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.

Microbially Induced Calcite Precipitation (MICP), or bio-cementation, is a promising bio-mediated technology that can improve the engineering properties of soils through the precipitation of calcium carbonate. Despite significant advances in the technology, concerns regarding the fate of produced NH₄⁺ by-products have remained largely unaddressed. In this study, five 3.7-meter long soil columns each containing one of three different soils were improved using ureolytic bio-cementation, and post-treatment NH₄⁺ by-product removal was investigated during the application of 525 L of a high pH and high ionic strength rinse solution. During rinsing, reductions in aqueous NH₄⁺ were observed in all columns from initial concentrations between ≈100 mM to 500 mM to final values between ≈0.3 mM and 20 mM with higher NH₄⁺ concentrations observed at distances furthest from the injection well. In addition, soil V_s measurements completed during rinse injections suggested that no significant changes in cementation integrity occurred during NH₄⁺ removal. After rinsing and a 12 hour stop flow period, all column solutions achieved cumulative NH₄⁺ removals exceeding 97.9%. Soil samples collected following rinsing, however, contained significant sorbed NH₄⁺ masses that appeared to have a near linear relationship with surrounding aqueous NH₄⁺ concentrations. While these results suggest that NH₄⁺ can be successfully removed from bio-cemented soils, acceptable limits for NH₄⁺ aqueous concentrations and sorbed NH₄⁺ masses will likely be governed by site-specific requirements and may require further investigation and refinement of the developed techniques.