N-nitrosodimethylamine (NDMA) formation has been observed during advanced treatment for potable reuse downstream of microfiltration (MF), reverse osmosis (RO) and UV/AOP treatment units, the latter two of which were installed in part to reduce NDMA concentrations. To identify the origin and mechanisms of the NDMA precursors and NDMA formation, we extracted and isolated the NDMA precursors from samples across the treatment train using an established method. The precursor isolates were analyzed using a LC/qTOF-MS instrument. Total ion chromatograms (TIC) showed considerable removal of ionizable organic matter across both older and newer RO membranes, and potentially, a new compound(s) in the UV/AOP product water. Further inspection of the newer vs older RO permeate samples indicated very little change in the TICs but variability in some specific compounds. Diagnostic fragments specific to NDMA precursors (<i>m/</i>z 58.0651 and 45.0578 u) were searched for and we found 3-hydroxymorphinan (dextromethorphan [cough syrup] metabolite) and methadone (chronic pain and heroin cessation) in the MF effluent (MFE) sample, but both were completely removed by the RO membranes. We have previously reported on these two compounds and their propensity to form NDMA during chloramination. Other compounds were searched for using a proprietary database of NDMA precursors, their retention times, and their fragmentation patterns. At least 9 NDMA precursors were putatively identified in the MFE, but were again well removed by the newer and older RO membranes. However, N,N-dimethyldodecan-1-amine oxide (surfactant) and N,N-dimethylaniline (industrial chemical) were not detected in the MFE isolate but were detected in all samples downstream, indicating that they may be associated with the treatment process. Both of these compounds are known NDMA precursors at low yield. Benzotriazole (anti-corrosion contained in dish detergent) was also detected downstream of the RO units. This compound appeared to be transformed in the UV/AOP unit with an oxygen substitution of nitrogen and polymerization into a trimer. The NDMA FP of either benzotriazole or the trimer is unknown, but this compound could be contributing to the observed NDMA “reformation” after the UV/AOP process and will be a subject of future research.

NDMA precursor transformation and identification during reverse osmosis and UV/peroxide water treatment for indirect potable reuse

253rd National Meeting (2017)

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