Microbial Fuel Cells: Effect of Electron Mediation on Alcohol Production in Baker's & White Wine Yeast

Given the 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), were 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 have been run with baker’s and white wine yeast.  Using a potentiostat, potential-time and current-time data was collected across a 10kµÙ resistor.  This data was then used to calculate the current output of each species in its MFC.  Trials were run using baker’s yeast, and white wine yeast while changing mediators and solutions in order to determine the effect of the electron mediator on current generation and alcohol production.  It was determined that the optimal current and alcohol production was observed with wine yeast.  Graphite rods are being tested as electrode materials and the current production is being compared to carbon felt electrodes.