Environmental Flotation Engineering (Handbook of Environmental Engineering, 21) 3030546403, 9783030546403

Citation preview

Handbook of Environmental Engineering 21

Lawrence K. Wang Mu-Hao Sung Wang Nazih K. Shammas Donald B. Aulenbach Editors

Environmental Flotation Engineering

Handbook of Environmental Engineering Volume 21

Series Editors Lawrence K. Wang PhD, Rutgers University, New Brunswick, NJ, USA MS, University of Rhode Island, RI, USA MSCE, University of Missouri, Rolla, MO, USA BSCE, National Cheng-Kung University, Taiwan, ROC Mu-Hao Sung Wang PhD, Rutgers University, New Brunswick, NJ, USA MS, University of Rhode Island, RI, USA BSCE, National Cheng-Kung University, Taiwan, ROC

The past 30 years have seen the emergence of a growing desire worldwide to take positive actions to restore and protect the environment from the degrading effects of all forms of pollution: air, noise, solid waste, and water. The principle intention of the Handbook of Environmental Engineering (HEE) series is to help readers formulate answers to the fundamental questions facing pollution in the modern era, mainly, how serious is pollution and is the technology needed to abate it not only available, but feasible. Cutting-edge and highly practical, HEE offers educators, students, and engineers a strong grounding in the principles of Environmental Engineering, as well as providing effective methods for developing optimal abatement technologies at costs that are fully justified by the degree of abatement achieved. With an emphasis on using the Best Available Technologies, the authors of these volumes present the necessary engineering protocols derived from the fundamental principles of chemistry, physics, and mathematics, making these volumes a must have for environmental pollution researchers.

More information about this series at http://www.springer.com/series/7645

Lawrence K. Wang • Mu-Hao Sung Wang Nazih K. Shammas • Donald B. Aulenbach Editors

Environmental Flotation Engineering

Editors Lawrence K. Wang Lenox Institute of Water Technology Lenox, MA and Newtonville, NY, USA

Mu-Hao Sung Wang Lenox Institute of Water Technology Lenox, MA and Newtonville, NY, USA

Nazih K. Shammas Lenox Institute of Water Technology Lenox, MA and Newtonville, NY, USA

Donald B. Aulenbach Lenox Institute of Water Technology Lenox, MA and Newtonville, NY, USA

ISSN 2512-1359 ISSN 2512-1472 (electronic) Handbook of Environmental Engineering ISBN 978-3-030-54640-3 ISBN 978-3-030-54642-7 (eBook) https://doi.org/10.1007/978-3-030-54642-7 © Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

The past 75 years have seen the emergence of a growing desire worldwide that positive actions be taken to restore and protect the environment from the degrading effects of all forms of pollution—air, water, soil, thermal, radioactive, and noise. Since pollution is a direct or indirect consequence of waste, the seemingly idealistic demand for “zero discharge” can be construed as an unrealistic demand for zero waste. However, as long as waste continues to exist, we can only attempt to abate the subsequent pollution by converting it to a less noxious form. Three major questions usually arise when a particular type of pollution has been identified: (1) How serious are the environmental pollution and water resources crisis? (2) Is the technology to abate them available? (3) Do the costs of abatement justify the degree of abatement achieved for environmental protection and natural resources conservation? This book is one of the volumes of the Handbook of Environmental Engineering series. The principal intention of this series is to help readers formulate answers to the above three questions. The traditional approach of applying tried-and-true solutions to specific environmental and chemical engineering problems has been a major contributing factor to the success of environmental chemical engineering and has accounted in large measure for the establishment of a “methodology of environmental control.” However, the realization of the ever-increasing complexity and interrelated nature of current environmental problems renders it imperative that intelligent planning of pollution abatement systems be undertaken. Prerequisite to such planning is an understanding of the performance, potential, and limitations of the various methods of environmental protection available for environmental scientists and engineers. In this series of handbooks, we will review at a tutorial level a broad spectrum of engineering systems (natural environment, processes, operations, and methods) currently being utilized, or of potential utility, for pollution abatement, environmental protection, and natural resources conservation. We believe that the unified interdisciplinary approach presented in these handbooks is a logical step in the evolution of environmental engineering.

v

vi

Preface

Treatment of the various engineering systems presented will show how an engineering formulation of the subject flows naturally from the fundamental principles and theories of chemistry, microbiology, physics, and mathematics. This emphasis on fundamental science recognizes that engineering practice has in recent years become more firmly based on scientific principles rather than on its earlier dependency on empirical accumulation of facts. It is not intended, though, to neglect empiricism where such data lead quickly to the most economic design; certain engineering systems are not readily amenable to fundamental scientific analysis, and in these instances we have resorted to less science in favor of more art and empiricism. Since an environmental flotation engineer must understand science within the context of applications, we first present the development of the scientific basis of a particular subject, followed by exposition of the pertinent design concepts and operations, and detailed explanations of their applications to natural resources conservation or environmental protection. Throughout the series, methods of mathematical modeling, system analysis, practical design, and calculation are illustrated by numerical examples. These examples clearly demonstrate how organized, analytical reasoning leads to the most direct and clear solutions. Wherever possible, pertinent cost data or models have been provided. Our treatment of environmental and chemical engineering is offered in the belief that the trained engineer should more firmly understand fundamental principles, be more aware of the similarities and/or differences among many of the engineering systems, and exhibit greater flexibility and originality in the definition and innovative solution of environmental system problems. In short, the environmental flotation engineers should by conviction and practice be more readily adaptable to change and progress. Coverage of the unusually innovative field of flotation science, technology, engineering, and mathematics (STEM) has demanded an expertise that could only be provided through multiple authorships. Each author (or group of authors) was permitted to employ, within reasonable limits, the customary personal style in organizing and presenting a particular subject area; consequently, it has been difficult to treat all subject materials in a homogeneous manner. Moreover, owing to limitations of space, some of the authors’ favored topics could not be treated in great detail, and many less important topics had to be merely mentioned or commented on briefly. All authors have provided an excellent list of references at the end of each chapter for the benefit of the interested readers. As each chapter is meant to be self-contained, some mild repetition among the various texts was unavoidable. In each case, all omissions or repetitions are the responsibility of the editors and not the individual authors. With the current trend toward metrication, the question of using a consistent system of units has been a problem. Wherever possible, the authors have used the British system (fps) along with the metric equivalent (mks, cgs, or SIU) or vice versa. The editors sincerely hope that this redundancy of units’ usage will prove to be useful rather than being disruptive to the readers.

Preface

vii

The goals of the Handbook of Environmental Engineering series are: (1) to cover entire environmental fields, including air and noise pollution control, solid waste processing and resource recovery, physicochemical treatment processes, biological treatment processes, biotechnology, biosolids management, flotation technology, membrane technology, desalination technology, water resources, natural control processes, radioactive waste disposal, hazardous waste management, and thermal pollution control, and (2) to employ a multimedia approach to environmental conservation and protection since air, water, soil, and energy are all interrelated. This book (Volume 21, Environmental Flotation Engineering) and its sister book (Volume 12, Flotation Technology) from the Handbook of Environmental Engineering series have been designed to serve as flotation STEM reference books as well as supplemental textbooks. We hope and expect they will prove of equal high value to advanced undergraduate and graduate students, to designers of flotation systems, and to scientists and researchers. The editors welcome comments from readers in all of these categories. It is our hope that the two flotation books will not only provide information on flotation STEM, but will also serve as a basis for advanced study or specialized investigation of the theory and analysis of various biological and physicochemical flotation systems. This book, Environmental Flotation Engineering, Volume 21, covers the topics on humanitarian engineering education of the Lenox Institute of Water Technology and its new potable water flotation processes; Innovative dissolved air flotation potable water filtration plant in Lee, Massachusetts, USA; fundamentals of chemical coagulation and precipitation; a new wave of flotation technology advancement for wastewater treatment; innovative circular gravity flotation and fiber detection for fiber separation; independent physicochemical wastewater treatment system consisting of primary flotation clarification, secondary flotation clarification, and tertiary treatment; wastewater treatment using activated sludge and flotation clarifications under cold weather conditions; operation and performance of the AquaDAF process system for water purification; operation and performance of the Clari-DAF process system for water purification; a spectrophotometric method for determination of dissolved proteins in water or wastewater; and biological and physicochemical sequencing batch reactors using sedimentation or flotation. This book’s sister book, Flotation Technology, Volume 12, covers the topics on principles of air flotation technology; gas dissolution release and bubble formation in flotation systems; separation of oil from wastewater by air flotation; fundamentals of wastewater flotation; electroflotation; wastewater treatment by electrocoagulationflotation; treatment of paper mill whitewater; recycling, and recovery of raw materials; ozone-oxygen oxidation flotation; wastewater renovation by flotation; flotation-filtration system wastewater reuse; algae removal by flotation; completely closed water systems in paper mills; lake restoration using DAF; Jiminy Peak, Hancock, Massachusetts, Wastewater Treatment Plant: the first RBC-flotation-UV wastewater treatment plant in the USA; Pittsfield Water Treatment Plant: once the world’s largest flotation-filtration plant; pretreatment of meat processing waste; treatment of seafood processing wastewater; and laboratory simulation and testing of air flotation and associated processes.

viii

Preface

The editors are pleased to acknowledge the encouragement and support received from Mr. Aaron Schiller, Executive Editor of the Springer Nature Switzerland, and his colleagues during the conceptual stages of this endeavor. We wish to thank the contributing authors for their time and effort, and for having patiently borne our reviews and numerous queries and comments. We are very grateful to our respective families for their patience and understanding during some rather trying times. Newtonville, NY, USA

Lawrence K. Wang Mu-Hao Sung Wang Nazih K. Shammas Donald B. Aulenbach

Contents

1

2

Humanitarian Engineering Education of the Lenox Institute of Water Technology and Its New Potable Water Flotation Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lawrence K. Wang Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee, Massachusetts, USA . . . . . . . . . . . . . . . . . . . . . . . . . . Lawrence K. Wang, Mu-Hao Sung Wang, and Edward M. Fahey

1

73

3

Fundamentals of Chemical Coagulation and Precipitation . . . . . . . Nazih K. Shammas, Hermann H. Hahn, Mu-Hao Sung Wang, and Lawrence K. Wang

95

4

A New Wave of Flotation Technology Advancement for Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Lawrence K. Wang and Mu-Hao Sung Wang

5

Innovative Circular Gravity Flotation and Fiber Detection for Fiber Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Lawrence K. Wang, Mu-Hao Sung Wang, and Joseph M. Wong

6

Independent Physicochemical Wastewater Treatment System Consisting of Primary Flotation Clarification, Secondary Flotation Clarification, and Tertiary Treatment . . . . . . . . . . . . . . . 189 Lawrence K. Wang, Mu-Hao Sung Wang, Nazih K. Shammas, and Marika S. Holtorff

7

Innovative Wastewater Treatment Using Activated Sludge and Flotation Clarifications Under Cold Weather Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Yuriy I. Pankivskyi and Lawrence K. Wang

ix

x

Contents

8

Operation and Performance of the AquaDAF® Process System for Water Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Joseph M. Wong, Ryan J. Hess, and Lawrence K. Wang

9

Operation and Performance of Clari-DAF® System for Water Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 Joseph M. Wong, James E. Farmerie, and Lawrence K. Wang

10

A Spectrophotometrical Method for Determination of Dissolved Proteins in Water or Wastewater . . . . . . . . . . . . . . . . 371 Lawrence K. Wang, Mu-Hao Sung Wang, and Aimee E. Thayer

11

Biological and Physicochemical Sequencing Batch Reactors Using Sedimentation or Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . 397 Lawrence K. Wang, Mu-Hao Sung Wang, Ping Wang, and Nicholas L. Clesceri

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

Contributors

Nicholas L. Clesceri PhD Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA Edward M. Fahey BS, ME Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA James E. Farmerie Xylem Water & Wastewater, Zelienople, PA, USA Hermann H. Hahn PhD Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Ryan J. Hess SUEZ Water Technologies and Solutions, Richmond, VA, USA Marika S. Holtorff BS, ME Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Yuriy I. Pankivskyi BS, ME, PhD Department of Ecology, Ukrainian National University of Forestry, Lviv, Ukraine Nazih K. Shammas PhD Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Aimee E. Thayer BS, ME Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Lawrence K. Wang PhD, PE, DEE Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Krofta Engineering Corporation, Lenox, MA, USA Mu-Hao Sung Wang PhD, PE, DEE Lenox Institute of Water Technology, Lenox, MA and Newtonville, NY, USA Ping Wang PhD Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA Joseph M. Wong BS, PE, BCEE Brown and Caldwell, Walnut Creek, CA, USA xi

About the Editors

Lawrence K. Wang has more than 28 years of experience in facility design, environmental sustainability, natural resources, resources recovery, global pollution control, construction, plant operation, and management. He has expertise in water supply, air pollution control, solid waste disposal, water resources, waste treatment, and hazardous waste management. He is a retired acting president/Director/VP of the Lenox Institute of Water Technology, Krofta Engineering Corporation, and Zorex Corporation, respectively, and was an Assistant Professor/Associate Professor/Professor of Rensselaer Polytechnic Institute, Stevens Institute of Technology, and the University of Illinois, respectively, in the USA. He has represented the US government to serve the United Nations Industrial Development Organization (UNIDO) as a Senior Advisor in Vienna, Austria. Dr. Wang is the author of over 700 papers and 45 books, and is credited with 24 U.S. patents and 5 foreign patents. He received his BSCE degree from National Cheng-Kung University, Taiwan, ROC, his two MS degrees from the University of Missouri and the University of Rhode Island, USA, and his PhD degree from Rutgers University, USA. Currently he is the Chief Series Editor of the Advances in Industrial and Hazardous Wastes Treatment series (CRC Press of Taylor & Francis Group), the Handbook of Environmental Engineering series (Springer), the Evolutionary Progress in Science, Technology, Engineering, Arts, and Mathematics series (Lenox Institute Press), and the Environmental Science, Technology, Engineering and Mathematics series (Lenox Institute Press). He is also the coeditor of the Handbook of Environment and Waste Management series (World Scientific) and the coauthor of the Water and Wastewater Engineering series (John Wiley). Mu-Hao Sung Wang has been an engineer, an editor, and a professor serving private firms, governments, and universities in the USA and the Republic of China (ROC) for over 25 years. She is a licensed Professional Engineer and a Diplomate of the American Academy of Environmental Engineers. Her publications have been in the areas of water quality, modeling, environmental sustainability, waste management, NPDES, flotation, and analytical methods. Dr. Wang is the author of over xiii

xiv

About the Editors

50 publications and an inventor with 14 US and foreign patents. She received her BSCE degree from National Cheng Kung University, Taiwan, ROC, her MSCE degree from the University of Rhode Island, USA, and her PhD degree from Rutgers University, USA. She was an Adjunct Associate Professor at Stevens Institute of Technology, NJ, USA; an Adjunct Professor at National Cheng Kung University, Taiwan, ROC, and a Professor at the Lenox Institute of Water Technology, MA, USA. She is the co-Series Editor of the Handbook of Environmental Engineering series (Springer) and coeditor of Environmental Science, Technology, Engineering and Mathematics STEM series (Lenox Institute Press). Dr. Wang is a member of AWWA, NEWWA, WEF, and OCEESA. Nazih K. Shammas was an environmental consultant and professor for over 45 years. He was an ex-Dean/Director of the Lenox Institute of Water Technology, and an Advisor to Krofta Engineering Corporation, USA. Dr. Shammas was the author of over 250 publications and 15 books in the field of environmental engineering. He had experience in environmental planning, curriculum development, teaching, scholarly research, and had expertise in water quality control, wastewater reclamation and reuse, physicochemical and biological processes, and water and wastewater systems. Professor Shammas received his BE degree from the American University of Beirut, Lebanon, his MS degree from the University of North Carolina at Chapel Hill, and his PhD degree from the University of Michigan, USA. He was the coeditor of the Advances in Industrial and Hazardous Wastes Treatment series (CRC Press of Taylor & Francis Group), the Handbook of Environmental Engineering series (Springer), the Environmental Science, Technology, Engineering and Mathematics series (Lenox Institute Press), and the Handbook of Environment and Waste Management series (World Scientific). In addition, Dr. Shammas was the coauthor of the Water and Wastewater Engineering series (John Wiley). Donald B. Aulenbach was a humanitarian environmentalist for over 50 years. After graduating from Franklin and Marshall college with a BS in Chemistry in 1950, he earned in MS and PhD in sanitation from Rutgers University in 1954. From 1954–1960, he worked as a biochemist for the Delaware Water Pollution Commission, where he was in charge of water quality laboratories and taught pollution control courses. From 1960–1993, he was a professor of environmental engineering at Rensselaer Polytechnic Institute (RPI), NY, USA. From 1981–2001, he was an Adjunct Professor at the Lenox Institute of Water Technology (LIWT), MA, USA. There he taught classes on environmental flotation technologies. He was active with the Fresh Water Institute at Lake George, where he published dozens of water quality reports. He had over 130 publications covering watershed hydrology, limnology, and various aspects of wastewater treatment. After retiring from RPI in 1993, he continued as Professor Emeritus at both RPI and LIWT. He also started his own firm, Environmental Engineering Consulting, providing analysis, legal advice, and instruction on water and wastewater treatment, solid waste disposal, radiological concerns, and lake and stream studies. Dr. Aulenbach was professional engineer and member of the ACS, WEF, AWWA, AEESP, AAEE, and HPS.

Chapter 1

Humanitarian Engineering Education of the Lenox Institute of Water Technology and Its New Potable Water Flotation Processes Lawrence K. Wang

Contents 1 Lenox Institute of Water Technology (LIWT) for Flotation Research and Education and Krofta Engineering Corporation (KEC) for Flotation Equipment Manufacturing . . . . 2 Research and Review of All Possible Flotation Technologies for Water Purification . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Research and Review of Dissolved Gas Flotation (DGF) . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Research and Review of Dispersed Gas Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Research and Review of Electroflotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Research and Review of Vacuum Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Research and Review of Biological Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Research and Review of Deep Shaft Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Research and Review of Plain Gravity Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Research and Initial Selection of Dispersed Air Flotation (or Induced Air Flotation, or Foam Separation) as a Water Purification Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Research and Subsequent Selection of Electroflotation for Water Purification . . . . . . . . . . . . 5 Research and Final Selection of Dissolved Gas Flotation as a Water Purification Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Development of a Potable Water DAF System by Replacing Conventional Sedimentation Clarifier with Innovative DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Development of a Potable Water Double DGF-DGF System by Replacing Conventional Double Sedimentation-Sedimentation Clarifiers with Innovative Double DGF-DGF Clarifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Development of a Potable Water Sedimentation-DAF System by Replacing a Conventional Double Pre-sedimentation-Sedimentation Water Clarification with an Innovative Combined Sedimentation-DAF Clarification . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Development of a Potable Water DAF-Filtration Clarifier by Replacing Conventional Sedimentation-Filtration System with Innovative DAF-Filtration System . . . . . . . . . . . . . . . . 9.1 Decision and Advantages of Having a DAF-Filtration (DAFF or Sandfloat) Package Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Engineering Design Criteria and Costs of DAF-Filtration (DAFF or Sandfloat) Package Clarifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Description of a DAF-Filtration (DAFF or Sandfloat) Package Plant . . . . . . . . . . . . . .

3 10 10 11 11 12 12 13 13 14 15 17 21 22

23

28 33 33 38 41

L. K. Wang (*) Lenox Institute of Water Technology, Newtonville, NY, USA © Springer Nature Switzerland AG 2021 L. K. Wang, M. -H. S. Wang, N. K. Shammas, D. B. Aulenbach (eds.), Environmental Flotation Engineering, Handbook of Environmental Engineering 21, https://doi.org/10.1007/978-3-030-54642-7_1

1

2

L. K. Wang

10

Lenox Water Treatment Plant: The First Potable Water Flotation-Filtration Plant in the Americas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pittsfield Water Treatment Plant: The Once-Largest Potable Water Flotation-Filtration Plant in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 More LIWT/KEC New Flotation Systems and Installations Pointing to New Research Directions and Engineering Applications . . . . . . . . . . . . . . . . . . . . . . 12.1 Adsorption Flotation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Sequencing Batch Flotation Systems and Sequencing Sedimentation Systems . . . 12.3 FloatPress: Flotation Thickening of Sludge Produced in Drinking Water Plants . . 12.4 Advanced DGF-DGF Water Treatment System Installation . . . . . . . . . . . . . . . . . . . . . . . 12.5 Advanced DGF-DGFF Water Treatment System Installation . . . . . . . . . . . . . . . . . . . . . . 12.6 Water Treatment by Dissolved Air Flotation Using Magnesium Carbonate as a Recyclable Coagulant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.7 Using Popular Flotation Processes as a Pretreatment to Equally Popular Membrane Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.8 Using Popular DAF-DAFF Clarifier (Sandfloat) for Granular Activated Carbon Filtration or Dual-Media Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.9 Using Circular Automatic Backwash Filter (CABF) as an Independent Process Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.10 Further Research for Cream Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Lenox Institute of Water Technology: A College of Humanitarian Engineering . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

45 47 48 48 48 49 49 50 50 52 53 54 54 55 56 60

Abstract It has been more than 37+ years since the first dissolved air flotation (DAF) drinking water treatment plant in the Americas came online in Lenox, Massachusetts, USA, in 1982. Since that time, the innovative DAF process – long favored for treating a wide variety of waste solids – has grown to become a popular process for drinking water plants in the Americas and throughout the entire world. The story of how the Lenox Water Treatment Plant (LWTP), and a much larger sister plant, Pittsfield Water Treatment Plant (PWTP), both in Massachusetts, USA, has blazed the trail for the current innovative wave of DAF-based potable water treatment plants. The author has participated in the conceptual development, laboratory tests, patent application, pilot plant demonstration, endless legal battles, state permit applications, and final construction of the award-winning LWTP and PWTP. It is the author’s honor and also the obligation to record this historical development of one of the outstanding innovations of this century. This chapter documents the impressive histories of a humanitarian flotation engineering college (Lenox Institute of Water Technology, or LIWT), a flotation manufacturer (Krofta Engineering Corporation, or KEC), the first drinking water flotation plant in the Americas (Lenox Water Treatment Plant, LWTP), and the oncelargest drinking water flotation plant in the world (Pittsfield Water Treatment Plant, PWTP). Their leader (Dr. Milos Krofta), inventors, educators, co-designers, governmental officers, design concepts, flow diagrams, DAF-filtration (DAFF), plant performance, awards, and DAF/DAFF future and related references are also documented. The details of flotation process chemistry, material balances, engineering calculations, hydraulics, water quality analysis, energy consumption, cost

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

3

estimations, etc., can be found in the literature of this chapter. Many innovative potable water flotation processes invented by LIWT, manufactured by KEC, and financed and collaborated by the above dedicated people are recorded here: (a) dispersed air flotation, or induced air flotation, or Foamer; (b) electroflotation; (c) dissolved air flotation, or DAF, or Supracell; (d) two-stage DAF-DAF clarifier system, or Supracell-Supracell system; (e) sedimentation-DAF clarifier, or SediFloat; (f) DAF-filtration, or DAFF, or Sandfloat; (g) two-stage DAF-DAFF clarifier system; (h) sequencing batch dissolved gas flotation, (i) sequencing batch induced gas flotation; (j) DAF-press thickener (FloatPress), (k) two-stage DAF-DAF water softening plant using magnesium carbonate as a recyclable coagulant, (l) DAF-membrane process combination, (m) circular automatic backwash filtration for dual-media filtration or granular activated carbon (GAC) filtration; and (n) a newly developed cream flotation process. This chapter is intended to be the author’s partial memoir which records only the author’s lifetime professional experience in drinking water for reference by future generations. This chapter is also written in memory of Dr. Milos Krofta, who was the founder and President of both LIWT and KEC as well as the author’s best friend and mentor. Although the academic process names (DAF, DAFF, etc.) and the equipment brand names (Supracell, Sandfloat, SediFloat, FloatPress, etc.) are used interchangeably throughout this chapter, the author introduces all new innovative flotation process ideas in general terms for everyone. The shape of a flotation clarifier can be either circular or rectangular. The unit processes can be either individual process units or packaged units. It is the author’s wish as well as Dr. Krofta’s 90th birthday wish that the innovative flotation ideas conceived and all processes developed by LIWT/KEC may be adopted or further improved upon by all flotation engineers, scientists, researchers, managers, and manufacturers in the world. The author acknowledges important contributions of all flotation experts and researchers and hopes that the proposed new research directions may be followed and accomplished by younger generations. Keywords Milos Krofta and Lawrence K. Wang’s memoir · Humanitarian engineering education · Lenox Institute of Water Technology (LIWT) · Krofta Engineering Corporation (KEC) · Century potable water innovations · Dissolved air flotation (DAF) · Supracell · Dissolved air flotation-filtration (DAFF) · Sandfloat · Drinking water · Lenox Water Treatment Plant (LWTP) · Pittsfield Water Treatment Plant (PWTP) · Massachusetts · USA · North America · South America · Historical plants · Dispersed air flotation · Induced air flotation · Foamer · Electroflotation · Sedimentation-DAF · SediFloat · Two-stage DAF-DAF system · Two-stage DAF-DAFF system · Sequencing batch sedimentation (sedimentation-SBR) · Dissolved air flotation sequencing batch reactor (DAF-SBR) · Flotation-press thickener · FloatPress · Two-stage DAF-DAF softening process · Magnesium carbonate · Recyclable coagulant · Flotation-membrane process combination · Circular automatic backwash filtration for sand filtration · dual-media filtration or GAC filtration · Cream flotation · New research direction · Awards · Flotation process contributors

4

L. K. Wang

Nomenclature CaCO3 Ca(HCO3)2 Ca(OH)2 CaSO4 CDBAC CO2 H 2O MgCO3 Mg(HCO3)2 Mg(OH)2 MgSO4 Na2CO3 Na2SO4

Calcium carbonate Calcium bicarbonate Calcium hydroxide Calcium sulfate Cetyldimethylbenzylammonium chloride Carbon dioxide Water Magnesium carbonate Magnesium bicarbonate Magnesium hydroxide Magnesium sulfate Sodium carbonate Sodium sulfate

1 Lenox Institute of Water Technology (LIWT) for Flotation Research and Education and Krofta Engineering Corporation (KEC) for Flotation Equipment Manufacturing The use of old dissolved air flotation (DAF) and dispersed air flotation technologies for solid separation was common in Europe and Asia as early as the 1950s [1–78]. Old DAF technology became known in North and South Americas in the late 1970s when Dr. Milos Krofta, who was an outstanding mechanical and paper engineer, established Krofta Engineering Corporation (KEC) in Massachusetts, USA, for manufacturing DAF clarifiers to be used in his own areas of expertise, namely, de-inking of waste paper pulp and fiber separation. KEC was an international company with branch offices around the world. Dr. Krofta was mainly assisted by Daniel Guss, VP. In 1978, with the authors’ encouragement and assistance, Dr. Milos Krofta established the not-for-profit Lenox Institute for Research (LIR) and later changed its name from LIR to Lenox Institute of Water Technology (LIWT). The author, Lawrence K. Wang, and his wife, Mu-Hao Sung Wang, were initially invited as the LIR/LIWT consultants and subsequently appointed to be the Institute Director and Adjunct Professor, respectively, with the purposes of (a) developing flotation process equipment to be used in conjunction with other physical-chemical and biological processes for various applications, such as drinking water treatment, wastewater treatment, algae harvesting, ore separation, and sludge thickening [1–222]; (b) obtaining the US and foreign patents for the Institute, and giving licenses of patent application rights to KEC and other companies or government agencies in exchange of their grants or other types of financial supports to the Institute and

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

5

Fig. 1.1 Lenox Institute of Water Technology (LIWT), Massachusetts, USA

students; and (c) developing the Institute as an accredited graduate college offering the degree of “Master of Engineering in Water Technology,” Postdoctoral Certificate, and continuing education for educating more qualified flotation engineers, managers, or researchers. The LIWT master’s degree program (34 credit hours) was licensed by the Commonwealth of Massachusetts, USA. LIWT was also a sponsor of the International Association for Continuing Education and Training, and so it awarded continuing education units (CEU) credits. An excellent LIWT library had cooperative agreements with the libraries of Rensselaer Polytechnic Institute and the University of Massachusetts. All LIWT graduate credits were accepted by area universities for their PhD programs. Dr. Krofta, the author, and many other appointed faculty members, such as Dr. Mu-Hao Sung Wang, Dr. Nazih K. Shammas, Dr. Donald B. Aulenbach, Dr. William A. Selke, Dr. Hermann H. Hahn, and Dr. James P. Smith, are highly qualified flotation experts. A student admitted to the Master’s degree program had at least a 4-year BS/BE/BA degree. For an environmental professional who wished to advance his/her career but did not need a Master’s degree might receive a Certificate in Water Science and Engineering after he/she completed 14 credit hours (equivalent to 21 Continuing Education Units). All students received full scholarship or internship (including their living expenses). Figures 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 document the LIWT campus, facility, and program curriculum. The Institute occupied over 18,000 square feet of classroom (Figs. 1.1, 1.2, and 1.3), laboratory, and supporting research equipment and facilities (Figs. 1.4, 1.5 and 1.6). Its research facilities featured advanced testing ad bench equipment to support faculty and student work, as well as the Institute’s R&D functions. A fully staffed and equipped machine shop (Fig. 1.5) was available to build, modify, or test experimental devices. The authors and Betty C. Wu

6

L. K. Wang

Fig. 1.2 Beautiful Lenox Institute campus with a lake

Fig. 1.3 A Lenox Institute classroom (shown) and a computer room (not shown)

(MS) developed the Institute’s modern chemical and microbiological laboratories which were equipped with atomic absorption spectrophotometric instrument (AA), gas chromatography instrument (GC), mass spectrometer (MS), total organic carbon instrument (TOC), chemical oxygen demand (COD), biochemical oxygen demand (BOD), spectrophotometers, turbidity meters, toxicity analyzers, ozone generators, ovens, digesters, incubators, balances, Jar Tester, DAF tester, particle counter, coliform tester, counters, sand filters, GAC filters, settlers, vacuum filters, stereoscopic microscopes, dryers, monitoring instrument, etc. The LIWT laboratory

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

7

Fig. 1.4. A chemical laboratory (shown), an instrumentation room (not shown), and a microbiology laboratory (not shown)

Fig. 1.5 Lenox Institute machine shop and pilot plant rooms

(Fig. 1.4) was certified by the states of New England and the states of NY, PA, and NJ, where the LIWT and KEC had flotation projects. The LIWT laboratory’s functions included (a) providing external public services at minimum charges as a not-for-profit organization and (b) performing internal sample analyses and benchscale tests, in turn suggesting optimum methods for water and wastewater treatment, process improvement, system monitoring, pollution control, and sample analyses. Students were educated to understand all aspects of physical-chemical and biological processes (including flotation technology), their process monitoring, cost estimation,

8

L. K. Wang

Fig. 1.6 One of the Lenox Institute pilot plant rooms for testing flotation processes

process control, and influent/effluent/sludge analyses [74–79, 94–168, 172–178, 180–189]. An array of pilot plant units (Figs. 1.5 and 1.6) offered students experience with crucial aspect of effective training in the flotation applications. These pilot plant units included dissolved air flotation clarifiers, dispersed air foam flotation clarifiers (or dispersed air flotation clarifiers), sedimentation-flotation clarifier, fractionators (spray filters), plastic media filtration pilot plant, flocculation pilot plant, sand filter pilot plant, granular activated carbon pilot plant, cooling tower, gas stripper, belt press, and ozone generators. Each student required completion of at least 34 credit hours (Table 1.1) toward graduation with a Master’s degree. The Institute did fulfill its noble mission. Between 1981 and 2002, it educated over 200 highly qualified flotation engineers, scientists, and managers who are now proudly serving their home countries around the world. Dr. Krofta passed away soon after he celebrated his 90th birthday, and his beloved LIWT also ended its 100% tuition-free graduate program. Figure 1.7 shows Dr. LK Wang awarding the Master’s degree diploma to one of the graduate students. Figure 1.8 is a photo of Dr. and Mrs. Krofta and Dr. MHS Wang. After LIWT’s mission completion, the faculty members (the author, Dr. Mu-Hao Sung Wang, Dr. Nazih K. Shammas, Dr. Donald B. Aulenbach, Dr. William A. Selke, Dr. Hermann H. Hahn, Daniel Guss, Betty C. Wu) of LIWT have continuously maintained the Institute’s spirit (also Dr. Krofta’s 90th birthday wish) in offering educational seminars and workshops, conducting R&D investigations, and publishing academic papers and books. Their important publications include hundreds of US Federal government reports, the Handbook of Environmental Engineering series (Springer/Humana Press, Switzerland), the Advances in Industrial and Hazardous Wastes Treatment series (CRC Press/Taylor & Francis Group, USA), the Water and

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

9

Table 1.1 Lenox Institute of Water Technology’s curriculum of Master of Engineering in Water Technology Degree requirements B10-501 Biological Treatment Processes B10-502 Biosolids Management I BIO-503 Biosolids Management II PHC-561 Physicochemical Unit Operations I PHC-562 Physicochemical Unit Operations II FLO-541 Flotation Processes I: Fundamentals FLO-542 Flotation Processes II: Theory & Design FLO-543 Flotation Processes III: Applications LAB-551 Water and Wastewater Analysis LAB-552 Water and Wastewater Treatment LAB-553 Advanced Water Laboratory or LAB-554 Field Studies Laboratory L1WT-591 Master’s Project

(3 CH) (2 CH) (1 CH) (2 CH) (2 CH) (3 CH) (2 CH) (2 CH) (1 CH) (½ CH) (½ CH) (3 6 CH) (1 CH) 34 CH

LIWT-592 Seminar Two elective courses are: (1) Intership Training at Humanitarian Organizations or Government Agencies Around the World; (2) Voluntary Environmental (Water Supply, Waste Treatment, Sanitation, or Public Health) Services in Underdeveloped or Developing Countries; Plus elective courses to make a total of Students who have few undergraduate engineering courses must take EGN-521, Fundamentals of Engineering, as a 2 CH elective course.

Fig. 1.7 Dr. Lawrence K. Wang, Dr. Nazih K. Shammas, and Dr. Donald B. Aulenbach of LIWT with some graduating students on Lenox campus

Wastewater Engineering textbook series (John Wiley, USA), and the Handbook of Environment and Waste Management series (World Scientific, Singapore). Most of the books published by the LIWT faculty members are the updated versions of previous LIWT lecture materials. Typical examples of the LIWT textbooks are listed below in comparison with the course numbers listed in Table 1.1:

10

L. K. Wang

Fig. 1.8 Dr. and Mrs. Milos Krofta with Dr. Mu-Hao Sung Wang who learned Dr. Krofta’s 90th birthday wish

(a) Wang, LK, NC Pereira, YT Hung, Biological Treatment Processes, Humana Press, 818 pages, 2009. (BIO-501) (b) Wang, LK, NK Shammas, YT Hung, Advanced Biological Treatment Processes, Humana Press, 738 pages, 2009. (BIO-501) (c) Wang, LK, NK Shammas, YT Hung, Biosolids Treatment Processes, Humana Press, 820 pages, 2007. (BIO-502) (d) Wang, LK, NK Shammas, YT Hung, Biosolids Engineering and Management, Humana Press, 800 pages, 2008. (BIO-503) (e) Wang, LK, YT Hung, NK Shammas, Physicochemical Treatment Processes, Humana Press, 723 pages, 2005. (PHC-561) (f) Wang, LK, YT Hung, NK Shammas, Advanced Physicochemical Treatment Processes, Humana Press, 690 pages, 2006. (PHC-562) (g) Wang, LK, YT Hung, NK Shammas, Advanced Physicochemical Treatment Technologies, Humana Press, 710 pages, 2007. (PHC-562) (h) Wang, LK, NK Shammas, WA Selke, and DB Aulenbach, Flotation Technology, Humana Press, 680 pages, 2010. (FLO-541, FLO-542 and FLO-543) (i) Krofta, M. and LK Wang. Flotation Engineering. Lenox Institute of Water Technology, Lenox, MA, USA. Technical Manual No. Lenox-1-06-2000/368. (2000) (FLO-541, FLO-542 and FLO-543) (j) AWWA, WEF, APHA, Standard Methods for the Examination of Water and Wastewater. (LAB-551) (k) Shammas, NK and LK Wang, Water Supply and Wastewater Removal. John Wiley & Sons. 820 pages, 2011. (LAB-551) (l) Shammas, NK and LK Wang, Water Engineering. John Wiley & Sons. 806 pages, 2016. (LAB-552) (m) Krofta, M, LK Wang, and MHS Wang. Laboratory Simulation and Optimization of Physical-Chemical Treatment Processes. US Dept. of Commerce, National Technical Information Service, NTIS-PB86-188794/AS, 42 pages, 1985. (LAB-553)

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

11

(n) Wang, LK, MHS Wang, YT Hung, and NK Shammas. Natural Resources and Control Processes. Springer, 632 pages, 2016. (LAB-554) The above typical LIWT textbooks indicate the caliber of Lenox professors (M Krofta, LK Wang, MHS Wang, NK Shammas, WA Selke, DB Aulenbach and HH Hahn) and the quality of advanced education that the LIWT provided to the students. The mission of the Lenox Institute of Water Technology was completed in terms of (a) developing many flotation technologies as well-established processes for water purification, domestic sewage treatment, industrial effluent treatment, sludge thickening, algae harvesting, ore mining, fiber recovery, fish powder recovery, arsenate removal, groundwater remediation, etc., in the world; (b) obtaining many process equipment patents in the USA and foreign countries based on the Institute’s research; (c) collaborating with KEC and other companies for pilot plant demonstrations, process equipment manufacturing, and commercialization of Lenox inventions; (d) transferring Lenox technologies in exchange of financial supports to the Institute and its faculty and students; (e) training of plenty flotation engineers, scientists, and managers who can and are willing to work in the field of environmental flotation technology; and (f) distributing the well-established environmental flotation knowledge to the general public through academic presentations and publications.

2 Research and Review of All Possible Flotation Technologies for Water Purification 2.1

Introduction

The Lenox Institute of Water Technology (LIWT) began to review all possible flotation technologies which may be used for water purification. In all flotation processes, micro air bubbles attach to flocculated particles, suspended solids, surface active substances, etc., carrying them to the surface where they are collected and removed. The flotation process is particularly effective for lighter particles, such as in algae, which are more easily floated to the top of the treatment structure than they are weighted to the bottom. There are several different kinds of flotation separation technologies, of which DAF is one. Depending on the influent water and the contaminants involved, a flotation treatment operation may use any of the following methods. The results of their reviews are presented in the following sections.

