The impact of Microbially Induced Calcite Precipitation (MICP) on sand internal erosion resistance: A microfluidic study

Aeolian sand is a type of special soil with a loose structure, fine and uniform particles, and poor self-stabilization ability. These characteristics easily lead to sand dune movement and wind erosion in dry desert conditions. Therefore, reinforcement technology for aeolian sand is an important research topic. Microbially induced calcite precipitation (MICP) is a novel microbial soil-strengthening technique considered in this study with a focus on the effect of the reactant injection rate on the microbial solidification of aeolian sand. The aeolian sand was solidified using MICP with different injection rates of the cementing solution. The physical and mechanical properties as well as the microstructure of the solidified aeolian sand samples were analyzed. The experimental results show that using Sporosarcina pasteurii and the cementing solution (a mixture of urea and calcium chloride) can effectively solidify aeolian sand using the MICP technology. The engineering performance of the sand was effectively improved with an unconfined compressive strength that approached 14.01 MPa. The permeability coefficient of the solidified aeolian sand was significantly reduced, and the injection rate of the cementing solution significantly affected its uniformity. When the injection rate of the cementing solution was too low, most of the calcium carbonate was generated and accumulated at the top of the sand sample. Therefore, the upper part of the sample was relatively dense and strong, while the lower part had the opposite properties. When the injection rate of the cementing solution was too high, the roles of the upper and lower parts of the sample were reversed. When the injection rate of the cementing solution was 0.278 mol L−1 h−1, the solidified aeolian sand sample was relatively uniform and had a moderate unconfined compressive strength of 4.58–5.03 MPa. The uniform and high strength of the solidified aeolian sand was obtained by controlling the reactant injection rate. The optical microscope and SEM analyses indicated that the calcium carbonate crystals were rhombic hexahedral with sizes of approximately 5–10 μm. The calcium carbonate crystals were generated from the MICP in the solidified aeolian sand, which cemented the sand particles together, filled the pores between particles, increased the density and strength of the sand, and reduced its permeability coefficient.

Seepage-induced internal erosion in earth-filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades. Microbially induced carbonate precipitation (MICP), owing to its proved performance in soil enhancement and permeability control, can potentially be used for internal erosion control. This paper examines the applicability of MICP for internal erosion control in gravel–sand mixtures using a large one-dimensional column test apparatus which incorporates the implementation of MICP. Visual observations, erosion characteristics and hydro-mechanical behaviours of non-MICP and MICP treated gravel–sand mixtures were investigated through a series of constant-pressure erosion tests. Test results confirm that MICP treatment can reduce the cumulative erosion weight, erosion rate and axial strain relative to non-MICP soil. The magnitudes of hydraulic conductivity for all tested samples before the erosion process fall into a range from 5·5 × 10−5to 8·0 × 10−3 m/s. After the erosion process, non-MICP soils and MICP treated soils with low cementation concentrations experience a significant increase in hydraulic conductivity. Furthermore, a hydro-mechanical coupling analysis was conducted and different erosion modes were identified for low and high concentrations of cementation solution. Fundamentally, the efficiency of internal erosion reduction is controlled by the calcium carbonate precipitation content within the tested soils. Higher precipitation content can facilitate the formation of larger clusters of cemented sand particles, thus reducing the likelihood of erosion.

Microbial induced calcite precipitation (MICP) is a geochemical process for ground improvement by enhancing the mechanical properties of the soil stratum. A bacteria and nutrient containing liquid are injected into the sand to precipitate the formation of calcium carbonate crystals through the metabolism of microorganisms. The calcium carbonate crystals precipitate in pores between the grains of sand, effectively cementing the particles of sand together and filling the pore volume, consequently, increasing the shear strength and reducing the permeability. However, the functioning of the MICP method is quite sensitive to environmental conditions such as temperature and humidity. Another way to cement the soil layers is to use a chemical process where a Na_2CO_3-CaCl_2 liquid mixture is added to produce CaCO_3 which helps to harden the soil. However, this method has significant undesirable side effects in the ground environment. In this study, a series of experiments is carried out comparing samples that have been improved by MICP and a chemical method under different conditions with the original non-improved samples. The experiments include direct shear testing, constant head testing and centrifuge testing. The results show that the treated sand layer has better resistance to liquefaction, decreased excess pore water pressure, and improved settlement which also shortens the excess pore water pressure dissipation time. In addition, it is also demonstrated that the temperature, humidity and nutritional liquid have a critical effect on the effectiveness of the MICP and chemical methods.

Bio-cementation, notably microbial induced calcite precipitation (MICP), and Enzyme induced calcite precipitation (EICP), binds soil particles together through calcium carbonate (CACO3) precipitation (cementation). Both MICP and EICP have significant potential for many scientific and engineering applications including improvement of strength, reducing soil liquefaction potential, surface erosion control, reducing permeability, and heavy metal contaminant remediation. However, the catalytic mechanism and the precipitation of CACO3 in MICP and EICP mainly depends on the source of urease enzyme and the treatment process used. This study evaluates the mechanical and microstructural behaviour of bio-cementation using the standard MICP and EICP treatment process. The results indicate that, for the same number of treatment cycles (NTC), a higher amount of precipitated CACO3 was achieved for MICP than EICP which affects the strength. For similar average CACO3 content (AC), the standard treatment method used in EICP produced a higher chemical efficiency (defined as the amount of CACO3 precipitated relative to the quantity of urea-CaCl2 used) than in MICP. The results from scanning electron microscopy (SEM) imaging shows that the morphologies of the precipitated CACO3 in MICP and EICP are similar, however, a high amount of vaterite was found in EICP than MICP. The outcome of this study indicates that the standard treatment processes used in MICP and EICP may influence the chemical efficiency, the amount, distribution, and polymorph of the precipitated CACO3 which may directly affect the strength.

