Selective oxidation of ammonia to dinitrogen gas by facile Co2+/PMS/chloridion process through reactive chlorine radicals

The selective oxidation of ammonia to dinitrogen gas in some special wastewater is of paramount significance, but still a challenge. In this study, chlorine radical (Cl•)-mediated oxidation process was developed to realize the selective oxidation of NH4+-N to N2, in which Cl• was generated in Co2+/peroxymonosulfate (PMS)/chloridion (Cl-) system. The effect of various operational parameters on the efficiency and selectivity of ammonia oxidation to N2 was investigated, such as PMS concentration, Co2+ concentration, Cl- concentration and pH value. The experiment results showed that Cl•-mediated NH4+-N oxidation reaction exhibited high NH4+-N removal efficiency and considerable selectivity to N2 in the range of pH from 2.0 to 6.5. The removal efficiency of NH4+-N was 90.39%, and the selectivity of NH4+-N to N2 achieved up to 97.16%. The possible mechanism for high efficient and selective oxidation of NH4+-N to N2 was tentatively proposed. The process developed in this study could provide a novel technology for the treatment and selective oxidation of ammonium in some special types of ammonium-containing wastewater.