This first-attempt study quantitatively assessed electron-mediating characteristics of bicyclic aromatics 1-amino-2-naphthol, 4-amino-1-naphthol (i.e., decolorized intermediates of azo dyes - orange I and II) for color removal and power generation in MFCs. According to cyclic-voltammetric profiles, the presence of reduction and oxidation peak potentials clearly suggested a crucial role of these intermediates as electron-shuttling mediators. Shake-flask cultures also showed that appropriate accumulation of 1A2N, 4A1N apparently enhanced color-removal efficiencies of bacterial decolorization. This study clearly suggested that suitable supplementation of electrochemically active electron shuttle(s) to dye-bearing MFCs is a promising strategy to stimulate reductive decolorization and bioelectricity generation. (c) 2014 Elsevier Ltd. All rights reserved.