Adsorption and regeneration on iron-activated biochar for removal of microcystin-LR

Novel iron activated biochars (FA-BCs) were prepared via simultaneous pyrolysis and activation of FeCl₃-pretreated bermudagrass (BG) for removing microcystin-LR (MC-LR) in aqueous solution. Compared to the raw BC (without activation), the surface area and adsorption capacity of FA-BC at iron impregnation ratio of 2 (2 g FeCl₃/g BG) were enhanced from 86 m²/g and 0.76 mg/g to 835 m²/g and 9.00 mg/g. Moreover, FA-BC possessed various iron oxides at its surface which provided the catalytic capacity for regeneration of MC-LR spent FA-BC and magnetic separation after the MC-LR adsorption. Possible mechanisms for the MC-LR adsorption onto FA-BC would include electrostatic attraction, π⁺-π, hydrogen bond, and hydrophobic interactions. The detailed adsorption studies indicated mainly chemisorption and intra-particle diffusion limitation would participate in the adsorption process. The thermal regeneration at 300 °C kept high regeneration efficiency (99-100%) for the MC-LR spent FA-BC during four cycles of adsorption-regeneration. In addition, the high regeneration efficiency (close to 100%) was also achieved by persulfate oxidation-driven regeneration. FA-BC also exhibited high adsorption capacity for the MC-LR from the real lake water to meet the MC-LR concentration below 1 μg/L as a safe guideline suggested by WHO.