Abstract
To investigate potential implications of microbial activity on sand bioconsolidation and subsurface environments, two ureolytic strains, Sporosarcina pasteurii and Bacillus subtilis were tested for the production of calcium carbonate (CaCO3). Laboratory experiments with monoculture S. pasteurii (column 1) and coculture S. pasteurii-B. subtilis (column 2) were conducted to determine urea and calcium chloride reactivity and volumetric carbonate formation. Both columns were able to consolidate sand, whereas, column 1 induced greater CaCO3 precipitation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed two columns with different mineralogy with calcite, and vaterite formation. Column 1 showed rhombohedral and trigonal crystals morphology, whereas column 2 developed the prismatic calcite and the spherulite vaterite crystals might be due to the differences of the micro-environment caused by the urease expression of these bacterial species. These results indicate the possibility of using those crystals to cement loose sand whereas, highlighted the importance of combining these techniques to understand the geomicrobiology found in the subsurface environments.
Highlights
Calcium carbonate (CaCO3 ) biogenic precipitation is considered as an important process in nature with respect to its role in early diagenesis of marine sediments, hydrochemical evolution of karst streams, application of Geological and Civil Engineering and environmental treatments [1]
The effect of two types of microbial systems were evaluated to study the distribution of their activity and calcium carbonate precipitation in sand column through a number of steps elaborated in Effluent Flow Rate (L/h)
The present hypothesis that B. subtilis extracellular polymeric substances (EPS)/EPS like chemical might release into the environment and influence the CaCO3 formation is from the laboratory experiment, there are wide implications for natural carbonate precipitation, since bacteria are ubiquitous in nature
Summary
Calcium carbonate (CaCO3 ) biogenic precipitation is considered as an important process in nature with respect to its role in early diagenesis of marine sediments, hydrochemical evolution of karst streams, application of Geological and Civil Engineering and environmental treatments [1]. MCP can occur via a variety of processes whereby microbial activities results in the generation of carbonate in a calcium rich environment. The urea hydrolysis by the enzyme urease of microorganisms in a calcium-rich environment is the most commonly MCP studied. Considerable research on MCP has been performed using ureolytic bacteria, which influence the precipitation of CaCO3 , by the production of the enzyme urease. The fact that hydrolysis of urea is a straightforward common microbial process and that a wide variety of microorganisms produce the urease enzyme makes it ideally suited for biotechnological applications. S. pasteurii has been widely used as a model organism for the MCP process because this strain is non-pathogenic with significantly high level of urease activity [15]. There are no adequate studies on the role of calcite precipitation by B. subtilis in coculture environments for sand bioconsolidation. A main part of this research focuses on studying coculture environment for sand bioconsolidation through carbonate precipitation and geomicrobiology in the subsurface environment
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