Study On The Electrogenic Performance Of Microbial Fuel Cell Based On Anaerobic Oxidation Of Methane

Methane is an important greenhouse gas that is second only to carbon dioxide.Anaerobic oxidation of methane（AOM）,as one of the most widespread pathways for environmental methane removal,plays an important role in global carbon cycle.Methane is also an important energy source.Microbial fuel cells（MFC）are devices that convert chemical energy of substrates into electrical energy.Up to now,MFCs mainly uses organic compounds in the solutions as the substrates to generate electricity,while the researches on MFCs the gas substrates are still very scarce.Recent studies have shown that AOM microorganisms can release electrons for MFC power generation by consuming methane.The emergence of methane-powered MFC（mMFC）may have a dual role in alleviating both the greenhouse effect of methane and energy crisis.However,since pure AOM microorganisms are not isolated,the electricity generation mechanism of mMFC is still unclear.Meanwhile,the problems of low solubility and bioavailability of methane and low electrogenic properties of mMFC remain to be resolved.In this study,we used AOM microorganisms as the research object,and explored their electrogenic abilities in bioelectrochemical systems（BESs）and mMFCs.By analyzing electrochemical activity,gas composition changes,intermediates,major functional bacteria,electrogenic performance and influencing factors,the following conclusions are obtained:1.The electroactive AOM microorganisms were enriched from anaerobic sludge and showed high activities of methane oxidation and electrical property after acclimation.During the long-term operation,the maximum voltage output reached above 0.6 V,and the maximum current density and power density were 1130.2 mA/m² and 703.89 mW/m²,respectively.2.Microbial community structure analysis showed that the dominant functional microorganisms were Methanobacterium and Geobacter.The main electrogenesis mechanism may be microbial syntrophic interaction mediated by interspecific electron transfer,namely the archaea（e.g.Methanobacterium）first oxidized methane into an intermediate,such as acetate.The electroactive bacteria oxidized intermediates further to CO₂and transferred electrons to the electrodes.3.The operating conditions affected greatly the electrogenic performance of mMFC:1)the gas diffusion cloth/carbon cloth composite（GDC）electrode showed the best electrogenic activities（1251.3 mA/m²）,which were 36 and 390 times that of hollow fiber film/graphene electrode（34.8mA/m²）and carbon cloth electrode（3.21 mA/m²）,respectively.2)The electrode potentials affected the biocurrent,which was the highest at a constant potential of 0.1V（vs.SHE）than at-0.1,0.3 and 0.5 V.3)The larger the anode area was,the faster mMFCs started up and the higher the current density was.4)The output voltage of mMFC at pH 7 was greatest than those at pH 5,6,8 or 9.Thus,the optimal pH of mMFC was 7.5)When the cathodic electron acceptor was dissolved oxygen（DO）,the electrogenic performance（703.9 mW/m²）was better than those of potassium ferricyanide（457.2）,potassium permanganate（20.7）and air cathode（124.2）.6)Connecting 2,3 or 4 of DO cathode mMFC in series or in parallel could enhance the output voltages.Among them,the output voltage of 3 mMFCs in series was the highest（0.97 V）,and the output voltage of 4 mMFCs in parallel（0.67 V）was higher than those of other parallel mMFCs.In summary,this study has demonstrated the strong electrogenic performance of mMFC,and revealed the electrogenesis mechanism of interspecies electron transfer between archaea and electroactive bacteria.The optimal electrogenic performance could be achieved when the electrode material,electrode potential,anodic pH,and the electron acceptor were GDC,0.1 V,7 and DO,respectively.These results provide a theoretical basis and a new perspective for understanding microscopic process of mMFC and developing mMFC technology.