Characteristics of Tetracycline Adsorption on Commercial Biochar from Synthetic and Real Wastewater in Batch and Continuous Operations: Study of Removal Mechanisms, Isotherms, Kinetics, Thermodynamics, and Desorption

Tetracycline (TC) is an antibiotic commonly used to treat bacterial infections. It is detected in wastewater and is considered an emerging contaminant that must be removed before discharge to water bodies. This study examined its adsorption on commercial biochar, a low-cost and sustainable adsorbent produced from the agricultural waste of citrus trees, in both batch and continuous flow systems and from synthetic and real wastewater. The surface area of the biochar was determined using Brunauer–Emmett–Teller (BET) analysis to be 364.903 m 2 /g. Batch experiments were conducted using biochar doses of 1.5–3.5 g/50 mL; initial TC concentrations of 30–90 mg/L; pH values of 4, 7, and 11; and temperatures of 20, 30, and 40 °C. The results show that TC was successfully removed from both synthetic and real wastewater at removal rates reaching 87% at pH = 4, an adsorbent dose of 3.5 g/50 mL, an initial adsorbate concentration of 90 mg/L, and a temperature of 20 °C in batch experiments for synthetic wastewater and at removal rates reaching 95% for real wastewater. Thermodynamic parameter estimation results revealed that the process is exothermic and spontaneous, while kinetic results showed that adsorption is a multi-step process. TC adsorption on biochar was found to be a physical process. In continuous-mode operation, removal reached 37% at a bed depth of 3 cm. Scanning electron microscopy (SEM) morphologies and Fourier-transform infrared (FTIR) spectroscopy confirmed the occurrence of adsorption.