After synthesis of the chitosan membrane, the microfluidic MFC was inoculated with G. sulfurreducens for 24 hours with anolyte (inoculant) and co-flowing catholyte at a balanced flow rate such that flow velocity was 0.01 m min -1 . The initial external resistor was set to 100 kΩ. After inoculation, a switching valve admitted a sterile stream of acetate anolyte, and a typical G. sulfurreducens growth curve was obtained (Figure ). A 10 h lag phase was observed during which G. sulfurreducens were switching to a sessile phenotype in order to switch to an anode respiration mode in the absences of dissolved fumarate. After that, G. sulfurreducens began to grow exponentially with changing growth rates of kI=0.09 h -1 , kII=0.04 h -1 , kIII=0.02 h -1 during the first 40 hours. The corresponding doubling times (calculated as 1/kI, 1/kII and 1/kIII) are longer than optimal observed values of approximately 6 hours. This is likely due to sub-optional grow temperature at 21 ℃. After around 60 hours of growth, the voltage became steady. The time reach to maturity is short compared to larger static MFCs, and demonstrates another advantage of microfluidic MFCs. To ensure the outputs were stable in the long term, we waited one week, then we conducted polarization tests under a constant flow rate of QT=0.1 mL h -1 . The polarization test was conducted by a switched resistor technique where different external resistors were applied after the voltage was settled under OCV conditions (Figure ). This approach prevents any acclimation to the decreasing external resistor values during the polarization test. Therefore the results are expected to produce conservative values, compared o the long-term operation at any single Rext. We note that the voltages always achieved stable values before voltage readings were obtained which indicates low internal resistance. From these results, power density (P ̅ ) and current density (I ̅