Tetracyclines Removal from Aquaculture Effluents by Waste Mussel Shells After Thermal Modification

As a class of low-cost and broad-spectrum antibiotics in wide aquaculture use, residues of tetracyclines (TCs) are imperiling aquatic organisms and public health worldwide, leading to a high demand for TC removal from the aquaculture environment. In addition, considerable consumption of thick-shell mussels generates massive mussel shell waste, and their treatment has been an economic and environmental issue. Herein, a low-cost and high-efficiency mussel shells-based material was successfully prepared for TC removal by thermal modification of shell waste of Mytilus coruscus. Morphological and structural characterizations revealed the phase transformation of calcium carbonate to calcium oxide. The shell-based material calcined at 1050 °C (MC1050) yielded a Langmuir-fitted maximum removal capacity (q_m) of 68.0 mg/g towards oxytetracycline (OTC). Thermodynamic calculations indicate that OTC removal by MC1050 is a spontaneous and endothermic process. OTC removal by MC1050 is likely achieved via multiple co-existing pathways, where Ca-OTC co-precipitation driven by CaO-phase hydration and resultant high-pH conditions dominates, accompanied by auxiliary surface-interaction contributions. Furthermore, MC1050 achieves removal efficiencies exceeding 96% for the ten target TCs spiked at 20 μg/L in real-world freshwater and marine aquaculture effluent matrices. Overall, the developed shell-based material shows promising performance for wastewater treatment and facilitates the resource utilization of waste mussel shells.