In the final part of the study, we tested whether microfluidic MFCs could benefit from acclimation to high current conditions via a low Rext (3.5 kΩ) either before standard polarization tests (pre-acclimation) or during microfluidic-assisted long-hold polarization tests (in situ acclimation). In the first approach, the MFC was pre-acclimated for 4 days to one of three external resistors (Rext=150, 20, and 3.5 kΩ) followed by a standard polarization test. Each experimental condition was applied three times in random order to prevent bias in the results. Pre-acclimation at the lowest external resistor (Rext=3.5 kΩ) was most efficient in improving outputs. Specifically, Pmax recovered to pre-overshoot levels (Pmax=370 mW m -2 ), and the overshoot was eliminated (Īf=Īmax). However, the Īmax value of 810 mA m -2 after pre-acclimation was still 20% lower than that at t=42 days (before the onset of overshoot) and was nearly equivalent to Īmax at t=45 and 48 days (during overshoot). We do not believe that this drop in current is the same as has been reported during MFC start-up because in this case the MFC was already mature. Rather, it is likely the result of the declining EAB health and loss of biomass after shear erosion. For comparison, we combine the pre-acclimated power density and polarization curves along with those data obtained at t=42 days in Figure . Pre-acclimation to higher resistances had the predictable effect of lowering Pmax and Īmax.