Insights into simultaneous removal of nitrate and carbamazepine using UV/sulfite process: performance and mechanisms

Nitrate is always present as the concomitant component during the advanced treatment of refractory organic emerging contaminants. The simultaneous achievement of effective denitrification is an ideal goal for environmentally friendly treatment, especially for those nitrogen-containing compounds. Herein, the performance and mechanisms for simultaneous removal of CBZ and nitrate by UV 254nm /S(IV) process were investigated. Results demonstrated that CBZ and NO 3 – - N could be efficiently removed together, and denitrification was mainly contributed by e aq - , while CBZ degradation was driven by e aq - (55.4%) and •OH (30.4%) collectively. Moreover, the presence of nitrate exerted more significant influences on CBZ degradation than the competition nitrate faced on its own. The removal of CBZ and nitrate both increased with the rise in solution pH and the decrease in their respective initial concentrations. However, the denitrification was accelerated by increasing sulfite concentration while CBZ degradation was obtained at an optimum sulfite concentration. Although nitrate could quench the hydrated electrons to impede CBZ degradation, the •OH radicals produced by nitrate photolysis could compensate partially for the loss. The final product of nitrate was almost completely the nitrogen gas, while both the reduction pathway and oxidation pathway of CBZ degradation were proposed based on DFT calculation and UPLC/MS analysis. The detoxification advantages of CBZ degradation were also revealed from the UV/sulfite process, and the intermediates obtained from reduction reactions generally showed lower toxicity than those from oxidation reactions. This study may provide insights into developing efficient and environmentally friendly advanced methods for the treatment of emerging contaminants.