A microbial fuel cell (MFC) is a device that utilizes bacteria to oxidize organic and inorganic matter, and through the process of extracellular electron transfer, generate electricity. When the electron transfer at the bacteria-electrode interface is rapid, the efficiency of a MFC is dependent on the flow distribution and mass transport in the anode, which controls the delivery of reactants and removal of waste products. It has been predicted that diffusion of soluble substrates is fast over the length scale of bacterium, but gets significantly slower over millimeter-scale distances and at the scale of centimeters, advection is required. Electrolyte advection along with optimal flow distribution will bring substrates to anode respiring bacteria and enable substrate utilization at high rates. Therefore, in this study we explored the influence of the anode configuration on flow distribution and MFC performance. The efficiency of the system was determined on the basis of chemical oxygen demand (COD) removal and Columbic Efficiency (CE). 

The MFC used for these studies was a membrane based tubular MFC with a submerged oxygen-reducing cathode. Three anode configurations were explored and included: 1) packed graphite granules (MFC 1); 2) bundles of stacked graphite granules (MFC 2); and 3) a small polypropylene mesh cylinder filled with packed graphite granules, wrapped with pleated carbon cloth (MFC 3). The volume of the anode compartment of each reactor was 1L. The reactors were operated under MFC, semi-batch mode with a downstream flow. The reactors were first inoculated with swine waste and lagoon sediment and subsequently fed with swine waste only 1,300 mg-COD/L.

Key parameters were measured on a weekly basis including COD, pH, dissolved oxygen (DO) and turbidity. Samples for 16S rRNA analysis were also collected on a weekly basis from the effluents of each reactor for the classification and identification of bacterial species present. Voltage data was recorded continuously and polarization curves and cyclic voltammetry were periodically performed to monitor biofilm development and MFCs operation.

The preliminary results indicate that due to the advanced flow distribution, MFC 3 demonstrated the highest performance. It showed a startup time of approximately 4 days and achieved a voltage of 0.40 V. MFC 2 also had a startup time of approximately 4 days and achieved a voltage of 0.15 V. MFC 1 had the slowest startup time of about 11 days with a voltage of ≈ 0.10 V. All MFCs were operated under 560 Ω resistors. Future work will include a comprehensive analysis of microbial dynamics and system performance to determine which anode structure was most correlated to improved wastewater treatment and energy recovery activities.