| In recent years,there are more and more emerging pollutants in aquatic environment,which are difficult to be removed by the traditional biological methods.These pollutants remaining in the water have potential harm to the whole ecosystem and human health.Electrochemical advanced oxidation processes（EAOPs）have been widely valued for its high efficiency and easy operation.However,there are some problems such as low mineralization ability and instability for the degradation of refractory organic pollutant,while it is easy to generate toxic by-products when treating organic wastewater containing chloride ions.This study focused on the matching of active or inactive anodes with activated carbon fiber（ACF）cathode in electro-Fenton（EF）and photoelectro-Fenton（PEF）processes,investigating to enhance the mineralization efficiency and contral the formation of toxic by-products by synergistic coupling of the anode and cathode.Through the comparison of anode materials,optimization of the operating parameters on degradation efficiency and toxic by-products generation,and exploration of the generation of reactive oxygen species,a series of key issues were proposed to strengthen mineralization efficiency and control the generation of undesired by-products.It can provide a theoretical basis for the removal of organic pollutants in the wastewater at high salt concentration.The main research contents and conclusions are as follows:（1）Mineralization of cefoperazone in acid medium by photoelectro-Fenton using a ACF cathode coupling with a Boron-doped diamond anode:The degradation efficiency of 125 m L 50～300 mg L-1 cefoperazone（CFPZ）solution treated by anodic oxidation（AO）,EF and PEF processes was investigated by using active electrode Ru O2/Ti or inactive electrode BDD/Si as anode.Microwave electrodeless lamp（MDEL）was used as UV light source.It was found that CFPZ degradation always followed the quasi-first-order kinetics,and the degradation rate constant was in order of AO<EF<MDEL-PEF,no matter which the anode material was used.The mineralization capacity with BDD/Si anode was much better than that with Ru O2/Ti anode,and the TOC removal in BDD/Si-MDEL-PEF process could achieve 88%under the optimal operating conditions of 0.36 A,p H 3.0 and 1.0 m M Fe2+.For exploring the synergistic effects,the concentrations of H2O2 and·OH generated were analyzed quantitatively.It was found that the final H2O2 concentration in AO-H2O2 with the Ru O2/Ti or BDD/Si anode was 2.27 and 2.58 m M,respectively,while 92.0 and 263.5μM·OH were accumulated in Ru O2/Ti-EF and BDD/Si-EF,respectively.In order to study the degradation mechanism of CFPZ,the generated inorganic ions NH4+and NO3-and four organic carboxylic acids（oxalic,oxalic,formic and fumaric acids）were also measured,illustrating the mineralization efficiency with different anodes during the degradation of CFPZ.（2）Influence of anode materials on EAOPs degradation of cefoperazone in chlorine-free medium:The oxidation capacity of several inactive anodes（Sn O2-Sb2O5/Ti,Pb O2/Ti,Ti4O7/Ti and BDD/Nb）coupled with ACF cathode for the degradation of CFPZ was evaluated.The oxygen evolution potential（OEP）of BDD/Nb electrode reaches 2.54 V,which was much higher than that of other inactive anodes.The H2O2 and·OH generated were quantitatively analyzed.The degradations of 200 mg L-1CFPZ in various anode in EF process matched ACF cathode were investigated,and the degradation rate followed Ti4O7/Ti<Pb O2/Ti<Sn O2-Sb2O5/Ti<BDD/Nb.The TOC removal in EAOPs with the BDD/Nb anode were above 90%.While TOC removal in EF process with Sn O2-Sb2O5/Ti anode reached 77.9%,which was much higher than the combined mineralization capacity of AO and AO-H2O2,indicating the superior synergistic effect between Sn O2-Sb2O5/Ti anode and ACF cathode in EF system.The formations of NH4+and NO3-,as well as seven aromatic intermediates and four organic carboxylic acids were identified in the degradation of CFPZ.The main behaviors,such as hydroxylation and decarboxylation,and feasible mineralization paths of CFPZ in EF process were proposed.（3）Evaluating the effects of anode materials on degradation efficiency and the formation of toxic by-products for EAOPs in chlorine-containing medium:In the chlorine-containing medium,the degradations of CFPZ in EF process with different anode materials（Ru O2/Ti,Sn O2-Sb2O5/Ti and BDD/Nb）were comparatively studied,and the formations of toxic by-products Cl O3-and Cl O4-were also investigated.In the presence of Na Cl,the degradation of CFPZ generally increased in AO and EF systems due to the participation of active chlorine,while the chlorine-containing medium inhibited TOC removal in EF system,and the higher the Na Cl concentration in EF system,the less the CFPZ mineralization.Both the mineralization capability and toxic by-products formation increased in sequence of Ru O2/Ti<Sn O2-Sb2O5/Ti<BDD/Nb.In the initial 10 m M Cl-medium,Cl O3-and Cl O4-were generated in AO and EF systems with BDD/Nb as anode,and the Cl O4-conversion rate reached 93.0%and 89.8%after360 min electrolysis.The formation of Cl O3-and Cl O4-could be reduced effectively by using a Ru O2/Ti or Sn O2-Sb2O5/Ti anode in EF process.Nine aromatic intermediates（including 4 chlorinated derivatives）were identified by UPLC-QTOF-MS,and 11volatile intermediates（including 4 chlorinated aromatic derivatives）were detected by GC-MS.Based on the evolutions of inorganic ions and carboxylic acids,the oxidation mechanism and possible mineralization paths of CFPZ in chlorine-containing media were proposed.（4）Mechanism of chlorine transformation in EAOPs and the control of toxic by-products generation:The mechanism of the transformation of different chlorine-containing anions at the micro-interface of electrode and the formation of toxic by-products were investigated to reveal the relationship between the anode characteristics and the oxidation or reduction of oxychloride in EAOPs.It was found that only a small amount of active chlorine and Cl O3-were generated with Ru O2/Ti,Sn O2-Sb2O5/Ti and Pb O2/Ti anodes during the AO and EF treatments of 10 m M Cl-,while with BDD/Nb anode,84.2%and 72.6%Cl-was oxidized to Cl O4-,respectively.Cl O4-could not be reduced in EAOPs,confirming the high stability of Cl O4-.However,Cl O3-could be electrocatalytic reduced in AO-H2O2 and EF processes with Ru O2/Ti,Sn O2-Sb2O5/Ti and Pb O2/Ti anodes,and the Fe2+/Fe3+significantly promoted the reduction of Cl O3-.High H2O2concentration could effectively inhibit the formation of Cl O3-and Cl O4-in BDD/Nb system,which had practical application value for contraling the formations of toxic by-products in electrochemical processes. |
