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Thermal Destruction Analyses of Water Related Pathogens at Domestic Hot Water System Temperatures

2003; Linguagem: Inglês

Anthony Spinks, RH Dunstan, Peter J Coombes, G. Kuczera,

Urban Heat Island Mitigation

Rainwater tanks are fast becoming accepted as a best practice device in urban water cycle management due to their ability to reduce mains water demand and to reduce stormwater runoff. However, concerns over health issues and bacterial contamination of hotwater systems have thus far hindered widespread recommendation of rainwater use in hotwater systems when an alternative mains water supply exists. While extensive research has been undertaken to determine heat tolerance ranges for pathogens under pasteurisation conditions in perishable goods, little data exists for thermal resistance in a freshwater medium. Laboratory experiments were conducted using a variety of water related bacteria to determine Dvalues within a water medium. D-values are defined as the time required to reduce a bacterial population by 90% at a given temperature. The bacteria were exposed to temperatures of E C, 60 C, and 5 C for varying lengths of time. The results showed that water related bacteria rapidly die off in temperatures relevant for domestic hot water systems. The Dvalues at 65 C and 60 C for E. coli were 3secs and 62secs respectively, while at 55 C E. coli displayed a biphasic death curve, with an initial Dvalue of 2lmins followed by 4mins. For Pseudomonas aeruginosa, the Dvalues at 65 C 60 C, and 55 C were 5secs, 49secs, and Smins, for Salmonella typhimurium, <2secs, 4secs, and 77secs, and for Klebsiella pneumoniae, <2secs, <2secs, and 35secs, respectively. The results indicate that after fifteen minutes at 60 C, E. coli concentrations will have been reduced by 15-log reductions, while the other pathogens experienced similar or even greater reductions. This is in agreement with water samples taken from domestic rainwater tanks and hot water systems which indicated almost complete kill off of bacteria through the hot water system. In view of Australian standards requiring temperature at or above 60 C to control L. pneumophila, these preliminary results suggest that it is highly improbable that human pathogens, if present in raintank water, will survive through a hot water system.