Advanced oxidation processes (AOPs) are utilized in wastewater treatment, drinking water purification, and hazardous waste site remediation. Common oxidants such as hydrogen peroxide or persulfate use reactive radical species to oxidize organic pollutants, but the mechanism of degradation and the fate of the contaminants remain under study. The transformation products of these oxidation reactions might also be toxic and necessitate further treatment. Substituted aromatics such as benzene, toluene, ethylbenzene, chlorobenzene, and nitrobenzene were treated in a UV/H2O2 or UV/S2O82- system. The formation of transformation products was monitored in varying conditions of pH and ionic strength. The substituent on the parent compound affected the yield of aromatic and ring cleavage products. In addition to the expected oxidation pathway of sequential ring hydroxylation, a new pathway was detected in which ring cleavage proceeds prior to hydroxylation, leading to the formation of α,β-unsaturated aldehydes. This is similar to an in vivo metabolic pathway for benzene that produces highly toxic aldehydes. Further experiments show that the ring cleavage products of the AOP system are persistent in conditions simulating groundwater. Due to the stability and potential toxicity of the aldehydic ring cleavage products, these findings have consequences for AOP treatment of contaminated water.

Formation of unanticipated ring cleavage products during OH● and SO4●- water treatment

253rd National Meeting (2017)

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