High-efficiency oxidation of fluoroquinolones by the synergistic activation of peroxymonosulfate via vacuum ultraviolet and ferrous iron

Fluoroquinolones in aquatic environments have caused worldwide concern due to the negative effects on human health and ecological environment. So far, the performance and mechanism for fluoroquinolones removal by the synergistic activation of peroxymonosulfate (PMS) via vacuum UV (VUV) irradiation and Fe2+ are still blank. Herein, compared with its sub-processes, VUV/Fe2+/PMS process significantly improved the degradation and mineralization efficiencies of three fluoroquinolones. Effect mechanisms of typical parameters (Fe2+ and PMS doses, initial pH) on norfloxacin (NOR) removal by VUV/Fe2+/PMS were elaborated and VUV/Fe2+/PMS showed excellent performance at wide initial pH (3-10). The results of fluorescence molecular probe and radical trapping experiments proved that hydroxyl radical, singlet oxygen, and sulfate radical were primary reactive oxygen species in VUV/Fe2+/PMS. The degradation pathways of NOR in VUV/Fe2+/PMS were mainly defluorination, piperazine ring transformation and quinolone group transformation, and its main inorganic by-products were F-, NO3-, and NH4+. Besides, the synergistic reaction pathways in integrated VUV/Fe2+/PMS process were elaborated. Furthermore, inorganic anions (such as Cl-, NO3-, SO42-, CO32-) hardly affected NOR removal by VUV/Fe2+/PMS, while dissolved organic matter showed slight inhibition. Finally, well-pleasing results of fluoroquinolones removal by VUV/Fe2+/PMS in actual waters highlighted its superiority in the advanced treatment of secondary effluent.