Temperature dependence of hydroxyl radical reactions with chloramine species in aqueous solution

Abstract

The absolute temperature-dependent kinetics for the reaction between hydroxyl radicals and the chloramine water disinfectant species monochloramine (NH₂Cl), as well as dichloramine (NHCl₂) and trichloramine (NCl₃), have been determined using electron pulse radiolysis and transient absorption spectroscopy. These radical reaction rate constants were fast, with values of 6.06 × 10⁸, 2.57 × 10⁸, and 1.67 × 10⁸ M^-1 s^-1 at 25 °C for NH₂Cl, NHCl₂, and NCl₃, respectively. The corresponding temperature dependence of these reaction rate constants, measured over the range 10-40 °C, is well-described by the transformed Arrhenius equations:giving activation energies of 8.57 ± 0.58, 6.11 ± 0.40, and 5.77 ± 0.72 kJ mol^-1 for these three chloramines, respectively. These data will aid water utilities in predicting hydroxyl radical partitioning and chemical contaminant removal efficiencies under real-world advanced oxidation process treatment conditions.

Keywords: Advanced oxidation processes; Chloramines; Hydroxyl radical kinetics; Temperature-dependent rate constants.