Characteristic Impedance Of Microbial Fuel Cells (MFCs) And Nitrafication In A Biocathode Of The MFCs

Microbial fuel cells (MFCs) are the bio-electroreactors converting chemical energy into electrical power by using the catalysis of microorganisms. The internal resistance and capacitance in MFCs are the important factors for the start-up period and power generation performance. In this thesis, the internal resistance and capacitance in MFCs were investigated by electrochemical impedance spectroscopy (EIS) method, polarization slope method and power density peak method during the start-up period. And we discussed the interrelationship among resistance, capacitance, operating voltage and open potential. There were a lot of researches that organic substrate in wastewater was removed by MFCs. However, low nutrient removal ability by MFCs was a challenge to make this techonlogy industrialized in the future. In this thesis, the electricity production as well as nitrification by the biocathode MFCs was investigated, and ferro/manganese-oxidizing bacterias and nitrifying bacterias in the biocathodes were counted.During the start-up period of MFCs, it was found that the total resistance and activation resistance were decreased, which reflected reproduction and domestication of electricigens. Activation resistance, ohmic resistance and concentration resistance can be obtained by the polarization slope method but values weren't stable. The volumetric power peak method obtained the stable values of the MFCs'internal resistance, which was highly significant for selecting external resistance in MFCs. During the start-up period, it was signficant positive correlation between capacitance and operating voltage, as well as between capacitance and open potential. But it was negative correlation between capacitance and resistance. The change of capacitance in MFCs also reflected reproduction and domestication of electricigens during the start-up period.Ferro/manganese-oxidizing bacterias as biocathode catalyst of MFCs could get the stable electricity production as well as nitrification. The nitrification rate was 0.792 mgNO3--N/ (L·h), while the highest concentration of NO2-N was 0.770 mg/L. The concentration of NH4+-N and dissolved oxygen in the cathodic influent were important factors. The amount of Ferro/manganese-oxidizing bacterias and nitrifying bacterias were 7.5×106 MPN/mL and 9.3×105 MPN/mL in the biocathode.