Pilot-scale ozone inactivation of Cryptosporidium and other microorganismsin natural water

A pilot-scale study was conducted to evaluate the inactivation by ozone aga inst Cryptosporidium oocysts, Giardia cysts, poliovirus, and B. subtilis en dospores spiked into Ohio River water. The indigenous Ohio River population s of total coliform bacteria, heterotrophic plate count bacteria and endosp ores of aerobic spore forming bacteria were also evaluated. Endospores were the only organisms found to be more resistant to ozone than Cryptosporidiu m oocysts. Endospores may serve as an indicator of microbial treatment effi ciency. Cryptosporidium oocysts were more resistant than Giardia cysts or p oliovirus. Although HPC bacteria were less resistant than Cryptosporidium o ocysts, variability limits their usefulness as an indicator of treatment ef ficiency. Ozone inactivation data generated in a pilot-scale study employin g natural surface waters were comparable to inactivation data derived from previously published bench-scale studies using laboratory waters. The ozone requirements for inactivation of Cryptosporidium oocysts may produce eleva ted levels of bromate and ozone byproducts.