The selective direct oxidation of ammonium in the contaminated water to nitrogen gas using the chemical-less VUV photochemical continuous-flow reactor

• Direct advanced oxidation of NH4+ to N2 was examined using chemical-less VUV reactor.
• Complete oxidation of various concentrations of NH4+ achieved in process with OH.
• High selectivity of NH4+ oxidation toward N2 obtained in the VUV reactor.
• VUV reactor efficiently worked for NH4+ oxidation to N2 in the real sample.
• VUV irradiation is an appropriate chemical-less AOP for ammonium removal.

A chemical-less process using vacuum-UV (VUV) as radiation source was used for direct oxidation of ammonium to N2 from the contaminated water. The effect of water pH, aeration, initial ammonium concentration, reaction time, and water anions on ammonium oxidation was evaluated in batch experiments. The oxidation of ammonium improved with the increase in water pH and the highest oxidation level obtained at the pH 8. Although the aeration partly improved ammonium oxidation efficiency, it inhibited the selective oxidation of ammonium to N2. The complete oxidation of ammonium at concentrations of 25, 50, 75 and 100 mg NH4+/L was obtained at the reaction times of 5, 6, 7.5 and 10 h, respectively, following pseudo first-order kinetic model. In addition, the selectivity to nitrate and N2 formation obtained in the range of 7.7–14.8% and 85.2–92.3%, respectively. In continuous flow experiments, the complete oxidation of 50 mg/L ammonium observed at HRT of 8 h with N2 selectivity above 99%. Sulfate had the lowest and carbonate had the highest scavenging effect among the selected anions on radicals species generated in the VUV photoreactor. Accordingly, the VUV photoreactor is an efficient and promising chemical-less advanced process for selective oxidation of ammonium to N2.