Impacts of domestic wastewater treatment plant influent and effluent water organic load on chlorine dioxide disinfection efficacy

This study has investigated the effect of organic load on the disinfection efficiency of chlorine dioxide in untreated synthetic and real municipal wastewater, and biologically treated secondary effluent. In this respect, Escherichia coli (E.coli) and total coliform (TC) in three different wastewaters were disinfected using various disinfectant dosages and organic matter concentrations. The bacteria inactivation data were correlated using appropriate kinetic models. The experimental results demonstrated that Escherichia coli inactivation in real wastewater was similar with that in artificial wastewater. The bactericidal effect of chlorine dioxide was lowest in the secondary effluent. The bacteria log inactivation increased by up to threefold when the COD concentration of raw wastewater was decreased by half.To explain the COD effect on bacteria inactivation, chlorine dioxide residuals were measured with time through each disinfection process. Residual ClO2 concentrations decreased with increasing wastewater organic load. Results from statistical analyses have revealed that, in comparison to the correlations using CT values, COD/ClO2 concentration ratios provided better explanations for the bacteria inactivation data. Results attained from the kinetic models have shown that for a given CT value or a COD to ClO2 ratio the killing effect of chlorine dioxide in artificial and influent domestic wastewater looks comparable, but it decreases in the secondary effluent.The bactericidal effect of chlorine dioxide was lower in the secondary effluent when compared to that in untreated synthetic and real wastewater. The reduced disinfection efficiency was attributed to the greater resistance of aged-microorganisms in the effluent water.Both experimental and model results confirmed that COD concentration is an important parameter for chlorine dioxide disinfection of treated and untreated domestic wastewater. It is thought that the results of this study would be a useful reference for the future studies attempting for the investigation of bacteria inactivation and disinfectant dose relationshps.