Regulation And Construction Of High Oxygen-Tolerant Bioanode For The Improving Performance Of Compact-Electrode Microbial Fuel Cells

The compact-electrode MFC is considered to be the ideal configuration,since the close separation distance between anode and cathode help to minimize internal resistance of the reactor and increase power generation.However,oxygen(diffused from the cathode)concentration around the anode increased as electrodes distance reduced,which would inhibit the performance of anode and result in“oxygen contamination”.Thus,development of oxygen-tolerant bioanode is required to the CEA-MFCs.In this paper,the influence of oxygen on the process of anode biofilm formation was explored.Through the directional regulation of anode biofilm formation,high performance oxygen-tolerant anode biofilm was constructed and used for improving the performance of CEA-MFCs.Firstly,single-walled carbon nanohorns(SWCNHs)modification and inoculum type were chosed to improve the electrochemical performance of bioanode.SWCNHs modification significantly reduced the anode resistance and improved the anode electricity generation.Compared with stainless steel anode,activated carbon or carbon nanotubes modified anode,the power generation of SWCNHs modified anode increased by 354%,34%and 25%,respectively.Using anode inoculum scraped from the anode biofilm in the single-chamber air-cathode MFCs increased the electricity generation of bioanode by 87%and reduced anode resistance by 26%compared with the bioanode enriched from cathode inoculum scraped from the cathode biofilm.Although the bioanode enriched from cathode inoculum had a high proportion of facultative microorganisms,oxygen still greatly reduced the anode performance.To construct oxygen-tolerant bioanode,the influence of oxygen on the anode biofilm formation,structure and electricity generation was investigated.The aerobic biofilms exhibited a multilayered sandwich structure with a sparse gap between the aerobe and amphimicrobe enriched outer layer and dense exoelectrogens enriched inner layer,whereas the anaerobic biofilm consisted of only a single dense layer dominated by Geobacter.Our results showed that the inner layer of aerobic anode biofilms performed electricity generation,while the outer layer only consumed oxygen.In this case,electron donor diffusion through the outer layer became the limiting factor in electricity generation by the bioanode.Consequently,as the anode biofilms matured,current generation decreased.Therefore,it would be necessary to regulate the growth of anode biofilm to form an efficient oxygen-resistant layer to improve the electrochemistry performance of oxygen-tolerant bioanode.To regulate the growth and formation of anodic biofilm,two regulation methods,which were shear stress raised from fluid flow and external resistance,were proposed.With the increase of shear stress and the reduce of external resistance,the anode resistance decreased,the current generation,biomass and biofilm viability increased.Anode biofilms enriched with high shear stress and small external resistance were compact and flat,while Anode biofilms enriched with low shear stress and large external resistance were porous.The difference in biofilm structure might affect the diffusion of oxygen into the biofilm.The oxygen tolerance of the anodic biofilm enriched with different shear stress and external circuit resistance was investigated.When the anode chamber was burbled with 20 mL/min air,the anode biofilms enriched with high shear stress and small external resistance could generate electricity normally,the internal of anode biofilms remained anaerobic.While the anode biofilms enriched with low shear stress and large external resistance could hardly work,the internal of anode biofilms were aerobic.Simulation of oxygen diffusion into the anode biofilm showed that the structure of the anode biofilm significantly affected the oxygen-tolerent ability of anode biofilm.Statistics showed that the porosity of the anode biofilm was positively correlated with the voltage loss ratio of the bioanode during aeration,indicating that the compact structure of the anode biofilm was the key to the construction of oxygen-tolerant bioanode.CEA-MFCs were constructed using high-performance oxygen-resistant anode biofilm enriched with high shear stress and low external resistance,obtaining a maximum power density of 4300 mW/m~2.The CEA-MFC showed high stability during long-term operation.The result is useful for develop high performance CEA-MFCs.