Dye decolorization and detoxification by laccase immobilized on porous glass beads

The decolorization and detoxification of textile dyes by fungal laccase immobilized on porous glass beads were evaluated. Anthraquinone (Reactive blue 19 and Dispersed blue 3) and indigoid (Acid blue 74) dyes were degraded more rapidly than the azo dyes (Acid red 27 and Reactive black 5). There was no dye sorption to the enzyme bed when decolorization rates were high (>12 μM dye/U-h) but at moderate rates (8 to >0.06 μM/U-h), there was a transient color which disappeared upon prolonged exposure. With Reactive black 5, permanent adsorption occurred most likely because laccase had been totally inactivated. Although laccase treatment was more efficient at decolorizing the anthraquinone dyes, their toxicity (as determined by the Microtox assay) increased while the less efficiently decolorized solutions of azo and indigoid dyes became less toxic. These results demonstrate the potential and limitations of using immobilized laccase to enzymatically decolorize a range of different dye classes and reduce dye toxicity in a single step.