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The objective of this experimental laboratory study was to test the hypothesis thatCryptosporidium parvum oocysts in conventionally filtered drinking water are aggregated andare, therefore, more resistant to ultraviolet light. Two independent filtration experiments werecarried out in which the alum dose was intentionally maintained at sub-optimal levels in order tosimulate poorly filtered water conditions. Samples of the filtered water were exposed to an ultraviolet (UV)fluence of 5 mJ/cmsup2/sup using a collimated beam apparatus. A tissue homogenizer was used todisrupt the aggregates and disperse the oocysts before or after UV exposure. Oocyst inactivationwas determined using a cell culture - foci detection method. The mean log inactivation ofsamples (n = 6) homogenized before and after UV exposure was 2.4 log and 1.6, respectively.The difference was statistically significant at the 95% confidence level (p-value = 0.02). Incomparison, the mean inactivation of oocysts seeded into phosphate buffered de-ionized waterwas 3.0 log at the same UV dose. These findings were interpreted as indirect evidence thatoocysts present in the filtered water samples were aggregated. Direct evidence of oocystaggregation was also observed by examination and enumeration of particulate matter captured ona series of PCTE membrane filters. The results of this study suggest that if C. parvum oocystsare present in poorly filtered drinking water, they are likely to be aggregated to some extent andwill exhibit a greater resistance to UV than oocysts seeded directly into clean water. AlthoughUV disinfection will provide an additional protective barrier against oocysts that breakthrough afiltration process, the degree of protection may be less than predicted based on seeding studiescarried out using clean water. Includes 12 references, tables, figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 12File Size: 1 file , 460 KB