Azo dyes decolorization by bacteria originated from textile wastewater

Abstract

This study investigated the ability of previously isolated bacteria Escherichia sp., Acinetobacter sp., Enterobacter sp. and Klebsiella sp. in decolorizing Acid Orange 7 and Reactive Black 5. Screening results indicated the decolorization of Acid Orange 7 under facultative anaerobic condition was faster in comparison to Reactive Black 5. No decolorization of Acid Orange 7 and Reactive Black 5 was observed under aerobic conditions in the tested strains. Due to the reason that two of the strains (Klebsiella sp. and Escherichia sp.) were more potent decolorizers and these strains were able to remove Acid Orange 7 faster than Reactive Black 5, they were selected for further characterization on decolorization of Acid Orange 7. The effects of temperature, pH and concentration of nitrogen (NH4)2SO4 on Acid Orange 7 decolorization were studied. For both of the strains, the optimum pH, temperature and (NH4)2SO4 concentration were found to be at pH7, 37°C and 0.5g/L respectively. At pH 7, 93% and 75% of Acid Orange 7 was decolorized by Klebsiella sp. and Escherichia sp., respectively. No decolorization was detected at pH 4 or 10. At optimum temperature (37°C), Klebsiella sp. and Escherichia sp. were found to be able to decolorize 84% and 68% of Acid Orange 7, respectively. The decolorization percentage was detected to be highest in both strains (Klebsiella sp., 83% and Escherichia sp., 68%) when the cells were incubated in medium contained 0.5g/l of (NH4)2SO4. Inducibility studies indicated Acid Orange 7 did not show an inducing effect on decolorization in Klebsiella sp. However, Acid Orange 7 was found to have a positive inducing effect on decolourization in Esherichia sp. It was observed that the Esherichia sp., which was pre-exposed to Acid Orange 7 displayed a higher percentage of decolorization compared with non pre-exposed cells.