PFOA adsorption onto biochar derived from invasive water hyacinth

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals widely used in consumer products, firefighting foams, and various industrial applications. These chemicals are pervasive, persistent, and degradation-resistant, posing a critical threat to human and environmental health. Currently, adsorption remains the most widely used technology for the remediation of PFAS. However, large-scale PFAS removal would require extensive usage of adsorbents such as activated carbon, which tends to be relatively expensive. Therefore, we investigated the upcycling of water hyacinth, an invasive aquatic plant, as a sustainable source for biochar production to remove perfluorooctanoic acid (PFOA), a type of PFAS. Different kinetic and isotherm models assessed PFOA adsorption to water hyacinth biochar. Pseudo-second-order kinetics and Langmuir isotherm models proved to be better fits in most experiments. Intra-particle diffusion and surface adsorption were determined to contribute to the rate-limiting step, and a monolayer distribution of PFOA through chemisorption was found to be the primary mechanism of adsorption. Water hyacinth biochar exhibited an adsorption capacity of 154.39 μg/g for PFOA removal at a solid-to-liquid ratio of 1 (in mg/mL). Experiments at different pH levels revealed that electrostatic interactions influenced PFOA adsorption, and, in acidic conditions, the removal capacity increased to 164.91 μg/g.