Mineralization Of Cefaclor And Cefoperazone By Photoelectro-Fenton Process Using Boron-doped Diamond Anode:Performance And Mechanism

Recently,the production and application of antibiotics was developing rapidly,which played an important role in the protection of human health.Among them,effective cephalosporin antibiotics are widely used for inhibiting cell wall formation while the fourth generations had been developed.However,the extensive production and their excessive usage of antibiotics were seriously.In addition,more than 85%antibiotics often cannot be completely metabolized in the body,it was discharged via urine and feces of human and animal into water.These antibiotics often can not be degraded by the traditional methods in WWTPs,which might not only bring tremendous pressure to the ecological environment,but threaten human health.Therefore,the development of new technology for treating containing antibiotics wastewater is very urgent.As new AOPs,electrochemical advanced oxidation processes（EAOPs）have attracted more attention because they can decompose organic pollutants efficiently by hydroxyl radical（’OH）,which have been used for the treatment of nondegradable organic wastewater.Among the EAOPs,photoelectro-Fenton（PEF）is particularly useful due to its strong mineralization ability.Therefore,in this paper the PEF process was used to treat two kinds of cephalosporin antibiotics（the second generation cephalosporin,Cefaclor,CFC,the third generation cephalosporin,Cefoperazone,CFPZ）,the degradation and mineralization of CFC and CFPZ were investigated and the experimantal conditions were optimized.For achieving complete mineralization of CFC,a boron-doped diamond（BDD）electrode was used as anode,Xe or UVA lamp was chozen as UV resource in PEF process.The following four preliminary results were achieved:（1）Study the mechanism of RuO₂/Ti-PEF system:Seven EAOPs systems using RuO₂/Ti anode were established for the comparative degradation and mineralization of CFC.Basing on the experimental results,the degradation rate and mineralization was increasing with the following:AO<AO-H₂O₂<UVA-AO-H₂O₂<Xe-AO-H₂O₂<EF<UVA-PEF<Xe-PEF.RuO₂/Ti-PEF（UVA-PEF and Xe-PEF）systems can efficiently degrade and mineralize CFC.The optimum conditions of Xe-PEF and UVA-PEF system were confirmed:I = 0.36 A,pH = 3.00,[Fe²⁺]= 1.00 mM.The mineralization rate of Xe-PEF system is 77.8%,higher than 68.2%by UVA-PEF system.Four carboxylic acids were detected during CFC degradation in EAOPs process,including oxalic acid,oxamic acid,formic acid and acetic acid.Three kinds of inorganic ions were determined,including NH₄⁺,NO₃^-,Cl^-,and the content of each ions was measured.Three aromatic intermediates were identified through the UPLC-QTOF-MS/MS technology.At last a possible CFC degradation pathway was proposed.（2）Complete mineralization of CFC by BDD-PEF system:Seven EAOPs systems using BDD anode were established for efficient mineralization of CFC.The results of comparative experiments showed that the degradation rate and mineralization increased with the following:BDD-AO<BDD-AO-H₂O₂<UVA-BDD-AO-H₂O₂<Xe-BDD-AO-H₂O₂<BDD-EF<UVA-BDD-PEF<Xe-BDD-PEF.The optimum conditions of Xe-BDD-PEF and UVA-BDD-PEF system were determined:I = 0.36 A,pH = 3.00,[Fe²⁺]= 1.00 mM,85.8%and 84.2%mineralization were reached for Xe-BDD-PEF and UVA-BDD-PEF,respectively,which inidicated BDD-PEF could achieve depth mineralization of CFC.Four carboxylic acids were detected during CFC degradation,including oxalic acid,oxamic acid,formic acid and acetic acid.Four kinds of inorganic ions were determined,including NH₄⁺,NO₃^-,Cl^-,ClO3-,in which ClO3-generation was related to BDD anode.Aromatic byproducts were also identified using UPLC-QTOF-MS/MS technology.（3）Effect of anode materials on the oxidation power of EAOPs:The reaction mechanisms of EAOPs systems using BDD and RuO₂/Ti anode were studied by comparing the H₂O₂ and ’OH formation,respectively.The maximum H₂O₂ yield of RuO₂/Ti-AO-H₂O₂ and BDD-AO-H₂O₂ system were 1405.3 μM and 1646.2 μM respectively;the maximum ’OH yield of RuO₂/Ti-EF and BDD-EF system were 38.1 μM and 178.9 μM,respectively,which showed that the BDD anode is able to promote the formation of H₂O₂ and ’OH,their oxidation ability was increased accordingly.The maximum TOC removal rates of RuO₂/Ti-Xe-PEF and BDD-Xe-PEF system were 77.8%and 85.8%,respectively.Carboxylic acid formation in EAOPs systems using RuO₂/Ti anode produced less than those using BDD anode,and ClO3-ion was detected only in BDD anode systems.In conclusion,the BDD anode material enhanced the oxidation ability of EAOPs largely.（4）Effect of Fe²⁺/Fe³⁺ concentrations on CFPZ mineralization in EF and Xe-PEF:The effect of Fe²⁺/Fe³⁺ concentrations on CFPZ degradation by EF and Xe-PEF system was comparatively studied by investigate the degradation kinetics and mineralization.In the low Fe²⁺/Fe³⁺ concentration range,the degradation rate and mineralization ability of EF and Xe-PEF system were improved with the increase of Fe²⁺/Fe³⁺ concentration.The best dosage of Fe²⁺ and Fe³⁺were determined to be 1.00 mM and 0.75 mM,respectively.The maximum TOC removal rate by EF system were 65.1%(adding Fe²⁺)and 58.4%(adding Fe²⁺);The maximum TOC removal rate for Xe-PEF system were 82%(adding Fe²⁺)and 80.4%(adding Fe²⁺),which showed that adding Fe²⁺was more conducive to improve efficiency.The effect of adsorbed Fe²⁺/Fe³⁺ on ACF surface for the EF and PEF system was studied by analyzing degradation kinetics of CFPZ and TOC removal rate,indicating that adsorbed Fe²⁺/Fe³⁺ still had catalytic ability for degradation of organic pollutants by heterogeneous Fenton reactions.