Screening of Calcite Precipitation Inducing Bacillus Strains from Different Geologic Sources for Bio-Mediated Lateritic Soil Improvement

Bio-cementation is a new approach used in the stabilization of soil, in which eco-friendly microorganisms are manipulated to improve the geotechnical properties of soil. This study focused on screening for Bacillus strains with the highest induced calcite precipitation potential from different geologic sources. Thirty-two Bacillus strains were screened for urease, an enzyme which initiates calcite precipitation and six strains were observed to produce urease enzyme reasonably. Bacillus sp-CE11 had the highest urease enzyme production. Bacillus strains with a significant amount of urease enzyme production were employed forthe bio-cementation process using lateritic soil. The Unconfined Compressive Strength property shows that the soil samples treated with urease producing strains (UPS) had more strength compared with the untreated lateritic soil sample (control). Bacillus mycoides-CE8 at pH 7 had the highest UCS value (329.6 kPa) and the least coefficient of permeability (1.01x10-7 cm/s) while Bacillus subtilis- KA71 had the least UCS value (223.9 kPa) at pH 7. The Highest coefficient of permeability (8.92×10-7 cm/s) at pH 6 was observed in the soil specimen treated with Bacillus subtilis-KA7. Bacillus strains isolated from Celica soil sample were found to induce calcite precipitation more than other strains from other soil samples. Hence, the best isolate (Bacillus mycoides) has the capacity of calcite production. It provides basic geotechnical characteristics and specifications for the bio-cementation of tropical lateritic soil.