Removal of dyes by Trametes versicolor laccase immobilized on NaY-zeolite

Abstract

In the present study, the immobilization of Trametes versicolor laccase (TvLac) was optimized on the synthesized NaY-zeolite by experimental of design. For this purpose, the central composite design was employed to study the effects of the immobilization parameters on the activity of the immobilized TvLac on the NaY-zeolite. The optimum conditions were occurred at 2.5 mg/mL of NaY-zeolite concentration, 1 U/mg of enzyme concentration, 1 mM of glutaraldehyde concentration for 4 h immobilization time at 4 °C. In these conditions, the laccase activity developed to 15.68 ± 0.56 U/mg, which was very close to the predicted amount (16.09 ± 1.6 U/mg). Generally, the immobilized TvLac showed stability higher than that of the free TvLac at the different temperatures and pHs. The activity of the immobilized TvLac on the NaY-zeolite was 88.2% and 98.3% after incubation for 120 min at 60 °C and pH 5, respectively. Moreover, the free TvLac and immobilized TvLac on NaY-zeolite retained about 54.2% and 78.3% of its initial activity after 15 days of storage. The immobilized TvLac lost near 20% of its initial activity after 5 cycles of uses. The immobilized TvLac exhibited higher efficiency (93.0 ± 1.7% and 80.3 ± 1.8%, respectively) in removal of bromothymol blue (BTB) and trypan blue compared with the free TvLac (23.7 ± 1.8% and 15.1 ± 1.5%, respectively). Meanwhile, the kinetic parameters (Km and Vmax) for immobilized TvLac were 0.07 µM and 1.38 µmol/min, respectively, for removal of BTB. Therefore, the immobilized TvLac as a good candidate could be suggested for the elimination of dye-containing pollutants due to its high efficiency (more than 80%), which requires further investigations.