Color removal in acidogenic reactor followed by aerobic granular sludge reactor: operational and microbiological aspects

Abstract

This work investigated the operational and microbiological aspects of the decolorization of the azo dye Reactive Black 5 in acidogenic reactors followed by aerobic granular sludge (AGS) reactors, evaluating the effect of the acidogenic hydraulic retention time (HRT) (3, 2, and 1 h), effluent recirculation in the AGS reactor (50 mL·min-1), dye concentration (50 and 100 mg·L-1), and the redox mediator sodium anthraquinone-2-disulfonate (AQS) (50 μM). The acidogenic reactors were mainly responsible for the dye decolorization, with AQS significantly improving its efficiency and enabling the use of a shorter HRT (2 h). The recirculation effect was not so evident, probably masked by the adaptation of the acidogenic microbiota. Increasing the dye concentration did not affect the total decolorization, but reduced nitrogen removal in the AGS reactors. Furthermore, the dye and its byproducts may have negatively affected the long-term AGS stability. While the acidogenic microbiota maintained its diversity, the AGS tended to become more specialist. However, in both, some abundant genera that may have acted in reducing the dye were found, such as Clostridium_sensu_stricto_1 and Raoutella in the acidogenic sludge and Dechloromonas and Defluviicoccus in the AGS.