UV-modified biochar-Bacillus subtilis composite: An effective method for enhancing Cd(II) adsorption from water

The adsorption of Cd(Ⅱ) in sewage by single-modified biochar systems have limitations, whereas composite modification can enhance the efficiency. In this study, reed straw biochar and Bacillus subtilis were used as raw materials. UV radiation was employed to modify the biochar, and subsequently, Bacillus subtilis was loaded onto the biochar by adsorption, creating modified biochar composites. The Cd(II) adsorption performance and removal efficiency of these composites were then investigated. It was characterized by BET, SEM-EDS, FT-IR, XRD and ZETA potential analysis. Adsorption experiments were conducted under varying conditions (initial Cd(Ⅱ) concentration, UV radiation time, initial pH, etc.), with adsorption isotherms and kinetic models used. Results indicated that 24 hours UV radiation significantly enhanced adsorption performance, increasing the biochar’s surface area by 40 % and pore volume by 20 %, and introducing numerous pores and oxygen-containing functional groups to the biochar's surface. Significantly enhancing the saturation adsorption capacity for Cd(II) from 23.98 mg/g to 49.93 mg/g after UV- Modified biochar was loaded with Bacillus. Modified biochar composites performed better compared to single-modified biochar across different initial Cd(Ⅱ) concentrations, particularly in slightly alkaline environments. The primary adsorption mechanisms were chemical adsorption, such as ion exchange and surface precipitation. The synergistic effect of UV radiation and microbial loading significantly enhanced Cd(Ⅱ) adsorption efficiency. This study demonstrates that composite modification is a more efficient method, aiding in the removal of heavy metal ion Cd(Ⅱ) from water.