Efficient photochemical denitrification by UV/sulfite system: Mechanism and applications

Abstract

Denitrification is an effective strategy to control eutrophication caused by excessive nitrate in water. However, the comparatively low efficiency of nitrate removal and N2 selectivity remains a challenge in the denitrification process. Herein, this study proposed a novel photochemical denitrification process by introducing hydrated electron (eaq-) to reduce nitrate in UV/sulfite system. The results indicated that the optimized UV/sulfite system could effectively reduce nitrate to N2 with a nearly 100% denitrification efficiency in 90 min. eaq- was identified as the mainly reactive species to achieve rapid removal of nitrate and nitrite, and the result was verified by quenching and laser flash photolysis tests. Benefiting from the high dispersion of eaq- in water and the rapid reaction rate between eaq- and the target, the generated N2O is susceptible to be reduced, leading to a high selectivity of N2 that was confirmed by 15N-isotopic. Besides, thermodynamic results based on the density functional theory (DFT) calculations suggested that the photochemical denitrification process was exothermic process and tend to transform to N2. Significantly, UV/sulfite system applied in the nickel-plating wastewater showed high denitrification efficiency, demonstrating that the novel photochemical denitrification process is promising for practical wastewater treatment.