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The effect of turbidity on ultraviolet inactivation characteristics of Cryptosporidium parvum oocysts and Giardia muris cysts suspended in samples of untreated lake water was determined. Prepared suspensions of parasites were exposed to controlled doses of UV radiation from a medium pressure UV lamp in collimated beam exposure experiments. The level of turbidity in the exposed suspensions was varied from 0.25 to 20.0 NTU by addition of aliquots of suspended solids concentrated from the lake water. Average germicidal UV dose was maintained at constant targets of 5 and 40 mJ/cm2 by increasing the exposure times to account for the effect of the turbidity on UV transmittance of unfiltered water samples. Inactivation of the parasites was determined using established mouse infectivity procedures. Analysis of variance conducted on the outcomes of factorial designed experiments revealed that turbidity had a modest, but statistically significant effect on the UV inactivation characteristics of C. parvum oocysts at the 99% level. An effect was also observed for G. muris, but was significant only at the 94% confidence level. On average, increasing turbidity from 0.25 to 20.0 NTU resulted in a 0.8 log-unit and 0.5 log-unit decreases in inactivation of C. parvum and G. muris, respectively, at average germicidal UV doses of 5 and 40 mJ/cm2. The turbidity effect was independent of UV dose in this UV dose range. The mechanism that accounted for the reduction of inactivation with increased turbidity was not determined, but should be investigated further. Includes 14 references, tables, figures.

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Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 11 File Size: 1 file , 310 KB