Utilizing anode-respiring bacteria, microbial fuel cells (MFCs) are a technology that is able to remove organic materials from waste streams and generate electricity in the process.  MFCs have been considered as an alternative to conventional wastewater treatment using activated sludge, due to potentially lower cost of operation (no pumping of oxygen) and the ability to directly control the removal of organics.

Our study is focused on designing modular and scalable MFC reactors that can be utilized in pilot-scale installations.  We tested several operational parameters and two different anode electrode configurations to study the effect on current production and chemical oxygen demand (COD) removal.  The operational parameters included running the systems in MFC-mode with a constant resistance, alternating open circuit/closed circuit operation (open circuit for 30 minutes, once a day), and applying a set voltage to the circuit.  The different anode electrode configurations included graphite-coated stainless steel bolts or carbon fiber brushes.  All of the reactors utilized the same gas diffusion oxygen reducing cathode design.  Samples were taken daily to evaluate the COD removal rates, monitor/control pH, and determine the concentration of dissolved oxygen in the reactors.  Current production was monitored in real-time and polarization measurements were executed periodically for the electrodes to evaluate the activities of the associated microbial communities at the anodes, as well as the efficiency of cathode operation.

Reactors under alternating open circuit/closed circuit operation demonstrated improved performance longevity than those held under constant resistance (MFC-mode). This may be a result of decreased biofouling on the cathode per our previous work^[1] or improving the charge storage capacity of the anode biofilms^[2]. Our preliminary results showed that lowering the applied resistance to 22Ω yielded current production up to ~15 mA and COD removal rates of 55 mg/L/day, as compared to a resistance of 560Ω, which yielded ~1mA and 21 mg/L/day, respectively.  In regards to anode material performance, our studies showed that carbon fiber brushes allowed for COD removal rates over 10 times higher than the coated stainless steel bolts, and up to an additional ~8mA of current production. Future work will include an analysis of COD removal and current production normalized by electrode surface area and electrode-associated biomass to better compare results and elucidate the system parameters that are highly correlated to improved MFC performance.