Preliminary investigation of generating electricity from wastewater via a single-compartment microbial fuel cell

Energy-efficient and low temperature water treatment is desirable for long-term space missions. A Microbial Fuel Cell (MFC) is a hybrid between a fuel cell and a biological reactor that has a potential to make water treatment an energy-generating (not consuming) process. Microorganisms in a MFC biodegrade contaminants and exchange electrons with the fuel cell electrodes, generating electricity at ambient temperature. To test the feasibility of MFC as an energy-generating and water treatment process, we constructed a single-compartment MFC to generate electricity from acetate. Three MFC electrodes were connected to a potentiostat as follows: the working electrode was a graphite rod with 0.312 OD connected to a wire using silver epoxy; the reference electrode was a standard silver-silver chloride reference electrode; and the auxiliary electrode was a membrane electrode assembly consisting of Nafion-117 and VUIcan XC-72 with standard platinum loading of 0.5 mg/cm ² . The reactor was inoculated with anaerobic digester sludge in a batch mode with the working electrode poised at +0.40 mV against the standard hydrogen electrode and with 120 mg COD/L of acetate. After 60 days, we obtained a stable current of about 1.06 mA with a current density of approximately 600 mA/cm ² . A potential-step experiment showed that the current depended on the working electrode potential in a manner similar to how the Monod equation describes saturation for a dissolved electron acceptor.