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Application of an indigenous bacterium in comparison with Sporosarcina pasteurii for improvement of fine granular soil

ABSTRACT

An indigenous non-spore-forming urease-positive bacterium, Staphylococcus pasteuri was isolated from the soil to reduce the risk of variation in the microbial flora of soil after bio-cementation and was evaluated for its potential to strengthen sands by microbial-induced calcite precipitation (MICP). Its effectiveness and survival time were compared to those of Sporosarcina pasteurii, a well-known bacterium that is commonly used for MICP. The results revealed that S. pasteuri has no viability in the soil for more than 10 days, whereas Sp. pasteurii remained in the soil for more than 30 days because of spore formation. The unconfined compressive strength of soil, after the bio-cementation by both bacteria, reached about 2.3 MPa at the strain rate of 0.005 mm/s. The hydraulic conductivity of soil columns treated with S. pasteuri and Sp. pasteurii was reduced from 13 to 7.5 m/day and 6.8 m/day, respectively. Finally, using either bacterium resulted in achieving the same geotechnical properties. Therefore, according to the results, a non-spore-forming indigenous bacterium with low viability, such as the one isolated here, could be applied for soil improvement applications to reduce the environmental impacts.