Control of Micropollutants in Water by Far-UVC Photolysis of Peracetic Acid

Increasing radical yields to reduce energy consumption for micropollutant degradation would make advanced oxidation processes more sustainable in the context of the United Nations’ Sustainable Development Goals and carbon neutrality. We herein demonstrate that switching the UV radiation source from conventional low-pressure UV (UV₂₅₄) to far-UVC (UV₂₂₂) increases the UV fluence-based concentration of hydroxyl radicals (HO^•) in the UV/peracetic acid (UV/PAA) process by 4.1-fold and 27.9-fold in deionized water and real surface water, respectively. Acetyloxyl radicals (CH₃C(O)O^•) are generated in the UV₂₂₂/PAA process at a steady-state concentration of 2.4 × 10^–12 M in deionized water, while they are undetectable in the UV₂₅₄/PAA process under the comparable conditions. The enhancement to radical production is mainly attributed to the 15.7-fold higher molar absorption coefficients of PAA⁰ at 222 nm than 254 nm (50 vs 3.5 M^–1 cm^–1), which suppresses the compromised 1.1-fold lower innate quantum yield at 222 nm than 254 nm (0.78 vs 0.86 mol einstein^–1). The enhanced radical generation and direct photolysis promote the fluence-based degradation rate constants of bisphenol A, phenol, and nitrobenzene by 4.1-fold, 3.3-fold, and 2.9-fold in the UV₂₂₂/PAA process than the UV₂₅₄/PAA process.