Particles in WaterProperties and Processes John Gregory University College London England A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the a
Trang 1Particles in Water
Properties and Processes
Trang 2Particles in Water
Properties and Processes
John Gregory University College London
England
A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.
Boca Raton London New York
© 2006 by Taylor & Francis Group, LLC
Trang 3Co-published by IWA Publishing, Alliance House, 12 Caxton Street, London SW1H 0QS, UK
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Published in 2006 by
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© 2006 by Taylor & Francis Group, LLC
CRC Press is an imprint of Taylor & Francis Group
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International Standard Book Number-10: 1-58716-085-4 (Hardcover)
International Standard Book Number-13: 978-1-58716-085-1 (Hardcover)
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Library of Congress Cataloging-in-Publication Data
Gregory, J (John),
1938-Particles in water : properties and processes / John Gregory.
p cm.
Includes bibliographical references and index.
ISBN 1-58716-085-4
1 Water chemistry 2 Particles I Title.
GB855.G74 2005
Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com
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TX854_Discl.fm Page 1 Tuesday, August 2, 2005 10:43 AM
Trang 4To my wife, Dzintra, for her tolerance and support over the many years of my involvement with the subject of particles in water.
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© 2006 by Taylor & Francis Group, LLC
Trang 5My professional involvement with particles in water began more than 40 years ago, with studies for my Ph.D (University of London, 1964) on the role of colloid interactions in deep bed filtration Since then, my research has been concerned mainly with various aspects of water treatment, especially the removal of particles from water This book is a distillation of a great deal
of experience in the area of aquatic particles, from a mainly fundamental standpoint but with some attention to more practical aspects
Although I have a degree in chemistry, I had no formal training in colloid science and am entirely self-taught in this subject For this reason, I have tended to acquire knowledge in a rather selective and piecemeal manner, without straying too far from topics directly relevant to my research Although this strategy has its limitations, the experience has given me a good appreciation of difficulties faced by those just entering the field, and I have tried to present material in an easily understandable manner, without going into a lot of technical detail In particular, although important math-ematical results are presented and their implications are discussed, very few derivations are given
This approach has some similarity to one advocated by Sir Walter Scott
“But, after all, it is better that the travellers should have to step over a ditch than to wade through a morass — that the reader should have to suppose what may easily be inferred than be obliged to creep through pages of dull explanation.” Although there could be some doubt in several cases about
“what may easily be inferred,” I hope that my readers will not mind taking convenient shortcuts
Chapter one is a brief introduction, outlining the origin, nature, and properties of particles in water This is followed by Chapter two, which deals with particle size, transport processes, and light scattering There is also a brief section dealing in broad outline with important techniques for particle size determination Chapter three covers the important topic of surface charge, which plays a major role in colloid stability Interactions between particles (“colloid interactions”) and colloid stability are discussed in Chap-ter four, with some emphasis on the role of dissolved salts ChapChap-ter five gives an account of particle aggregation kinetics, the form of aggregates, and aggregate strength, all of which are of considerable fundamental and
prac-TX854_C000.fm Page vii Tuesday, August 2, 2005 10:30 AM
Trang 6tical importance Chapter six deals with coagulation and flocculation and the modes of action of some common additives that are used in these pro-cesses The book concludes with Chapter seven, which gives an overview
of some important solid–liquid separation processes and the principles on which they are based
