Microbial fuel cells (MFC) are fuels cells that utilize microorganisms as catalysts for the production of electricity. MFCs have important potential for power generation in remote locations and to complement waste water treatment facilities with waste removal and power generation. In order to achieve these goals, power output needs to be increased as well as an understanding the effect that varying electron donors has on electricity production. In order to move the field forward, the research presented herein utilizes the gamma-proteobacteria Pseudomonas areuginosa in pure culture for electricity production. Most research for MFCs utilizing P. aeruginosa have been run using mix cultures and taking advantage of electron mediators produced by P. aeruginosa to increase power output of MFC. While this tends to improve power density for the MFC, it prevents studies that elucidate the effects of individual species.
These studies utilized P. aeruginosa as the sole biological catalyst to oxidize organic substrates and produce electrical power. A two-chamber H-style MFC constructed from polypropylene bottles and using a 1 mil Nafion® membrane was utilized for these experiments. Using this setup, several issues were investigated including the
effect of the growth substrates glucose, formate, succinate, lactose, and cellobiose on cell growth and electricity production and the effect of glucose and succinate concentration on cell growth and electricity production. It was found that P. aeruginosa is capable of oxidizing glucose and succinate to generate electricity. When using glucose as electron donor, the maximum power density was 46 mW/m2 with the current of approximately 0.35mA – 0.45mA (peak value 0.7 mA) and the electrical potential of approximately 0.05 to 0.15 V. When using succinate as electron donor, the power density was nearly 40.6 mW/m2 with current of 0.39-0.41mA and the electrical potential of approximately 0.1-0.13 V.
The most suitable substrates for growth and electricity production were glucose and succinate; which are also the important carbon sources/intermediate substrates in glycolysis/tricarboxylic acid cycle. The optimum concentration of substrates in these studies was found to be 0.7% (w/v) each of glucose or succinate in mineral salt medium. At this level, the batch MFC model can maintain the maximum power output more than three days. Higher concentrations of substrate did not increase net power and, in fact, led to a reduced power density.
Other common substrates, such as acetate and formate, which had been utilized as electron donors in many MFCs, were not suitable for MFC solely using P. aeruginosa. Not only was there no net power output, but also the bacteria could not survive and grow in medium with these substrates as the sole carbon source. These findings confirm that P. aeruginosam, and more generally other individual bacteria species, can only utilize specific substrates. This suggests the mixed cultures would be more efficient in processes such as wastewater treatment, which contains many types of electron donors at comparatively low concentrations.