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Distributed Chlorine Injection To Minimize NDMA Formation during Chloramination of Wastewater

N-Nitrosodimethylamine (NDMA), an important contaminant for potable reuse of municipal wastewater, forms from reactions of dichloramine and amine precursors. Injection of concentrated free chlorine stock solutions into wastewaters containing low levels of ammonia can promote NDMA formation because the high chlorine:ammonia ratio at the point of chlorine injection fosters dichloramine formation during mixing. This study combined chemical kinetic modeling, laboratory mixing studies using deionized water and authentic wastewater effluents, and a pilot-scale disinfectant contactor at a wastewater reuse facility to demonstrate that the distribution of the injection of concentrated hypochlorite stock solutions can reduce the level of NDMA formation by ≤50% compared to injection at a single location. Modeling and deionized water experiments indicated that this reduction was associated with a reduction in the level of dichloramine formation.