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Stochastic Modelling of Drinking Water Treatment in Quantitative Microbial Risk Assessment

Stochastic Modelling of Drinking Water Treatment in Quantitative Microbial Risk Assessment

Patrick W. M. H. Smeets

(2010)

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Book Details

Abstract

Special Offer: KWR Drinking Water Treatment Set - Buy all five books together and save a total £119! 
Safe drinking water is a basic need for all human beings. Preventing microbial contamination of drinking water is of primary concern since endemic illness and outbreaks of infectious diseases can have significant social and economic consequences. Confirming absence of indicators of faecal contamination by water analysis only provides a limited verification of safety. By measuring pathogenic organisms in source water and modelling their reduction by treatment, a higher level of drinking water safety can be verified. 
This book provides stochastic methods to determine reduction of pathogenic microorganisms by drinking water treatment. These can be used to assess the level and variability of drinking water safety while taking uncertainty into account. The results can support decisions by risk managers about treatment design, operation, monitoring, and adaptation. Examples illustrate how the methods can be used in water safety plans to improve and secure production of safe drinking water. 
More information about the book can be found on the Water Wiki in an article written by the author here: http://www.iwawaterwiki.org/xwiki/bin/view/Articles/Quantifyingmicro-organismremovalforsafedrinkingwatersupplies 


