Inactivation of Cryptosporidium at 1°C using ozone or chlorine dioxide

Inactivation of cesium chloride purified, bovine-derived C. parvum oocysts was studied at bench-scale using ozone or chlorine dioxide at 1 degrees C. Experiments were conducted in 200 mt of 0.05 M phosphate buffer using a temperature controlled water bath. Animal infectivity using neonatal CD-1 mice was used for evaluation of oocyst viability after treatment. The results showed that while the parasite could be killed at 1 degrees C, the level of effort was substantially higher than that found at 22 degrees C. An ozone Ct product (final residual and contact time product) of 7.2 to 15 mg.min./L at pH 6.9 and 1 degrees C resulted in an inactivation of 0.7 to 1.3 log-units. This was about one-third to one-fifth of that observed at room temperature using a similar Ct product. A chlorine dioxide Ct product of 120 to 135 mg.min./L at pH 6.0 and 1 degrees C resulted in an inactivation of 0.5 to 0.6 log-units. This was about one-fourth the kill observed at 22 degrees C using a similar Ct product.