Mitigation of the liquefaction potential of soil by Ca-carbonate precipitation induced by indigenous urease-producing Staphylococcus sp. IR-103

Abstract

Biocementation is a microbially induced technology that increases the shear strength of soil through the production of soil particle-binding materials known as calcite (calcium carbonate). This process makes use of urease-positive microorganisms, urea and calcium ions. The main aim of this study was to introduce an indigenous soil bacterium belonging to the genus Staphylococcus that was capable of hydrolyzing urea and precipitating calcium carbonate (CaCO3). Molecular identification of this isolate by 16S rDNA sequencing showed 98% homology to Staphylococcus sp. Several culture media were employed to investigate the growth, urease production and CaCO3 precipitation of this strain (designated Staphylococcus sp. IR-103, accession number LT853888). When Staphylococcus sp. IR-103 was grown in YN medium containing 20 g L−1 of yeast extract and 10 g L−1 of NH4Cl, maximal growth yield (OD600), urease activity and carbonate precipitation values of 2.8 ± 0.1, 3.33 ± 0.12 IU and 47.6 ± 0.9 mg mL−1 were obtained, respectively. The precipitated CaCO3 was characterized by FTIR, AAS, XRD and SEM analyses. In order to study the effects of the bacterium’s biocementation activities on soil strength, bacterial suspension and cementation solution was injected into a column packed with uniform sandy soil under defined condition. In conclusion, Staphylococcus sp. IR-103 is a high urease producer, which can grow on a simple and cost-effective medium without staying viable for long following the biocementation process. Hence this newly isolated strain has the potential to be employed in soil improvement for large-scale field applications.