Examination of discrete and counfounding effects of water quality parameters during the inactivation of MS2 phages and Bacillus subtilis spores with chlorine dioxide

The role of water quality (pH, temperature, turbidity, and natural organic matter (NOM)) on the efficacy of chlorine dioxide to inactivate Bacillus subtilis spores and MS2 phages was investigated in synthetic waters. Modelling the curves describing tailing inactivation with a parallel Chick-Watson model proved to be a valid approach. The formation of aggregates was exacerbated when using chlorine dioxide as opposed to free chlorine. The origin of these aggregates lies in the interactions of chlorine dioxide with the water matrix and the microorganisms. Higher temperature and higher turbidity were dominant factors in predicting spores tailing, while decreasing the pH from 8.5 to 6.5 was responsible for increasing the fraction of MS2 aggregates from 0.06% to 9.0% (138-fold). The resistance of aggregates were, on average, 18–21 times higher than for single organisms. The addition of dissolved organic carbon significantly (p < 0.01) improved inactivation with chlorine dioxide. Turbidity (5 NTU) did not significantly hinder MS2 inactivation, but it increased the concentration–time (Ct) 1-log of B. subtilis spores from 386 to 600 mg·min·L^–1. Key words: drinking water, disinfection, spores, MS2 coliphages, chlorine dioxide, water quality, turbidity, natural organic matter.