Chloride-enhanced ammonia removal in heat/peroxymonosulfate system: Production and contribution of chlorine

Abstract

Heat-activated peroxymonosulfate (PMS) has been widely accepted as an attractive approach in degrading organic contaminants. Nevertheless, heat/PMS process possesses poor performance on the removal of ammonia (NH4+−N). In this study, the commonly existing anion of chloride ion (Cl−) was employed to augment the removal of NH4+−N in the heat/PMS process. Heat/PMS/Cl− process possesses well performance on the removal of NH4+−N over the wide pH range of 3–11. The removal of NH4+−N in the heat/PMS/Cl− process adhered to the pseudo-zero order kinetic model, and kobs rose from 0.294 mg/L min−1 to 1.61 mg/L min−1 with the addition of 30 mM Cl− at pH 7. Chlorine (HClO), instead of HO, SO4−, Cl and 1O2, was identified as the primary oxidant responsible for NH4+−N removal according to the quenching experiments. The formation of HClO was proved to be mostly through the direct reaction between PMS and Cl−, rather than the reactions of reactive species with Cl−. The environmentally friendly gas of N2 predominated as the primary degradation product during the removal of NH4+−N with heat/PMS/Cl− process, although nitrite and nitrate nitrogen were also detected. Increasing Cl− concentration, PMS dosage and reaction temperature facilitated the removal of NH4+−N. Br− could significantly accelerate the removal of NH4+−N in heat/PMS/Cl− process. The other anions of SO42−, CO32− and NO3−, the cations of Cu2+ and Fe3+, humic acid and landfill leachate had negligible effects on the removal of NH4+−N. Overall, this study offered an efficient approach to boost the oxidation capacity of heat/PMS process towards the removal of NH4+−N, and these findings had significant implications for the utilization of heat/PMS process in Cl−-containing water.