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 k_obs 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.