Assessing the engineering aspects of azo dye decolorization in aerobic granular reactors

Abstract

This investigation evaluated the impact of the azo dye Reactive Black 5 (RB5) (50 mg·L⁻¹) on the formation and stability of aerobic granular sludge (AGS). Additionally, the effects of the reactor configuration (conventional and simultaneous fill/draw), use of pre-granulated sludge, and addition of the redox mediator anthraquinone-2,6-disulfonate (AQDS) (25 and 50 µM) on the removal of C, N, P, and color were assessed. Although granulation was achieved, the AGS grown in the presence of RB5 showed lower concentration, worse settleability, and smaller size. Nevertheless, the dye did not compromise C, N, and P removals (above 90 %, 75 %, and 35 %, respectively). However, color removal was considered low (∼50 %). Neither the reactor configuration nor the use of pre-granulated sludge significantly affected N, P, and color removals. Therefore, except for C removal, using an AGS previously grown in dye presence is not a prerequisite. Finally, AQDS addition increased RB5 decolorization (from 48 % to 64 % at 50 µM). However, unexpectedly, it had a slight negative impact on N removal.