USING VETIVER BIOCHAR TO ADSORB LEAD

Lead (Pb)-based paint was extensively used to paint buildings until it was banned in 1978. This has created a major environmental health risk because of weathering and chipping of paint results in soil contamination with Pb. Soil Pb poses a significant risk to people, particularly children, living in surrounding areas. Ex-situ Pb treatment by soil disposal is the usual practice, which is highly expensive and causes ecological disruptions. In comparison, in-situ extraction is more realistic for Pb pollution control in residential properties. Biochar has been utilized in the soil for multiple purposes, such as carbon sequestration, water retention, and nutrient uptake. Its adsorptive nature also makes it a potential candidate for heavy metal retention in contaminated soil. Vetiver grass is used extensively for phytoremediation, slope stabilization, and as a wind break in agricultural systems primarily because of its dense and extensive root network, and tolerance of various contaminants. The waste vetiver biomass could be used sustainably to generate biochar. As a waste-to-resource process, biochar production from vetiver under different pyrolysis conditions usually leads to different physicochemical properties of biochar, which affects its functions. This study focused on the remediation of Pb in soil by biochar generated from vetiver grass at various pyrolysis conditions (i.e., pyrolysis at 300, 500, and 750˚C for 60 mins). Both shoots and roots of vetiver grass were tested in the experiment. Results showed that biochar yield from the shoots (12-23%) was much lower than that from roots (32-56%). Similarly, the BET (Brunauer-Emmett-Teller) specific surface area of the shoot biochar was in the range of 1-6 m²/g, which is significantly lower compared to those of the root biochar (24-308 m²/g). The adsorption isotherm studies with Pb(NO₃)₂ as the Pb source at concentrations from 2 to 32 mg/L indicated that Langmuir isotherm could more accurately represent the adsorption pattern of Pb by biochar, compared to the Freundlich isotherm. The adsorption capacity of biochars increased with an increase in pyrolysis temperatures, indicating that high-temperature pyrolysis might produce biochars with a high capacity for Pb retention.