Modeling NDMA Formation Kinetics During Chloramination of Model Compounds and Surface Waters Impacted by Wastewater Discharges

N-nitrosodimethylamine (NDMA) is a chloramination disinfection by-product (DBP). Despite extensive research on NDMA occurrence and evaluation of formation potential from select precursors and in different matrices, less information exists on the kinetics of NDMA formation. A kinetic model is developed and parameterizered using the limited amount of previously published kinetic data involving addition of model compounds to pH buffered ultrapure water and/or surface waters containing organic matter. A simple second-order kinetic model was developed using a NDMA precursor concentration, based upon a measured maximum NDMA concentration as the initial precursor concentration, and measured monochloramine concentrations. The second order model was able to fit NDMA formation kinetics well by determining the best-fit apparent rate constant (k(app)), suggesting the model represents a common rate limiting step and/or an intermediate product. An associated reaction may exist during the transformation of a wide variety of precursors into NDMA. Values for k(app) ranged by approximately one-order of magnitude and were lower in the presence of natural organic matter (NOM), which may suggest that more reactive chloramine species or NDMA intermediate products are scavenged by NOM. Overall, the modeling suggests lines of future research to help elucidate and predict NDMA formation mechanisms such that strategies to control its formation could be applied during drinking water treatment.