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The goal of this study was to examine the potential for microorganism aggregation infiltered drinking water and the effect on the efficacy of ultraviolet (UV) inactivation. A sample of naturalriver water was spiked with Bacillus subtilis spores and was then coagulated with alum,flocculated and settled using a jar-test apparatus. The settled water was then filtered through abed of anthracite and sand in a laboratory-scale filtration column. Spore aggregation in thefiltered effluent was measured directly using a series of PCTE membrane filters or knownnominal pore size. A measurable fraction of the spores in the filter effluent were associated withparticles greater than 10 m in size. Aggregation of the spores with particulate matter present inthe filter effluent was associated with an increase in overall resistance to UV at higher UV doses.This increased resistance was presumably due to a protective shielding mechanism. A similaraggregation effect was also apparent in the filter backwash water but was not detected whenspores seeded directly into filtered water were exposed to UV. The results of this study suggestthat a fraction of the microorganisms that breakthrough conventional granular media filtersduring turbidity excursions will likely be aggregated with particulate matter and that thisaggregation will have an adverse affect on UV disinfection performance. Includes 10 references, tables, figures.

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Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 14File Size: 1 file , 370 KB