Chlorine-Enhanced UV-Activated Persulfate System Controls Ammonia Oxidation Product Formation: Contribution of Active Chlorine Species

The removal of ammonia nitrogen (NH4+-N) using advanced oxidation processes (AOPs) has garnered increasing attention in wastewater purification. However, the application of the UV-activated persulfate (PS) system for treating NH4+-N wastewater is limited by the low reaction rate between NH4+-N and the reactive species (·OH and SO4·−) generated in the system. In this study, common chloride ions (Cl−) were employed to enhance the removal of NH4+-N in the UV/PS process; when the system conditions were pH = 7, [PS]0 = 10mM, [Cl−]0 = 35 mM, 30 mg/L NH4+-N was completely degraded within 40 min. The total nitrogen removal rate was 75.50%, and the reaction rate constant increased from 0.0026 min−1 to 0.0801 min−1. The introduction of Cl− led to the generation of reactive chlorine species (RCS) in the system that could efficiently oxidize NH4+-N over a wide pH range (3–9), and the RCS, which efficiently oxidized NH4+-N across a wide pH range (3–9). Quenching experiments confirmed that these RCS were gradually produced through the activation of Cl− by ·OH and SO4·−. The common anions present in water bodies had little impact on the degradation performance of NH4+-N in the UV/PS/Cl− system. Overall, the UV/PS/Cl− system proposed in this study offers an effective approach for the efficient removal of NH4+-N.