Study On The Degradation Performance Of Broad-Spectrum Antimicrobial Antibiotics By Photocatalytically Assisted Microbial Fuel Cells

The pharmaceutical industry is an important component of China’s national economy,whose output accounts for 2.7% of the national Gross Domestic Product（GDP）.Insufficient treatment of fermentated pharmaceutical wastewater has drawn increasing attention from researchers due to the complicated component and high microbial resistance to antibiotics.Especially for the abuse of antibiotics,various bacteria thrived with high tolerance to antibiotic drugs.As a result,pathogenic bacteria make their way into humans via polluted water and food chain,seriously threatening human’s survival and health.Statistically,0.7 million people died from drug-resistant infections each year.Therefore,it is of great practical significance to eliminate the biological resistance of antibiotics,antibiotic detoxification,for instance.Since it is difficult for traditional sewage treatment processes could not work effectively in antibiotics removal,alternative solutions addressing at improved degradation of antibiotics is crucial to prevent the resistance genes from being spread into the human ecology.This thesis focused on the degradable performance of two typical broad-spectrum antibacterial antibiotics（metronidazole and trimethoprim）via a constructed three-electrode photocatalytic microbial fuel cell（PMFC）system.Degradation efficiency,mineralization rate and degradation pathway between the two antibiotics were compared in MFC system.Meanwhile,difference in electron transfer efficiency of the two systems,the PMFC and MFC（set as Control group）,were indicated and analyzed.Furthermore,changes in the microbial community structure of the biological anode membrane in the two systems were monitored and compared,to provide potential microbial basis for improved efficiency of antibiotic detoxification.The specific research contents and results are as follows:（1）A three-pole chamber PMFC reaction system was constructed,with a two-pole chamber MFC as control,by a high-borosilicate glass cell with a volume of 40 m L.A photocatalytic material prepared by hydrothermal method with Ti O₂adhesion amount of 0.08 g was used as anode for the PMFC.While carbon anodes（with 3.0 cm in diameter and 3.5 cm in length）are used for the biological anode and cathode in the control system.Then,the systems started up for 5～10consecutive cycles by feeding 20 mg/L metronidazole（MNZ）and trimethoprim（TMP）as substrates and inoculating activated sludge in anaerobic pond as seed sludge.A real-time monitoring system was equipped to monitor the current changes until stable operation was achieved.As revealed,the maximum current in the MFC and PMFC reaction system reached 0.15 and 0.25 m A at the stable operation period.Besides,mor-phology observations by scanning electron microscopy revealed that rod-shaped microorganisms had adhered to the surface of the carbon fiber,indicating that the successful colonization of electroactive micro-organisms.（2）MNZ and TMP degradation efficiency in PMFC and MFC were investigated.As showed,degradation efficiency and mineralization rate of the two antibiotics in the PMFC system were significantly promoted,with almost complete removal,compared with 77%and 96%for MNZ and TMP in traditional MFC system.By analyzing the total organic carbon content of the degradation system,of the two antibiotics the MNZ rateindicated by total organic carbon content are also analyzed.It reached 48 to 60%for the PMFC system,1.3 times higher than that in the MFC system.As result of the detoxification,the toxicity of effluent biological was anticipated to decline,as revealed by the activity of E.coli.The effluent of PMFC system has lower toxicity than that of MFC effluent,with OD₆₀₀ value of 0.26,and 0.18,respectively.Finally,a certain difference between the degradation pathway of the two antibiotics in PMFC and MFC was detected by intermediates analysis via Liquid chromatography-mass spectrometer（LC-MS）.The presence of photocatalysis in the PMFC system enlarged the role of hydroxylation to convertelarge,the antibiotic to an intermediate product with more biodegradability,which is further degraded and mineralized.This was also the potential reason for the large difference in degradation efficiency and mineralization rate between the two systems.（3）Electron transfer efficiency in the MFC and PMFC systems were examined indicated by maximum current,power densities,cyclic voltammetry and impedance analysis.The maximum current and maximum power densities of the PMFC system were 1.2 times and 1.5 times higher than that of the MFC system.As revealed the maximum power densities were 11.2 and 75.1 m W/m²in MNZ and TMP treatment system by the PMFC.Cyclic voltammetry（CV）analysis showed that the initial position of the oxidation peak of the PMFC system was higher than that of the MFC,so is the peak current（with 1.2-1.4 times lower）.-0.2 V vs.SHE was in line with the cell Pigment C transfers electrons The impedance analysis showed that the charge transfer resistance of the PMFC system is half of that in the MFC,indicating faster electron transfer in the system.（4）Anode functional microbial communities of the two systems were analyzed by high-throughput sequencing technology.Relative abundance of microbial communities at the phyla,class,and genus levels were also evaluated.It was found that in the total proportion of dominant bacteria,PMFC system treated MNZ and TMP were 58.1%and 38.4%,respectively,much higher than MFC system（11.5%and 20.2%）.For example,the content of Rhodopseudomonas in the PMFC system reaches 2.21%and 7.11%respectively,which is higher than the2.04%and 5.24%of the MFC system,which is why the PMFC system has the advantage of power generation.The genus Brucella and Bradyrhizobium are the unique dominant genus in the PMFC system,the contents are（10.78%and 5.55%）and（6.64%and 6.47%）,According to the investigation and study,it is found that these two genera are directly related to the efficient degradation of nitro organic intermediates produced during the degradation process.