Remediation of Chromium (VI) from Contaminated Agricultural Soil Using Modified Biochars

Chromium (Cr) is a potentially toxic metal occurring in the soil as a result of natural and anthropogenic activities and is mainly found in Cr³⁺ and Cr⁶⁺. The hexavalent chromium has toxic effects on plants, animals, humans and microorganisms depending on exposure level, duration and doses. Biochar is a stable carbon-based material that has been widely documented to immobilize metals in contaminated soils and for soil remediation effectively. The present 90 days incubation study was conducted to investigate the potential use of rice stubble and sawdust-derived modified biochars on Cr⁶⁺ remediation and their effects on nutrient availability. Among the treatments, modified rice stubble biochar (RSB-M) contained the highest surface area, pore volume and CEC. The unmodified and modified biochars significantly increased soil pH, EC, CEC, and N, K availability ((p < 0.001)). Statistical analysis showed that modified rice stubble (RSB-M) and sawdust biochars (SDB-M) significantly reduced the Cr⁶⁺ with incubation days compared to unmodified biochars, possibly due to the greater porous structure and various functional groups. The submerged incubation condition also greatly impacted Cr⁶⁺ reduction since a gradual decrease (up to ~70 mg kg-1 of Cr⁶⁺) was observed in control treatments. Therefore, applying modified biochars is imperative to alleviate Cr⁶⁺ polluted soils and improve soil fertility.