Impact of the redox mediator sodium anthraquinone-2,6-disulphonate (AQDS) on the reductive decolourisation of the azo dye Reactive Red 2 (RR2) in one- and two-stage anaerobic systems

This work assessed the impact of the redox mediator sodium anthraquinone-2,6-disulphonate (AQDS) on the reductive decolourisation of the azo dye Reactive Red 2 (RR2) in one- and two-stage anaerobic systems (R1 and R2, respectively). The two-stage system achieved better colour removal efficiencies (52–62%) than the single-stage system (23–33%) in the absence of AQDS. Addition of AQDS accelerated the electrons transfer from the substrate (ethanol) to the dye, which increased the colour removal efficiency of both anaerobic systems (∼85%). Finally, the impact of acidogenic and methanogenic phases separation was masked by AQDS supplementation.