Short-Term Effect of Sewage Sludge Biochar on Availability and Fractionation of Pb in a Contaminated Calcareous Soil

Conversion of sewage sludge (SL) to biochar is one of the methods that can convert this material into a useful product in agriculture. Heavy metals are present in various forms in SL, which largely determine their bioavailability. Converting SL to biochar can alter the bioavailability of heavy metals. The aim of this study was to compare the effect of SL and its biochar on the availability and fractionation of lead (Pb) in a contaminated calcareous soil (100 mg.kg-1 pb as solution added to soil and incubate for 2 weeks).  This research was performed as a factorial experiment in a completely randomized design with three replications[H1] . After one week of incubation, EC and pH, soluble and available Pb, as well as Pb fractionations in the soil samples were studied by the Tessier method. The results showed that the EC of the soil increased in all treatments compared to the control. pH decreased in SL treatment (1.3% to 5.5%) and increased in biochar treatment at both temperatures[H2] . The highest increase was observed in the treatment of 4% B600 (5.97%). The total amount of Pb increased in all treatments, the available Pb in SL treatment increased (8.2% in 4% treatment) and decreased in biochars treatment (7.6% in 4% B600 treatment). Application of biochar compared to SL changed the fractionation of Pb from the bioavailability to more stable forms. The highest increase in Pb content compared to the control was bonded to the organic matter fraction (43.4% to 80.4%). The results of this research showed that, due to increased pH, specific surface area, or change in surface functional groups, biochar can re-distribute Pb fractions and reduce Pb availability in soil.