Microbial anodes were formed under polarization at -0.3 V/SCE on graphite plates in effluents from a pulp and paper mill. The bioanodes formed with the addition of acetate led to the highest current densities (up to 6 A/m(2)) but were then unable to oxidize the raw effluent efficiently (0.5 A/m2). In contrast, the bioanodes formed without acetate addition were fully able to oxidize the organic matter contained in the effluent, giving up to 4.5 A/m(2) in continuous mode. Bacterial communities showed less bacterial diversity for the acetate-fed bioanodes compared to those formed in raw effluents. Deltaproteobacteria were the most abundant taxonomic group, with a high diversity for bioanodes formed without acetate addition but with almost 100% Desulfuromonas for the acetate-fed bioanodes. The addition of acetate to form the microbial anodes induced microbial selection, which was detrimental to the treatment of the raw effluent. (C) 2014 Elsevier Ltd. All rights reserved.