Abstract: The widespread presence of antibiotics in the environment poses a significant threat due to the development of antibiotic resistance, making the development of efficient and eco-friendly removal technologies a critical step in environmental management. As a major watermelon producer, China faces an urgent need for the effective treatment of watermelon rind, a type of kitchen waste. Utilizing watermelon rind as a raw material to produce biochar (WBC) through pyrolysis presents a promising solution.This study characterized the prepared biochar using scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area and pore size analysis (BET), and Fourier-transform infrared spectroscopy (FTIR). The influence of pH on adsorption performance was investigated, and adsorption behaviors were analyzed under both single-solute and multi-solute systems. The single-solute system examined the adsorption of trimethoprim (TMP), ciprofloxacin (CIP), enrofloxacin (ENO), and sulfamethoxazole (SMX), while the multi-solute system included additional pharmaceutical compounds, clozapine (CLZ), and carbamazepine (CBZ), to study competitive adsorption behaviors.Results indicated that pH significantly affected the adsorption efficiency of WBC. In the single-solute system, WBC showed the highest adsorption capacity for ENO, reaching 64.73 mg·g⁻¹. In the multi-solute system, WBC demonstrated varying adsorption capacities for different compounds, with most adsorption capacities decreasing compared to the single-solute system. This reduction was primarily attributed to the differences in molecular size, which influenced molecular diffusion. CLZ exhibited a competitive adsorption advantage in the multi-solute system, displaying a mixed mode of monolayer and multilayer adsorption, while the adsorption mode of TMP shifted compared to the single-solute system.Batch adsorption experiments and FTIR analysis revealed that hydrogen bonding was the dominant mechanism driving the adsorption of antibiotics onto WBC. The adsorption process was also influenced by electrostatic interactions, hydrophobic effects, hydrogen bonding, and π–π interactions.This study provides a comprehensive analysis of the removal efficiency and adsorption mechanisms of WBC for antibiotics and pharmaceuticals in water under both single-solute and multi-solute conditions, offering theoretical and practical insights for the application of biochar materials in environmental remediation.