Microbial Fuel Cells: Determining and Improving Current Output

Given the apparent high energy efficiency of some known organisms and their wide range of acceptable 'food' molecules,
interesting possibilities for clean power generation have arisen. A number of genera (such as yeast and some types of bacteria) are capable of using
macroscopic electrodes in place of oxygen as electron acceptors. These electrodes can facilitate the use of a Microbial Fuel Cell (MFC) to generate
current. MFCs hold much promise for clean energy and waste remediation, but they do have limitations. One of these is the rate of electron transfer at
the cell membranes of the organisms being used. The other may be the effect of electron transfer on the production of ethanol as a by-product.
    In order to investigate the efficiency of electron transfer and to examine the viability of using a dye as an electron mediator, as well as
examine the effect on alcohol production, Methylene Blue (MB), was added to an electrolyte solution containing a yeast suspension. The effect on
electron transfer and alcohol production was observed through current vs time and refractive index vs time curves. Knowing the effect of electron
mediators on the mechanisms by which electron transfer occurs and alcohol production may enable different possibilities for utilization of electronic
processes within cells of the genera being tested.
    Experiments were run with baker's yeast. Using a potentiostat, potential-time and current-time data was collected across a 10 kOhm
resistor. This data was  then be used to calculate the current output of each species in its MFC. Additionally, trials were run using bakers yeast
with MB to determine the effect of this electron mediator on current generation and alcohol production.