Near real-time N-nitrosodimethylamine monitoring in potable water reuse via online high-performance liquid chromatography-photochemical reaction-chemiluminescence

Direct potable reuse requires stringent water quality assurance to protect public health. This study developed an online analytical technique?high-performance liquid chromatography followed by photochemical reaction and chemiluminescence detection (HPLC-PR-CL)?for determination of the concentration of N-nitrosodimethylamine (NDMA) and three other N-nitrosamines. Its feasibility for near real-time analysis was evaluated by analyzing an ultrafiltration (UF)-treated wastewater before and after a pilot-scale reverse osmosis (RO) treatment system. The online instrument with a method detection limit of 0.3?2.7 ng L?1 requires a direct injection (i.e., no sample pre-concentration) of only 20?200 μL sample volume for the determination of N-nitrosamine concentrations every 20 min. NDMA concentrations in UF-treated wastewater were successfully monitored in a range of 50?200 ng L?1 over the course of 24 h. Likewise, NDMA concentrations in RO permeate ranged from 26?81 ng L?1 over the course of 48 h. The online monitor was capable of recording variations in N-nitrosamine concentration in RO permeate that occurred following changes in feedwater concentration and temperature. This study demonstrates the potential for online water quality assurance via direct measurement of trace levels of organic contaminants, which is highly relevant to the implementation of potable reuse

Transport of N-Nitrosamines through a Reverse Osmosis Membrane: Role of Molecular Size and Nitrogen Atoms

© 2018 American Chemical Society. Reliable and adequate removal of small and uncharged trace organic chemicals, particularly N-nitrosodimethylamine (NDMA) that is carcinogenic and known to occur in treated effluent, is essential for implementing direct potable water use. This study provides new insights to explain the low rejection of NDMA and other N-nitrosamines by reverse osmosis (RO) membranes by examining the role of molecular size and polarity in their molecular structure. The results show that molecular weight is not a suitable molecular property for evaluating the rejection of small uncharged chemicals. In this study, NDMA and two other uncharged chemicals have similar molecular weights (i.e., 72-74 g/mol), but their rejection by the ESPA2 RO membrane varied considerably from 30 to 88%. Instead, a minimum projection area was identified as a more suitable molecular property, indicating that size exclusion plays a primary role in their rejection. It was also determined that chemicals with more nitrogen atoms in their chemical structure consistently showed rejections lower than those of their similarly sized counterparts. The results suggest that chemicals bearing more nitrogen atoms (e.g., NDMA) have higher affinity to amide or amine functional group of a polyamide RO membrane possibly through hydrogen bonding interactions

A rapid and reliable technique for N-nitrosodimethylamine analysis in reclaimed water by HPLC-photochemical reaction-chemiluminescence.

A fast and reliable analytical technique was evaluated and validated for determination of N-nitrosodimethylamine (NDMA) formation and rejection by reverse osmosis (RO) membranes in potable water reuse applications. The analytical instrument used in this study is high-performance liquid chromatography (HPLC), photochemical reaction (PR) and chemiluminescence (CL) - namely HPLC-PR-CL. Results reported here show that HPLC-PR-CL can be used to measure NDMA with a similar level of accuracy compared to conventional and more time-consuming techniques using gas chromatography and tandem mass spectrometry detection in combination with solid phase extraction. Among key residual chemicals (i.e. monochloramine, hydrogen peroxide and hypochlorite) in reclaimed wastewater, hypochlorite was the only constituent that interfered with the determination of NDMA by HPLC-PR-CL. However, hypochlorite interference was eliminated by adding ascorbic acid as a reducing agent. Direct injection of ultrafiltration (UF)-treated wastewater samples into HPLC-PR-CL also resulted in an underestimation of the NDMA concentration possibly due to interference by organic substances in the UF-treated wastewater. Accurate determination of NDMA concentrations in UF-treated wastewater was achieved by reducing the sample injection volume from 200 to 20 μL, though this increased the method detection limit from 0.2 to 2 ng/L. In contrast, no interference was observed with RO permeate. These results suggest that RO membranes could remove part of substances that interfere with the NDMA analysis by HPLC-PR-CL. In addition, RO treatment experiments demonstrated that HPLC-PR-CL was capable of evaluating near real-time variation in NDMA rejection by RO