Sequential Inactivation ofCryptosporidiumUsing Ozone Followed by Free Chlorine in Natural Water

Sequential inactivation of Cryptosporidium parvum oocysts in modified natural water using ozone followed by free chlorine was studied. Experiments were conducted at 22°C in modified North Saskatchewan River water at pH 8.5 and pH 6. Animal infectivity using neonatal CD-1 mice was used to measure oocyst viability after treatment. The results showed that the overall inactivation of C parvum using ozone followed by free chlorine in modified NSR water was greater at pH 6 compared; to pH 8.5, but that a synergistic effect was observed at pH 8.5 and not at pH 6. The results also indicated that models developed for ozone inactivation in lab water adequately predicted the inactivation of C. parvum in the modified natural water but models developed for free chlorine in lab water did not give an adequate prediction of the free chlorine inactivation. There were no natural water effects on the inactivation of C. parvum when chemical treatment was not applied.