Assessment of anthraquinone-dye conversion by free and immobilized crude laccase mixtures

This paper reports on the assessment of two enzyme-based processes for the conversion of synthetic dyes. A crude laccase mixture from Pleurotus ostreatus was immobilised on EUPERGIT C 250L©, an acrylic resin with epoxy functionalities. This biocatalyst was used in the conversion of the anthraquinonic dye Remazol brilliant blue R. Two different fixed bed reactors were used to assay the solid biocatalyst activity and to characterize the dye conversion kinetics. The immobilisation procedure was optimized providing a maximum immobilisation yield of 7% of the initial laccase activity in solution. The kinetics of dye conversion was in line with a product-inhibited kinetic model. The biocatalyst underwent moderate deactivation along with conversion. The kinetic models were implemented to describe dye conversion in a continuous fixed bed reactor (CFBR), operated with immobilised laccases, and in a stirred tank reactor (STR), operated with free laccases. The CFBR option enables the remediation of a wastewater volume larger than the one processed in the STR under comparable operating conditions. The better performance of CFBR results from the balanced effect of an improved stability of immobilised laccases and of a loss of activity following immobilisation.