Evaluation of the decolorization potential of azo dyes by aerobic granular sludge

Abstract

This study assessed the azo dye decolorization potential by aerobic granular sludge (AGS), particularly investigating the effects of different electron donor substrates, redox mediators, dye structures, and alternative electron acceptors. Additionally, the stability and performance of an AGS reactor were evaluated during the treatment of a synthetic azo dye-containing effluent in the absence and presence of a redox mediator. Propionate and anthraquinone-2-sulfonate (AQS) were the best substrate (k1 1.1–1.9-fold higher) and redox mediator (k1 1.4-fold higher), respectively, for Reactive Black 5 (RB5) decolorization. AQS (50 μM) had a greater impact on Reactive Orange 16 (k1 = 15.60 h−1) than on Reactive Red 120 (k1 = 0.48 h−1) and RB5 (k1 = 7.92 h−1). Nitrate and sulfate (100 and 200 mg·L−1) inhibited dye reduction (decreasing k1 from 5.52 to 0.72 and 2.40 h−1, respectively), possibly because they compete with the dye for the electrons in the environment. However, AQS minimized their impact on this process (except for nitrate at 200 mg·L−1). In the reactor, RB5 and AQS did not alter the physical characteristics of AGS and its ability to remove organic matter and nutrients. Finally, the effect of AQS on decolorization was not so intense, increasing only ∼15%.