The Study Of Electricity Generation And Oxytetracycline Biodegradation Of Graphene Modified Bioelectrode MFC By In Situ Microbial-induced Reduction

This study prepared graphene modified biocathode microbial fuel cell?MFC?by in situ microbial-induced reduction of graphene oxide?GO?and polarity reversion,prepared dual graphene modified bioelectrode MFC by“three-step method”,and discussed the oxytetracycline?OTC?biodegradation of dual graphene modified bioelectrode MFC.The reduced graphene was characterized by morphology and structure,the electrochemical performance and bacterial community shift were analyzed,the OTC biodegradation efficiency was discussed in dual graphene modified bioelectrode MFC,and the pathway of extracellular electron transfer?EET?in graphene modified bioelectrode MFC was proposed.The main conclusions of this study were as followed:?1?The reduced graphene exhibited randomly polymerized,crumpled sheets loosely packed together,and the single layer of graphene thickness was approximately1 nm.Raman spectrum showed that D/G intensity ratio?I_D/I_G?increased to 0.91,and the enhanced disorder was beneficial for oxygen reduction reaction?ORR?.X-ray diffraction?XRD?demonstrated that the reduced graphene was no longer have the feature peaks of GO at 10.4°,and the feature peaks appeared at 26.6°and 43.5°.Fourier transform infrared?FT-IR?proved that the reduced graphene decreased the functional group of O-H and C-O.X-ray photoelectron spectroscopic?XPS?showed that C/O atomic ratio added from 2.13 to 4.45,and indicated the effects of microbial-induced reduction were similar to chemical reduction.Cyclic voltammetry?CV?curve of graphene modified biocathode recorded an obvious redox peaks at-0.50 V?vs.SCE?,and it was beneficial for ORR.The interfacial charge transfer resistance of graphene modified biocathode was 10.84?,which decreased by 79%.The maximum power density of graphene modified biocathode MFC was 65.40±3.20mW/m²,which increased by 22%.The analysis of biofilm morphology demonstrated that bacteria were of good biocompatibility with graphene,and graphene and bacteria supported each other.The mechanisms of enhanced electricity generation for graphene modified biocathode MFC were expounded from the aspects of the excellent conductivity,large specific area and good biocompatibility.?2?The bacterial community analysis of in situ microbial-induced reduction of GO and polarity reversion to prepare graphene modified biocathode MFC in phylum level were that Firmicutes occupied 48.75%in graphene modified bioanode,while Proteobacteria occupied 62.99%in graphene modified biocathode,both were dominant bacteria.The alpha diversity analysis demonstrated that graphene modified bioelectrode would decrease the abundance of bacterial community and tend to the dominant population.Typical exoelectrogens were enriched in graphene modified bioelectrode,and graphene modified biocathode formed by polarity reversion would exist a relatively anaerobic micro-ecological environment,which could make some anaerobic active bacteria survive.The ratio of typical exoelectrogens in graphene modified bioanode and biocathode were 26.66%and 17.53%,respectively.The maximum power density of graphene modified bioanode MFC and biocathode MFC were 71.60±3.80 mW/m² and 65.40±3.20 mW/m²,respectively,which increased by33.10%and 21.70%compared with control MFC.The mechanisms of enhanced electricity generation for graphene modified biocathode MFC were expounded from the aspects of the enrichment of typical exoelectrogens in graphene modified bioelectrode,and excellent electrochemical performance of the reduced graphene.?3?Dual graphene modified bioelectrode MFC was prepared by“three-step method”,and its electrochemical performance and bacterial community were discussed.CV curve of graphene modified bioanode recorded an obvious redox peaks at-0.36 V?vs.SCE?,which was OmcZ and beneficial for the long distance transport for electrons,and the response current and peak current increased significantly.CV curve of graphene modified biocathode recorded an obvious redox peaks at-0.30 V?vs.SCE?,and the peak position was advanced,which was beneficial to facilitate the ORR in cathode.The interfacial charge transfer resistance of graphene modified bioanode and biocathode were 11.60?and 14.80?respectively,which decreased by79%and 75.70%and were beneficial for the charge transport.The maximum power density of dual graphene modified bioelectrode MFC were 122.40±6.90 mW/m²,and it was 2.40 times of the control MFC,which demonstrated that dual graphene modified bioelectrode MFC could enhance the energy output significantly.The anode coulombic efficiency of dual graphene modified bioelectrode MFC was 58.10%,and it was increased by 112%,which showed high electron recovery efficiency.The