Evaluation of Green Waste and Popular Twigs Biochar Produced at Different Pyrolysis Temperatures for Remediation of Heavy Metals Contaminated Soil

摘要

Remediation of heavy metals contaminated soil through biochar addition depends upon the characteristics of biochar. Feedstock and pyrolysis temperature used for biochar production are the main factors that influence the properties of biochar important for metals immobilization in soil. In this study, immobilization of the most prevalent heavy metals [(lead (Pb (II)), cadmium (Cd) and chromium (Cr)] by green waste and popular twigs biochar produced at different pyrolysis temperatures (low 350°C and high 650°C), has been investigated, following the determination of physical and chemical properties of biochar. Soil was spiked with Pb, Cd and Cr and then amended with different biochar types in an incubation experiment. Soil chemical properties and available concentration of metals were measured at three incubation durations (0, 45 and 90 days). Biochar produced from green waste at 350°C pyrolysis temperature had maximum concentration of oxygen-containing functional groups (0.38 meq g -1 ) and had maximum CEC (43.7 cmol c kg -1 ) as compared with all other biochars. However, fixed carbon content (69.8%) and surface area (309.58 m 2 g -1 ) was found maximum in the biochar produced at 650°C pyrolysis temperature from popular twigs and green waste, respectively. Available concentrations of all three heavy metals were significantly decreased with the passage of time after biochar addition as compared with control and the minimum available concentrations of metals (Pb 6.33 mg kg -1 , Cd 1.42 mg kg -1 and Cr 3.14 mg kg -1 ) were determined in the treatment where green waste biochar produced at 350°C pyrolysis temperature was added to soil after 90 days of incubation duration. Soil chemical properties was significantly improved after biochar addition, especially soil CEC which was found maximum (21.90 cmol c kg -1 ) in the treatment where green waste biochar produced at 350°C pyrolysis temperature was added to soil. We concluded that the addition of green waste biochar produced at low pyrolysis temperature (350°C) to heavy metals contaminated soil showed minimum available concentration of metals due to its better physicochemical characteristics and more oxygen-containing functional groups and by improving the soil chemical properties as compared with other biochars.