Enhanced peracetic acid activation under Far-UVC Radiation: Micropollutant degradation and radical assessment

Traditional ultraviolet/peracetic acid process (UV/PAA) was limited by energy utilization. Herein, an efficient advanced oxidation process (AOP) for activating PAA by the far-ultraviolet of 222 nm (UV₂₂₂/PAA) was established for micropollutant degradation. UV₂₂₂/PAA system can effectively degrade various kinds of micropollutants, and the degradation rate of naproxen (NAP) in UV₂₂₂/PAA system were about 2.61, 3.50 and 4.92 times higher than that in UV₂₂₂/H₂O₂, UV₂₂₂ and UV₂₅₄/PAA systems within 300 s, respectively. The innate quantum yields of molecular state PAA (PAA⁰) and dissociated state PAA (PAA⁻) photolysis under UV₂₂₂ irradiation were determined to be 0.51 and 0.84 mol Einstein⁻¹ at pH 5.0 and pH 9.6, respectively. Based on an established kinetic model, the second-order rate constants of acetylperoxyl radical (CH₃(O)OO•) and acetyloxyl radical (CH₃(O)O•) with NAP were determined to be 1.74 × 10⁷ and 1.08 × 10⁶ M⁻¹s⁻¹, respectively. UV₂₂₂, hydroxyl radical (HO•) and CH₃(O)OO• were mainly responsible for the degradation of NAP, and their relative contributions were 33.00 %, 8.15 %, and 58.83 %, respectively. The increase of pH showed a promoting effect on NAP degradation, and the steady-state concentration of radicals increased with the increase of pH in UV₂₂₂/PAA system. Cl^– and HCO₃^– have inconspicuous impact on NAP degradation, while HA inhibits the degradation of NAP. The degradation pathway of NAP was proposed on the basis of product identification and theoretical calculation analysis. Finally, the effectiveness of the UV₂₂₂/PAA system for NAP degradation was also verified in real water. This work develops an efficient PAA activation AOP with high radical yield for micropollutant degradation in practical applications.