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.

ABSTRACT

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 (εSMX, 275 nmprotonated = 17,527 M-1 cm-1, ΦSMX, 275 nmprotonated = 0.239, εSMX, 275 nmdeprotonated = 8430 M-1 cm-1, and ΦSMX, 275 nmdeprotonated = 0.026), nitrobenzene (εNB, 275 nm = 7176 M-1 cm-1 and ΦNB, 275 nm = 0.057), and ibuprofen (εNB, 275 nm = 200 M-1 cm-1 and ΦIBF, 275 nm = 0.067). The photon reactivity of chlorine species, i.e., HOCl and OCl-, were determined at 275 nm (εHOCl, 275 nm = 28 M-1 cm-1, ΦHOCl, 275 nm = 1.97, εOCl-, 275 nm = 245 M-1 cm-1, and ΦOCl-, 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 (εHOCl, 254 nm = 60 M-1 cm-1, ΦHOCl, 254 nm = 1.46, εOCl-, 254 nm = 58 M-1 cm-1, and ΦOCl-, 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.