Rapid startup of microbial fuel cells (MFCs) and other bioreactors is desirable when treating wastewaters. The startup time with unamended wastewater (118 h) was similar to that obtained by adding acetate or fumarate (110-115 h), and less than that with glucose (181 h) or Fe(III) (353 h). Initial current production took longer when phosphate buffer was added, with startup times increasing with concentration from 149 h (25 mM) to 251 h (50 mM) and 526 h (100 mM). Microbial communities that developed in the reactors contained Betaproteobacteria. Acetoanaerobium noterae, and Chlorobium sp. Anode biomass densities ranged from 200 to 600 mu g/cm(2) for all amendments except Fe(III) (1650 mu g/cm(2)). Wastewater produced 91 mW/m(2), with the other MFCs producing 50 mW/m(2) (fumarate) to 103 mW/m(2) (Fe(III)) when amendments were removed. These experiments show that wastewater alone is sufficient to acclimate the reactor without the need for additional chemical amendments. (C) 2011 Elsevier Ltd. All rights reserved.