The effect of a quinone-based redox mediator on the decolourisation of textile wastewaters: a comparative study between mesophilic (30°C) and thermophilic (55°C) anaerobic treatments by granular sludge

A comparative study between mesophilic ( https://www.w3.org/1998/Math/MathML" display="inline"> 30 ∘ C ) and thermophilic ( https://www.w3.org/1998/Math/MathML" display="inline"> 55 ∘ C ) anaerobic treatments by granular sludge was performed on the decolourisation of a reactive textile wastewater, both in presence and absence of the redox mediator anthraquinone-2-sulfonate (AQS). The investigations evidenced the advantage of colour removal at https://www.w3.org/1998/Math/MathML" display="inline"> 55 ∘ C compared with https://www.w3.org/1998/Math/MathML" display="inline"> 30 ∘ C . In the presence of anthraquinone-2,6-disulfonate (AQDS), the generation of the hydroquinone form https://www.w3.org/1998/Math/MathML" display="inline"> A H 2 Q D S , i.e. the reduced form of AQDS , was greatly accelerated at https://www.w3.org/1998/Math/MathML" display="inline"> 55 ∘ C compared in comparison with https://www.w3.org/1998/Math/MathML" display="inline"> 30 ∘ C . Furthermore, no lag-phase was observed at https://www.w3.org/1998/Math/MathML" display="inline"> 55 ∘ C . Based on the present results we postulate that the production/transfer of reducing equivalents is the process rate-limiting step, which was accelerated by the temperature increase. It is conclusively stated that https://www.w3.org/1998/Math/MathML" display="inline"> 55 ∘ C is a much better temperature for colour removal than https://www.w3.org/1998/Math/MathML" display="inline"> 30 ∘ C , which on the one hand can be attributed to the faster production/transfer of reducing equivalents, but also due to the decrease of activation energy requirements.