Bactericidal activity of mixed oxidants: Comparison with free chlorine

In a small water treatment system, electrolytically produced mixed oxidants (MIOX; LATA Inc., USA) have shown promise as an alternative disinfectant to chlorine. However, the efficacy of mixed oxidants as a disinfectant for microorganisms such as E. coli and Bacillus subtilis has not been reported widely and those that have been reported are controversial in some aspects, particularly in comparison with free chlorine. In this study, we evaluated the efficacy of a mixed oxidant solution as a disinfectant and compared it with that of a free chlorine solution on the basis of an equal weight of the total oxidants per unit volume. From our results, we found that mixed oxidants are approximately 20 ~ 50% more efficient than free chlorine at inactivating E. coli and Bacillus subtilis spores at certain pH conditions (pH 8.2). This report is consistent with the results of previous studies, in that the disinfection efficacy of a mixed oxidant solution is different than that of a free chlorine solution. However, the extent of the difference contrasts greatly with the results of the previous studies, which reported a significant difference in the disinfection efficacy between mixed oxidants and free chlorine for inactivating Cryptosporidium parvum oocysts.