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

The rate of Cryptosporidium parvum inactivation decreased with decreasing temperature (1–20°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°C and 22 times faster at 1°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°C to 64 600 mg min l−1 at 1°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°C to 1350 mg min l−1 at 1°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.