Relationship Between Biofilm Structure And Electrocatalytic Activity Of Microbial Fuel Cell

Microbial fuel cell (Microbial Fuel Cells, MFCs) is a technology to use microbial as catalysts to decompose organic substrate, converting chemical energy into electrical energy. Moreover, many strains of microorganisms have electrochemical activity, which greatly broaden MFCs applications, such as wastewater treatment, electricity production and biological sensors. Therefore, The research and application toward MFCs is significant to alleviate the current shortage of resources and the environmental crisis. In this thesis, MFCs systems with anode biofilms were successfully constructed, including the dual-chamber MFCs. The method of biomass determination was established on the base of MFC systems. MFCs with Air-cathode were also explored to investigate the impact of the carbon loading MnO2 as a catalyst for the electricity production. The performance of cathode materials with different MnO2 content was compared. Finally, the mediator effect of riboflavin on Enterococcus faecalis and electricity production were explored.1 Establishment of MFCs system with anode biofilms and the method of biomass measurementAt first, this chapter examined the growth of the biofilm anode and the battery discharge situation after the successful launch of MFCs. The bacterial growth curve was measured after adjusting the experimental conditions. Meanwhile, phospholipids-P and microbial protein, as the indicator of microbial biomass, were measured and discussed, respectively. The relationship between the microbial biomass on the anodes and the current passing through the electrode was preliminarily studied. It was found that the anode without microbial inoculation inhibited lower electricity production than anodes inoculated sludge owing to the accumulating on the surface of the sludge inoculated cell anode, indicating that the formation of biofilm is necessary electricity production in MFCs system. The battery can withstand a maximum current of 6mA by using the method established for measurement of the microbial biofilms attached onto the surface of anodes with different current values. There is a linear relationship between the anode attached microbial biomass and the current value in the limiting current range, indicating that the biofilm growth could be improved by enhancing anodic current as a result of the electrocatalytic activity of biofilms was enhanced.2 The impact of the electrochemical properties of carbon load MnO2 as a catalyst for the air cathode type MFCsIn this chapter, the MFCs with air cathode were constructed directly. The cathode catalyst, carbon supported MnO2, was synthesized from active carbon and potassium permanganate under hydrothermal conditions. The MnO2 cathode materials with different content were characterized and the electrochemical performance of air-cathode MFCs was studied. The Characterization by XRD, N2 adsorption/desorption indicated that the synthesized carbon supported MnO2 materials have mesoporous structure, and properties of materials containing 8% MnO2 was the best material with the maximum aperture of 11.69 nm. The electrochemical performance test results showed that the pure activated carbon exhibits poor performance compared to the carbon supported MnO2 catalyst. Among the carbon supported MnO2 materials, the catalyst containing 8% MnO2 showed the best discharge electrochemical performance.3 Riboflavin-shuttled extracellular electron transfer from Enterococcus faecalis to electrodes in microbial fuel cells.Great attention has been focused on Gram-negative bacteria in the application of microbial fuel cells. In this study, the Gram-positive bacterium Enterococcus faecalis was employed in microbial fuel cells. Bacterial biofilms formed by E.faecalis ZER6 were investigated with respect to electricity production through the riboflavin-shuttled extracellular electron transfer. Trace riboflavin was shown to be essential for transferring electrons derived from the oxidation of glucose outside the peptidoglycan layer in the cell wall of E. faecalis biofilms formed on the surface of electrodes, in the absence of other potential electron mediators.