2.2

Research and Review of Dissolved Gas Flotation (DGF)

DGF is a process involving pressurization of gas at 25–95 psig for dissolving gas into water and subsequent release of pressure (to 1 atm) under laminar flow hydraulic

12

L. K. Wang

conditions for generating extremely fine gas bubbles (20–80 microns) which become attached to the impurities to be removed and rise to the water surface together. The impurities or pollutants to be removed on the water surface are called float or scum which are scooped off by sludge collection means. The clarified water is discharged from the flotation clarifier’s bottom. The gas flow rate is about 1% of influent liquid flow rate. The attachment of gas bubbles to the impurities can be a result of physical entrapment, electrochemical attraction, surface adsorption, and/or gas stripping. The specific gravity of the bubble-impurity agglomerate is less than one, resulting in buoyancy or nonselective flotation (i.e., save-all process). Dissolved gas flotation is achieved using any kinds of extremely fine gas bubbles generated from a gas dissolving tube or tank under high pressure and laminar hydraulic conditions. When air bubbles are used as the gas bubbles, DGF becomes DAF. DAF was finally selected for construction of water purification plants and it is suitable for both small and large communities.

2.3

Research and Review of Dispersed Gas Flotation

Dispersed gas flotation (or induced gas flotation (IGF), or foam separation, or froth flotation) is a process involving introduction of gas directly into the water through a revolving impeller, a diffuser system, or an ejector, or a combination of them, at low pressure (slightly higher than 1 atm) for generating big gas bubbles (80 microns to over 1 mm) in large volume under turbulent hydraulic flow conditions. The gas flow rate is about 400% of the influent water flow rate. Physical entrapment and electrochemical attraction play minor roles in an induced gas flotation system. The attachment of gas bubbles to the impurities is mainly a result of surface adsorption, gas stripping, and oxidation. Surface active substances (inks, detergents, ores, soaps, etc.) together with impurities are selectively separated in a foam phase at the water surface. The foam containing the surfactant and the impurities are removed by a suction device. Volatile substances are removed by gas stripping action. The clarified water is discharged from the flotation clarifier’s bottom. Reducing agents, such as ferrous ions, can be oxidized to ferric ions for subsequent separation in ferric hydroxide form if air is used as a gas. Since this flotation is achieved using low cost coarse gas bubbles generated under low pressure and turbulent hydraulic conditions, this process was initially selected for investigation and demonstration but was not selected for full-scale plant construction because the surfactant to be used in the process as a collector would require the review and approval by the US Environmental Protection Agency (USEPA) and local governments.

2.4

Research and Review of Electroflotation

Electroflotation is a process involving the generation of hydrogen and oxygen bubbles in a dilute electrolytic aqueous solution by passing a direct current between

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

13

two electrodes: (a) anode and (b) cathode. Anode reaction generates oxygen bubbles and hydrogen ions, while cathode reaction generates hydrogen bubbles and hydroxide ions. Either aluminum or steel sacrificial electrodes can be employed for generating the gas bubbles as well as coagulants at the same time. Non-sacrificial electrodes are employed for generating the gas bubbles only and can be made of titanium (as the carrier material) and lead dioxide (as the coating material). Electrical power is supplied to the electrodes at a low voltage potential of 5–20 volts DC by means of a transformer rectifier. Small bubbles in the range of 20–50 m microns are produced under laminar hydraulic flow conditions feasible for flotation separation of fragile flocs from water in a small system. The floats on the water surface are the impurities/pollutants removed from water. The clarified water is discharged from the flotation clarifier’s bottom. There can be unexpected advantages and disadvantages when electroflotation is employed. For instance, chlorine bubbles may be generated as a water disinfectant if the water contains significant amount of chloride ions. Certain unexpected gas bubbles may be generated and may be undesirable [151]. Since electroflotation is achieved using hydrogen and oxygen (or chlorine when many chlorides are present) bubbles generated between anode and cathode electrodes, this more complex process was selected for research and development. A small potable water electroflotation process unit was developed for small communities [102, 134].

2.5

Research and Review of Vacuum Flotation

In a vacuum flotation system, the influent process water to be treated is usually almost saturated with air at atmospheric pressure. There is an air-tight enclosure on the top of the flotation chamber in which partial vacuum is maintained. The fine air bubbles (20–80 microns) are generated under laminar hydraulic flow conditions by applying a vacuum (negative pressure) to the flotation chamber. The theory is that the lower the pressure, the lower the air solubility in water. The soluble air originally in water is partially released out of solution as extremely fine bubbles due to a reduction in air solubility caused by negative vacuum pressure. The bubbles and the attached solid particles rise to the water surface to form a scum blanket, which can be removed by a continuous scooping or skimming mechanism. Grit and other heavy solids that settle to the bottom are raked to a central sludge sump for removal. Auxiliary equipment includes an aeration tank for saturating the water or wastewater with air, vacuum pumps, and sludge pumps [151]. Vacuum flotation is achieved using the gas bubbles generated by negative vacuum pressure that suck out the soluble gas in water originally. The process is not suitable for potable water treatment due to low solubility of air in water. Vacuum flotation works fine for other gases (such as carbon dioxide) with high solubility in water.

14

L. K. Wang

Fig. 1.9 Biological flotation of activated sludge under covered anaerobic condition, using uncovered gravity sedimentation as a control test

2.6

Research and Review of Biological Flotation

In a biological flotation system, fermentations take place in the presence of anaerobic bacteria, nitrates, and substrates under anaerobic environment; anaerobic bacteria in waste sludge convert nitrate and the substrate with carbon source (such as methanol, or residual BOD) to nitrite, water, and carbon dioxide fine bubbles. Nitrite further reacts with a substrate (such as methanol or residual BOD) in the same waste sludge, producing fine nitrogen bubbles, more fine carbon dioxide bubbles, and water and hydroxide ions. The biological waste sludge, such as activated sludge, can then be floated to the surface by the fine nitrogen and carbon dioxide bubbles and be thickened (i.e., concentrated). The thickened sludge which is the final product of the biological flotation thickening process is skimmed or scooped off from the liquid sludge surface, while the subnatant clarified water is discharged from the biological flotation thickener’s bottom. The energy consumption of this process is low. Its detention time is long. More research is needed for this newly developed sludge thickening process [151]. Since biological flotation is accomplished using mainly nitrogen and carbon dioxide bubbles (and under extreme anaerobic conditions, some methane and/or hydrogen sulfide gas) generated under anaerobic conditions in the presence of organics (Fig. 1.9), it is obviously not suitable for potable water treatment.

2.7

Research and Review of Deep Shaft Flotation

In a deep shaft flotation system (or micro-flotation system, or vertical shaft flotation system), the entire volume of water to be treated is subjected to the increased pressure by passing the water down and up a shaft approximately 10 meters deep. At the bottom of the shaft, on the down-comer side, air is injected by one air blower under low pressure (20 psig). Undissolved air rises up the shaft against the flow, thus

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

15

increasing the saturation of the water. As the water rises in the up-flow section, the hydrostatic pressure decreases. Some of the soluble air is then released out of solution in the form of fine air bubbles due to a reduction in air solubility caused by pressure reduction. Floc agglomeration and bubble generation occur simultaneously and gently, providing good attachment of the air bubbles to the flocs. The amount of air which can be dissolved is limited by the depth of shaft (e.g., hydrostatic pressure provided). The saturation of the water with air at that depth is dependent on the way the air is introduced to the system (e.g., size of air bubbles produced at point of injection). Similarly, the floats collected on water surface are the impurities/pollutants removed from the water. The floats are collected by a rotating sludge collection scoop or equivalent. The bottom flotation clarified water is discharged as the treated water [151]. Since this deep shaft flotation is accomplished using the gas bubbles generated under high pressure and laminar hydraulic conditions within an extremely long water column (such as a 500-ft.-deep water well), it is not suitable for potable water treatment unless there is an existing water well available.

2.8

Research and Review of Plain Gravity Flotation

In natural gravity flotation, oil, grease, wax, fiber, or other substances lighter than water (specific gravity is less than 1) are allowed to rise naturally to the water surface of quiescent tank, where they are skimmed off or scooped off. The bottom clean water is discharged as the treated water. The floats skimmed off or scooped off from the water surface are either the impurities/pollutants to be removed or the resources (such as fibers, or oils) recovered for reuse. Since gravity flotation is accomplished by gravity without any bubbles if the solids to be floated to the water surface are lighter than water (i.e., density is less than one), it is not suitable for potable water treatment. It is only good for oil-water separation, or wax-water separation, or fiber recovery. The following are the author’s views on the final process selection: (a) Dissolved gas flotation (DGS) is a nonfoaming process that can also feature several different catalysts. Ozone and carbon dioxide can also be used selectively in drinking water treatment. (b) DAF is one of the DGF processes, and air is the gas of choice in the DAF drinking water treatment process due to the fact that air is sufficient to achieve the goals of the process and is the least expensive alternative. (c) The nature of all DGS (including DAF) methods involves creating a laminar flow, thereby avoiding turbulence and foam. This uniform upward flow is achieved by pressurizing, gas dissolving, and then gas releasing into the clarification reactor for formation of fine gas bubbles, which account for only about 1% of the total flow (gas flow to water flow).

16

L. K. Wang

(d) DAF is a nonselective process because all contaminants that can be attached onto the gas bubble surface are separated. These contaminants include all suspended matter, colloids, chemical and microbial flocs, plant fibers, inorganic solids with high hardness, turbidity, color substances, and precipitated heavy metals. (e) Dispersed air flotation (or induced air flotation, or foam separation) needs a surfactant (such as cetyldimethylbenzylammonium chloride (CDBAC), or equivalent) as a collector or foaming agent; thus, it may not be suitable for potable water treatment until the surfactant is approved by the Federal and local governments for water purification. (f) Electroflotation is suitable for potable water applications in individual homes or by small communities. (g) Vacuum flotation, biological flotation, deep shaft flotation, and plain gravity flotation are not suitable for potable water applications; therefore, they were not studied by the LIWT for water purification research. Although biological flotation was not selected for further study, Fig. 1.9 introduces this interesting process by an experiment using waste activated sludge. It can be seen that the carbon dioxide and methane gas bubbles generated under anaerobic condition successfully float the sludge to the water surface and clarify the subnatant water phase. The following sections show the step-by-step R&D projects conducted by the LIWT toward the final selection of DAF for the first two potable water flotation plants in the Americas.

3 Research and Initial Selection of Dispersed Air Flotation (or Induced Air Flotation, or Foam Separation) as a Water Purification Process Dispersed air flotation (or induced air flotation, or foam separation) was initially selected as an innovative water purification process. Specifically, dispersed air flotation is a process involving introduction of air directly into the water through a revolving impeller, a diffuser, or an ejector at low pressure (slightly higher than 1 atm) for generating large air bubbles (normally 80 microns to over 1 mm) in large volumes under turbulent conditions. The air flow rate is about 400% of influent liquid flow rate. Physical entrapment and electrochemical attraction play minor roles in a dispersed air flotation system. The attachment of air bubbles to the impurities is mainly a result of surface adsorption, gas stripping, and oxidation. Surface-active substances (CDBAC, inks, detergents, and so on) are selectively separated in foam phase [20, 21, 97, 107]. Volatile substances are simultaneously removed by gas stripping action. Reducing agents, such as ferrous ions, can be simultaneously oxidized to ferric ions by air for subsequent separation in ferric hydroxide form. Dispersed air flotation can be used in ore separation, coal purification, fiber de-inking, surfactant separation, lignin separation, and so on [30, 31]. Since CDBAC was developed as an effective organic disinfectant for environmental

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

17

Fig. 1.10 A flow diagram of a simplified dispersed air flotation clarifier (Foamer)

control [71], the authors combined both CDBAC and dispersed air flotation and developed a sequencing batch dispersed air flotation (or sequencing batch foam separation) process, shown in a figure in the literature [107, 210, 228, 229], and a continuous dispersed air flotation (or continuous foam separation) process, shown in Figs. 1.10, 1.11, and 1.12, which are potentially suitable for water purification or other applications. Krofta and Wang’s research data were published by the US National Technical Information Service in 1983 [107]. Figure 1.10 shows the top view of a full-scale dispersed air flotation (or induced air flotation (IAF), or Foamer, or foam separation), shown in Fig. 1.11. Efficiency of the IAF clarifier (Figs. 1.10 and 1.11) for foam separation is proportional to the surface area and not the clarifier depth. The full-scale IDF clarifier has very low water head (1 meter or 39 inches), and surface area requirement is proportional to the water flow. The optimum foaming is achieved in a spiral formed channel where the influent is treated six times by repeatedly injecting the air through special jets and then aspirating the formed foam away. The IAF clarifier installed in one room recycles the air with minimum discharge. Figure 1.12 shows another full-scale IAF clarifier (Foamer) developed and commercialized by LIWT/KEC with a 20-ft. diameter and multiple air injectors. It is equally effective as a foam separation clarifier.

18

L. K. Wang

Fig. 1.11 A full-scale dispersed air flotation clarifier (Foamer) developed and manufactured by LIWT/KEC

Fig. 1.12 Another full-scale dispersed air flotation clarifier (Foamer) developed and manufactured by LIWT/KEC

A sequencing batch dispersed air flotation (or sequencing batch induced air flotation, or sequencing batch foam separation) was also developed and patented [107, 189, 210, 229]. A complete continuous water treatment plant involving the use of a dispersed air flotation clarifier will include screening, influent pumping, chemical feeding, pre-disinfection, coagulation, dispersed air flotation (Foamer), filtration, carbon adsorption, post-disinfection, and corrosion control. Carbon adsorption is needed for removal of any residual surfactant (CDBAC) that is used in dispersed air flotation clarifier [130]. The entire innovative water purification system’s flow diagram will be similar to a conventional water system, except that a dispersed air flotation clarifier is used to replace a conventional sedimentation clarifier.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

19

The Institute’s initial research data related to the potable water dispersed air flotation system were published in JAWWA [71, 79] and by AIChE and the US National Technical Information Service [107]. The dispersed air flotation process is technically feasible for water purification because CDBAC is a chemical approved by FDA for human consumption. However, the water purification field is controlled by the USEPA and local governments. It would be very time-consuming and difficult for CDBAC to be approved as a drinking water treatment chemical by both the Federal and local governments. The invention is not wasted; however, CDBAC and its similar cationic surfactants are widely adopted later by the industry as an effective disinfectant for swimming pool algae control, roof moss control, and many other environmental control applications.

4 Research and Subsequent Selection of Electroflotation for Water Purification The gas bubbles used in electroflotation consist of hydrogen and oxygen bubbles produced by the electrolysis of water [230]. The chemical reactions occurring at the electrodes to produce these gas bubbles are as follows: (a) Anode reaction: 2 H2O ¼ 4 H+ + O2 (bubbles) + 4 e (b) Cathode reaction: 4 e + 4 H2O ¼ 2 H2 (bubbles) + 4 OH (c) Total reaction: 2 H2O ¼ 2 H2 (bubbles) + O2 (bubbles) From the above reactions, it can be seen that for each flour electrons of current passed between the anode and cathode electrodes, one molecule of oxygen bubbles and two molecules of hydrogen bubbles are produced. Or in more specific terms, 0.174 mL of gas bubbles, measured at standard temperature and standard pressure, is produced by each coulomb of electric current. The extremely fine bubbles in the order of about 100 microns are formed at the electrodes of the electroflotation clarifier, and the bubbles rise to the clarifier’s water surface as fine mist. Generation of fine hydrogen and oxygen bubbles through electrolysis reactions has many advantages: (a) Purity: since the gas bubbles are created from water and no actual handling or transport of the gases occurs before their use, gas bubbles remains uncontaminated. (b) Process control: controlling the rate of generation is easy because the more current applied, the more gas generated. Conversely, the less current applied, the less gas generated. (c) Simplicity: the resulting unit is easy to manufacture and simple in operation. Figure 1.13 is a flow diagram of the LIWT/KEC potable water electroflotationfiltration plant. Figure 1.14 shows a small electroflotation-filtration water treatment

20

L. K. Wang CHEMICALS MIXING AND FLOCCULATION

TO CONSUMER DISINFECTION (UV OR CHLORINATION)

FILTRATION

BACKWASH WATER

RAW WATER SUPPLY

ELECTROFLOTATION CLARIFICATION

SLUDGE

SOFTENING (OPTIONAL)

Fig. 1.13 A flow diagram of the potable water electroflotation-filtration plant developed by LIWT/ KEC

Fig. 1.14 A small electroflotation-filtration water treatment plant developed by LIWT/KEC for serving individual home owners, apartments, or small lake communities

plant commercially developed by LIWT/KEC for serving individual home owners, apartments, or small lake communities. Figure 1.15 is an operational diagram showing how a complete electroflotationfiltration package plant is operated. It is noted from Fig. 1.15 that raw water influent is pumped (Fig. 1.15 # 4) into the plant through an influent pipeline. As this fluid enters the alum flocculation cylinder (Fig. 1.15 # 10), it is mixed with a concentrated solution of alum which is pumped [9] to this point from the alum storage cylinder.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

21

GASES VENT 39

M M BY-PASS

SLUDGE DISCHARGE

16

7

WASTEWATER RECYCLE

17

SIGHT GLASS

14

10 12

PURIFIED WATER TO CUSTOMER

13

20

36

19

23 30

24 11

33

9

RAW WATER

I

II ρ

20

INFLUENT STORAGE TANK 32

Fig. 1.15 Operation of a complete electroflotation-filtration package plant

The alum solution and the fluid swirl in this tank to form a precipitate called alum flocs. The liquid and floc emerge from the cylinder where another chemical, polyelectrolyte or sodium aluminate, is added in a similar fashion (Fig. 1.15 # 11). The fluid then flows through a mixing cylinder (Fig. 1.15 # 12) to a point in the tank (Fig. 1.15 # 13) just below the electroflotation unit (Fig. 1.15 # 14). This unit electrically separates the molecules of hydrogen and oxygen in the water and, thereby, forms gaseous bubbles which immediately rise to the water surface. These bubbles attach themselves to the flocs, which have now entrapped the foreign

22

L. K. Wang

matter in the fluid, and rise to the surface. Being buoyant, the sludge floats on the water surface and is collected (Fig. 1.15 # 16) and returned to the front section of the influent storage tank by the sludge discharge pump (Fig. 1.15 # 17). Gaseous materials are removed through a vent and a fan (Fig. 1.15 # 39). The fluid, which now fills the tank (Fig. 1.15 # 13), is drawn down through the bottom of the tank by means of the discharge pump (Fig. 1.15 # 32). As water flows down the tank, it passes through a layer of sand (Fig. 1.15 # 24) and a fine screen where unfloated particulates are filtered out. The water then passes through an ultraviolet (UV) disinfection unit (Fig. 1.15 # 38) where pathogens are killed. The purified potable water product is now fit for domestic consumption. Water flow from the filter is controlled by a flow meter (Fig. 1.15 # 33). Water flow into the system from the influent pump (Fig. 1.15 # 4) which is in excess of the purified outflow is bypassed back to the influent storage tank through a bypass line (Fig. 1.15 # 7). As material builds up in and on the surface of the sand, the flow through the sand decreases. In order to maintain the design flow in the water system over an extended period of time, the sand must be cleansed periodically. This is accomplished by a timer, which shuts off the influent flow and energizes the backwash cycle. During this short (20 seconds) cycle, water is pumped (Fig. 1.15 # 28) back through the sand (Fig. 1.15 # 24) from the clear well (Fig. 1.15 # 30). This backwash flow lifts the foreign matter from the sand. To facilitate this process, a small portion of the backwash water is diverted through a surface wash pipe (Fig. 1.15 # 23) to help in the cleansing of the sand surface. The backwashed material is then collected (Fig. 1.15 # 19) and discharged back to the influent storage tank by means of a wastewater recycle pump (Fig. 1.15 # 20). The excellent performance of the LIWT/KEC jointly developed electroflotationfiltration package plant can be found in the literature [134, 230]. It has been used successfully for treating well water, lake water, and highly contaminated water. Due to high energy cost, the system was ruled out to be used for the city of Pittsfield, which had a population over 50,000. Other electroflotation application has been reported by Krofta and the author [102].

5 Research and Final Selection of Dissolved Gas Flotation as a Water Purification Process For developing an innovative water treatment system for large communities, the authors and the Institute dropped dispersed air flotation and electroflotation for water purification and began investigation of dissolved gas flotation process for water purification instead [221]. Basically, dissolved gas flotation (DGF) is a process involving pressurization of air at 25–95 psig for dissolving gas into water and subsequent release of pressurized water to a clarifier under normal atmospheric pressure (1 atm) and laminar hydraulic

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

23

flow conditions for generating extremely fine gas bubbles (normally 20–80 microns in diameter), which become attached to the impurities to be removed. The gas flow rate is about 1% of influent liquid flow rate. The attachment of gas bubbles to the impurities can be a result of physical entrapment, electrochemical attraction, surface adsorption, and/or gas stripping. The specific gravity of the bubble-impurity agglomerates is less than one, resulting in buoyancy or nonselective flotation (i.e., save-all process). The LIWT’s standard textbook, Flotation Technology (LK Wang, NK Shammas, WA Selke, and DB Aulenbach, Humana Press, 680 pages, 2010), presents theory, principles, operation, maintenance, design criteria, costs, chemical additives, process control, tests, and design examples [226]. DGF becomes (a) dissolved air flotation (DAF) if air is used; (b) dissolved nitrogen flotation (DNF) if nitrogen gas is used; (c) dissolved carbon dioxide flotation (DCDF) if carbon dioxide is used; (d) dissolved ozone flotation (DOF) if ozone is used, etc. In the past, DAF was mainly used for sludge thickening and fiber recovery. The authors and other LIWT researchers work together to develop it as a water purification process. Our efforts and laboratory experimental results and pilot plant demonstrations can be found in the literature [90–100, 105, 106, 112–114, 117, 119, 122–128, 221].

6 Development of a Potable Water DAF System by Replacing Conventional Sedimentation Clarifier with Innovative DAF The very first innovative DAF water purification system adopted Krofta Engineering Corporation’s existing DAF clarifier, Supracell. A complete water treatment plant (Potable Water DAF System 1) involving the use of the existing DAF (Supracell) will include the individual unit processes of influent screening/ pumping, chemical feeding, predisinfection, coagulation, DAF (Supracell), filtration, post-disinfection, and corrosion control. This entire innovative water purification system’s flow diagram will be similar to conventional water system, except that DAF clarifier is used to replace conventional sedimentation clarifier (Figs. 1.16 and 1.17) [231]. The LIWT/KEC developed high rate DAF (shown in Figs. 1.18 and described in Table 1.2), has many advantages: (a) a very low retention time of 2 minutes, 30 minutes, or say 3 minutes means a much smaller total volume; (b) high specific clarification capacity (4–5 gpm per square foot) means a much smaller surface area; (c) installation cost is low because the clarifier is delivered fully prefabricated, no heavy supports are needed, and the weight is as low as 150 lbs. per square foot; (d) the clarifier maintains value because it can be easily relocated when/if necessary; (e) space requirement, or footprint, is minimal because of its low headroom and being able to be erected above ground level (such as on the second floor, on the rooftop, or on top of an existing sedimentation basin); (f) easy

24

L. K. Wang Well 2 Surface water source

Well 1

Well 3 Well field groundwater source

Screen Intake Dam

Raw water storage reservoir Presedimentation

Low lift pump or booster pump

Valve Gravity flow

Diversion works

Pumped flow

Chemical feeders

Aeration/oxidation/stripping

Primary disinfection Chemicals

Control signal

Rapid mix

Flow Cartridge filtration

Coagulationflocculation Pumped flow Gas Chemical

Sedimentation or flotation Gravity flow

Pressure filters Sand, dual-media greensand GAC, IX, AA, DE, membrane Secondary disinfection

Gravity filters Sand, dual-media, slow sand, GAC

Backwash water probes

“Direct” filtration alternative may omit rapid mix, flocculation and setting.

Backwash water

Corrosion control Degasification

Clearwell or treated water storage tank

Pressure tank Pumped flow to Water distribution system High-service booster pumps

or Gravity flow to water distribution system

Fig. 1.16 The flow diagram of a general water treatment system. (Credit: Shammas and Wang [231], p. 326)

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . . Primary disinfection

Chemical feeding Sedimentation or DAF clarification

Raw water influent Recycle stream

Pump screen

25

Filtration

Coagulation flocculation

Rapid mixing

Filter-to-waste (unregulated)

Sludge Clearwell water storage

Optional PCWWT

Water

To receiving water (NPDES/SPDES permit) To sewage treatment plant for phosphate removal

Spent filter backwash (regulated)

Equalization or lagoon

Sludge (regulated)

Finished water to water distribution system

Corrosion control Secondary disinfection

Optional sludge thickening/dewatering

Sludge slurry or cake to landfill or chemical recovery unit

Fig. 1.17 The flow diagram of a simplified water treatment system. (Credit: Shammas and Wang [231], p. 667)

to clean because the clarifier is completely open and the bottom is self-cleaning during operation; and (g) water clarification to below 20–30 ppm of filterable solids in the clarified effluent and sludge thickening to above 2–3% in consistency. Figure 1.19 shows a high rate DAF (Supracell 62) installed in the UK. It had a diameter of 62 ft., and 9265 gpm (35.2 M3/min). The DAF was installed on the second floor with extremely small footprint due to its extremely shallow tank depth of B ¼ 29.5 in. and its low weight. Figure 1.20 shows the flow diagram of a complete water treatment plant in which (a) a dissolved air flotation clarifier (Supracell or equivalent) replaces a conventional sedimentation clarifier and (b) a dissolved air flotation clarifier replaces a conventional gravity thickener for overall cost saving and foot-print reduction. Although there are so many advantages for the newly developed water system, Dr. Milos Krofta and KEC did accept this new water system for the city of Pittsfield and village of Lenox because Dr. Krofta was a mechanical engineer (not a civil engineer); thus, he preferred to have an all-in-one package water treatment plant. This can be an excellent totally new water treatment system, or it can be extremely useful for improving an existing conventional water treatment plant by simply installing a shallow, high rate DAF (Supracell) on the top of an existing sedimentation basin [145].

26

L. K. Wang 1 2 3 4 5 6 7 8 9 10 11

ROTATING CENTER SECTION CLARIFIED WATER OUTLET SETTLED SLUDGE SUMP SETTLED SLUDGE OUTLET KROFTA ROTARY CONTACT KROFTA SPIRAL SCOOP FLOATED SLUDGE OUTLET UNCLARIFIED WATER INLET CLARIFIED WATER EXTRACTION PIPES GEAR MOTOR DISTRIBUTION DUCT

6

5

B

D

C

4

3

8

7

2

1

9

11

10

½A

Fig. 1.18 An innovative high rate dissolved gas flotation clarifier (Supracell)

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

27

Table 1.2 Dimensions versus capacities of high rate dissolved gas flotation clarifier (Supracell) Type A ft 8 10 12 15 18 20 22 24 27 30 33 36 40 44 49 56 62 70

Dimensions A mm B in 2400 23.5 3200 23.5 3900 25.5 4500 25.5 5600 255 6100 255 6700 25.5 7200 25.5 8100 25.5 9000 255 10000 255 11000 25.5 12200 26 13400 27 14800 27 16800 27 19900 29.5 21300 30.7

B mm 600 600 650 650 650 650 650 650 650 650 650 650 660 685 685 685 750 780

C in 33 33 35 37 37 37 37 37 37 37 37 37 38 39 39 39 37.5 42.7

C mm 850 850 900 950 950 950 950 950 950 950 950 950 960 985 985 985 1050 1080

D in 45 49 51 57 58 61 62 63 67 71 72 73 76 78 82 87 87 90.5

D mm 1150 1250 1300 1450 1480 1560 1580 1600 1700 1820 1840 1860 1920 1980 2070 2200 2200 2300

Flow m3/min 0.56 1.00 1.60 2.00 3.00 3.65 4.40 5.08 6.44 7.95 9.80 11.87 14.60 17.60 21.50 27.70 35.20 44.90

US GPM 148 263 394 525 789 961 1160 1340 1695 2090 2580 3125 3840 4630 5650 7290 9265 11800

m3/h 34 60 90 120 180 219 264 305 386 477 588 712 876 1056 1290 1662 2112 2692

A Diameter of supracell; B Depth of supracelltank; C Depth of supracell tank with 80TT0M support; D Minimum overall height of supracell

Fig. 1.19 A high rate dissolved gas flotation clarifier in the UK (Supracell 62; tank depth ¼ 750 mm; flow ¼ 35.2 m3/min; diameter ¼ 62 ft. ¼ 19,900 mm)

28

L. K. Wang Chemical feeding

Corrosion control

Primary disinfection

Secondary disinfection Air saturation tank Wash water tank Compressor

Suction well

Flow meter

Screen

Filtration

Dissolved air flotation unit

Lake Rapid mixing

Clearwell Spent filter backwash

Flocculation

Finished water to water distribution system

Filter-to-waste Sludge

Backwash water equalization basin

Supernatant Water pump and sludge pump Sludge DAF thickened sludge To receiving water (NPDES/SPDES permit)

To dewatering units, drying beds, or landfill

Dissolved air flotation (DAF) thickener

Fig. 1.20 A flow diagram of a complete water treatment plant in which (a) a dissolved air flotation clarifier (Supracell or equivalent) replaces a conventional sedimentation clarifier and (b) a dissolved air flotation clarifier replaces a conventional gravity thickener for overall cost saving and foot-print reduction. (Credit: Shammas and Wang [231])

7 Development of a Potable Water Double DGF-DGF System by Replacing Conventional Double Sedimentation-Sedimentation Clarifiers with Innovative Double DGF-DGF Clarifiers Recarbonation is frequently applied to a “two-stage lime-soda ash softening process system,” shown in Figs. 1.21 and 1.22. Figure 1.21 shows mainly the softening chemicals used and the precipitates produced in the system, while Fig. 1.22 is the flow diagram of a typical lime-soda ash softening water treatment plant. Because different chemicals must be used and different pH conditions must be controlled in each stage, two clarifiers will be required for the two-stage process system. Normally, two sedimentation clarifiers are adopted. LIWT/KEC developed a double DGF-DGF clarification system shown in Fig. 1.23. It is noted that this highly efficient and commercially available double DGF-DGF clarification system has extremely small footprint and very low detention time. For removing hardness in a water softening process system, the double DGF-DGF clarification system can be dissolved carbon dioxide flotation (DCDF) and/or dissolved air flotation (DAF) depending on whether or not separate recarbonation units will be used. In case ozone will be used for predisinfection, dissolved ozone flotation (DOF) may be adopted in the first stage for cost saving because a separate ozonation unit may not be needed. The double DGF-DGF

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . . SECOND STAGE TREATMENT WITH SODA ASH

FIRST STAGE TREATMENT WITH EXCESS LIME

FIRST STAGE RECARBONATION WITH CARBON DIOXIDE

pH > 10.8

pH > 9.5

PRECIPITATES AS CALCIUM CARBONATE

PRECIPITATES AS CALCIUM CARBONATE

PRECIPITATES AS CALCIUM CARBONATE

CARBON DIOXIDE; CALCIUM BICARBONATE; MAGNESIUM BICARBONATE;

EXCESS CALCIUM HYDROXIDE

CALCIUM SULFATE

29

SECOND STAGE RECARBONATION WITH CARBON DIOXIDE

pH = 8.6 ±

CONVERTS CALCIUM CARBONATE TO CALCIUM BICARBONATE; CONVERTS MAGNESIUM HYDROXIDE TO MAGNESIUM CARBONATE

PRECIPITATES AS MAGNESIUM HYDROXIDE MAGNESIUM SULFATE; MAGNESIUM BICARBONATE

Fig. 1.21 Water treatment for hardness removal using two-stage lime/soda ash softening process. (Credit: Wang et al. [232], p. 221)

clarifier (double Supracell) system is delivered fully prefabricated. Larger units are delivered in parts which flange together. No heavy foundation or support structure is needed as the total load factor when filled with water weighs less than 150 lbs. per square foot for each DGF (Supracell) unit. The unique compact and efficient design is made possible by use of the principle of “zero velocity.” Each DGF water level in the tank is extremely low (16 inches). This means reduced size and weight as well as low retention time (3 minutes for each DGF). The DGF is smaller in surface area for its capacity because a very high specific clarification degree is attained at 4–5 gpm per square foot.

L. S. A. CS, SH, F

CI

P,C,

2

CO2

A,CO2

3

4

5

6

7

8

CI

TO FILTERS

9

KANSAS RIVER

NORTH PLANT

1 L.S.A.CS, RS

2

CO2

A,CO2

3

4

5

6

7

8

CI, F, SH

9

TO FILTERS

SOUTH PLANT

CI 1. PRE - SEDIMENTATION 2. SED. AND BREAK PT CHLORINATION 3. PRIMARY RAPID MIX 4. PRIMARY FLOCCULATION 5. PRIMARY CLARIFIERS 6. SECONDARY RAPID MIX 7. SECONDARY FLOCCULATION 8. SECONDARY SEDIMENTATION 9. SECONDARY RECARBONATION

A = ALUM C = CARBON Cl = CHLORINE CO2 = RECARBONATION CS = CAUSTIC SODA F = FLUORIDE L = LIME P = POLYELECTROLYTE RS = RETURN SLUDGE S = SODA ASH SL = SODIUM ALUMINATE SH = SODIUM HEXAMETAPHOSPHATE SS = SODIUM SILICATE

Fig. 1.22 A flow diagram of lime-soda ash softening plant in Topeka, Kansas, USA. (Credit: Reh [233])

∅16,7 m 16 7,6 m 11

15 13

1 12

3

3,9 m

5

14

6

8

2

1 15

15

12

9 3 7

13

9 4

11

10 8

15

5

1 RAW WATER COLLECTION TANK 2 SUPRACELL FEED PUMP 3 SUPRACELL INLET PIPE (inbedded in ground) 4 INLET COMPARTMENT 5 SETTLED SLUDGE SUMP 6 SETTLED SLUDGE DISCHARGE 7 CLARIFIED WATER OUTLET 8 CLARIFIED WATER RETURN for LEVEL CONTROL (1) 9 LEVEL CONTROL in SUPRACELL with PNEUMATIC SENSOR and CLARIFIED WATER DISCHARGE REGULATING VALVE 10 PRESSURE PUMP for RECYCLING of CLARIFIED WATER to the AIR DISSOLVING TUBES 11 AIR DISSOLVING TUBES 12 SUPRACELL MAIN TANK 13 SPIRAL SCOOP for COLLECTION of the FLOATED SLUDE 14 FLOATED SLUDGE 15 STEEL LEGS 16 SECOND ELEVATED SUPRACELL in STEEL CONSTRUCTION

15

2 1 14

6

Fig. 1.23 Top view and side view of a double DGF-DGF clarifier (double Supracell)

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

31

8 Development of a Potable Water Sedimentation-DAF System by Replacing a Conventional Double Pre-sedimentation-Sedimentation Water Clarification with an Innovative Combined Sedimentation-DAF Clarification The quality of reservoir raw water usually is poor (having high turbidity, color, and silt) soon after a big storm. Under this engineering situation, a pre-sedimentation step is needed prior to normal water treatment, as shown in Fig. 1.24. Upflow contact clarifier in Fig. 1.24 is one of the conventional sedimentation clarification processes. DAF in Fig. 1.24 is for the plant’s wastewater treatment and waste sludge thickening. The conventional system shown in Fig. 1.18 works fine in terms of its product water (plant water effluent) quality and waste management. Almost all wastewater is treated by DAF and recycled to the pre-sedimentation basin for reprocessing and reproduction of drinking water. Both construction costs and O&M costs of this fine process system are very expensive. LIWT/KEC developed and manufactured an innovative and very cost-effective sedimentation-DAF clarifier (Fig. 1.25; SediFloat or SDF) to replace both pre-sedimentation and upflow contact sedimentation clarifier shown in Fig. 1.24. The sedimentation-DAF clarifier is much smaller (in terms of equipment volume and footprint) than the combined pre-sedimentation clarifier and upflow contact clarifier when processing the same water flow. A complete water treatment plant involving the use of the innovative sedimentation-DAF clarifier will include screening, influent Peak daily flow = 48 MGD Peak instantaneous flow = 35,000 gpm Raw water reservoir

Upflow contact clarifiers (14)*

Presedimentation basin

M

Multimedia filters (14)*

Coagulant/polymer feed

Flowmeter

Backwash

M

Clearwell

Gravity 12 inch pipe Backwash, filter-to-waste, pre-backwash draindown

Pumped 8 inch pipe Recycled waste stream (2000 gpm)

Sludge

Flocculators (4)*

Gravity 6 inch pipe

Equalization basin

Chemical addition

Finished water to distribution system

Outlet flow control (2000 gpm) Gravity 10 inch pipe

Pumped 8 inch pipe

Dissolved air flotation (4)*

Sludge-drying beds (16)* Pumped 8 inch pipe

Pumped 8 inch pipe * Number in parenthesis indicates number of treatment units.

Fig. 1.24 A conventional water treatment plant involving the use of pre-sedimentation and upflow contact sedimentation clarifiers [231]

32

L. K. Wang

7

6

3

5

5 2

9

4

1

10

Floated matter is removed by the rotating spiral scoop (7) which discharges the sludge through the sludge pipe in the center distributor (2) to a sludge well (8) at the tank perifery.

8

8

6 13

10

1

12

14

11

7

The untreated effluent (1) is fed by gravity or pump to the center distributor (2) where it mixes with the air released from the recycled air carrier water and then enters the tank. Fine air bubbles lift the suspended, flocculated solids to the water surface (3). Heavier particles settle rapidly to the tank floor (4). The zone of clear water formed between the floated and settled solids is then discharged into the outlet annulus (5) where it overflows through an adjustable outlet weir (6). Adjustment of this weir controls the water level in the tank.

A suspended bottom scraper (9) is supported from the scoop structure and moved forward by the scoop drive. The settled sludge is scraped to the center of the tank and into a sludge pit (14) constructed in the foundation. From here, the sludge is removed intermittently through an automatically operated pneumatic valve (10). The scraper is so constructed as to allow it to rise and slip over any excessive obstructing sludge build-up in order to prevent any damage to the scoop drive. The recycled air carrier water is pumped (11) at a pressure of about 80 psi into the retention tank (12). Compressed air (13) enters the retention tank directly. The air carrier water is then released into the center distributor after mixing with the raw infludent. For small installations, it may be more economical to pressurize the whole of the effluent inflow.

