Effect of microbial-induced calcite precipitation (MICP) on the strength of soil contaminated with lead nitrate

Abstract

Abstract Microbial induced calcite precipitation method MICP is a sustainable and eco-friendly technique for soil stabilization. To show the optimum effectiveness of the bioremediation within the silty sand matrix, a model of plastic boxes and PVC molds was made with an air pump placed in an isolated room at a temperature range of 25–27°C. The molds were perforated from sides and bottoms and opened from the top with a transparent film of filter paper (placed on the inner surface). The major feature of this treatment system is allowing the cementation solution to penetrate easily into soil samples. The results showed a positive effect of Bacillus subtilis in enhancing the strength properties of lead contaminated soil. Unconfined compressive strength increased from 65 kPa to 539, 527, and 525 kPa. Cohesion increased from 4.5 to 40, 41.9, and 42 kPa at concentrations of 15, 20, and 25% respectively. Angle of internal friction increased from 18.94° to 38.2°, 40°, and 40.74° respectively after 14 days. Thereafter, it become 40.92° and 41.5° at concentrations of 15 and 20%, respectively and decreased to 36.75° of 25% at 28 days. Microstructural characteristics represent the formation of calcium carbonate and lead compounds, which were the reasons for the improvement in the strength and the alteration in lead from a soluble to insoluble form, a hence less toxic element.