Investigation of Chloramines, Disinfection Byproducts, and Nitrification in Chloraminated Drinking Water Distribution Systems

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus detectable residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to 0.05 mg-Cl2/L, indicating little to no effective disinfectant residual remained. (C) 2022 American Society of Civil Engineers

Automated summary

This study investigated the water quality and disinfectant residual stability in four chloraminated drinking water distribution systems. The results showed that the stability of disinfectant residual decreased with increasing water age, and non-disinfectant positive interference had a significant impact on total chlorine measurements when the residual concentration was low.