Fig. 1.25 Design and operation of a sedimentation-DAF clarifier (SDF; or SediFloat)

Fig. 1.26 Construction of sedimentation-flotation clarifier (SDF-36FT) in acid-resistant tiles (Holland)

pumping, chemical feeding, predisinfection, coagulation, sedimentation-DAF clarifier, filtration, post-disinfection, and corrosion control. This entire innovative water purification system’s flow diagram will be similar to conventional water system (Fig. 1.24), except that a much smaller sedimentation-DAF clarifier replaces both pre-sedimentation and upflow contact clarifier. Figure 1.25 shows the engineering design and operation procedures of a sedimentation-DAF clarifier. Figure 1.26

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

33

Fig. 1.27 Construction of two sedimentation-DAF clarifiers (SDF-55FT) in Italy

shows a full-scale sedimentation-DAF clarifier (SDF-36FT; diameter, 36 ft.) which was built with acid-resistant tiles in Holland, while Fig. 1.27 shows the construction of two sedimentation-DAF clarifiers (SDF-55FT; each diameter, 55 ft.) in Italy. Although the sedimentation-DAF is fully developed and has been widely applied in waste treatment, its excellent potable water application in the Americas needs more promotion by water engineers and managers. With the authors’ collaboration and the UNIDO (United Nations Industrial Development Organization) cooperation, LIWT/ KEC technologies have been distributed to many developing and industrial countries [207]. Fig. 1.28 shows how Dongshin EnTech has successfully used a combined sedimentation-DAF clarifier for potable water treatment in South Korea [145, 200]. For transferring the DAF technology to South Korea, Dr. LK Wang received an engineering award from the Korean Society of Water Pollution Research and Control and South Korean government [200].

9 Development of a Potable Water DAF-Filtration Clarifier by Replacing Conventional Sedimentation-Filtration System with Innovative DAF-Filtration System 9.1

Decision and Advantages of Having a DAF-Filtration (DAFF or Sandfloat) Package Plant

The reason for DAF’s or DAFF’s absence from drinking water treatment in the New World in early 1980s was a combination of plentiful land, relatively strong municipal finances, and reliance on a tried-and-true sedimentation process that was familiar to owners and profitable for municipal engineering designers and equipment suppliers.

34

L. K. Wang

Fig. 1.28 Removal of chlorophyll a by sedimentation alone and combined sedimentation-DAF. (Credit: Dongshin EnTech, South Korea [145, 200])

DAF got its chance in the Americas in the late 1970s to early 1980s, sparked by the authors’ flotation doctoral theses and the authors’ research that caught the attention and imagination of Dr. Milos Krofta, a prominent paper industry expert and engineering firm owner. Previous sections have introduced many possible potable water treatment systems developed by LIWT/KEC, but only the dissolved air flotation-filtration (DAFF) package system, also known as Sandfloat system (Figs. 1.29, 1.30, 1.31, and 1.32), is adopted by LIWT/KEC for the Lenox Water Treatment Plant (LWTP) and the Pittsfield Water Treatment Plant (PWTP). Why did Dr. Krofta and KEC want to have the all-in-one package water treatment plants for the LWTP and PWTP? The authors gave the answer before: Dr. Krofta

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . . Chemical feeding Primary disinfection Air saturation tank

35

Corrosion control

Package potable water flotation-filtration (DAFF) clarifier

Secondary disinfection

Floated scum/sludge Compressor Dissolved air flotation clarification Suction Flow well meter

Automatic backwash filtration

Lake

Reservoir

Clearwell Screen

Non-mechanical rapid mixing and flocculation

Finished water to water distribution

Spent filter backwash

Filter-to-waste Sludge

Backwash water equalization basin

Supernatant Water pump and sludge pump Sludge

DAF thickened sludge Sludge drying beds To receiving water (NPDES/SPDES permit)

Dissolved air flotation (DAF) thickener

Fig. 1.29 General flow diagram of a typical dissolved air flotation-filtration (DAFF or Sandfloat) water treatment plant. (Credit: Shammas and Wang [231])

was a mechanical engineer whose products should be like a mechanical unit, such as a car, a machine, a crane, or a mechanical package plant. The author then visited Lowell Water Treatment Plant in Massachusetts, USA, finding out the details of their rectangular Automatic Backwash Sand Filtration (ABSF) System. Later, finally, a DAF-ABF (also known as DAFF plant, or Sandfloat plant) was developed and commercialized. In a new Sandfloat package water treatment system (Fig. 1.29), the unit processes of chemical feeding, coagulation, DAF clarification, automatic backwash sand filtration (ABF), disinfection, and corrosion are all included. It is important to note that a patented circular ABF was used instead of Lowell Water Treatment Plant’s rectangular ABF.

36

L. K. Wang

Fig. 1.30 Bird’s eye view and description of a DAF-filtration (Sandfloat or DAFF) clarifier [161]

Fig. 1.31 Top view, side view, and sizes of DAF-filtration clarifiers (Sandfloat or DAFF)

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

37

Fig. 1.32 A flow diagram of a DAF-filtration clarifier (Sandfloat, DAFF)

Since both the Americas’ first two DAF-filtration (DAFF) plants (LWTP and PWTP) were identical in their Sandfloat design, the design features of both LWTP and PWTP are introduced together in this section. Other than floating the clarified contaminants rather than settling them, a DAF-filtration plant’s flow diagram is essentially the same as a conventional water filtration plant’s flow diagram, except the clarification-filtration portion. For instance, the unit processes of an innovative DAF-filtration plant include rapid mixing, flocculation, DAF clarification, filtration, disinfection, and corrosion control, while the unit processes of a conventional water filtration plant include rapid

38

L. K. Wang

mixing, flocculation, sedimentation clarification, filtration, disinfection, and corrosion control. The rest of unit processes can be identical, and even the types and dosages of water treatment chemicals may be identical. Accordingly, the total treatment ultimately results in a drinking water product of equal quality. Figure 1.29 shows the flow diagram of a typical DAFF plant. Figures 1.30, 1.31, and 1.32 introduce the package unit of DAFF (Sandfloat) itself. Specifically, Fig. 1.30 is a bird’s eye view of DAFF; Fig. 1.31 presents DAFF’s top view, side view, and various sizes; and Fig. 1.32 shows the internal flow diagram within the DAFF clarifier. The primary advantage of DAFF technologies is the reduction in water clarification detention time. Conventional sedimentation-filtration treatment requires 2–4 hours of detention time, while DAFF clarification requires only 3–15 minutes of detention time for achieving identical water clarification-filtration efficiency. This drives other benefits, including less infrastructure required, small footprint, and lower initial cost, building heating cost, and life cycle cost. Figure 1.33 shows a DAF clarifier side by side with a sedimentation clarifier each treating about the same flow, and the DAF is so small in terms of volume and can be installed on the second plant floor (meaning zero ground floor footprint), but the comparable sedimentation clarifier is huge in volume. For the DAFF construction, the flotation compartment is installed on the top of an automatic backwash filter, so the footprinter becomes even smaller. Figure 1.34 shows a 30-ft.-diameter Sandfloat (SASF 30FT; DAFF) which was installed on an existing settler’s top in Berlin, Germany, because of limited space in the plant. Figure 1.35 illustrates why and how the footprint and volume of a package DAF-filtration clarifier (DAFF, or Sandfloat) are both much lower in comparison with that of a conventional sedimentation clarifier and a conventional sand filter. The Krofta Sandfloat (DAFF clarifier) with its compact design and water treatment in one unit by chemical flocculation, dissolved air flotation, and filtration has received more and more acceptance due to its high clarification, low total installation cost, low O&M cost, and extremely small space requirement.

9.2

Engineering Design Criteria and Costs of DAF-Filtration (DAFF or Sandfloat) Package Clarifier

Modern flotation clarifiers produce 6 gallons per minute of clarified water per square foot of surface area (6 GPM per square foot; 240 L/min per square meter). Sedimentation clarifiers only produce 0.2 to 1.0 GPM per square foot (10–20 L/min per square meter). Flotation clarifiers process approximately ten times more water with the same surface area in comparison with sedimentation clarifiers. Flotation clarifiers operate with only 16 inches of depth (0.4 M), with a retention time of 2–3 minutes. Sedimentation clarifiers require a depth of approximately 80 inches (2.0 M) and a retention time of 2–4 hours.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

39

Fig. 1.33 A comparison between a DAF clarifier and a sedimentation clarifier

Flotation requires a clarifier with a volume of 1.67 gallons to clarify 1.0 GPM (1.0 cubic meter per minute). Sedimentation requires a clarifier with a volume of 75 gallons to clarify water at the same rate (1 GPM). The volume of sedimentation clarifiers is more than 45 times larger than flotation clarifiers. Initial construction cost is reduced by 30–50%. Compact clarifiers are less costly to build than large conventional settling tanks. Enclosing the system in a building and the use of corrosion-resistant materials offer odor control and lower maintenance. Land use is substantially reduced. Operational costs are reduced by approximately 30%. Operational costs are composed of three almost equal parts:

40

L. K. Wang

Fig. 1.34 Construction of a 30-ft-diameter DAF-filtration (DAFF, Sandfloat) unit on the top of an existing sedimentation clarifier in Berlin, Germany

(a) Repayment of investment costs. The repayment of principal and interest is proportionally reduced by the reduced total investment cost (b) Cost of chemicals and power. Less flocculating chemicals are required for flotation as only a small floc is necessary, compared with the large floc size necessary for settling. New flotation techniques operate with low power requirements, normally reducing power consumption by approximately 30%. (c) Labor and maintenance costs. Advanced flotation plants are fully automated in an enclosed building and require only a few hours daily of attendance, reducing labor costs by 50% or more.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

41

Fig. 1.35 A footprint and volume comparison between a DAF-filtration (DAFF, Sandfloat) clarifier and a conventional sedimentation-filtration combination

Flotation technology allows the building of a plant that is profitable, facilitates financing, and reduces the need for government grants or privatization schemes. Flotation clarifiers are extremely compact allowing the system to be completely enclosed in a building, preventing odor and noise. The old concept of locating wastewater treatment plants as far away as possible from inhabited areas of towns and cities is no longer necessary. Long pipelines can be avoided, and valuable buildings, land, and expanding areas can be saved.

42

L. K. Wang

Several individual plants can be built where collection sewers would otherwise be difficult or impossible to locate. For municipal potable water plants, the compact size allows flotation clarifiers to be located close to the source, permitting the use of low cost land and eliminating the use of additional pumping stations.

9.3

Description of a DAF-Filtration (DAFF or Sandfloat) Package Plant

Components of the DAFF system include moving carriage and flocculation module (including rapid mixing), flotation clarification chamber, ABF filtration module containing filter media, clear well for disinfection and corrosion control, instrumentation and control system, and air dissolving system, which can be found in Figs. 1.30, 1.31, and 1.32, and are described in the following subsections.

9.3.1

Moving Carriage and Flotation Module (Including Rapid Mixing)

A moving carriage includes inlet structure, rapid mixing chamber, flocculator, air dissolving tube, backwash pump, spiral sludge scoop, and traveling hood (Fig. 1.30 B, C, D, E, F, G, H, I, and V, respectively) and is made of 1/16 in. minimum thickness stainless steel plate, stiffened and reinforced as required to withstand normal handling and operational stresses. Stiffening of partition walls is provided to allow for draining of adjacent modules in the water treatment flotation tank (Fig. 1.30 J). Marine aluminum is used instead of stainless steel for the flocculation chamber (Fig. 1.30 F). Each flocculation module is divided into a specified number of compartments of identical capacity by means of baffles with an adjustable opening, extending to the entire depth of the module. Each section of baffle is manually adjustable to provide for adequate slow mixing.

9.3.2

Flotation Clarification Tank

At the end of the flocculator (Fig. 1.30 F) within the flotation tank (Fig. 1.30 J), the flocculated water is saturated at several times atmospheric pressure (45–85 psig) by a pressurizing pump (Fig. 1.30 N). The pressurized feed stream is held at this high pressure for at least 10 seconds in an air dissolving tube (ADT; Fig. 1.30 G) to provide efficient dissolution of air into the water stream. The pressurized stream enters the ADT tangentially at one end and is discharged at the opposite end. During the short passage, the water cycles inside the tube and passes repeatedly by an insert, fed by compressed air. Very thorough mixing under pressure then dissolves the air in the water. Figures 1.36 and 1.37 explain the ADT system for dissolving air into water.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

43

Fig. 1.36 Top view and side view of an air dissolving tube

A radial distribution pipe with small holes covered by a deflector feeds the pressurized water at the bottom of the flocculator outlet. The sudden reduction of pressure in the flotation chamber results in the release of microscopic air bubbles (a diameter of 80 mm or smaller) that attach to suspended or colloidal particles in the process water in the flotation chamber. This results in agglomeration, which, due to the entrained air, gives a net combined specific gravity less than that of water and causes flotation. The floated materials rise to the surface of the flotation tank (Fig. 1.30 J) to form a floated layer that is carried away by a spiral scoop

44

L. K. Wang

Fig. 1.37 An air dissolving tube design diagram

(Fig. 1.30 I). Clarified water (flotation effluent) is near the bottom of the flotation tank and is further polished by automatic backwash filters (Fig. 1.30 R). The design of the dissolved air flotation tank (main tank) is of circular shape and made possible by use of the principle of “zero velocity.” The flotation influent (flocculator effluent) distribution duct moves backward with the same velocity as

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

45

the forward incoming flotation influent. A nearly “zero velocity” quiescent state in the flotation tank is created for flotation.

9.3.3

Automatic Backwash Filtration (ABF) Module Containing Filter Media

Each filtration module (Fig. 1.30 R) is fabricated of 1/4 in. minimum thickness fiberglass plate and 1/16 in. minimum thickness marine aluminum plate. The filter module is placed between the flotation chamber and the clear well. The filter underdrains are made of stainless steel grid and a heavy-duty screen and placed to ensure uniform wash water distribution and filtrate collection. Alternatively, the filter media can be supported by 3 inches of coarse garnet and graded gravel. The filter media can be either a single medium system comprised of 12 in. of fine silica sand (ES, 0.36 mm; UC, 1.6) or a dual-media system comprised of 3 in. of fine garnet in the bottom portion of the bed and 9 in. of fine silica sand in the upper portion to provide the necessary polishing action. Dual media are provided, in sizeidentified bags, in sufficient volume by type and grade to enable a total depth of 12 inches after skimming of fines.

9.3.4

Clear Well for Disinfection and Corrosion Control

The filter effluent from ABF (Fig. 1.30 R) is treated with disinfectant (such as chlorine or equivalent) and corrosion control chemicals in a clear well (Fig. 1.30 S) before the treated water is pumped to a water storage tank to be used for domestic or industrial consumptions.

9.3.5

Air Dissolving System Including Air Compressors

An air dissolving system, shown in Figs. 1.36 and 1.37, includes (a) an air dissolving tube (ADT, or a pressure chamber) with a pneumatic sensor; (b) a water pump pumping recycled clean water to the ADT; and (c) air compressors of a sufficient size providing compressed air to the recycled clean water line through an injector. Both the recycled clean water and the compressed air are mixed together and discharged to the ADT where air is completely dissolved in the pressured water. The ADT effluent containing supersaturated air is released to the DAF clarification chamber where a swarm of extremely fine air bubbles are formed for the flotation actions.

46

9.3.6

L. K. Wang

Instrument Control Panel and Control System

Each DAF-filtration clarifier (DAFF, or Sandfloat) has one floor mounted (in the base) electrical control panel for total automatic plant operation and process monitoring. Each DAF-filtration water treatment unit is furnished with a float type level sensing system that transmits a 3–15-psig signal to control the 18-inch influent valve (modulate) and maintains a level over approximately 6 inches. The level controller is arranged to decrease the inlet flow on the rising water level and decrease the inlet valve opening. Conversely, inlet flow increases on a lowering filter level and increases the valve opening.

10

Lenox Water Treatment Plant: The First Potable Water Flotation-Filtration Plant in the Americas

The new Lenox Water Treatment Plant (LWTP) in Lenox, Massachusetts, USA, is the first potable water flotation-filtration plant built in the Americas. LIWT grew from the town of Lenox’s need to lessen risks from trihalomethane (THM) reducing the level of turbidity, color, and other THM precursors in its water. LIWT and KEC jointly showed the town and the Massachusetts Department of Environmental Quality Engineering (DEQE) – now called the Department of Environmental Protection (DEP) – that a DAF-filtration plant would efficiently and less expensively serve all residents and tourists in the scenic town in the Berkshire Mountains [105, 106, 112–114, 121, 144, 170, 197, 218, 219, 224]. A full-scale potable water flotation system was constructed to improve the quality of Lenox water. The heart of the 1.2-million-gallon-per-day (MGD) Lenox Water Treatment Plant is an award-winning process consisting of chemical feeding, flocculation, dissolved air flotation, automatic backwash filtration, disinfection, and corrosion control, shown in Figs. 1.29, 1.30, 1.31, and 1.32. The uniqueness of the Lenox DAF drinking water treatment plant does not end with its status as the first in the USA. The team, led by LIWT and KEC, incorporated innovative technologies that exceeded those being used at the time in drinking water treatment plants in other parts of the globe. The Lenox plant, which began in 1981 and was completed in about a year, features a treatment chamber only about 22 feet in diameter and 6 feet in height. Yet it can process up to 1.2 MGD for the 6000 year-round residents of tourist destinations as well as the additional 4000 seasonal visitors. The Lenox plant’s treatment tank is circular rather than the traditional rectangular shape. A primary benefit is that it allows for a continuous flow for backwashing filters. This circular “automatic backwash filtration (ABF)” process was inspired by a similar rectangular ABF process in use at a conventional plant in nearby Lowell Water Treatment Plant in Massachusetts. The LIWT/KEC team incorporated the

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

47

circular ABF process into to the DAF tank design to form a combined DAF-filtration process unit, known as DAFF, or Sandfloat. Milos Krofta and Lawrence K. Wang formally introduced the Americas’ first DAF-filtration plant at American Water Works Association (AWWA) conference in San Diego, California, USA. AWWA Research Foundation our engineering data in 1984 [170], and New England Water Works Association published our results in 1985 [218, 219], and both Krofta and Wang received a 5-Star Engineering Award from Pollution Engineering for the LIWT/KEC accomplishment in Lenox [100]. It was a century’s innovation because the entire LWTP detention time (not counting post-disinfection) was only about 15–30 minutes. A comparable conventional water treatment plant (not counting post-disinfection) treating the same influent flow of 1.2 MGD will need a detention time of 4–9 hours. The water treatment facility’s volume is almost directly proportional to the detention time. This is why the 1.2-MGD Lenox plant (Sandfloat 22-ft diameter) serving 10,000 people can be as small as a car garage. Building DAF directly on the top of sand filters also significantly reduces the plant’s footprint and the winter’s heating energy. Since a DAF-filtration is so small, it may be built next to the reservoir level, without losing hydraulic head. The plant effluent, or product water, may be delivered to all customers by gravity. On behalf of LIWT, KEC, and, of course, our beloved late Dr. Milos Krofta, the author would like to thank LIWT Professor Mu-Hao Sung Wang, Professor Donald B. Aulenbach, Professor William A. Selke, Supervisor Betty C. Wu, KEC Vice President Daniel Guss, KEC Marketing Manager Craig C. Gaetani, Massachusetts Regional Environmental Engineer Angelo Iantosca, and Tri-Town Sanitarian Peter J. Kolodziej for their technical assistance, collaboration, and encouragement for successful completion of this twenty-first century’s revolutionary Lenox project.

11

Pittsfield Water Treatment Plant: The Once-Largest Potable Water Flotation-Filtration Plant in the World

With the success of the Lenox plant assured, the Commonwealth of Massachusetts, USA, approved a much larger DAF water filtration plant in the nearby city of Pittsfield. When the 37.5-MGD (142 million liters per day) Pittsfield water treatment plant was installed in 1986, it was then the world’s largest water treatment plant using dissolved air flotation (DAF). This status has since been eclipsed by other plants in the USA and abroad [122–124, 163–165, 214, 220, 226]. The decision to build such a large Pittsfield plant was driven by concern that the DAF process may not work as advertised, despite the example of the small Lenox full-scale DAF water filtration plant. As a result, the Commonwealth of Massachusetts wanted a new Pittsfield flotation-filtration plant to handle double the amount needed by the city of Pittsfield. Since the Lenox DAF-filtration (DAFF) plant came fully online in July of 1982 and was operated successfully, the Commonwealth of Massachusetts gave final

48

L. K. Wang

CLEVELAND RESERVOIR

CLEVELAND SUPPLY SYSTEM

ASHLEY RESERVOIR

FROM SACKET RESERVOIR HYDROELECTRIC PLANT FROM FARNHAM RESERVOIR

WATER TREATMENT PLANT CHLORINATION STATION

FLOW CONTROL STATION

CITY DISTRIBUTION SYSTEM CENTRAL PRESSURE ZONE

STANDPIPE(S)

5 MILLION GALLON CONCRETE TANK

TYPICAL HIGH PRESSURE ZONE

BOOSTER PUMPING STATION(S)

ASHLEY SUPPLY SYSTEM

Fig. 1.38 Pittsfield Water Treatment Plant System: (a) Cleveland Plant: four DAFF (Sandfloat SAF49) units; (b) Ashley Plant: two DAFF (Sandfloat SAF49) units

approval of the much larger plant in the 50,000-resident city of Pittsfield, Massachusetts. A waiver from the state was necessary because DAF was not a standard process; DAF was not included as a form of treatment for drinking water in the “10 State Standards” guideline publication. The heart of the Pittsfield Water Treatment Plant System is two potable DAF-filtration plants: (a) the Ashley Plant has two DAF-filtration clarifiers, and (b) the Cleveland Plant has four DAF-filtration clarifiers. Each DAF-filtration clarifier has a capacity of 6.25 MGD, for a total capacity of 37.5 MGD. Each DAF-filtration clarifier is 49 ft. in diameter and 6 ft. in depth and is a Krofta Sandfloat Model SAF49 package clarifier consisting of mainly dissolved air flotation and automatic backwash sand filtration, shown in Figs. 1.29, 1.30, 1.31, 1.32 and 1.38.

12

12.1

More LIWT/KEC New Flotation Systems and Installations Pointing to New Research Directions and Engineering Applications Adsorption Flotation Process

Adsorption flotation is either a dissolved gas flotation (DGF), or induced gas flotation (IGF, or dispersed air flotation), in which powdered activated carbon is added for taste, odor, THM, VOC, and/or color reductions in a drinking water treatment plant [138, 185, 223]. Again, the author is hoping that more research and practicing applications can be carried out by researchers and plant managers, respectively.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

12.2

49

Sequencing Batch Flotation Systems and Sequencing Sedimentation Systems

The author, L Kurylko, and MHS Wang have developed the Sequencing Batch Flotation (SBF) systems and Sequencing Batch Sedimentation (SBS) systems for potable water treatment applications. The readers are referred to the literature for the details [210, 228, 229]. SBF can be divided into Sequencing Batch Dissolved Gas Flotation (SBDGF) or Sequencing Batch Induced Gas Flotation (SBIGF). SBIGF is Sequencing Batch Foam Separation (SBFS). The clarifiers can be in any shapes, circular or rectangular. The authors invented these sequencing batch processes [229], hoping that there will be more further improvements and more construction of fullscale plants to be done by the young generations in the future.

12.3

FloatPress: Flotation Thickening of Sludge Produced in Drinking Water Plants

Under the joint research of LIWT and KEC, a special process equipment, known as FloatPress, was successfully developed and installed in Lenox Water Treatment Plant (LWTP) in 1982. FloatPress is a combination of dissolved air flotation and sludge press. The full-scale unit is shown in Fig. 1.39. The process description and performance are recorded elsewhere by Krofta and Wang [219].

Fig. 1.39 A full-scale FloatPress (a combination of dissolved air flotation and sludge press) installed at Lenox Water Treatment Plant, Lenox, MA, USA, in 1982

50

L. K. Wang

Fig. 1.40 A full-scale installation of a two-stage DAF-DAF system

12.4

Advanced DGF-DGF Water Treatment System Installation

Due to Dr. Milos Krofta’s passing, both LIWT and KEC do not exist at present. KEC business portion has changed its names and management hands many times. LIWT students are serving as flotation engineers, scientists, researchers, professors, and managers around the world. LIWT professors are compiling previous lecture materials for publication as the university textbooks and reference books and continuously developing new potable water flotation systems for the benefit of humanity. Section 1.7 introduces a double DGF-DGF system for a water treatment situation (Figs 1.21 and 1.22, two-stage lime-soda ash softening process system) that two clarifiers are needed. DGF-DGF two-stage system can be used for both two-stage water treatment and wastewater treatment. Figure 1.40 shows the full-scale installation of a two-stage DAF-DAF system because air is used for generation of gas bubbles.

12.5

Advanced DGF-DGFF Water Treatment System Installation

In the final days of LIWT/KEC, a double DGF-DGFF (or DAF-DAFF if air is used) was developed for potable water treatment or wastewater treatment. Figures 1.41 and 1.42 illustrate the innovative DGF-DGFF process system and its full-scale installation, respectively, which are self-explanatory. The readers are encouraged to read Sect. 1.7 and the related literature regarding its theories and principles [225, 227, 234].

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

51

Fig. 1.41 Graphic illustration of a double DGF-DGFF (or DAF-DAFF, or Supracell-Sandfloat) system for potable water treatment plant

Fig. 1.42 Full-scale double DGF-DGFF (or DAF-DAFF, or Supracell-Sandfloat) system

12.6

Water Treatment by Dissolved Air Flotation Using Magnesium Carbonate as a Recyclable Coagulant

A raw water having ten units of color, 13 NTU of turbidity, and 417 mg/L of calcium hardness in terms of CaCO3 was successfully treated by a continuous pilot plant consisting of a static hydraulic flocculation, a dissolved air flotation clarifier (Krofta Supracell Model SPC3; diameter, 3 ft.), a recarbonation facility, and three sand

52

L. K. Wang

(a) (b) (c) (d) (e) (f) (g) (h)

Ca(HCO3)2 + Ca(OH)2 = 2 CaCO3 + H2O Mg(HCO3)2 + Ca(OH)2 = 2 CaCO3 + H2O MgCO3 + Ca(OH)2 = Mg(OH)2 + CaCO3 CaSO4 + MgCO3 = CaCO3 + MgSO4 MgSO4 + Ca(OH)2 = Mg(OH)2 + CaSO4 CaSO4 + Na2CO3 = CaCO3 + Na2SO4 CO2 + Ca(OH)2 = CaCO3 + H2O CO2 + Mg(OH)2 = MgCO3 + H2O

Fig. 1.43 Chemical reactions of a two-stage DAF-DAF lime-magnesium carbon softening process using magnesium carbonate as a recyclable coagulant

Regeneration Chemicals

Flocculation/Clarification (First–Stage)

To Consumer Chlorine

Filtration

Backwash water

Raw Water Supply

Recarbonation (First–Stage)

Sludge

CO2

CO2 Recarbonation (Second–Stage)

Flocculation/Clarification (Second–Stage)

Sludge

Chemicals Regeneration

Fig. 1.44 A flow diagram of a two-stage DAF-DAF lime-magnesium carbon softening process for hardness removal using magnesium carbonate as a recyclable coagulant

filters. The raw water was dosed with 42.3 mg/L of magnesium carbonate as coagulant. Figures 1.43 and 1.44 present the chemical reactions and flow diagram, respectively. The readers are referred to a US government report [96] for the experimental results and are urged for continuous research using any manufacturer’s flotation equipment and using either dissolved air flotation (DAF) or dissolved carbon dioxide flotation (DCDF). Reaction (h) in Figure 1.43 is for carbonation of

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

53

the magnesium hydroxide sludge, and the reproduced magnesium carbonate is a recyclable coagulant.

12.7

Using Popular Flotation Processes as a Pretreatment to Equally Popular Membrane Processes

It will be very logical if the best available flotation process is used as a pretreatment step to the best available membrane process for (a) potable water treatment especially in the areas where the sources of fresh water are limited in quantity or poor in quality or (b) for industrial process water recycle [206, 216, 231, 235, 237]. The readers are referred to the literature for more detailed technical information.

12.8

Using Popular DAF-DAFF Clarifier (Sandfloat) for Granular Activated Carbon Filtration or Dual-Media Filtration

Figures 1.45 and 1.46 show the rectangular automatic backwash filters (RABF) used as granular activated carbon filtration and dual-media filtration, respectively. The bottom of the DAF-DAFF clarifier is a circular automatic backwash filtration

Fig. 1.45 Rectangular automatic backwash filter installed at Lowell Regional Utility, Massachusetts, USA, for dual-media filtration. (Credit: Superintendent Steve Duchesnel, LRU, [236])

54

L. K. Wang

Fig. 1.46 Rectangular automatic backwash filter installed at Lowell Regional Utility, Massachusetts, USA, for granular activated carbon filtration. (Credit: Superintendent Steve Duchesnel, LRU, [236])

(CABF) unit. Currently, all circular DAF-DAFF clarifiers (Sandfloat clarifiers) in operation worldwide are applied to sand filtration only. Equipment manufacturers may be interested in this new applications because a CABF has certain advantages over an RABF due to the fact that each filter section can be backwashed in proper order in circular direction without losing any operational times.

12.9

Using Circular Automatic Backwash Filter (CABF) as an Independent Process Unit

Again a process equipment manufacturer may be interested in this new invention and applications. The bottom portion of a DAF-DAFF clarifier (Sandfloat) may be cut out and patented as a new process equipment – circular automatic backwash filter (CABF), which can be used as a sand filter and a dual-media filter, or a GAC filter. The author invites professors, students, researchers, consulting engineers, and equipment manufacturers to continue the authors’ proposed new research directions (in Sect. 1.12) and explore further process improvement or new applications to an existing process equipment. Will new continue all proposed new research directions in Sect. 1.12.

12.10

Further Research for Cream Flotation

Cream flotation process was invented by the author and reported as a Federal Government report as follows [151]:

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

55

Wang, L. K., “Theory and Application of Flotation Processes,” U.S. Dept. of Commerce, National Technical Information Service, PB86-194198/AS, 15 p., Nov. 1985

Although cream flotation was invented by the author at the Lenox Institute of Water Technology long time ago, it is still in developmental stage. The new process involves pressurization of air or other gases at 25–60 psig for dissolving air or other gas into water containing surfactant and subsequent release of pressure (to 1 atm) under laminar hydraulic flow conditions for generation of thick cream or foam bubbles, which become attached to the suspended matter (impurities or the recoverable substances) to rise together to the water surface. The attachment of foam bubbles to the suspended matter can be a combined result of physical entrapment, electrochemical attraction, and surface adsorption. The specific gravity of foamsuspended agglomerate is less than one, resulting in rapid buoyancy or flotation. Cream flotation can also be operated in different modes: (a) full flow pressurization, (b) partial flow pressurization, and (c) recycle flow pressurization. It is economically feasible for separation of insoluble matter from a water stream which already contains surfactant [151]. The author invites flotation researchers and equipment manufacturers to investigate this conceptually developed cream flotation process further and make it useful for wastewater treatment or resources recovery.

13

Lenox Institute of Water Technology: A College of Humanitarian Engineering

The practice of humanitarian engineering is discussed by Daley and Anderson [238]. The Glossary Section of this chapter gives the definitions of humanitarian engineering, and environmental humanitarian engineering. The establishment of the Lenox Institute of Water Technology (LIWT) was, a practice of environmental humanitarian engineering because LIWT was established to (a) provide totally free water engineering (flotation) education to cross-cultural, international students with any engineering and science disciplines; (b) voluntarily offer continuous education and training courses to the international communities at large, (c) continuously distribute environmental and ecological knowledge to the general public through worldwide public speeches and publication of US government reports, UN reports, books, and journal articles, again all free of charge and (d) provide environmental services and education to some marginalized people and disadvantaged communities in developing countries through the United Nations Industrial Development Organization (UNIDO). Due to the passing of the LIWT founder, Dr. Milos Krofta, at his old age of 90, the function of (a) or free flotation engineering education only lasted for 20+ years; the only flotation college in the world closed its campus. Although the faculty and graduates of LIWT still carry on the functions of (b) and (c) listed above assuming LIWT is still a college without walls, these voluntary activities and services are not

56

L. K. Wang

sustainable. The author along with other faculty and students is still documenting the R&D and engineering experiences of both LIWT and KEC to be our academic contributions to the society, such as (a) Handbook of Environmental Engineering series (Springer, 18 books), (b) Advances in Industrial and Hazardous Wastes Treatment (CRC Press, ten books), (c) Handbook of Environment and Waste Management series (World Scientific, three books); (d) Water and Wastewater Engineering series (John Wiley & Sons, two books); and (e) US government reports (many). The society needs more donors, like the late Dr. Milos Krofta, more humanitarian engineering colleges like LIWT, more academic researchers like Dr. James K. Edzwald and his coworkers [241–253], and more volunteers.

Glossary [151, 225, 227, 231, 239, 240] Adsorption flotation: The powdered activated carbons (PAC) may be dosed into a dissolved air flotation system for taste and odor control and/or toxic substances removal. A flotation process involving the use of PAC is adsorption flotation. Adsorptive bubble separation: Any water, wastewater, or sludge treatment system that involves the use of gas bubbles for water-solid separation. Automatic backwash filtration (ABF): A filtration system that is divided into many identical-shape filtration sections for automatic filtration operation and backwash. There is a moving carriage having a backwash hood and a backwash pump and traveling back and forth on top of the filtration sections. When the backwash hood covers one filtration section for automatic backwash (controlled by a timer), the rest of the filtration sections are in filtration mode. One filtration section is backwashed at a time, until all filtration sections are backwashed and restored to filtration mode again. Biological flotation: In a biological flotation system, fermentations take place in the presence of anaerobic bacteria, nitrates, and substrates under anaerobic environment; anaerobic bacteria in waste sludge convert nitrate and the substrate with carbon source (such as methanol, or residual BOD) to nitrite, water, and carbon dioxide fine bubbles. Nitrite further reacts with a substrate (such as methanol or residual BOD) in the same waste sludge, producing fine nitrogen bubbles, more fine carbon dioxide bubbles, and water and hydroxide ions. The biological waste sludge, such as activated sludge, can then be floated to the surface by the fine nitrogen and carbon dioxide bubbles and be thickened (i.e., concentrated). The thickened sludge which is the final product of the biological flotation thickening process is skimmed or scooped off from the liquid sludge surface, while the subnatant clarified water is discharged from the biological flotation thickener’s bottom. The energy consumption of this process is low. Its detention time is long. More research is needed for this newly developed sludge thickening process [151]. Cream flotation: It is a new process invented by the Lenox Institute of Water Technology. The new process involves pressurization of air or other gases at

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

57

25–60 psig for dissolving air or other gas into water containing surfactant and subsequent release of pressure (to 1 atm) under laminar hydraulic flow conditions for generation of thick cream or foam bubbles, which become attached to the suspended matter (impurities or the recoverable substances) to rise together to the water surface. The attachment of foam bubbles to the suspended matter can be a combined result of physical entrapment, electrochemical attraction, and surface adsorption. The specific gravity of foam-suspended agglomerate is less than one, resulting in rapid buoyancy or flotation. Cream flotation can also be operated in different modes: (a) full flow pressurization, (b) partial flow pressurization, and (c) recycle flow pressurization. It is economically feasible for separation of insoluble matter from a water stream which already contains surfactant [151]. DAF-DAF: A two-stage water or wastewater treatment process system consisting of double dissolved air flotation clarifiers (two DAF clarifiers) connected in series, usually one DAF is on the top of another DAF. DAF-DAFF: A two-stage water or wastewater treatment process system consisting of a dissolved air flotation (DAF) clarifier and a dissolved air flotation-filtration (DAFF) clarifier connected in series, usually DAF is on the top of a DAFF. Deep shaft flotation: Same as micro-flotation. Dispersed air flotation: Same as induced air flotation (IAF). It is one of the induced gas flotation (IGF) processes in which air is used for generation of gas bubbles. Dispersed gas flotation: Same as induced gas flotation (IGF). Dispersed nitrogen flotation: Same as induced nitrogen flotation (IGF). It is one of the induced gas flotation (IGF) processes in which nitrogen is used for generation of gas bubbles. Dissolved air flotation (DAF): One of the dissolved gas flotation (DGF) processes where air is used for generation of gas bubbles. A typical example is Krofta Engineering Corporation’s Supracell clarifier; see dissolved gas flotation (DGF). Dissolved air flotation-filtration (DAFF): A package plant which consists of both dissolved air flotation and filtration. A typical example is Krofta Engineering Corporation’s Sandfloat clarifier. Dissolved carbon dioxide flotation (DCDF): One of the dissolved gas flotation (DGF) processes in which carbon dioxide is used for generation of gas bubbles. See dissolved gas flotation (DGF). Dissolved gas flotation (DGF): It is a process involving pressurization of gas at 25 to 95 psig for dissolving gas into water and subsequent release of pressure (to 1 atm) under laminar flow hydraulic conditions for generating extremely fine gas bubbles (20–80 microns) which become attached to the impurities to be removed and rise to the water surface together. The impurities or pollutants to be removed on the water surface are called float or scum which are scooped off by sludge collection means. The clarified water is discharged from the flotation clarifier’s bottom. The gas flow rate is about 1% of influent liquid flow rate. The attachment of gas bubbles to the impurities can be a result of physical entrapment, electrochemical attraction, surface adsorption, and/or gas stripping.

