Comparative decolorizing efficiency of textile dye by mesophilic and thermophilic anaerobic treatments

Abstract

Anaerobic decolorization of two kinds of dye, viz., azo type represented by Methyl Orange (MO) and anthraquinone type represented by Reactive Blue 4 (RB4) was performed using digested sludge under mesophilic (35°C) and thermophilic (55°C) conditions. Decolorization of dye was investigated to compare the efficiency and extent of decolorization, and additionally to evaluate the effect of temperature and dye on decolorizing microorganisms. Glucose was used as an electron donor in terms of co-substrate without the addition of other nutrients. Under thermophilic treatment, high efficiency of decolourisation was shown in both of the dyes at high concentration, 1000 mg·L-1of MO and 600mg·L-1 of RB4 compared with mesophilic treatment. MO, 200mg·L-1, was decolorized 95-98% under both mesophilic and thermophilic conditions. High decolorizing efficiency of RB4, 100mg·L-1, obtained under thermophilic conditions, was 80% when compared with mesophilic conditions (70%). The reduced form of MO showed an auto-oxidizing effect with pink to violet color when exposed to air, while RB4 showed no auto-oxidizing reaction. The inhibition of MO was effected on sugar conversion to fatty acids, and CH4 productivity resulted in slow reduction of TOC. While RB4 inhibited only on methane productivity, in which TOC reduction was similarly used as control. Due to the increase of temperature, methanogenesis was inhibited and which low CH4 production, whereas an increase of decolorizing efficiency on both dye decolorization and a high rate of TOC reduction was observed.