Optimisation of reactive textile dyes degradation by laccase-mediator system

BACKGROUND: In the textile industry, large quantities of intensely coloured and toxic effluents are released, causing serious environmental pollution. Several biotechnological approaches have been suggested to eliminate this pollution source in an eco-efficient manner. Laccase can be used to decolourise dyes and its substrate range can be extended by inclusion of a mediator. RESULTS: A screening using several laccase mediators (2,2-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS), 1-hydroxybenzotriazole (HBT), N-hydroxyacetanilide (NHA), polioxometalates, violuric acid (VA) and (2,2,6,6-tetrameth-slipiperidin-l-vloxy) (TEMPO)) was performed on the degradation of six reactive textile dyes. ABTS was the most effective mediator leading to higher decolourisation. The efficiency of ABTS depends on the type of dye, pH, temperature and dye concentration. The optimum temperature and pH values were 35 degrees C and 5.0, respectively, for maximum decolourisation (above 70%) of reactive black 5, reactive blue 114 and reactive yellow 15. For reactive red 239 the optimum conditions were found to be a temperature of 40 degrees C and pH of 4.5 (above 56% decolourisation). ABTS has no effect at low concentrations, except for reactive blue 114, where it resulted in the best decolourisation (93%). A comparison of decolourisation based on the percentage absorbance reduction at the maximum absorbance wavelength of each dye and throughout the visible spectrum was made. CONCLUSIONS: These results suggest that the laccase mediator system could be used to treat textile dying wastewaters. (C) 2008 Society of Chemical Industry