58

L. K. Wang

The specific gravity of the bubble-impurity agglomerate is less than one, resulting in buoyancy or nonselective flotation (i.e., save-all process). Dissolved nitrogen flotation (DNF): One of the dissolved gas flotation (DGF) processes in which nitrogen is used for generation of gas bubbles. See dissolved gas flotation (DGF). Dissolved ozone flotation (DOF): One of the dissolved gas flotation (DGF) processes in which ozone is used for generation of gas bubbles. See dissolved gas flotation (DGF). Electroflotation: It is a process involving the generation of hydrogen and oxygen bubbles in a dilute electrolytic aqueous solution by passing a direct current between two electrodes: (a) anode and (b) cathode. Anode reaction generates oxygen bubbles and hydrogen ions, while cathode reaction generates hydrogen bubbles and hydroxide ions. Either aluminum or steel sacrificial electrodes can be employed for generating the gas bubbles as well as coagulants at the same time. Non-sacrificial electrodes are employed for generating the gas bubbles only and can be made of titanium (as the carrier material) and lead dioxide (as the coating material). Electrical power is supplied to the electrodes at a low voltage potential of 5 to 20 volts DC by means of a transformer rectifier. Small bubbles in the range of 20–50 m microns are produced under laminar hydraulic flow conditions feasible for flotation separation of fragile flocs from water in a small system. The floats on the water surface are the impurities/pollutants removed from water. The clarified water is discharged from the flotation clarifier’s bottom. There can be unexpected advantages and disadvantages when electroflotation is employed. For instance, chlorine bubbles may be generated as a water disinfectant if the water contains a significant amount of chloride ions. Certain unexpected gas bubbles may be generated and may be undesirable [151]. Electrolytic flotation: Same as electroflotation. Environmental humanitarian engineering: It is an interdisciplinary engineering field of broad scope that draws on such displines as physics, thermodynamics, hydraulics, hydrology, biology, chemistry, microbiology, economics, mathematics, and business management, for helping marginalized people and disadvantaged communities in designing, developing, operating and managing environmental systems (water supply, distribution, waste collection, waste treatment, air pollution control, solid waste management, hazardous waste management, noise control, population control, regional planning, etc.) Flotation-sludge press (FloatPress): A combination of dissolved air flotation thickener and sludge press with the flotation thickener at the bottom and the sludge press on the top. A typical example is FloatPress manufactured by Krofta Engineering Corporation. Foam separation: Same as induced gas flotation (IGF); normally, air is used for generation of gas bubbles. Granular activated carbon (GAC) filtration: A filtration bed consists of granular activated carbon.

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

59

Gravity flotation: It is a water-solid separation process by flotation relying on natural specific gravity difference of a water and the lightweight solids (specific gravity is less than one) within water. In natural gravity flotation, oil, grease, wax, fiber, or other substances lighter than water (specific gravity is less than one) are allowed to rise naturally to the water surface of quiescent tank, where they are skimmed off or scooped off. The bottom clean water is discharged as the treated water. The floats skimmed off or scooped off from the water surface are either the impurities/pollutants to be removed or the resources (such as fibers, or oils) recovered for reuse. Humanitarian engineering: It is a new interdisciplinary academic field of broad scope that draws on such displines as STEAM (Science, Technology, Engineering, Arts and Mathematics), emphasing the application of STEAM to improving the well-being of marginalized people and disadvantaged communities in any country. Induced gas flotation (IGF): It is a process involving introduction of gas directly into the water through a revolving impeller, a diffuser system, or an ejector, or a combination of them, at low pressure (slightly higher than 1 atm) for generating big gas bubbles (80 microns to over 1 mm) in large volume under turbulent hydraulic flow conditions. The gas flow rate is about 400% of the influent water flow rate. Physical entrapment and electrochemical attraction play minor roles in an induced gas flotation system. The attachment of gas bubbles to the impurities is mainly a result of surface adsorption, gas stripping, and oxidation. Surface active substances (inks, detergents, ores, soaps, etc.) together with impurities are selectively separated in a foam phase at the water surface. The foam containing the surfactant and the impurities are removed by a suction device. Volatile substances are removed by gas stripping action. The clarified water is discharged from the flotation clarifier’s bottom. Reducing agents, such as ferrous ions, can be oxidized to ferric ions for subsequent separation in ferric hydroxide form if air is used as a gas. Krofta Engineering Corporation (KEC): It is an equipment manufacturer and engineering design company in Lenox, Massachusetts, USA, working closely with the Lenox Institute of Water Technology (LIWT) for development, production, sales, installation, and operation of innovative water and wastewater treatment processes, monitoring devices, and analytical methods. Lenox Institute of Water Technology (LIWT): It is a nonprofit college in Massachusetts, USA, with expertise in environmental STEAM (science, technology, engineering, arts, and mathematics) education, R&D, invention, process development, monitoring system/methods development, patent application, licensing, fundraising, engineering design, and project management. LIWT teams up with Krofta Engineering Corporation (KEC) for technology transfer, equipment design, and voluntary humanitarian global service through free education, training, and academic publications. Micro-flotation: In micro-flotation, the entire volume of water to be treated is subjected to the increased pressure by passing the water down and up a shaft approximately 10 meters deep. At the bottom of the shaft, on the downcomer side, air is injected by one air blower under low pressure (20 psig). Undissolved air

60

L. K. Wang

rises up the shaft against the flow, thus increasing the saturation of the water. As the water rises in the up-flow section, the hydrostatic pressure decreases. Some of the soluble air is then released out of solution in the form of fine air bubbles due to a reduction in air solubility caused by pressure reduction. Floc agglomeration and bubble generation occur simultaneously and gently, providing good attachment of the air bubbles to the flocs. The amount of air which can be dissolved is limited by the depth of shaft (e.g., hydrostatic pressure provided). The saturation of the water with air at that depth is dependent on the way the air is introduced to the system (e.g., size of air bubbles produced at point of injection). Similarly, the floats collected on water surface are the impurities/pollutants removed from the water. The floats are collected by a rotating sludge collection scoop or equivalent. The bottom flotation clarified water is discharged as the treated water [151]. Natural flotation: Same as gravity flotation, or natural gravity flotation. Sedimentation-flotation (SediFloat): A combined sedimentation and dissolved air flotation clarifier, with sedimentation at the bottom and dissolved air flotation on the top. A typical example is SediFloat manufactured by Krofta Engineering Corporation. Vacuum flotation: In vacuum flotation, the influent process water to be treated is usually almost saturated with air at atmospheric pressure. There is an air-tight enclosure on the top of the flotation chamber in which partial vacuum is maintained. The fine air bubbles (20–80 microns) are generated under laminar hydraulic flow conditions by applying a vacuum (negative pressure) to the flotation chamber. The theory is that the lower the pressure, the lower the air solubility in water. The soluble air originally in water is partially released out of solution as extremely fine bubbles due to a reduction in air solubility caused by negative vacuum pressure. The bubbles and the attached solid particles rise to the water surface to form a scum blanket, which can be removed by a continuous scooping or skimming mechanism. Grit and other heavy solids that settle to the bottom are raked to a central sludge sump for removal. Auxiliary equipment includes an aeration tank for saturating the water or wastewater with air, vacuum pumps, and sludge pumps [151]. Vertical shaft flotation: Same as deep shaft flotation.

References 1. Boyd JL, Shell GL (1972) Dissolved air flotation application to industrial wastewater treatment. In: Proceedings of the 27th Industrial Waste Conference 2. Stander GJ, Van Vuuren LRJ (1970) Flotation of sewage and waste solids. In: Gloyna EF, Eckenfelder WW Jr (eds) Water quality improvement by physical and chemical processes. Univ. of Texas Press, Texas, pp 190–199 3. Metcalf & Eddy, Inc. (1972) Wastewater engineering, collection, treatment, disposal. McGraw—Hill Book Co., New York, pp 296–301 4. Anon (1968) Electrolysis—bred Bubbles Clarify Water, Chemical Engineering, 82–84, 29 July 1968 5. Lemlich R (1972) Adsorptive bubble separation techniques. Academic Press, New York 6. Wang LK (1974) Environmental engineering glossary. Calspan Corporation, Buffalo, New York, USA, p 439

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

61

7. Greives RB (1970) Foam Separations for Industrial Wastes: Process Selection, Proceedings of the 25th Industrial Waste Conference, Purdue University, Indiana, USA, pp 398–405 8. London M et al (1953) Fractionation of an enzyme by foaming. Notes 75:1746 9. Charm SE et al (1966) The separation and purification of enzymes through foaming. Anal Biochem 15:498–508 10. Schnepf RW, Gaden EL Jr (1959) Foam fractionation of proteins: concentration of aqueous solutions of bovine serum albumin. J Biochem Microbiol Technol Eng 1(1):1–8 11. Wallace GT, Wilson DF (1969) foam separation as a tool in chemical oceanography, Naval Research Laboratory Report 6958, 20 p 12. Kevorkian V, Gaden EL Jr (1957) Froth—frothate concentration relations in foam fractionation. J Am Inst Chem Eng 3:180 13. Hargis LG, Rogers LB (1969) Enrichment and fractionation by foaming. Sep Sci 4 (2):119–127 14. Wood RK, Tran T (1966) Surface adsorption and the effect of column diameter in the continuous foam separation process. Can J Chem Eng 15. Sheiham I, Pinfold TA (1972) Some parameters affecting the flotation of cationic surfactants. Sep Sci:25–41 16. Harding CI (1963) Foam fractionation in kraft black liquor oxidation, Ph.D. Thesis, University of Florida, Gainesville, Florida 17. Georgia Kraft Company (1969) Foam separation of kraft pulping wastes, Water Pollution Control Research Series, DAST-3, U.S. Department of the Interior, Federal Water Pollution Control Administration 18. Michelsen DL (1970) Treatment of dyeing bath waste streams by foaming and flotation techniques, Project Report of Water Resources Research Center, Virginia Polytechnic Institute and State University, Virginia, USA 19. Karger BL, Grieves RB, Lemlich R, Rubin AJ, Sebba F (1967) Nomenclature recommendations for adsorptive bubble separation methods. Sep Sci 2:401 20. Wang MHS (1973) Separation of lignin from aqueous solution by adsorptive bubble separation processes, Ph.D. Thesis, Rutgers University, New Brunswick, N.J., USA; Selected Water Resources Abstracts, 6(4) 21. Wang MHS, Granstrom ML, Wilson TE, Wang LK (1974) “Removal of lignin from water by precipitate flotation”, Proceedings of American Society of Civil Engineers. J Environ Eng Div 100(EE3):629–640 22. King LJ et al (1968) Pilot plant studies of the decontamination of low level process waste by a scavenging precipitation foam separation process, U.S. Atomic Energy Commission, ORNL3808, 57 p 23. Davis BM, Sebba F (1967) The removal of radioactive caesium contaminants from simple aqueous solutions. J Appl Chem 17:40–43 24. Mahne EJ, Pinfold TA (1969) Precipitate flotation: flotation of silver, uranium and gold. J Appl Chem 19:57–59 25. Lusher JA, Sebba F (1966) Separation of aluminum from beryllium in aqueous solutions by precipitate flotation. J Appl Chem 16:129–132 26. Rubin AJ, Johnson JD (1967) Effect of pH on ion and precipitate flotation systems. Anal Chem 39(2):98–302 27. Mahne EJ, Pinfold TA (1968) Precipitate flotation, separation of palladium from platinum, gold, silver, Iron, cobalt and nickel. J Appl Chem 18:140–142 28. Grieves RB, Bhattacharyya (1968) Foam separation of cyanide complexed by iron. Sep Sci 3 (2):185–202 29. Bhattacharyya D (1966) Foam separation processes. Ph.D. Thesis, Illinois Institute of Technology, Illinois, USA 30. Wilson TE, Wang MHS (1970) Removal of lignin by foam separation processes. In: Proceedings of the 25th industrial Waste Conference, Purdue University, Indiana, USA, pp 731–738 31. Wang MHS, Granstrom ML, Wilson TE, Wang LK (1974) Lignin separation by continuous ion flotation: investigation of physical operational parameters. Water Resour Bull 10 (2):283–294

62

L. K. Wang

32. Karger BL, Rogers LB (1961) Foam fractionation of organic compounds. Separation 33 (9):1165–1169 33. Karger BL et al (1966) Foam fractionation under Total reflux. Separation 38(6):764–767 34. Grieves RB et al (1969) Optimization of the ion flotation of dichromate. In: Journal of the Sanitary Engineering Division, Proceedings of the American Society of Civil Engineers, p 515 35. Grieves RB et al (1967) Continuous dissolved—air ion flotation of hexavalent chromium. J Am Inst Chem Eng 13(6):1167–1170 36. Karger BL, DeVivo DG (1968) General survey of adsorptive bubble separation processes. Sep Sci 3:393–424 37. Rubin AJ, Cassell EA (1965) Microflotation of bacteria. Proc South Water Res Poll Control Conf, USA 14:222 38. Rubin AJ et al (1966) Microflotation: new low gas flow rate foam separation technique for bacteria and algae. Biotechnol Bioeng 8:135 39. Rubin AJ (1968) Microflotation: coagulation and foam separation of aerobacter aerogenes. Biotechnol Bioeng 10:89 40. Henderson O (1967) The effect of pH on algae flotation. Ph.D. Thesis, University of North Carolina, Chapel Hill, USA 41. Dobias B, Vinter V (1966) Flotation of microorganisms. Folia Microbiol 11:314 42. Cassell E, Rubin AJA et al (1968) Removal of organic colloids by microflotation. In: Proceedings of the 23rd Industrial Waste Conference, Purdue University, Indiana, USA 43. Kozhukhovskaya AN et al (1968) (USSR), Selective flotation of microlite and rutile. Nauch. Tr., Irkutsk. Gos. Nauch. Issled. Inst. Redk. Tsvet. Metal., No. 19, 105–111 (Russ) 44. Katashin LV et al (1968) (USSR), Flotation of Pyrochlore from Slimes Left After Gravitational Concentration of Rare Metal Carbonatite Ores. Nauch. Tr., Irkutsk. Gos. Nauch. Issled. Inst. Redk. Isvet. Metal., No. 19 45. Onoprienko NN et al (1969) (USSR), Flotation of iron oxides. Izr. Vyssh. Ucheb. Zaved., Gorn. Zh., 12(1), pp 157—161 (Russ) 46. Wang LK et al. (1974) Treatment of tannery effluents by physical-chemical processes. In: Proceedings of the 45th Annual Conference of the Water Pollution Control Federation, Atlanta, Georgia, USA, 36 p, October 1972; Selected Water Resources Abstract, 7(5) W74—02175, pp 56—57 47. Wang LK et al (1973) Surface adsorption: a promising approach for the treatment of tannery effluents. Report No. VT-3045-M-2, Cornell Aeronautical Laboratory, Inc., Cornell University, Buffalo, N.Y., USA. 60 p, October 1971; Selected Water Resources Abstracts, 6(21), W73—13648 48. Wang LK et al (1973) Evaluation and development of physical-chemical techniques for the separation of emulsified oil from water. Report No. 189, Calspan Corporation, Buffalo, NY, USA, 31 p; Selected Water Resources Abstract, 6(21), w73—13642, p 90 49. Kim YS, Zeitlin H (1972) The separation of zinc and copper from seawater by adsorption colloid flotation. Sep Sci 7(1):1–12 50. Pinfold TA (1970) Adsorptive bubble separation methods. Sep Sci 5(4):379–384 51. KondrataviciUs V (1969) Removal of synthetic surface-active agents from waste waters of tanneries. Kozk Obur Prom (USSR) 11(1):18 52. Wang LK et al (1972) Treatment of glue factory wastes by physicochemical processes. Report No. VT-3045-M-3, Cornell Aeronautical Laboratory, Inc., Cornell University, Buffalo, N.Y., 79 p; Pollution Abstracts, p. 113 53. Dorman DC, Lemlich R (1965) Separation of liquid mixtures by non-foaming bubble fractionation. Nature 4993:145–146 54. Harper DO (1967) Bubble and foam fractionation. Ph.D. Thesis, University of Cincinnati, Cincinnati, OH 55. Lemlich R (1966) Theoretical approach to non-foaming adsorptive bubble fractionation. AI ChE J 12(4):802–804

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

63

56. Lemlich R (1972) Adsubble processes: foam fractionation and bubble fractionation. J Geophys Res 77(27):5204–5210 57. Wang LK (1972) Continuous bubble fractionation process. Ph.D. Thesis, Rutgers University, New Brunswick, NJ, USA 58. Cannon KD, Lemlich R (1972) A theoretical study of bubble fractionation. A I Ch E Symp Ser, 68(124) 59. Kown BT, Wang LK (1971) Solute separation by continuous bubble fractionation. Separat Sci 6(4):537–552; (1973) Selected Water Resources Abstracts, 6(21):W73—l3638, 89 60. Maas K (1969) A new type of Adsubble methods: booster bubble fractionation – hastened and improved bubble fractionation of low foaming solutions. Sep Sci 4(6):457–465 61. Wang LK et al (1972) Continuous bubble fractionation: part I, theoretical considerations. Environ Lett 3(4):251–265 62. Wang LK et al (1973) Continuous bubble fractionation: part II, effects of bubble size and gas rate. Environ Lett 4(3):233–252 63. Wang LK et al (1973) Continuous bubble fractionation: part III, experimental evaluation of flow parameters. Environ Lett 5(2):71–89 64. Shah GN, Lemlich R (1970) Separation of dyes in non— foaming adsorptive bubble columns. Ind Eng Chem Fundam 9(3):350–355 65. Bruin S et al (1972) Continuous nonfoaming adsorptive bubble fractionation. Ind Eng Chem Fundam 11(2):175–181 66. Karger BL, Caragay AB, Lee SB (1967) Studies in solvent sublation: extraction of methyl orange and rhoda-mine B. Sep Sci 2(1):39–64 67. Sheiham I, Pinfold TA (1972) The solvent sublation of hexadecyltrimethylammonium chloride. Sep Sci 1:43–50 68. Quigley RE, Hoffman EL (1966) Flotation of oily wastes. In: Proceedings of the 21st Industrial Waste Conference, Purdue University, Indiana, pp 527–533 69. Hart JA (1970) Air flotation treatment and reuse of refinery wastewater. In: Proceedings of the 25th Industrial Waste Conference, Purdue University, Indiana, pp 406–413 70. Lundgren H (1969) Air flotation purifies wastewater from latex polymer manufacturer. Chemical Engineering Progress Symposium Series—Water, pp 191–195 71. Wang LK et al (1978) Water treatment with multiphase flow reactor and cationic surfactants. J Am Water Works Assoc 70(9):522–528 72. Krofta M, Wang LK, Barris D, Janas J (1981) Treatment of pittsfield raw water for drinking water production by innovative process systems. US Department of Commerce, National Technical Information Service, Technical Report No. PB82-118795, USA, 87p 73. Hyde RA et al (1977) Water clarification by flotation. J Am Water Works Assoc 69 (7):369–374 74. Krofta M, Wang LK (1981) Development of an innovative process system for water purification and recycle. In: Proceedings of American Water Works Association. Water Reuse Symposium II, vol 2. pp 1292–1315 75. Wang LK, Wang MHS, Hu GY (1981) Determination of lignin and tannin in aqueous solution by a modified method. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA., Report No. PB82-133042 (NSF/RA-81052), 14 p 76. Krofta M, Wang LK (1981) Potable water pretreatment for turbidity and color removal by dissolved air flotation and filtration for the town of Lenox, Massachusetts. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA., USA, Report No. PB82-182064, 48 p 77. Krofta M, Wang LK (1982) Report on projected water treatment plant for the city of Pittsfield, Massachusetts with the application of flotation technology. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA., USA, Report No. PB82-118779 78. Krofta M, Wang LK (1982) Innovation in the water treatment field and systems appropriate and affordable for smaller communities. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA., USA, Report No. PB82-2O1476, 30 p 79. Krofta M, Wang LK (1982) Potable water treatment by dissolved air flotation and filtration. J Am Water Works Assoc 74(6)

64

L. K. Wang

80. Vrablik ER (1959) Fundamental principles of dissolved air flotation of industrial wastes. In: Proceedings of the 14th Industrial Waste Conference, May 5–7, Purdue University, Lafayette, IN, USA 81. Barton CA, Byrd JF, Peterson RC, Walter JH, Woodruff PH (1968) A total systems approach to pollution control at a pulp and paper mill. J Water Pollut Control Fed 40:1471 82. Wang LK (1974) Removal of organic pollutants by adsorptive bubble separation processes. In: 1974 Earth Environment and Resources Conference Digest of Technical Papers, vol. 1(74), pp 56–57 83. Mennell M, Merrill DT, Jorden RM (1974) Treatment of primary effluent by lime precipitation and dissolved air flotation. J Water Pollut Control Fed 46:2471 84. Wang LK et al (1975) Treatment of tannery effluents by surface adsorption. J Appl Chem Biotechnol 25:475–490. (ENGLAND) 85. Wang LK et al (1976) Treatment of a wastewater from military explosive and propellants production industry by physicochemical processes. U.S. Defense Technical Information Center, Alex., VA, USA, AD-A027329, 121 p 86. Wang LK (1976) Mathematical modeling and experimental evaluation of surfactant transfer in a two-phase bubble flow reactor. The 7th Northeast Regional Meeting of American Chemical Society, USA 87. Woodard FE, Hall MW, Sproul OJ, Ghosh MM (1977) New concepts in treatment of poultry processing wastes. Water Res 11:873–877 88. Coertze JA (1978) Dissolved air flotation treatment of paper mill effluent. Prog Wat Tech 10 (1/2):449–457 89. Cooper RN, Denmead CF (1979) Chemical treatment of slaughterhouse wastes with protein recovery. J Water Pollut Control Fed 51:1017 90. Szabo AJ (1980) Dissolved air flotation for treatment of seafood wastewater. In: Proceedings of the Seafood Waste Management, September 23–25, Orlando, FL, USA 91. Henry JG, Gehr R (1981) Dissolved air flotation for primary and secondary clarification. Canada Mortgage and Housing Corporation. Report SCAT – 9. Ottawa, ON, Canada 92. Jedele K, Hoch W, Rölle R (1980) Einsatz der Entstpnnungsflotation in Belebtschlammanlagen anstelle herkömmlicher Nachklärbecken. Korrespondenz Abwasser, Heft 27:611–618 93. Krofta M, Wang LK (1982) Potable water treatment by dissolved air flotation. J Am Water Works Assoc 74(6):304–310 94. Wang LK (1982) Monitoring and control of Lenox water treatment plant, Lenox, Massachusetts. U.S. Department of Commerce, National Technical Information Service, USA, PB84192079, 17 p 95. Krofta M, Wang LK (1982) First full-scale flotation plant in U.S.A. for potable water treatment. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB82-220690, 67 p 96. Krofta M, Wang LK (1982) Alternative water treatment systems using flotation technology. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB82-211400, 34 p 97. Wang LK, Wood GW (1982) Water treatment by disinfection, flotation and ion exchange process system. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB82-213349, 115 p 98. Krofta M, Wang LK (1982) Startup and continuous operation of Lenox water treatment plant, Lenox, Massachusetts, USA. U.S. Dept. of Commerce, National Technical Information Service, PB85-182616/AS, 28 p 99. Krofta M, Wang LK (1982) Operational data of Lenox water treatment plant, Lenox, Massachusetts, USA. U.S. Dept. of Commerce, National Technical Information Service, PB84192061, 46 p 100. Krofta M, Wang LK (1983) Development of innovative sandfloat systems for water purification and pollution control. ASPE Journal of Engineering Plumbing 0(1):1–16, 1984 (Recipient of 1982 Pollution Engineering Five-Star Award). U.S. Department of Commerce, National Technical Information Service, PB83-107961

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

65

101. Wang LK (1982) Compact nitrogen removal options for Lake Como, Italy. Effluent Water Treat J 22(11):435–437. (ENGLAND) 102. Krofta M, Wang LK, Wang MHS (1989) Septic tank effluent treatment options: electroflotation and filtration, New England Water Pollution Control Association (NEWPCA), Boston, NY, USA, January 22–25, 1989 103. Wang LK (1982) Principles and kinetics of oxygenation – ozonation waste treatment system. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB83-127704, 139 p 104. Krofta M, Wang LK (1984) Tertiary treatment of secondary effluent by dissolved air flotation and filtration. Civil Eng Pract Design Eng 3:253–272. (NTIS-PB83-171165) 105. Krofta M, Wang LK (1983) Design, construction and operation of Lenox water treatment plant, project summary. U.S. Dept. of Commerce, National Technical Information Service, USA, PB83-171264, 40 p 106. Krofta M, Wang LK (1983) Design, construction and operation of Lenox water treatment plant, project documentation. U.S. Dept. of Commerce, National Technical Information Service, USA, PB83-164731, 330 p 107. Krofta M, Wang LK (1983) Potable water treatment by foam separation and dissolved air flotation. In: American Institute of Chemical Engineers, National Conference, Houston, TX, USA. (NTIS-PB83-232843) 108. Krofta M, Wang LK (1983) Design of dissolved air flotation systems for industrial pretreatment and municipal wastewater treatment – design and energy considerations. In: American Institute of Chemical Engineers National Conference, Houston, TX, USA, 30 p. (NTIS-PB83-232868) 109. Krofta M, Wang LK (1983) Design of dissolved air flotation systems for industrial pretreatment and municipal wastewater treatment – case history of practical applications. In: American Institute of Chemical Engineers National Conference, Houston, TX, USA, 25 p. (NTIS-PB83-232850) 110. Krofta M, Wang LK, Spencer RL, Weber J (1983) Separation of algae from lake water by dissolved air flotation and sand filtration. In: Proceedings of the Water Quality and Public Health Conference, WPI, MA, USA. PB93-219550, pp 103–110 111. Krofta M, Wang LK, Wu BC, Bien CCJ (1983) Recent advances in titanium dioxide recover, filler retention and white water treatment. U.S. Dept. of Commerce, National Technical Information Service, USA, PB83-219543, 39 p 112. Krofta M, Wang LK (1983) Over one-year operation of lenox after treatment plant–part 1. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB83247270, 1–264 p 113. Krofta M, Wang LK (1983) Over one-year operation of lenox water treatment plant-part 2. U. S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA, PB83247288, 265–425 p 114. Wang LK, Kolodziej (1983) Removal of trihalomethane precursors and coliform bacteria by Lenox flotation-filtration plant. In: Proceedings of the Water Quality and Public Health Conference, USA, PB83-244053, pp 17–29. (PB83-244053) 115. Krofta M, Wang LK, Kurylko L, Thayer AE (1983) Pretreatment and ozonation of cooling tower water, part I. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA. PB84-192053, 34 p 116. Krofta M, Wang LK, Kurylko L, Thayer AE (1983) Pretreatment and ozonation of cooling tower water, part II. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, USA. PB84-192046, 29 p 117. Wang LK, Barris C, Milne P, Wu BC, Hollen J (1982) Removal of extremely high color from water containing trihalomethane precursor by flotation and filtration. U.S. Dept. of Commerce, National Technical Information Service, USA, PB83-240374, 11 p 118. Wang LK (1984) Design of innovative flotation -filtration wastewater treatment systems for a nickel-chromium plating plant. U.S. Dept. of Commerce, National Technical Information Service, PB88-200522/AS, USA, 50 p

66

L. K. Wang

119. Krofta M, Wang LK, Wang MHS (1983) Laboratory simulation and optimization of physicalchemical treatment processes. U.S. Dept. of Commerce, National Technical Information Service, PB86-188794/AS, USA, 42 p 120. Wang LK, Wu BC (1984) Development of two-stage physical-chemical process system for treatment of pulp mill wastewater. Lenox Institute of Water Technology Technical Report #LIR/05-84/2, USA, 65 p 121. Krofta M, Wang LK (1984) Symposium on environmental technology and management 1984. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, PB84209337, USA, 149 p 122. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley Reservoir Water by Krofta Sandfloat Process System – Project Summary. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200647/AS, USA, 40 p 123. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley Reservoir Water by Krofta Sandfloat Process System – Project Documentation. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200654/AS, USA, 188 p 124. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley Reservoir Water by Krofta Sandfloat Process System – Final Project Report. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200639/AS, USA, 194 p 125. Krofta M, Wang LK (1983) Treatment of Rome Raw Water by Krofta Sandfloat Process System – Project Summary. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200662/AS, USA, 35 p 126. Krofta M, Wang LK (1984) Treatment of Rome Raw Water by Krofta Sandfloat Process System – Project Documentation Part A. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200670/AS, USA, 238 p 127. Krofta M, Wang LK (1984) Treatment of Rome Raw Water by Krofta Sandfloat Process System – Project Documentation Part B. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200688/AS, USA, pp 239–276 128. Krofta M, Wang LK (1984) Treatment of Rome Raw Water by Krofta Sandfloat Process System – Project Documentation Part C. U.S. Department of Commerce, National Technical Information Service, Technical Report No. PB88-200696/AS, USA, 145 p 129. Shuster WW, Wang LK (1983) Role of polyelectrolytes in the filtration of colloidal particles from water and wastewater. U.S. Department of Commerce, National Technical Information Service, Technical Report No. AD-A131-109, USA, 49 p 130. Reid HJ, Wang LK (1984) The effects of cationic surfactant concentration on bubble dynamics in a bubble fractionation column. U.S. Department of Commerce, Technical Report No. PB86197845/AS, 47p, July 1984. National Technical Information Service, USA 131. Krofta M, Wang LK (1984) Waste treatment by innovative flotation-filtration and oxygenation-ozonation process. U.S. Dept. of Commerce, National Technical Information Service, PB85-174738-AS, USA, 171 p 132. Ross RG, Wang LK (1984) Process control using zeta potential and colloid titration techniques. U.S. Dept. of Commerce, National Technical Information Service, PB87-179099/AS, USA, 126 p 133. Krofta M, Wang LK (1985) Treatment of cooling tower water by dissolved air-ozone flotation. In: Proceedings of the Seventh Mid-Atlantic Industrial Waste Conference, USA, pp 207–216 134. Krofta M, Wang LK (1984) Development of innovative electroflotation water purification system for single families and small communities. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, PB85-207595/AS, USA, 57 p 135. Krofta M, Wang LK (1984) Development of a total closed water system for a deinking plant. In: Proceedings of the American Water Works Association, Water Reuse Symposium III, vol 2, 881–898 p 136. Krofta M, Wang LK (1984) Total waste recycle system for a wastewater treatment system using primary coagulants containing aluminum. Lenox Institute of Water Technology Technical Report # LIR/01-84/6, USA, 21 p 137. Wang LK, Wu BC, Meier A, Marshall J, Zepka J, Foote R, Janas J, Mulloy M (1984) Removal of arsenic from water and wastewater. U.S. Dept. of Commerce, National Technical Information Service, PB86-169299, USA, 45 p

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

67

138. Krofta M, Wang LK, Boutroy M (1984) Development of a new treatment system consisting of adsorption flotation and filtration. U.S. Dept. of Commerce, National Technical Information Service, PB85-209401/AS, USA, 28 p 139. Layer W, Wang LK (1984) Water purification and wastewater treatment with sodium aluminate. U.S. Dept. of Commerce, National Technical Information Service, Springfield, VA, PB85-214-492/AS, USA, 17 p 140. Krofta M, Wang LK (1984) Removal of arsenic and other contaminants from Storm Run-off water by flotation, filtration, adsorption and ion exchange. U.S. Dept. of Commerce, National Technical Information Service, PB88-200613/AS, USA, 54 p 141. Krofta M, Wang LK, Wu BC, Janas J (1984) Analysis of sludges generated from flotation treatment of storm run-off water. U.S. Dept. of Commerce, National Technical Information Service, PB88-20062I/AS, USA, 20 p 142. Wang LK, Wu BC (1984) Treatment of groundwater by dissolved air flotation systems using sodium aluminate and lime as flotation aids. OCEESA J 1(3):15–18. (NTIS-PB85-167229/ AS), USA 143. Zabel T (1884) Flotation in water treatment, NATO ASI Series. Martinus, Nijhoff Publishers, Boston 144. Krofta M, Wang LK (1985) Development of an innovative and cost-effective municipalindustrial waste treatment system. U.S. Dept. of Commerce, National Technical Information Service PB88-168109/AS, USA, 27 p 145. Krofta M, Wang LK (1985) Treatment of potable water from Seoul, Korea by flotation, filtration and adsorption. U.S. Dept. of Commerce, National Technical Information Service, PB88-200530/AS, USA, 21 p 146. Krofta M, Wang LK (1985) Pollution abatement using dissolved air flotation technology in the paper and pulp industry. In: Proceedings of the 1985 Powder and Bulk Solids Conference, Chicago, IL, USA, 28 p 147. Wang LK, Wu BC, Fat R, Rogalla F (1985) Treatment of scallop processing wastewater by flotation, adsorption and ion exchange. U.S. Dept. of Commerce, National Technical Information Service, PB89-143556/AS, USA, 17 p 148. Huntley GM, Wang LK, Layer LW (1985) Evaluation of sodium aluminate as a coagulant for cost savings at water treatment plants. U.S. Dept. of Commerce, National Technical Information Service, PB88-168075/AS, 23 p 149. Krofta M, Wang LK (1987) Wastewater treatment by biological-physicochemical two-stage process system. In: Proceedings of the 41st Industrial Waste Conference. Lewis Publishers, Inc, Chelsea, MI, USA, pp 67–72 150. Krofta M, Wang LK, Foote R (1985) Separation of high grade sulfur from an ore by flotation. Lenox Institute of Water Technology Report #LIR/09-85/155, USA, 15 p 151. Wang LK (1985) Theory and application of flotation processes. U.S. Dept. of Commerce, National Technical Information Service, PB86-194198/AS, USA, 15 p 152. Wang LK (1985) Secondary treatment of Bangor primary effluent by Supracell Clarifier. Lenox Institute of Water Technology Technical Report #LIR/11-85/160, USA, 10 p 153. Krofta M, Wang LK (1986) Investigation of municipal wastewater treatment by a compact innovative system. Lenox Institute of Water Technology Technical Report #LIR/01-86/165, USA, 59 p 154. Wang LK (1988) Removal of algae from lagoon effluent. Lenox Institute of Water Technology Technical Report #LIR/01-88/167, USA 155. Krofta M, Wang LK (1986) Tertiary wastewater treatment. U.S. Dept. of Commerce, National Technical Information Service, PB88-168133/AS, USA, 23 p 156. Wang LK (1986) Recent advances in water and wastewater treatment. Symposium on Environmental Technology and Management, PB88-2005589/AS, USA, 137 p 157. Wang LK (1986) A promising and affordable solution to sludge treatment. U.S. Dept. of Commerce, National Technical Information Service, PB88-168398/AS, USA, 12 p 158. Krofta M, Wang LK (1987) Flotation technology and secondary clarification. Tech Assoc Pulp Paper Ind J 70(4):92–96

68

L. K. Wang

159. Krofta M, Wang LK (1986) Municipal waste treatment by Supracell flotation, chemical oxidation and star system. U.S. Dept. of Commerce, National Technical Information Service, PB88-200548/AS, USA, 22 p 160. Pappanchen A, Kurylko L, Wang LK (1987) Development of a new water treatment process for decreasing the potential for THM formation. U.S. Dept. of Commerce, National Technical Information Service, USA, PB81-202541, 80 p 161. Krofta M, Wang LK (1986) Dissolved air flotation processes. U.S. Dept. of Commerce, National Technical Information Service, USA, PB88-168448/AS, 35 p 162. Wang LK, Wang MHS, Wang JC (1987) Design, operation and maintenance of the nation’s largest physicochemical waste treatment plant, vol 1. Lenox Institute of Water Technology Report #LIR/03-87-248, USA, 183 p 163. Wang LK, Wang MHS, Wang JC (1987) Design operation and maintenance of the nation’s largest physicochemical waste treatment plant, vol. 2. Lenox Institute of Water Technology Report #LIR/03-87/249, USA, 161 p 164. Wang LK, Wang MHS, Wang JC (1987) Design operation and maintenance of the nation’s largest physicochemical waste treatment plant, vol 3. Lenox Institute of Water Technology Report #LIR/03-87/250, USA, 227 p 165. Krofta M, Wang LK (1987) Winter operation of nation’s largest potable flotation plants. Joint Conference of American Water Works Association and Water Pollution Control Federation, Cheyenne, WY, USA. (NTIS-PB88-200563/AS) 166. Krofta M, Guss D, Wang LK (1988) Development of low-cost flotation technology and systems for wastewater treatment. In: Proceedings of the 42nd Industrial Waste Conference, USA, p 185 167. Wang LK, Daly PG (1987) Preliminary design report of a 10-MGD deep shaft-flotation plant for the city of Bangor. U.S. Dept. of Commerce, National Technical Information Service, PB88-200597/AS, USA, 42 p 168. Wang LK, Daly PG (1987) Preliminary design report of a 10-MGD deep shaft-flotation plant for the city of Bangor. Appendix. U.S. Dept. of Commerce, National Technical Information Service, PB88-200605/AS, USA, 171 p 169. Odegaard H (1987) Particle separation in wastewater treatment. Documentation at the 6th EWPC Association Symposium, München, pp 351–400 170. Krofta M, Wang LK (1984) Development of innovative flotation-filtration system for water treatment, part a: first full-scale sandfloat plant in US. American Water Works Association Water Reuse Symposium III, San Diego, CA, USA. Published by AWWA Research Foundation, Denver, CO, USA 171. Jokela P, Jormalainen S, Keskitalo P, Rantala P (1988) Efficient pretreatment of foodstuff industry wastewater. In: Panswald T, Polprasert C, Yamamoto K (eds) Water pollution control in Asia. Pergamon Press, Oxford, pp 535–540 172. Krofta M, Guss D, Wang LK (1988) Development of low-cost flotation technology and systems for wastewater treatment. In: Proceedings of the 42nd Industrial Waste Conference, May 12–14, 1987, Purdue Univ., Lewis Publishers, Chelsea, MI, USA, pp 185–195 173. Krofta M, Wang LK, Pollman CD (1989) Treatment of seafood processing wastewater by dissolved air flotation, carbon adsorption and free chlorination. In: Proceedings of the 43rd Industrial Waste Conference. Lewis Publishers, Chelsea, MI, USA, p 535 174. Krofta M, Wang LK (1989) Total closing of paper mills with reclamation and deinking installations. In: Proceedings of the 43rd Industrial Waste Conference, USA, p 673 175. Wang LK (1988) Recent development in cooling water treatment with ozone. Lenox Institute of Water Technology LIR/03-88/285, USA, 237 p 176. Wang LK (1988) Treatment of cooling tower water with ozone. Lenox Institute of Water Technology Report #LIR/05-88/303, USA, 55 p 177. Krofta M, Guss D, Wang LK (1988) Pretreatment of food industry wastewater using a high rate flotation Clarifier. In: Proceedings of the 1988 Food Processing Waste Conference, GIT, Atlanta, GA, USA

