Application of laccase immobilized rice straw biochar for anthracene degradation

The present study explores the immobilization of ligninolytic enzyme-laccase on the surface of rice straw biochar and evaluates its application for anthracene biodegradation. The rice straw biochar was acid-treated to generate carboxyl functionality on its surface, followed by detailed morphological and chemical characterization. The surface area of functionalized biochar displayed a two-fold increase compared to the untreated biochar. Laccase was immobilized on functionalized biochar, and an immobilization yield of 66% was obtained. The immobilized enzyme demonstrated operational stability up to six cycles while retaining 40% of the initial activity. Laccase immobilization was further investigated by performing adsorption and kinetic studies, which revealed the highest immobilization concentration of 500 U g−1 at 25 °C. The adsorption followed the Langmuir isotherm model at equilibrium, and the kinetic study confirmed pseudo-second-order kinetics. The equilibrium rate constant (K2) at 25 °C and 4 °C were 3.6 × 10−3 g U−1 min−1 and 4 × 10−3 g U−1 min−1 respectively for 100 U g−1 of enzyme loading. This immobilized system was applied for anthracene degradation in the aqueous batch mode, which resulted in complete degradation of 50 mg L−1 anthracene within 24 h of interaction exposure. [Display omitted] •Laccase immobilized rice straw biochar for anthracene biodegradation.•Mixed acid-treatment of biochar resulted in high negative charge on it.•Immobilization increased enzyme stability and its reusability up to 6 cycles.•Immobilization followed Langmuir isotherm and pseudo-second-order kinetics. Summary: The study proposes valorization of abundant crop residue (rice straw) by immobilizing its biochar with laccase. The immobilized system has been shown to be very effective in the biodegradation of anthracene present in water.