A column study was conducted to assess the fate of two nitrosamines, N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR), in an anaerobic aquifer mimicking the field conditions of managed aquifer recharge (MAR) using recycled water over a period of two years. Two sets of experiments, low concentration column experiments (200 ng L-1 of NDMA and NMOR) and high concentration stop-flow column experiments (590 g L-1 of NDMA and 650 g L-1 of NMOR), were conducted using stainless steel columns packed with anaerobic Leederville aquifer material. Each set of experiments consisted of a sterile control column (with sodium azide) and a non-sterile experimental column (without sodium azide). For the low concentration column experiments, recycled water spiked with NDMA, NMOR and a bromide tracer, were flowed through the columns throughout the experiments, while for the high concentration stop-flow column experiments, the flow of the spiked recycled water was terminated to increase the column residence time. Water samples were taken from sampling ports in all columns during the study to monitor the concentration of NDMA and NMOR. Sorption studies confirmed the high mobility of NDMA and NMOR in the aquifer with the low retardation coefficients of 1.1 for NDMA and 1.2 to 1.6 for NMOR. The sorption isotherms of NDMA and NMOR were not significantly concentration-dependent over the tested concentrations. Degradation studies showed that NDMA and NMOR degraded biologically in the Leederville aquifer sediment and that the onset of degradation occurred within 3 months after the injection of NDMA and NMOR. Degradation of NDMA was inhibited at higher concentration (590 ng L-1) with a half-life of 290±25 days. Degradation half-life of NDMA at lower concentration (200 ng L-1) varied from 26 to 160 days. By contrast, degradation of NMOR was not inhibited at higher concentration with comparable half-lives of 40-45 days at two tested concentrations (200 ng L-1 and 650 g L-1).
|Publication status||Unpublished - 2011|