Continuous electricity generation from domestic wastewater and organic substrates in a flat plate microbial fuel cell

A microbial fuel cell (MFC) is a device that converts organic matter to electricity using microorganisms as the biocatalyst. Most MFCs contain two electrodes separated into one or two chambers that are operated as a completely mixed reactor. In this study, a flat plate MFC (FPMFC) was designed to operate as a plug flow reactor (no mixing) using a combined electrode/proton exchange membrane (PEM) system. The reactor consisted of a single channel formed between two nonconductive plates that were separated into two halves by the electrode/PEM assembly. Each electrode was placed on an opposite side of the PEM, with the anode facing the chamber containing the liquid phase and the cathode facing a chamber containing only air. Electricity generation using the FPMFC was examined by continuously feeding a solution containing wastewater, or a specific substrate, into the anode chamber. The system was initially acclimated for 1 month using domestic wastewater or wastewater enriched with a specific substrate such as acetate. Average power density using only domestic wastewater was 72 ± 1 mW/m² at a liquid flow rate of 0.39 mL/min [42% COD (chemical oxygen demand) removal, 1.1 h HRT (hydraulic retention time)]. At a longer HRT = 4.0 h, there was 79% COD removal and an average power density of 43 ± 1 mW/m². Power output was found to be a function of wastewater strength according to a Monod-type relationship, with a half-saturation constant of K_s = 461 or 719 mg COD/L Power generation was sustained at high rates with several organic substrates (all at ∼1000 mg COD/L), including glucose (212 ± 2 mW/ m²), acetate (286 ±3 mW/m²), butyrate (220 ± 1 mW/ m²), dextran (150 ±1 mW/m²), and starch (242 ± 3 mW/ m ²). These results demonstrate the versatility of power generation in a MFC with a variety of organic substrates and show that power can be generated at a high rate in a continuous flow reactor system.