[Adsorption of Mn²⁺ by Modified Biochar Fixed Bed in Simulated Lakes and Reservoir Waters]

Lakes and reservoirs are important water resources for human survival and sustainable development. The seasonal excess of manganese ions (Mn²⁺) in drinking water in lakes and reservoirs has become an important factor threatening human life in health and social safety in production. Firstly, a batch study of NaOH-modified biochar was carried out. The effects of pyrolysis temperature (400, 500, and 600℃) and modification conditions (unmodified, pre-alkali modified, and post-alkali modified) on the adsorption performance of biochar were investigated. The results showed that the alkali pretreatment could improve the adsorption capacity of biochar, and the maximum adsorption capacity of the modified biochar obtained by alkali pretreatment at 400℃ was 41.06 mg·g^-1. Additionally, the dynamic adsorption characteristics of Mn²⁺in the application on the fixed bed were investigated. The results showed that the stronger the adsorption capacity of biochar in the batch experiment, the longer its breakthrough point (c/c₀=0.1) and saturation point (c/c₀=0.9) in the dynamic adsorption process. In addition, when the initial concentration of Mn²⁺ and the influent flow rate were increased, the breakthrough point of the fixed bed was shortened from 360 min to 160 min and 200 min, respectively, and the saturation point was shortened from 865 min to 700 min and 600 min, respectively. The Thomas model could better fit the adsorption process of the fixed bed, indicating that the removal of Mn²⁺ by biochar was also dominated by chemical adsorption. This outcome can provide theoretical guidance for actual operations.