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Salamander Bay, Australia

The aim of this study was to develop a modified quantitative microbial risk assessment (QMRA) framework that could be applied as a decision support tool to choose between alternative drinking water interventions in the developing context. The impact of different household water treatment (HWT) interventions on the overall incidence of diarrheal disease and disability adjusted life years (DALYs) was estimated, without relying on source water pathogen concentration as the starting point for the analysis. A framework was developed and a software tool constructed and then implemented for an illustrative case study for Nepal based on published scientific data. Coagulation combined with free chlorine disinfection provided the greatest estimated health gains in the short term; however, when long-term compliance was incorporated into the calculations, the preferred intervention was porous ceramic filtration. The model demonstrates how the QMRA framework can be used to integrate evidence from different studies to inform management decisions, and in particular to prioritize the next best intervention with respect to estimated reduction in diarrheal incidence. This study only considered HWT interventions; it is recognized that a systematic consideration of sanitation, recreation, and drinking water pathways is important for effective management of waterborne transmission of pathogens, and the approach could be expanded to consider the broader water-related context. © 2016 Society for Risk Analysis. Source

Petterson S.R.,Water and Health Pty Ltd. | Petterson S.R.,Norwegian University of Life Sciences | Stenstrom T.A.,Durban University of Technology | Ottoson J.,Swedish University of Agricultural Sciences | Ottoson J.,National Food Agency
Water Research

Monitoring of faecal indicator organisms, such as Escherichia coli, in environmental and drinking waters is inadequate for the protection public health, primarily due to the poor relationship between E. coli and the occurrence of human pathogens, especially viruses, in environmental samples. Nevertheless, measurements of faecal indicator organisms within the risk based approach, can provide valuable information related to the magnitude and variability of faecal contamination, and hence provide insight into the expected level of potential pathogen contamination. In this study, a modelling approach is presented that estimates the concentration of norovirus in surface water relying on indicator monitoring data, combined with specific assumptions regarding the source of faecal contamination. The model is applied to a case study on drinking water treatment intake from the Glomma River in Norway. Norovirus concentrations were estimated in two sewage sources discharging into the river upstream of the drinking water offtake, and at the source water intake itself. The characteristics of the assumed source of faecal contamination, including the norovirus prevalence in the community, the size of the contributing population and the relative treatment efficacy for indicators and pathogens in the sewage treatment plant, influenced the magnitude and variability in the estimated norovirus concentration in surface waters. The modelling exercise presented is not intended to replace pathogen enumeration from environmental samples, but rather is proposed as a complement to better understand the sources and drivers of viruses in surface waters. The approach has the potential to inform sampling regimes by identifying when the best time would be to collect environmental samples; fill in the gaps between sparse datasets; and potentially extrapolate existing datasets in order to model rarer events such as an outbreak in the contributing population. In addition, and perhaps most universally, in the absence of pathogen data, this approach can be used as a first step to predict the source water pathogen concentration under different contamination scenarios for the purpose of quantifying microbial risks. © 2016 Elsevier Ltd. Source

Petterson S.R.,Water and Health Pty Ltd. | Petterson S.R.,Norwegian University of Life Sciences | Stenstrom T.A.,Durban University of Technology
Journal of Water and Health

To support the implementation of quantitative microbial risk assessment (QMRA) for managing infectious risks associated with drinking water systems, a simple modeling approach for quantifying Log10 reduction across a free chlorine disinfection contactor was developed. The study was undertaken in three stages: firstly, review of the laboratory studies published in the literature; secondly, development of a conceptual approach to apply the laboratory studies to full-scale conditions; and finally implementation of the calculations for a hypothetical case study system. The developed model explicitly accounted for variability in residence time and pathogen specific chlorine sensitivity. Survival functions were constructed for a range of pathogens relying on the upper bound of the reported data transformed to a common metric. The application of the model within a hypothetical case study demonstrated the importance of accounting for variable residence time in QMRA. While the overall Log10 reduction may appear high, small parcels of water with short residence time can compromise the overall performance of the barrier. While theoretically simple, the approach presented is of great value for undertaking an initial assessment of a full-scale disinfection contactor based on limited site-specific information. © IWA Publishing 2015. Source

Petterson S.,Water and Health Pty Ltd. | Petterson S.,Norwegian University of Life Sciences | Grondahl-Rosado R.,Norwegian University of Life Sciences | Nilsen V.,Norwegian University of Life Sciences | And 2 more authors.
Water Research

Methods for analysing water for viruses are known to have variable and relatively poor recovery efficiencies. Quantitative method recovery data are needed to correct virus enumeration results so that estimates of virus concentrations in surface waters for QMRA are not too low. Obtaining quantitative data representing method recoveries for different pathogenic viruses is a significant challenge. In this study, we investigated the use of mengovirus process control data for quantifying recovery efficiency of human adenovirus (AdV) and noroviruses GI (NoVGI) and GII (NoVGII) from surface waters. Samples were collected from the inlet to a drinking water treatment plant on the Glomma River, Norway. Performance of the sample concentration procedure was quantified by comparing the virus concentrations found in concentrated and unconcentrated samples. The mean recovery of viruses (1.2%, 0.31%, 0.15% and 0.053% for mengovirus (n = 86), AdV (n = 20), NoVGI (n = 33) and NoVGII (n = 21) respectively) estimated in this study were lower than expected, and the between sample variability in estimated recovery was very high, spanning around 6 orders of magnitude for mengovirus. Within-sample correlation between the estimated recovery of mengovirus and human viruses was poor, and therefore sample specific mengovirus data could not be used to correct all human virus concentrations. Instead beta distributions were fitted to human virus-specific recovery estimates. The magnitude and variability of virus concentration when corrected for the variable recovery efficiency was orders of magnitude higher than the uncorrected concentration. Better estimates of virus concentration could be achieved if a sample-specific spiking control could be developed that mimicked closely the behaviour of human viruses in environmental samples. © 2015 Elsevier Ltd. Source

Sokolova E.,Chalmers University of Technology | Petterson S.R.,Norwegian University of Life Sciences | Petterson S.R.,Water and Health Pty Ltd. | Dienus O.,Ryhov County Hospital | And 5 more authors.
Science of the Total Environment

Norovirus contamination of drinking water sources is an important cause of waterborne disease outbreaks. Knowledge on pathogen concentrations in source water is needed to assess the ability of a drinking water treatment plant (DWTP) to provide safe drinking water. However, pathogen enumeration in source water samples is often not sufficient to describe the source water quality. In this study, the norovirus concentrations were characterised at the contamination source, i.e. in sewage discharges. Then, the transport of norovirus within the water source (the river Göta älv in Sweden) under different loading conditions was simulated using a hydrodynamic model. Based on the estimated concentrations in source water, the required reduction of norovirus at the DWTP was calculated using quantitative microbial risk assessment (QMRA). The required reduction was compared with the estimated treatment performance at the DWTP. The average estimated concentration in source water varied between 4.8×102 and 7.5×103 genome equivalents L-1; and the average required reduction by treatment was between 7.6 and 8.8 Log10. The treatment performance at the DWTP was estimated to be adequate to deal with all tested loading conditions, but was heavily dependent on chlorine disinfection, with the risk of poor reduction by conventional treatment and slow sand filtration. To our knowledge, this is the first article to employ discharge-based QMRA, combined with hydrodynamic modelling, in the context of drinking water. © 2015 Elsevier B.V. Source

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