Molecular dynamics simulation of realistic biochar models with controlled porosity

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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<0.01). DHA was strongly inhibited in biochar amended soils by 82%-96% in the order 4BC˃˃2BC˃2BCP˃4BCP. MBC was enhanced by 84% and 82.2% in 2BC and 4BCP treated soils respectively, while 2BCP did not affect, and 4BC slightly reduced MBC in soil by 22%. Biochar surface O-containing functional groups, mineral content, and alkaline pH could have contributed to Cd and Zn immobilization by electrostatic attraction, surface complexation, and precipitation. The impact of biochar on heavy metal immobilization, enzyme activity, and microbial biomass carbon varied with biochar type and application rate. Biochar pH, organic matter, and surface functional groups are important parameters to evaluate when considering biochar for soil applications