We recently found that application of ozone, commonly employed in wastewater reuse before either membrane filtration (to control biofouling) or biological activated carbon (to break down larger molecules into digestible fragments) produces large quantities (up to ~50 µg/L) of nitromethane in wastewater effluent. Nitromethane itself is unlikely to be a major human health concern, however in this work we show that the nitromethane formed during wastewater ozonation can be transformed to chloropicrin, a highly genotoxic unregulated disinfection byproduct, at nearly 100% yield during subsequent chlorination. We further demonstrate via standard addition assays that nearly 100% of the chloropicrin formation in ozonated wastewater during subsequent chlorination (as would likely happen in a direct potable reuse scenario) can be attributed to nitromethane. A search for potential precursors to this reaction lead to N-methylamine stimulant drugs, including methamphetamine and ephedrine, which have been routinely measured in wastewater and which contain an N-methylamine functional group anticipated to serve as an efficient precursor. We found that these N-methylamine drugs ubiquitously form nitromethane upon ozonation, generally at high molar yield (&gt;50%), and are currently quantifying the contribution of each to the nitromethane precursor pool. Finally, we examined the removal efficiency of nitromethane during advanced treatment as practiced during water reuse. We found removal to be very poor by reverse osmosis at both the bench and full scale (&lt; 50% removal), likely because nitromethane is small, polar, and uncharged. Transformation rates by advanced oxidation were also poor (&lt;50%), because nitromethane is a poor chromophore and its reaction rate constant with hydroxyl radical is low. These results are potentially troubling for future direct potable reuse scenarios in which recycled wastewater directly becomes a drinking water source. However, we found that biofiltration (including during O3/BAC) may be a useful treatment technique for removing nitromethane.

Formation of nitromethane during wastewater ozonation and implications for direct potable reuse

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.