Inactivation of Cryptosporidium parvum oocysts with sequential application of ozone and combined chlorine.

Single-step inactivation experiments with ozone and monochloramine revealed the presence of a CT lag followed by pseudo-first order inactivation kinetics. Sequential disinfection experiments with ozone followed by monochloramine revealed that ozone pretreatment resulted in the removal of a more prominent CT lag observed for monochloramine. In addition, the rate of inactivation for ozone-pretreated oocysts was approximately 2.5x greater than that observed for the post-lag phase portion of the monochloramine primary inactivation curve.

Inactivation of Cryptosporidium parvum oocysts with ozone and monochloramine at low temperature.

The rate of Cryptosporidium parvum inactivation decreased with decreasing temperature (1-20 degrees C) for ozone and for monochloramine applied alone as well as after pre-treatment with ozone. Synergy was observed at all temperatures studied for the ozone/monochloramine sequential disinfection scheme. The synergistic effect was found to increase with decreasing temperature. The inactivation rate with monochloramine after ozone pre-treatment was 5 times faster at 20 degrees C and 22 times faster at 1 degree C than the corresponding post-lag phase rates of inactivation with monochloramine at these temperatures when no ozone pre-treatment was applied. The CT required for achieving 2-logs of inactivation ranged from 11,400 mg min l-1 at 20 degrees C to 64,600 mg min l-1 at 1 degree C when monochloramine was applied alone. In contrast, the CT required for an overall sequential inactivation of 2-logs ranged from 721 mg min l-1 at 20 degrees C to 1350 mg min l-1 at 1 degree C when applying monochloramine after ozone pre-treatment. The presence of excess ammonia in the monochloramine solutions was not responsible for the synergy observed in ozone/monochloramine sequential disinfection.