Selective oxidation of ammonia nitrogen to nitrogen gas by Fe2+/PMS/Cl−: The role of reactive chlorine species

Abstract

Ammonia nitrogen (NH4+-N) can pose a threat to ecosystems and human health. Many methods have been used for the removal of NH4+-N. In particular, reactive chlorine species (RCS, including Cl·, Cl2·−, and ClO·) show superior performance for the selective oxidation of NH4+-N to nitrogen gas (N2). Herein, Fe2+/peroxymonosulfate (PMS)/Cl− process was proposed to generate RCS for the conversion of NH4+-N to N2, in which Fe2+ was used as the activator of PMS in the presence of Cl−. Fe2+, PMS, and Cl− concentrations could affect the removal of NH4+-N in Fe2+/PMS/Cl− process. Fe2+/PMS/Cl− exhibited good performance in removing NH4+-N at pH 3.5–8.0. At all investigated conditions, NH4+-N was mainly converted to N2, and N2 selectivity was more than 90 %. Under optimal conditions, 50 % of NH4+-N was removed in 5 min, and the removal efficiency reached the maximum of 96 % within 120 min with the high N2 selectivity of 100 %. The electron spin resonance tests, scavenging experiments, and probe experiments demonstrated the generation of RCS in Fe2+/PMS/Cl− reaction system. Experimental results and model analysis consistently proved that ClO· and Cl· were crucial radicals during the selective oxidation of NH4+-N, especially ClO·. Fe2+/PMS/Cl− system could remove NH4+-N and COD simultaneously in real wastewater. This study can provide an efficient strategy for the removal of NH4+-N.