Much of the material is applicable to rather dilute suspensions of parti-cles and is relevant to water treatment processes However, many of the principles discussed are of more general application and should be of some interest to all who deal with aqueous suspensions Some knowledge of basic chemistry, physics, and mathematics is assumed
I am grateful to many colleagues and students around the world, who have provided much needed intellectual stimulation from time to time Special thanks go to my long-term colleague, friend, and Ph.D advisor, Professor Ken Ives, who introduced me to the subject of particles in water and gave me the opportunity to pursue research in this area
John Gregory
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© 2006 by Taylor & Francis Group, LLC
Trang 7About the author
John Gregory is Emeritus Professor of Water Chemistry, Department of Civil and Environmental Engineering, University College London He has
a B.Sc (chemistry) and a Ph.D (physical chemistry), both from the Univer-sity of London
Although nearly all of his professional life has been spent at University College London, Professor Gregory has had sabbatical periods at universi-ties in Pittsburgh and Delaware (United States), Karlsruhe (Germany), and Perth (Australia)
Professor Gregory has about 40 years of experience in teaching and research in the areas of water pollution and water treatment His research work has focused mainly on physicochemical treatment processes, especially flocculation and filtration, and he has authored more than 100 publications
in these and related areas He is internationally known for his research on polymeric flocculants, colloidal interactions, and monitoring techniques He introduced the well-known “electrostatic patch” model for flocculation by polyelectrolytes in 1973 During the 1980s, he was involved in the develop-ment of a simple monitoring technique for particles and aggregates in flow-ing suspensions, which has been commercialized and is widely used around the world He has been invited to lecture on his research at many interna-tional conferences
Professor Gregory has served in various capacities on several profes-sional bodies, including as Advisor to the AWWA Research Committee on Coagulation and Chairman of the Filtration Society (United Kingdom) He has been on the Council of the International Association of Colloid and Interface Scientists (IACIS) and was an Associate Member of the IUPAC Commission on Colloid and Surface Chemistry He is European Editor of
Environmental Engineering Science and serves on the editorial boards of Aqua
and Colloids and Surfaces.
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Trang 8Chapter one Introduction 1
1.1 Particles in the aquatic environment 1
1.1.1 Origin and nature 1
1.1.2 Particle size ranges 2
1.1.3 Effects of particles in water 5
1.2 Colloidal aspects 5
1.2.1 Classification of colloids 6
1.2.2 Stability of hydrophobic colloids 7
1.2.3 Particle separation processes 8
Further reading 8
Chapter two Particle size and related properties 9
2.1 Particle size and shape 9
2.2 Particle size distributions 10
2.2.1 General 10
2.2.2 The log-normal distribution 14
2.2.3 The power law distribution 17
2.3 Particle transport 19
2.3.1 Fluid drag 20
2.3.2 Diffusion 22
2.3.3 Sedimentation 23
2.3.4 Effect of particle size 25
2.4 Light scattering and turbidity 26
2.4.1 General 26
2.4.2 Turbidity and light transmission 28
2.4.3 Rayleigh theory 30
2.4.4 Mie theory 33
2.4.5 Anomalous diffraction 37
2.4.6 Rayleigh-Gans-Debye scattering 38
2.5 Measurement of particle size 38
2.5.1 Direct methods (microscopy) 39
2.5.2 Particle counting and sizing 40
2.5.3 Static light scattering 43
2.5.4 Fraunhofer diffraction 44 TX854_book.fm Page xi Monday, June 20, 2005 12:04 PM
© 2006 by Taylor & Francis Group, LLC
Trang 92.5.5 Dynamic light scattering 44
2.5.6 Sedimentation methods 45
Further reading 46
Chapter three Surface charge 47
3.1 Origin of surface charge 47
3.1.1 Dissolution of constituent ions 47
3.1.2 Surface ionization 49
3.1.3 Isomorphous substitution 51
3.1.4 Specific adsorption of ions 51
3.2 The electrical double layer 52
3.2.1 The double layer at a flat interface 52
3.2.2 Charge and potential distribution in the double layer 55
3.2.3 Spherical particles 57
3.3 Electrokinetic phenomena 58
3.3.1 The plane of shear and the zeta potential 59
