Study On Efficacy And Mechanism Of Biocathode Degradation Of Tetracycline In Microbial Fuel Cells

Tetracycline is a kind of commonly used antibiotic for medical and veterinary use.Tetracycline in water environment can destroy the ecological environment,induce the generation of resistance genes and endanger human health.Due to the stress of tetracycline residues on microorganisms in water,it is difficult to realize the efficient removal of tetracycline in wastewater treatment system at present.Therefore,it is urgent to seek efficient and environment-friendly tetracycline degradation technology.Microbial fuel cell technology（MFC）is a system that generates electricity to drive and enrich and degrade functional bacteria,so it can co-metabolize difficult-degradable organic matter and generate electricity.Studies have found that MFC has a good degradation effect on tetracycline.However,the conventional MFC bioanode degradation of tetracycline has some disadvantages,such as slow start-up,slow degradation rate and need of additional catalyst.However,the conventional MFC bioanode degradation of tetracycline has some disadvantages,such as slow start-up,slow degradation rate and need of additional catalyst.It is concluded that the degradation of pollutants by biological cathode has the advantages of high degradation efficiency,fast degradation rate and non-toxicity of the products.Therefore,this paper intends to start MFC biocathode through gradient acclimation,and construct the research system of MFC biocathode degradation of tetracycline.CV,impedance,output voltage and power density were used to characterize the effects of tetracycline concentration on the electrical performance of MFC.Through single factor experiment,the influence of major factors on the degradation of tetracycline by MFC biocathode was explored,the suitable conditions and effects of the degradation of tetracycline by MFC biocathode were determined,the optimal regulation strategy was proposed,and the kinetic model of the degradation reaction was fitted.High throughput sequencing technology was used to obtain the information of the main functional bacteria on the MFC biological cathode.The degradation intermediates were determined by LC-MS.According to the degradation intermediates of tetracycline,the degradation pathway of tetracycline by MFC biocathode was speculated.Combined with the results of high throughput sequencing of cathode biofilm,the mechanism of tetracycline degradation by MFC biocathode was discussed.In addition,the E.coli growth inhibition test was used to assess the toxicity of degradation intermediates,real-time fluorescence PCR was used to determine the abundance of resistance genes,and the ecological risk of MFC biocathode degradation tetracycline degradation system was evaluated.The main results and conclusions are as follows:（1）Tetracycline concentration has an important effect on the electrical performance of the biological cathode MFC,and the concentration range of 2～10 mg/L tetracycline can promote the improvement of the electrical performance of the biological cathode MFC.When the concentration of tetracycline was 10 mg/L,the bicathode MFC had the best electrical performance,and the corresponding bicathode MFC had the maximum output voltage of 0.34V,the maximum power density of 230 m W/m³,and the Rct value of bicathode was12Ω.Tetracycline can change the membrane permeability of electricity-producing microorganisms so as to be more favorable for cathodic ORR reaction and improve the electrochemical activity of biological cathode,but the concentration of tetracycline above 20mg/L will inhibit the activity of electricity-producing microorganisms or even kill them,resulting in the degradation of electrochemical performance of biological cathode.（2）The main influencing factors of tetracycline degradation by MFC biocathode include initial tetracycline concentration,carbon source type,carbon source concentration,external resistance,aeration intensity,etc.The suitable conditions which initial concentration of tetracycline 5-20 mg/L,carbon source of sodium acetate 0.2-0.7 g/L,external resistance100-200Ω,aeration strength 12-18 L/h.Under the suitable conditions,the degradation rate of tetracycline can reach more than 90%.Compared with the aerobic biodegradation of tetracycline and the bioanode degradation of MFC were significantly improved.The degradation kinetics of tetracycline by MFC biocathode was in accordance with pseudo-first order kinetic model.Under suitable conditions,the kinetic constant K of tetracycline degradation was in the range of 0.060～0.070 h^-1.（3）Five main degradation intermediates were identified,two degradation paths of tetracycline deaminated,denitrodimethyl and dedimethyl were deduced based on the degradation intermediates.During the degradation process,the inhibition rate of escherichia coli in the system was reduced by 60.9%compared with that in raw water after 36 h reaction,indicating that the ecotoxicity of tetracycline was greatly weakened.Five tetracycline resistance genes were detected in inoculated sludge,MFC biocathode and microbial aerobic degradation antibiotic samples.In the process of degradation of tetracycline by MFC biocathode,the concentration of tet O basically remained at 10¹.Tet A,tet C,tet M and tet X were enriched in the MFC biocathode,and their concentrations increased to 3.4×10³,8.8×10²,8.1×10²and 6.2×10³Copi/μL,respectively.Compared with the microbial aerobic degradation tetracycline samples,the concentrations of tetracycline resistance genes were 1.6×10⁶,5.1×10⁵,9.4×10⁵and 1.0×10⁶Copi/μL,respectively,which were much higher than that of MFC biocathode.MFC biocathode degradation of tetracycline is an ecological friendly degradation method.（4）A large number of electricity-producing bacteria and tetracyclin-degrading bacteria were enriched in the biocathode,and the main electricity-producing bacteria were Acetobacter and Rhodopseudomonas,whose relative abundance was 15.06%and 7.84%,respectively.The main tetracycline degrading bacteria were Clostridium,Hyphomicrobium,Stenotrophomonas and Mycobacterium,with relative abundance of 12.05%,7.84%,4.47%and 3.64%,respectively.At low current,MFC biocathode can enrich functional bacteria producing electricity and functional bacteria degrading tetracycline.Microbial degradation is the main role of MFC biocathode in tetracycline degradation,while other functions including hydrolysis,adsorption,electrochemical oxidation and other processes have little effect on tetracycline degradation.This study provides a theoretical basis for the research and development of the treatment of tetracycline containing wastewater by MFC biological cathode.