Preparation of sludge-based biochar and its adsorption performance on tetracycline
Freeman Madhau, Zhenjun Wu, Dongjin Wan, Zihao He, Qingwen Qin, Yanru Li, Rethabile Debra Moteletsana, Xin Chen, Zhisan Lin
Abstract
Municipal sludge (MS) presents significant potential for environmental remediation, energy production, and agricultural applications; however, its direct utilization is constrained by various contaminants. Pyrolysis provides a viable solution, converting MS into valuable products like municipal sludge biochar (MSBC). This study investigates MSBC produced at 500 °C, 700 °C, and 900 °C (MSBC 500, MSBC 700, and MSBC 900) for removing tetracycline (TC) from wastewater. Adsorption performance was evaluated under varying pH, contact time, dosage, initial TC concentration, temperature, and ionic strength. The physicochemical characteristics of MSBC were thoroughly characterized, revealing a highly developed porous structure, rich in functional groups and distinct crystalline phases. Raman spectroscopy analysis demonstrated that MSBC 900 had the lowest I D /I G ratio compared to MSBC 500 and MSBC 700, indicating a higher degree of graphitization. Adsorption thermodynamics indicated that TC adsorption onto MSBC was spontaneous and endothermic, while the kinetic data followed the pseudo-second-order model. The highest equilibrium removal capacities for MSBC 500, MSBC 700, and MSBC 900 were 31.31 mg/g, 42.44 mg/g, and 48.33 mg/g, respectively. However, the presence of Mg 2 ⁺ (0–1.0 mol/L) significantly hindered TC adsorption, highlighting the impact of competing ions on removal efficiency. MSBC 900 exhibited excellent regeneration performance, retaining over 90% of its removal capacity after five regeneration cycles. These findings highlight MSBC, particularly MSBC 900, as a sustainable adsorbent for removing antibiotics in wastewater.