Vetiver biochar application for heavy metal sequestration in water treatment: bridging perfumery waste and environmental sustainability

Abstract

Converting industrial byproducts into functional adsorbents supports circular and sustainable approaches to water treatment. This study evaluated biochar derived from spent vetiver ( Chrysopogon zizanioides ) roots, a byproduct of the perfumery essential-oil industry, for the competitive adsorption of copper (Cu), cadmium (Cd), zinc (Zn), and lead (Pb). Vetiver root biochar produced at 500 °C for 60 min exhibited a high surface area of 308.2 m 2 /g and a yield of 53.8%. Batch adsorption experiments were performed in triplicate at a pH of 5.5 ± 0.2, in 0.1 M NaNO 3 , at 24 °C ± 2 °C, using 1% (w/v) biochar (10 g/L), with initial metal concentrations of 100 mg/L for each metal, along with a control. After 24 h, removal efficiencies reached 100% for Pb, 99.9% for Cu, 92.6% for Zn, and 77.0% for Cd. Adsorption was rapid, with nearly complete removal of Pb and Cu and approximately 60% removal of Zn and Cd within the first 30 min. High maximum adsorption capacities were achieved particularly for Pb, along with other tested metals, although competition in multi-metal systems influenced adsorption performance. Adsorption edge analysis and surface complexation modeling indicated that chemisorption was the dominant removal mechanism, supporting strong metal retention under the tested extraction conditions. Mild extraction released <3.5% of adsorbed metal, and TCLP/SPLP leachates were below U.S. EPA thresholds. Overall, these findings demonstrate that spent vetiver roots can be converted into high-performance biochar adsorbents, offering a sustainable, value-added strategy for heavy-metal remediation in water treatment systems.