AWWA JAW60120

Among chemical disinfectants, ozone and chloride dioxide have been deemed the only viable barriers against Cryptosporidium oocysts. Chlorine and chloramine have been considered ineffective against Cryptosporidium, and no C ¿ T table for the inactivation of Cryptosporidium with chlorine and chloramine is included in the proposed Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). However, the concept of synergistic inactivation between a strong disinfectant (such as ozone) and a weak disinfectant (such as chlorine or chloramine) has been discussed in the literature, and several researchers have published results of their investigations. The authors of this article consolidated data from three of these studies and used them to develop a C ¿ T table for the inactivation of Cryptosporidium with chloramine downstream of ozone. Their findings indicate that synergistic Cryptosporidium inactivation with extended chloramine contact time downstream of ozone can provide substantial benefits to water treatment plants. Utility managers may find the article's conclusions and proposed table help to improve their facilities' ability to meet potential Cryptosporidium inactivation under the LT2ESWTR. It is the authors' hope that such a C ¿ T table will be included in the rule's final version.