Reclaiming selenium from water using aluminum-modified biochar: Adsorption behaviors, mechanisms, and effects on growth of wheat seedlings

Although selenium is an essential nutrient, its contamination in water poses serious risks to human health and ecosystems. In this study, aluminum-modified bamboo biochar (Al-BC) was developed to reclaim Se(VI) from water. Compared to pristine biochar (BC), Al-BC had a larger specific surface area (176 m²/g) and pore volume (0.180 cm³/g). The modification, achieved by loading AlOOH and Al₂O₃ particles onto the surface, enabled Al-BC to achieve a maximum adsorption capacity of 37.6 mg/g for Se(VI) within 2 h and remove 99.6% of Se(VI) across a pH range of 3-10. The main adsorption mechanism of Se(VI) involved electrostatic attraction, forming outer-sphere complexes between Se(VI) and AlOOH sites on the biochar. The bioavailability of Se sorbed on the spent biochar (Al-BC-Se) was thus evaluated. It was discovered that Al-BC-Se successfully released Se(VI), which impacted the growth of wheat seedlings. The Se content reached 134 μg/g dry weight (DW) in wheat shoots and 638 μg/g DW in roots, significantly exceeding normal selenium content (<40 μg/g DW). By successfully applying the modified biochar to capture selenium from water through adsorption and then reusing it as an essential nutrient in soil, this study suggests the promising feasibility of the "removal-collection-reuse" approach for the circular economy of selenium in wastewater.