In this study different process parameters for dye decolorization of 8 synthetic textile dyes by spore laccase of isolated Bacillus amyloliquefaciens were optimized. It was found that increasing dye concentration decreased the dye decolorization activity. On the other hand, increasing the enzyme concentration enhanced the decolorization efficiency. The optimum temperature for dye decolorization was 30 ºC for acid red 337, acid black 24 and crystal violet. However, 35 ºC was the best temperature for decolorization of acid blue 335, direct red 81, methylene blue, congo red, and methyl orange. pH7 was the best for decolorization of acid red 337, direct red 81, methylene blue and congo red; however, pH 8 was the optimum for acid blue 335 and acid black 24. While decolorization of methyl orange was the maximum at pH6, crystal violet was efficiently decolorized at pH 7-8. Dye decolorization efficiency under illuminating conditions was enhanced about 2-26% in comparison with incubation under dark conditions. Shaking was an important factor affecting dye decolorization of different tested dyes. Decolorization by spore laccase was enhanced by shaking from 11-72% for some dyes while for some other dyes the decolorization activity was decreased by 14-16%. Increasing the contact time increased the decolorization of different dyes. Addition of redox mediator, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) showed 5-48% dye decolorization enhancement. Direct red 81 was the most decolorized dye by spore laccase without mediator and showed 94% decolorization after 24 h followed by acid black 24 which showed 79% decolorization, and these percentages increased to 98% and 94%, respectively after addition of ABTS. These results suggest that spore laccase was efficient in decolorization of tested dyes especially direct red 81 and acid black 24 and is promising for industrial dye wastewater bioremediation.
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