Enhanced disinfection efficiency of mechanically mixed oxidants with free chlorine

To the best of our knowledge, this study is the first investigation to be performed into the potential benefits of mechanically mixed disinfectants in controlling bacterial inactivation. The purpose of this study was to evaluate the disinfection efficiency of mechanically mixed oxidants with identical oxidant concentrations, which were made by adding small amounts of subsidiary oxidants, namely ozone (O₃), chlorine dioxide (ClO₂), hydrogen peroxide (H₂O₂) and chlorite (ClO ₂^-), to free available chlorine (Cl₂), using Bacillus subtilis spores as the indicator microorganisms. The mechanically mixed oxidants containing Cl₂/O₃, Cl₂/ClO ₂ and Cl₂/ClO₂^- showed enhanced efficiencies (of up to 52%) in comparison with Cl₂ alone, whereas no significant difference was observed between the mixed oxidant, Cl ₂/H₂O₂, and Cl₂ alone. This enhanced disinfection efficiency can be explained by the synergistic effect of the mixed oxidant itself and the effect of intermediates such as ClO₂ ^-/ClO₂, which are generated from the reaction between an excess of Cl₂ and a small amount of O₃/ClO ₂^-. Overall, this study suggests that mechanically mixed oxidants incorporating excess chlorine can constitute a new and moderately efficient method of disinfection.