INSEAD Library

Includes bibliographical references and index

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Water Treatment and Pathogen Control Process Efficiency in Achieving Safe Drinking-Water Contents Foreword ......................................................................................................... ix Acknowledgements............................................................................................... xiii Acronyms and abbreviations used in the text...................................................... xv Executive summary............................................................................................. xvii 1 Introduction....................................................................................................... 1 1.1 Purpose and scope .................................................................................. 1 1.2 Multiple barriers ..................................................................................... 2 1.3 Process control measures......................................................................... 3 2 Removal processes............................................................................................. 5 2.1 Pretreatment.............................................................................................. 6 2.1.1 Roughing filters........................................................................ 6 2. 1 .2 Micro strainers.......................................................................... 7 2.1.3 Off-stream storage.................................................................... 8 2.1.4 Bank infiltration .....................................................................10 2.2 Coagulation, flocculation and sedimentation........................................ 12 2.2.1 Conventional clarification......................................................13 2.2.2 High-rate clarification............................................................ 17 2.2.3 Dissolved air flotation............................................................ 18 2.2.4 Lime softening....................................................................... 19 2.2.5 In-line coagulation................................................................. 19 2.3 Ion exchange..........................................................................................20 2.4 Filtration..................................................................................................20 2.5 Granular high-rate filtration....................................................................21 2.5.1 Design of granular filtration...................................................22 2.5.2 Mechanism of action of granular filtration............................ 23 2.5.3 Importance of chemical coagulation pretreatment.................23 2.5.4 Effect of filter media design...................................................24 2.5.5 Importance of filter backwash............................................... 25 2.6 Slow sand filtration.................................................................................26 2.6.1 Design and action of slow sand filters................................... 26 2.6.2 Protection provided by slow sand filtration........................... 30 2.7 Precoat filtration..................................................................................... 32 2.7.1 Removal of microbes............................................................. 32 2.7.2 Importance of chemical pretreatment.................................... 33 2.8 Membrane filtration................................................................................ 33 2.8.1 Microfiltration........................................................................ 35 2.8.2 Ultrafiltration..........................................................................36 2.8.3 Nanofiltration and reverse osmosis........................................37 2.9 Bag, cartridge and fibrous filters ........................................................... 39 3 Inactivation (disinfection) processes............................................................. 41 3.1 Factors affecting disinfection ................................................................ 41 3.2 Pretreatment oxidation............................................................................43 3.3 Primary disinfection................................................................................44 3.3.1 Chlorine..................................................................................44 3.3.2 Monochloramine.................................................................... 50 3.3.3 Chlorine dioxide.....................................................................52 3.3.4 Ozone..................................................................................... 54 3.3.5 Ultraviolet light...................................................................... 58 3.3.6 Mixed oxidants.......................................................................61 3.4 Secondary disinfection........................................................................... 62 3.4.1 Maintenance of water quality in the distribution system....... 62 3.4.2 Factors affecting microbial occurrence..................................62 3.4.3 Other non-chlorine disinfectants............................................65 4 Performance models....................................................................................... 67 4.1 Removal process models........................................................................ 67 4.1.1 Transport................................................................................ 68 4.1.2 Attachment............................................................................. 68 4.1.3 Effects of process variables on removal efficiency............... 68 4.2 Disinfection models................................................................................72 4.2.1 Integrated disinfection design framework............................. 74 5 Treatment variability..................................................................................... 75 5.1 Effects of process variability..................................................................76 5.2 Relationships between treatment processes........................................... 76 5.3 Dynamic nature of treatment processes................................................. 77 5.4 Effects of changes in raw water quality................................................. 78 5.5 Variability due to process measurements...............................................78 6 Process control................................................................................................ 81 6.1 Risk assessment and process control......................................................82 6.2 Source water protection..........................................................................83 6.3 Coagulation, flocculation and clarification............................................ 85 6.4 Filtration................................................................................................. 88 6.5 Disinfection............................................................................................ 90 6.6 Distribution system.................................................................................91 7 Reference list................................................................................................... 93 Index............................................................................................................ 107