Increasing power production and coulombic efficiency (CE) of microbial fuel cells (MFCs) is a common research ambition as the viability of the technology depends to some extent on these measures of performance As MFCs are typically time varying systems comparative studies of controlled and un-controlled external load impedance are needed to show if control affects the biocatalyst development and hence MFC performance The application of logic based control of external load resistance is shown to increase the power generated by the MFC when compared to an equivalent system which has a static resistive load The controlled MFC generated 1600 400 C compared to 300 10 C with an otherwise replicate fixed load MFC system The use of a parsimonious gradient based control was able to increase the ( E to within the range of 15 1-227% while the CE for a 200 Omega statically loaded MFC lay in the range 3 3-3 7% The controlled MFC improves the electrogenic anodic biofilm selection for power production indicating that greater power and substrate conversion can be achieved by controlling load impedance Load control ensured sustainable current demand applied microbial selection pressures and provided near-optimal impedance for power transference compared to the un-controlled system (c) 2010 Elsevier B V All rights reserved