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

Denitrification is an effective strategy to control eutrophication caused by excessive nitrate in water. However, the comparatively low efficiency of nitrate removal and N-2 selectivity remains a challenge in the denitrification process. Herein, this study proposed a novel photochemical denitrification process by introducing hydrated electron (e(aq)(-)) to reduce nitrate in UV/sulfite system. The results indicated that the optimized UV/sulfite system could effectively reduce nitrate to N-2 with a nearly 100% denitrification efficiency in 90 min. e(aq)(-) 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 e(aq)(-), in water and the rapid reaction rate between e(aq)(-) and the target, the generated N2O is susceptible to be reduced, leading to a high selectivity of N-2 that was confirmed by N-15-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 N-2. 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.

Automated summary

A novel photochemical denitrification process was proposed to effectively reduce nitrate to N-2 with nearly 100% denitrification efficiency. Experimental and theoretical calculations confirmed hydrated electron (e(aq)(-)) as the main reactive species for rapid removal of nitrate and nitrite. The high dispersion of e(aq)(-) in water and the rapid reaction rate contributed to the high selectivity of N-2, making the process promising for practical wastewater treatment.