Efficiency And Mechanisms On The Removal Of Antibiotic Cefoperazone In Aqueous Solutions By Direct Vacuum Ultraviolet Photolysis

Ever since first discovered,antibiotics have been widely used in both human and veterinary medicine,most antibiotics ingested excrete directly into municipal wastewater with no further metabolism.Since traditional wastewater treatment plants usually cannot remove these antibiotics efficiently,diverse non-metabolized compounds continuously release into aquatic environment,which can not only cause the pollution of water sources,but also raise environmental problems such as bacterial resistance.Therefore,it is urgent to develop an efficient process to remove antibiotics from water source and municipal wastewater.In this paper,VUV(vacuum ultraviolet)photolysis,a novel class of chemical-less AOPs,was chosen as treatment method,and a widely usedβ-lactams,CFPZ was chosen as a target pollutant.Three light sources named VUV,VUV/UVC and UVC(Ultraviolet C)were applied,effects of UV wavelength and VUV light intensity on CFPZ degradation and mineralization,along with their mechanisms were studied at pH = 7.0 and 3.0,respectively.Besides,the effects of aeration conditions on CFPZ degradation and mineralization were also investigated under VUV irradiation,meanwhile,the reaction mechanism and possible degradation pathway of CFPZ were deeply studied.Lastly,enhanced mineralization of CFPZ by introducing Fe(II)to UVC and VUV irradiation were also studied.The results are as follows:(1)UV wavelength and VUV light intensity had significant effect on CFPZ mineralization,and higher VUV light intensity led to better CFPZ mineralization efficiency.Under neutral condition,complete CFPZ degradation were obtained within 5 min under three irradiation conditions,while their mineralization efficiencies followed the order of VUV(70.2%)>VUV/UVC(62.5%)>>UVC(29.7%).Conforming to this order,13.81 13.5 and 10.3 mg L-1 of SO42-were released,and total inorganic nitrogen(the sum of NH4+-N and NO3--N)were accumulated at 2.88,2.28,and 0.64 mg L-1,respectively.Besides,five organic acids were detected under VUV irradiation,while four organic acids were detected under VUV/UVC and UVC irradiation.Under acidic condition(pH = 3.0),CFPZ degradation were also completed within 5 min,while CFPZ mineralization efficiency,accumulation of inorganic ions and organic acids followed the order of VUV>VUV/UVC>>UVC.(2)Aeration conditions had significant influence on CFPZ mineralization,among them,O2 condition performed best.During VUV irradiation at pH = 7.0,CFPZ degradation rate showed no difference under O2,Air and N2 condition,while TOC removal rate were 70.2%,61.2%and 36.6%,respectively,meanwhile,the formation of insoluble yellow material was found under N2 condition.Besides,the release of SO42-and total inorganic nitrogen under O2,Air and N2 conditions were 13.8,14.0,1.00 mg L-1 and 2.88,2.30,0.61 mg L-1,respectively.Five organic acids were detected under O2 and Air condition,respectively,while three were detected under N2 condition.In addition,five aromatic intermediate products were detected under O2 and Air condition,respectively,and four were detected under N2 condition.Based on the above detected intermediates,a possible reaction sequence was proposed for CFPZ degradation.(3)The degradation and mineralization mechanism of CFPZ were direct photodegradation and ·OH(ROS)oxidation,respectively.As for degradation,it is easy for CFPZ to absorb photon and lead to the cleavage of molecular bonds,besides,the addition of 1,5,10 mM t-BuOH as ·OH scavenger caused insignificant decrease to CFPZ degradation rate,indicating that ’OH played insignificant role in CFPZ degradation.For CFPZ mineralization,H2O2 stabilized at 8.33 and 5.91 μM at 150 min under VUV and VUV/UVC irradiation at pH = 7.0,while H2O2 gradually accumulated and eventually stabilized at 3.79 μM under UVC irradiation.Same trend of H2O2 accumulation can be found under different irradiation conditions at pH = 3.0.On the other hand,H2O2 stabilized at 8.33,9.09,and 3.51 μM under O2,Air,and N2 condition at VUV irradiation.In summary,the correspondence between H2O2 concentration and CFPZ mineralization efficiency led to the conclusion that CFPZ mineralization mechanism was ·OH(ROS)oxidation.(4)The addition of Fe(Ⅱ)to UVC and VUV system can enhance the mineralization efficiency of CFPZ.Optimal conditions of Fe(Ⅱ)-UVC/VUV system were set up to 15 mg L-1 Fe(Ⅱ),pH = 3.0 and O2 condition after adjustments of Fe(Ⅱ)dosage,initial pH and aeration conditions.Comparing with UVC and VUV system,CFPZ mineralization efficiency increased by 26.7%and 14.7%under the optimal conditions of Fe(Ⅱ)-UVC/VUV system,respectively.Under Fe(Ⅱ)-UVC and Fe(Ⅱ)-VUV systems,SO42-were accumulated at 14.0 and 14.4 mg L-1,respectively.Besides,the generation of total inorganic nitrogen increased by 24.4%and 12.9%comparing with direct UVC and VUV photolysis systems,respectively.In addition,the concentration of organic acids increased significantly after the addition of Fe(Ⅱ)to UVC and VUV systems.