The Role of Pre-Oxidation in Controlling NDMA Formation: A Review

N-nitrosodimethylamine (NDMA), a probable human carcinogen, is a disinfection by-product (DBP) that has been detected in chloraminated drinking water systems. Options for NDMA control include the physical removal of either precursors or precursor deactivation prior to chloramination. This review summarizes some of the recent findings related to the control of NDMA formation with commonly used oxidants in drinking water treatment. Each oxidant (chlorine, chlorine dioxide, ozone) has the potential to reduce NDMA formation with varying degree of efficiencies depending on the precursors in source waters. In general, ozone and chlorine are effective oxidants for controlling NDMA precursors, likely due to their high reaction rate constants with amines. In some cases, the oxidants themselves have been shown to increase the NDMA formation. The selection of pre-oxidant type, dose and application location for NDMA control would site-specific. Utilities intend on using pre-oxidation as a strategy for NDMA control should also the impacts on the formation of regulated DBPs and other unintended consequences that can be associated with those oxidants.