Discharge Characteristics Of Microbial Fuel Cells

Industrial development and human population explosion have become serious threatens to the resources and environment of the earth. Utilizing resource economically and developing ways for waste reuse are effective ways to solve resource shortage. Biofuel cells can utilize organic compounds in wastewater as fuel to generate electricity thus the wastewater can be reused. It is interesting that using biofuel cells to treat wastewater can enhance the efficiency of wastewater treatment and generate less biomass remarkably compared with conventionality wastewater biotreatment. In this thesis, the author committed himself to improve the current and power output of a biofuel cell. By analyzing the discharge properties and the polarization characteristics of electrodes, the bottleneck of biofuel. cell was checked. The experiment results are listed below.1. The maximum current output of biofuel cell would reach a bottleneck when the amount of bacteria and fuel in anode compartment increased. The maximum current output was not affected in spite of that the stirring parameters of biofuel cell was altered. The biofuel cell runs at best conditions when the temperature was controlled between 30-35 °C. The temperature either lower or higher than that was harmful to it. Current output boosted largely when electron transfer mediator was used. The performance of fat-solubility mediator was higher than that of water-solubility mediator, and inorganic compound better than organic compound. The current output mediated by ferricyanide was much greater than that mediated by organic compound such as thionine. Operational parameters must be optimized in order to increase the power output.2. By determining the discharge curve of a biofuel cell and polarization curve of electrodes, we pointed out that the amount of electron transferred to anode was the main bottleneck of a biofuel cell. Low kinetic parameters of electron transfer between bacteria and electrode was caused by the shortage of electron available on anode surface and 90% of biofuel cell voltage decline was attributed to anode polarization. The experiment results demonstrated that increase the biomass on anode surface remarkably enhanced quality and efficiency of electron transfer to anode. The maximum power and current outputs were 173.7 mW m-2 (anode surface area) and 1296 mA m-2 (anode surface area) respectively.3. We also discovered that ferricyanide anion used as oxidizing reagent in cathode compartment can permeate through the cation exchange membrane and the ferricyanide could be served as effective redox mediator in anode compartment of a biofuel cell. When there existed a 200 mM ferricyanide concentration difference across the 0.24 mm thick perfluorosulfonic acid membrane, a 5 mM cm'2 (membrane surface area) permeation could be observed at 6 hours. For ferricyanide in anode compartment would cause serious problem both experimental and applied, pervasion of ferricyanide must be avoided.4. We prepared polymer-modified anode by electropolymerization of methylene blue on graphite anode. Increased current output of 5-folders was obtained with modified anode, which demonstrating that using modified electrode was an effective way to overcome the disadvantage of using dissolved redox mediator. The stability of the polymer modified on electrode surface was well according to our research.The effect of operational parameters to the power output of a biofuel cell was partially tested in this thesis. The bottleneck of the biofuel cell was pointed out and suggestions to improve the performance of biofuel cells were given. Work presented in this thesis would certainly promote the development of biofuel cells.