(724e) Microbial Fuel Cells for Production of Biopower and Bioproducts

Background: Wastewater treatment operations use nearly 4% of USA’s electrical load, enough to power 9.6 million households per year. Interestingly, wastewater streams can contain 10 times the energy required for treatment. In recent years, the microbial fuel cell (MFC) has emerged as a promising bioelectrochemical system to take advantage of this phenomenon by employing the technology of a battery. Organic wastewater is the electrolyte, and added microbes trigger the chemical reactions that convert organic waste into electricity while treating the wastewater. The ideal two-chamber configuration consists of an anode (anaerobic chamber) and cathode (aerobic chamber) separated by a proton exchange membrane (PEM). Anaerobic microbes are introduced into the anode to oxidize the substrate, generating protons and electrons. The protons pass through the PEM, while the electrons pass through an external circuit to generate current. Biogas is also produced from the anode which could contain CO₂, CH₄, and H₂. These can be converted to useful compounds or captured for use as fuel. Lipid production on the cathode is also a possible bioproduct of MFCs. The lipids could be utilized for various applications such as fuel and lubricant.

Methods/Objectives: Performance of MFCs is heavily dependent upon the configuration of the electrode, the medium for external electron transfer. The main focus of this research is determining how performance is impacted by modifying the electrode configuration in a two-chamber MFC. Modifications of the electrodes involve adding granular activated carbon (GAC) to increase the electrodes’ surface area. The effect of the electrode modification on bioelectricity output, lipid production, useful biogas emissions, and wastewater treatment effectiveness was determined. Glucose was used as the contaminant-representative in the synthetic wastewater. Liquid samples were periodically taken during the performance of the experiments to determine the concentration of residual contaminants.

Results: The results of the study showed that electrode modifications significantly affect biopower, biogas, and lipid production. The treatment effectiveness was also affected as indicated by residual glucose and organic acids remaining in both chambers. In the initial stages of the experimental runs, MFC with electrodes of equal surface areas (unmodified and modified) showed the highest biopower production. However, towards the end of the 14-day run, the MFC with GAC-modified cathode resulted in higher voltage output. Anaerobic chamber with GAC-modified electrode tend to have lower treatment effectiveness than those with unmodified electrodes as indicated by higher residual glucose and remaining organic acids after the 14-day experiment. For all the experimental runs, most of the gases from anaerobic chamber were produced during the first 5 days of fermentation, after which production ceased (except for CO₂) indicating microbial viability for the duration of the runs. The biomass concentration in the aerobic chamber were lowest for GAC-modified cathodes. In terms of lipid productivity, the lowest concentrations of lipids were also observed in GAC-modified cathodes.

Conclusions: Simultaneous biopower and bioproduct production from MFC can be accomplished using a two-chamber configuration. The modifications of the MFC electrodes using GAC suggest the process can be used to tailor specifically to biopower, lipids or treatment effectiveness. MFCs with unequal electrode surface areas show excellent biopower production, but choosing which chamber to modify ultimately depends on other desired bioproducts and run time. GAC-modified cathodes effectively treat wastewater in seven days with an ending lipid concentration of 1.7 g/L. In contrast, GAC-modified anodes do not quite fully treat wastewater after 14 days, but should have more sustained power production as a result.