The influence of the pre-oxidation of natural organic matter on the formation of N-nitrosodimethylamine (NDMA)

NDMA is a recently recognized disinfection byproduct that can be formed by a reaction of monochloramine with natural organic matter (NOM). This study was undertaken to examine the influence of various preoxidation strategies (including prechlorination) on the subsequent formation of NDMA and to determine how this is correlated to the subsequent loss in specific UV absorbance (SUVA) that preoxidation causes. Batch experiments were conducted using surf ace-water-derived NOM exposed to various oxidants that included free chlorine, permanganate, hydrogen peroxide, and ozone. Photochemical oxidation was also studied by exposing the water to simulated sunlight. The amount of NDMA formed after monochloramine was added or formed in situ, in the case when free chlorine was the preoxidant, was significantly reduced by these treatments. The reduction was proportional to the reduction in SUVA that also occurred as a consequence of these treatments indicating that SUVA may be a good surrogate for NDMA precursor content. Furthermore, the change in NDMA formation per unit change in SUVA was a constant that did not depend on the nature of the oxidant.