Degradation Of Ciprofloxacin Wastewater By Electrolysis Coupled Microbubble Ozonation Process: Performance And Mechanism Study

Antibiotic is considered one of the most difficult pollutants to remove from aquatic environments because of its high toxicity and difficult biodegradation.In this study,a novel electrolytically coupled ozone microbubble process（E-MB-O₃）was proposed and constructed to study the removal of a typical antibiotic,ciprofloxacin（CIP）,from water.The synergistic effect between electrolysis,microbubbles,and ozone and the CIP removal performance of the E-MB-O₃ process was evaluated.The reaction mechanism and main degradation pathways of CIP were revealed.Finally,potential applications of the E-MB-O₃process were explored.The main conclusions of this study are as follows:1)The results exhibited a good synergistic effect among electrolysis,microbubbles,and ozone,with a synergistic index（SI）of 2.75.Compared with other oxidation processes,the E-MB-O₃ process can completely degrade CIP within 60 min and achieve a total organic carbon（TOC）mineralization rate of approximately 30%within 90 min.Furthermore,the system did not detect the escape of ozone throughout the reaction process,and the ozone utilization rate was close to 100%.The investigation of the effect of the operation parameters indicated that improving the ozone dosage,applied current,electrolyte concentration,and gas flow could promote the removal efficiency of CIP in the E-MB-O₃process.However,when they reached a certain value,further improving these parameters did not significantly promote the effect,instead resulting in varying degrees of inhibition.In addition,the E-MB-O₃ process was more conducive to CIP removal under neutral conditions.Because of the limited production of oxidants in this process within a certain period,it is necessary to consider the appropriate initial concentration of the target pollutant in practical applications.2)Hydroxyl radicals（·OH）,singlet oxygen（¹O₂）,superoxide radicals（·O₂^-）,and ozone（O₃）were involved in the oxidation and removal of CIP in the E-MB-O₃ process,with contributions for CIP removal of 66.79%,23.57%,2.98%,and 6.67%,respectively.·OH played the dominant role in CIP removal.Further studies showed that the generation of·OH in the E-MB-O₃ process involved four pathways:the peroxone reaction,cathodic electroreduction of ozone,electrooxidation of hydroxyl ions at the anode surface,and shrinkage and rupture of microbubbles.Ten intermediate degradation products of CIP in the E-MB-O₃ process were detected using HPLC-MS,and three reasonable degradation pathways were proposed:hydroxylation,piperazine ring cleavage,and substitution defluorination.ECOSAR software was used to predict the toxicity of CIP and its intermediate products.The results showed that the toxicity of the intermediate products may be higher than that of the parent product,posing certain eco-environmental risks.Therefore,special attention is required during the emission treatment.3)Finally,potential applications of the E-MB-O₃ process were assessed.The results showed that the presence of PO₄^3-,HCO₃^-,and HA in actual water bodies had a significant inhibition on CIP removal by the E-MB-O₃ process.A low concentration of Cl^-also had an inhibitory effect on CIP removal,whereas at high concentrations,it promoted its removal.Moreover,the E-MB-O₃ process has been proven to achieve stable and efficient removal of various antibiotic pollutants（e.g.sulfamethoxazole,amoxicillin,norfloxacin,tetracycline hydrochloride）.These results demonstrated that the E-MB-O₃ process has practical application prospects in water treatment.