Selective oxidation of ammonium to nitrogen with VUV/UV/Cl process: Efficiency, pathway and mechanism.

Conversion of chloride ions (Cl⁻) into reactive chlorine species (RCS) is an effective strategy for ammonium (NH⁺-N) selective oxidation to nitrogen (N) under high salinity conditions. Herein, vacuum ultraviolet (VUV) irradiation was introduced for NH⁺-N removal in simulated recirculating mariculture systems (RMS) water treatment. Complete oxidation of NH⁺-N and 88.3 % N selectivity were achieved for VUV/UV/Cl⁻ process. Mechanism analysis revealed that Cl⁻ were effectively converted into RCS under VUV irradiation and chlorine oxide radical (ClO) was the predominant RCS responsible for NH-N removal. The pathway of NH-N oxidation was proposed as chlorination because chloramine was identified as the main intermediate. Influence factor investigation indicated that Cl⁻ and bicarbonate (HCO⁻) could significantly promote the removal of NH-N in VUV/UV/Cl⁻ process due to acceleration of ClO generation. Ultimately, the NH-N removal performance of VUV/UV/Cl⁻ process in practical application was also investigated. The results showed that not only NH-N in actual seawater or RMS could be converted effectively to N, but also nitrite (NO⁻-N) and partial nitrate (NO-N) could be removed efficiently by VUV/UV/Cl⁻ process. Hence, the VUV/UV/Cl⁻ process has promising potential in NH-N and total nitrogen (TN) removal for RMS water treatment.