AWWA WQTC60724

Recently a new test has been developed for assessing Cryptosporidium infectivity and viability based on cell culture propagation of life cycle stages followed by identification and enumeration using real-time PCR (CC-PCR). Due to the test's simplicity and capability this has for the first time allowed convenient assessment of disinfection effectiveness and permitted complex studies on the survival of the Cryptosporidium parasite in the natural environment and through the water treatment process. This paper considers the early results from two Australian Cooperative Research Centre for Water Quality and Treatment projects that tackle these issues. The first project focuses on the issue of whether certain water treatment processes may in fact reduce the viability of oocysts or perhaps pre-stress oocysts making them more susceptible to subsequent disinfection. The use of alum and ferric chloride coagulants at different doses has been examined and no significant effect on viability has been revealed using CC-PCR. The study also examined the influence of chlorine and chloramine on coagulated oocysts and there appears to be no discernible effect either. In the second project the issue of environmental survival of oocysts in catchments prior to treatment was considered, with factors such as sunlight and temperature being evaluated. So far, only water temperature has been fully evaluated but the results are striking in terms of their implications on catchment and reservoir management. While at 4°C oocysts remain viable for many months, as the temperature is raised to 37°C nearly 4log₁₀ inactivation is evident after just 5 days. At a water temperature of 25°C there is a 3Log₁₀ reduction in viability after 4 weeks. These periods are much less than calculated using the more conservative viability assays previously available. Includes 2 references.