Immobilization of laccase on grape seed-derived hydrochar and biochar as sustainable biocatalysts for efficient pharmaceutical degradation in real wastewater

Abstract

Pharmaceutical active compounds pose a serious global threat due to their continuous release into aquatic systems. This study explores an innovative approach for the degradation of acetaminophen (APAP), sulfamethoxazole (SMX) and tetracycline (TC) by the covalent immobilization of crude laccase from Lentinus sajor-caju on grape seed-derived biochar (GS-BC-Lac) and hydrochar (GS-HC-Lac). Characterization through Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) confirmed the successful covalent immobilization of laccase. The immobilized enzyme retained nearly 90% of its activity after 30 days and exhibited high degradation efficiency toward pharmaceutical compounds. Complete removal of APAP was achieved in just 30min using GS-HC-Lac and 90min with GS-BC-Lac, both assisted by syringaldehyde (SYR) as a redox mediator at pH 5.0. Under the same conditions, SMX was efficiently degraded within 30min, whereas TC required 5h to reach comparable degradation levels. The biocatalysts maintained high SMX degradation efficiency over eight reuse cycles and demonstrated consistent performance even in wastewater matrices. Additionally, degradation pathways involving different transformation products were proposed, highlighting key oxidative and coupling reactions. Hence, covalently immobilized laccase on GS-BC and GS-HC proved to be efficient biocatalysts for the degradation of pharmaceuticals in wastewater, offering promising potential for environmental remediation and industrial-scale applications.