Adsorptive removal of methylene blue using water hyacinth roots: batch and column adsorption, kinetics, isotherm and ANN–GA modeling, scale-up, phytotoxicity, and disposal pathways

Methylene Blue (MB), a widely used cationic dye, is of particular concern due to its persistence and adverse effects on ecosystems and human health. This study used batch and fixed-bed column adsorption studies to evaluate dried water hyacinth roots as an environmentally benign, affordable, and sustainable adsorbent for MB removal. The effects of operating parameters on MB adsorption were systematically investigated in batch experiments. Under optimized conditions (pH 6, 0.2 g dose, 90 min contact time), a maximum extraction efficiency of 96.5% was achieved. The pseudo-second-order model best describes the adsorption process. At the same time, isotherm analysis confirmed multilayer adsorption with a maximum capacity of 154.54 mgg−1 as predicted by the Freundlich model. Column experiments were conducted to evaluate continuous adsorption performance. Kinetic models, including Thomas, Yoon–Nelson, and Bohart-Adams, were utilized, with the Thomas model (R2 = 0.96) showing the strongest agreement with experimental data. A Genetic Algorithm (GA) was employed to accurately predict adsorption performance. Phytotoxicity tests of the treated effluent confirmed reduced toxicity, underscoring the environmental safety of the process. Overall, the findings establish water hyacinth root as a promising green adsorbent for the remediation of industrial dyes, with clear potential for scale-up.