Degradation Mechanism And Application Of Antibiotic Wastewater Based On High-efficiency Electrochemical Technology

As a new type of organic pollutant,sulfonamides lead to serious pollutions to water environment and human beings.Electrochemical oxidation has the characteristics of simple and efficient degradation of antibiotic wastewater and have been applied to the treatment of antibiotic wastewater.Among many electrode materials,Boron-doped diamond(BDD)electrodes are widely used because of their wide electrochemical window,low background current,strong corrosion resistance and stable chemical properties.The electric Fenton system constructed by adding iron and carbon composites to the traditional BDD anode carbon felt(CF)cathode electrochemical system,which can remove antibiotic organic pollutants more efficiently without increasing the external energy consumption,making the system more practical application prospects.In the present study,electrochemical oxidation of sulfamethoxazole(SMX)with BDD anode and Stainless Steel(SS)cathode was investigated systematically.The effects of current density,initial pH,supporting electrolyte and natural organic matter on SMX degradation were explored.Under the conditions of current density 30 mA·cm-2,0.1 M Na2SO4 used as supporting electrolyte,pH of 7 and without natural organic matter affect,SMX was completely removed after 3 h electrolysis.COD removal efficiency,current efficiency and energy consumption were 65.6%,40.1%,72 kwh·kg COD-1,respectively.Degradation mechanism was analyzed based on the active sites of SMX identified by density functional theory(DFT)calculation and intermediates analysis by HPLC-Q-TOF-MS/MS.Three possible degradation pathways were proposed,with the replacement of-NH2 at aromatic ring by-OH,the oxidation of-NH2 to-NO2 and the addition of-OH on isoxazole ring observed.The active sites detected in reaction matched the DFT calculation results exactly.The toxicity of intermediates produced during electrolysis process was evaluated by Escherichia coli experiment.Results showed that,after 2 h electrolysis,the inhibition ratio was decreased from the initial value of 22.8%to 10%,which has already achieved the safety boundary.After 4 h electrolysis,the toxicity was almost zero even with still 60%COD remained in the solution.This phenomenon demonstrated that the toxicity of SMX and its intermediate products was reduced significantly during electrolysis process.The iron-carbon composite was prepared by soaking and sintering process.Sulfamethazine(SMT)wastewater was degraded by BDD-CF systems to explore its mechanism.Compared with the system without iron-carbon composites,SMT removal efficiency of iron-carbon composites was improved,the kinetic constant kSMT of 0.2 g FeSO4@C dosage was 0.015 min-1,much higher than that of 0.006.SMT was completed removed within 6 h when the dosage was 0.2 g FeSO4@C.SEM and XRD spectra showed that FeSO4 particles were successfully loaded onto the activated carbon surface,and distributed uniformly on the surface of activated carbon without clusters and promotes the reaction.The concentration of total irons and divalent ions in the solution increased gradually to a stable trend during degradation,and the total irons in the solution mainly existed in the form of divalent iron ions.Degradation mechanism was analyzed based on the active sites of SMX identified by DFT calculation and intermediates analysis by HPLC-Q-TOF-MS/MS.Two possible degradation pathways were proposed,the gradual oxidation of aniline,the cleavage of sulfanilamide bond and the oxidation of pyrimidine ring.