<i>N</i>-nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct formed from reactions between chloramines and nitrogenous precursors. At potable reuse facilities with both reverse osmosis (RO) and advanced oxidation processes (AOP), NDMA is typically reduced to below detection limits by AOP, but in some cases NDMA concentrations increase to low ppt concentrations during conveyance, near some state regulatory limits. The precursors which evade both RO and AOP and contribute to down-process NDMA formation are not currently known. Prior work has shown that dimethylamine (DMA) does not substantially contribute to the NDMA precursor pool in treated wastewater or surface water, leading, by extension, to the thought that DMA’s overall importance as an NDMA precursor is low. There are, however, no investigations of DMA occurrence in reuse facilities. To investigate the importance of DMA during treatment for water reuse, we sampled four full- and one pilot-scale water reclamation facility utilizing RO followed by AOP. The median DMA concentrations in AOP product and finished water samples were 0.4 μg/L at the four full-scale facilities across six sampling events. We sampled one of the four plants three times over a year and DMA in the finished water was in the relatively narrow range of 0.4 to 1.4 µg/L. Based on the occurrence of DMA, standard addition experiments, and measured NDMA molar yields (1.7%), DMA contributed ~43% to the total NDMA precursor pool in RO+AOP treated waters. These results enable the implementation of treatment strategies that reduce NDMA formation to below state regulatory levels, ultimately leading to greater security of the future of water reuse.

Dimethylamine is an important NDMA precursor in full advanced treated water from potable reuse facilities

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ACS Fall 2022

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