Oxidative treatment of water and wastewater: contaminant abatement and byproduct formation

Wastewater increasingly serves as a drinking water source, either deliberately through potable water reuse, or accidently during de facto wastewater reuse, when wastewater effluent is released into surface waters upstream of a water treatment plant. Wastewater reuse is a promising solution to water scarcity, however toxic chemical contaminants in treated wastewater may threaten public health and confidence in public water supplies.
This presentation will focus on two classes of contaminants recently found in oxidatively treated wastewater: nitroalkanes and aldehydes. We recently identified nitromethane as a major ozonation byproduct in wastewater and found that it serves as the key intermediate toward chloropicrin, a potent genotoxin, during subsequent chlorination. We further found that, at wastewater reuse plants, downstream nitromethane removal by reverse osmosis (RO) and advanced oxidation processes (AOP) were poor. Unlike RO and AOP, biofiltration showed promise, with nitromethane removals up to 95%.
The second part of this presentation will focus on a new treatment technology for low molecular weight aldehydes, recently shown to comprise a large fraction of the organic carbon in finished recycled wastewater. We repurposed transition metal catalysts from the organic synthesis literature to oxidize aldehydes to (non-toxic) carboxylates under mild conditions, with ambient dissolved oxygen serving as the terminal electron acceptor. We documented aldehyde oxidation kinetics, elucidated a mechanism to explain the variation in reaction rates for different aldehydes, and demonstrated long-term catalyst operation in a flow-through column reactor. To the best of our knowledge, this is the first abiotic application of ambient dissolved oxygen as a useful oxidant for water treatment.