The ability of dual-chambered microbial fuel cell, fed with slaughterhouse wastewater with an anaerobic mixed-sludge as initial source of bacteria, to generate power is investigated. MFC voltage generation across a fixed 100 Omega load indicates power generation capability, with power production correlated to changes in anolyte VFA content. A maximum MFC power density of 578 mW/m(2) is obtained for an MFC developed under 100 Omega load, compared to a maximum power density of 277 mW/m(2) for an MFC developed under higher resistance (1 M Omega) control conditions. Voltammetry of the biofilm developed under 100 Omega load displays a current-voltage signal indicative of bioelectrocatalytic oxidation of feed at a potential of -0.35 V vs. Ag/AgCl, compared to negligible signals for biofilms developed under control conditions. Denaturing gradient gel electrophoresis of PCR amplified 16S rRNA gene fragments reveals that the anodic bacterial communities in reactors operated under 100 Omega load result in communities of lower diversity than for the control condition, with Geovibrio ferrireducens dominant in the anodic biofilm community. These results indicate that in MFC reactors, functionally stable electroactive bacteria are enriched under 100 Omega load compared to high resistance control conditions, and were able to sustain higher power in MFCs. (C) 2011 Elsevier B.V. All rights reserved.