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

69

178. Krofta M, Wang LK (1988) Development of innovative flotation processes for water treatment and wastewater reclamation. In: National Water Supply Improvement Association Conference, San Diego, USA, 42 p 179. Bennoit H (1988) Anwendung der Entspannungsflotation bei der Abwasserreinigung in der Chemischen Industrie. GVC-Kongress in Baden-Baden, Preprints, Band 1:53–65 180. Wang LK, Wang MHS (1990) Bubble dynamics and air dispersion mechanisms of air flotation process systems, part a: material balances. In: Proceedings of the 44th Industrial Waste Conference, USA, pp 493–504 181. Krofta M, Wang LK (1990) Bubble dynamics and air dispersion mechanisms of air flotation process systems, part b: air dispersion. In: Proceedings of the 44th Industrial Waste Conference, USA, pp 505–515 182. Wang LK, Mahoney WJ (1994) Treatment of storm run-off by oil-water separation, flotation, filtration and adsorption, part a: wastewater treatment. In: Proceedings of the 44th Industrial Waste Conference, pp 655–666, 1990. Water Treat 9(1994):223–233 183. Wang LK, Wang MHS, Mahoney WJ (1990) Treatment of storm run-off by oil-water separation, flotation, filtration and adsorption, part b: waste sludge management. In: Proceedings of the 44th Industrial Waste Conference, USA, pp 667–673 184. Wang LK (1989) Using air flotation and filtration in removal of color, trihalomethane precursors and giardia cysts. In: NYSDOH Workshop on Water Treatment Chemicals and Filtration, Ramada Inn, Saratoga Springs, NY, May 1989. American Slow Sand Association Annual Meeting, NY, USA, 30 p 185. Wang LK, Wang MHS, Hoagland FM (1992) Reduction of color, odor, humic acid and toxic substances by adsorption, flotation and filtration. In: Annual Meeting of American Institute of Chemical Engineers, Symposium on Design of Adsorption Systems for Pollution Control, Philadelphia, PA, August 1989. (P926-08-89-20; 18 p). Water Treat 7(1992):1–16 186. Wang, L. K., and Van Dyke, J. P. (1989) Treatment of rotating biological contactor effluent by dissolved air flotation. Annual Meeting of Engineering Foundation, Palm Coast, FL, 23 p 187. Wang LK (1990) Decontamination of groundwater and hazardous industrial effluents by highrate air flotation processes. In: Great Lakes 90 Conference Proceedings, Hazardous Materials Control Research Institute, Silver Spring, MD, USA 188. Wang LK (1990) Modern technologies for prevention and control of groundwater contamination. In: Proceedings of New York – New Jersey Environmental Exposition, NYNJEE, Belmont, MA, USA 189. Wang LK (1990) New dawn in flotation treatment of industrial water and wastes. In: Proceeding of the 1990 Modern Engineering Technology Seminar, Taipei, Taiwan, R.O.C., 25 p 190. Pieterse T, Kfir R (1991) Plant quartet proves potable water reuse. Water Qual Int 4:31 191. Rusten B, Eikebrokk B, Thorvaldsen G (1990) Coagulation as pretreatment of food industry wastewater. Water Sci Tech 22(9):108 192. Keskitalo P, Sundholm I (1990) Poultry and vegetable processing wastewater treatment with two stage dissolved air flotation and biological purification. In: Proceeding of the 6th International Symposium on Agricultural and Food Processing Wastes, December 17–18, Chicago, IL, USA 193. Kiuru HJ (1990) Tertiary wastewater treatment with flotation filters. Water Sci Tech 22:139 194. Kollajtis JA (1991) Dissolved air flotation applied in drinking water clarification. In: Proceedings of the Annual AWWA Conference – Water Quality for the New Decade, Philadelphia, PA, USA, pp 433–448 195. Wang LK (1991) Water and waste treatment using advanced dissolving air flotation. In: Proceedings of the 1991 Annual Conference of the Korea Society of Water Pollution Research and Control, Seoul, Korea, 33 p 196. Malley JP, Edzwald JK (1991) Concepts of dissolved air flotation of drinking water. J Water SRT Aqua 40(1):7–17

70

L. K. Wang

197. Wang LK, Wang MHS, Kolodzicj (1992) Innovative and cost-effective Lenox water purification plant. Water Treat 7(1992):387–406 198. Graham KA, Venkatesh M (1992) Improve the performance and increase the capacity of an activated sludge plant with a dissolved air flotation clarifier. In: Proceeding of the 47th Industrial Waste Conference, Lewis Publishers, Chelsea, Michigan, USA 199. Peter A, Libra J, von Wagenheim U, Wiesmann U (1992) Abwasserreinigung in Hochreaktoren und Abtrennung von Belebtem Schlamm durch Flotation – Messungen zur Flotation und Ergebnisse einer Wirtschaftlichkeitsrechnung. 2. GVC-Kongress in Würzburg, Preprints, Band 2, pp 63–80 200. Wang LK, Hwang CS (1993) Removal of trihalomethane precursor (humic acid) by innovative dissolved air flotation and conventional sedimentation. In: Proceedings of the 1991 Annual Conference of the Korea Society of Water Pollution Research and Control, Seoul, Korea, 10 p, Febuary 1991. Water Treat 8(1):7–16 201. Chandra S (1993) The effluent-free paper mill. Myth or reality ? Papermaker (November):40–42 202. Cizinska S, Matejo V, Wase C, Klasson Y, Krejci J, Dalhammar G (1992) Thickening of waste activated sludge by biological flotation. Water Res 26:139 203. Dewitt N, Shammas NK (1992) Flotation: a viable alternative to sedimentation in wastewater treatment. In: Water Environment Federation’s, 65th Annual Conference & Expo, September 20–24, New Orleans, LA, USA 204. Viitasaari M (1993) Finnish experience of water pollution control: case study – pulp and paper industry. Environ Safty Tech (Summer) 49:51, 53, 55. 205. Pascual B, Tansel B, Shalewitz R (1994) Economic sensitivity of the dissolved air flotation process with respect to the operational variables. In: Proceedings of the 49th Industrial Waste Conference, Lewis Publishers, Chelsea, MI, USA 206. Wang LK, Cheryan M (1995) Application of membrane technology in food industry for cleaner production. United Nations Industrial Development Organization (UNIDO) Technical Paper No. 8-6-95, Vienna, Austria, 44 p 207. Wang LK (1995) The state-of-the-art technologies for water treatment and management. United Nations Industrial Development Organization (UNIDO) Training Manual No. 8-895, Vienna, Austria, 145 p 208. Wang LK, Wang MHS (1995) Bubble dynamics and material balances of dissolved gas flotation process. Water Treat 10(1995):41–54 209. Viitasaari M, Jokela P, Heinänen J (1995) Dissolved air flotation in the treatment of industrial wastewater with a special emphasis on forest and foodstuff industries. Water Sci Tech 31 (3-4):299–313 210. Wang LK, Wang P, Clesceri NL (1995) Groundwater decontamination using sequencing batch processes. Water Treat 10(1995):121–134 211. Wang LK, Wang MHS (1995) Laboratory simulation of water and wastewater treatment processes. Water Treat 10(1995):261–282 212. Carawan RE, Valentine EG (1996) Dissolved Air Flotation Systems (DAF’s) for Bakeries. North Carolina Cooperative Extension Service, CD-43, March 1996 213. Gnirss R, Peter-Fröhlich A (1996) Biological treatment of municipal wastewater with deep tanks and flotation for secondary clarification. Water Sci Tech 34(3–4):257–265 214. Wang LK (1996) Potable water treatment using dissolved air flotation. OCEESA J 13 (1):12–16 215. Guss D, Klaer RL (1997) Improvement of biological wastewater systems using dissolved air flotation. In: Water Environment Federation’s Conference, October 19–22, Chicago, IL, USA 216. Wang LK (1997) City of cape coral reverse osmosis water treatment facility. US Department of Commerce, National Technical Information Service, Springfield, Virginia 22161, USA. 15 p

1 Humanitarian Engineering Education of the Lenox Institute of Water Technology. . .

71

217. Mels AR, Van Nieuwenhuijzen AF, Van der Graaf JHJM, Klapwijk A, De Koning J, Rulkens WH (1998) Sustainability criteria as a tool in the development of new sewage treatment methods. Options for Closed Water Systems, Wageningen 218. Krofta M, Wang LK (1985) Application of dissolved air flotation to the Lenox, Massachusetts water supply: water purification by flotation. J New Engl Water Works Assocation 99 (3):249–264 219. Krofta M, Wang LK (1985) Application of dissolved air flotation to the Lenox, Massachusetts water supply: sludge thickening by flotation and lagoon. J New Engl Water Works Assoc 99 (3):265–284 220. Forestell W, Wang LK (1991) Air flotation and sand filtration: a success for innovation in Pittsfield, MA. J New Engl Water Works Assoc 105(3):223–243 221. Wang LK, Fahey EM, Wu Z (2005) Dissolved air flotation. In: Wang LK, Hung YT, Shammas NK (eds) Physicochemical treatment processes. Humana Press, Totowa, NJ, USA, pp 431–500 222. Wang LK, Shammas NK, Aulenbach DB, Selke WA, Guss DB (2010) Pittsfield water treatment plant: once the world’s largest flotation-filtration plant. In: Wang LK, Shammas NK, Selke WA, Aulenbach DB (eds) Flotation technology. Humana Press, Totowa, NJ, USA, pp 485–502 223. Wang LK (2006) Adsorptive bubble separation and dispersed air flotation. In: Wang LK, Hung YT, Shammas NK (eds) Advanced physicochemical treatment processes. Humana Press, Totowa, NJ, USA, pp 81–122 224. Wang LK (2018) Development and construction of the first two potable DAF-filtration plant in two America continents. J New Engl Water Works Assoc (2018):90–95 225. Wang LK (2007) Emerging flotation technologies. In: Wang LK, Hung YT, Shammas NK (eds) Advanced physicochemical treatment technologies. Humana Press, Totowa, NJ, USA, pp 449–484 226. Wang LK, Shammas NK, Selke WA, Aulenbach DB (2010) Flotation technology. Humana Press, Totowa, NJ, USA, 680 p 227. Shammas NK, Wang LK, Guild J, Pollock D (2009) Vertical shaft bioreactors. In: Wang LK, Shammas NK, Hung YT (eds) Advanced biological treatment processes. Humana Press, Totowa, NJ, USA, pp 59–108 228. Wang LK, Li Y (2009) Sequencing batch reactors. In: Wang LK, Pereira NC, Hung YT (eds) Biological treatment processes. Humana Press, Totowa, NJ, USA, pp 459–512 229. Wang LK, Kurylko L, Wang MHS (1994). Sequencing batch liquid treatment. US Patent 5354458, October 11, 1994 230. Wang LK, Shammas NK, Wu BC (2010) Electroflotation. In: Wang LK, Shammas NK, Selke WA, Aulenbach DB (eds) Flotation technology. Humana Press, Totowa, NJ, USA, pp 165–198 231. Shammas NK, Wang LK (2016) Water engineering: hydraulics, distribution and treatment. Wiley, Hoboken, NJ, USA, 806 p 232. Wang LK, Hung YT, Shammas NK (2004) Physicochemical treatment processes. Humana Press, Totowa, NJ, USA. 723 p 233. Reh CW (1979) Lime-soda softening processes. In: Sanks RL (ed) Water treatment plant design. Ann Arbor Science, MI, USA, pp 567–596 234. Wang LK, Wu J, Shammas NK, Vaccari DA (2004) Recarbonation and softening. In: Wang LK, Hung YT, Shammas NK (eds) Physicochemical treatment processes. Humana Press, Totowa, NJ, USA, pp 199–228 235. Wang LK, Chen JP, Hung YT, Shammas NK (2011) Membrane and desalination technologies. Humana Press, Totowa, NJ, USA, 716 p 236. Wang LK, Duchesnel S (2019) Personal communication, email, August 26, 2019. Steve Duchesnel, Superintendent of Operations, Lowell Regional Utility, City of Lowell, MA, USA (www.Lowell.org)

72

L. K. Wang

237. Joykutty S, Ranganathan K (2019) Reducing poverty through economic growth: MCC’s water investment in Mongolia. Clear Waters 49(2):57–59 238. Daley D, Anderson G (2019) Humanitarian engineering: education and application. Clear Waters 49(2):16–21 239. Wang MHS, Wang LK (2016) Glossary of land and energy resources engineering. In: Wang LK, Wang MHS, Hung YT, Shammas NK (eds) Natural resources and control processes. Springer, New York, USA, pp 493–623 240. Wang MHS, Wang LK (2015) Environmental water engineering glossary. In: Yang CT, Wang LK (eds) Advances in water resources engineering. Springer, New York, pp 471–556 241. Edzwald JK (1995) Principles and applications of dissolved air flotation. Water Sci Technol 31 (3–4):1–23 242. Edzwald JK (2007) Fundamentals of dissolved air flotation. J New Engl Water Works Assoc 121(3):89–112 243. Edzwald JK (2007) Developments of high rate dissolved air flotation for drinking water treatment. J Water Supply Res Technol AQUA 56(6–7):399–409 244. Edzwald JK, Malley JP Jr, Yu C (1990) A conceptual model for dissolved air flotation in water treatment. Water Supply 8:141–150 245. Edzwald JK, Walsh JP, Kaminski GS, Dunn HJ (1992) Flocculation and air requirements for dissolved air flotation. J Am Water Works Assoc 84(3):92–100 246. Edzwald JK, Olson SC, Tamulonis CW (1994) Dissolved air flotation: field investigations. American Water Works Association Research Foundation, Denver 247. Edzwald JK, Tobiason JE, Amato T, Maggi LJ (1999) Integrating high rate dissolved air flotation technology into plant design. J Am Water Works Assoc 91(12):41–53 248. Edzwald JK, Tobiason JE, Parento LM, Kelley MB, Kaminski GS, Dunn HJ, Galant PB (2000) Giardia and Cryptosporidium removals by clarification and filtration under challenge conditions. J Am Water Works Assoc 92(12):70–84 249. Edzwald JK, Tobiason JE, Udden C, Kaminski GS, Dunn HJ, Galant PB, Kelley MB (2003) Evaluation of the effect of recycle of waste filter backwash water on plant removals of Cryptosporidium. J Water Supply Res Technol AQUA 52(4):243–258 250. Edzwald JK, Han M (2007) In: Edzwald JK, Han M, editors. The 5th international conference on flotation in water and wastewater systems. Seoul National University, Seoul, South Korea, p 393 251. Edzwald JK, Kaminski GS (2009) A practical method for water plants to select coagulant dosing. J New Engl Water Works Assoc 123(1):15–31 252. Edzwald JK, Kelley MB (1998) Control of Cryptosporidium: from reservoirs to clarifiers to filters. Water Sci Technol 37(2):1–8 253. Edzwald JK, Wingler BJ (1990) Chemical and physical aspects of dissolved air flotation for the removal of algae. J Water Supply Res Technol AQUA 39(2):24–35

Chapter 2

Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee, Massachusetts, USA Lawrence K. Wang, Mu-Hao Sung Wang, and Edward M. Fahey

Contents 1 2 3 4 5

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Description of the Lee Flotation-Filtration Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Criteria for the Lee Flotation-Filtration Clarifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Description of Lee Flotation-Filtration Clarifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Chemical Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Dissolved Air Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Dual Media Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Comparison of the Innovative Lee Flotation-Filtration Plant with Conventional Water Treatment Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Start-Up Operation of the Lee Flotation-Filtration Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Current Operation of the Lee Flotation-Filtration Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Corrosion Control for Compliance with the Federal Lead and Copper Rule . . . . . . . . 8.2 Removal of Perchlorate, Barium, Sodium, DBPs, THMs, HAAs, Microbial Contaminants, Turbidity, Iron, and Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Further Study of Dissolved Air-Ozone Flotation for Potable Water Treatment . . . . . . 10.2 Further Study of Arsenic Removal by DAF-ABF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Detailed Study of Filter Backwash Water Recycle in DAF Systems . . . . . . . . . . . . . . . . . 10.4 Further Study of Sequential Batch DAF Developed by Dr. Lawrence K. Wang . . . . 10.5 More Theoretical and Kinetic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6 Further Development and Improvement to DAF-ABF Systems . . . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 75 76 77 78 78 78 81 81 82 83 83 84 85 87 87 87 87 87 88 88 88 90

Abstract The Town of Lee’s potable flotation-filtration plant in Massachusetts, USA, with a design capacity of 2.0 MGD (7570 m3/day) was commissioned in December 1998 to serve a population of approximately 6400 residents. The Lee plant utilizes the following treatment processes: chemical addition, oxidation,

L. K. Wang (*) · M.-H. S. Wang · E. M. Fahey Lenox Institute of Water Technology, Newtonville, NY, USA © Springer Nature Switzerland AG 2021 L. K. Wang, M. -H. S. Wang, N. K. Shammas, D. B. Aulenbach (eds.), Environmental Flotation Engineering, Handbook of Environmental Engineering 21, https://doi.org/10.1007/978-3-030-54642-7_2

73

74

L. K. Wang et al.

coagulation, dissolved air flotation, automatic backwash dual media filtration, and disinfection/corrosion control. To comply with the required filtering of their three surface water sources, the town chose to install an innovative dissolved air flotation (DAF) system as the best and most economical answer to their needs. In clarification of the design 2.0 MGD (7570 m3/day) flow, two Krofta Sandfloat SAF BP-24 dissolved air flotationfiltration (DAFF) clarifiers were utilized as the main treatment system in the plant. This chapter presents the overall structural design, design criteria, and performance data of the Krofta Sandfloat flotation-filtration clarifiers (DAFF) installed at the Lee plant for the treatment of surface water for potable purposes. This chapter has been written in memory of the late Dr. Milos Krofta, who was the President of the Lenox Institute of Water Technology (LIWT) and Krofta Engineering Corporation (KEC), and the late Professors Dr. Donald B. Aulenbach and Dr. William A. Selke of LIWT. LIWT invented and patented the innovative DAFF system, while KEC manufactured and installed the Lee plant. The current corrosion control program in order to comply with the US Federal Copper and Lead Rule and the current DAF-filtration plant’s performance for the removal of perchlorate, barium, sodium, disinfection by-products (DBP), total trihalomethane (THM), total haloacetic acid (HAA), microbial contaminants, turbidity, iron, and manganese are also discussed. The 19-year-old innovative Lee DAF-filtration plant met all US Environmental Protection Agency and Commonwealth of Massachusetts primary and secondary drinking water standards in accordance with the 2018 Water Quality Report. The town successfully uses zinc orthophosphate and pH adjustment to stabilize the water throughout the Lee distribution system for lead, copper, and pipe corrosion control. Keywords Milos Krofta · Donald B. Aulenbach · William A. Selke · Lenox Institute of Water Technology · Krofta Engineering Corporation · Dissolved air flotation · DAF · DAF-filtration · DAFF · Potable water · Backwash · Lead · Copper · Corrosion control · Zinc orthophosphate · Recommended future research · Sandfloat BP · Lee · Massachusetts · USA · Memoir

Acronyms and Nomenclature ABF ADT AL Al2(SO4)3 Cl2 DAF DAFF DBP DEP DGF FDA

Automatic backwash filtration Air dissolving tube Action level Aluminum sulfate Chlorine Dissolved air flotation Dissolved air flotation-filtration clarifier Disinfection by-products Massachusetts Department of Environmental Protection Dissolved gas flotation US Food and Drug Administration

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

GAC GPM HAA KEC KMnO4 Krofta Sandfloat LIWT MCL MCGL MGD Na2Al2O4 NaOH ND PLC PPB PPM TT US EPA VOC

75

Granular activated carbon Gallons per minute Haloacetic acid Krofta Engineering Corporation, USA Potassium permanganate DAFF clarifier Lenox Institute of Water Technology, USA Maximum contaminant level Maximum contaminant level goal Million gallons per day Sodium aluminate Sodium hydroxide Non-detection Programmable logic controller Parts per billion Parts per million Treatment technique US Environmental Protection Agency Volatile organic carbon

1 Background The history of this type of dissolved air flotation technology for the treatment of potable water began in 1982 with the installation of an innovative 1.2 MGD (4542 m3/day) design capacity dissolved air flotation (DAF) system for the Town of Lenox, Massachusetts, USA. This clarifier (Krofta Sandfloat type SAF) was designed to treat only about 2.5 GPM/FT2 (0.102 m3/min/m2); today, this rate has increased to a hydraulic loading of 5.0 GPM/FT2 (0.204 m3/min/m2) due to improved design. These design improvements include incorporation of inclined plates, an additional layer of anthracite coal for dual media filtration, air-assisted backwashing, and several other proprietary changes. In the years since this first installation, there have been many other communities which have chosen to install this type of dissolved air flotation clarifier for the treatment of their municipal potable water supplies. Municipalities in the states of New York, Massachusetts, New Jersey, Pennsylvania, and Indiana have all benefited from choosing DAF technology over conventional treatment consisting of chemical feeding, mixing coagulation/flocculation, and sedimentation followed by filtration. DAF is one of the dissolved gas flotation (DGF) processes. The readers are referred to the Glossary section for the details of DGF, DAF, etc., and the References section for the literature of potable water treatment plants [1–54].

76

L. K. Wang et al.

2 Introduction The Town of Lee is located in the Berkshire Hills of Western Massachusetts, USA. The town’s population is approximately 6400 persons. Two main surface water sources for potable purposes are utilized, Leahey and Schoolhouse Reservoirs, which supply approximately 1.2 MGD (4542 m3/day) to the town. A third small source (Vanetti Reservoir) is utilized only as an emergency water supply as needed. Before 1998, the town utilized chlorination alone for the treatment of Leahey and Vanetti Reservoirs, which are characterized by low to moderate turbidity, color, and trihalomethane (THM) precursors. Schoolhouse Reservoir was unable to be utilized without clarification due to high levels of turbidity, color, iron, and manganese present. The center of the Lee flotation-filtration facility is a package plant consisting of chemical pretreatment, coagulation, dissolved air flotation, and automatic backwash filtration (ABF) (trade name: Krofta Sandfloat BP). On-site pilot plant testing was conducted from 1994 to 1996 (using a 5-ft-diameter pilot plant system shown in Fig. 2.1), with plant construction and start-up in 1997–1998 (installing a 24-ftdiameter full-scale plant shown in Fig. 2.2). In this chapter, Lee water quality, treatment plant design, construction, water clarification performance, and chemical pretreatment are discussed. Performance and operational data from 6 months of operation on Leahey Reservoir are summarized.

Fig. 2.1 Krofta Engineering Corporation’s DAF-filtration pilot trailer (Sandfloat Type SAF-BP-5; 5-inch diameter)

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

77

Fig. 2.2 A full-scale DAF-filtration water treatment plant (Krofta Sandfloat Type SAF-BP-24; 24-inch diameter)

3 General Description of the Lee Flotation-Filtration Plant The Lee plant employs the following stages of treatment for water purification: (a) chemical addition and mixing, (b) oxidation, (c) coagulation, (d) clarification by dissolved air flotation (DAF), (e) dual media filtration, and (f) disinfection/corrosion control. The following is a brief description of the process flow scheme utilized at the Lee plant: gravity flow from either Schoolhouse or Leahey Reservoir is directed to a turbine to generate electricity for the treatment plant. Water then flows to a small mixing tank where it is injected with chlorine (Cl2), sodium hydroxide (NaOH), and, when treating Schoolhouse Reservoir water, potassium permanganate (KMnO4). Chemically treated water then flows through two baffled pre-oxidation tanks with approximately 77,500-gallon (293 m3) total capacity to allow a minimum of almost 1-hour retention time at design flow to oxidize the manganese and iron present in Schoolhouse Reservoir. After leaving the pre-oxidation tanks, water is injected with sodium aluminate (Na2Al2O4) and aluminum sulfate (Al2(SO4)3) for coagulation and passed through a static mixer. The flow then enters the inlet chamber of the flotationfiltration unit for clarification by dissolved air flotation and dual media filtration. Filtered water leaving the clarifier is dosed with chlorine for disinfection and zinc orthophosphate for corrosion control and is pumped to two 560 dia.  420 high (17.1 m dia.  12.8 m high) 775,000 gallon (2933.4 m3) effluent storage tanks which in turn supply the town distribution system via gravity flow. The treatment building housing the clarifiers, chemical storage and dosing equipment, laboratory, turbine, and mixing tank has a total footprint of 720  940 ¼ 6768 ft2 (22 m  28.7 m ¼ 631 m2); the pre-oxidation tanks and effluent storage tanks are located outside, adjacent to the treatment building.

78

L. K. Wang et al.

4 Design Criteria for the Lee Flotation-Filtration Clarifiers Specific design criteria for each Krofta flotation-filtration clarifier (DAFF) at the Lee plant are listed as follows: Design flow: Clarifier diameter: Clarifier retention time: Total filter area: DAF hydraulic loading: No. of filter cells: Filter cell area: Filtration rate: Anthracite coal media: Quartz sand media: Filter backwash (full): Filter backwash (partial):

2.0 MGD (7570 m3/day) 24 feet (7.3 meter) 16 min 400 FT2 (37.2 m2) 3.5 GPM/FT2 (0.141 m3/min/m2) 17 23.5 FT2 (2.19 m2) 3.5 GPM/FT2 (0.141 m3/min/m2) 1200 (30.5 cm) layer of 1.1 mm dia. 1200 (30.5 cm) layer of 0.35 mm dia. 20 GPM/FT2 (0.812 m3/min/m2) 16 GPM/FT2 (0.650 m3/min/m2)

5 Mechanical Description of Lee Flotation-Filtration Clarifiers The following is a detailed description of how the package Krofta Sandfloat BP flotation-filtration clarifiers function. Figure 2.3 shows a bird’s eye view of a Krofta Sandfloat Type SAF-BP system, while Fig. 2.4 shows the features and advantages of this innovative DAF-filtration (DAFF) system.

5.1

Chemical Treatment

The chemically pretreated water enters the bottom of the central flocculator, an internal mixing chamber separate from the rest of the unit, and flows tangentially Fig. 2.3 A bird’s eye view of a Krofta Engineering Corporation’s DAFfiltration water treatment plant (Sandfloat Type SAF-BP)

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

79

Fig. 2.4 Special features and advantages of a DAF-filtration package plant (Krofta Sandfloat Type SAF-BP)

in a slow mix to allow chemical reactions to occur and flocs to form. Detention time in this inner chamber at 2.0 MGD (7570 m3/day) is approximately 1.2 minutes.

5.2

Dissolved Air Flotation

After the chemical pretreatment/slow mixing stage, the water reaches the top of the flocculator where a stream of aerated, filtered water at approximately 277 GPM (1.05 m3) or 20% of the raw flow containing microbubbles in the 80-micron range is

80

L. K. Wang et al.

Fig. 2.5 Innovative air dissolving tube (ADT) system

added. This aerated water is created by injecting compressed air into an air dissolving tube (ADT) which dissolves the air into the water (see Fig. 2.5). The internal ADT pressure is approximately 65–75 psi (448–517 kPa); 20–30 SCFH (0.57–0.85 standard m3/h) of compressed air is added and dispersed into the tube

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

81

through multiple porous plastic panels. Water spiraling past the panels picks up the air and carries it to the pressure release points at the top of the flocculator. Upon release to atmospheric pressure, the air comes out of solution in the form of millions of tiny bubbles, giving the water a “milky white” appearance. Flow and pressure are controlled by several globe type throttling valves. Excess, undissolved air is purged from the center of the ADT in a side stream of air and water piped to drain to prevent coalescing and formation of larger bubbles which are not conducive to optimum flotation. When in contact with the raw water stream, the microbubbles in the aerated water stream attach to the flocs formed by chemical addition, reducing their density to less than that of water resulting in flotation of the agglomerates to the surface of the unit where they collect in a scum layer of up to several inches deep. The scum layer is then removed by a rotating spiral scoop mounted on a traveling carriage and discharged into a central sludge well and ultimately to the POTW (Publicly Owned Treatment Works). The floated sludge TS consistency ranges from 1% to 2% solids depending upon operator adjustment of the spiral scoop speed and clarifier water depth. The clarified water then flows downward through a series of inclined plates which act as a “water break,” reducing the velocity of the water which allows any remaining flocs to float to the surface for removal.

5.3

Dual Media Filtration

Below the inclined plates, the water passes through a 1200 (30.5 cm) layer of 1.1-mm crushed anthracite coal followed by a 1200 (30.5 cm) layer of 0.35-mm-diameter quartz sand. Filtered water is collected in a slotted pipe arrangement below the media beds which retains the media while allowing filtered water to pass into an external annular ring where it is discharged to a chlorination station. The rotating carriage stops periodically to individually and automatically backwash each of the sectors of the filter bed in sequence. Compressed air is used in conjunction with a flow of filtered water to cleanse the media during backwashing. A two-stage backwash flow is employed, first at a rate of 20 GPM/FT2 (0.812 m3/min/m2) for 60–90 seconds followed by a partial flow of approximately 16 GPM/FT2 (0.650 m3/min/m2) for 25–35 seconds to redistribute the media. The backwash water (containing any small particles which were captured by the filter beds) is collected in a hood equipped with a fabric reinforced EPDM flexible seal which inflates to isolate each cell during backwashing. The hood is attached to the rotating carriage and directs backwash water back to the inlet flocculator for optional re-treatment or to POTW. The previously described flotation enhancing inclined plates also serve to retain the media during the backwashing process. After the backwash sequence is completed, the hood seal deflates, and flow passing through the freshly backwashed media (first filtrate water) is directed to the air dissolving system supply pump for a predetermined period of time to allow

82

L. K. Wang et al.

turbidity levels to stabilize prior to being sent to the final clarified effluent storage tanks. All processes described are controlled by a dedicated PLC (programmable logic controller) tied to the treatment plant main computer system.

6 Comparison of the Innovative Lee Flotation-Filtration Plant with Conventional Water Treatment Plant In terms of water treatment plant’s flow diagram, there is very little difference between a conventional water treatment plant and an innovative DAF-filtration water treatment plant. Generally, a conventional water treatment plant (conventional water filtration plant) includes at least the unit operations and unit processes of screening, pumping, rapid mixing for chemical feeding, flocculation, sedimentation, filtration, post-disinfection, corrosion control, storage and water distribution, and, of course, also waste disposal. On the other hand, an innovative dissolved air flotation water treatment plant (innovative dissolved air flotation water filtration plant) includes at least the unit operations and unit processes of screening, pumping, rapid mixing for chemical feeding, flocculation, dissolved air flotation, filtration, post-disinfection, corrosion control, storage and water distribution, and waste disposal. It appears that the only difference is that DAF clarification in the innovative water plant replaces the sedimentation clarification in the conventional water plant. There are several key differences between a conventional water treatment system which utilizes sedimentation followed by filtration in two separate steps and the Lee flotation-filtration plant (DAFF plant). The Krofta Sandfloat BP unit is an innovative two-stage clarifier that incorporates dissolved air flotation with dual media filtration in one footprint, which minimizes space requirements. Use of dissolved air flotation also allows higher possible hydraulic loading rates (up to 5 GPM/FT2 (0.204 m3/ min/m2) as opposed to up to 2 GPM/FT2 (0.081m3/min/m2) for typical sedimentation) and reduced overall clarifier diameter. The total treatment detention time of the Lee flotation-filtration plant including chemical pretreatment, oxidation, coagulation, flotation, and dual media filtration is approximately 71 minutes. Of this time, approximately 55 minutes at design flow is utilized for oxidation of dissolved metals prior to removal by dissolved air flotation. Because of the DAF clarifiers’ compact design and short 16-minute retention time (two units for complete redundancy, each having a diameter of 24 feet (7.3 meter) and a depth of 7 feet (2.1 meter)), capital equipment installation costs and building size requirements were all reduced when compared to a conventional treatment system. Smaller size also allows fast start-up of the clarifiers, with full flow reached within 5 minutes of activation. The Lee unit employs semi-continuous backwashing of the segmented filter bed, with optional recycling of the backwash water to the central inlet chamber for

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

83

re-treatment to minimize waste. Due to the low volume used in backwashing the innovative Lee clarifiers, the supply water can be provided from the clarified effluent piping, effectively eliminating the need for large capacity backwash water storage tanks such as required by standard filtration units.

7 Start-Up Operation of the Lee Flotation-Filtration Plant Start-up plant operation has been very successful in treating the Leahey and Schoolhouse Reservoirs for potable purposes. All pilot-scale and full-scale operational data can be found in Edward M. Fahey’s Master of Engineering thesis, entitled “PilotScale Demonstrations and Full-Scale Operation of Potable Water Flotation-Filtration Plants” (Lenox Institute of Water Technology, Massachusetts, USA; January 7, 2001; 91 pages; Major Research Advisor Dr. Lawrence K. Wang). Based on a summary of 6 months of Leahey Reservoir treatment performance data, the authors have reviewed and summarized in below. A review of these data indicates that the treated water flow increased in the summer months to an average high of 1,237,656 GPD (4684.5 m3/day) in July 1999. The single highest recorded flow of the year was on June 28 with 1,491,512 GPD (5645.4 m3/day). Leahey Reservoir raw water temperature ranged from 57  F (14  C) to 75  F (24  C) over the 6-month data range. Influent pH averaged 5.6 and effluent 6.3 units. Influent turbidity averaged 0.8 NTU and effluent averaged 0.07 NTU for a removal efficiency of over 91%. Effluent aluminum and iron levels were both well below required discharge limits, averaging 0.007 mg/L and 0.023 mg/L, respectively. The Town of Lee currently employs two full-time operators for the treatment plant. Complete automation includes continuous monitoring of pH, turbidity, chlorine residual, and flow with alarms to alert the operator of any malfunction. Typical chemical dosage for coagulation of Leahey Reservoir consists of a low dose of sodium hydroxide (to raise the pH to 6.5–7) followed by 0.5 mg/L of sodium aluminate and 12–15 mg/L of aluminum sulfate (as AL2(SO4)3). Estimated cost for this level of chemical pretreatment is approximately $0.01/1000 gallons ($0.01/ 3.785 m3) treated. These were the year 2001 costs.

8 Current Operation of the Lee Flotation-Filtration Plant 8.1

Corrosion Control for Compliance with the Federal Lead and Copper Rule

Soluble copper is an essential nutrient to human health, but some people who drink water containing copper in excess of the action level of 1.3 ppm over a relatively

84

L. K. Wang et al.

short period of time could experience gastrointestinal distress. Some people who drink water containing copper in excess of the copper’s action level over many years could suffer liver and/or kidney damage. People with Wilson’s disease should consult their personal doctor. Lead exposure remains a concern for pregnant and lactating women. There is increasing awareness that exposures to lead adversely affect maternal and infant health, including the ability to become pregnant, maintain a healthy pregnancy, and have a healthy baby. Lead is also an established risk factor for hypertension in adults. The action level of lead in drinking water is 15 ppb. It is known that lead in drinking water is primarily from materials and components associated with water distribution service lines and home plumbing system. A water treatment plant is responsible for providing high-quality drinking water throughout the water distribution system; therefore, corrosion control as the last step of water treatment is required. However, a water treatment plant cannot control the variety of materials used in home plumbing components. When a water consumer’s water is sitting for several hours, he/she can minimize the potential for lead exposure by flushing the tap water for 30 seconds to 2 minutes before using water for drinking or cooking. Following the passage of the Federal Lead and Copper Rule and initial copper and lead sampling in 1991, the Lee Water Department failed to meet the regulated action levels (AL) of copper and lead. The Commonwealth of Massachusetts Department of Environmental Protection (DEP) distributed the notification, bill stuffers, etc., to the Town of Lee forcing the town to comply with regulations until a water treatment facility could be constructed [54]. In 1998, the Town of Lee completed construction of the innovative dissolved air flotation potable water filtration plant. A combined pH adjustment and zinc orthophosphate addition stabilizes the water throughout the Lee water distribution system, reducing the aggressive and corrosive action of the water and therefore reducing copper and lead concentrations. The town’s water is now under the AL for lead (15 ppb) and the AL for copper (1.3 ppm) based on the water samples taken in September 2018 [54].

8.2

Removal of Perchlorate, Barium, Sodium, DBPs, THMs, HAAs, Microbial Contaminants, Turbidity, Iron, and Manganese

Quantitatively, the Town of Lee’s DAF-filtration plant is well positioned to treat up to 2 million gallons a day (2 MGD), and its water supply is abundant [54]. Qualitatively, any water treatment plant (including Lee plant) is responsible for the removal of contaminants in drinking water supply, such as the following: (a) Microbial contaminants: They include viruses, bacteria, etc., which may come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife. Determination of total coliforms (as an indicator) is for controlling microbial contaminants.

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

85

(b) Organic chemical contaminants: They include synthetic and volatile organic chemicals (VOCs), which are the by-products of industrial processes and petroleum production, and can also come from gas stations, urban stormwater runoff, and septic systems. (c) Pesticide and herbicide contaminants: They may come from a variety of sources such as agricultural livestock operations and urban stormwater runoff. (d) Inorganic contaminants: They include salts and soluble metals, which can be naturally occurring or result from urban stormwater runoff, industrial or domestic wastewater discharge, oil and gas production, mining or farming, etc. (e) Radioactive contaminants: They can be naturally occurring or be the result of oil and gas production and mining activities. Each year the Town of Lee conducts water quality testing according to the requirements set by the DEP and the US Environmental Protection Agency (US EPA). In order to ensure that the Lee plant’s tap water is safe to drink, the US EPA prescribes the Primary Drinking Water Standards and the Secondary Drinking Water Standards that limit and recommend, respectively, the amount of the above contaminants in water provided by the public water systems, such as the Lee plant. It should be noted that the US Food and Drug Administration (FDA) only limits the contaminant level in bottled water. Table 2.1 summarizes the drinking water quality of the Town of Lee’s DAFfiltration plant in 2018. It appears that the innovative DAF-filtration plant has successfully removed perchlorate, barium, sodium, disinfection by-products (DBPs), total trihalomethanes (THMs), total haloacetic acids (HAAs), microbial contaminants, turbidity, iron, and manganese from raw reservoir water. The readers are referred to the Glossary section for the definitions of action levels (AL), maximum contaminant level (MCL), maximum contaminant level goal (MCGL), treatment technique (TT), 90th percentile level, etc.

9 Conclusion This chapter introduces mainly the structural design, design criteria, and water purification performance data for the Lee flotation-filtration plant. Improved design has allowed the hydraulic limit of the Krofta Sandfloat clarifier to be increased from 2.5 GPM/FT2 (0.102 m3/min/m2) in 1982 to up to a design 5.0 GPM/FT2 (0.204 m3/min/m2) in 1999. Based on the operation and performance data generated during the Lee plant’s start-up period in 1999 and now in 2018, the innovative Lee plant consisting of chemical pretreatment, oxidation, coagulation-flocculation, dissolved air flotation, automatic backwash dual media filtration and disinfection, and corrosion control has proven to be a feasible system for water purification for over 19 years.

