Improvement of the Decolorization of Azo Dye (Direct Red 81) by Immobilized Cells of Bacillus pumilus and Free Cells of Aspergillus clavatus in Textile Waste Waters

Abstract

Journal homepage: http://www.ijcmas.com In this study, the effluent wastewater samples collected from dyestuff industrial area have been examined for biological treatment. The rate of decolorization was assessed using spectrophotometer at 508 nm and the percentage of decolorization was ascertained. The metabolites of Direct Red 81 (DR81) obtained after biodegradation were determined by HPLC. In order to improve the decolorization process, the effect of process factors like pH, temperature, agitation and dye wastewater concentration on dye decolorization was studied. From the results, a potential bacterium and fungus isolates, namely, Bacillus pumilus and Aspergillus clavatus, respectively, have been isolated and identified from dyestuff industrial area for the decolorization of DR81. After 5 days of incubation period with Bacillus pumilus and Aspergillus clavatus, the bacterium showed 17% of decolorization, while the fungus showed 95% of decolorization at a dye concentration of 100 mg/L at 30 ± 0.2 °C under aerobic processes. Mixed culture of Bacillus pumilus and Aspergillus clavatus were found to decolorize 88% of DR 81 after 5 days of incubation. Bacillus pumilus showed the best extent degradation of DR81 (97%) when supplemented with yeast extract after 5 days of incubation. Furthermore, supplemented cells of Aspergillus clavatus with yeast extract showed 99% of DR81 while it showed 98% of when supplemented with glucose, and non-supplemented cells showed 95% of degradation after 5 days of incubation too. Free cells of Aspergillus clavatus showed 95% decolorization of DR81 after 5 days of incubation compared to immobilized cells (74%) on activated charcoal (20 g/L) in mineral salt medium (MSM), while immobilized cells of Bacillus pumilus on kaoline (20 g/L) showed 71% decolorization of DR81 compared to free cells (17%). Therefore, the potential of these microbial isolates can be exploited for the removal of residual dyes from the industrial wastewater for environmental cleanup and restoration of the ecosystem. K e y w o r d s