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Keywords:

  • estrogens;
  • dye;
  • enzyme immobilization;
  • laccase;
  • sol–gel;
  • encapsulation

Abstract

Laccase from Myceliophthora thermophila was immobilized by encapsulation in a sol–gel matrix based on methyltrimethoxysilane and tetramethoxysilane. The amount of laccase used for the preparation of the hydrogel was in the range 2.2–22 mg of protein/mL sol and the corresponding enzymatic activities were in the range 5.5–17.0 U/g biocatalyst. The kinetic parameters of the encapsulated laccase showed that the immobilized enzyme presented lower affinity for the substrate 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS). However, the stability of laccase was significantly enhanced after immobilization; thus, both pH and thermal stability improved about 10–30% and tolerance to different inactivating agents (NaN3, ZnCl2, CoCl2, CaCl2, methanol, and acetone) was 20–40% higher. The reusability of the immobilized laccase was demonstrated in the oxidation of ABTS for several consecutive cycles, preserving 80% of the initial laccase activity after 10 cycles. The feasibility of the immobilized biocatalyst was tested for the continuous elimination of Acid Green 27 dye as a model compound in a packed-bed reactor (PBR). Removals of 70, 58, 57, and 55% were achieved after four consecutive cycles with limited adsorption on the support: only 10–15%. Finally, both batch stirred tank reactor (BSTR) operated in several cycles and PBR, containing the solid biocatalyst were applied for the treatment of a solution containing the endocrine disrupting chemicals (EDCs): estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2). Eliminations of EDCs in the BSTR were higher than 85% and the reusability of the biocatalyst for the degradation of those estrogens was demonstrated. In the continuous operation of the PBR, E1 was degraded by 55% and E2 and EE2 were removed up to 75 and 60%, at steady-state conditions. In addition, a 63% decrease in estrogenic activity was detected. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011