This study aims at investigating azo dye reduction performance of a sulfidogenic anaerobic baffled reactor (ABR) for around 400 days. ABR was operated at 30 degrees C in a temperature-controlled room and hydraulic retention time (HRT) was kept constant at 2 days. The robustness of ABR was assessed under varying azo dye loadings and COD/sulfate ratios. Additionally, oxygen was supplied (1-2 L air/m(3) reactor min) to the last compartment to investigate the removal of azo dye breakdown products. ABR performed well in terms of COD, sulfate and azo dye removals throughout the reactor operation. Maximum azo dye, COD and sulfate removals were 98%, 98% and 93%, respectively, at COD/sulfate ratio of 0.8. Aeration created different redox conditions in last compartment, which enhanced the removal of COD and breakdown products. The adverse effects of aeration on azo dye reduction were eliminated thanks to the compartmentalized structure of the ABR. (c) 2013 Elsevier Ltd. All rights reserved.