20

Copper

Secondary contaminants Iron ND Manganese 0.0077

Disinfection by-products Total 56 Avg. range 25.0–110.0 trihalomethane PPB Total haloacetic 30.0 Avg. range 21.0–46.0 acid PPB Microbial contaminants Turbidity 0.091 NTU

Barium 0.0064 PPM Unregulated contaminants Sodium 9.9 PPM

. Contaminant Level detected (units) Inorganic contaminants Perchlorate ND PPM

15 PPB

20

None None

None

TT-0.3 NTU 0.3 0.05

None

None

None

60 PPB

2.0 PPM

None

0 PPM

0.0020 PPM 2.0 PPM

80 PPB

MCLG

0.055 PPM

3.8 PPB

90th percentile

MCL

1.3 PPM

AL

Sites sampled

Contaminant (units) Lead and copper Lead

2018 2018

2018

2018

2018

2018

2014

2018

Sample date

Sept. 2018 Sept. 2018

Sample date

No No

No

Yes

No

No

No

No

Violation

0

0

Exceeding AL

Corrosion of household plumbing system Corrosion of household plumbing system

Possible source of contamination

Naturally occurring Naturally occurring

Soil runoff

By-product of drinking water chlorination (see front page)

By-product of drinking water chlorination

By-product of corrosion control, naturally occurring

Fireworks, flares, rocket propellants, and blasting agents Erosion of natural deposits

Possible source of contamination

No

No

Violation

Table 2.1 The 2018 water quality report of the Lee dissolved air flotation potable water filtration plant in Massachusetts, USA

86 L. K. Wang et al.

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

87

It is concluded that the innovative Lee flotation-filtration plant represents a costeffective, feasible treatment solution that warrants consideration by all municipalities. Although Lee flotation-filtration plant is a DAF-ABF package plant shown in Figs. 2.2, 2.3, and 2.4, any potable water plants with separate, individual DAF, and filtration unit processes will perform equally well [55]. DAF is now a main stream potable water treatment process. It has also been demonstrated that a combination of pH adjustment and zinc orthophosphate addition is an excellent method for corrosion control and, in turn, for complying with the Federal Copper and Lead Rule.

10 10.1

Recommendations Further Study of Dissolved Air-Ozone Flotation for Potable Water Treatment

Pilot plant testing for the Town of Lee, MA, included some operation of the DAF-ABF pilot unit with ozone (O3) in a pretreatment stage. The main purpose was to evaluate the possibility of utilizing ozone for precipitation of the iron and manganese present in the raw water into an insoluble form prior to removal by the dissolved air stage. The evaluation had to be abandoned before completion due to time constraints but did show some promise as an alternative to the chemical pretreatment program of potassium permanganate. It was visually noted the addition of O3 to the raw water produced a floatable floc and yielded significant reductions in iron and manganese levels similar to the permanganate. Dosages were not able to be optimized, however. Additional evaluation of ozone as an oxidizing agent or coagulant for the treatment of potable water with DAF-ABF units is recommended.

10.2

Further Study of Arsenic Removal by DAF-ABF

Treatment of groundwater contaminated with arsenic by DAF-ABF technology is a potential application which has not been thoroughly explored.

10.3

Detailed Study of Filter Backwash Water Recycle in DAF Systems

The recycling of backwash water for re-treatment in potable applications introduces several questions with regard to the actual impact recycling has on final effluent qualities and chemical pretreatment dosages. Further testing is recommended.

88

10.4

L. K. Wang et al.

Further Study of Sequential Batch DAF Developed by Dr. Lawrence K. Wang

Wang, Kurylko, and Wang (1994) and Wang and Clesceri (1995) invented and described, respectively, a sequential batch DAF process which was developed for groundwater decontamination. This should be further investigated as an alternative to the DAF-ABF unit for the treatment of contaminated groundwater [31, 35, 36].

10.5

More Theoretical and Kinetic Studies

Theoretical and kinetic studies of DAF systems will lead to a more complete understanding of system dynamics and perhaps will provide models for a more energy-efficient unit [41–53].

10.6

Further Development and Improvement to DAF-ABF Systems

The DAF-ABF water clarifier (Krofta type SAF-BP) utilized for the testing of potable water sources presented in this chapter was a third-generation DAF clarifier which has been developed over the past 20 years. Continued advances and modifications to the unit as tested will facilitate increased acceptance of this device by municipalities and consulting engineers for the treatment of surface waters for potable purposes. The following are the recommended specific improvements which should be investigated in the future: • Utilization of ozone instead of oxygen for production of dissolved air • Improved head loss measuring devices to minimize backwashing and save energy consumption. • Inclusion of lamella plates in the flocculation section for higher possible hydraulic loading rates (>5.0 gpm/ft2) • Evaluation of replacing the anthracite media with a layer of GAC in the filter bed sectors for removal of VOC from contaminated groundwater Acknowledgments This research was sponsored by a research grant from the Lenox Institute of Water Technology. At the time of this research investigation, Lawrence K. Wang, Mu-Hao Sung Wang, and Edward M. Fahey were Acting President (Dean and Professor), Adjunct Professor, and Research Assistant/Graduate Student (Master of Engineering in Water Technology), respectively. The late Dr. Donald B. Aulenbach also provided advice to this research. This chapter has been written in memory of the late Dr. Milos Krofta (former President of Lenox Institute of Water Technology and former President of Krofta Engineering Corporation) and the late Dr. and Professor Donald B. Aulenbach.

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

89

Glossary [37–40, 54] 90th percentile level: It means that out of ten sites sampled, nine out of ten were at or below this level. Action level (AL): The concentration of a contaminant which, if exceeded, triggers water treatment or other requirements which a water system must follow. Conventional water treatment plant (conventional water filtration plant): It includes at least the unit operations and unit processes of screening, pumping, rapid mixing for chemical feeding, coagulation-flocculation, sedimentation, filtration, post-disinfection, corrosion control, storage and water distribution, and waste disposal. Copper: Soluble copper is an essential nutrient to human health, but some people who drink water containing copper in excess of the action level of 1.3 ppm over a relatively short period of time could experience gastrointestinal distress. Some people who drink water containing copper in excess of the copper’s action level over many years could suffer liver and/or kidney damage. People with Wilson’s disease should consult their personal doctor. Disinfection by-product contaminants: Disinfection by-products (DBPs) are organic compounds produced when chlorine and/or bromine are used as the disinfectant(s) to kill microbial contaminants, such as bacteria, in the water supply. These disinfectants react with naturally occurring organic matters forming DBPs. Dissolved air flotation (DAF): One of the dissolved gas flotation (DGF) processes where air is used for generation of gas bubbles. A typical example is Krofta Engineering Corporation’s Supracell clarifier; see dissolved gas flotation (DGF). Dissolved air flotation-filtration (DAFF): A package plant which consists of both dissolved air flotation and filtration. A typical example is Krofta Engineering Corporation’s Sandfloat clarifier. Dissolved gas flotation (DGF): It is a process involving pressurization of gas at 25–95 psig for dissolving gas into water and subsequent release of pressure (to 1 atm) under laminar flow hydraulic conditions for generating extremely fine gas bubbles (20–80 microns) which become attached to the impurities to be removed and rise to the water surface together. The impurities or pollutants to be removed on the water surface are called float or scum which are scooped off by sludge collection means. The clarified water is discharged from the flotation clarifier’s bottom. The gas flow rate is about 1% of influent liquid flow rate. The attachment of gas bubbles to the impurities can be a result of physical entrapment, electrochemical attraction, surface adsorption, and/or gas stripping. The specific gravity of the bubble-impurity agglomerate is less than one, resulting in buoyancy or nonselective flotation (i.e., save-all). Innovative dissolved air flotation water treatment plant (innovative dissolved air flotation water filtration plant): It includes at least the unit operations and unit processes of screening, pumping, rapid mixing for chemical feeding,

90

L. K. Wang et al.

coagulation-flocculation, dissolved air flotation, filtration, post-disinfection, corrosion control, storage and water distribution, and waste disposal. Inorganic contaminants: They include salts and soluble metals, which can be naturally occurring or result from urban stormwater runoff, industrial or domestic wastewater discharge, oil and gas production, mining, or farming. Lead: Lead exposure remains a concern for pregnant and lactating women. There is increasing awareness that exposures to lead adversely affect maternal and infant health, including the ability to become pregnant, maintain a healthy pregnancy, and have a healthy baby. Lead is also an established risk factor for hypertension in adults. The action level of lead in drinking water is 15 ppb. It is known that lead in drinking water is primarily from materials and components associated with water distribution service lines and home plumbing system. A water treatment plant is responsible for providing high-quality drinking water throughout the water distribution system; therefore, corrosion control as the last step of water treatment is required. However, a water treatment plant cannot control the variety of materials used in home plumbing components. When a water consumer’s water is sitting for several hours, he/she can minimize the potential for lead exposure by flushing the tap water for 30 seconds to 2 minutes before using water for drinking or cooking. Microbial contaminants: They include viruses, bacteria, etc., which may come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife. Determination of total coliforms (as an indicator) is for controlling microbial contaminants. Maximum contaminant level (MCL): The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCGLs as possible using the best available treatment technology. Maximum contaminant level goal (MCGL): The level of a contaminant in drinking water below which there is not known or expected risk to health. MCGLs allow for a margin of safety. Organic chemical contaminants: They include synthetic and volatile organic chemicals (VOCs), which are the by-products of industrial processes and petroleum production, and can also come from gas stations, urban stormwater runoff, and septic systems. Pesticide and herbicide contaminants: They may come from a variety of sources such as agricultural livestock operations and urban stormwater runoff. Radioactive contaminants: They can be naturally occurring or be the result of oil and gas production and mining activities. Treatment technique (TT): It is a required process intended to reduce the level of a contaminant in drinking water. 0.5 NTU must be met 95% of the time. The TT was met 100% of the time.

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

91

References 1. Fahey EM (2001) Master of engineering thesis, entitled. Pilot –scale demonstrations and fullscale operation of potable water flotation-filtration plants. (Lenox Institute of Water Technology, Massachusetts, January 7, 2001, 91 pages; Major Research Advisor Dr. Lawrence K. Wang) 2. Kollajtis JA (1991) Dissolved air flotation applied in drinking water clarification. In: Proceedings of the annual AWWA conference – water quality for the new decade, Philadelphia 3. Krofta M, Wang LK (1981) Development of an innovative process system for water purification and recycle. In: Proceedings of American Water Works Association. Water reuse symposium II, vol 2, pp 1292–1315, August 1981 4. Krofta M, Wang LK (1981) Potable water pretreatment for turbidity and color removal by dissolved air flotation and filtration for the Town of Lenox, Massachusetts. U.S. Department of Commerce, National Technical Information Service, Springfield. Report No. PB82-182064, 48 p, October 1981 5. Krofta M, Wang LK, Barris D, Janas J (1981) Treatment of Pittsfield raw water for drinking water production by innovative process systems. US Department of Commerce, National Technical Information Service. Technical Report No. PB82-118795, 87 p 6. Krofta M, Wang LK (1982) Report on projected water treatment plant for the city of Pittsfield, Massachusetts with the application of flotation technology. U.S. Department of Commerce, National Technical Information Service, Springfield. Report No. PB82118779, January 1982 7. Krofta M, Wang LK (1982) Innovation in the water treatment field and systems appropriate and affordable for smaller communities. US Department of Commerce, National Technical Information Service, Springfield. Report No. PB82-201476, 30 p, March 1982 8. Krofta M, Wang LK (1982) Potable water treatment by dissolved air flotation and filtration. J Am Water Works Assoc 74(6):305–310 9. Krofta M, Wang LK, Kurylko L, Thayer AE (1983) Pretreatment and ozonation of cooling tower water, part I. U.S. Department of Commerce, National Technical Information Service, Springfield. PB84-192053, 34 p, April 1983 10. Krofta M, Wang LK, Kurylko L, Thayer AE (1983) Pretreatment and ozonation of cooling tower water, part II. U.S. Department of Commerce, National Technical Information Service, Springfield. PB84-192046, 29 p, August 1983 11. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley reservoir water by Krofta Sandfloat process system – project summary. US Department of Commerce, National Technical Information Service. Technical Report No. PB88-200647/AS, 40 p, January 1984 12. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley reservoir water by Krofta Sandfloat process system – project documentation. US Department of Commerce, National Technical Information Service. Technical Report No. PB88-200654/AS, 188 p, January 1984 13. Krofta M, Wang LK (1984) Treatment of Farnham and Ashley reservoir water by Krofta Sandfloat process system – final project report. US Department of Commerce, National Technical Information Service. Technical Report No. PB88-200639/AS, 194 p, February 1984 14. Krofta M, Wang LK (1984) Development of innovative electroflotation water purification system for single families and small communities. US Department of Commerce, National Technical Information Service. Technical Report No. PB85-207595/AS, 57 p, August 1984 15. Krofta M, Wang LK (1985) Treatment of cooling tower water by dissolved air-ozone flotation. In: Proceedings of the seventh Mid-Atlantic industrial waste conference, pp 207–216 16. Krofta M, Wang LK (1987) Winter operation of nation’s largest potable flotation plants. In: Joint conference of American Water Works Association and Water Pollution Control Federation, Cheyenne, September 1987 17. Malley JP, Edzwald JK (1991) Concepts of dissolved air flotation of drinking water. J Water SRT-Aqua 40(1):7–17 18. Millett P, McKelvey G (2000) Overview of packaged water treatment systems. J N Engl Water Works Assoc 114(1):41–45

92

L. K. Wang et al.

19. Nickols D, Crossley IA (1996) The current status of dissolved air flotation in the U.S.A. Technical Report. Hazen and Sawyer, P.C., New York 20. Pieterse T, Kfir R (1991) Plant quartet proves potable water reuse. Water Qual Int 4:31 21. Shuster WW, Wang LK (1983) Role of polyelectrolytes in the filtration of colloidal particles from water and wastewater. US Department of Commerce, National Technical Information Service. Technical Report No. AD-A131-109, p 49, June 1983 22. Wang LK (1972) Continuous bubble fractionation process. Ph.D. thesis, Rutgers University, New Brunswick 23. Wang LK, Wang MHS, Yaksich SM, Granstrom ML (1978) Water treatment with multiphase flow reactor and cationic surfactants. J Am Water Works Assoc 70(9):522–528 24. Wang LK, Wu BC, Meier A, Marshall J, Zepka J, Foote R, Janas J, Mulloy M (1984) Removal of arsenic from water and wastewater. U.S. Department of Commerce, National Technical Information Service. PB86-169299, 45 p, October 1984 25. Wang LK (1985) Theory and application of flotation processes. U.S. Department of Commerce, National Technical Information Service. PB86-194198/AS, 15 p, November 1985 26. Wang LK, Wang MHS, Hoagland FM (1992) Reduction of color, odor, humic acid and toxic substances by adsorption, flotation and filtration. Annual meeting of American Institute of Chemical Engineers, symposium on design of adsorption systems for pollution control, Philadelphia, August 1989. (P926-08-89-20, 18 p). Water Treat 7:1–16 27. Wang LK, Wang MHS, Kolodzicj P (1992) Innovative and cost-effective Lenox water purification plant. Water Treat 7:387–406 28. Wang LK, Hwang CS (1993) Removal of trihalomethane precursor (humic acid) by innovative dissolved air flotation and conventional sedimentation. Proceedings of the 1991 annual conference of the Korea Society of Water Pollution Research and Control, Seoul, 10 p, February 1991. Water Treat 8(1):7–16 29. Wang LK (1995) The state-of-the-art technologies for water treatment and management. United Nations Industrial Development Organization (UNIDO) Training Manual No. 8-8-95, 145 pages, August 1995 30. Wang LK (1995) Bubble dynamics and material balances of dissolved gas flotation process. Water Treat 10:41–54 31. Wang LK, Wang P, Clesceri NL (1995) Groundwater decontamination using sequencing batch processes. Water Treat 10:121–134 32. Wang LK, Wang MHS (1995) Laboratory simulation of water and wastewater treatment processes. Water Treat 10:261–282 33. Wang LK (1996) Design and specifications of Pittsfield water treatment system consisting of air flotation and sand filtration. Water Treat 6:127–146 34. Wang LK, Shammas NK, Selke WA, Aulenbach DB (2010) Flotation technology. Humana Press, Totowa, 680 pages 35. Wang LK, Li Y (2009) Sequencing batch reactors. In: Wang LK, Pereira NC, Hung YT (eds) Biological treatment processes. Humana Press, Totowa, pp 459–512 36. Wang LK, Kurylko L, Wang MHS (1994) Sequencing batch liquid treatment. US Patent 5354458, October 11, 1994 37. Shammas NK, Wang LK (2016) Water engineering: hydraulics, distribution and treatment. Wiley, Hoboken, 806 pages 38. Wang LK, Hung YT, Shammas NK (2004) Physicochemical treatment processes. Humana Press, Totowa, 723 pages 39. Wang MHS, Wang LK (2016) Glossary of land and energy resources engineering. In: Wang LK, MHS W, Hung YT, Shammas NK (eds) Natural resources and control processes. Springer, New York, pp 493–623 40. Wang MHS, Wang LK (2015) Environmental water engineering glossary. In: Yang CT, Wang LK (eds) Advances in water resources engineering. Springer, New York, pp 471–556 41. Edzwald JK (1995) Principles and applications of dissolved air flotation. Water Sci Technol 31 (3–4):1–23

2 Innovative Dissolved Air Flotation Potable Water Filtration Plant in Lee. . .

93

42. Edzwald JK (2007) Fundamentals of dissolved air flotation. J N Engl Water Works Assoc 121 (3):89–112 43. Edzwald JK (2007) Developments of high rate dissolved air flotation for drinking water treatment. J Water Supply Res Technol AQUA 56(6–7):399–409 44. Edzwald JK, Malley JP Jr, Yu C (1990) A conceptual model for dissolved air flotation in water treatment. Water Supply 8:141–150 45. Edzwald JK, Walsh JP, Kaminski GS, Dunn HJ (1992) Flocculation and air requirements for dissolved air flotation. J Am Water Works Assoc 84(3):92–100 46. Edzwald JK, Olson SC, Tamulonis CW (1994) Dissolved air flotation: field investigations. American Water Works Association Research Foundation, Denver 47. Edzwald JK, Tobiason JE, Amato T, Maggi LJ (1999) Integrating high rate dissolved air flotation technology into plant design. J Am Water Works Assoc 91(12):41–53 48. Edzwald JK, Tobiason JE, Parento LM, Kelley MB, Kaminski GS, Dunn HJ, Galant PB (2000) Giardia: and Cryptosporidium: removals by clarification and filtration under challenge conditions. J Am Water Works Assoc 92(12):70–84 49. Edzwald JK, Tobiason JE, Udden C, Kaminski GS, Dunn HJ, Galant PB, Kelley MB (2003) Evaluation of the effect of recycle of waste filter backwash water on plant removals of Cryptosporidium. J Water Supply Res Technol AQUA 52(4):243–258 50. Edzwald JK, Han M (2007) In: Edzwald JK, Han M (eds) The 5th international conference on flotation in water and wastewater systems. Seoul National University, Seoul, p 393 51. Edzwald JK, Kaminski GS (2009) A practical method for water plants to select coagulant dosing. J N Engl Water Works Assoc 123(1):15–31 52. Edzwald JK, Kelley MB (1998) Control of Cryptosporidium: from reservoirs to clarifiers to filters. Water Sci Technol 37(2):1–8 53. Edzwald JK, Wingler BJ (1990) Chemical and physical aspects of dissolved air flotation for the removal of algae. J Water Supply Res Technol AQUA 39(2):24–35 54. Town of Lee (2019) 2018 Water quality report. Town of Lee, 32 Main Street, Massachusetts, 01238, USA, March 2019 55. Wong J (2013) Clarifying treatment: dissolved air flotation provides alternative for treating raw water with light particles. Water World. August 2, 2013. https://www.waterworld.com/munic ipal/technologies/article/16190938/clarifying-treatment-dissolved-air-flotation-provides-alter native-for-treating-raw-water-with-light-particles

Chapter 3

Fundamentals of Chemical Coagulation and Precipitation Nazih K. Shammas, Hermann H. Hahn, Mu-Hao Sung Wang, and Lawrence K. Wang

Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Chemistry of Aggregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Reason for Suspended Particles to Remain Suspended . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Double Layer Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Adsorption Coagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Flocculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Particle Removal by Enclosure in Precipitation Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Types of Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Types of Chemicals Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Differences in Reactivity of Coagulating Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Coagulant Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Selection of Chemicals in Practical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Simultaneous Coagulation and Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 The Role of Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Types of Used Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Plug Flow and Completely Mixed Continuous Flow Reactors . . . . . . . . . . . . . . . . . . . . . . . 4.2 Detention Time Characteristics in Real Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Recommendation for Stepwise Design of Coagulation/Flocculation Reactors . . . . . . . 5 Products of Aggregation: The Liquid Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 The Average Quality of the Liquid Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 The Selection of Physical Parameters in View of Optimal Quality of Liquid Phase 5.3 Actual Plant Efficiency Data as Reported from Process Operation . . . . . . . . . . . . . . . . . . . 6 Products of Aggregation: The Solid Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Amounts of Solids Produced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Sludge Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

97 99 99 103 104 106 107 109 110 110 112 113 115 115 117 117 120 122 123 123 125 125 127 128 131 139 140

Abstract Chemical treatment is considered as a useful tool for (a) pretreatment of harmful wastes, (b) early removal of undissolved precipitating substances,

N. K. Shammas · H. H. Hahn · M.-H. S. Wang · L. K. Wang (*) Lenox Institute of Water Technology, Newtonville, NY, USA © Springer Nature Switzerland AG 2021 L. K. Wang, M. -H. S. Wang, N. K. Shammas, D. B. Aulenbach (eds.), Environmental Flotation Engineering, Handbook of Environmental Engineering 21, https://doi.org/10.1007/978-3-030-54642-7_3

95

96

N. K. Shammas et al.

(c) reduction of load fluctuations, (d) combating bulking activated sludge, (e) polishing effluents, and (f) phosphorus removal. Chemical treatment as a rule means addition of chemicals. Such chemicals are usually inorganic (such as iron or aluminum salts) or organic (such as cationic, anionic, and non-ionic polymers). These chemicals cause precipitation and/or aggregation (i.e., coagulation and flocculation) of the suspended phase in the wastewater system under consideration. The addition of chemicals in the phase of chemical treatment changes water constituents into a form that improves removal by all liquid-solid separation processes. This chapter describes the effects of chemicals upon particle aggregation and the interrelationship of the aggregation process with the flotation process. The chemicals used include inorganic, mostly metal salt-type chemicals and organic, mostly polymeric chemicals. Examples of inorganic chemicals that might come into consideration are calcium (salts), iron III (salts), and aluminum (salts). Organic coagulants or better flocculants are of the following type: low molecular weight substances with (opposite) charges, high molecular weight material adsorbing on oppositely charged surfaces, and high molecular weight material adsorbing on surfaces with a charge of the same sign (possibly due to some intermediary reaction). For practical design (and operation), the following recommendations are made on the effects on the detention time distribution: flow rate relative to volume, energy dissipation in the reactor (relative to the energy introduced with the throughput), stirrer type and geometry (relative to the reaction chamber), inflow and outflow configuration (relative to the geometry of the reactor), compartmentalization of the reactor, and baffles and other flow directing devices in the reactor (relative to the reactor geometry). The process of aggregation, that is, formation of larger (better separable) solids from small suspended solids, has traditionally been designed and operated to ensure a maximum efficiency in terms of aggregate growth. Aggregate growth means increase of average particle diameter and therefore better removal in all liquidsolid separation. In many instances of practical application of this process, one has not only accomplished this goal but also obtained large amounts of solids that cause great difficulties in separation and dewatering. Thus, today, one will have to design and operate the aggregation process such that both products, the liquid phase (i.e., the original focus in design and operation) and the solid phase (i.e., the sludge to be expected), will be optimized. Keywords Chemical coagulation · Chemical precipitation · Principles · Flocculation · Clarification · Flotation · Sedimentation · Coagulant · Polymer · Dissolved air flotation · Memoir

Nomenclature d/dt k n Ni Ne

Derivative with respect to reaction time Reaction rate constant Particle or chemical agent concentration Influent concentration Effluent concentration (also corresponding to the concentration within the reactor)

3 Chemical Treatment

No Nt Q t

97

Particle or reagent concentration at time t ¼ 0 Concentration at time “t” Rate of flow through the reactor L/V time elapsed between two points of tubular reactor

1 Introduction Classical wastewater treatment, developed primarily for domestic wastewater, employs unit processes from the catalogue of the mechanical and biological treatment. Such processes are reflected in the following elements of treatment plants [1, 2]. 1. 2. 3. 4. 5.

Screens Grit chambers (Primary) Sedimentation or flotation tanks Activated sludge or trickling filter units (Secondary) Sedimentation or flotation tanks

The advantages of this concept of wastewater treatment are non-specificity, robustness, and acceptable cost [3]. The disadvantages of such treatment plants are vulnerability toward poisonous material, difficulties in following load fluctuations, lack of specificity, and non-flexibility in terms of re-orientation of the treatment concept. Chemical treatment of wastewater, that is, the removal or inactivation of constituents of the wastewater phase, has existed before today’s concept of treatment was developed. Subsequently, it has been utilized and developed further in the realm of treating waters in the industrial sector. Today, chemical treatment is considered as a useful tool for the following [4, 5]: (a) (b) (c) (d) (e) (f)

Pretreatment of harmful wastes Early removal of undissolved precipitating substances Reduction of load fluctuations Combating bulking activated sludge Polishing effluents Phosphorus removal

The extraordinary rise of the chemical sales for the water and wastewater industry is a witness to this. Chemical treatment as a rule means addition of chemicals. Such chemicals are causing acid-base reactions, coordination reactions, and oxidationreduction reactions. In the context of this discussion, that is, primarily directed to the more nonspecific treatment of a larger number of wastewater constituents, only such chemicals are considered further which cause acid-base reactions in the sense of the definition by Lewis. The acid-base reactions considered here can take place in the aqueous phase or on surfaces [6].

98

N. K. Shammas et al.

Such chemicals are usually inorganic (such as iron or aluminum salts) or organic (such as cationic, anionic, or non-ionic polymers). These chemicals cause precipitation and/or aggregation (i.e., coagulation and flocculation) of the suspended phase in the wastewater system under consideration. The addition of chemicals in the phase of chemical treatment changes water constituents into a form that improves removal by all liquid-solid separation processes. Chemical treatment, therefore, is incomplete without a step of solid removal. Unit processes to be considered for this are as follows: (a) (b) (c) (d)

Screening Sedimentation Flotation Filtration

The application of flotation in industrial wastewater treatment has many advantages over the other separation processes, such as the following: (a) High efficiency under high loading conditions (b) Very good flexibility in terms of loading rate and type of wastewater (c) Low investment cost (in combination with load-proportional operating costs, which are somewhat higher) Flotation is a unit process that has proven very valuable in various instances of industrial wastewater treatment. Yet, flotation has not been applied to that degree in domestic wastewater treatment that would be expected on the basis of its known advantages. Thus, a transfer of this process into the field of domestic wastewater treatment could and should lead to significant savings and gains in treatment efficiencies [6]. Addition of chemicals and flotation can be seen as two separate unit processes. They do affect each other, however. The addition of chemicals might change the character of the flotation system by altering the nature of the dissolved phase. Such alterations will affect the particle-bubble contact. The addition of pressurized water, for instance, as is necessary in flotation may introduce additional energy, which can change the collision rate of the aggregating particles [7]. It is within the scope of this chapter to describe the effects of chemicals upon particle aggregation and the interrelationship of the aggregation process with the flotation process. A basic understanding of the process of flotation, in particular in terms of the mechanical realization of this process in treatment plants, is presupposed. Points of addition of chemicals and therefore points of application of the flotation process in the classical domestic treatment plant are as follows: (a) (b) (c) (d) (e)

Preceding the actual treatment plant (PRECEDE) Into/prior to the primary sedimentation tank (PRE) Into/prior to the secondary sedimentation tank (SIMULTANEOUS) Past the mechanical-biological treatment plant into a third stage (POST) For the treatment, that is, conditioning, of sludge (SLUDGE)

3 Chemical Treatment

99

Such points of application are shown schematically in Fig. 3.1. In addition to the here described areas of application, it is reasonable to assume that addition of chemicals and flotation might be a useful tool in the treatment of stormwater overflow. Aspects to be considered in the decision for one or another point of application are as follows: (a) (b) (c) (d) (e) (f)

Type of wastewater and its constituents to be removed Characteristics of the loading of the treatment plant Frequency and amplitude of load fluctuations Existing treatment steps Goal of wastewater treatment and requirements for discharge Installed or intended facilities for sludge handling and sludge utilization

2 Chemistry of Aggregation 2.1 2.1.1

Reason for Suspended Particles to Remain Suspended Surface Charge Phenomena

1. Surface charge from lattice imperfections O

O Sl

O

O

O Sl

O Al O

O

2. Surface charge from adsorbed ion phenomena

OH-

solid surface

OH-

OH-



Al

Al

BIOLOGICAL AERATION

SIMULTANEOUS TREATMENT

Fig. 3.1 Points of application of chemicals in conventional mechanical-biological plants

“MECHAN. / CHEM.” SLUDGE

“MECHAN. / CHEM./BIOLOG.” SLUDGE

WHEN RETURN

PRIMARY SEDIMENTATION

Fe (III)

Fe (II)

Fe (III)

PRE-TREATMENT

“BIOLOG. / CHEM.” SLUDGE

“CHEMICAL” SLUDGE

Al

Al

SECONDARY SEDIMENTATION

Fe (III)

Fe (III)

Ca

POST TREATMENT

100 N. K. Shammas et al.

3 Chemical Treatment

101

3. Surface charge from surface chemical reactions in general (see the above reaction as an example) O

O

O

O

O

Sl O

OH Sl O

+ H+

NOTE: Most particular matter in natural waters and in wastewater appears to have a negative charge at neutral pH values or slightly basic conditions (HAHN, 1968).

2.1.2

Repulsion Forces

Particles with charges of equal sign will repel each other. The repulsion forces increase with decreasing distance between the particles (see Fig. 3.2).

2.1.3

Attraction Forces (London-Van der Waals)

Through non-compensated charge or potential effects, that is, steric inhomogeneities, matter presents itself as disordered dipoles. Ordering of these dipoles can lead to overall organization and thus to dipole (or magnet-type) effects manifested to the outside. Dipole elements in small particles might become ordered by the approach of such particles to each other. This means that decreasing distances between two particles will lead to increased order and increased attraction [8, 9]. The water molecule might serve as an example.

-

-

+ H + + + H + +

O

-

-

+

Two particles approaching each other could he described schematically as follows.

+

+

+

-

+

-

-

-

2.1.4

-

-

+

-+

+

-

+

-

+

-

+ +

-

+

Resultant Force/Energy Balance

Figure 3.2 [10] shows schematically the change in repulsive energy and attraction energy between two approaching particles (spheres). It is seen that both energy

102 Fig. 3.2 Repulsion and attraction forces of two approaching particles (Top: low salt concentration. Bottom: high salt concentration)

N. K. Shammas et al.

VR

PARTICLE SEPARATION VA

min.

VR

PARTICLE SEPARATION

VA

min.

3 Chemical Treatment

103

components increase with decreasing particle distance. Since both energy terms change in a different way with particle distance, the resultant or net energy also changes with particle distances. Upon particle approach, the repulsive energy increases faster than the attractive energy. The result is an increasing energy barrier which disappears at very close particle distances.

2.2 2.2.1

Double Layer Compaction What Is a So-Called Counterion and What Are Its Effects?

Particle

-

+ + + + + + +

+

-

+ + +

-

+

+

+

-

-

+

+

-

-

As the schematic drawing shows, the increase in concentration in so-called counterions leads to a much more intensive compensation of the surface charge, that is, the (repulsive) effect of the surface charge is felt only at much shorter distances.

2.2.2

How Do Counterions of Different Charge Affect the Charge Compensation? (Or the Schulze-Hardy Rule)

The effects of differently charged counterions can be expressed by changes in approximate “thickness” of the so-called double layer (i.e., the two layers are the surface charge and the compensating counterion charge). At a counterion concentration of 0.01 mole/L, the thickness for a monovalent ion is 1000 A, and that for a divalent ion is 500 A only. At a counterion concentration of 100 mole/L, the thickness for a monovalent ion is 10 A, and that for a divalent ion is 5 A [10].

104

2.2.3

N. K. Shammas et al.

What Happens when the Concentration of the Counterion Is Increased to Very High Values?

In Fig. 3.3, a representation of a double layer, it is shown schematically that with increasing salt concentrations (i.e., counterion concentrations), the diffuse part of the double layer is compacted. It is also seen that there is a finite thickness, which cannot be reduced further. Even large concentrations of coagulating salts will not lead to a reversal of charge or potential. (Such charge or potential reversals are described in Sect. 2.4.)

2.2.4

Dosing Effect

For practical purposes, one can conclude that dosing problems do not exist if a certain minimum concentration is attained (the concentration is independent of the particle concentration), that overdosing does not lead to reduced efficiency, and that the coagula formed are of relatively dense nature.

2.3

Adsorption Coagulation

As described in Sect. 2.1, there are surface chemical reactions causing dissolved species to be adsorbed to a surface or removed from it. Similarly, charged species may be attracted to a surface for physical reasons. Such chemisorption (case 1) or physical adsorption (case 2) may cause a direct change in the surface charge (surface potential). These effects are to be distinguished from charge compensation as discussed in Sect. 2.2. Examples of such changes in surface charge, as opposed to compensation of surface charge, can be represented as follows [11]. +

Si

O O

H-

pH raised

H

Si

O

- + H+

isoelectric point

O - + H+

pH

-

It is possible to describe the relationship between ions in solution and those attached onto a surface in a quantitative way by an adsorption isotherm. (An adsorption isotherm describes the surface coverage as function of the equilibrium concentration in the solution phase for a given and constant temperature.) Vice versa it is also possible to clarify whether adsorption occurs by testing whether such

3 Chemical Treatment

105

←

←

Cation

-

Anion

←

A

← Water dipole

←

←

←

←

←

← ← ←

←

←

K+

+

K

←

←

Particle Surface

←

←

+

← ←

←

K

←

K

←

←

←

← +

←

A-

←

←

←

←

←

← K+

←

K+

←

←

←

←

←

←

K+

←

←

A-

3

←

A-

2

←

1

←

Fig. 3.3 Schematic of double layer concept (1) Inner Helmholtz plane; (2) outer Helmholtz plane; (3) plane of shear

adsorption isotherms do explain the observed behavior. The frequently used Langmuir isotherm is given below along with a schematic graph [12]. loading

Q (M/m2)

saturation

Q

=

+C

cL

b.C +

equil. conc.

l

C (M/1)

As the mechanism of adsorption states, the amount of material adsorbed increases with increasing amounts added (in an exponential way as illustrated, for instance, by the Langmuir isotherm). Thus, it is possible to adsorb such amounts of oppositely charged ions that the original surface charge of the particle is completely balanced, that is, neutralized, and the particle appears to have a zero charge. Furthermore, one must note that the surface concentration available, that is, the surface of the particles in suspension, directly affects the amount of material adsorbed: at constant salt additions, the amount of surface coverage (or change in charge) will decrease with increasing particle concentrations (more precisely with increasing surface concentrations). At increased coagulant dosages, that is, high equilibrium concentration of the oppositely charged ion, the extent of adsorption may be such that the original surface charge is not only eliminated but also reversed. An originally negatively charged particle can thus become positively charged. This causes high stability, again. Such increase in stability with very high coagulant dosages of adsorbing ions resulting from charge reversal is referred to as restabilization.

106

N. K. Shammas et al.

From a practical point of view, the following conclusions are significant: • The necessary dosage depends on the original particle charge and the particle concentration. • The pH value is of great significance to the overall system. • Constant dosage leads necessarily to fluctuating efficiency when applied under real-world conditions. • High dosages may lead to restabilization. • The resulting coagula are dense (similar to the products of the process described under 2.2).

2.4

Flocculation

Flocculation is understood to be a process where aggregates of lower density are formed in a three-dimensional way. Particles are not destabilized on an individual basis and do not collide individually as described in the concept of coagulation. In this example, the particles rather find themselves incorporated into a threedimensional network (the picture of a sponge may illustrate this). Flocculation is accomplished by long-chain molecules or ions. Frequently, organic polymers are used for flocculation. Along with the molecular weight, the charge of such molecules is of great significance for their use as flocculants. The following figures show cationic polymers, anionic polymers and nonionic polymers [5, 13]. - cationic polymers CH2 CH C

CH3 CH2 C

M NH2

O

O - anionic polymers CH2 CH C

M O

NA+

O - non-ionic polymers CH2 CH C O

C

N NH2

CH3 O

CH2

CH2

CH2 N CH3

3 Chemical Treatment

107

To explain the observations made with polymer-induced aggregation, a so-called bridging model has been invoked. Long-chain molecules adsorb (for reasons described above) with one end to one particle and with the other end to another one. Thus, there must always be free adsorption sites on the particle surface in order to allow bridge formation. At higher flocculant concentration, surface coverage becomes so high that free adsorption sites for molecules extending from other particles are no longer available. This is shown schematically below [1, 5].

There is also another mechanism that can be invoked for the explanation of aggregation phenomena observed with shorter-chain molecules. This so-called Patch Model stipulates that the (in this case oppositely) charged molecules will adsorb onto the particle surface and change the surface charge [1, 5]. From a practical point of view, the following may be said about the use of flocculants: • The amount of chemicals added is crucial to the success of the process. • The pH value, controlling the surface charge and the adsorption process, must be observed. • Overdosing may cause restabilization. • The intensity of mixing in the phase of flocculant addition is to be controlled carefully. • The resulting products, that is, the floccules, are usually less dense than the coagula.

2.5

Particle Removal by Enclosure in Precipitation Products

In water and wastewater treatment, frequently, metal ions (i.e., metal salts) are used. These metal ions will hydrolyze. They will also react with the acid-base-system “water” and form hydroxo-complexes. These reactions are shown schematically below.

