W, A. R, Coagulation and Flocculation in Water and Wastewater Treatment Second Edition 02,/f John Bratby,» :.'; '5 s " - ' '! ' " ; i '. ', ' j ',... -,..,.,.-* ;, 0 61^/16*36 S "+ "J6 27 48 FAX 0 6151/16 37 58 Publishing LONDON SEATTLE
Contents Preface 1 Introduction 1 1.1 General 1 1.2 Stability and Destabilization 3 1.3 Definitions 5 1.4 Performance Criteria 6 1.5 Summary 7 1.6 References 8 2 Colloids and interfaces 9 2.1 Introduction 9 2.2 Origin of Surface Charge 13 2.3 Effect of Surface Charge 14 2.4 Adsorption 14 2.5 Inner Part of Electrical Double Layer 17 2.6 Diffuse Part of Electrical Double Layer 18 2.6.1 Assumptions 18 2.6.2 Distribution of Potential with Distance from the Charged Surface 20 2.6.3 Thickness of Double Layer 22 2.6.4 Effect of Ionic Strength on Double Layer 24 2.6.5 Effect of Nature of Counter Ions 25 2.7 Stern's Model of Complete Double Layer 25 2.8 Colloid Stability in Terms of the Double Layer 26 2.8.1 Energy of Interaction Between Particles 26 xi
vi Contents 2.8.2 Theoretical Optimal Concentration of Electrolyte Required for Destabilization 28 2.8.3 Schulze-Hardy Rule 29 2.9 Electrokinetic Measurements 29 2.9.1 Introduction 29 2.10 References 30 3 Coagulants 31 3.1 Introduction 31 3.2 Metal Coagulants 32 3.2.1 Commonly Used Metal Coagulants 32 3.2.2 Chemistry of Metal Coagulants 42 3.3 Polymers 50 3.3.1 General 50 3.3.2 Activated Silica 51 3.3.3 Natural Polyelectrolytes 52 3.3.4 Synthetic Polymers 56 3.4 References 69 4 Treatment with metal coagulants 72 4.1 Introduction 72 4.2 Destabilization of Hydrophobic Colloids 75 4.2.1 Extent of Hydrolysis and Adsorption. 75 4.2.2 Effect of Coagulant Dosage 75 4.2.3 Effect of Colloid Concentration 77 4.2.4 Effect of ph 80 4.3 Destabilization of Hydrophilic Colloids 86 4.4 Removal of Natural Organic Matter 87 4.4.1 Organic Color _ 87 4.4.2 Enhanced Coagulation 98 4.5 Pathogen Removal 113 4.5.1 Removal of Giardia and Cryptosporidium 113 4.5.2 Virus Removal 114 4.6 Effect of Anions 116 4.6.1 General 116 4.6.2 Effect of Sulfate 117 4.6.3 Effect of Phosphate 118 4.7 Chemical Phosphorus Removal in Wastewater Treatment 120 4.7.1 General 120 4.7.2 Mechanisms of Chemical Phosphorus Removal 124 4.7.3 Applications of Chemical Phosphorus Removal 138 4.8 Wastewater Treatment by Coagulation 152 4.9 Arsenic Removal 159 4.10 Staged Coagulation and Sequencing 161 4.11 Effects of Preozonation 169 4.12 Effects of Temperature 171
Contents vii 4.13 Residual Aluminum 173 4.14 References 176 5 Treatment with polymers 186 5.1 Introduction 186 5.2 Mechanisms of Destabilization 187 5.2.1 General 187 5.2.2 The Bridging Mechanism 188 5.2.3 The Electrostatic Patch Mechanism 192 5.3 Polyelectrolytes as Primary Coagulants 194 5.3.1 General 194 5.3.2 Turbidity Removal Using Polyelectrolytes 196 5.3.3 Orgariics Removal Using Polyelectrolytes 200 5.3.4 Removal of Microorganisms Using Polyelectrolytes 204 5.4 Polyelectrolytes as Flocculant Aids 206 5.4.1 