Electricity generation in a membrane-less microbial fuel cell with down-flow feeding onto the cathode

► Oxygen was utilized readily from air while wastewater feeding onto the cathode. ► DO did not affect power generation while COD, flow rate and electrode spacing did. ► Maximum power density was twice as high as that obtained by up-flow feeding. ► Readily to be scaled up due to its simple configuration and easy operation. A novel membrane-less microbial fuel cell (MFC) with down-flow feeding was constructed to generate electricity. Wastewater was fed directly onto the cathode which was horizontally installed in the upper part of the MFC. Oxygen could be utilized readily from the air. The concentration of dissolved oxygen in the influent wastewater had little effect on the power generation. A saturation-type relationship was observed between the initial COD and the power generation. The influent flow rate could affect greatly the power density. Fed by the synthetic glucose wastewater with a COD value of 3500mg/L at a flow rate of 4.0mL/min, the developed MFC could produce a maximum power density of 37.4mW/m2. Its applicability was further evaluated by the treatment of brewery wastewater. The system could be scaled up readily due to its simple configuration, easy operation and relatively high power density.