The use of different redox mediators on colour removal of azo dyes by anaerobic granular sludge was investigated under mesophilic (30ºC) and thermophilic (55ºC) conditions. Additionally, the use of different electron donors on the reductive decolourisation was studied in both temperatures. The addition of catalytic concentrations of redox mediators had an evident impact on the decolourisation process, enhancing the rates up to one order of magnitude. Compared to mesophilic conditions, colour removal under thermophilic conditions was extremely accelerated, and the impact of redox mediators on the decolourisation rates was considerably decreased at 55ºC. For instance, in a continuous flow experiment, efficiencies of around 95% and 56% were obtained at 55ºC and 30ºC, respectively, in the absence of redox mediators. Hydrogen was a much better electron donor for sustaining dye reduction than glucose, formate and acetate. The present results bring good prospects for the use of thermophilic anaerobic treatment and redox mediators on colour removal of textile wastewaters.
Colour removal; azo dyes; anaerobic treatment; redox mediators; mesophilic and thermophilic treatment
