Anaerobic Decolorization of Sulfonated Azo Dyes by Sulfate Reducing Bacteria

Aim: The present study was done to find out ability of sulfate reducing bacteria to reduce sulfonated azo dyes found in the textile effluent. Study Design: Isolate Sulfate reducing bacterial strains from dye contaminated soil samples, inoculate and incubate dye supplemented media under static anaerobic condition and measure the decolorization using UV-VIS spectrophotometer. Place and Duration of Study: The samples were collected from Travancore textiles Nemom, Thiruvananthapuram, Kerala, India. Laboratory analysis were performed at Department of Environmental Sciences, University of Kerala, Thiruvananthapuram, India. The study was done for a period of six months. Methodology: The isolated sulfate reducing bacterial (SRB) strains were screened to test the tolerance to selected sulfonated azo dye Direct blue 71. The decolorization assay was done in Postgate media and an aliquot of samples (3mL) were withdrawn periodically, centrifuged at 10,000rpm for 15min. The supernatant was used to assay azo dye reduction by measuring residual absorption at the wavelength 594 nm of the Direct Blue 71. Results were compared with the uninoculated control. The optimization of physicochemical conditions for effective decolorization of the selected bacterial strains was studied at different environmental conditions (pH, temperature, concentration and added co-substrates such as sodium acetate, lactate and mannitol). The biodegradation of sulfonated azo dye was assessed by characterizing the metabolites formed after degradation by Fourier Transform Infrared Spectroscopy (FT-IR). FT-IR analysis revealed only decolorization had occurred without degradation of the dye during the short incubation period of one week. Conclusion: Degradation of azo dyes and other recalcitrant compounds by obligate anaerobes such as sulfate reducing bacteria is a slow process. Hence, extension of incubation period is necessary for the effective and complete degradation of the dye by SRB.