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.
Industrialization and population growth have increased the emission and buildup of environmental heavy metals. These components' bioaccumulation as exposure have been related to a range of illnesses and cancer, and the mechanical and physical properties of soil are altered. The "Microbial Induced Calcite Precipitation" is an environmentally green, friend, and sustainable method. This review focused on the metal remediation technology's effects and how to make them sustainable and more environmentally friendly. Many bacteria produce urease, the bacillus is a more common type. Bacteria, with sizes ranging from 0.5 to 3.0µm, are the most common microbes found in soils. It is critical to examine the type of soil, Bacterial size, and size of pore throat. The calcium carbonate majority tends to coat the surface of soils with coarse particles in the state of the contact points in soils with particles smaller than bacterial size (heterogeneous and limited precipitation). The bacterial concentration appears to affect crystal shape, calcium carbonate formation, and the cementation effect of geomaterials. Calcite precipitation takes place most when the pH is between 7.5 and 9.5. Calcite is formed three times at 50°C, while the unconfined compressive strength is only 60% of that at 25°C. Calcium carbonate can be immobilized or formed into undissolved compounds by binding free ions to the calcium carbonate's surfaces, resulting in a form of non-toxic and chemically stable.
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