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 b efore and after treatment. Survival curves of the oocysts following treatme nt 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 si gnificant factor at pH 6-11. Inactivation kinetics at different temperature s was expressed as a Chick-Watson model with different reaction rate consta nts adjusted by van't Hoff-Arrhenius relationship. Between 1 degreesC and 3 7 degreesC, for every 10 degreesC decrease in temperature, the reaction rat e constant decreased by a factor of 2.3, corresponding to an activation ene rgy of 54.9 kJ/mol. Design criteria targeting 0.5 to 2.0 log-units of inact ivation of C. parvum were developed for different water temperatures and th eir 90% confidence intervals were provided.