Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes: A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV

Highlights: • Micropollutants could be oxidized by 275 nm LED-UV alone and -UV/chlorine systems • Direct photolysis reactivity of selected micropollutants were determined at 275 nm • Radical yields from chlorine photolysis depend on the wavelength, pH, and Cl₂ dose • 275 nm UV/chlorine system has higher removal efficiencies at pH 7 and 8 than 254 nm • Higher photo-reactivity of OCl⁻ at 275 nm than at 254 nm gives higher radical yields The aim of this study is to evaluate the micropollutant removal capacity of a 275 nm light-emitting diode (LED)-UV/chlorine system. The sulfamethoxazole, ibuprofen, and nitrobenzene removal efficiencies of this system were compared with those of a conventional 254 nm low-pressure (LP)-UV system as a function of the UV dose. In a direct photolysis system, the photon reactivity of sulfamethoxazole is higher than that of nitrobenzene and ibuprofen at both wavelengths. The molar absorption coefficients and quantum yields of each micropollutant were as follows: sulfamethoxazole (ε_{SMX, 275 nm}^protonated = 17,527 M⁻¹ cm⁻¹, Φ_{SMX, 275 nm}^protonated = 0.239, ε_{SMX, 275 nm}^deprotonated = 8430 M⁻¹ cm⁻¹, and Φ_{SMX, 275 nm}^deprotonated = 0.026), nitrobenzene (ε_{NB, 275 nm} = 7176 M⁻¹ cm⁻¹ and Φ_{NB, 275 nm} = 0.057), and ibuprofen (ε_{NB, 275 nm} = 200 M⁻¹ cm⁻¹ and Φ_{IBF, 275 nm} = 0.067). The photon reactivity of chlorine species, i.e., HOCl and OCl-, were determined at 275 nm (ε_{HOCl, 275 nm} = 28 M⁻¹ cm⁻¹, Φ_{HOCl, 275 nm} = 1.97, ε_{OCl−, 275 nm} = 245 M⁻¹ cm⁻¹, and Φ_{OCl−, 275 nm} = 0.8), which indicate that the decomposition rate of OCl⁻ is higher and that of HOCl is lower by 275 nm photolysis than that by 254 nm photolysis (ε_{HOCl, 254 nm} = 60 M⁻¹ cm⁻¹, Φ_{HOCl, 254 nm} = 1.46, ε_{OCl−, 254 nm} = 58 M⁻¹ cm⁻¹, and Φ_{OCl−, 254 nm} = 1.11). In the UV/chlorine system, the removal rates of ibuprofen and nitrobenzene were increased by the formation of OH and reactive chlorine species. The 275-nm LED-UV/chlorine system has higher radical yields at pH 7 and 8 than the 254 nm LP-UV/chlorine system.