Application of activated carbon-immobilized laccase for tetracycline degradation

Abstract

Tetracycline (TC) antibiotics have been widely used in aquaculture and medical industries owing to their low cost, high efficiency, and broad-spectrum characteristics. However, it is difficult to degrade naturally in the environment, leading to its large accumulation in wastewater. The enzymatic degradation method using laccase exhibits good application potential in TC removal. In this study, low-cost activated carbon (AC) was used as the carrier to immobilize laccase using the adsorption–cross-linking method, forming Laccase@AC, characterized by high efficiency, eco-friendliness, and cost-effectiveness. Laccase@AC was used to treat TC-contaminated water. Its stabilities and catalytic activity for TC were comprehensively investigated. The results showed that Laccase@AC exhibited high enzyme loading capacity (407.97 mg/g), activity retention (1.36 U/mg), and stabilities. Moreover, Laccase@AC exhibited a higher TC removal efficiency than free laccase. The removal rates of 20 mg/L of TC using Laccase@AC were 78.7 % and 99 % after 6 h and 24 h, respectively, in the presence of a mediator (syringaldehyde, SA), whereas only 14.9 % of TC was removed using the same amount of free laccase. Temperature and TC concentration affected the performance of Laccase@AC. The TC optimal removal rate was achieved at 40–60℃ using 1 mg of Laccase@AC per 15 mg TC. Degradation product analysis revealed that catalytic oxidation was the main reaction catalyzed by laccase and enhanced by SA. The AC provided a stable reaction substrate and enhanced adsorption capacity. Meanwhile, the biocatalytic system effectively degraded TC and produced downstream products with low toxicity, demonstrating its potential for treating antibiotic wastewater using immobilized laccase. Therefore, immobilized laccase is an efficient biocatalyzer for eliminating TC in wastewater, and it has a broad application prospect in the treatment of antibiotic-contaminated wastewater. • Laccase@AC exhibited high enzyme loading capacity (407.97 mg/g), activity retention (1.36 U/mg), and stabilities. • The tetracycline removal rate of Laccase@AC with syringaldehyde mediation reached 78.7 % within 6 h and 99 % after 24 h. • The biocatalytic system effectively degraded tetracycline and generated downstream products with low toxicity.

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