastewater, or sludge at anoverflow rate of 3.5 gpm/ft2 for a single unit, and up to 10.5 gpm/ft2 for triple stackedunits. A comparison between a DGF clarifier and a sedimentation tank shows that (13):

a. DGF floor space requirement is only 15% of the sedimentation tank.b. DGF volume requirement is only 5% of the sedimentation clarifier.c. The degrees of clarification of a DGF are similar to that of a sedimentation tank using the

same flocculating chemicals.d. The operational cost of the DGF clarifier is slightly higher than that for the sedimentation

unit, which is offset by the considerably lower cost for financing the installation.


Fig. 5. A single-cell high rate DAF system (Supracell).

e. DGF clarifiers are usually prefabricated using stainless steel. This results in lower erectioncost, better flexibility in construction, and ease of possible future upgrade compared withthe in situ constructed heavy concrete sedimentation tanks.

Currently used DGF units are more reliable, have excellent performance for sludgethickening, and require less land area than gravity thickeners. However, the gas releasedto the atmosphere may strip volatile organic material from the sludge. The volume ofsludge requiring ultimate disposal or reuse may be reduced, although its compositionwill be altered if chemical flotation aids are used. US EPA data from various air flota-tion units indicate that solids recovery ranges from 83 to 99% at solids loading rates of7–48 lb/ft2/d. A summary of US EPA data that illustrate the excellent performance ofDAF for thickening various types of sludges is shown in Table 3.

DAF is also an excellent process for solids separation in water treatment and waste-water reclamation (14–17). DAF is an integral part of the Oxyozosynthesis wastewaterreclamation system. A bird’s eye view of the advanced DAF unit with built-in chemicalflocculation and filtration (Sandfloat) is shown in Fig. 7. The influent raw water orwastewater enters the inlet at the center near the bottom, and flows through a hydraulic


Fig. 6. A double-cell high rate DAF system (Supracell).

rotary joint and an inlet distributor into the rapid mixing section of the slowly moving car-riage. The entire moving carriage consists of rapid mixer, flocculator, air dissolving tube,backwash pump, sludge discharge scoop, and sludge recycle scoop. From the rapid mixing


Table 3Sludge Thickening by Dissolved Air Flotation

Loading rate Loading rateFeed solids w/o polymer w/polymer Float solidsconc. (%) (lb/ft2/d) (lb/ft2/d) conc. (%)

Primary + WAS 2 20 60 5.5Primary + (WAS + FeCl3) 1.5 15 45 3.5(Primary + FeCl3) + WAS 1.8 15 45 4WAS 1 10 30 3WAS + FeCl3 1 10 30 2.5Digested primary + WAS 4 20 60 10Digested primary + 4 15 45 8

(WAS + FeCl3) Tertiary (alum) 1 8 24 2

Source: US EPA.

Fig. 7. Bird’s eye view of a flocculation/flotation/filtration package unit (Sandfloat).

section, the water enters the hydraulic flocculator where flocs are gradually built up by gentlemixing. The flocculated water moves from the flocculator into the flotation tank clock-wise with the same velocity as the entire carriage including the flocculator, which is mov-ing counterclockwise simultaneously. The flocculator effluent velocity is compensated bythe opposite velocity of the moving carriage, resulting in a “zero” horizontal velocity ofthe flotation tank influent. The flocculated water thus stands still in the flotation tank foroptimum clarification. At the outlet of the flocculator, clarified or recycled water streamwith microscopic air bubbles is added to the flotation tank, in order to float the insolubleflocs and suspended matter to the water surface. The float (scum/sludge) accumulated atthe top of the unit is scooped off by a sludge discharge scoop and discharged into the cen-ter sludge collector, where there is a sludge outlet to an appropriate sludge treatment facil-ity. The bottom of the Sandfloat is made up of multiple sections or wedges of sand filterand clear well. The clarified flotation effluent passes through the sand filter downward andenters the clear well. Through the circular hole underneath each sand filter section, the fil-ter effluent enters the center portion of the clear well, where there is an outlet for theSandfloat effluent. The filter sections are backwashed sequentially.

For the wastewater reclamation plant, DAF is an important process unit. Filtration isused for final polishing of the plant effluent. Table 4 represents the US EPA data onremoval of various classical pollutants, toxic heavy metals, and toxic organics by flota-tion. For more information on the DAF process the reader is referred to refs. 18 and 19.

