Chlorination and bromination kinetics of emerging contaminants in aqueous systems

Second-order rate reaction constants of micropollutants with chlorine are essential for evaluating their removal efficiencies from water during chlorine disinfection. In this study, the reactions of five selected emerging contaminants with unavailable kinetic data (Benzotriazole, N,N-diethyl-m-toluamide or DEET, Chlorophene, 3-Methylindole, and Nortriptyline HCl) with chlorine and bromine have been investigated, and their apparent second-order rate constants have been determined as a function of the pH. For the chlorination process, the intrinsic rate constants for the elementary reactions of the ionized and neutral species were also evaluated. The sequence of reaction rates was Methylindole > Chlorophene > Nortriptyline HCl > Benzotriazole > DEET. The bromination of the selected emerging contaminants in ultra-pure water provided exactly the same sequence of reaction rates as in the chlorination process, although higher values of rate constants. The efficiency of the chlorination process for the degradation of these ECs when present in several aqueous systems (surface water from a public reservoir, and two effluents from municipal wastewater treatment plants) was investigated. During wastewater or drinking water treatment, chlorine is a good option for the degradation of Methylindole, and in a lower extent for Chlorophene and Nortriptyline. However, it is not a suitable oxidant for the abatement of Benzotriazole and DEET. Finally, chlorination in the presence of bromide revealed that low bromide concentrations enhanced slightly the degradation of the selected compounds during chlorine oxidation.

► Chlorination and bromination kinetics of emerging contaminants was investigated.
► Apparent rate constants were pH dependent and the primary oxidant species was HOCl.
► Chlorine was specially efficient for the removal of 3-Methylindole and Chlorophene.
► The additional presence of bromide enhanced slightly the chlorination of ECs.