biocathode analysis of different CV scan rates demonstrated that graphene modified biocathode could enhance the electron transfer rates from electrode surface to the final electron acceptor and accelerate the ORR of cathode.The bacterial community analysis of dual graphene modified bioelectrode MFC in phylum level were that Firmicutes and Proteobacteria were dominant bacteria,which occupied 70.00%and 69.20%,which demonstrated that graphene decreased the ratio of gram-negative bacteria to some extent in phylum level.The alpha diversity analysis demonstrated that graphene modified bioelectrode would increase the total number of community and community distribution in MFC.Typical exoelectrogens,including Geobacter,Pseudomonas and Ignavibacterium,were accounted for 13.02%and 8.83%in graphene modified bioanode and biocathode,which were much higher than those in control bioanode and biocathode?1.92%and 2.31%?,and this explained the reasons of enhanced MFC performance in genus level.The electrochemical performance and bacterial community analysis showed that“three-step method”for preparing dual graphene modified bioelectrode MFC was simple,effective and environmentally friendly.?4?This chapter analyzed electrochemical performance,OTC biodegradation efficiency and bacterial community in OTC-dual graphene modified bioelectrode MFC.CV curve of OTC-graphene modified bioanode?O-GM-BA?recorded an obvious redox peaks at-0.40 V?vs.SCE?,and the response current and peak current increased significantly,which showed that the electrochemical reaction rate of electrode surface was significantly improved.CV curve of OTC-graphene modified biocathode?O-GM-BC?recorded no obvious redox peaks,and the response current and peak current increased significantly,which still showed good electrochemical properties.The interfacial charge transfer resistance of O-GM-BA and O-GM-BC were 12.30?and 14.60?respectively,which decreased by 78.30%and 76.30%.The maximum power density of OTC-dual graphene modified bioelectrode MFC was 86.6±5.1 mW/m²,and it was 2.10 times of the OTC-control MFC,however,which were decreased by 29.20%and 18.10%compared with dual graphene modified bioelectrode MFC and control MFC.These demonstrated that the antibacterial properties of OTC may affect the MFC power output to some extent.The OTC biodegradation in O-GM-BE MFC showed that aerobic and anaerobic biodegradation mainly occurred in the first 2 days,and then the biodegradation rate was slower.The OTC concentration decreased from 16.10 mg/L to 0.80 mg/L,and the removal efficiency was 95.00%in eight days in O-GM-BC.The OTC concentration decreased from 12.50 mg/L to 1.00 mg/L,and the removal efficiency was 91.80%in eight days in O-GM-BA.The modification of graphene accelerated the electron transfer efficiency of bioelectrode and improved the OTC biodegradation efficiency.The OTC biodegradation was co-substrates metabolism,its biodegradation process was destroying the ring of OTC one by one,and the OTC biodegradation in aerobic condition was more thoroughly.The bacterial community analysis showed that Salmonella was dominant bacteria,and it accounted for 51.10%,Trabulsiella was accounted for 31.94%,both were important antimicrobial species in OTC condition.The most typical exoelectrogen?Geobacter?was accounted up to 5.08%,which demonstrated that Geobacter could survive in OTC condition,graphene modified bioelectrode was beneficial to enrich Geobacter,and the EET efficiency and electrochemical properties could be improved.Moheibacter,Comamonas,Ensifer,Sphingopyxis and Nitrosomonas were enriched in O-GM-BC,and they were related with OTC biodegradation.Pseudomonas,Dechloromonas,Nitrospira,Methylomicrobium and Clostridium sensu stricto were not only related with OTC biodegradation,but also related with EET process in O-GM-BC.The resistance gene analysis showed that encoding efflux pumps gene,encoding ribosome protectin gene and encoding modifying and passivating enzyme gene were all generated in long-term OTC-MFC.The resistance gene in O-GM-BA were mainly tetA,tetC,tetL,tetM,tetW,Tn916/1545 and intI 1.The resistance gene in O-GM-BC were mainly tetA,tetG,tetO and tetX.O-D-GM-BE MFC showed a high removal efficiency of OTC biodegradation and realized electricity generation synchronously.This chapter provided reference data to reduce antibiotics pollution and multiple uses of dual graphene modified bioelectrode MFC.This study provided technical support and theoretical basis for the electrochemical properties,bacterial community analysis and OTC biodegradation performance of in situ preparing graphene modified bioelectrode MFC by microbial-induced reduction.This study also provided available pathways to drive the development of bioelectrode modification by carbon materials and the biodegradation of OTC.