2.3. Filter Belt Press

The filter belt press or simply the belt press is used for sludge dewatering. Resemblinga conveyor belt, the filter belt press consists of an endless filter belt that runs over a driveand guide rollers at each end. Several rollers support the filter belt along its length. Abovethe filter belt is a press belt that runs in the same direction and at the same speed; its driveroller is coupled with the drive roller of the filter belt. The press belt can be pressed onthe filter belt by means of a pressure roller system whose rollers can be individuallyadjusted either horizontally or vertically. The sludge to be dewatered is fed onto the upperface of the filter belt and is continuously dewatered between the filter and press belts.After having passed the static pressure zone, further dewatering is achieved by the super-imposition of shear forces to expedite the dewatering process. The supporting rollers ofthe filter belt and the pressure rollers of the pressure belt are adjusted in such a way thatthe belts and the sludge between them describe a S-shaped curve. Thus, there is a paral-lel displacement of the belts relative to each other owing to the differences in the radii.After further dewatering in the shear zone, the sludge is removed by a scraper.

Some units consist of two stages, where the initial draining zone is on the top level fol-lowed by an additional lower section wherein pressing and shearing occur. A significantfeature of the filter belt press is that it employs a coarse mesh, relatively open weave, andmetal medium fabric. This is feasible because of the rapid and complete cake formationobtainable when proper flocculation is achieved. Belt filters do not need vacuum systemsand do not have the sludge pickup problem that is occasionally experienced with rotaryvacuum filters. The belt press can handle the hard-to-dewater sludges more readily. Thelow moisture cake produced permits incineration of primary/secondary sludge combina-tions without auxiliary fuel. A large filtration area can be installed in a minimum of floor



Table 4Removal of Various Pollutants, Toxic Heavy Metals, and Organics by Flotation

Data Effluent Removalpoints concentration efficiency (%)

FullPollutant scale Range Median Range Median

Classical pollutants (mg/L)BOD5 9 140–1000 250 4–87 68 COD 12 18–3200 1200 8–96 66 TSS 12 18–740 82 6–98 88 Total phosphorus 6 <0.05–12 0.66 50 to >99 98 Total phenols 10 <0.001–23 0.66 3 to >94 12 Oil and grease 11 16–220 84 57–97 79

Toxic pollutants (μg/L)Antimony 9 ND to 2300 20 4–95a 76 Arsenic 7 ND to 18 <10 8 to >99 45 Xylene 3 ND to 1000 200 95 to >99 97 Cadmium 9 BDL to <72 3 0 to >99 98a

Chromium 12 2–620 200 20–99 52Copper 12 5–960 180 9–98 75 Cyanide 7 <10–2300 54 0 to <62 10 Lead 13 ND to 1000 70 9 to >99 98 Mercury 8 BDL to 2 BDL 33–88 75 Nickel 12 ND to 270 41 29 to >99 73 Selenium 3 BDL to 8.5 2 NM Silver 5 BDL to 66 19 45 Thallium 3 BDL to 50 14 NM Zinc 11 ND to 53,000 200 12 to >99 89 Bis(2-ethylhexyl) 8 30–1100 100 10–98 72

phthalateButyl benzyl phthalate 5 ND to 42 ND 97 to >99 >99Carbon tetrachloride 3 BDL to 210 36 75Chloroform 6 ND to 24 9 20 to >99 58 Dichlorobromomethane 1 ND >992,4-Dichlorophenol 1 6 NMDi-N-butyl phthalate 6 ND to 300 20 0 to >99 97 Diethyl phthalate 1 ND >99 Di-N-octyl phthalate 6 ND to 33 11 61 to >99 78 N-Nitrosodiphenylamine 1 620 66N-Nitroso-di-N- 1 84 NM

propylamine 2-Chlorophenol 1 2 NM2,4-Dimethylphenol 2 ND to 28 14 >99 Pentachlorophenol 5 5–30 13 19Phenol 8 9–2400 71 0–80 57 2,4,6-Trichlorophenol 1 3 NM Benzene 3 5–200 120 NM Chlorobenzene 1 57 NM

(Continued)

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