Sustainable recycling of spent grain for laccase immobilization as dyes removal tool

Laccase from white-rot fungi was immobilized onto delignified spent grain by the H2SO4/NaOH digestion. Characteristics of biocatalyst were evaluated by scanning electronic microscope and by kinetic parameters (Km and V-max) after the optimization of immobilization conditions (pH 3, 4 degrees C, 24 h and the ratio of initial activity laccase on support 0.2 U/mg). The biocatalyst was used in batch and with recirculation for the decolourization of three dyes: methyl orange (15 mg/L), murexide (50 mg/L) and methylene blue (10 mg/L) at pH 5 and 30 degrees C. The decolourization rate was accelerated when 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonicacid)dia-mmoniumsalt mediator was added to the mixture. Our results showed that the immobilized laccase on delignified spent grain, a by-product of the brewing industry, could be efficiently used for the removal of synthetic dyes from industrial effluents and could be an appealing alternative to conventional treatments.