Additional Information
Book Details
Abstract
The factors affecting the presence and growth of micro-organisms in piped networks are reviewed in this book, as are the practices of water supply organisations that can directly or indirectly influence their presence and growth. The information and conclusions are intended for policy makers and those responsible for formulating "Water Safety Plans" for the supply of drinking-water. It is also relevant to engineers and scientists who are responsible for water supply planning, operations and monitoring. The review shows that there are often public health reasons for adopting a more proactive approach to many of the traditional practices used in designing, operating and maintaining distribution networks, and to modifying the composition of the water that is fed into the network. Contents include the following topics: The microbiology of piped distribution systems and public health                        Composition of treated waters to minimise potential for microbiological changes                        Design and operation of distribution networks.                        Planned maintenance and survey of distribution systems                        Precautions during construction and repairs                        Small animals in drinking water distribution systems                       Risk management for distribution systems
Table of Contents
| Section Title | Page | Action | Price |
|---|---|---|---|
| Cover | Cover | ||
| Contents | v | ||
| Foreword | xi | ||
| REFERENCES | xiv | ||
| Acknowledgements | xv | ||
| CONTRIBUTORS | xvi | ||
| Acronyms and abbreviations used in | xix | ||
| 1: The microbiology of piped distribution systems and public health | 1 | ||
| 1.1 INTRODUCTION | 1 | ||
| 1.2 WATERBORNE DISEASE DUE TO CONTAMINATION OF THE DISTRIBUTION SYSTEM | 3 | ||
| 1.3 MICROORGANISMS IN THE DISTRIBUTION SYSTEM | 5 | ||
| 1.3.1 Microorganisms entering distribution systems by surviving the treatment processes | 5 | ||
| 1.3.2 Growth of microorganisms in the distribution system | 6 | ||
| 1.3.3 The fate of pathogens gaining access to distribution systems | 8 | ||
| 1.3.4 Households and large building systems | 9 | ||
| 1.3.5 Controlling microorganisms in distribution systems | 11 | ||
| 1.4 TRADITIONAL APPROACHES TO MICROBIAL MONITORING IN DISTRIBUTION SYSTEMS | 12 | ||
| 1.4.1 Regulations and guidelines for microbiological parameters | 12 | ||
| Total coliforms | 12 | ||
| Escherichia coli and thermotolerant coliforms | 12 | ||
| Heterotrophic plate count | 13 | ||
| 1.4.2 Principles of microbial monitoring in distribution systems | 13 | ||
| 1.5 SUMMARY | 15 | ||
| 1.6 REFERENCES | 15 | ||
| 2: Minimizing potential for changes in microbial quality of treated water | 19 | ||
| 2.1 INTRODUCTION | 19 | ||
| 2.2 MICROBIAL GROWTH FACTORS | 20 | ||
| 2.3 TREATED WATER QUALITY OBJECTIVES | 21 | ||
| 2.3.1 Disinfection strategy and the distribution system | 22 | ||
| Chlorine | 22 | ||
| Monochloramine | 23 | ||
| Chlorine dioxide | 24 | ||
| Management of disinfectant residuals | 25 | ||
| 2.3.2 Particulate content, turbidity and coagulant residual | 26 | ||
| 2.3.3 Organic matter | 27 | ||
| Assimilable organic carbon | 27 | ||
| Biodegradable dissolved organic carbon | 27 | ||
| Biofilm formation potential | 28 | ||
| 2.3.4 Limiting the potential for corrosion and scale | 29 | ||
| 2.4 OPTIMIZATION OF TREATMENT | 30 | ||
