Quantitative risk assessment of Cryptosporidium in surface water treatment

Medema, Gertjan; Hoogenboezem, Wim; Veer, A.J. van der; Ketelaars, Henk A. M.; Hijnen, W.A.M.; Nobel, P.J.

doi:10.2166/wst.2003.0202

Cited by 41 publications

(29 citation statements)

References 6 publications

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“…In addition, investigations recently carried out indicate that cyanobacterial cells, protozoans (Cryptosporidium, Giardia) and respiratory viruses were not transported by the infiltrating water into deeper sediment layers (Medema et al, 2003;Hijnen et al, 2004;Grützmacher et al, 2007;). Our results support the idea of the biological filter function and clearly point out the high significance of biological processes.…”

Section: Infiltration and Particle Transportmentioning

confidence: 99%

Bank filtration in the sandy littoral zone of Lake Tegel (Berlin): Structure and dynamics of the biological active filter zone and clogging processes

Hoffmann

Gunkel

2011

Limnologica

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a b s t r a c tThis study focused on clogging processes and on the benthic microalgal and meiofaunal assemblage in the sandy littoral zone of Lake Tegel, which are significantly involved in bank filtration, in a long-term. Our approach combined field studies and ''in situ'' experiments to highlight the structure of the biological active filter zone as well as the mechanisms and effects of clogging in the interstices that influence the infiltration process.Campaigns to measure ''in situ'' infiltration rates and hydraulic potential were conducted monthly from March 2004 to April 2005. Meiofaunal abundances and fine particulate organic matter (FPOM) were determined every 6 weeks in freeze cores down to depths of 50 cm. In parallel, concentrations of carbon, nitrogen and chlorophyll a were measured in samples of unfrozen sediment cores, that were divided in 1-cm steps down to depths of Z 10 cm. Similar sediment profiles were generated for analysis of colloidal carbohydrates, extracellular polymeric substances (EPS) and proteins between December 2005 and June 2006. Electron microscopy was used to visualize biofilm structure. Long-term experiments with natural FPOM and melamine resin particles as fluorescent tracers were performed to study ''in situ'' particle retention and transport, respectively. Additionally seston input was quantified during a 1-week period in April 2005.Infiltration rates showed a high temporal and spatial variability, but were not correlated with hydraulic conductivities as hydraulic gradients changed a lot. Likewise a correlation between infiltration rates and hydraulic potentials was not observed, indicating clogging processes. These are triggered to a high extend by biological compounds. In addition, seston input and intermittent gas intrusion are considered to reduce the hydraulic conductivity considerably. No significant ''in situ'' transport of inert natural fluorescent tracers was observed. However, a complete and permanent clogging of the sandy sediment does not occur, and daily infiltration rates of 0.7-27 L m À 2 h À 1 (mean 9 L m À 2 h À 1 ) guarantee a sufficient water supply by bank filtration for decades.

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Section: Infiltration and Particle Transportmentioning

confidence: 99%

Bank filtration in the sandy littoral zone of Lake Tegel (Berlin): Structure and dynamics of the biological active filter zone and clogging processes

Hoffmann

Gunkel

2011

Limnologica

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“…Though they can vary in practice, and avoiding technicalities as far as possible, the methods described below constitute the general framework that a QMRA practitioner would apply to assess a water supply system (Teunis et al 1997;Haas et al 1999;Benford 2001;Haas & Eisenberg 2001;Medema et al 2003). This is also the current guideline course of action for Dutch utilities to follow when assessing their systems as required by domestic law (de Roda Husman et al 2005).…”

Section: Relevant Qmra Propertiesmentioning

confidence: 99%

Comparing probabilistic microbial risk assessments for drinking water against daily rather than annualised infection probability targets

Signor

Ashbolt

2009

Journal of Water and Health

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Some national drinking water guidelines provide guidance on how to define 'safe' drinking water.Regarding microbial water quality, a common position is that the chance of an individual becoming infected by some reference waterborne pathogen (e.g. Cryptsporidium) present in the drinking water should ,10 24 in any year. However the instantaneous levels of risk to a water consumer vary over the course of a year, and waterborne disease outbreaks have been associated with shorter-duration periods of heightened risk. Performing probabilistic microbial risk assessments is becoming commonplace to capture the impacts of temporal variability on overall infection risk levels. A case is presented here for adoption of a shorter-duration reference period (i.e. daily) infection probability target over which to assess, report and benchmark such risks. A daily infection probability benchmark may provide added incentive and guidance for exercising control over short-term adverse risk fluctuation events and their causes. Management planning could involve outlining measures so that the daily target is met under a variety of pre-identified event scenarios. Other benefits of a daily target could include providing a platform for managers to design and assess management initiatives, as well as simplifying the technical components of the risk assessment process.

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“…QMRA has been suggested by various authors as the scientific basis for assessing risks of pathogen exposure (Regli et al 1991;Teunis et al 1997;Haas et al 1999;Havelaar et al 2000;Medema et al 2003). When assessing the exposure to pathogens through drinking water, both the concentration of pathogens in drinking water and the volume of drinking water consumed are important parameters.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the consumption of cold tap water for microbiological risk assessment: an overview of studies and statistical analysis of data

Mons

Wielen

Blokker

et al. 2007

Journal of Water and Health

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The volume of cold tap water consumed is an essential element in quantitative microbial risk assessment. This paper presents a review of tap water consumption studies. Study designs were evaluated and statistical distributions were fitted to water consumption data from The Netherlands, Great Britain, Germany and Australia. We conclude that the diary is to be preferred for collecting water consumption data. If a diary is not feasible, a 24 h recall would be the best alternative, preferably repeated at least once. From the studies evaluated, the mean daily consumption varies from 0.10 L to 1.55 L. No conclusions could be drawn regarding the effects of season, age and gender on tap water consumption. Physical activity, yearly income and perceived health status were reported to influence water consumption.Comparison of the different statistical probability distribution functions of the datasets demonstrated that the Poisson distribution performed better than the lognormal distribution as suggested by Roseberry and Burmaster.For quantitative microbiological risk assessment (QMRA) it is recommended to use country-

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Quantitative risk assessment of Cryptosporidium in surface water treatment

Cited by 41 publications

References 6 publications

Bank filtration in the sandy littoral zone of Lake Tegel (Berlin): Structure and dynamics of the biological active filter zone and clogging processes

Bank filtration in the sandy littoral zone of Lake Tegel (Berlin): Structure and dynamics of the biological active filter zone and clogging processes

Comparing probabilistic microbial risk assessments for drinking water against daily rather than annualised infection probability targets

Estimation of the consumption of cold tap water for microbiological risk assessment: an overview of studies and statistical analysis of data

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