Efficiency And Mechanism Of Fluoroquinolones Dedradation By Vacuum Ultraviolet Advanced Oxidation Technology

Emerging pollutants represented by antibiotics are continuously detected in the water environment all over the world.Although the concentration is low,the hazards cannot be ignored,and they are receiving more and more attention.The existing water and sewage treatment facilities were not equipped with specific treatment units at the beginning of the design,resulting in the unsatisfactory efficiency of the existing technology for antibiotic treatment.Vacuum ultraviolet advanced oxidation is a technology that uses high-energy spectroscopy to irradiate water molecules in situ to generate hydroxyl radicals(·OH)and other active species to degrade pollutants.It has the advantages of simple operation,no chemical dosage and energy saving.This technology has been reported in the middle of the last century,but in recent years the development that relies on light sources has received more and more attention,and has even been listed as the next generation of UV-based advanced oxidation technology by the European Center for Excellence in Sustainable Water Technology(Wetsus).This paper uses vacuum ultraviolet advanced oxidation technology to degrade typical fluoroquinolone antibiotics(FQs),respectively,VUV/UV direct photo-oxidation FQs,the effect of dissolved oxygen on VUV/UV photooxidation of fluoroquinolone antibiotics,and the degradation of VUV/UV/PMS systems Research on fluoroquinolone antibiotics and the above-mentioned system for degradation of fluoroquinolone antibiotics in actual water quality.Focus on the kinetics,residual antibacterial activity removal and energy consumption characteristics,and reveal the degradation path and mechanism.Under the condition of dissolved oxygen,the internal circulation flow rate is 60L/h,the initial concentration of fluoroquinolone antibiotics is 15?M and the reaction temperature is 45?,fluoroquinolone antibiotics have the highest degradation rate.The highest degradation rate constants of norfloxacin and ciprofloxacin appeared at p H=7/9±0.05 and p H=9±0.05,respectively,but the initial p H value had little effect on the degradation rate of levofloxacin.PO₄^3-and HCO₃^-enhanced the degradation of norfloxacin and ciprofloxacin due to p H buffering,and SO₄^2-,Cl^-and NO₃^-inhibited the degradation process due to the quenching effect of·OH.All anions have inhibitory effects on levofloxacin.VUV/UV photooxidation of fluoroquinolone antibiotics mainly exists in two active species:·OH and singlet oxygen(¹O₂):In the UV photolysis system,¹O₂ is the main active species,and it is effective against norfloxacin,ciprofloxacin and levofloxacin.The contribution rates were 71.98%,94.52%and 62.99%respectively;in the VUV/UV photooxidation system,the contribution rate of OH to the degradation of fluoroquinolone antibiotics was significantly increased,and the contribution rate to norfloxacin,ciprofloxacin and levofloxacin From 25.5%,3.35%and 22.94%of UV photolysis system to 60.25%,15.44%and 64.64%respectively.·OH induces defluorination of fluoroquinolone antibiotics,and at the same time induces the decarboxylation of norfloxacin and ciprofloxacin,and the demethylation of levofloxacin.The degradation pathways of the three fluoroquinolone antibiotics of VUV/UV photooxidation and UV photolysis are the same.The degradation pathways of norfloxacin and ciprofloxacin are mainly:defluorination,piperazine epoxidation and decarboxylation process;except for levofloxacin In addition to the above degradation pathways,there are also demethylation pathways.Under the same light source power,the EE/O of the VUV/UV system to degrade fluoroquinolone antibiotics was significantly lower than that of UV photolysis,especially the EE/O of levofloxacin was reduced by 77.2%.The effects of dissolved oxygen on the degradation kinetics of four fluoroquinolone antibiotics such as VUV/UV photooxidation and UV photolysis of norfloxacin,ciprofloxacin,pefloxacin and levofloxacin were studied.In the presence of dissolved oxygen,the UV photolysis of fluoroquinolone antibiotics is inhibited,but the VUV/UV photooxidation rate is faster.Further research results show that oxygen molecules inhibit the degradation of fluoroquinolone antibiotics mainly by physically quenching the third excited state.Under the condition of dissolved oxygen,the amount of·OH generated in the VUV/UV system is more,which is conducive to the destruction of the conjugated structure and the degradation of organic matter is more thorough.However,TOC testing showed that fluoroquinolone antibiotics in all systems were almost non-mineralized during the test period,and more were converted into small molecule products.The main pathways of norfloxacin are mainly divided into four:decarboxylation,piperazine ring destruction+defluorination,piperazine epoxidation and defluorination.There are three main degradation pathways of levofloxacin:defluorination pathway,demethylation pathway and piperazine epoxidation pathway.A VUV/UV/PMS advanced oxidation system was constructed,and studies on degradation of pefloxacin and levofloxacin were carried out.The VUV/UV/PMS system has a higher degradation rate of fluoroquinolone antibiotics and a lower unit energy consumption than a single PMS oxidation,UV photolysis,VUV/UV photooxidation,and UV/PMS degradation system.Antibiotic conjugate structure destruction ability is stronger.In the VUV/UV/PMS system,the degradation rate at p H=3?5±0.05 has little difference and the efficiency is higher.At p H=11±0.05,it has a higher degradation rate constant due to alkali activation,and fluoride is cultivated.Floxacin and levofloxacin reached 1.426 min^-1 and 0.351 min^-1,respectively.The two fluoroquinolone antibiotics have a higher degradation rate at an initial concentration of 7.5?M,an initial concentration of PMS of 5?M and a reaction temperature of 45?.When the light source power is 4 W,under the VUV/UV light source,·OH can promote the removal of TOC,and under the 8 W light source,the oxidant is the absolute factor of TOC removal.In the VUV/UV/PMS system,·OH,SO₄^·-and ¹O₂ are the main active species,of which·OH occupies the contribution to the degradation of levofloxacin and the contribution rate is 84.46%.VUV and PMS activate the PMS pathway through hydration electrons to form a synergistic degradation of fluoroquinolone antibiotics.VUV/UV/PMS system removes fluoroquinolone antibiotics in tap water,river water and sewage water before disinfection.The effectiveness of the system is higher than VUV/UV photooxidation and UV photolysis.The impurities in the water before sewage disinfection can activate PMS to strengthen fluoroquinolone antibiotic degradation.