| 2.4.1 Water sources | 30 | ||
| 2.4.2 Drinking-water treatment plant | 30 | ||
| 2.4.3 Decentralized treatment | 33 | ||
| 2.5 SUMMARY | 33 | ||
| 2.6 REFERENCES | 34 | ||
| 3: Design and operation of distribution networks | 38 | ||
| 3.1 INTRODUCTION | 38 | ||
| 3.2 DESIGN AND OPERATION OF PIPED NETWORKS | 39 | ||
| 3.2.1 Hydraulics | 39 | ||
| Excessive capacity | 39 | ||
| Low-flow dead-ends and loops | 39 | ||
| Negative pressures | 40 | ||
| Appropriate pressures | 40 | ||
| Hydraulic models | 40 | ||
| Intermittent supply | 41 | ||
| 3.2.2 Pumps and control valves | 42 | ||
| 3.2.3 Access for maintenance | 43 | ||
| 3.2.4 Surge events | 44 | ||
| Recommended techniques for avoiding surge effects | 44 | ||
| Inadvisable techniques for avoiding surge effects | 45 | ||
| 3.2.5 Integrated operations | 45 | ||
| 3.3 DESIGN AND OPERATION OF SERVICE RESERVOIRS | 46 | ||
| 3.3.1 Shape and configuration | 47 | ||
| Shape and dimension | 47 | ||
| Depth of water | 47 | ||
| Inlet | 48 | ||
| Baffles | 48 | ||
| Outlet | 48 | ||
| 3.3.2 Flow pattern | 48 | ||
| Residence time | 49 | ||
| Pumping and loss of supply | 49 | ||
| Stratification | 49 | ||
| 3.3.3 General issues | 49 | ||
| Security of site | 49 | ||
| Risk assessment before operations | 49 | ||
| Sampling facilities | 50 | ||
| Records | 50 | ||
| 3.4 CONTROLLING DISINFECTANT RESIDUALS BY BOOSTER (RELAY) DOSING | 50 | ||
| 3.4.1 Reasons for booster dosing | 50 | ||
| 3.4.2 Locating booster sites | 51 | ||
| 3.4.3 Equipment | 51 | ||
| 3.5 AVOIDING POTENTIAL PROBLEMS WHEN MIXING WATER SOURCES IN DISTRIBUTION | 53 | ||
| 3.5.1 Modelling and planning | 53 | ||
| 3.5.2 Introducing a new supply | 54 | ||
| 3.5.3 Potential effects of mixing waters on disinfectant residual and microbial quality | 55 | ||
| 3.5.4 Changing flow conditions and existing deposits | 56 | ||
| 3.6 POTENTIAL EFFECTS OF ZONING NETWORKS | 57 | ||
| 3.6.1 Potential benefits | 57 | ||
| 3.6.2 Potential disadvantages | 57 | ||
| 3.6.3 Implementing changes | 57 | ||
| 3.7 PIPE MATERIALS | 58 | ||
| 3.8 PIPE LOCATION | 59 | ||
| 3.9 PROTECTION FROM CROSS-CONNECTION AND BACKFLOW AT POINT OF DELIVERY | 59 | ||
| 3.9.1 Sanitary significance | 59 | ||
| 3.9.2 Cross-connection control | 60 | ||
| 3.9.3 Backflow prevention devices | 62 | ||
| Air gap | 62 | ||
| Break tank | 62 | ||
| Mechanical control valves | 62 | ||
| 3.9.4 Typical property hazard ratings | 63 | ||
| 3.9.5 Field testing and maintenance of backflow protection devices | 64 | ||
| 3.10 HEALTH RELATED DESIGN AND OPERATIONS CHECKLIST | 65 | ||
| Pipe network | 65 | ||
| Service reservoirs | 66 | ||
| Controlling disinfectant residuals | 66 | ||
| Zoning networks | 66 | ||
| Materials of construction and pipe location | 66 | ||
| Cross-connections and backflow | 67 | ||
| 3.11 SUMMARY | 67 | ||
| 3.12 REFERENCES | 67 | ||
| 4: Maintenance and survey of distribution systems | 69 | ||
| 4.1 INTRODUCTION | 69 | ||
| 4.2 MAINTENANCE AND SURVEY OF RESERVOIRS, TANKS AND FITTINGS | 70 | ||
| 4.2.1 Sanitary significance | 70 | ||
| 4.2.2 Service reservoirs and tanks | 71 | ||
| Cleaning of internal surfaces | 73 | ||
| Frequency of inspection and cleaning | 73 | ||
| 4.2.3 Valves and other fittings | 74 | ||
| 4.3 MAINTENANCE AND SURVEY OF PIPES | 75 | ||
| 4.3.1 Sanitary significance | 75 | ||
| 4.3.2 Strategies for pipe networks | 76 | ||
| 4.3.3 Planning mains-cleaning programmes | 78 | ||
