Keiichi KUBOTA
Generation of Electricity from Organic Wastewater by Microbial Fuel Cells
Takashi YAMAGUCHI
Current wastewater treatment technology has some problem concerning the environmental load. For example, the active sludge process of aerobic wastewater treatment system requires the large consumption of electricity and the high excess sludge disposal cost. The methane fermentation process of anaerobic wastewater treatment system is energy saving technology, but this system has problem of diffusion of dissolved methane (Methane has a GWP: global warming potential of 23.) in effluent. For the solution of these problems, development of new wastewater treatment is necessary. Utilization of Microbial Fuel Cells (MFC) has attracted attention as new generation wastewater treatment. MFC is a kind of Fuel Cells using bio-catalyst, this technology generate electricity from biodegradation of organic matter. It is anticipated that excess sludge and treatment energy are less than conventional wastewater technology. Additionally, wastewater is converted efficiently into electricity. However MFC system is far-out technology on wastewater treatment. In this study, a single chamber MFC that is energy saving system of MFC was applied to the continuous operation of synthetic wastewater, in order to evaluate the efficiencies on electricity generation and on organic treatment.
As a result, during the start-up period, electrical generation performance was very low, but was increased after the 19th. After the 150 days of operation, power density was observed 0.55 W/m3, additionally coulombic efficiency (electron recovery ratio) and COD removal were observed 13% and 24%. However, over the long term operation (over 200 days), the power density and the coulombic efficiency decreased by increasing COD removal from methane fermentation. Moreover, internal resistance increased with the deterioration of proton exchange membrane. In order to improve the performance of electricity generation by the MFC, following three factors was tried: addition of an inhibitor for methanogens, increase of the anode electrode surface area and replacement of proton exchange membrane. As a result, power density was observed 0.64 W/m3, additionally coulombic efficiency (electron recovery ratio) and COD removal were observed 25% and 18%. So, power density and coulombic efficiency were increased, but COD removal was decreased by inhibition of methane fermentation. It is often reported that the performance (e.g. power generation) of an MFC changes according to the composition of wastewater. In this study, the performance of the single-chamber MFC was evaluated under the variation of wastewater composition (including addition of sulfate or electrolyte, and changes in organic composition). As a result, increase of electrolyte concentration had enhanced power density. And more, lower molecular organic matter (e.g. acetate) made better performance of the power density performance and the biodegradation, but this time observed methane fermentation of acetate was increasing.
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