Radical Treatment of Haloacetonitriles in Aqueous Systems: A Kinetic Study

Haloacetonitriles (HANs) are important drinking water disinfection byproducts formed through the chlorination and chloramination of amino acids. Although HAN concentrations in treated water are usually lower than trihalomethanes, they are still of major concern due to their higher cyto- and genotoxicity. HANs undergo chemical transformations by hydrolysis on the hour to week time scales; however, for possible direct water reuse situations, their active removal using advanced oxidation/reduction processes (AO/RPs) may be required. We report here our systematic kinetic study of the four major AO/RP radiolysis species, oxidizing hydroxyl (·OH) and sulfate (SO₄ ^-·) radicals and reducing hydrated electron (e_aq ^-) and hydrogen atoms (H^·) with five HANs (mono-, di-, and trichloroacetonitriles and mono- and dibromoacetonitriles) in water measured using electron pulse radiolysis techniques. At ambient temperatures and pH 1-7, significant reactivity was found for e_aq ^- (k = (1-5) × 10¹⁰ M^-1 s^-1) and H^· atoms (k = (1 - 40 × 10⁷ M^-1 s^-1), but only minimal oxidation by ^·OH (k = (0.6-10) × 10⁷ M^-1 s^-1) and SO₄ ^-· (k = (0.2-4) × 10⁶ M^-1 s^-1) occurred. These data suggest that the large-scale AO/RP treatment of these contaminants will be effective for deaerated reducing systems, where the reductive electron-induced degradation of HANs will occur.