Effect of temperature on ozone inactivation of Cryptosporidium parvum in oxidant demand-free phosphate buffer

Ozone inactivation of Cryptosporidium parvum oocysts was studied at bench-s cale in 0.05 M phosphate buffer at 1 to 37 degreesC, pH 6-8. Animal infecti vity using neonatal CD-1 mice was used for evaluation of oocyst infectiousn ess following treatment. Survival curves of ozone inactivation were charact erized by a tail-off effect, with an initial shoulder most evident at low t emperature. Temperature was a critical factor for ozone inactivation kineti cs with a significant decrease of ozone efficacy at low temperature. Accoun ting for ozone residual stability at different pH conditions, pH was found to have no significant effect on the activation of C. parvum by ozone. Inac tivation kinetics at different temperatures were expressed as an Incomplete gamma Hom model with different reaction rate constants, adjusted for water temperature using the van't Hoff-Arrhenius relationship. Between 1 and 37 degreesC, for every 10 degreesC decrease in the water temperature, the inac tivation rate constant decreased by a factor of 2.2, corresponding to activ ation energy of 51.7 kJ/mol. Ozone disinfection design criteria for 1.0 and 2.0 log-units of inactivation of Cryptosporidium were developed for variou s water temperatures, and 90% confidence intervals are also provided.