Characteristics And Mechanism Of Heterogeneous Catalytic Ozonation For The Degradation Of Ofloxacin In Water

Antibiotic water pollution has become more and more serious,which will endanger the health of animals and plants,even human.Conventional wastewater treatment technologies connot degrade organics in wastewater efficiently.Thus,development of advanced oxidation technologies to treat organic wastewater,has become the research focus.In the present study,catalytic ozonation has been used to treat simulated ofloxacin wastewater.The main contents of this study are as follows:preparation and selection of catalysts,analysis and optimization of system operation parameters,analysis of degradation kinetics and mechanism of ofloxacin,pilot-scale study of pharmaceutical wastewater and textile wastewater.MnOx-CeOx/?-Al2O3 catalyst was prepared by loading MnOx and CeOx on the surface and pore of alumina support.Based on the removal efficiency of ofloxacin in wastewater,the optimum catalyst preparation parameters were determined as follows:the loading amount was 1.0 wt%with the ratio of Mn and Ce by 2:3,the sintering temperature was 600? and the impregnation solution pH was 2.0.SEM,XRD,XPS and BET results showed that the actie component in the catalyst was MnO2,Mn2O3,CeO2 and Ce2O3.The specific surface area of catalyst is 203.0 m2·g-1 and the average aperture is 7.16 nm.Simulated ofloxacin wastewater was treated by heterogeneous catalytic ozonation technology,combined with the prepared MnOx-CeOx/?-Al2O3 catalyst.The optimal operating parameters of the system are as follows:the ozone dosage was 300 mg·L-1,the water matrix pH was 2.0,the contact time was 15 min and the gas-liquid ratio was 20.4,respectively.Continuous experiments under the above conditions results showed that the removal efficiency of COD,ofloxacin and the ozone utilization efficiency were 76.6%,98.2%,and 91.39%,respectively.CO32-,PO43-,NH4+ will inhibit the reaction,while SO42-,Mg2+,Ca2+ have no effect on the reation.The results of continuous experiments showed that the active component content of catalyst remained stable after long-term application.In the study of the kinetics and mechanism of ofloxacin degradation,the data of the experiment were analyzed.The results showed that the degradation of ofloxacin in the simulated wastewater was in accordance with the pseudo-first-order kinetic model,and the apparent reaction rate constant was 15.216×10-2 min-1.The ofloxacin degradation process was mainly composed of ring-opening of benzene ring,carbon addition of double-bond and chain-breaking of aliphatic compound.4-hydroxy-4-methyl-dipentanone was the main conpound in final oxidation products,with the concentration of 28.8 mg·L-1.Tert-butyl alcohol can inhibit the degradation of the ofloxacin,but connot completely inhibit.It is suggested that the degradation of ofloxacin is the result of direct oxidation with ozone and indirect oxidation with hydroxyl radical.Heterogeneous catalytic ozonation technology was used to treat actual pharmaceutical wastewater.With the ozone dosage was 350 mg·L-1,the effluent COD was reduced from 125 mg·L-1 to less than 10 mg·L-1,and ofloxacin was no longer retained in the wastewater.In the pilot-scale study of textile wastewater,under the optimal operating parameters with the ozone dosage of 100 mg·L-1 and the contact time of 15.7 min,the average COD was reduced from 414 mg·L-1 to 287 mg·L-1,and the chromaticity was reduced from 4033 times to 27 times and remained stable.