Thermophilic treatment by anaerobic granular sludge as an effective approach to accelerate the electron transfer and improve the reductive decolorization of azo dyes in bioreactors

The effects of temperature, hydraulic retention time (HRT), and the redox mediator, anthraquinone-2,6-disulfonate (AQDS), on electron transfer and subsequent reductive decolorization of dyes from textile wastewater was assessed in mesophilic and thermophilic anaerobic bioreactors. The results clearly show that compared to mesophilic anaerobic treatment, thermophilic treatment at 55 °C is an effective approach for increasing the electron transfer capacity in bioreactors, and thus improving the decolorization rates. At an HRT of 2.5 h and in the absence of AQDS, the color removal was 5.3-fold higher at 55 °C compared to 30 °C. Furthermore, similar decolorizations were found at 55 °C between the AQDS-free and AQDS-supplemented reactors, whereas a significant difference (up to 3.6-fold) on dye reduction occurred at 30 °C.