Rapid Oxidation of Ammonia Nitrogen to Nitrogen Gas by UV-Activated Persulfate with Calcium Oxide

Advanced oxidation processes (AOPs) for removing ammonia nitrogen (NH4+-N) are of increasing interest in wastewater treatment. In this paper, the UV-activated persulfate (PS) process with CaO was applied to oxidize NH4+-N to nitrogen gas (N2). Nearly all of the NH4+-N (30 mg N/L) could be removed within 15 min, and the N2 selectivity was achieved at 95.0%. The addition of CaO made NH4+-N exist in the form of NH3, and HO• was the critical reactive species for NH4+-N oxidation. NO, N2H4, and NO2– were identified as oxidation intermediates and could be further removed. The reaction between N2H4 and NO2– with the assistance of UV/CaO promoted N2 generation during NH4+-N oxidation. The increased dosages of CaO (0.2 to 4.0 g/L) and PS (0.6 to 2.4 g/L) could enhance the NH4+-N oxidation, while the presence of CO32– (100 mM) significantly retarded the removal of NH4+-N. As high removal of NH4+-N (100%) and high N2 selectivity (>79.5%) could be achieved in lake water and secondary wastewater, the proposed UV/PS/CaO process could be potentially applied for the oxidation of NH4+-N in practical water treatment.