N-Nitrosodimethylamine (NDMA) is a member of a family of extremely potent carcinogens, the N-nitrosamines. Until recently, concerns about NDMA mainly focused on the presence of NDMA in food, consumer products, and polluted air. However, current concern focuses on NDMA as a drinking water contaminant resulting from reactions occurring during chlorination or via direct industrial contamination. Because of the relatively high concentrations of NDMA formed during wastewater chlorination, the intentional and unintentional reuse of municipal wastewater is a particularly important area of concern. Although ultraviolet (UV) treatment can effectively remove NDMA, there is considerable interest in the development of less expensive alternative treatment technologies. These alternative technologies include approaches for removing organic nitrogen-containing NDMA precursors prior to chlorination and the use of sunlight photolysis, and in situ bioremediation to remove NDMA and its precursors.

A kinetic model of the reacting aqueous chlorine-ammonia system is proposed which describes equally well the rapid "breakpoint" oxidation of ammonia, where the applied chlorine dose (Cl2) to ammonia-nitrogen molar ratio (Cl/N) is greater than approximately 1.6; the slow oxidation of ammonia in aqueous chloramine solutions (Cl/N < 1); and the transition region of 1 < Cl/N < 1.6, where rapid initial decay results in chloramine species residuals.Calculated time-dependent concentrations of the chlorine species, determined by numerical solution of the rate expressions, compare favorably to measured values, determined during experiments performed over ranges of initial pH (6-8) and Cl/N (0.25-2.0) conditions. The experimentally measured species include free chlorine (HOC1 + OCT), monochloramine (NH2C1), and dichloramine (NH-Cl2). In addition, the model appropriately considers the catalysis of certain key reactions by several commonly encountered inorganics, such as bicarbonate and phosphate species.

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