Thermophillic 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, thraquinone- 2,6-disulfonate (AQDS), on electron transfer and subsequent reductive decolorization of dyes rom textile wastewater was assessed in mesophilic and thermophilic anaerobic bioreactors. The results clearly show that compared to mesophilic anaerobic treatment, thermophilic treatment at 55 8C 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 8C compared to 30 8C. Furthermore, similar decolorizations were found at 55 8C between the AQDS-free and AQDSsupplemented reactors, whereas a significant difference (up to 3.6-fold) on dye reduction occurred at 30 8C. Keywords Azo dye; color removal; electron transfer; anaerobic treatment; mesophilic; thermophili