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

Area of Science:

• Environmental Chemistry
• Photochemistry
• Water Treatment Technologies

Background:

• Eutrophication due to excess nitrate necessitates effective water treatment.
• Current denitrification methods face challenges with efficiency and N₂ selectivity.

Purpose of the Study:

• To develop a novel photochemical denitrification process.
• To enhance nitrate removal efficiency and N₂ selectivity.
• To investigate the role of hydrated electrons (e_aq^-) in nitrate reduction.

Main Methods:

• Utilized a UV/sulfite system to generate hydrated electrons (e_aq^-).
• Employed quenching and laser flash photolysis to identify reactive species.
• Conducted ¹⁵N-isotopic tests to confirm N₂ selectivity.
• Performed density functional theory (DFT) calculations for thermodynamic analysis.

Main Results:

• Optimized UV/sulfite system achieved nearly 100% denitrification efficiency within 90 minutes.
• Hydrated electrons (e_aq^-) were identified as the primary reactive species for nitrate and nitrite removal.
• High N₂ selectivity was achieved due to the rapid reduction of intermediates.
• DFT calculations indicated an exothermic process favoring N₂ formation.
• The system demonstrated high efficiency in treating nickel-plating wastewater.

Conclusions:

• The novel photochemical denitrification process effectively removes nitrate using hydrated electrons.
• The UV/sulfite system offers high efficiency and N₂ selectivity, overcoming limitations of traditional methods.
• This process shows significant potential for practical application in industrial wastewater treatment.