This study evaluated how different types of industrial wastewaters (bakery, brewery, paper and dairy) affect the performance of identical microbial fuel cells (MFCs): and the microbial composition and electrochemistry of MFC anodes. MFCs fed with paper wastewater produced the highest current density (125 +/- 2 mA/m(2)) at least five times higher than dairy (25 +/- 1 mA/m(2)), brewery and bakery wastewaters (10 +/- 1 mA/m(2)). Such high current production was independent of substrate degradability. A comprehensive study was conducted to determine the factor driving current production when using the paper effluent. The microbial composition of anodic biofilms differed according to the type of wastewater used, and only MFC: anodes fed with paper wastewater showed redox activity at -134 +/- 5 mV vs NHE. Electrochemical analysis of this redox activity indicated that anodic bacteria produced a putative electron shuttling compound that increased the electron transfer rate through diffusion, and as a result the overall MFC performance. (C) 2011 Elsevier Ltd. All rights reserved.