Construction of a continuous packed bed laccase reactor for the elimination of tetracyclines in seawater

Tetracycline antibiotics (TCs) are extensively present in the marine environment and have adverse effects on human health and aquatic ecosystems. Laccases are a type of green biocatalyst for TCs degradation. In this study, a continuous packed bed reactor based on the immobilized modified laccase was constructed to degrade TCs at environmentally relevant levels in seawater. Results showed that the chemical modification and immobilization of laccase had a synergistic effect on its activity and stability in seawater: after incubation in seawater for 12 h, the residual activity of free laccase was only 22.3%, while that of the immobilized modified laccase (A/PhA-Lac) was 79.3%. A laccase reactor was constructed based on A/PhA-Lac, and the response surface regression model was established to optimize the laccase reactor operating conditions. The laccase reactor under optimal conditions could continuously degrade TCs (5 μg/L each) in seawater within 10 h and reach the highest removal rate at 4 to 5 h (removal rates of tetracycline, oxytetracycline, and chlorotetracycline were 94.7%, 86.6% and 98.0%, respectively). The luminescent bacteria microtoxicity and seawater microbial community analysis revealed that the laccase reactor significantly mitigated the toxicity of TCs in seawater. This study provided an environmentally friendly and effective method for the elimination of antibiotics in seawater.