Volume 100, Issue 7     July 2008    ISSN 1551-8833

The author describes a statistical model that can be used to account for the error in estimating the required chloramine concentration times time (C x T) to inactivate Cryptosporidium oocysts with ozone followed by chloramine in drinking water. The safety factor described in the article can be used to determine whether the required C x T takes account of specific known uncertainties. The fact that lots are not all identical needs to be accounted for when the safety level of C x T is calculated. Because lot variability is accounted for in the current Long Term 2 Enhanced Surface Water Treatment Rule, water utilities may want to use a similar factor for a sequential inactivation approach that also takes lot variability into account. This study shows that a sequential application of ozone and chloramine is a promising alternative to a single application of ozone or chloramine to control C. parvum oocysts in drinking water. Water utilities can calculate the required C x T for the secondary disinfectant in order to achieve a specified inactivation level of C. parvum oocysts.—MKK