Measurement of OH radical CT for inactivating Cryptosporidium parvum using photo/ferrioxalate and photo/TiO₂ systems

Aim: This study investigates the inactivation of Cryptosporidium parvum using the OH radical and reports the OH radical CT (OH radical concentration x contact time) values for C. parvum inactivation. Methods and Results: Although a wealth of information has demonstrated the efficacy of the microbial inactivation activity of the OH radical, no studies have performed a quantitative estimation of the OH radical for C. parvum inactivation. The CT value of the OH radical required for 2 log C. parvum inactivation was measured with two OH radical-generating systems, photo/ferrioxalate and photo/TiO ₂. The OH radical was approx. 10⁴-10⁷-fold more effective for microbial inactivation than other popular chemical disinfectants such as ozone, chlorine dioxide and free chlorine. Conclusions: The OH radical appears to be suitable for microbial inactivation with a calculated CT value required for 2 log C. parvum inactivation of 9·3 × 10^-5 mg min l^-1. Significance and Impact of the Study: This study is the first report of an investigation on the role of the OH radical in the photo/ferrioxalate and photo/TiO₂ systems and on the OH radical CT required for C. parvum inactivation.