Effects of ozonation and chlorination on viability and infectivity of Cryptosporidium parvum oocysts

Experimental studies on ozonation and chlorination were conducted to determine capacity for inactivating Cryptosporidium parvum oocysts in batch modes at pH 7, 20°C. In both experiments, the log reduction of animal infectivity was linear and clearly decreased as disinfectant CT product increased. However, the curve of reduction in viability determined by both in vitro excystation assay and DAPI/PI permeability assay exhibited a shoulder. The CT products of ozone per 1 log reduction in infectivity were 3 mg middot min/L for 0.5 mg/L and 1.5 mg · min/L for 0.3 mg/L, while viability determined by in vitro excystation was reduced by only 0.2 logs for the CT product of 3 mg · min/L. In the chlorination experiment, thereduction of animal infectivity was up to 3 logs for the CT product of 2,700 mg middot; min/L, while reduction of viability was smaller at 0.16 logs in in vitro excystation and 0.04 logs in DAPI/PI permeability (in PI exclusion) for the same CT product. The CT product of free chlorine per 1 log reduction in infectivity was estimated to be in the range of 800 to 900 mg · min/L.