| 4.3.4 Monitoring effectiveness of mains cleaning | 79 | ||
| 4.4 NONAGGRESSIVE PIPE CLEANING METHODS | 79 | ||
| 4.4.1 Introduction | 79 | ||
| 4.4.2 Flushing | 80 | ||
| 4.4.3 Swabbing | 81 | ||
| 4.4.4 Air scouring | 83 | ||
| 4.5 SUMMARY | 84 | ||
| 4.6 REFERENCES | 85 | ||
| 5: Precautions during construction and repairs | 87 | ||
| 5.1 INTRODUCTION | 87 | ||
| 5.2 PRECAUTIONARY WORKING PRACTICES | 89 | ||
| 5.3 PERSONNEL | 90 | ||
| 5.4 CLEANING AND DISINFECTION PROCEDURES | 91 | ||
| 5.4.1 Typical cleaning and disinfection procedures | 91 | ||
| 5.4.2 Methods for dosing chlorine into the mains | 94 | ||
| 5.4.3 Practical problems | 95 | ||
| 5.4.4 Effectiveness of guidance for field disinfection | 95 | ||
| 5.5 RISK ASSESSMENT AND MONITORING | 96 | ||
| 5.6 SMALL COMMUNITY-MANAGED SYSTEMS | 97 | ||
| 5.7 SUMMARY | 99 | ||
| 5.8 REFERENCES | 99 | ||
| 6: Small animals in drinking-water distribution systems | 101 | ||
| 6.1 INTRODUCTION | 101 | ||
| 6.2 OCCURRENCE OF ANIMALS IN DISTRIBUTION SYSTEMS | 102 | ||
| 6.2.1 Extent | 102 | ||
| 6.2.2 Sampling | 103 | ||
| 6.2.3 Ingress | 104 | ||
| 6.2.4 Population size | 106 | ||
| 6.3 SIGNIFICANCE OF METAZOAN ANIMALS IN DRINKING-WATER DISTRIBUTION SYSTEMS | 108 | ||
| 6.3.1 Aesthetic problems | 108 | ||
| 6.3.2 Metazoan parasites | 108 | ||
| 6.3.3 Effect of animals on occurrence of microorganisms in water mains | 109 | ||
| 6.3.4 Association between animals and pathogens | 110 | ||
| 6.3.5 Protection from disinfection | 110 | ||
| 6.4 REMEDIAL MEASURES | 112 | ||
| 6.4.1 Range of methods | 112 | ||
| 6.4.2 Physical methods | 112 | ||
| Systematic unidirectional flushing | 112 | ||
| Swabbing | 113 | ||
| Air scouring | 113 | ||
| 6.4.3 Chemical methods | 113 | ||
| Chlorine | 113 | ||
| Pyrethroids | 114 | ||
| Other substances | 115 | ||
| 6.4.4 Measures suitable for different groups of animals | 115 | ||
| Isopoda | 115 | ||
| Amphipoda | 115 | ||
| Insecta | 116 | ||
| Oligochaeta (true worms) e.g. Nais | 116 | ||
| Nematoda | 116 | ||
| Gastropoda (aquatic snails) | 116 | ||
| Smaller crustacea | 117 | ||
| 6.4.5 Long-term control measures | 117 | ||
| Removal of particulate organic matter at treatment works | 117 | ||
| Removal of assimilable organic matter at treatment works | 117 | ||
| Removal of animals at treatment works | 117 | ||
| Measures taken in the distribution system | 118 | ||
| 6.5 SUMMARY | 118 | ||
| 6.6 REFERENCES | 119 | ||
| 7: Risk management for distribution systems | 121 | ||
| 7.1 INTRODUCTION | 121 | ||
| 7.2 WATER SAFETY PLANS | 122 | ||
| 7.2.1 Elements of a water safety plan | 122 | ||
| 7.3 WATER SAFETY PLANS FOR DISTRIBUTION SYSTEMS | 124 | ||
| 7.3.1 Assemble team | 124 | ||
| 7.3.2 Document and describe the system | 124 | ||
| 7.3.3 Hazard assessment and risk characterization | 125 | ||
| Desktop risk assessment | 126 | ||
| Sanitary survey | 127 | ||
| Prioritizing risks | 128 | ||
| 7.3.4 Control measures | 130 | ||
| 7.3.5 Monitoring to support risk management | 131 | ||
| Operational monitoring and selection of operational control parameters | 132 | ||
| Establish corrective action for deviations that may occur | 133 | ||
| 7.3.6 Verification | 133 | ||
| Process validation | 134 | ||
| 7.3.7 Supporting programmes and management procedures | 135 | ||
| 7.3.8 Documentation | 135 | ||
| 7.5 SUMMARY OF WATER SAFETY PLAN CONTENT | 136 | ||
| 7.6 REFERENCES | 137 | ||
| Index | 139 |