AWWA WQTC52992

Disinfectants like ozone and chlorine dioxide have been shown to beeffective in inactivating Cryptosporidium parvum, whereas others like free chlorine and monochloramine, require excessively high contact times to achieve comparable levels of inactivation when applied alone. Sequential application of chlorine species (e.g. free chlorine, monochloramine) after a stronger chemical disinfectant like ozone or chlorine dioxide, has been explored in the last few years as an alternative to control C. parvum. In general, an enhancement in the performance of the secondary disinfectant has been found to be the most important effect of this process for some disinfection schemes. The objective of this study was to investigate the synergy involved in the sequential inactivation of C. parvum with ozone followed by free chlorine at low temperature (1-20 degrees C). Viability of treated oocysts was assessed using the modified in vitro excystation method that has been shown to be consistent with animal infectivity data in previous studies. Includes 14 references, figures.