Efficient decolorization and detoxification of reactive orange 7 using laccase isolated from Paraconiothyrium variabile, kinetics and energetics

• Fractional factorial design was used to select most effective variables.
• The dye removal process was optimized using central composite design.
• Kinetic and energetic parameters of decolorization process were calculated.
• Toxicity of laccase-treated dye was decreased.

The fungal laccase isolated from Paraconiothyrium variabile was applied to optimize the enzymatic decolorization and detoxification of the azo dye reactive orange 7 using response surface methodology. Initial screening using fractional factorial design was carried out to select important independent variables that significantly affect the yield of decolorization including enzyme activity, pH, and incubation time. Optimum condition for maximal dye decolorization obtained by central composite design and surface plots were laccase activity 1.25 U/mL, pH 6.0, and incubation time 12.5 min. In addition, the kinetic and energetic parameters for enzymatic decolorization of reactive orange 7 were studied and the calculated values for Km, Vmax, Ea, ΔH, and ΔS were 1.14 mM, 283.28 mM/min.mg, 40 kJ/mol, 89 kJ/mol, and 285 J/mol.K, respectively. Decolorization is endothermic and spontaneous at temperatures higher than 37.8 °C. Microtoxicity evaluation demonstrated a decrease in toxicity of the laccase-treated dye in comparison with the parent dye.

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