Effect of biochar on heavy metal immobilization in contaminated soil

Soil contamination by potentially toxic metals is a serious environmental problem faced worldwide, hence sustainable and effective amendment methods are required. Biochar is a carbon material with a multitude of functionalities that have attracted wide research interest and application in soil amendment for toxic metal immobilization. In this study biochar produced at 550°C from spent growing media with and without 2.5% plastic grow bag (BCP and BC) were used in a 3month laboratory incubation study to assess their effect at two rates (2% and 4%w/w) on Cd and Zn bioavailability, dehydrogenase activity (DHA) and microbial biomass carbon (MBC) in contaminated soil. Both BC and BCP contained aromatic C, O-containing functional groups, mineral ash, organic compounds, and alkaline pH. BCP contained more surface functional groups, VM, FC, and 36% more organic compounds in abundance compared to BC. However, BC was highly aromatic (H/C=0.39) with a higher pH and ash content compared to BCP. Results revealed BC significantly increased soil pH and EC (p<0.01), especially at 4% application rate. Biochar applied at 4% had the greatest reduction in CaCl2 extractable Cd and Zn, with the highest reduction efficiency of 92.3% and 96% respectively obtained in 4BC amended soil. CaCl2 extractable Cd and Zn were significant and negatively correlated to pH (p