Oxidation of ciprofloxacin by the synergistic effect of DBD plasma and persulfate: reactive species and influencing factors analysis

A synergistic system of water falling film dielectric barrier discharge (DBD) plasma and persulfate (PS) was set up and used for oxidizing ciprofloxacin (CIP) in water. Results of reactive species formation in the DBD-only system as well as the DBD–PS system verified the PS activation in the DBD system. Influencing factors on CIP degradation and the degradation process were also been studied. The obtained results showed that the presence of PS could greatly improve the degradation and mineralization of CIP and that the degradation efficiency could reach 97.73% after only 40 min treatment with 4 mM PS addition. The increase of PS concentration, the lower CIP concentration, the acidic solution pH and the addition of metal ions (Fe²⁺ and Cu²⁺) enhanced the CIP degradation, while the existence of Cl^- and HC${\mathrm{O}}_3^{-}$ had a negative effect. The experiments related to scavenger addition confirmed the contribution of the main reactive species to the CIP oxidation. Three probable degradation pathways were proposed by analyzing the inorganic ions and organic byproducts formed during the CIP degradation. The toxicity evaluation results of the CIP and its intermediates confirmed the effectiveness of the DBD–PS synergistic system.