Table of Contents

Section Title Page Action Price
Half Title 1
Title 3
Copyright 4
Contents 5
Acknowledgements 11
Summary 13
STOCHASTIC MODELLING OF DRINKING WATER TREATMENT IN QUANTITATIVE MICROBIAL RISK ASSESSMENT 13
Chapter 1: Introduction 17
HISTORY OF MICROBIALLY SAFE DRINKING WATER 17
STATE OF THE ART OF QMRA IN 2002 19
Treatment assessment for QMRA 19
Distribution of pathogens in water 20
Treatment variation and rare events 20
Correlation between treatment steps 21
Direct assessment of pathogens in drinking water 21
QMRA in drinking water guidelines and legislation 22
QMRA: ITS VALUE FOR RISK MANAGEMENT 22
Complying with health targets 23
Quantifying normal events and special events 24
Setting critical limits 24
Designing monitoring programs 24
Preparing corrective actions 25
Treatment design: comparing alternatives 25
FOCUS OF THIS BOOK 25
APPROACH OF THE PRESENTED STUDY 26
Catchment to Tap System (CTS) 26
The treatment assessment framework 27
REFERENCES 28
Chapter 2: A stochastic pathogen reduction model for full-scale treatment 31
ABSTRACT 31
INTRODUCTION 32
MATERIALS AND METHODS 32
Case study system 32
Microbial monitoring 33
Pathogen reduction model 33
Process model for ozonation 34
Point estimate assessment 34
Stochastic assessment 35
Approaches 35
RESULTS 36
Microbial monitoring results 36
Approach 1: Point estimate 36
Approach 2: Pathogen data 37
Approach 3: Indicator organism data 39
Approach 4: Treatment modelling 40
DISCUSSION 41
Point estimate versus stochastic assessment 41
Pathogen versus indicator organism 43
Use of process models 43
Uncertainty of the assessment 44
CONCLUSIONS 44
REFERENCES 44
Chapter 3: How can the UK statutory Cryptosporidium monitoring be used for quantitative risk assessment of Cryptosporidium in drinking water? 47
ABSTRACT 47
INTRODUCTION 48
METHODS 49
RESULTS AND DISCUSSION 51
Overview of monitoring results 51
QMRA based on treated water monitoring 54
Cryptosporidium removal 57
Design and operation 58
Accumulation 58
Peaks in source water 59
Short treatment failure 59
Reduction related to microbial density 59
Modelling treatment in QMRA 59
CONCLUSIONS 60
ACKNOWLEDGEMENTS 61
REFERENCES 61
Chapter 4: Inactivation of Escherichia coli by ozone under bench-scale plug flow and full-scale hydraulic conditions 63
ABSTRACT 63
INTRODUCTION 64
MATERIALS AND METHODS 64
Bench-scale dissolved ozone plug flow reactor 64
Full-scale installation 65
Microbial methods 66
Ozone analysis 66
Experimental procedures 66
Hydraulic model of the DOPFR 67
Ozone profile calculations 67
Disinfection calculations 69
RESULTS 70
Hydraulic model of the DOPFR 70
Hydraulic model of the full-scale installation 70
Ozone decay 70
E. coli inactivation in the DOPFR 71
E. coli inactivation at full-scale 71
DISCUSSION 71
E. coli inactivation in literature 71
Comparing DOPFR and full-scale inactivation 73
T10 and CSTR calculations for E. coli inactivation in full-scale plant 73
Signifi cance for water treatment 73
CONCLUSIONS 75
REFERENCES 75
Chapter 5: Improved methods for modelling drinking water treatment in quantitative microbial risk assessment; a case study of Campylobacter reduction by filtration and ozonation 77
ABSTRACT 77
INTRODUCTION 78
METHODS 79
Case description 79
Microbial analysis 80
Non-parametric MPN bootstrapping 81
Non-parametric validation of treatment efficacy 81
Parametric extrapolation of bootstrap samples 82
Non parametric treatment model 82
Parametric treatment model 83
Risk calculation 83
RESULTS 83
Microbial monitoring 83
Methods to present distribution of concentrations 84
Non-parametric treatment model 86
Parametric treatment model 87
Parametric model of total chain 89
Modelled risk of infection 90
DISCUSSION 92
CONCLUSIONS 93
REFERENCES 94
Chapter 6: On the variability and uncertainty in quantitative microbial risk assessment of drinking water 97
ABSTRACT 97
INTRODUCTION 97
METHODS 99
Statistical methods 99
Monitoring data 100
RESULTS 100
Treatment performance assessment 100
Optimised method 103
Currently applied date method 104
Mean in/out method 104
Yearly variability of treatment performance 106
Validity of the calibrated stochastic treatment model 107
Use of surrogate organisms 107
DISCUSSION 109
Treatment assessment 109
Stochastic model calibration 110
Stochastic model applications 110
CONCLUSIONS 111
REFERENCES 111
Chapter 7: Practical applications of quantitative microbial risk assessment for water safety plans 113
ABSTRACT 113
INTRODUCTION 113
METHODS 115
RESULTS 116
Compliance with health-based targets 116
Including uncertainty of log credits 116
Reducing uncertainty of log credits with site specific information 117
Including uncertainty of disinfection modelling 118
Including site specific variability in disinfection modelling 121
Modelling improvements of disinfection processes 121
Verification of treatment efficacy 122
Design of microbial monitoring 123
Design of process monitoring 125
Operation of treatment 128
Setting critical limits 128
Preparing corrective actions 131
CONCLUSIONS 132
REFERENCES 132
Chapter 8: General discussion 135
INTRODUCTION 135
COMBINING INFORMATION IN THE TREATMENT FRAMEWORK 135
INCLUDING VARIABILITY AND UNCERTAINTY BY STOCHASTIC MODELLING 136
MICROBIAL MONITORING OF DRINKING WATER 137
PROCESS MODELLING FOR QMRA 138
QUANTIFYING TREATMENT EFFICACY USING MICROBIAL MONITORING 139
ACCURACY OF STOCHASTIC TREATMENT MODELLING 140
APPLICATIONS OF QMRA IN THE WSP 141
System assessment 141
Risk prioritisation 141
Design monitoring 141
Setting critical limits 142
Corrective actions 142
IMPLICATIONS FOR THE DRINKING WATER INDUSTRY 143
CONSIDERATIONS FOR THE REGULATORS 144
Choice of QMRA method 145
Selecting pathogens 145
Dose-response 145
Health effect and severity weight 146
Guidance by the legislator 146
FUTURE RESEARCH 146
Process models 146
Indexing new pathogens 147
Interaction between processes 147
REFERENCES 147