Degradation of antibiotics by modified vacuum-UV based processes: Mechanistic consequences of H2O2 and K2S2O8 in the presence of halide ions.

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K2S2O8 was superior to H2O2 under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K2S2O8. The ofloxacin degradation rate was accelerated as concentrations of H2O2 and K2S2O8 was increased to 3 mM, but the degradation rate was slightly decreased with excess H2O2 (>3 mM). The performance of modified VUV processes (i.e., VUV/H2O2 and VUV/K2S2O8) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl- and Br-) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K2S2O8) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.