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| 2. |
- Schönning, Caroline, et al.
(författare)
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Microbial risk assessment of local handling and reuse of human faeces
- 2007
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Ingår i: Journal of Water and Health. - : I W A Publishing. - 1477-8920 .- 1996-7829. ; 5:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Dry urine-diverting toilets may be used in order to collect excreta for the utilisation of nutrients. A quantitative microbial risk assessment was conducted in order to evaluate the risks of transmission of infectious disease related to the local use of faeces as a fertiliser. The human exposures evaluated included accidental ingestion of small amounts of faeces, or a mixture of faeces and soil, while emptying the storage container and applying the material in the garden, during recreational stays to the garden, and during gardening. A range of pathogens representing various groups of microorganisms was considered. Results showed that 12-months' storage before use was sufficient for the inactivation of most pathogens to acceptable levels. When working or spending time in the garden the annual risk of infection by Ascaris was still slightly above 10-4 in these scenarios, although the incidence rate for Ascaris is very low in the population in question. Measures to further reduce the hygienic risks include longer storage, or treatment, of the faeces. The results can easily be extended to other regions with different incidence rates.
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| 3. |
- Westrell, Therese, et al.
(författare)
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A systems analysis comparing drinking water systems – central physical-chemical treatment and local membrane filtration
- 2002
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Ingår i: Water Science & Technology: Water Supply. - 0273-1223. ; 2:2, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a first attempt at an integrated systems analysis of drinking water systems using Microbiological Risk Assessment (MRA) and Material Flow Analysis (MFA) with focus on the comparison of central physical-chemical treatment (conventional system) and local membrane filtration. The MFA shows that energy use is the most significant environmental impact of the three studied drinking water systems, but there are no considerable differences in energy use comparing central physical-chemical treatment and local membrane filtration. According to the MRA, the conventional system might not reduce the microbial risks sufficiently, but such a reduction can not confidently be achieved in a one-step ultrafiltration system either, since membrane filter integrity can hardly be guaranteed over the service life of the equipment. A quite costly two-step membrane filtration system, where water for all household purposes passes microfiltration and further reverse osmosis for drinking and cooking, seems to fulfil this criterion. On the other hand, this system does not reduce the microbial risks from ingestion of water from showers compared with the one-step ultrafiltration alternative. In order to achieve drinking water systems with sufficient microbial barriers and with reasonable costs for operation, a promising solution seems to be a combination of one-step membrane filtration and other methods e.g. biological treatment.
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| 4. |
- Westrell, Therese, et al.
(författare)
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A theoretical approach to assess microbial risks due to failures in drinking water systems
- 2003
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Ingår i: International Journal of Environmental Health Research. - : Informa UK Limited. - 0960-3123 .- 1369-1619. ; 13:2, s. 181-197
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Tidskriftsartikel (refereegranskat)abstract
- A failure in treatment or in the distribution network of a surface water-works could have serious consequences due to the variable raw water quality in combination with an extended distribution. The aim of this study was to examine the theoretical impact of incidents in the drinking water system on the annual risk of infection in a population served by a large water treatment plant in Sweden. Reported incidents in the system were examined and a microbial risk assessment that included three pathogens, Cryptosporidium parvum, rotavirus and Campylobacter jejuni, was performed. The main risk incidents in water treatment were associated with sub-optimal particle removal or disinfection malfunction. Incidents in the distribution network included cross-connections and microbial pollution of reservoirs and local networks. The majority of the annual infections were likely to be due to pathogens passing treatment during normal operation and not due to failures, thus adding to the endemic rate. Among the model organisms, rotavirus caused the largest number of infections. Decentralised water treatment with membranes was also considered in which failures upstream fine-pored membranes would have little impact as long as the membranes were kept intact.
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| 5. |
- Westrell, Therese, et al.
