Sequential inactivation of Cryptosporidium using ozone followed by free chlorine in natural water

Sequential inactivation of Cryptosporidium parvum oocysts in modified natur al water using ozone followed by free chlorine was studied. Experiments wer e conducted at 22 degreesC in modified North Saskatchewan River water at pH 8.5 and pH 6. Animal infectivity using neonatal CD-1 mice was used to meas ure oocyst viability after treatment. The results showed that the overall i nactivation 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 ef fect was observed at pH 8.5 and not at pH 6. The results also indicated tha t models developed for ozone inactivation in lab water adequately predicted the inactivation of C. parvum in the modified natural water but models dev eloped for free chlorine in lab water did not give an adequate prediction o f the free chlorine inactivation. There were no natural water effects on th e inactivation of C. parvum when chemical treatment was not applied.