Ammonia pollution in the water environment poses significant risks and hazards to the environment and human health. This study explored efficient removal of ammonia nitrogen (NH4+-N) from water using millet shell biochar (MS-400) through static and dynamic column experiments. In static experiments, three factors were investigated using Box-Behnken design (BBD) method and it was found that MS-400 removed 95.07 % of NH4+-N under optimal adsorption conditions. Equilibrium data fitted well with the Freundlich isotherm (R2 = 0.990), while the pseudo-second-order model (R2 = 0.955) better described NH4+-N adsorption behavior, indicating chemisorption involving electron sharing and transfer between MS-400 and NH4+-N ions. In the dynamic column experiment, BBD was also applied, achieving a maximum NH4+-N adsorption rate of 78.02 % under optimal conditions. Moreover both the Thomas model and Yoon-Nelson model demonstrated excellent fitting performance, offering practical insights for industrial scale-up and production applications. Furthermore significant reductions in intensities for C-C/C-H, C=O, and -OH peaks were observed upon NH4+-N adsorption and direct hydrogen bonding between NH4+-N and oxygen-functional groups enhanced negatively charged sites for NH4+-N adsorption, suggesting electrostatic attraction, ion exchange and hydrogen bonding in the adsorption process. This study introduced MS-400 as a promising biosorbent for NH4+-N removal, providing a comprehensive analysis of NH4+-N adsorption behavior through static and dynamic column experiments. The findings offer practical guidance for operational applications.