(författare)
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Drinking water consumption patterns in Sweden
- 2006
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Ingår i: Journal of Water and Health. - 1477-8920. ; 4:4, s. 511-522
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Tidskriftsartikel (refereegranskat)abstract
- Estimates on drinking water consumption are necessary in risk assessments on microbial hazardsin drinking water. Large differences in consumption habits between countries have beenreported. In order to establish estimates for the Swedish population, water consumption datafrom a waterborne outbreak investigation (157 people), a small water consumption study(75 people) and a large study on health and environmental factors (10,957 people) were analysed.A lognormal distribution for the daily direct/cold water intake in litres with m¼20.299 ands ¼ 0.570 was fitted to the quantitative data, representing the general population. The averagedaily consumption of tap water as plain drinking water and as heated tap water, e.g. in coffeeand tea, was 0.86 ^ 0.48 l and 0.94 ^ 0.69 l, respectively. Women consumed more cold tap waterthan did men, while men appeared to have a higher consumption of heated tap water. Cold tapwater intake was highest in the oldest age group, ($70 years). The consumption of bottled waterwas very low (mean 0.06 l/d) when compared to other countries.
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| 6. |
- Westrell, Therese
(författare)
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Microbial risk assessment and its implications for risk management in urban water systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Infectious disease can be transmitted via various environmental pathways, many of which are incorporated into our water and wastewater systems. Quantitative microbial risk assessment (QMRA) can be a valuable tool in identifying hazard exposure pathways and estimating their associated health impacts. QMRA can be applied to establish standards and guidelines and has been adopted by the World Health Organisation for the management of risks from water-related infectious diseases. This thesis aims at presenting a holistic approach for the assessment of microbial health risks in urban water and wastewater systems. The procedure of QMRA is presented, together with the data collected for the case studies, and the results are discussed in a risk management framework.Decentralised drinking water treatment with membranes was shown to be competitive with centralised conventional treatment regarding environmental impacts and health. To attain sufficient die-off of pathogens in order to reduce risks to acceptable levels, facilities that permit the long-term storage of locally collected faeces are required. Issues of operation and mangement are likely to determine the health risks in decentralised systems. While failures in distribution are more likely to result in detectable waterborne disease outbreaks, the number of people at risk of becoming infected with pathogens passing normal treatment, calculated on a yearly basis, can be larger. Site-specific pathogen monitoring of source waters was identified as an important factor for the accurate estimation of risk. Noroviruses, an emerging waterborne pathogen, were shown to have fluctuating concentrations in surface water, with significant peaks during the wintertime. Time series analysis has potential as an early warning system if complemented by regular monitoring to discriminate peaks from random fluctuations. Groups already sensitive to infection, i.e. the elderly, the sick and children, were shown to consume higher volumes of cold tap water than the rest of the population, which may call for special atention in the risk management of drinking water systems. Microbial health risks associated with the handling and reuse of wastewater and sludge were shown to be successfully addressed within the management system Hazard Analysis and Critical Control Points (HACCP). Most exposure points identified could be controlled through easy measures.
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| 7. |
- Westrell, Therese, et al.
(författare)
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QMRA (quantitative microbial risk assessment) and HACCP (hazard analysis critical control points) for management of pathogens in wastewater and sewage sludge treatment and reuse
- 2004
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 50:2, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m3/d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion. The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming. A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E. coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes. Human exposures were treated as individual risks but also related to the endemic situation in the general population. The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1). The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden). Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model.
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| 8. |
- Westrell, Therese, et al.
(författare)
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Short- and long-term variations of norovirus concentrations in the Meuse river during a 2-year study period
- 2006
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354. ; 40:14, s. 2613-2620
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Tidskriftsartikel (refereegranskat)abstract
- Faecally impacted surface waters used for drinking water production may encompass risk for norovirus infections. To be able to assess a possible health risk, noroviruses should be quantified and fluctuations identified. In 2001, norovirus concentrations in the river Meuse displayed a seasonal distribution with high peaks during wintertime as determined by RT-PCR on serially diluted RNA. An intensified day-by-day sampling scheme in the winter of 2002/2003 revealed that the winter peak consisted of several peaks of varying duration and magnitude, possibly due to contamination events in the catchment. The highest estimated concentration was 1700 PCR-detectable units per litre (95% CI 250–8000), which if coinciding with failing treatment could lead to significant numbers in drinking water. Adaptive dynamic filtering was shown to adequately predict subsequent sample concentrations. If valid, such analyses could prove to be useful as early warning systems in risk management of water sources.
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