Here we discuss the percentage power increase, ΔP (%), as a function of flow rate over the minimum flow rate (QT=0.1 mL h -1 ). This is shown in Figure with flow rate transformed to flow velocity. A maximum percentage power increase was obtained from QT=10 mL h -1 but did not significantly increase above 10 mL h -1 . This supports a previous conclusion that previously observed reduction in power density at high flow rates may be the result of electrode contamination due to flow-based instabilities that cause solution cross-over. While power did not significantly increase with flow over 10 mL h -1 , the membrane did not fail at any attempted flow rates (up to 140 mL h -1 ). It should also be noted that the membrane enabled very slow flow rates, while membraneless MFCs were not stable due to pump instability at these flow rates (data not shown). The power increases versus flow velocity for membrane MFCs and membraneless MFCs were compared in Figure . The results from membrane MFCs showed that at smaller QT values, ranging from 0.2 mL h -1 to 0.5 mL h -1 , percentage power increase improved from 20.5% to 24.4%. After that, percentage power increase grew slow slowly, from QT=1 mL h -1 to QT=5 mL h -1 . When the flow rate reached 10 mL h -1 , the percentage power increase became stable at 29.4%. Further increasing QT to 20 mL h -1 did not affect the percentage power increase. To facilitate a comparison with a membraneless MFC, which has different channel dimensions, we calculate the flow velocity, ranging from 0.02 to 1.22 m min - 1 . Compared with the membraneless MFC, the percentage power increase for the membrane MFC increased faster at lower flow rate and resulted in a maximum ΔP of 5% higher than for the membraneless MFC.