The main aim of this study is to investigate the simultaneous azo dye removal and bioelectricity production at sulfate-reducing conditions in a continuously fed dual-chamber microbial fuel cell (MFC). Initially, optimization of sulfate reduction was performed at different sulfate concentrations (100-900 mg/L) and the constant COD of 1000 mg/L, corresponding to COD/sulfate ratio of 1.11-10, and varying HRT of 12-48 h. Optimum COD/sulfate ratio and HRT was found 1.66 and 36 h, respectively, corresponding to 96% COD removal, 44% sulfate removal and yielded about 24 W/m(2) power density. Further, MFC was fed with azo dye containing (50-1000 mg/L) simulated wastewater to evaluate dye removal performance of sulfate-reducing bacteria. Addition of azo dye slightly enhanced the power production to 26 W/m2, the highest value obtained during our study. Sulfate and COD removals were adversely affected at azo dye concentrations over 300 mg/L and 150 mg/L, respectively. Additionally, color removal performance of MFC was excellent however, chemical azo dye reduction out-competed with enzymatic reduction at high azo dye levels (>500 mg/L) leading to a poor sulfate (<15%) and COD (<45%) removal and recovery of azo dye reduction efficiency to 91%.