N-Nitrosamine formation kinetics in wastewater effluents and surface waters

Abstract

N-Nitrosodimethylamine (NDMA) is a chloramination disinfection by-product (DBP) with an uncertain regulatory future. While extensive literature exists on NDMA formation potentials (FP) for natural waters and for model compounds considered as NDMA precursors, less data exists on the kinetics of NDMA formation in surface and wastewaters. NDMA formation kinetics experiments were conducted in seven source waters at two monochloramine doses. NDMA formation was modeled by a simple, second-order model, using the measured NDMA_max and monitored monochloramine concentrations at selected reaction times. The model fits NDMA formation well (R² > 0.88) in all source waters. While the extent of NDMA formation was highly variable, the rate constant (k_app) values from different waters fell in a narrow range (0.01–0.09 M⁻¹ s⁻¹). This suggests that a common precursor or rate limiting step for NDMA formation likely exists despite the differences in matrices. Although further studies are needed to validate the model over a wider range of water conditions such as pH and N : Cl₂ ratios, the model could help water utilities to predict NDMA formation in distribution systems.