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 Vsmeasurements 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.
Bio‐mediated soil improvement technologies leverage microbial enzymatic and metabolic processes to generate minerals, gases and biopolymers that can improve soil engineering behaviours with the potential to reduce detrimental environmental impacts when compared with conventional methods. Ureolytic biocementation is perhaps the most widely researched of these processes and relies on urea hydrolysis in the presence of calcium to initiate the precipitation of calcium carbonate minerals on soil particle surfaces and contacts, thereby improving soil behaviours. Although effective, urea hydrolysis generates aqueous ammonium by‐products that may result in undesirable environmental and human health impacts, if left unaddressed. Recent studies have shown the potential of rinse solution injections to effectively remove generated ammonium following biocementation through both advective flow and the removal of sorbed ammonium from soil surfaces; however, critical gaps remain in our understanding of the effect of rinse solution composition and injection strategies on ammonium removal efficacy. In this study, 16 soil column experiments were performed to investigate the effect of rinse solution cation types, cation concentrations, applied injection sequences and biocementation treatment variations on the removal of ammonium from a biocemented poorly graded sand. All columns receiving cation‐enriched rinse solutions achieved greater than 98% aqueous, 65% sorbed and 95% total ammonium removal after injecting 12 pore volumes, with no detectable impacts on cementation integrity. Cation‐enriched solutions specifically enhanced sorbed ammonium removal and achieved sorbed ammonium concentrations up to 2 orders of magnitude less than those observed in columns rinsed with deionized water alone. Columns receiving K+‐based rinse solutions and 12 daily 1‐PV rinse injections also achieved greater total ammonium removal when compared with comparable columns receiving rinse solutions containing other cations and continuous 12‐PV rinse injections.
more » « less- PAR ID:
- 10487432
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Soil Use and Management
- Volume:
- 40
- Issue:
- 1
- ISSN:
- 0266-0032
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Microbially induced calcite precipitation (MICP) or biocementation is a bio-mediated process that can be used to improve the engineering properties of granular soils through calcium carbonate precipitation. Although most commonly this process is accomplished using microbial urea hydrolysis, other microbial metabolic pathways can be used to enable biocementation with the potential to eliminate ammonium byproducts. Microbial organic acid oxidation presents one alternative pathway by which increases in solution carbonate species can be generated to enable calcium carbonate mineral formation. While past studies have considered the potential of this microbial pathway to enable biocementation for surficial applications, to date few studies have examined the feasibility of this pathway for subsurface applications wherein dissolved oxygen is more limited. In this study, 18 small-scale batch experiments were performed to investigate the ability of microbial organic acid oxidation to enable biocementation soil improvement. Experiments investigated the feasibility of using both acetate and citrate oxidation to mediate biocementation as well as the effect of differences in techniques used to supply dissolved oxygen, the effect of supplied growth factors, bicarbonate salt additions, and solution sampling frequency. Results suggest that aerobic oxidation of acetate and citrate can be used to enable calcium carbonate biocementation, though ensuring dissolved oxygen availability appears to be critical towards enabling this process.more » « less
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Abstract Specimens of silica sand treated via enzyme induced carbonate precipitation (EICP) showed surprisingly high strength at a relatively low carbonate content when non-fat powdered milk was included in the treatment solution. EICP is a biologically-based soil improvement technique that uses free urease enzyme to catalyze the hydrolysis of urea in an aqueous solution, producing carbonate ions and alkalinity that in the presence of calcium cations leads to precipitation of calcium carbonate. The strength achieved at less than 1.4% carbonate content via a single cycle of treatment was unprecedented compared to results reported in the literature from both EICP and microbially induced carbonate precipitation (MICP). Scanning electron microscope images show that in the specimens treated with the solution containing powdered milk the carbonate precipitate was concentrated at interparticle contacts. The impact of these results include reductions in the concentration of substrate and enzyme required to achieve a target compressive strength, reduction in the undesirable ammonium chloride by-product, and, depending on the desired strength, reduction in the number of cycles of EICP treatment. These advantages enhance the potential for development of a sustainable method of soil improvement via hydrolysis of urea.
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Biocementation is an exciting biomanufacturing alternative to common cement, which is a significant contributor of CO2greenhouse gas production. In nature biocementation processes are usually modulated via ureolytic microbes, such as
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