Abstract
Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that can improve the engineering properties of granular soils through the precipitation of calcite. The process is made possible by soil microorganisms containing urease enzymes, which hydrolyze urea and enable carbonate ions to become available for precipitation. While most researchers have injected non-native ureolytic bacteria to complete bio-cementation, enrichment of native ureolytic microorganisms may enable reductions in process treatment costs and environmental impacts. In this study, a large-scale bio-cementation experiment involving two 1.7-meter diameter tanks and a complementary soil column experiment were performed to investigate biogeochemical differences between bio-cementation mediated by either native or augmented (Sporosarcina pasteurii) ureolytic microorganisms. Although post-treatment distributions of calcite and engineering properties were similar between approaches, the results of this study suggest that significant differences in ureolysis rates and related precipitation rates between native and augmented microbial communities may influence the temporal progression and spatial distribution of bio-cementation, solution biogeochemical changes, and precipitate microstructure. The role of urea hydrolysis in enabling calcite precipitation through sustained super-saturation following treatment injections is explored.
Highlights
Potential applications of Microbially Induced Calcite Precipitation (MICP) include geotechnical soil improvement for mitigation of earthquake-induced soil liquefaction[4,5], immobilization of groundwater contaminants[6], sealing of rock fractures for waste storage and carbon sequestration[7], modification of flow in porous media for contaminant transport and petroleum recovery[8,9], and healing of cracked concrete materials[10]
The use of native ureolytic microorganisms may reduce treatment costs and environmental impacts by eliminating the materials and energy associated with bacterial cultivation and transportation and potential ecological impacts related to the introduction of high densities of non-indigenous bacterial species into soil ecosystems[22]
To further characterize biological and chemical differences between approaches, a complementary soil column experiment was performed under conditions similar to the tank experiments and ureolysis rates and cell densities were evaluated in time
Summary
Potential applications of MICP include geotechnical soil improvement for mitigation of earthquake-induced soil liquefaction[4,5], immobilization of groundwater contaminants[6], sealing of rock fractures for waste storage and carbon sequestration[7], modification of flow in porous media for contaminant transport and petroleum recovery[8,9], and healing of cracked concrete materials[10]. A large-scale tank experiment was completed to investigate biogeochemical differences between bio-cementation mediated by native ureolytic microorganisms and augmented S. pasteurii. Initial hydraulic properties in tanks were evaluated using passive tracer testing prior to treatment injections. In both tanks, biological treatments were first completed to establish either native or S. pasteurii microorganisms and eight cementation injections were subsequently performed. Differences in ureolysis and precipitation kinetics, aqueous chemical changes, and precipitate spatial distributions and microstructures between tank experiments were investigated to improve our understanding of the implications of using native ureolytic microorganisms for the bio-cementation process as an alternative to a more traditional augmentation approach
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