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In this paper we studied the ability of four Tunisian-isolated fungi (i.e. Coriolopsis gallica, Bjerkandera adusta, Trametes versicolor and Trametes trogii) immobilized into Ca-alginate beads to decolorize the metal textile dye Lanaset Grey G (LG). The effect of different operational conditions, such as initial dye concentration, temperature, pH, beads/medium ratio and agitation, on dye decolorization by the immobilized fungi was investigated. Maximal decolorization percentages of 88.7%, 89.3%, 82.1% and 81.3% for C. gallica, B. adusta, T. versicolor and T. trogii were attained, respectively, when operating at an initial LG concentration of 150 mg/L, pH values of 5.0-6.0, temperatures of 40-45 °C and a beads/medium ratio of 20% (w/v) in static conditions after 72 h of incubation. Subsequently, the re-usability of the immobilized fungi was evaluated. After three decolorization cycles, the decolorization percentage of free cell cultures dropped to values below 36%, while decolorization percentages of about 75%, 70%, 60% and 68% were obtained by the immobilized cultures of C. gallica, B. adusta, T. versicolor and T. trogii, respectively., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Response surface methodology (RSM) was applied to optimize the decolourization of 3 dyes belonging to 3 dye families such as reactive black 5 (diazoic), indigo carmine (indigoid) and aniline blue (anthraquinonic). Crude laccase from Trametes trogii and the laccase-mediator 1-hydroxybenzotriazole (HBT) were used in this study. Box-Behnken design using RSM with six variables namely pH, temperature, enzyme concentration, HBT concentration, dye concentration and incubation time was used in this study to optimize significant correlation between the effects of these variables on the decolourization of reactive black 5 (RB5), indigo carmine (IC) and aniline blue (AB). The optimum of pH, temperature, laccase, HBT, RB5 and reaction time were 4.5, 0.5 U ml(-1), 0.5 mM, 100 mg ml(-1) and 150 min respectively, for a maximum decolourization of RB5 (about 92.92% ± 7.21). Whereas, the optimum decolourization conditions of both IC (99.76% ± 7.75) and AB (98.44% ± 10) were: pH 4.5, temperature of 45 °C, enzyme concentration of 0.1 U ml(-1) and 0.5 U ml(-1), HBT concentration of 0.9 mM and 0.5 mM, dye concentration of 60 mg l(-1) and reaction time of 150 and 90 min, respectively. The experimental values were in good agreement with the predicted ones and the models were highly significant, the correlation coefficient (R(2)) being 0.864, 0.663 and 0.776 for RB5, IC and AB, respectively. In addition, when the kinetic parameters for the three dyes decolourization were calculated according to Hannes-Wolf plot, the following values were obtained: Km of 268.4, 47.94 and 44.64 mg l(-1) then V(max) of 35.58, 10.43 and 9.23 mg l(-1) min for the RB5, IC and AB decolourizations by laccase, respectively., (Copyright © 2012 Elsevier Ltd. All rights reserved.)