108

N. K. Shammas et al. Al+3 + H2O = Al (OH) +2 + H+ + Al (OH)+2 + H2O = Al (OH)2 + H Al (OH) 2+ + H2O = (Al (OH)3)S + H+ Al (OH) 3 (S) + OH- = Al (OH)4-

In Fig. 3.4, a solubility diagram that has been constructed from the above reaction equations and the corresponding equilibrium constants, it is seen that at average 0 Al (OH)3

-LOG [Al(III)] IN MOLES

2 4

Range of Experiments

6 Al13(OH)

3+

8

Al7(OH)

+5

+4

17

Al (OH)4-

10

Al+3

12

AlOH+2

14 0

2

4

6

8

10

12

14

10

12

14

SOLUTION pH ALFA COLLISION EFFICIENCY FACTOR

Fig. 3.4 Solubility diagram of hydrolyzing aluminum and corresponding coagulation effect (100 mg/ L Min-U-Sil 30–2.42.106 M/L Al)

.14 .12 .10 .08 .06 .04 .02 0 0

2

4

6

8

SOLUTION pH

3 Chemical Treatment

109

dosages and the most frequently observed pH conditions, metal-hydroxide formation will occur. It is significant in what way this equilibrium point is reached. (It must be pointed out that in a strictly thermodynamic sense, there will be no equilibrium between metal hydroxide and the dissolved species in such short time as is provided in those technical systems that are discussed here.) If the domain of insolubility is reached for a given total metal concentration by increasing pH from originally acidic values to neutral values, then there will be kinetic intermediaries that resemble those positively charged metal-hydroxo-complexes. Analogous observations can be made when approaching the domain of insolubility from very high pH values; this may lead to negatively charged intermediaries. In all real systems such as wastewater, one will rarely be able to distinguish between coagulation/flocculation and precipitation. Both processes will occur simultaneously with a rate and to an extent that is determined by the composition of the dissolved phase. The significance of the precipitation phenomena for wastewater treatment processes lies in the fact that metal-hydroxide precipitates may and will incorporate suspended particles into the newly formed solid phase. From a practical point of view, the following may be said about precipitation: 1. Under most conditions, hydroxide formation is favored. 2. Hydroxide formation means additional consumption of chemicals. 3. Hydroxide formation supports suspended material removal, in particular such suspensions that might not respond to classical aggregation processes. 4. The resulting products do not show great strength. 5. The resulting products have a higher water content.

3 Types of Chemicals In many instances, the reactors for liquid-solid separation do exist, and the overall plant efficiency can be increased by an improvement of the separability of the solids, that is, inducing aggregation of particles [14]. The most important decision in such instances is point of chemical addition and dosage of chemical. For this reason, the selection of chemicals deserves great interest, be it for the optimization of the clear water quality or of the sludge characteristics or for reasons of operational reliability and robustness. As will become clear from the following discussion, the various chemicals available to the operator of the wastewater treatment plant have significantly different effects and also significantly different consequences for the overall purification process. Therefore, it is necessary to describe briefly each of the chemical types used today [15–17].

110

3.1

N. K. Shammas et al.

Types of Chemicals Used

There are basically inorganic, mostly metal salt-type chemicals and organic, mostly polymeric chemicals used in today’s water technology [5, 18]. Inorganic chemicals that might come into closer consideration are as follows: • Calcium (salts) • Iron III (salts) • Aluminum (salts) In addition to this, clay-type substances are used to support the aggregation process, such as bentonite. These clay-type suspensions might either cause co-coagulation (i.e., a positively charged suspension is coagulated by a negatively charged sol) or they might improve the reaction kinetics. The latter phenomenon is explained by an increase in particle number and also by an increase in particle collision per unit time. Organic coagulants or better flocculants are of the following type: • Low molecular weight substances with (opposite) charges • High molecular weight material adsorbing on oppositely charged surfaces • High molecular weight material adsorbing on surfaces with a charge of the same sign (possibly due to some intermediary reaction)

3.2 3.2.1

Differences in Reactivity of Coagulating Chemicals Calcium

• Effects: coagulation due to counterion effect (precipitation of calcium is negligible). • Remarks: no problems with overdosing, high amounts of chemicals needed (Fig. 3.5), higher pH values used in actual operation, larger amounts of solids (sludge) are produced, dewatering. Of these, solids are not too problematic.

3.2.2

Fe(III)/Al

• Effects: counterion coagulation at lower pH values and surface charge reduction (coagulation) at higher pH values of about 5–7. At even higher pH values, hydroxide precipitation will occur. • Remarks: at low pH values, the necessary dosage is relatively low (Fig. 3.5); at intermediate pH values, the system is very pH sensitive but very effective in terms of necessary dosing; at higher pH values, large amounts of chemicals are needed for the precipitate formation. Overdosing in a sense of decreasing effectivity at increased dosage rates becomes a problem when the system is to be operated at

3 Chemical Treatment

111

100 Coagulation

Al++

Ca++

Na+

50

0 100 Adsorption Coagulation

Hydrolyzed Al3+

Remaining Turbidity

50

0 100 Precipitation Al (OH)3 (s)

50

Precipitation 0 100 Flocculation 50

Hydrolyzed Polyacrylamide

0 10-8

10-6

10-4

10-2

chemicals concentration

Fig. 3.5 Different aggregation effectivity of various chemicals

intermediate pH values. The amount of solids forming and the problems in dewatering the resulting sludge are large when the system is operated at the hydroxide formation stage while at all other conditions, these aspects are non-problematic. Fe(II) is a less efficient coagulant. However, if oxidized or oxidizable, it is an economic one. 3.2.3

Polyaluminum

• Effects: change of surface charge through adsorption of highly charged low molecular weight hydroxo-complexes • Remarks: conditions for application as above for Fe(III)/Al at intermediate pH values, pH sensitivity less pronounced

112

3.2.4

N. K. Shammas et al.

Polymers

Cationic, lower molecular weight • Effects: modification of surface charge through adsorption of material • Remarks: close similarity to (inorganic) polyaluminum in dosing requirements and effects Cationic, high molecular weight • Effects: bridging through adsorption of long-chain molecules at more than one particle surface. • Remarks: very low dosage requirements; the pH regime must be closely controlled; when overdosing occurs, then the sign of the (charged) surface charge is reversed and restabilization begins; aggregates formed are voluminous and frequently show unsatisfactory dewatering properties. Anionic, high molecular weight • Effects: bridging between particles that frequently carry a charge of the same sign, intermediary reactions with other constituents of the dissolved phase are assumed (e.g., with Ca2+) • Remarks: very low dosage requirements; the pH regime must not be controlled as closely as described above since charge variations do not have such effects; similarly, dosing must not be controlled as accurately as above mentioned, solid (sludge) characteristics as mentioned above. Non-ionic, high molecular weight • Effects: bridging between particles (see above) • Remarks: pH effects completely disappeared (for practical purposes), all other conditions as above described

3.3

Coagulant Aids

In practice, flocculating reagents are frequently employed not separately and independently but in conjunction with coagulating chemicals. In this instance, one postulates that the mostly inorganic coagulants initiate the aggregation process leading to the formation of small flocs. The organic flocculants lead the process of aggregation to the formation of very large (for instance, visible) flocs and therefore aid the coagulation process. This practice is coupled very often with a delayed dosing of the coagulant aid, such that the initiation of floc growth is well on the way.

3 Chemical Treatment

3.4

113

Selection of Chemicals in Practical Applications

The basic principles of reactivity of the different chemicals have been described before. The following remarks are intended to serve predominantly the operator of a coagulation/flocculation plant. Under conditions of day-to-day operation, it is important to know how sensitive the process reacts to fluctuations in dosage or how stable the aggregates are with respect to shear stress. This is to be described in brief in the following paragraphs.

3.4.1

Calcium/Ca2+

• Effects (mechanisms): coagulation due to counterion presence; to a reduced extent also calcium hydroxide precipitation. • Remarks: high pH values are required; higher dosages are necessary; larger amounts of solids are produced (i.e., sludge produced). 3.4.2

Iron(III)/Fe3+ and Aluminum/Al3+

• Effects (mechanisms): (a) At pH values below 4, coagulation due to counterion presence. (b) At pH values below 6–7, coagulation due to surface charge compensation from the adsorption of hydroxo-complexes. (c) At pH values where precipitation occurs, that is, pH 6 for Fe(III) and pH 7 for Al, there will be an enmeshment of particles into precipitates. • Remarks: For case (a), lower dosages required and no problem with overdosing For case (b), very low dosages required, very high pH sensitivity, significant problem when overdosing occurs For case (c), higher metal ion dosages necessary, no problem of overdosing if pH values are kept in the range of hydroxide precipitation

3.4.3

Polyaluminum

• Effects (mechanisms): Coagulation due to surface charge compensation, which is adsorption of polynuclear aluminum hydroxo species

114

N. K. Shammas et al.

• Remarks: (a) Very low dosages required (b) Significant problem with imprecise dosing (c) Lesser pH sensitivity than in case of in situ formed aluminum hydroxocomplexes

3.4.4

Polymers

Cationic (lower molecular weight) • Effects (mechanisms): coagulation due to surface potential chance from the adsorption of highly charged species • Remarks: Operating conditions as for polyaluminum or aluminum-hydroxo-complexes Cationic (high molecular weight) • Effects (mechanisms): bridge formation due to the adsorption of long-chain polymeric substances onto more than one suspended solution • Remarks: (a) There is a definite pH optimum. (b) The problem of overdosing still exists and results in this case from high degree of surface coverage at higher polymer dosages. (c) The resulting (three-dimensional) flocs cause voluminous amounts of sludge. (d) The sludge handling properties of the separated solids are frequently not very satisfactory. Anionic (mostly of high molecular weight) • Effects (mechanisms): bridging supported most likely by surface chemical reactions of calcium or magnesium ions, present in the aqueous phase, leading to a reduction of charge and/or adsorption of the oppositely charged polymers • Remarks: (a) Slight pH dependence (lower than in case of cationic polymers) (b) Dosing sensitivity less evident than in case of cationic polymers (c) Due to unknown mechanisms, process not in all instances successful Non-ionic (mostly of high molecular weight) • Effects (mechanisms): bridging due to adsorption of longer-chain molecules at more than one surface

3 Chemical Treatment

115

• Remarks: (a) Next to no pH effect (b) All other conditions as described for high molecular weight polymers

3.5

Simultaneous Coagulation and Precipitation

Coagulation is the formation of larger aggregates from solid substances, that is, no change in phase. Precipitation, the formation of solid, undissolved species, implies a phase transition. In chemical terms, coagulation and precipitation are distinctly different processes. In wastewater systems, however, in particular when metal ions (metal salts as coagulants) are used, both processes might occur simultaneously. To what extent these two different processes occur and with what reaction rate they proceed depends upon the composition of the dissolved phase. This dissolved phase is very complex and changing in its nature in wastewater systems. In Fig. 3.6, there is a schematic representation of all processes that might occur in wastewater when metal ions are added. It is seen that in particular in the presence of phosphate ions, for instance, precipitation will prevail. If, for instance, the hydroxide ions predominate, then metal hydroxides will be primarily formed. Under conditions of intermediate pH values, dissolved hydroxo-complexes will be formed leading to coagulation. It is also important to note that all pathways indicated in Fig. 3.6 will be followed simultaneously but to a differing extent and with possibly different reaction rate. And, furthermore, there are chances from one pathway to another if the chemical situation does allow this. Such switches are illustrated by the possibility or even necessity to complete a precipitation step in practice by coagulation or flocculation step.

3.6

The Role of Adsorption

Addition of chemicals in this discussion leads by definition only to a chance of phase or to aggregation/fIoc formation. It does not allow per se the elimination or modification of substances that do not precipitate or coagulate. However, in practical applications, one has observed that constituents of the dissolved phase that do not belong to either of the abovementioned categories are also reduced in their concentration. The most plausible explanation is a sorption process which is favored by the very large specific surfaces formed, for instance, in metal hydroxide precipitation [15, 19, 20].

116

N. K. Shammas et al.

METAL SALT ( e.g. Cu, Fe (III), Al )

Dissolved anions (e.g. PO4)

Hydroxide ions

PRECIPITATION Nondissolved Solids ( e.g. Fe PO4 )

Metal Hydroxide

SUSPENDED MATTER

Coagulation

Sweep Floc Removal Suspended Matter

Separable Flocs

Inclusion

Dissolved Matter

ADSORPTION

SLUDGE (precipitating anions, unflocculation/ flocculation, suspended matter, adsorb, matter, water) LIQUID / SOLID - SEPARATION

Fig. 3.6 Parallel reactions in chemical treatment with metal salt

It is reasonable therefore to expect such adsorption processes to occur in situations where solid surfaces are formed or reformed and where surface active species are available (as is the case in wastewater). Examples of such elimination by adsorption onto coagulated solids are heavy metal removal or DOC (dissolved organic carbon) reduction in wastewater systems treated with coagulants.

3 Chemical Treatment

117

4 Types of Used Reactors 4.1

Plug Flow and Completely Mixed Continuous Flow Reactors

In order to understand what is happening in real aggregation reactors, as well as in flotation units, it is expedient to define two ideal or extreme situations of reactor dynamics or reactor flow [15, 21]: plug flow (PF) and completely mixed continuous flow reactors [15, 22]. Figure 3.7 illustrates schematically the principal form of each reactor type and connected flow conditions. It is seen that the PF reactor distinguishes itself by the fact that no mining takes place between neighboring (fluid) elements. They move

a

REACTOR WITH MECHANICAL STIRRER

b

‘HYDRAULIC’ REACTION CHAMBER (POSSIBLY ALSO TUBULAR)

c

COUTTE TYPE OR CYLINDER STIRRER REACTOR

Fig. 3.7 Schematic drawing of different reactor forms (a) Completely mixed; (b) plug flow; (c) combination

118

N. K. Shammas et al.

independent of each other through the reactor. Such reactors are, for instance, tubular reactors, or rivers (from certain points of view) or the reaction chambers preceding the so-called auto-analyzers. The CMCF reactor ideally is the very opposite of the plug flow reactor; here, each additional fluid (or reacting) element is, upon entering the reactor, immediately completely mixed with all other elements that entered this reactor earlier. Examples of such reactors are equalization or neutralization basins or also activated sludge reactors if designed as completely mixed units. The behavior of these reactors can also be illustrated by recording the movement of a tracer substance through the system. Such tracer materials are usually not dosed continuously but rather added on an impulse or pulse basis. Such responses to DELTA pulses are shown in Fig. 3.8. Quite clearly, such a pulse moves by definition unchanged through the PF reactor since there is no mixing with neighboring elements and therefore no dilution (if one assumes that no other reaction takes place). If one envisions a tubular reactor with one port for tracer addition and another one for sampling, then the time T elapsing until the slug of tracer appears (completely) equals the detention or reaction time in the system. The CMCF reactor shows a very different characteristic [22]. Here, the slug of tracer is, upon entering, immediately mined with the total content of the reactor. All fluid (or reacting) elements entering later will be mixed in completely and lead to a dilution of the tracer in the reactor. The tracer concentration monitored at the outlet of the reactor will therefore decrease with time. It can be shown that the concentration change follows an exponential decrease. Similarly, as for the decay of a radioactive substance, one can formulate a half-life time. Furthermore, the mathematical model indicated in Fig. 3.8 allows to predict the concentration, which corresponds to a detention time of V//Q, that is, the hydraulic detention time. Thus, one can monitor for this concentration and determine in this way the actual detention or reaction time of the system. If one superimposes a reaction rate over the hydraulic characteristics of these systems, then again there will be differences in the progress of the reaction for different times. For illustration’s sake, a first order reaction rate process is assumed. d=dt ðnÞ ¼ k:n where: n ¼ particle or chemical agent concentration k ¼ reaction rate constant d/dt ¼ derivative with respect to reaction time In a PF reactor, this reaction will proceed to an extent that can be predicted from the integrated rate law. N t ¼ N o ekt

3 Chemical Treatment

119

Tracer Concentration

PLUG FLOW REACTOR

Input

Output

Reaction Time Detention Time

Time

Tracer Concentration Input

COMPLETELY MIXED CONTINUOUS FLOW REACTOR

Output

Reaction Time Detention Time

Time

Fig. 3.8 Detention time characteristics of plug flow reactor and of completely mixed reactor

where: No ¼ particle or reagent concentration at time t ¼ 0 Nt ¼ concentration at time “t” t ¼ L/V time elapsed between two points of tubular reactor

120

N. K. Shammas et al.

If one draws this curve as function of the reaction time, one finds a logarithmic decrease in the final concentration with increased reaction time. In a CMCF reactor, the same reaction will proceed differently; in particular, the reaction end point after specified reaction time has elapsed will change in a different way from the above reactor. Or in other words, increase of reaction time will lead to different results in terms of reaction end point in the CMCF reactor. The effect can be seen from the following mass-balance equation: Inflow  change due to reaction  outflow ¼ overall change and for a steady state equilibrium with the assumption of no overall change, one finds: Q N i  kN e V  QN e ¼ V dn=dt where: Q ¼ rate of flow through the reactor Ni ¼ influent concentration Ne ¼ effluent concentration (also corresponding to the concentration within the reactor) Frequently, for technical systems, there is a steady state for which one then finds dNe/dt ¼ 0 and consequently N e ¼ N i =ð k t þ 1Þ The effect of prolonged reaction or detention time upon the reaction end point is significantly different from the logarithmic one for the PF reactor.

4.2

Detention Time Characteristics in Real Reactors

Figure 3.9 shows the recording of an actual tracer experiment for two real reactors. The reactors distinguish themselves, as is indicated in that figure, by different stirring and possibly by the existence of baffles. The data show clearly that the effluent concentration changes in a different way in both reactors if measured with time. In the instance of the reactors without stirring and baffles, the effluent concentration is for a longer period of time close to zero; then it increases rapidly to higher values, and finally, it drops rather rapidly again to zero. The pattern resembles the PF reactor characteristics. The intensively stirred reactor (without baffles) shows an immediate reading on the effluent concentration scale. This reading or concentration is reduced monotonously with increased time. The pattern very much resembles the CFCM reactor characteristics.

Tracer - Concentration [mg Cl/l]

Case 1 Case 2

3 Chemical Treatment

121

T Case 1 T = Theoretical detention time t = Average detention time

35 60

T Case 2 25 40

t Case1 15 20 t Case 2 5

10

15

20

25

TIME, minutes

Fig. 3.9 Detention time distribution in different reactors, unstirred/stirrer, with/without baffles

It is important to note that neither pattern completely repeats the characteristics of the two ideal reactors discussed above. Furthermore, it should be mentioned that it is very difficult to design reaction chambers such as neither one of the ideal reactors results or is approached (with the exception of the pipe flow reactor). The actually observed detention time distribution can be explained in qualitative terms as a combination of plug flow reactor and completely mixed continuous flow reactor. In some instances, it was possible to describe a real reactor (i.e., observations on the so-called displacement curves) in quantitative terms as a combination of PF and CFCM reactors. Such combination entails arrangements of several reactor units in series and in parallel. For practical design (and operation), the following recommendations may be made on the basis of the above-described phenomena: The detention time distribution is affected by the following: 1. Flow rate relative to volume 2. Energy dissipation in the reactor (relative to the energy introduced with the throughput) 3. Stirrer type and geometry (relative to the reaction chamber) 4. Inflow and outflow configuration (relative to the geometry of the reactor) 5. Compartmentalization of the reactor 6. Baffles and other flow directing devices in the reactor (relative to the reactor geometry)

122

N. K. Shammas et al.

In the past, these parameters have not been controlled closely or extensively, whether in the phase of reactor design or for the repeated optimization during operation. This is true for both types of application, aggregation reactors and flotation reactors. Frequently, a sweeping effect of chemicals used in the aggregation reaction and the flotation reaction has masked possible problems resulting from non-optimal design (and operation). Yet, presently, it appears necessary and also possible to exploit reactor dynamics more extensively in order to save chemicals or to attain higher degrees of efficiency.

4.3

Recommendation for Stepwise Design of Coagulation/ Flocculation Reactors

1. The design objective is, for instance, a reactor that converts a known suspension (i.e., of known average particle diameter) into one with a larger diameter in order to guarantee removal by a liquid-solid separation process such as sedimentation or flotation. 2. In the next step, experiments of an exploratory nature are to be performed which should show the possibilities for aggregating the suspension (and the necessary type and amount of chemicals). 3. Then from the idealized rate law, an estimate is made for the necessary detention time and the required power input. Both parameters must only be estimated within certain ranges. They are also interdependent: a high energy input will lead to a lower necessary reaction time and vice versa. Estimates for these parameters can also be taken from the literature. 4. Now the reactor geometry has to be determined (after the overall size has been set by the determination of the detention or reaction time). This should and can only be done by “scale-model” experiments.

3 Chemical Treatment

123

5. It is important to point out that the scale-up of these models is difficult and critical and that there exist no rules for this scale-up. Depending upon the situation, one can choose between various dimensionless or characteristic numbers, such as the Froude number or the Reynolds number (for the reactor or the stirrer) or a powerinput related scale-up number [23]. 6. Finally, it must be stated that jar-test-type experiments on the potential for aggregation of the suspension should be used to optimize the operation. Such optimization will be necessary again and again if the characteristics of the influent suspension will change. The analysis can also help to overcome possible shortcomings of the design.

5 Products of Aggregation: The Liquid Phase The process of aggregation, that is, formation of larger (better separable) solids from small suspended solids, has traditionally been designed and operated to ensure a maximum efficiency in terms of aggregate growth. Aggregate growth means increase of average particle diameter and therefore better removal in all liquidsolid separation. In many instances of practical application of this process, one has accomplished this goal but also obtained large amounts of solids that cause great difficulties in separation and dewatering. Thus, today, one will have to design and operate the aggregation process such that both products, the liquid phase (i.e., the original focus in design and operation) and the solid phase (i.e., the sludge to be expected), will correspond to certain standards. There is much experience and experimental evidence available for the optimization of the aggregation process in order to obtain a very good clear water quality. This will be presented and interpreted in the following paragraphs. The second objective, that is, to produce not too large amounts of separable and treatable sludge, is presently the aim of several laboratory and technical investigations. The little evidence available for the optimal setting of design and operation to attain this goal is to be presented in the next chapter.

5.1

The Average Quality of the Liquid Phase

Aggregation accomplishes the formation of larger suspended solids from small suspended material. It has been pointed out earlier that in wastewater systems, aggregation frequently is initiated by the addition of metal ions (metal salts). Thus, depending upon the composition of the dissolved phase, there will be more or less pronounced precipitation of substances that form insoluble complexes with the added metal ion (for instance, Me-phosphate).

124

N. K. Shammas et al.

When discussing the efficiency of the process in terms of clear water quality, then one has to bear in mind that only aggregating and precipitating substances will be affected. It has also been indicated earlier that there is adsorption onto the freshly formed solid surface when aggregation and precipitation processes occur. Thus, also adsorbing substances will be affected in their concentration by this process. At the same time, it must be pointed out and emphasized that none of the constituents of the dissolved phase of a wastewater system will be removed or altered if those substances are not amenable to precipitation and/or adsorption. Nitrogen species are a case in point. They will not be removed in any instance of chemical dosing that has been described here. For practical purposes, one can conclude that the addition of coagulating and precipitating chemicals leads to the following: 1. Reduction of undissolved substances (nearly completely) 2. Reduction of dissolved matter of mostly inorganic anionic nature (with high degree of efficiency) 3. Reduction of dissolved organic matter that precipitates and/or adsorbs (with medium efficiency) It is important to point out that any quantitative information on removal efficiencies or on effluent quality can only and must be problem specific. There are so many interfering reactions that it is difficult to predict for an unknown or un-investigated wastewater system the type and extent of all processes that might occur. A general listing of process efficiency data that might be desirable for the design engineer is not possible. However, one can inspect efficiency data reported in the literature, evaluate and discuss them within the context of the specific situation, and derive from these orders of magnitude for the process efficiency to be expected. The progress of the process is measured in agreement with the above-described principles in terms of (a) turbidity reduction and/or (b) reduction in filter residue and/or (c) decrease in the concentration of specific ions (e.g., phosphate, heavy metals) and/or (d) decrease in biochemical/chemical oxygen demand (filtered or unfiltered sample). These are by far not all parameters that one would select on the basis of the known process efficiencies. However, routine analysis during (treatment) plant operation usually does not allow more specific investigations, such as chance in particle size distribution (very specific for the description of this process), or reduction in specific organic substances. Furthermore, it must be pointed out that from a practical point of view, such parameters should be listed in more than one dimension, for instance, as (a) first statistical moment (mean, etc.) of distribution of effluent concentrations and/or (b) second statistical moment (standard deviation, etc.) of distribution of effluent concentration and/or (c) similar measures for (relative) concentration reduction in the effluent. Each measure will describe a different aspect of process efficiency and operation. And each might be of particular importance under different conditions.

3 Chemical Treatment

5.2

125

The Selection of Physical Parameters in View of Optimal Quality of Liquid Phase

The exact description or analysis of the physical parameters under conditions of plant operation is not only difficult but also rarely done. Thus, the more theoryoriented measures have to be translated into practical terms. In most instances, the following conditions will show good to optimal results: 1. Intensive mixing of coagulation/flocculation chemicals with energy input values significantly greater than s-1. In this phase, even high stirring rates/energy input will not cause negative effects. 2. Floc or aggregate preserving stirring of lower intensity with a magnitude of 100–200 s-1. Here, the material to be aggregated will influence the absolute size of the energy input that should be considered optimal. It is also conceivable to adjust the energy input in this phase to the changing floc quality. This is done in practice by reducing the stirring speed in two or more steps in subsequent reactor compartments. 3. Reaction times necessary in the phase of chemical addition are mostly less than 1–2 min at maximum. Reaction times in the stage of aggregate growth, depending upon the energy input, can range from 2 min to 20 min. Here, it must be pointed out that increased reaction time will lead to higher process yield, that is, better floc growth. Yet, larger flocs are more susceptible to destruction in shear flow. Increase of reaction time must therefore always be seen in conjunction with the actual energy input (expressed as energy dissipation per unit volume reactor space). 4. A combined optimization of energy input and reaction time (i.e., the product of Gt) has proven useful for practical purposes. These practice-oriented recommendations for the setting of physical parameters usually lead to optimal aggregate growth, that is, optimal quality of the liquid phase after separation of the aggregates. As will be described later (see Sect. 6), such settings must not necessarily lead to a solid phase that has good qualities in terms of sludge handling, that is, sedimentation/flotation or thickening or dewatering.

5.3

Actual Plant Efficiency Data as Reported from Process Operation

As indicated above, the use of precipitating or coagulating chemicals is always then commendable when the following wastewater constituents are to be controlled: (a) suspended solids, which are registered in the parameter turbidity or filter residue; (b) suspended or dissolved adsorbing organic substances, which are registered in the parameter BOD or COD; and (c) dissolved inorganic substances with the metal ion.

126

N. K. Shammas et al.

This practical limitation of the process to the control of only some wastewater constituents has been documented in practice for the treatment of textile industry waste [24], dairy wastewater [25], and the removal of impurities from seawater [26]. It has also been shown that there are always several processes occurring at the same time when metal ions (or coagulants) are added to a wastewater system. As stated before, it depends upon the relative preponderance of the specific wastewater constituents, which specific reaction pathway is favored. When discussing process efficiency in real system, it is also necessary to point out that coagulation/flocculation and the competing precipitation process depend in their success upon the subsequent step of liquid-solid separation. Thus, in all discussions, it is assumed that there is an optimal unit process of solids separation available. Furthermore, one must be aware of the limitations of the process in terms of not controlling non-adsorbing or non-precipitating or non-coagulating substances. One group of wastewater constituents that is discussed intensively in wastewater pollution control is the nitrogen compounds. Dosing chemicals that cause precipitation/ coagulation will not significantly affect the concentration of any nitrogenous substance even if liquid-solid separation is an optimal one. The comparison of plant efficiency of a mechanical biological plant built to the standard of “generally available technology” with efficiency data for such a mechanical biological plant that is supported by chemical dosing is given in Fig. 3.10 [3, 27, 28]. It is very clear that the addition of chemicals leads to a significant increase in the quality of performance. In addition to the absolute increase in the removal or reduction rate of undesirable wastewater constituents, there is also an increase in the stability of the performance, that is, a reduction in the scattering of the efficiency data when chemicals are used. This is shown in Fig. 3.11 by giving statistical data on the plant performance. Cumulative frequency distributions obtained for plants with chemical dosing show a much steeper line, that is, a lower standard deviation than those lines obtained or observed with mechanical biological treatment alone. The observed improvement of plant performance, that is, the reduction in fluctuations of the effluent concentrations, results from two phenomena: • Inflow fluctuations are dampened by the frequently flow-proportional operated chemical dosing. • The process of precipitation/coagulation allows a rather rapid response to known or anticipated load fluctuations such as from stormwater runoff. This possibility of stabilizing or equalizing the plant effluent is by far not yet realized to its utmost. The automation of this particular process is at best at its beginning. Contrary to the traditional biological processes, this chemical process is described and controlled by analyses that are readily and rapidly feasible. And there is already some experience in such plant control. Finally, it should be pointed out that all other reactions in the course of the wastewater treatment process will profit from the addition of a treatment step that leads to load reduction and to an evening-out of load fluctuations. Thus, the overall plant performance of such plants where chemicals are used for precipitation/coagulation is more than linearly improved.

127

N

P

SF

(SWW UBA)

N

BSB

P

EFFICIENCY INCREASE THROUGH CHEMICAL DOSING INTO BIOL. PLANT

BSB

Eckenfelder SF

N

P

BSB

SF

(GERMAN MIN. INTERIOR)

SF CONVENTIONAL BIOLOG. Eckenfelder P TREATMENT PLANT N

BSB

80

85

90

95

100

3 Chemical Treatment

Fig. 3.10 Comparison of efficiency of mechanical-biological plant with same type plant aided by chemicals (lower part of the figure)

6 Products of Aggregation: The Solid Phase It has been pointed out in the preceding section that there is a new focus in wastewater treatment on simultaneous optimization of the quality of the liquid phase and the solid phase. This means that a process is no longer operated such that the effluent quality is optimal without consideration for the amount and characteristics of the resulting solid phase. Today, one rather selects a specific output

128

N. K. Shammas et al. Frequency

Frequency

[%] [%]

Full scale prototype 90

99, 98

Pilot Plant Bench scale Plant Jar Test

90

50

chemicals added

70 50 30 10

10 5 0

conventional plant

1 00, 2 0

40

30

20

10

0 [%]

0

20

COD Reduction (%)

40

60

80

100

[g/m3]

Effluent COD (g/m3)

Fig. 3.11 Reduction in effluent variability through chemicals

quality for the liquid phase, the “necessary condition” to be observed in the operation, and then optimizes the process such that the resulting solids are easily separated, thickened, and dewatered. Figure 3.12 shows schematically the type of options open to the operator of a precipitation/coagulation plant. It has been learned from operational experience that alternative II is preferable from a point of view of sludge handling (while both alternatives, I and II, produce an effluent of comparable quality). If one looks at the process of aggregation (and liquid-solid separation) in a more basic way (Fig. 3.13), then one understands that the amount and quality of solids produced depend to a significant degree upon the kind of chemical added (including the solvent used for dosing the chemicals) and also the more physical conditions of mixing energy and aggregation formation. It is clear that these are design and operation variables that will affect or even control the solid phase produced by the processes discussed here.

6.1

Amounts of Solids Produced

The schematic representation of the precipitation-coagulation process in Fig. 3.13 also shows very clearly that the amount of solids produced – in the terminology of the operator the “amount of sludge produced” – depends upon the following: (a) The (mostly solid) wastewater constituents removed (b) The amount of chemicals added and removed with the formed aggregates (c) The water (from chemical dosing and from the wastewater phase) incorporated into the aggregates that are removed

3 Chemical Treatment

129 CHEMICALS

CLEAR WATER

RAW WATER

SLUDGE

ALTERNATIVE 1

CHEMICALS

CLEAR WATER

RAW WATER

SLUDGE

ALTERNATIVE 2

Fig. 3.12 Possible options in plant operation and consequences for sludge production (schematic)

One can formulate a mass balance on the basis of this observation. Such a mass balance would read as follows: Total amount

most of =

chemicals

substances +

eliminated

of solids

added

from water

generated

(90 - 99%)

(N, PO4)

or in more mathematical terms: VOLUME = f (solids, water) Or

VOLUME = f (absolute amount solids, solids content)

+

H2O

130

N. K. Shammas et al.

a Portion of precipitable/ flocculable matter

Precipitation/flocculation chemicals (with mixing water)

Portion of “transport-water”

Precipitation/Flocculation Stage

Residual amount of precipitable flocculable matter

Residual amt. of added chemicals

Purified Effluent

Substances removed and chemicals used incl. enclosed water

Solid/Water Mixture “Sludge” Vol. = 100. Removed Sub. + Chem. used Solids Content (%)

b ENCLOSED WATER

SOLIDS

CHEMICALS

1 - 2.5%

1 - 2.5%

95 - 98%

REMOVED SOLIDS SLUDGE VOLUME

+

CHEMICALS ADDED

= SOLIDS CONTENT

Fig. 3.13 (a) Schematic representation of sludge mass balance. (b) How to formulate an actual mass balance including water, solids, and chemicals

3 Chemical Treatment

131

The absolute amount of solids incorporated into the sludge is readily determined from the difference between inflow concentration of those substances that are affected and their respective effluent concentration. These parameters are routinely monitored in any plant operation. Furthermore, the amount of chemicals added and not discharged with the process effluent is to be included into the solid balance. In most practical situations, the amount of coagulant remaining in the treated water is not monitored (with the exception of water purification technology in the field of drinking water supply). Here, one will have to rely on estimates of the amount of chemicals incorporated into the aggregates. As indicated above in the verbally formulated mass balance, this fraction is very high and can be estimated for all practical purposes to be about 90–95%. The second variable listed in the functional description (or prediction) of the sludge vo1ume is the solids content. This is certainly the most sensitive parameter and also the most difficult parameter to be determined. However, solids content is a standard parameter for the characterization of sludge quality. Thus, it is determined on a routine basis. There is a large amount of empirical evidence available in the literature. Figure 3.14 exemplifies this. It is seen from the data shown in this figure that [5, 15]: (a) The solids content depends upon the amount of chemical (and the type) added. (b) The solids content decreases with increasing amounts of the most frequently used iron or aluminum salts. (c) The solids content can be improved if the inorganic coagulant is substituted in part by organic coagulant (aid) or more precisely called “flocculation.” (d) The absolute size of the solids content is lower than that of the so-called primary sludge and in the same order of magnitude as that of the secondary sludge. With these two variables set, one can attempt a prediction on the amount of sludge to be expected when chemicals are added to improve the performance of a wastewater treatment process. Figure 3.15 shows the result of such a prognosis on the basis of the above-described function. The figure also indicates the quality of such prognoses by showing for comparison’s sake the actually observed sludge volume. The prediction is undoubtedly satisfactory. (One must point out that the measurement of the second parameter entering the above-described function, the solids content, is not easily reproduced, that is, it yields fluctuating results.

6.2

Sludge Characteristics

There are four coals in sludge treatment in the realm of wastewater technology: (a) (b) (c) (d)

Volume reduction (sedimentation or flotation) Stabilization (here not considered) Dewatering (by belt or filter press) Disinfection (here not considered)

132

N. K. Shammas et al.

Solids Content [g/L]

16 12 8 4 0 0

100

200

300

400 Average amount of coagulant

500 [mg/L]

(technical) aluminium concentration

16 Solids Content [g/L]

50 mg/L 150 mg/L 250 mg/L 350 mg/L

12

8 4 0

0 0.5

2.5

5.0 9.0 Polymer Dosage [mg/L]

Fig. 3.14 Solids content of sludges resulting from differently operated chemical plants

[l/m3 AW] 50

30 (confidence interval)

10

AVR 100

200

300

400

500 [mg/L]

Fig. 3.15 [28] Projecting the amount of chemical sludge to be expected. Circle for measurement; square for computed value

3 Chemical Treatment

133

These requirements for the ultimate sludge usage or deposit are attained by different unit processes. For all these processes, the volume and the characteristics of the sludge are decisive. Thus, in addition to the prediction of the sludge volume to be expected, the average qualities of this sludge fraction must be known in order to design and operate sludge handling installations. The most important processes prior to the incineration of chemical sludge are thickening and dewatering. Thus, parameters describing the thickening properties and the dewatering characteristics must be known or assessed. Prior to the presentation of average quality parameters for the sludge, it is necessary to state that in most practical instances, the chemical sludge is not treated separately from the primary and secondary sludge. Thus, the properties of the sludge fractions to be treated are only in part determined by those of the here discussed chemical sludge fraction. Furthermore, it must be said that there are numerous possibilities to design a sludge handling installation due to the larger number of phases in the treatment process and due to the great diversity of unit processes available to accomplish these goals. The above-mentioned survey has produced results that indicate the existence of more than 25 distinctly different variations. Again, it is not possible to present data or information that could be considered representative or indicative of standard conditions. The data to be given in the following paragraphs are intended to serve as illustration. The survey also led to the insight that there is no uniform and predictable chance in the sludge properties when precipitating/coagulating chemicals are used. If one analyzes the data from this survey in great detail, then one finds the operational conditions as well as the process of liquid-solid separation determine not only the amount but also the properties of the resulting solids. The sedimentation properties of the wastewater solids are changed by the addition of chemicals. Since the velocity of sedimentation depends upon the specific gravity of the suspensor as well as upon the density/porosity of the aggregate, it is reasonable to postulate that so-called primary, that is, non-aggregated, particles sediment more rapidly than hydroxide flocs or composites of hydroxide and biological flocs. The reason is the increased inclusion of water into the solid aggregate. The worsening of the sedimentation properties as a rule is paralleled by an improved floatability of these aggregates of biological and chemical sludge particles. There is one exception to this worsening of the sedimentation properties upon the addition of chemicals. This is the use of inorganic reagents, that is, metal ions, to combat bulking sludge. In this instance, the velocity of separation by sedimentation is increased. Bulking sludge might be controlled better by the use of flotation as standard liquid-solid separation process, however. One must also take into consideration, when discussing liquid-solid separation by sedimentation, that the use of chemicals leads to an increase in the removal of suspended solids. Thus, one could expect increased sludge volume indices for the biological excess sludge when pre-precipitation/coagulation is used: here, all particles that might be enhancing the specific gravity of the biological floc have been

134

N. K. Shammas et al.

removed in the preceding step. Plant observations have indicated that this effect exists but is of no great significance. Figure 3.16 shows results from technical plants as well as from pilot plant studies. Here, the sludge volume after 2 h (120 min) has been reported for varying amounts 60

SV120 [mL/L]

a

Pre-Precipitation/ Flocculationt

40

20

0

0

10

20

30

200

ISV[mL/gTS]

b

40

50 60 Me3+ [mg/L]

Simultaneous Precipitation/ Flocculation

150 100 50 0

c

0

5

10

15

SV120 [mL/L]

50

20

25 30 Me3+ [mg/L]

Pre-Precipitation/ Flocculation

30

10 0

0

5

10

15

20

25

30

Me3+ [mg/L]

Fig. 3.16 [30] Sludge thickening as function of coagulant dosage: (a) pre-precipitation; (b) simultaneous; (c) post-precipitation

3 Chemical Treatment

135

of chemicals added. From the discussions on the principles of the process, it becomes clear that one has to distinguish between the different points of application. The following conclusions are of particular importance for the design and operation of treatment plants: (a) Any addition of chemicals prior to or into the primary sedimentation tank, that is, pretreatment, leads to increased sludge volume after 120-min sedimentation time, that is, reduced sedimentation velocity. (b) A similar decrease in the sedimentation velocity with increased chemical dosage has been observed when chemicals are dosed past the biological unit, that is, post-treatment. (c) Only in the case of dosing chemicals prior to or into the secondary sedimentation tank (i.e., simultaneous treatment) there is an improvement of the sedimentation velocity.

