Inactivation of bacteriophage MS2 upon exposure to very low concentrations of chlorine dioxide

This study investigates the effects of very low concentrations of ClO2 applied in drinking water practice on the inactivation of bacteriophage MS2. Concentrations of 0.5 mg/L, 0.1 mg/L and 0.02 mg/L ClO2 inactivated at least 5 log units of MS2 after an exposure time of approximately 20, 50 and 300 min respectively. When the ClO2 concentration was as low as 0.005 mg/L, inactivation of 1 log unit MS2 was observed after 300 min exposure. Increasing the contact time to 24 h did not increase the inactivation any further. Non-linear inactivation kinetics (tailing) were observed for all conditions tested. Repeated addition of MS2 to the reactor showed that tailing was not caused by a reduction of the biocidal effect of ClO2 during disinfection. The Modified Chick-Watson, the Efficiency Factor Hom (EFH) model and the Modified Cerf model, a modification of the two-fraction Cerf model, were fitted to the non-linear inactivation curves. Both the EFH and the modified Cerf model did fit accurately to the inactivation data of all experiments. The good fit of the Modified Cerf model supports the hypothesis of the presence of two subpopulations. Our study showed that ClO2 is an effective disinfectant against model organism MS2, also at the low concentrations applied in water treatment practice. The inactivation kinetics followed a biphasic pattern due to the presence of a more ClO2-resistant subpopulation of MS2 phages, either caused by population heterogeneity or aggregation/adhesion of MS2.

Research highlights
► Very low levels of chlorine dioxide are able to inactivate MS2.
► Inactivation of MS2 with chlorine dioxide results in non-linear inactivation.
► The Modified Cerf and the EFH model fit accurately to non-linear MS2 inactivation.
► Resistant viral subpopulations may pose a threat for human health.