Sodium Alginate–Starch Composite Hydrogel Encapsulated Laccase–Tetracycline-Degrading Bacteria Synergistic System: Construction and Tetracycline Degradation Performance in Coastal Sediments

Aiming at the pain points of the multi-phase coexistence of tetracycline antibiotics in coastal marine sediments and the difficulty of efficient removal by traditional single remediation technologies, this study constructed an immobilized laccase–tetracycline-degrading bacteria synergistic remediation system using a sodium alginate–starch double-network hydrogel as the carrier. Through component ratio optimization, the optimal mass ratio of sodium alginate to starch was determined to be 1:1.5. The SA-S-4 hydrogel beads prepared under this condition exhibited excellent mechanical properties and adsorption performance, and could effectively encapsulate both laccase- and tetracycline-degrading bacteria. The results of coastal sediment remediation experiments showed that the hydrogel encapsulated laccase–tetracycline-degrading bacteria synergistic system (HLTB) could achieve a tetracycline removal efficiency of 63.16% within 10 days, which was significantly better than the pure adsorption group and the free laccase–functional bacterial group. The system exhibited favorable removal performance under relatively low-concentration and low-ambient-temperature conditions, and the optimal dosage of this system was determined to be 0.5 wt%. On the basis of UPLC-MS analysis, this study observed that the synergistic combination of laccase and functional bacteria facilitated extensive structural transformation of the tetracycline parent skeleton, with the formation of abundant low-molecular-weight intermediate products. This performance was associated with the cascade coordination between laccase catalysis and microbial intracellular metabolism, and presented a higher level of structural transformation than the single laccase system, which could effectively reduce the potential ecological risk of tetracycline degradation intermediates. This study provides new technical ideas and theoretical support for the in situ green remediation of tetracycline pollution in coastal sediments.