Enhancing sulfonamide removal from water using wood biochar: Adsorption mechanisms and regeneration potential

Background The improper release of sulfonamides (SAs) into the environment poses significant health and ecological risks. Methods Biochar was produced from poplar wood chips at three pyrolysis temperatures (350 °C, 500 °C, and 650 °C) to investigate its characteristics and adsorption mechanism for SAs and to evaluate a suitable method for regenerating spent biochar. Significant Findings Rising the pyrolysis temperature increased the aromaticity of biochar, leading to greater volatile release, which subsequently enhanced pore formation and expanded the specific surface area at temperatures exceeding 500 °C. Thermodynamic calculations revealed that the adsorption process was spontaneous (ΔG < 0) and exothermic (ΔH < 0). The decreasing affinity of biochar for sulfonamides follows the order: sulfapyridine (SPD) > sulfamethoxazole (SMZ) > sulfadiazine (SDZ). This trend can be attributed to the functional groups with higher pK a2 (SPD), which are more likely to form negative charge-assisted hydrogen bonds ((-)CAHBs) due to their stronger cohesive interactions with the O- and N- functional groups in biochar. After the first and second regeneration cycles using water, 78.5 % and 58.6 % of the adsorption capacity of the spent BC650 for SPD was restored, respectively. This study introduces a waste-to-resource approach for the utilization of forest waste to address the issue of pharmaceutical contaminants in water.