Primary (1°) and secondary (2°) amine moieties are found in the structures of water contaminants such as pharmaceuticals (atenolol, gabapentin) and industrial chemicals (ethanolamine). The presence of amines in drinking water sources is of concern, as they can be transformed into toxic nitrogenous disinfection byproducts (N-DBPs) during water disinfection with chlorine/chloramine. Pre-oxidation with ozone or ferrate can mitigate the N-DBP formation by destroying amine moieties, however, it may promote the formation of (halo)nitro compounds. Transformation of amine compounds can be significantly enhanced in sequential and combined use of chlorine and UV (UV/chlorine) due to formation and photolysis of organic chloramines. We investigated the transformation kinetics, products, and mechanisms of some 1° & 2° amine compounds during water treatment with chlorine, ferrate, ozone, and UV/chlorine, and discovered several new and important amine transformation chemistries. The 1° amine of gabapentin was rapidly (t1/2 ~1 min) transformed to nitrile moiety with a molar yield of &gt;87% during chlorination. Di-chlorinated amine (N-Cl2) of gabapentin had a much higher decomposition rate than N-Cl2 of other simple aliphatic amines due to the influence of nearby carboxyl group and quaternary b-carbon. Ozonation of gabapentin mainly produced nitrate with little nitro product, unlike other amine compounds. Chlorinated amines of atenolol (2°) and ethanolamine (1°) were stable but their decomposition could be significantly enhanced by UV photolysis. Identified/quantified transformation products could be explained by a reaction mechanism involving aminyl radicals that were transformed via 1,2-H shift, b-scission, intramolecular addition, and 1,2-alkyl shift. Ferrate oxidation of some 1° amine compounds mainly formed nitrile products. Practical implications of this new kinetic, product, and mechanistic information will be discussed in terms of N-DBP control strategy and advanced amine wastewater treatment technology.

Transformation of amine micropollutants during water oxidation and disinfection: Kinetics, mechanisms, and practical implications

ACS Spring 2022

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