Abstract

Azo dyes constitute around 70% of the total dyes in the world. Almost 10%–15% of dye is released in wastewater during manufacture of the dye and its application, and is a prime source of pollution. Various physiochemical methods available for their decolorization have some or the other disadvantages like cost or time inefficiency. Hence, bacterial decolorization has been studied for cheap and efficient decolorization. In this study, Citrobacter sp. strain EBT-2 was isolated from a textile industry dumping site and used to optimize dye decolorization conditions for three Azodyes: methyl orange (MO), congo red (CR), and Eriochrome Black T (EBT). Decolorization was measured by UV–Vis spectroscopy analysis. The strain showed 100% decolorization for all the three dyes up to 100 mg/l concentration in 96–120 hours. It was able to decolorize till 300, 500, and 500 mg/l of dye concentration for MO, CR, and EBT, respectively. Decolorization efficiency was independent of initial dye concentration. Optimum pH for decolorization was 7, 7, and 9 for MO, CR, and EBT, respectively. The effect of agitation on decolorization was studied under static and agitated (200 rpm) condition. About 90% decolorization was observed at static condition and about 20% decolorization was observed under agitated condition in all the three dyes in 96 hours. Complete decolorization was obtained for MO and EBT at 35°C and 45°C, respectively. CR showed complete decolorization only at 35°C. The results conclude that Citrobacter sp. can be used for the successful dye decolorization of Azo dyes, primarily MO, CR, and EBT under optimum physiochemical conditions.

Key words: Azo dyes, Decolorization, Optimization, Methyl Orange, Congo Red, Eriochrome Black T, Citrobacter