Halonitromethane Treatment Using Advanced Oxidation Process: Rates, Mechanisms and Kinetic Modeling

Halonitromethanes (HNMs) are low molecular weight halogenated disinfection-by-products (DBPs) found to be formed during ozonation, chlorination, or chloramination of waters containing natural bromide ion and nitrogenous organic matter. This work identifies the absolute rate constants for the oxidative hydroxyl radical (•OH) and reductive hydrated electron e- aq extinction of HNM compounds. Three forms of HNMs included in this study are the chlorinated, brominated, and mixed halogenated compounds. Electron pulse radiolysis and transient absorption spectroscopy were used to measure •OH and e- aq radical absolute reaction rate constants for a total of nine HNMs. To elucidate the decomposition reaction mechanism, six HNMs were exposed to 60Co gamma (γ) irradiation at various times (absorbed doses). The disappearance of the parent compound in the 60Co irradiated samples was monitored and the mass balance of ionic residuals was determined. Using reaction rate constants and the mechanistic data, a preliminary reaction mechanism was proposed and used in a kinetic model to describe the removal of the HNMs in aqueous solution. The model was then extended to simulate the electron beam process on waters of defined chemical composition and used for estimating the economics of the treatment of trichloronitromethane at large scale