Evaluation of the design of anaerobic-aerobic systems for treating azo dye-containing effluents

This study investigated the treatment of a synthetic effluent containing the azo dye Reactive Black 5 (50 mg center dot L-1) in acidogenic reactors followed by different aerobic post-treatment units, namely, moving bed biofilm reactors (MBBRs) and tricking filters (TFs). The effect of the addition of the redox mediator anthraquinone-2-sulfonate (AQS) (50 mu M) to the system, hydraulic retention time (HRT) (6 and 4 h) in the MBBRs, and type of support medium (polyurethane foam cubes and K1 biomedia) in the TFs was evaluated. The acidogenic reactors were mainly responsible for the decolorization of RB5 in the anaerobic-aerobic designs evaluated in this study, and AQS significantly improved their decolorization efficiency. The use of a shorter HRT (4 h) in the MBBRs negatively influenced the color and COD removal performance in the reactors. Polyurethane foam proved to be more viable as a support medium, as it is a more accessible and low-cost material. Finally, acidogenic reactors followed by TFs filled with polyurethane foam cubes seemed to be the most promising design, both in terms of removing color, COD, and ammonia, and concerning the energy demand for system aeration.