A novel process for the covalent immobilization of laccases on silica gel and its application for the elimination of pharmaceutical micropollutants

In the present work, pharmaceutical micropollutant degradation by laccase immobilized on silica through an innovative process is proposed. The influence of different parameters on the immobilization conditions was evaluated by a 2(3) full factorial design, and parameters leading to the highest activity were identified. Under these conditions, laccase activity reached 14 +/- 2 U g(-1) of silica with a protein immobilization yield of 35%. The biocatalyst characterization did not show any change in pH and thermal stabilities but enhanced the long-term storage of laccases. Immobilized T. versicolor laccases were then tested to remove four pharmaceutical micropollutants (amoxicillin, ciprofloxacin, carbamazepine, and sulfamethoxazole) in the presence of redox mediators (syringaldehyde, p-coumaric acid, and ABTS). High removal yields (50-100% according to the pollutant) were obtained within 4 h of treatment due to the synergistic effect of laccase-mediator biotransformation and adsorption on the support. Overall, the pharmaceuticals' removal efficiency was highly influenced by their physicochemical properties; however, the presence of redox mediators impacted not only the oxidation mechanism but also the interactions between the biocatalyst and micropollutants. Finally, the reusability of the biocatalyst was proved during 7 degradation cycles.

Automated summary

The study proposed a novel process of degrading pharmaceutical micropollutants using laccase immobilized on silica, achieving high removal yields of four pharmaceutical micropollutants within 4 hours under specific conditions. The removal efficiency was influenced by the physicochemical properties of the pollutants, and the presence of redox mediators impacted the oxidation mechanism and interactions between the biocatalyst and micropollutants. The reusability of the biocatalyst was demonstrated during 7 degradation cycles.