Performances And Mechanisms During The Degradation Of Antibiotic Cefalexin In Water By Induced Electro-Fenton Processes

The antibiotic abuse has become a global ecological threat,causing the emergence of antibiotic-resistant bacteria（ARB）and antibiotic-resistant genes（ARGs）.Antibiotics in wastewater can pose great difficulties for current technologies once discharged into the aqueous environment.Moreover,China is one of the countries with highest amount of antibiotic production and usage,so it is of practical significance to develop new technologies for the treatment of antibiotic wastewater.In this paper,cefalexin（CLX）was used as the target pollutant.With Sn O₂-Sb₂O₅/Ti as the anode and activated carbon fiber（ACF）as the cathode,the induction electro-Fenton（IEF）process was developed for the degradation of CLX in water by introducing an induction electrode to achieve the gradual addition of Fe²⁺.The reaction mechanisms of the IEF process were investigated,including the generation of H₂O₂and^·OH,and the operating conditions of the IEF process were optimized.Finally,UVA was proven to achieve efficient CLX mineralization in the induction photoelectro-Fenton（IPEF）process.The main results are as follows:（1）The reaction mechanisms in IEF process:The high specific surface area of the ACF electrode contribute to the rapid H₂O₂generation,the highest concentration of H₂O₂was achieved at pH 3.00 and 0.36 A.The accumulation of^·OH in different systems followed the sequence of IEF>AO-H₂O₂>AO.The factors that affecting^·OH generation were compared and the maximum^·OH concentration was generated at pH7.00 and 0.36 A.It was found that the addition of induction electrode could substantially increase the^·OH production.（2）Efficient degradation of CLX by IEF process:The degradation and mineralization rates during CLX removal followed IEF>AO-H₂O₂>AO,indicating that the IEF system was able to oxidatively degrade CLX and destroy its molecular structure.The optimal conditions for the IEF system were as follows:current intensity0.36 A,initial pH 7.00,induction iron electrode area 1.92 cm²,and initial concentration200 mg/L CLX,where the process exhibited highest oxidation power.Complete CLX degradation was achieved within 90 min,which was in accordance with the quasi-first-order reaction kinetics with an apparent rate constant of 4.10×10^-2min^-1and62%TOC removal after 360 min electrolysis.（3）Complete mineralization of CLX by IPEF process:Compared with the IEF process,the IPEF process could oxidize CLX with faster degradation rate and higher mineralization degree,with 70%TOC removal after 360 min electrolysis.The TOC removal after 360 min IEF treatment could be achieved in less than 270 min IPEF electrolysis,and the overall mineralization degree was increased by 8%.By studying the degradation efficiency and mineralization rate of different processes,as well as the generation of intermediates such as ammonia and organic acids,it is shown that the IPEF system could efficiently mineralize CLX.（4）Degradation mechanism of CLX in IEF and IPEF systems:Four organic acids were generated during CLX degradation by IEF,including oxalic,formic,acetic and oxamic acids.The amount of oxalic acid increased continuously during the electrolysis,reaching a maximum value of 2.26 m M at 270 min,after which it started to decrease.The amount of total iron and Fe²⁺were accumulated during the degradation process,indicating that the IPEF system can induce the production of Fe²⁺and Fe³⁺.The UV-Vis absorption spectra and ammonia production during the degradation process showed that the characteristic absorption peaks disappeared the fastest and the ammonia production concentration was the highest during the IPEF degradation,indicating that the system had the higher oxidative ability.The pH decreases rapidly after applying current,and then stays around 3.00.