Abstract

Reactive azo dyes are widely used as textile colorants, typically for cotton dyeing, due to their variety of color shades, and minimal energy consumption. In the present study, commercial laccase from Trametes versicolor was used for the biodecolorization of Reactive Black 5 (RB-5) dye using different redox mediators viz,N-hydroxybenzotriazole (HBT), 2,2′-azino-bis-(3-ethylbenzthiazoline- 6-sulfonic acid(ABTS), 2,6-dimethoxy phenol (DMP), syringaldehyde, vanillin, aceto-vanillone, p-coumaric acid and catechol. Commercial laccase alone did not show any considerable decolorization of RB-5. However, the laccase in the presence of syringaldehyde showed the strongest decolorization rate (98%), followed by vanillin (55.21%), aceto-vanillone (53.25%), ABTS (42.78%), p-coumaric acid (41.9%), DMP (39%), and catechol (36.33%); while least decolorization was observed with HBT at dye/mediator ratio of only 1:5 after 30 min. Therefore, syringaldehyde performance was evaluated at different mediator/dye ratios (1:1, 1:5 and 1:10) using commercial laccase and it was compared with that of synthetic mediator like HBT. It was found that the presence of syringaldehyde was essential for biodecolorization of RB-5. Moreover, it was observed that syringaldehyde was an effective natural redox mediator as compared to synthetic HBT. Enhanced decolorization (98%) of RB-5 by laccase was observed with 1:5 syringaldehyde and dye ratio for 30 min but maximum removal (22%) of RB-5 was recorded with HBT at 1:1 after 40 min. Thus, the study reveals that the phenolic compounds could be used as potential redox mediators for enhanced laccase-mediated decolorization of azo dyes.

Key words: Reactive Black 5 (RB-5), redox mediators, laccase, biodegradation, azo dyes.

Abbreviation

Abbreviations: RB-5, Reactive Black 5; HBT, N-hydroxybenzotriazole; ABTS, 2,2′-azino-bis-(3-ethylbenzthiazoline- 6-sulfonic acid; DMP, 2,6-dimethoxy phenol.