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

Abstract

Advanced oxidation processes (AOPs) for removing ammonia nitrogen (NH 4 + -N) are of increasing interest in wastewater treatment. In this paper, the UV-activated persulfate (PS) process with CaO was applied to oxidize NH 4 + -N to nitrogen gas (N 2 ). Nearly all of the NH 4 + -N (30 mg N/L) could be removed within 15 min, and the N 2 selectivity was achieved at 95.0%. The addition of CaO made NH 4 + -N exist in the form of NH 3, and HO • was the critical reactive species for NH 4 + -N oxidation. NO, N 2 H 4, and NO 2 – were identified as oxidation intermediates and could be further removed. The reaction between N 2 H 4 and NO 2 – with the assistance of UV/CaO promoted N 2 generation during NH 4 + -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 NH 4 + -N oxidation, while the presence of CO 3 2– (100 mM) significantly retarded the removal of NH 4 + -N. As high removal of NH 4 + -N (100%) and high N 2 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 NH 4 + -N in practical water treatment.