Use of local waste for biochar production: Influence of feedstock and pyrolysis temperature on chromium removal from aqueous solutions.

Sediment enrichment with biochar, a high‐carbon material produced by the pyrolysis of biomass, is a promising remediation strategy for metal pollution. The metal immobilization capacity of biochar can be explained by its porous structure, surface functional groups, pH greater than 7, and cation exchange capacity. However, the effectiveness in reducing metal bioavailability depends on the physicochemical characteristics of the biochar, which are strongly associated with the process conditions and feedstock. The aims of this study were to analyze the effect of pyrolysis temperature on the properties of biochars derived from different locally available biomass materials, biochar potential to adsorb Cr, and biochar phytotoxicity in seed germination. Poultry litter (PL), maize straw, the macrophyte Juncus imbricatus, and phytoremediation wastes from the macrophyte previously exposed to Cr were pyrolyzed into biochar at 300 °C and 600 °C. The properties and capacity of biochar to remove Cr from the aqueous phase were determined. Finally, a germination assay was performed to evaluate biochar phytotoxicity. Biochar yield decreased with increasing pyrolysis temperature, whereas ash content and pH increased. Biochar C content and total surface area increased with temperature. Biochar Cr removal capacity improved under the highest temperature, reaching a maximum sorption value of 13.7 mg g−1 Cr at 300 °C in PL biochar and of 42.6 mg g−1 Cr at 600 °C in J. imbricatus biochar. Despite the comparatively high metal content in the biochar, the germination indices of all biochars produced at 600 °C were higher than 80%, suggesting no phytotoxicity. Considering the metal sorption capacity and the phytotoxicity, biochars produced from J. imbricatus, PL, and phytoremediation residues at 600 °C were suitable for use in the removal of Cr from water. Integr Environ Assess Manag 2023;19:717–725. © 2022 SETAC Key Points: The sorption of Cr was more effective in biochars produced from lignin and cellulose‐rich biomass at 600 °C.The germination indices of Lactuca sativa seeds exposed to biochars produced at 600 °C were higher than 80%, suggesting no phytotoxicity.Juncus imbricatus plants used for phytoremediation could be recycled by their transformation into biochar for chromium immobilization and have a safe final disposal. [ABSTRACT FROM AUTHOR]