3.3.2 Electrophoresis and electrophoretic mobility 60
Further reading 62
Chapter four Colloid interactions and colloid stability 63
4.1 Colloid interactions — general concepts 63
4.1.1 Importance of particle size 63
4.1.2 Force and potential energy 64
4.1.3 Geometry of interacting systems 65
4.1.4 Types of interaction 66
4.2 van der Waals interaction 67
4.2.1 Intermolecular forces 67
4.2.2 Interaction between macroscopic objects 67
4.2.3 Hamaker constants 70
4.2.4 Effect of dispersion medium 72
4.2.5 Retardation 74
4.3 Electrical double-layer interaction 75
4.3.1 Basic assumptions 75
4.3.2 Interaction between flat plates and spheres 76
4.4 Combined interaction — DLVO theory 78
4.4.1 Potential energy diagram 78
4.4.2 Effect of ionic strength — critical coagulation concentration 80
4.4.3 Specific counterion adsorption 84
4.4.4 Stability ratio 86
4.5 Non-DLVO interactions 88
4.5.1 Hydration effects 88
4.5.2 Hydrophobic attraction 89
4.5.3 Steric repulsion 90
4.5.4 Polymer bridging 91
Further reading 92 TX854_book.fm Page xii Monday, June 20, 2005 12:04 PM
Trang 10Chapter five Aggregation kinetics 93
5.1 Collision frequency — Smoluchowski theory 93
5.2 Collision mechanisms 94
5.2.1 Brownian diffusion — perikinetic aggregation 95
5.2.2 Fluid shear — orthokinetic aggregation 102
5.2.3 Differential sedimentation 105
5.2.4 Comparison of rates 106
5.2.5 Effect of hydrodynamic interactions 107
5.3 Form of aggregates 109
5.3.1 Fractals 110
5.3.2 Collision rate of fractal aggregates 113
5.3.3 Density of fractal aggregates 115
5.4 Strength and breakage of aggregates 116
Further reading 119
Chapter six Coagulation and flocculation 121
6.1 Terminology 121
6.1.1 “Coagulation” and “flocculation” 121
6.1.2 Destabilizing agents 122
6.2 Hydrolyzing metal coagulants 123
6.2.1 Hydrolysis of metal cations 123
6.2.2 Polynuclear hydrolysis products 126
6.2.3 Action of hydrolyzing coagulants 127
6.2.4 Charge neutralization by adsorbed species 127
6.2.5 “Sweep” flocculation 129
6.2.6 Overview 131
6.2.7 Practical aspects 132
6.3 Polymeric flocculants 133
6.3.1 Nature of polymers and polyelectrolytes in solution 133
6.3.2 Examples of polymeric flocculants 135
6.3.3 Polymer adsorption 137
6.3.4 Bridging flocculation 139
6.3.5 Charge neutralization and “electrostatic patch” effects 140
6.3.6 Kinetic aspects of polymer flocculation 142
6.3.7 Applications 147
Further reading 148
Chapter seven Separation methods 149
7.1 Introduction 149
7.2 Flocculation processes 149
7.2.1 Rapid mixing 150
7.2.2 Floc formation 151
7.3 Sedimentation 153
7.3.1 Basics 153
7.3.2 Sedimentation in practice 154
7.3.3 Upflow clarifiers 156 TX854_book.fm Page xiii Monday, June 20, 2005 12:04 PM
© 2006 by Taylor & Francis Group, LLC
Trang 117.4 Flotation 157
7.4.1 General 157
7.4.2 Dissolved air flotation 158
7.5 Filtration 162
7.5.1 Deep bed filtration 162
7.5.2 Membrane filtration 170
Further reading 173 TX854_book.fm Page xiv Monday, June 20, 2005 12:04 PM
Trang 12chapter one Introduction
1.1 Particles in the aquatic environment
1.1.1 Origin and nature
Natural waters contain a wide range of impurities, mostly arising from
espe-cially domestic and industrial wastewaters, can also be important Aquatic life is also a significant source of numerous constituents of natural waters The most fundamental point concerning impurities in the aquatic
this is a simple concept in principle, distinguishing between these forms is not always straightforward (see later in this chapter).Water is a good solvent for many substances, especially inorganic salts, and the vast majority of
the TDS level is of the order of 35 g/L, most of which is sodium chloride, with other salts making up nearly all of the rest
Substances that are relatively insoluble in water may exist as small
level In many natural waters this is very much less than the TDS level, usually of the order of 10–20 mg/L However, there are important exceptions, especially where heavy seasonal rainfall carries large quantities of particulate material into rivers For instance, the Yellow River in China can carry up to several g/L of suspended solids The combined (dissolved + suspended)
The main types of suspended particles found in natural waters are as follows:
• Inorganic
• Organic, including macromolecules
• Living and dead organisms
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© 2006 by Taylor & Francis Group, LLC