Adsorption Performance and Mechanism of Waste Myriophyllum aquaticum Biochar for Malachite Green in Wastewater: Batch and Column Studies

The indiscriminate discharge of common dyes, such as malachite green (MG), poses significant risks to water quality and human health. To address this issue, a biochar (MBC) was synthesized from waste Myriophyllum aquaticum biomass (MAB) and further activated with KOH to produce micro-mesoporous biochar (KMBC) with enhanced adsorption efficiency. Characterization results demonstrated that KMBC exhibits a higher specific surface area (1632.7 m2/g) and a larger pore volume (0.759 cm3/g) compared to MBC. Batch adsorption experiments revealed that the adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm model, with the theoretical maximum adsorption capacities of MBC and KMBC reaching 1772.3 mg/g and 2570.7 mg/g, respectively and the adsorption is a spontaneous, endothermic, and entropy-driven process. Key mechanisms involved in the adsorption process include hydrogen bonding, hydrophobic interactions, and surface complexation. Due to electrostatic attraction, selective adsorption experiments confirmed that MBC can effectively separate cationic dyes such as MG from mixed anionic-cationic systems. Dynamic experiments showed that the breakthrough curve data fit well with the Thomas model. In summary, MAB-derived biochar demonstrates significant potential for practical applications in the treatment of MG-contaminated wastewater.