Removal of sulfamethoxazole and trimethoprim from water using phosphoric acid-activated corncob biochar

The pseudo-persistence of antibiotics like sulfamethoxazole (SMX) and trimethoprim (TMP) in aquatic environments poses a growing threat to ecosystems and human health due to the increasing prevalence of antimicrobial resistance. This study evaluated the removal of SMX and TMP from water using corncob-activated biochar (CB700) synthesized via phosphoric acid activation and pyrolysis at 700 °C. Batch adsorption experiments evaluated the effects of contact time, pH, dosage, initial concentration, and temperature, while kinetic and isotherm models elucidated adsorption mechanisms. CB700 achieved maximum removal efficiencies of 82.51% for SMX and 87.7% for TMP at 1 mg L^-1, with dosages of 6 g L^-1 and 4 g L^-1 and contact times of 20 min and 40 min, respectively, corresponding to adsorption capacities of 0.12 mg g^-1 for SMX and 0.15 mg g^-1 for TMP. Unlike most previous studies, this study is among the few to utilize corncob biochar for SMX and TMP removal at environmentally relevant concentrations (0-6 mg L^-1). Adsorption was pH-dependent, indicating that electrostatic interactions and hydrogen bonding governed the process. In contrast, temperature (20-40 °C) had a negligible influence on adsorption performance. Kinetic data fitted pseudo-first-order and pseudo-second-order models, indicating both physisorption and chemisorption. Isotherm analysis aligned with the Dubinin-Radushkevich, Freundlich, and Temkin models, suggesting multilayer adsorption on a heterogeneous surface with pore filling. These findings highlight CB700's potential as an effective adsorbent for antibiotic removal in water treatment. However, its effectiveness in actual wastewater may be limited by competition with coexisting contaminants. Future research should evaluate its performance in complex wastewater matrices.