EFFECT OF INTRATYPIC VARIABILITY IN FREE CHLORINE RESISTANCE ON THE ESTIMATION OF INACTIVATION EFFICIENCY OF VIRUS

Abstract

 Viruses are highly diverse even in a genotype. This may affect the required chlorine intensity (CT value: chlorine concentration × contact time) to achieve a sufficient inactivation of viruses in drinking water treatment plant. Recently, it was reported that some environmental strains were more resistant against chlorination than a lab strain. However, few studies have assessed the effect of intratypic variability in free chlorine resistance on the estimation of required CT values for virus inactivation. The objectives of this study were (i) to examine a total of 35 environmental stains of F-RNA phage genotype GI collected in Tama and Sagami rivers for free chlorine resistance, and (ii) to develop the inactivation model to predict the overall inactivation efficiency of heterogeneous F-RNA phage GI strains by assuming a probability density function of free chlorine resistance. The results indicated that most environmental strains of F-RNA phage GI exhibited higher free chlorine resistance than MS2 and fr, laboratory strains of GI phage. The developed model suggested that the overall inactivation efficiency of GI phages was limited to 5.6 log and 5.3 log in Tama and Sagami river, respectively, in the case that 8 log MS2 inactivation was expected. Therefore, the heterogeneity in free chlorine resistance within specific reference pathogens should be incorporated into the model to accurately predict the inactivation efficiency in environmental water.