Selective oxidation of ammonium to nitrogen with VUV/UV/Cl⁻ process: Efficiency, pathway and mechanism
Lingdan Wang1, Bing Chen1, Gaozu Liao1
1School of Environment, South China Normal University, Guangdong Provincial Engineering Technology Research Center for Drinking Water Safety, Guangdong Provincial Key Lab of Functional Materials for Environmental Protection, China.
Abstract:
Conversion of chloride ions (Cl⁻) into reactive chlorine species (RCS) is an effective strategy for ammonium (NH4⁺-N) selective oxidation to nitrogen (N2) under high salinity conditions. Herein, vacuum ultraviolet (VUV) irradiation was introduced for NH4⁺-N removal in simulated recirculating mariculture systems (RMS) water treatment. Complete oxidation of NH4⁺-N and 88.3 % N2 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 NH4+-N removal. The pathway of NH4+-N oxidation was proposed as chlorination because chloramine was identified as the main intermediate. Influence factor investigation indicated that Cl⁻ and bicarbonate (HCO3⁻) could significantly promote the removal of NH4+-N in VUV/UV/Cl⁻ process due to acceleration of ClO• generation. Ultimately, the NH4+-N removal performance of VUV/UV/Cl⁻ process in practical application was also investigated. The results showed that not only NH4+-N in actual seawater or RMS could be converted effectively to N2, but also nitrite (NO2⁻-N) and partial nitrate (NO3⁻-N) could be removed efficiently by VUV/UV/Cl⁻ process. Hence, the VUV/UV/Cl⁻ process has promising potential in NH4+-N and total nitrogen (TN) removal for RMS water treatment.
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