Degradation Of Ofloxacin By MnO_x-CeO₂ Catalyzed Ozonation Coupled With Peroxymonosulfate

With the acceleration of the industrialization process in China,the discharge volume and treatment difficulty of wastewater continue to increase.Traditional wastewater treatment technologies can hardly cope with the increasingly serious water pollution problem.Therefore,the innovation and improvement of the treatment technology of refractory wastewater was an urgent issue.Advanced oxidation processes（AOPs）are very promising technologies in advanced wastewater treatment that could degrade or even completely mineralize most of the organic pollutants in wastewater using the large number of reactive oxygen species generated.However,the single advanced oxidation technology has bottlenecks that make it difficult to achieve deeper treatment of wastewater.In this study,a synergistic advanced oxidation technology based on hydroxyl radicals（HO·）and sulfate radicals（SO₄·^-）was developed for the deep treatment of refractory pollutants in wastewater by constructing a synergistic process of catalytic activation of ozone（O₃）and peroxymonosulfate（PMS）simultaneously.The synergistic effect of the catalytic ozonation coupled with PMS process was evaluated by investigating the degradation of ofloxacin（OFX）.The mechanism of the synergistic process was explored by analyzing the physicochemical properties of catalysts,identifying reactive oxygen species in water,and deducing the degradation pathways of organic pollutants.The main contents and conclusions of this paper are listed as follows.（1）Bimetallic oxide catalysts MnO_x-CeO₂/γ-Al₂O₃（MC）were prepared by equal volume impregnation method.The degradation and mineralization efficiencies of different oxidation processes on OFX simulated wastewater were investigated in batch experiments.The COD removal efficiencies of O₃/PMS,MC/PMS,MC/O₃and MC/O₃/PMS processes were 27.85%,50.60%,67.11%and 80.44%,respectively.The MC/O₃/PMS process exhibited the highest degradation efficiency as well as the apparent reaction rate constant,with a synergy factor of 1.87（（29）1）based on the reaction kinetics,which showed good synergistic effects.MC/O₃/PMS process applies to a wider p H range than MC/O₃process.The cycling tests also demonstrated the good stability of the catalyst.The inorganic anions CO₃^2-,Cl^-,and HCO^3-slightly inhibit the removal efficiency by the MC/O₃/PMS process,while humic acid and PO₄^3-produce greater inhibition.（2）The physicochemical properties of the MnO_x-CeO₂/γ-Al₂O₃catalyst were characterized,and it was found that Mnand Ceexisted mainly in the form of Mn₂O₃and CeO₂,which grew uniformly on the support surface with petal-like structures.The loading of manganese cerium composite oxide increased the Lewis acid site density(10.26μmol·g^-1)of the catalyst.Electrochemical tests and XPS results revealed that interfacial electron transfer and electron cycling between different valence metals were the main determinants of catalyst activity.The presence of O₃and PMS could increase the interfacial electron transfer rate of the catalyst and generates surface oxygen species,thus accelerating the production of reactive oxygen species.（3）MC/O₃/PMS process has the highest ozone utilization efficiency and ozonation index at any given time.It was found that HO·,SO₄·^-,O₂·^-,and ¹O₂all contributed to the degradation of OFX by EPR and reactive oxygen species scavenging experiments.The yields of HO·and SO₄·^-in MC/O₃/PMS process were 0.6345 and 0.7707 m M,respectively,obtained by the complete capture method.Fifteen degradation intermediates of OFX were detected by liquid chromatography-mass spectrometry（LC-MS/MS）and possible degradation pathways were proposed.HO·generally attacked the piperazinyl and oxazinyl by hydrogen extraction,while SO₄·^-was able to decarboxylate and defluorinate the quinolone.