Coagulation and Flocculation in Water and Wastewater Treatment

Size: px

Start display at page:

Download "Coagulation and Flocculation in Water and Wastewater Treatment"

Job Hart
8 years ago
Views:

1 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 "+ "J FAX / Publishing LONDON SEATTLE

2 Contents Preface 1 Introduction General Stability and Destabilization Definitions Performance Criteria Summary References 8 2 Colloids and interfaces Introduction Origin of Surface Charge Effect of Surface Charge Adsorption Inner Part of Electrical Double Layer Diffuse Part of Electrical Double Layer Assumptions Distribution of Potential with Distance from the Charged Surface Thickness of Double Layer Effect of Ionic Strength on Double Layer Effect of Nature of Counter Ions Stern's Model of Complete Double Layer Colloid Stability in Terms of the Double Layer Energy of Interaction Between Particles 26 xi

3 vi Contents Theoretical Optimal Concentration of Electrolyte Required for Destabilization Schulze-Hardy Rule Electrokinetic Measurements Introduction References 30 3 Coagulants Introduction Metal Coagulants Commonly Used Metal Coagulants Chemistry of Metal Coagulants Polymers General Activated Silica Natural Polyelectrolytes Synthetic Polymers References 69 4 Treatment with metal coagulants Introduction Destabilization of Hydrophobic Colloids Extent of Hydrolysis and Adsorption Effect of Coagulant Dosage Effect of Colloid Concentration Effect of ph Destabilization of Hydrophilic Colloids Removal of Natural Organic Matter Organic Color _ Enhanced Coagulation Pathogen Removal Removal of Giardia and Cryptosporidium Virus Removal Effect of Anions General Effect of Sulfate Effect of Phosphate Chemical Phosphorus Removal in Wastewater Treatment General Mechanisms of Chemical Phosphorus Removal Applications of Chemical Phosphorus Removal Wastewater Treatment by Coagulation Arsenic Removal Staged Coagulation and Sequencing Effects of Preozonation Effects of Temperature 171

4 Contents vii 4.13 Residual Aluminum References Treatment with polymers Introduction Mechanisms of Destabilization General The Bridging Mechanism The Electrostatic Patch Mechanism Polyelectrolytes as Primary Coagulants General Turbidity Removal Using Polyelectrolytes Orgariics Removal Using Polyelectrolytes Removal of Microorganisms Using Polyelectrolytes Polyelectrolytes as Flocculant Aids Polymers as Filter Aids Polymers as Sludge Conditioners References Rapid mixing Introduction Requirements for Rapid Mixing Devices 220 6:2.1 General Comparison of Back-Mix and Plug-Flow Reactors Velocity Gradient Requirements Rapid Mixer Retention Time Tapered Rapid Mix Velocity Gradient Coagulant Feed Concentration 227,6.2.7 Sequence of Chemical Addition Design of Rapid Mixing Devices General Back-mix Reactors In-line Mixers without Controlled Velocity Gradient In-line Mixers With Controlled Velocity Gradient References Flocculation Introduction Perikinetic Flocculation Orthokinetic Flocculation Theoretical Development Working Equation Flocculation Reactors in Series Adequacy of G and GT as Design Parameters Experimental Determination of Flocculation Parameters 252

5 viii Contents 7.4 Design of Flocculation Basins General Types of Flocculation Chambers and Devices Short-Circuiting in Flocculation Reactors Compartmentalization Combined Flocculation-Sedimentation Basins Transfer of Flocculated Water References Testing and control of coagulation and flocculation Introduction Optimizing Primary Coagulant Type, Dosage and ph ' General, Apparatus ' Chemical Solutions Criteria Describing Process Performance Jar Test Procedure Analysis of Results Using the Jar Test to Evaluate Settling Evaluating Flocculant Aids General Initial Choice of Flocculant Aid Preparation of Polyelectrolyte Solutions" Experimental Procedure Evaluating Sludge Conditioners General Experimental Procedures Optimizing Flocculation Parameters General Apparatus Experimental Procedure Analysis of Data Control Systems for Coagulation Introduction Electrokinetic Measurements Monitoring Floe Formation Data-Driven Control Systems 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

6 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

Coagulation and Flocculation

Coagulation and Flocculation Groundwater and surface water contain both dissolved and suspended particles. Coagulation and flocculation are used to separate the suspended solids portion from the water.