Increased power generation in a continuous flow MFC with advective flow through the porous anode and reduced electrode spacing

The maximum power generated in a single-chamber air-cathode microbial fuel cell (MFC) has previously been shown to increase when the spacing between the electrodes is decreased from 4 to 2 cm. However, the maximum power from a MFC with glucose (500 mg/L) decreased from 811 mW/ m(2) (R-ex = 200 Omega, Coulombic efficiency of CE = 28%) to 423 mW/m(2) (Rex = 500 Omega, CE = 18%) when the electrode spacing was decreased from 2 to 1 cm (batch mode operation, power normalized by cathode projected area). This decrease in power was unexpected as the internal resistance decreased from 35 Omega (2-cm spacing) to 16 Omega (1-cm spacing). However, providing advective flow through the porous anode toward the cathode substantially increased power, resulting in the highest maximum power densities yet achieved in an air-cathode system using glucose or domestic wastewater as substrates. For glucose, with a 1-cm electrode spacing and flow through the anode with continuous flow operation of the MFC, the maximum power increased to 1540 mW/m(2) (51 W/m(3)) and the CE increased to 60%. Using domestic wastewater (255 +/- 10 mg of COD/L), the maximum power density was 464 mW/m(2) (15.5 W/m(3); CE = 27%). Although flow through the anode could lead to plugging, especially for particulate substrates such as domestic wastewater, the system was operated using glucose for over 42 days without clogging. These results show that power output in this air-cathode single-chamber MFC can be increased by reducing the electrode spacing if the reactors are operated in continuous flow mode with advective flow through the anode toward the cathode.