AWWA JAW56656

Until recently, drinking water suppliers have emphasized the use of sophisticated techniques at the treatment plant to ensure good water quality. Such an approach, however, may be risky if water quality significantly deteriorates in the distribution system. This study tracked the fate of chlorine dioxide (ClO2) and its major inorganic by-products, chlorite and chlorate ions (ClO2- and ClO3-), in a full-scale distribution system. In a network fed by a treatment plant using ClO2 in postdisinfection, ClO2- concentrations decreased with increasing water residence time, most likely because of the ion's chemical instability and reactions with the pipe material's ferrous ion. In the two networks fed by plants using free chlorine in postdisinfection, ClO2- levels were below the method detection limit (MDL). ClO3- concentrations in the first network were either below the MDL or stable at low levels in cold water and decreased slightly with increasing residence time in warm water. ClO3- levels in the other two networks showed significant variations, some of which may be attributable to microbial biomass. Increasingly stringent regulations under the Disinfectants/Disinfection Byproducts Rule are forcing water suppliers to reconsider their use of chlorine. This study's findings should help drinking water providers more accurately assess the feasibility of using ClO2 as an alternative disinfectant. Includes 83 references, table, figure.