Covalent Immobilization of Laccase onto Nanofibrous Membrane for Degradation of Pharmaceutical Residues in Water

Enzymatic degradation with ligninolytic enzyme, e.g., laccase, is a potential green solution for removal of pharmaceutical compounds that are released into the environment through wastewater effluent. However, the deficiencies of using the enzyme in its free forms, such as reusability and stability, should be addressed before industrial applications. In this study, laccase was immobilized onto tailor-made polyacrylonitrile–biochar composite nanofibrous membrane through covalent bonding, and the parameters of immobilization were optimized. The obtained biocatalyst was utilized for removal of chlortetracycline (CTC), carbamazepine (CBZ), and diclofenac (DCF) at an environmentally relevant concentration in batch mode. These pharmaceutical compounds represented three main categories of pharmaceutical compounds, i.e., antibiotics, antidepressant, and anti-inflammatory. The results showed that the immobilized laccase has improved storage, temperature, and pH stability compared to free laccase. Also, it maintained more than 17% of its initial activity after 10 cycles of ABTS oxidation which indicated improved reusability of the enzyme. Using immobilized laccase for degradation, three pharmaceutical compounds in batch experiments exhibited 72.7%, 63.3%, and 48.6% degradation efficiency for DCF, CTC, and CBZ, respectively, after 8 h of reaction. The decreasing trend of adsorption extent during reaction time for all compounds confirmed the regenerative effect of laccase on adsorption sites of biochar.