Chlorine dioxide inactivation of Cryptosporidium parvum in oxidant demand-free phosphate buffer

Chlorine dioxide inactivation of Cryptosporidium parvum oocysts was studied at bench-scale in oxidant demand-free 0.05 M phosphate buffer at pH 6, 8, and 11, and temperature from 1 degreesC to 37 degreesC. Animal infectivity using neonatal CD-1 mice was used for evaluation of oocyst infectiousness before and after treatment. Survival curves of the oocysts following treatment declined linearly with the chlorine dioxide C(avg)t product. Temperature was critical for C. parvum inactivation, while pH was found not to be a significant factor at pH 6-11. Inactivation kinetics at different temperatures was expressed as a Chick-Watson model with different reaction rate constants adjusted by van't Hoff-Arrhenius relationship. Between 1 degreesC and 37 degreesC, for every 10 degreesC decrease in temperature, the reaction rate constant decreased by a factor of 2.3, corresponding to an activation energy of 54.9 kJ/mol. Design criteria targeting 0.5 to 2.0 log-units of inactivation of C. parvum were developed for different water temperatures and their 90% confidence intervals were provided.