Polymers as Filter Aids. 210 5.5 Polymers as Sludge Conditioners 211 5.6 References 214 6 Rapid mixing 219 6.1 Introduction 219 6.2 Requirements for Rapid Mixing Devices 220 6:2.1 General 220 6.2.2 Comparison of Back-Mix and Plug-Flow Reactors 222 6.2.3 Velocity Gradient Requirements 225 6.2.4 Rapid Mixer Retention Time 226 6.2.5 Tapered Rapid Mix Velocity Gradient 227 6.2.6 Coagulant Feed Concentration 227,6.2.7 Sequence of Chemical Addition 228 6.3 Design of Rapid Mixing Devices 228 6.3.1 General 228 6.3.2 Back-mix Reactors 229 6.3.3 In-line Mixers without Controlled Velocity Gradient 229 6.3.4 In-line Mixers With Controlled Velocity Gradient 235 6.4 References 238 7 Flocculation 240 7.1 Introduction 240 7.2 Perikinetic Flocculation 241 7.3 Orthokinetic Flocculation 243 7.3.1 Theoretical Development 243 7.3.2 Working Equation 249 7.3.3 Flocculation Reactors in Series 250 7.3.4 Adequacy of G and GT as Design Parameters 250 7.3.5 Experimental Determination of Flocculation Parameters 252
viii Contents 7.4 Design of Flocculation Basins 253 7.4.1 General 253 7.4.2 Types of Flocculation Chambers and Devices 254 7.4.3 Short-Circuiting in Flocculation Reactors 267 7.4.4 Compartmentalization 268 7.4.5 Combined Flocculation-Sedimentation Basins 270 7.4.6 Transfer of Flocculated Water 274 7.5 References 276 8 Testing and control of coagulation and flocculation 279 8.1 Introduction 279 8.2 Optimizing Primary Coagulant Type, Dosage and ph ' 280 8.2.1 General, 2 8 0 8.2.2 Apparatus ' 281 8.2.3 Chemical Solutions 282 8.2.4 Criteria Describing Process Performance 285 8.2.5 Jar Test Procedure 289 8.2.6 Analysis of Results 291 8.3 Using the Jar Test to Evaluate Settling 293 8.4 Evaluating Flocculant Aids 296 8.4.1 General 296 8.4.2 Initial Choice of Flocculant Aid 296 8.4.3 Preparation of Polyelectrolyte Solutions" 297 8.4.4 Experimental Procedure 298 8.5 Evaluating Sludge Conditioners 299 8.5.1 General 299 8.5.2 Experimental Procedures 299 8.6 Optimizing Flocculation Parameters 304 8.6.1 General - 304 8.6.2 Apparatus 306 8.6.3 Experimental Procedure 308 8.6.4 Analysis of Data 312 8.7 Control Systems for Coagulation 315 8.7.1 Introduction 315 8.7.2 Electrokinetic Measurements 315 8.7.3 Monitoring Floe Formation 323 8.7.4 Data-Driven Control Systems 327 8.8 References 332 Appendix: Processing and Disposal of Coagulant Sludges 338 A.I Introduction 338 A.2 Production of Water Plant Residuals 341 A.2.1 Estimating Sludge Quantities 341 A.2.2 Alternative Coagulants and Dosage Reduction 344 A.2.3 Sludge Characteristics 345 A.2.4 Sludge Conditioning 347
Contents ix A.3 Filter Backwash 353 A.4 Sludge Lagoons 357 A.5 Sludge Drying Beds 360 A.6 Mechanical Thickening and Dewatering 365 A.6.1 Sludge Thickening 365 A.6.2 Sludge Dewatering 373 A.7 Coagulant Recovery 380 A.8 Sludge Disposal 388 A.8.1 Introduction 388 A.8.2 Disposal to Municipal Sewers 390 A.8.3 Land Application of Water Plant Sludge 393 A.9 References 394 Index 401