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

► Sulphonated dye reduction in one- and two-stage anaerobic systems. ► Impact of phase separation on electron transfer capacity. ► Impact of redox mediators in one- and two-stage anaerobic systems. ► Impact of acidogenic phase in the overall colour removal. ► Possibility of application to other reductive processes.