Decolorization of textile dye direct yellow 12 using bacteria isolated from soil contaminated with textile industry effluents

Abstract

This investigation was taken up to study the decolorization of the textile dye, Direct Yellow 12 by making use of free and immobilized bacterial cells isolated from soil contaminated with textile industry effluents. A total of 12 isolates capable of decolorizing Direct yellow 12 were obtained. With screening, 2 isolates namely DY9 and DY 10 were selected for further decolorization studies of the dye. Biochemical characterization of both the isolates was carried and both were tentatively identified as Bacillus species. Optimization of decolorization the dye with respect to various parameters was carried out with one factor at a time approach. The optimum pH for both cultures was found to be 9. A temperature of 37ºC, a Shaking speed of 150 rpm and Bushnell Haas medium supplemented with 100 mg/L Starch and a Dye concentration of 2% were optimum for both cultures. Optimum decolorization with DY9 was obtained with 100 mg/L KNO₃ and that with DY10 was with 100 mg/L Yeast extract. A comparative study on the decolorization of Direct Yellow 12 under unoptimized and optimized conditions using both isolates was carried out. The results showed a marked increase in decolorization with both isolates under optimized conditions. The two cultures, individually and as a consortium were immobilized in Calcium alginate. Batch decolorization of the dye using free and immobilized cultures of DY9 and DY10 was carried out. The immobilized cultures showed an increase in decolorization compared to free cells. At a lower dye concentration, the immobilized consortium showed a higher decolorization. However, with increase in concentration of the dye, individual immobilized cultures proved better for decolorization. Repeated batch decolorization was carried out to check the stability of the calcium alginate beads. The current investigation showed that free and immobilized cells of both the isolates could be used in the water and soil bioremediation.