Effect of Initial Carbon Sources on the Performance of a Microbial Fuel Cell Containing Environmental Microorganism Micrococcus luteus

Abstract

A microbial fuel cell (MFC) is a device that uses microorganisms as a catalyst for the direct conversion from chemical energy to electrical energy without internal combustion steps. Environmental friendliness and high efficiency have projected an MFC as one of the promising and alternative future energy sources. The fact that there is a large selection of microorganisms and substrates offers additional advantages over conventional fuel cells in that various types of MFCs could be devised, meeting the specific environmental requirements. There are reports that direct energy production is possible even from marine sediments using geobacters. In an MFC, electrons are initially trapped as a form of reduced intermediates following the degradation of substrate and transferred to the anode. Microorganisms as well as redox mediators thus constitute an essential part of the microbial fuel cell, in that a large improvement in a fuel cell operation could be achieved by selecting suitable catalytic bacteria. It is notable that mediator-less MFCs have been developed using Shewanella putrefaciens in which cytochromes located in the outer membrane are responsible for the direct electron transfer to the anode. Also notable is the MFC that utilizes even light energy by Anabaena variabilis or Synechococcus sp. It is our ongoing effort to develop a high performance MFC in which a maximum utilization of substrates and high power density can be achieved. In the previous research, we have shown that the MFC performance quite depends on the various operating factors such as temperature, choice of mediators, concentration of substrates and mediators, and environmental shock. Also found was that carbon sources crucially affected performance. This paper describes the preliminary study of the microbial fuel cells using Micrococcus luteus, a typical environmental microorganism, which is found in soil, dust, water, and air. It is known to tolerate high salt concentration. This halophilic nature can make this bacterium a promising candidate for a MFC. We have carried out a systematic study of the effect of initial culture conditions on the MFC performance using a variety of carbohydrates as an initial substrate and a fuel to see whether this bacterium could be used as an effective biocatalyst in MFCs. Although the fuel cell efficiency was not as high as when more common bacteria such as Proteus vulgaris and Escherichia coli were used, the results showed Micrococcus luteus is a promising environmental microorganisms from which a MFC could be constructed.