Formulation and characterization of immobilized laccase biocatalysts and their application to eliminate endocrine disrupting chemicals

Nair, Rakesh [UCL] Demarche, Philippe [UCL] Agathos, Spiros N. [UCL]

Over the past decades, water pollution by trace organic compounds (ng L-1) has become a major societal issue of developed countries. To date there is no effective and sustainable remediation strategy available. Laccases from white rot fungi were found particularly suitable for the removal of micropollutants such as the plasticizer bisphenol A (BPA), the anti-inflammatory drug diclofenac (DF) and the steroidal hormone 17-α-ethinylestradiol (EE2). Laccase immobilization is a prerequisite for the enzyme’s application in continuous water treatment processes. In this study, laccase from Coriolopsis sp. was immobilized on mesoporous silica particles in a two-step adsorption-crosslinking procedure. The initial laccase activity, crosslinker (glutaraldehyde) concentration and extra-protein (albumin) concentration were varied following a central composite experimental design and optimized with respect to immobilization yield, biocatalyst activity and thermal stability. Immobilized biocatalyst particles were physically characterized by scanning electron microscopy, small angle X-ray diffraction and Brunauer-Emmett-Teller surface area analysis revealing modifications of the surface structure and area during immobilization. After a multi-objective optimization of biocatalyst formulation, a maximum biocatalyst activity of 383 U g-1 [determined with 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonate at pH 4.5] was obtained. The immobilized biocatalyst showed a significantly higher thermal stability than the free enzyme with a half life of 35 h and 10 h compared to 5.5 h and 0.43 h at 55 °C and 75 °C respectively. The immobilized biocatalyst was able to eliminate continuously more than 80 % of 10 μM BPA, 10 μM DF and 10 μM EE2 individually and in a mixture in a stirred membrane reactor for more than 72 h. This illustrates the great potential of the new biocatalyst for the treatment of aquatic micropollutants.