Sludge Volume

Fig. 3.17 Sludge thickening as function of energy input

SV120 [ml/L]

Note: it is not possible to conclude from this that there is necessarily an improvement of the flotation tendency when the sedimentation characteristics are worsened. Another interesting and promising operational measure to control sludge handling properties is the variation of the stirring rate and stirring time. Fig. 3.17 shows data, again from operating plant and pilot plant studies, where the separation characteristics (i.e., the settled volume after 120 min) are improved if the energy input is increased. The energy input is expressed as the CAMP number in this instance [29]. The CAMP number can be increased either by intensifying the energy dissipation, usually done by increasing the rotational speed of the stirring device, or by

50

40

30

20 G • t = 1, 3 • 104 G • t = 2, 6 • 104

10

G • t = 5, 4 • 104 G = const. = 20/10

0 0

5

10

15

20

25

30

35

Chemical Dosage Al3+ [mg/L]

136

N. K. Shammas et al.

increasing the stirring time or the residence time. In the instance of Fig. 3.17, the stirring rate has been kept constant, and the detention time has been increased. Investigations on the effect of varying the stirring rate and keeping the detention time constant have shown the feasibility of this concept. A possible explanation of the effect of increased CAMP numbers might be the destruction and recombination of aggregates in reactors with high detention times and/or with high shear rates. It is known that upon destruction and recombination, denser aggregates result. This increased density leads to increased floc stability and also increased sedimentation velocity. A similar observation for a coagulationflotation system does not exist. One might speculate, however, that increased aggregate strength will also further the robustness of the flotation separation (while the slight increase in specific gravity might easily be overcome by the correction of the air-solids ratio). The next phase after solids separation is the sludge thickening, that is, a separation of the water that is included in between the individual particles that form an aggregate. Thickening might well be the most decisive process in the whole line of sludge handling: malfunctioning thickeners lead to reduced volume reduction and by this to a (volumetric) overloading of all subsequent processes. Thickening has been accomplished in the past by sedimentation technique. Here, however, the flotation process [30] has entered the field, competed successfully, and in part substituted the gravity thickeners. Thickening properties, that is, separation of included water fractions, could be quantified by the same measures as those used to describe the liquid-solid separation. In this discussion, the solids content of the thickened sludge (after a defined and constant time of thickening) has been selected for the description of these properties. Figure 3.18 shows the change of the thickening properties, that is, solids content, as consequence of changed operational conditions. It is seen that [30]: (a) The less water containing primary sludges reach the highest end concentration of solids – corresponding to a medium-volume reduction. (b) The secondary sludges with usually high water content also reach very high end concentration of solids – corresponding to a very high-volume reduction. (c) The tertiary sludges with the usually high water content reach a lower end concentration of solids – corresponding to a medium-volume reduction. Decisive factors for these changes are among others the (a) organic content, (b) chemical content, (c) average particle size, and (d) three-dimensional floc network of the sludge. Naturally, it is very difficult to quantify these effects or even to explain observations evidence for the correctness of these statements and therefore for the usefulness of recommendations that are based on these parameters. After separation of solids and thickening of the sludge, the solids fraction usually has to be dewatered further for reasons of transport, for the building-in in landfills, and for incineration (if applicable). Dewatering properties are also difficult to evaluate. As in other unit processes, there is a discrepancy between the concept of the process and the feasibility of analysis. In the case of sludge dewatering, two types of analysis have proven useful:

3 Chemical Treatment

25

30

40

[ g/L ] 22

18

20

Pre-precipitation/ flocculation

Dry matter at beginning of thickening

16

14 12

10

Simultaneous precipitation/ flocculation

8

Dry matter of the thickened sludge

[ g/L ]

Fig. 3.18 Control of thickening properties by adjusting operation

137

6 6

Post-precipitation/ flocculation

2 0

0 100

80

60

40

20

0

Volume Reduction [%]

(a) the measurement of a specific filter resistance (higher analytic effort, better interpretation of process) and (b) the measurement of a capillary suction time, the time that pore water leaving the filter cake needs to move in a defined filter paper over a specified distance (easily determined but difficult in process-oriented interpretation). Figures 3.19 and 3.20, again the result of technical and pilot plant type investigations, shows the change in the capillary suction time for varying chemical dosage and for the three different points of application of chemicals. It is seen that: (a) In all instances, the capillary suction time is reduced, that is, the dewatering quality improved, when more chemicals are added. (b) The improvement of the dewatering characteristics upon increased chemical dosage is most pronounced in the instance of tertiary sludge, that is, sludge from post-precipitation/coagulation. Such improvement might have been anticipated in the case of precipitation/ coagulation with metal ions. These reagents have been used successfully in the sludge treatment process for so-called chemical conditioning: the addition of these chemicals prior to a dewatering step has led to improved efficiency of almost any dewatering instrument (vacuum filters, belt filters, filter presses, etc.).

138

N. K. Shammas et al.

Pre-precipit./flocc.

CST [s]

240

160

80

0

0

10

20

30

40

50

Me3+ [mg/L] Simult. precipit./flocc.

CST [s]

240

160

80

0

0

5

10

15

20

Me3+

[mg/L]

Post-Precipit./flocc.

240

CST [s]

25

160

80

0

0

10

20

30

40

Me3+

50

[mg/L]

Fig. 3.19 Dewatering properties as function of coagulant dosage: (a) pre-precipitation; (b) simultaneous; (c) post-precipitation

[ s]

40

Capillary suction time

3 Chemical Treatment

30

139

20

0

1,0

2,0

3,0 4,0 Number of particles (106/ mL)

Fig. 3.20 Dewatering properties correlated with total number of particles in sludge sample

Glossary [30–32] Adsorption: It is a chemical reaction or a physical-chemical reaction that the attraction and adhesion of molecules of a gas, liquid, or dissolved substances to a surface. Adsorption is a passive and reversible reaction or process. Adsorption-destabilization: It is a chemical mechanism for the coagulation of particles in which counterions are adsorbed on the surface of stable particles; thus, the particles can approach one another close enough to stick together and lose their stability in water. Advanced treatment plant (ATP): (a) A treatment facility using treatment processes that provide treatment to a higher level than that considered conventional; (b) an advanced water treatment plant may include processes such as granular activated carbon adsorption, ion exchange, ozonation, etc., in addition to a conventional surface water treatment plant consisting of mixing, coagulation/ precipitation, flocculation, clarification (either sedimentation or flotation), and filtration; (c) an advanced wastewater treatment plant may include processes such as tertiary filtration, denitrification, granular activated carbon adsorption, ion exchange, ozonation, advanced oxidation process, post-aeration, etc., in addition to a conventional biological wastewater treatment consisting of preliminary treatment, primary clarification (sedimentation or flotation), biological oxidation, and secondary clarification (sedimentation or flotation).

140

N. K. Shammas et al.

Chemical coagulation: It is a chemical reaction or unit process in which colloidal and finely divided suspended matters are destabilized and aggregated together due to addition of inorganic coagulant or polyelectrolyte. Chemical precipitation: It is a chemical reaction or unit process in which insoluble solids are generated from the soluble matters by changing the equilibrium conditions of a solution or by adding chemicals that react with the soluble matters. Chemical: It is a substance produced or used in a chemical reaction. Completely mixed continuous flow: It is a hydraulic flow regime in which a heterogeneous mixture of constituents exists throughout the liquid stream. Completely mixed continuous flow reactor: It is a chemical engineering reactor in which hydraulic behavior is such that the liquid in the reactor is completely mixed. Filtrate: It is the liquid that has passed through a filter medium. Filtration: It is a physical process for the removal of suspended materials in a liquid stream by passage of the liquid through a filter medium. Flocculation: It is a mechanical or physical process following chemical feeding, chemical coagulation, and chemical precipitation that uses gentle stirring to bring small suspended particles together so they may form larger, more settleable (or floatable) clumps called floc. Plug flow: It is a hydraulic flow regime in which no longitudinal dispersion (mixing in the direction of flow) occurs. Plug flow reactor: It is a chemical engineering reactor in which the hydraulic behavior is such that the residence time of a given input, or plug, is exactly equal to the theoretical hydraulic retention time. Polymer: It is high molecular weight organic chemical that can be used as a coagulating aid.

References 1. Shammas NK, Wang LK (2016) Water engineering: hydraulics, distribution and treatment. Wiley, New York 2. Fair GM, Geyer JC, Okun DA (1968) Water and wastewater engineering. Wiley, New York 3. Imhoff K (1979) Taschenbuch der Stadtentwasserung, 25th edn. Oldenbourg Verlag, Munchen 4. Dunbar W (1954) Leitfaden fur die Abwassereinigungsfrage, 3rd edn. Oldenbourg Verlag, Munchen 5. Shammas NK (2005) Coagulation and flocculation. In: Wang LK, Hung YT, Shammas NK (eds) Physiochemical treatment processes. Humana Press, Totowa 6. Hahn H (1983) Einsatz von Fallungs-und Flockungsmitteln. In: Weitergehende Abwassereinigung. Fortbildungskurs C/4 der Abwassertechnischen Vereinigung St, Augustin 7. Wang LK, Shammas NK, Selke WA, Aulenbach DB (2010) Flotation technology. Humana Press, Totowa 8. Kruyt HR (1969) Editors, colloid chemistry, 5th edn. Elsevier Publishing Company, Amsterdam/New York 9. Amouda OS, Amoo IA (2017) Coagulation/flocculation process and sludge conditioning in beverage industrial wastewater treatment. http://scholar.google.com/scholar_url?url¼https:// www.researchgate.net/profile/Ia_Amoo/publication/6831726_Coagulationflocculation_pro cess_and_sludge_conditioning_in_beverage_industrial_wastewater_treatment/links/

3 Chemical Treatment

141

00b7d53cd7fa5c9be6000000.pdf&hl¼en&sa¼X&scisig¼AAGBfm3yPDYnFTlpFhwtf8RU5iG_ogHxQ&nossl¼1&oi¼scholarr, 27 July 2006. PDF file retrieved 15 April, 2017 10. Van Olphen H (1963) Clay colloid chemistry. Interscience Publishers, New York/London 11. Hahn HH, Stum W (1968) The role of adsorption in the kinetics of coagulation. J Colloid Interface Sci 28:134–144 12. Glasstone S, Lewis D (1960) Elements of physical chemistry. Van Nostrand, Princeton 13. Sahu OP, Chaudhari PK (2013) Review of chemical treatment of industrial wastewater. J Appl Sci Environ Manage 17(2):241–257. http://www.google.com/url?sa¼t&rct¼j&q¼&esrc¼s& source¼web&cd¼15&ved¼0ahUKEwiR8rrN9qXTAhXH7oMKHSFuANI4ChAWCGMwB A&url¼http%3A%2F%2Fwww.bioline.org.br%2Fpdf%3Fja13028&usg¼AFQjCNGnnjLps7vsnQ6mmUNrGJ2GKgF2w&sig2¼4GmeJw7JrKq0V_LuaAiTvg. Retrieved, April 17, 2017 14. Amuda OS, Amoo OS, Ajayi OO (2017) Performance optimization of coagulant/flocculant in the treatment of wastewater from a beverage industry. http://scholar.google.com/scholar_url? url¼http://www.academia.edu/download/33723265/JHAZ_1.pdf&hl¼en&sa¼X& scisig¼AAGBfm2iZSw5OVPyy3NqQt2wDOF7Es2Djw&nossl¼1&oi¼scholarr, 2005. Retrieved April 15, 2017 15. Wang LK, Hung YT, Shammas NK (eds) (2005) Physicochemical treatment processes. Humana Press, Totowa, pp 526–671 16. Wang LK, Hung YT, Shammas NK (eds) (2006) Advanced physicochemical treatment processes. Humana Press, Totowa, pp 203–260 17. Wang LK, Hung YT, Shammas NK (eds) (2007) Advanced physicochemical treatment technologies. Humana Press, Totowa, pp 295–390 18. Ives KJ (ed) (1982) The scientific basis of flocculation. The Hague, Martinus Nijhoff Publishers 19. Culp RL, Culp GL (1972) Advanced wastewater treatment. Van Nostrand Reinhold Environmental Engineering Series, New York 20. Weber JW (1972) Physicochemical processes for water quality control. Wile-Interscience, New York 21. Levenspiel O (1962) Chemical reaction engineering. Wiley, New York 22. Herbert D (1960) A theoretical analysis of continuous culture systems. Soc Chem Ind Monogr 12:21–53 23. Brodkey KR (1975) Turbulence in mixing operations. Academic Press, Bonn 24. Abu Hassan MA, Li TP, Noor ZZ (2008) Coagulation and flocculation treatment of wastewater in textile industry using chitosan. J Chem Nat Resour Eng 4(1):43–53. http://scholar.google. com/scholar_url?url¼https://www.researchgate.net/profile/Zainura_Zainon_Noor/publication/ 228634338_Coagulation_and_flocculation_treatment_of_wastewater_in_textile_industry_ u s i n g _ c h i t o s a n / l i n k s / 0 0 b 4 9 5 1 7 9 f 0 7 1 9 9 2 3 6 0 0 0 0 0 0 . p d f & h l ¼e n & s a ¼X & scisig¼AAGBfm3zUVKwHpp3uB0OQj-U4Djnxy9k9A&nossl¼1&oi¼scholarr. Retrieved April 15, 2017 25. Ayeche R (2012) Treatment by coagulation-flocculation of dairy wastewater with the residual lime of National Algerian Industrial Gases Company (NIGC-Annaba). Energy Procedia 18:147–156. http://www.sciencedirect.com/science/article/pii/S1876610212007965. Retrieved April 15, 2017 26. Prakash NB, Sockan B, Jayakaran P (2014) Wastewater treatment by coagulation and flocculation. IJESIT 3(2). http://www.google.com/url?sa¼t&rct¼j&q¼&esrc¼s&source¼web& cd¼7&ved¼0ahUKEwiIzLvU46XTAhVD44MKHXnSBncQFghUMAY&url¼http%3A%2F %2Fwww.ijesit.com%2FVolume%25203%2FIssue%25202%2FIJESIT201402_61.pdf& usg¼AFQjCNG5sjDzLnOktLqq26G-i3hkxtF2ng&sig2¼6RIbHNbrVeiEt-oXsJvHsw. Retrieved, April 17, 2017 27. Eckenfelder WW Jr (1975) Wastewater treatment design – part II. Water Sewage Works 122:70–92

142

N. K. Shammas et al.

28. Rao LN (2015) Coagulation and flocculation of industrial wastewater by Chitosan. IJEAS 2:7, https://www.google.com/?client¼safari&channel¼iphone_bm#channel¼iphone_bm& q¼coagulation+and+flocculation+of+industrial+wastewater&spf¼1. Retrieved April 15, 2017 29. Camp TR, Stein PC (1943) Velocity gradients and internal work in fluid motion. J Boston Soc Civ Eng 30:219–238 30. Wang LK, Wang MHS, Shammas NK (2020) Environmental flotation engineering. Springer, New York, USA 31. Wang MHS, Wang LK (2020) Glossary of environmental and natural resources engineering. In: Wang LK, Wang MHS, Shammas NK (eds) Environmental and natural resources engineering. Springer, New York, USA 32. Wang MHS, Wang LK (2020) Glossary of adsorptive bubble separation, flotation, and water purification. In: Wang LK, Wang MHS, Shammas NK (eds) Environmental flotation engineering. Springer, New York, USA

Chapter 4

A New Wave of Flotation Technology Advancement for Wastewater Treatment Lawrence K. Wang and Mu-Hao Sung Wang

Contents 1 2 3 4

Introduction: A New Wave of Flotation Technology Advancement . . . . . . . . . . . . . . . . . . . . . . . History of Improvement in Dissolved Air Flotation Clarification . . . . . . . . . . . . . . . . . . . . . . . . . History of Improvement in Sedimentation Clarification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Review of DAF Performance Investigated and Recommended by the US Environmental Protection Agency (USEPA) and the Lenox Institute of Water Technology (LIWT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Groundwater Treatment Using DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Treatment of Textile Mill Effluent by DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Treatment of Pulp Mill and Paper Mill Effluent by DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Treatment of Petroleum Refining Wastewater by DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Treatment of Auto and Laundry Wastewater by DAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Treatment of Seafood Processing Wastewater by DAF and Granular Activated Carbon (GAC) Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Treatment of Storm Runoff by DAFF and Sand Filtration for Arsenic Removal . . . . 5 Additional Case Study: Parallel Comparison of an Old Sedimentation Clarifier and a New Replacement DAF Clarifier for Treating Same Flow of Process Water in a Paper Mill . . 6 Additional Case Study: Comparison Between an Innovative DAF-Sedimentation Clarifier and a Conventional Sedimentation Clarifier for Treating a Paper Mill Effluent . . . . . . . . . . . 7 Additional Case Study: A Compact Municipal Biological Wastewater Treatment Using a DAF for Primary Clarification and Secondary Clarification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

145 146 147

148 148 150 150 151 153 153 155 157 157 159 161 161 162

Abstract This chapter describes the progress made during the last 70 years in the design, operation, and performance of dissolved air flotation (DAF). Open tank sedimentation clarifiers are presently used as primary clarifier, secondary clarifier, or tertiary clarifier. This is mainly because of reluctance to accept new technology in DAF clarifier development. In industry, particularly in paper mills, DAF clarifiers have obtained a growing acceptance. L. K. Wang (*) · M.-H. S. Wang Lenox Institute of Water Technology, Newtonville, NY, USA © Springer Nature Switzerland AG 2021 L. K. Wang, M. -H. S. Wang, N. K. Shammas, D. B. Aulenbach (eds.), Environmental Flotation Engineering, Handbook of Environmental Engineering 21, https://doi.org/10.1007/978-3-030-54642-7_4

143

144

L. K. Wang and M.-H. S. Wang

The development of open tank sedimentation clarifiers during the last 70 years has been very limited. The specific clarification is still limited to 0.5 GPM per square foot (20 L/square m/min). With chemical treatment, the specific load and the clarification have been improved. Retention times of sedimentation are still 60–200 min. Lamella-type sedimentation clarifiers have been developed and have obtained application in potable water clarification with very low solid loads. Therefore, they are still not applicable to wastewater sedimentation clarification. Rapid development of dissolved air flotation has reached the present clarification loads of 3.5 GPM/square foot (140 L/square m/min.) up to 10.5 GPM/square foot (420 L/square m/min.) for triple stacked units. The maximum flow into one DAF unit is presently 8000 GPM (30.4 cubic m/min.). For triple stacked DAF units, the maximum flow is 24,000 GPM (91.0 cubic m/min.). The retention time is reduced to 3 minutes. The comparison between an open tank sedimentation clarifier and DAF clarifier shows: (a) DAF floor space requirement is 15% of the sedimentation clarifier and (b) DAF volume (retention time) requirement is about 5% of the sedimentation clarifier. The degree of clarification of the DAF clarifier is about the same as for the sedimentation clarifier with the same flocculating chemical addition. The operational cost of the DAF clarifier is slightly higher than that for the sedimentation clarifier, but this is largely offset by considerably lower cost of the installation’s financing. DAF clarifiers are mainly built in stainless steel, while sedimentation clarifiers use concrete tanks. The stainless steel construction improves corrosion resistance. Prefabricated construction gives lower erection cost and better flexibility for future changes. Examples of industrial applications of DAF clarifiers are shown for paper mill in-plant clarification, final effluent clarification, and recycled water clarification in waste paper deinking facilities. Several examples of major industrial and municipal wastewater treatment plants with DAF clarifiers for primary and secondary clarification are shown. The installation cost and space requirement are considerably reduced. This chapter presents DAF’s technical performance data for treating groundwater, textile mill effluent, pulp and paper mill effluent, auto and laundry wastewater, seafood processing wastewater, and municipal wastewater all involving the use of DAF for industrial pretreatment, primary flotation clarification, and secondary flotation clarification. A comparison between DAF clarification and sedimentation clarification is made. Although the engineering data have been generated using the Lenox Institute of Water Technology (LIWT) and Krofta Engineering Corporation (KEC) process equipment, any DAF manufacturer’s process equipment can be used to achieve similar DAF performance results. A pilot plant demonstration is highly recommended by the authors before purchasing any DAF process equipment. Keywords Milos Krofta · Clarification · Dissolved air flotation · Sedimentation · Industrial effluent treatment · Municipal wastewater treatment · Primary clarifier · Secondary clarifier · US Environmental Protection Agency results · Lenox Institute of Water Technology · Krofta Engineering Corporation · Case histories · Memoir ·

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

145

Groundwater · Textile mill effluent · Pulp and paper mill effluent · Auto and laundry wastewater · Seafood processing wastewater · Municipal wastewater · DAF · DAFF · Supracell · Sandfloat · Sedifloat · Clari-DAF · AquaDAF

Acronyms ADT AWWA BOD COD DAF GAC GPM IAF KEC LIWT NSF O&G TP USEPA USFDA

Air dissolving tubes American Water Works Association Biochemical oxygen demand Chemical oxygen demand Dissolved air flotation Granular activated carbon Gallon per minute Induced air flotation Krofta Engineering Corporation Lenox Institute of Water Technology National Sanitation Foundation Oil and grease Total phosphorus US Environmental Protection Agency US Food and Drug Administration

1 Introduction: A New Wave of Flotation Technology Advancement The first wave of flotation technology advancement has been for drinking water treatment. The very first dissolved air flotation (DAF) water filtration plant was designed and installed jointly by the Lenox Institute of Water Technology (LIWT) and Krofta Engineering Corporation (KEC) for the town of Lenox, Massachusetts, USA (1 million gallons per day or 1 MGD capacity), in 1982. Later, with the joint effort of LIWT, KEC, and consulting engineering firms, the world’s once-largest DAF water filtration plant (37.5 MGD) was installed in 1986 for the city of Pittsfield, Massachusetts, USA. Now, the DAF goes to main stream for potable water treatment. Too many potable water DAF plants have been built in the world; even the world’s largest city, New York, has adopted the DAF technology. It has been a big success. Famous commercial potable DAF plants include Sandfloat (a combined DAF-filtration plant, known as DAFF), KAMWT (a combined DAF-DAFF two-stage flotation plant), AquaDAF, Clari-DAF, etc. Now, it is time for all researchers, engineers, and plant managers to study, promote, consider, and welcome the second wave of flotation technology advancement for wastewater treatment.

146

L. K. Wang and M.-H. S. Wang

There are two types flotation processes for wastewater treatment: (a) dissolved air flotation and (b) dispersed air flotation or induced air flotation or IAF. The expression “flotation” or DAF is used for dissolved air flotation in this chapter. The air flow to water flow ratio of DAF is about 1%, and the air flow to water flow ratio for IAF is about 400%. IAF involves the use of surfactant as the flotation aid and is widely used in mining industry. IAF pilot plant tests conducted jointly by the Lenox Institute of Water Technology (LIWT) and Krofta Engineering Corporation (KEC) show that the Pittsfield (Massachusetts) raw water can be successfully treated by IAF and sand filtration to meet the US Environmental Protection Agency (USEPA) and the Commonwealth of Massachusetts Drinking Water Standards. The surfactant used in the IAF was approved by the US Food and Drug Administration (USFDA) but is difficult to be quickly approved by the American Water Works Association (AWWA) and the National Sanitation Foundation (NSF). The lesson we have learned is that for DAF to compete with conventional sedimentation, the conventional types of chemicals or chemical aids should be used.

2 History of Improvement in Dissolved Air Flotation Clarification The following progress has been made since 70 years ago [1–70]: (a) Specific clarification load increased from 1.5 GPM/ft2 (60 L/m2/min) to 3.5 GPM/ft2 (140 L/m2/min) and that for triple stacked unit to 10 GPM/ft2 (420 L/ m2/min). (b) The retention time of water in the flotation clarifier decreased from 30 to 3 min. (c) The largest unit size increased from 260 GPM (1000 L/min) to 7900 GPM (3000 L/min) and that for triple stacked units to 23,700 GPM (90,000 L/min). (d) The size of modern DAF units is much smaller. It allows construction predominantly in stainless steel, prefabricated for easy erection. (e) The smaller size and weight (120 lb./ft2, 600 kg/m2) allow installation on posts leaving free passage under the unit. It is easier to find available space for indoor installation and to construct inexpensive housing. (f) Air dissolving is improved and now requires a retention time of only 10 s in the air dissolving tube instead of the previous 60 s. This reduction in retention time results in smaller air dissolving tubes (ADT) which are predominantly built from stainless steel. (g) Availability of excellent flocculating chemicals gives a high stability of operation and high clarification degree.

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

147

Presently, the DAF clarifiers have not yet reached the theoretical limit of specific clarification. Normal flotation velocity is 12 inch/min (300 mm/min), corresponding to 7.5 GPM/ft2 (300 L/min/m2). The highest present specific clarification is 3.75 GPM/ft2 (150 L/min/m2) for normal operation. Further development is in process to develop an X-Cell which would come closer to the theoretical limit of the flotation process.

3 History of Improvement in Sedimentation Clarification From the very start, sedimentation operated with the maximum theoretical specific clarification rate. The normal settling velocity is approximately 0.8 inch/min (20 mm/min); that corresponds to 0.5 GPM/ft2 (20 L/min/m2). Present sedimentation clarifiers are designed with this clarification load. Because the settled sludge does not compact readily, the sludge bed must be kept rather deep, 39 inches (1 m) or more, and this restricts the design of shallow sedimentation clarifiers. Improvements made in the past 70 years are: (a) Use of flocculating chemicals to improve clarification and compacting of settled sludge. (b) In settling cones, bottom stirrers are installed for better thickening of the settled sludge or for preventing packing of the settled sludge, particularly in coating the final effluent clarification. (c) Inclined lamella settling clarifiers have been developed, allowing a substantial specific load increase, but still requiring rather deep sludge hoppers. In clarification of fresh water with very low amount of settled material, these units are successful. (d) Criss-cross lamella packages can be mounted on the free surface of a settling tank with central shaft bottom scraper drive. In this way, the specific clarification per surface can be increased by 50–100%. However, the settled sludge may require a still deeper sludge level. These surface inserts are applicable when the suspended solids in the raw water are low. The above improvements in settling clarifiers are of rather marginal importance, and the fact remains that sedimentation operates close to the theoretical limit without possibility of improvement in space requirement, retention time, and sludge thickening.

148

L. K. Wang and M.-H. S. Wang

4 Review of DAF Performance Investigated and Recommended by the US Environmental Protection Agency (USEPA) and the Lenox Institute of Water Technology (LIWT) 4.1

Groundwater Treatment Using DAF

Table 4.1 indicates the toxic organic compounds commonly found in the US groundwater. According to the government data presented in Table 4.2, DAF is not only an excellent process for the removal of classical pollutants, such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), total

Table 4.1 Toxic organic compounds commonly found in the US groundwater Organic compounds in groundwater Carbon tetrachloride Chloroform Dibromochloropropane DDD DDE DDT CIS-1,2-dichloroethylene Dichloropentadiene Diisopropyl ether Tertiary methyl-butylether Diisopropyl methyl phosphonate 1,3-dichloropropene Dichlorethyl ether Dichloroisopropylether Benzene Acetone Ethyl acrylate Trichlorotrifloroethane Methylene chloride Phenol Orthochlorophenol Tetrachloroethylene Trichloroethylene 1, 1, 1-Trichloroethane Vinylidiene chloride Toluene Xylenes EDB Others

Percent of occurrences 5 7 1 1 1 1 11 1 3 1 1 1 1 1 3 1 1 1 3 3 1 13 20 8 3 1 4 1 1

Concentration range 130 ug/L–10 mg/L 20 ug/1–3.4 mg/L 2–5 mg/L 1 ug/L 1 ug/L 4 ug/L 5 ug/L–4 mg/L 450 ug/L 20–34 ug/L 33 ug/L 1250 ug/L 10 ug/L 1.1 mg/L 0.8 mg/L 0.4–11 mg/L 10–100 ug/L 200 mg/L 6 mg/L 1–21 mg/L 63 mg/L 100 mg/L 5 ug/L–70 mg/L 5 ug/L–16 mg/L 60 ug/L–25 mg/L 5 ug/L–4 mg/L 5–7 mg/L 0.2–10 mg/L 10 ug/L Not available

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

149

Table 4.2 Control technology summary for dissolved air flotation Pollutant Classical pollutants, mg/L: BOD (5-day) COD TSS Total phosphorus Total phenols(a) Oil and grease Toxic pollutants, ug/L: Antimony Arsenic Xylene Cadmium Chromium Copper Cyanide Lead Mercury Nickel Selenium Silver Zinc Bis (2-ethylhexyl) phthalate Butyl benzyl phthalate Carbon tetrachloride Chloroform Dichlorobromomethane Di-n-butyl phthalate Diethyl phthalate Di-n-octyl phthalate N-nitrosodiphenylamine 2, 4-Dimethylphenol Pentachlorophenol Phenol Dichlorobenzene Ethylbenzene Toluene Naphthalene Anthracene/phenanthrene

Effluent concentration Range Median

Percent removal

140–1000 18–3200 18–740 0.001–23 16–220

250 1200 82 0.66 0.66 84

68 66 88 98 12 79

ND-2300 ND-18 ND-1000 BDL-99 78 66 >99 19 57 76 65 39 77 81

ND-300 ND-33 ND-28 5–30 9–2400 18–260 ND-970 ND-2100 ND-840 0.2–600

Source: U.S. EPA BDL below detection limit, ND not detected, NM not meaningful a Approximate value

150

L. K. Wang and M.-H. S. Wang

phosphorus (TP), total phenols, and oil and grease (O&G), but also an excellent process for the removal of toxic pollutants, such as heavy metals, and toxic organic compounds.

4.2

Treatment of Textile Mill Effluent by DAF

Tables 4.3A and 4.3B are the USEPA data and the LIWT data, respectively, for treatment of textile mill wastewater. Senior author Lawrence K. Wang received an engineering award from a Korean professional association in Seoul, Korea, for transferring DAF technology from the USA to South Korea.

4.3

Treatment of Pulp Mill and Paper Mill Effluent by DAF

Table 4.4 presents the USEPA data on treatment of pulp and paper mill effluent by DAF. Generally, a pilot plant demonstration is needed to obtain actual performance of DAF because there are so many commercial DAF manufacturers. Table 4.3A Treatment of textile mills effluent by dissolved air flotation Removal data Sampling: average of two 24-hour samples Concentration Influent Pollutant/parameter Classical pollutants, mg/L: BOD (5) 400 COD 1000 TSS 200 Total phenol 0.092 Toxic pollutants, ug/L: Copper 320 Lead 14 Bis(2-ethylhexyl) phthalate 570 Di-n-butyl phthalate 13 Pentachlorophenol 37 Phenol 94 Benzene 18 Ethylbenzene 460 Toluene 320 Naphthalene 250 Source: U.S. EPA ND not detected

Analysis: data sets 1 Effluent

Percent removal

50 28–70 84 72

81 ND 45 ND 30 26 12 160 130 ND

75 >99 92 >99 19 72 33 65 59 >99

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

151

Table 4.3B Performance of a dissolved air flotation pilot plant at a textile mill in Seoul, Korea (December, 1990) Time vs. parameter 12/19/90 (1st) Flow COD pH TSS 12/19/90 (2nd) Flow COD pH TSS 12/20/90 (1st) Flow COD pH TSS 12/20/90 (2nd) Flow COD pH TSS 12/21/90 Flow COD PH TSS 12/22/90 Flow COD pH TSS a

Influent characteristicsa

Effluent characteristicsb

Percent reduction

80 m3/day 280 mg/L 7.2 unit 800 mg/L

99

Source: U.S. EPA ND not detected Table 4.5 Treatment of petroleum refining wastewater by dissolved air flotation Removal data Sampling: 3-daily grab composite Pollutant/parameter Toxic pollutants, ug/L: Chromium Copper Lead Zinc Phenol Anthracene/phenanthrenea Naphthalene

Analysis: data sets 1 Concentration Influent

Effluent

Percent removal

720 16 250 110 4900 1100 1100

570 5 210 83 2400 600 700

5 69 16 22 51 45 36

Source: U.S. EPA a Concentration represent sums for these two compounds which elute simultaneously and have the same major ions for GC/MS

has been demonstrated by professional engineers many times worldwide. LIWT and KEC together have designed and installed too many DAF (Supracell) and DAFF (Sandfloat) units for major petroleum refineries around the world. Figure 4.1 shows that one of the petroleum refineries has adopted three Krofta flotation units for its needs: (a) one DAFF (Sandfloat) unit for treating the oil separation effluent in order to remove sulfides; (b) one DAF (Supracell) unit for treating the bioreactor effluent; and (c) one DAFF (Supracell) unit for treating the plant’s tertiary pond effluent for the purpose of water reuse. There are huge industrial applications for DAF and DAFF. All

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

153

CHEMICALS OIL SEPARATION

SULFIDE BEARING SPENT CUSTIC STREAMS

SANDFLOAT FOR SULFIDES REMOVAL DEWATERING

THICKENING

SLOP OIL TANK

SLUDGE LAGOONS

LANDFILL

SUPERNATANT

PROCESS

OIL SEPARATION

SUMP

RAIN WATER

&

HOUSE

STREAMS

BIOLOGICAL TREATMENT

BIOREACTOR

SUPRACELL

BLOW DOWN

P

DISPOSAL

TERTIARY PONDS

SURGE PONDS

COOLING TOWER

SEWAGE

OIL SEPARATION

EQUALIZATION POND

PUMP

OTHER

SANITARY

RECV’NG

SANDFLOAT

SCREEN & GRIT

REUSE

Fig. 4.1 A case history of a petroleum refining plant having multiple dissolved air flotation clarifiers for various applications

researchers, engineers, and flotation manufacturers should take notes. It is understood that if Supracell and Supracell units work, other manufacturers’ DAF products may also work. This chapter is written for everyone because LIWT is a nonprofit organization with a goal to serve all mankind and to promote peace on earth.

4.5

Treatment of Auto and Laundry Wastewater by DAF

The USEPA results showing how DAF can treat the auto and laundry wastewater successfully are presented in Tables 4.6A and 4.6B. The good results are expected because DAF is good for O&G removal.

4.6

Treatment of Seafood Processing Wastewater by DAF and Granular Activated Carbon (GAC) Adsorption

The Lenox Institute of Water Technology (LIWT) presents the Institute’s own results in Table 4.7 for combined DAF-GAC treatment of a seafood processing wastewater. Industrial scale pilot plant and GAC columns were installed in a

154

L. K. Wang and M.-H. S. Wang

Table 4.6A Treatment of auto and laundry wastewater by dissolved air flotation Removal data Sampling: 2-day composite and grab Concentration Influent Effluent Pollutant/parameter Classical pollutants, mg/L: COD 6400 3200 TOC 1700 690 TSS 390 98 Oil and greasea 700 140 Total phosphorus 42 1.7 Toxic pollutants, ug/L: Antimony 94 BDL Arsenic 10 2 Cadmium 110 BDL Chromium 480 270 Copper 1500 500 Cyanide 57 54 Lead 4800 130 Nickel 350 250 Zinc 3700 230 Bis (2-ethylhexyl) phthalate 1200 220 Butyl benzyl phthalate 310 ND Di-n-butyl phthalate 92 19 Di-n-octyl phthalate 150 33 2,4 Dimethylphenol 460 ND Phenol 98 42 Dichlorobenzene 1100 260 Anthracene/phenanthrene 380 66 Naphthalene 4800 840 Methylene chloride 2 2 1,1,1-Trichloroethane 18 14

Analysis: data sets 1 Percent removal

Detection limit

50 59 75 80 96 95b 80 >99b 44 67 5 97 29 94 82 >99 79 78 >99 57 76 83 83 0 22

10 1 2 4 4 22 36 1 0.04 0.03 0.02 0.89 0.4 0.01 0.007 0.4 2

Source: U.S. EPA Blanks indicate data not available BDL below detection limit, ND not detected a Average of four samples b Approximate value Chemical dosages ¼ 1800 mg/L CaCl2 & 2 mg/L polymer

selected seafood processing plant for an extensive period time. LIWT pilot plant or full-scale plant testing results are reported elsewhere in detail. The readers are referred to the original technical paper for the testing samples, locations, conditions, time, etc. It can be seen from Table 4.7 that DAF alone may not meet the direct effluent discharge standards to a receiving stream, and GAC may be needed. However, DAF alone may properly pretreat the seafood wastewater to get permission to discharge the plant’s DAF pretreated effluent to the municipal sewage treatment for further treatment.

4 A New Wave of Flotation Technology Advancement for Wastewater Treatment

155

Table 4.6B Treatment of auto and laundry wastewater by dissolved air flotation Removal data Sampling: 2-day composite and grab Concentration Influent Effluent Pollutant/parameter Classical pollutants, mg/L: COD 500 460 TOC 140 87 TSS 50 32 Oil and greasea 39 16 Total phenol 0.43 0.39 Toxic pollutants, ug/L: Copper 55 50 Cyanide 29 25 Zinc 290 240 Bis (2-ethylhexyl) phthalate 82 74 Butyl benzyl phthalate 17 ND Di-n-butyl phthalate 2 ND Di-n-octyl phthalate 28 11 Anthracene/phenanthrene 0.9 0.2 Naphthalene 0.9 0.6 Pyrene 0.3 0.3 Chloroform* 41 24 Methylene chloride 57 22 Tetrachloroethylene 2 2 1,1,1-Trichloroethane 2 ND

Analysis: data sets 1 Percent removal

Detection limit

8 38 36 59 9 9 14 17 10