Inactivation of Cryptosporidium parvum oocysts and Bacillus subtilis spores by chlorine dioxide in laboratory reagent and natural waters

grantor: University of TorontoThe chlorine dioxide inactivation of 'Cryptosporidium parvum' oocysts (Iowa isolate, genotype 2 (C)) was measured at bench scale in various water matrices using 'in vitro' excystation and a most probable number cell culture infectivity assay. 'In vitro' excystation underestimated inactivation compared to the infectivity assay. There was a significant difference (Ã = 0.05) in the inactivation of oocysts among the diverse water matrices measured by the infectivity assay but not by ' in vitro' excystation. A 'Ct' of 1000 mg·min/L was necessary for 2.0 log10 inactivation in type I deionised-distilled water adjusted to pH 8 at 22°C. This degree of resistance to chlorine dioxide by 'C. parvum' oocysts has not been quantified previously in the literature. 'Bacillus subtilis' spores (ATCC 19659) were found to be an unsuitable surrogate for 'C. parvum' oocysts in bench- and pilot-scale chlorine dioxide inactivation studies, but could function as a surrogate in pilot scale filtration removal studies.M.A.Sc