OZONE INACTIVATION OF CRYPTOSPORIDIUM-PARVUM IN DEMAND-FREE PHOSPHATEBUFFER DETERMINED BY IN-VITRO EXCYSTATION AND ANIMAL INFECTIVITY

Inactivation of Cryptosporidium parvum oocysts by ozone was performed in ozone demand-free 0.05 M phosphate buffer (pH 6.9) in bench-scale b atch reactors at 7 and 22-degrees-C. Ozone was added to each trial fro m a concentrated stock solution for contact times ranging from 5 to 15 min. The viability of the control and treated oocysts was determined by using in vitro excystation and infection in neonatal CD-1 mice. It was found that excystation consistently underestimated inactivation wh en compared with animal infectivity (P less-than-or-equal-to 0.05). As inactivations increased, the difference between excystation and infec tivity also increased. The inactivation kinetics of C. parvum by ozone deviated from the simple first-order Chick-Watson model and was bette r described by a nonlinear Hom model. The use of the Hom model for pre dicting inactivation resulted in a family of unique concentration and time values for each inactivation level rather than the simple CT prod uct of the Chick-Watson model.