BCH modelling studies on biocementation process in mitigating leaks from a CO2 sequestrated aquifer

This research project addresses one of the goals of the U.S. Department of Energy (DOE) Carbon Storage Program (CSP) aimed at developing Advanced Wellbore Integrity Technologies to Ensure Permanent Geologic Carbon Storage. The technology field-tested in this research project is referred to as microbially induced calcite precipitation (MICP), which utilizes a biologically-based process to precipitate calcium carbonate. If properly controlled MICP can successfully seal fractures, high permeability zones, and compromised wellbore cement in the vicinity of wellbores and in nearby caprock, thereby improving the storage security of geologically-stored carbon dioxide. This report describes an MICP sealing field test performed on a 24.4 cm (9.625 inch) diameter well located on the Gorgas Steam Generation facility near Jasper, Alabama. The research was aimed at (1) developing methods for delivering MICP promoting fluids downhole using conventional oil field technologies and (2) assessing the ability of MICP to seal cement and formation fractures in the near wellbore region in a sandstone formation. Both objectives were accomplished successfully during a field test performed during the period April 1-11, 2014. The test resulted in complete biomineralization sealing of a horizontal fracture located 340.7 m (1118 feet) below ground surface. A total of 24 calcium injections andmore » six microbial inoculation injections were required over a three day period in order to achieve complete sealing. The fractured region was considered completely sealed when it was no longer possible to inject fluids into the formation without exceeding the initial formation fracture pressure. The test was accomplished using conventional oil field technology including an 11.4 L (3.0 gallon) wireline dump bailer for injecting the biomineralization materials downhole. Metrics indicating successful MICP sealing included reduced injectivity during seal formation, reduction in pressure falloff, and demonstration of MICP by-products including calcium carbonate (CaCO3) in treated regions of side wall cores. This project successfully integrated mesoscale laboratory experiments at the Center for Biofilm Engineering (CBE) together with simulation modeling conducted at the University of Stuttgart to develop the protocol for conducting the biomineralization sealing test in the field well.« less

Experimental study on the effect of cementation curing time on MICP bio-cemented tailings

Mineral precipitation via microbial activity is a well-known process with applications in various fields. This relevance of microbially induced calcite precipitation (MICP) has pushed researchers to explore various naturally occurring MICP capable bacterial strains. The present study was performed to explore the efficiency of microbially induced calcite precipitation (MICP) via locally isolated bacterial strains and role of guar gum, which is a naturally occurring polymer, on the MICP process. The strains were isolated from local soil and screened for urease activity Further, the urease positive strain was subjected to urea and calcium chloride based medium to investigate the efficacy of isolated strain for microbial induced precipitation. Among screened isolates, the soil bacterium that showed urease positive behaviour and precipitated calcium carbonate was subjected to 16S rRNA gene sequencing. This strain was identified as Bacillus velezensis. Guar gum-a natural polymer, was used as a sole carbon source to enhance the MICP process. It was observed that the isolated strain was able to breakdown the guar gum into simple sugars resulting in two-fold increase in calcium carbonate precipitate. Major bio-chemical activities of isolated strain pertaining to MICP such as ammonium ion concentration, pH profiling, and total reducing sugar with time were explored under four different concentrations of guar gum (0.25%, 0.5%, 0.75% and 1% w/v). Maximum ammonium ion concentration (17.5 μg/ml) and increased pH was observed with 1% guar gum supplementation, which confirms augmented MICP activity of the bacterial strain. Microstructural analysis of microbial precipitation was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, which confirmed the presence of calcium carbonate in different phases. Further, XRD and SEM based studies corroborated that guar gum supplemented media showed significant increase in stable calcite phase as compared to media without guar gum supplementation. Significant diverse group of nitrogenous compounds were observed in guar gum supplemented medium when subjected to Gas Chromatography-Mass spectrometry (GC-MS) profiling.

Mineral precipitation via microbial activity is a well-known process with applications in various fields. This relevance of microbially induced calcite precipitation (MICP) has pushed researchers to explore various naturally occurring MICP capable bacterial strains. The present study was performed to explore the efficiency of microbially induced calcite precipitation (MICP) via locally isolated bacterial strains and role of guar gum, which is a naturally occurring polymer, on the MICP process. The strains were isolated from local soil and screened for urease activity Further, the urease positive strain was subjected to urea and calcium chloride based medium to investigate the efficacy of isolated strain for microbial induced precipitation. Among screened isolates, the soil bacterium that showed urease positive behaviour and precipitated calcium carbonate was subjected to 16S rRNA gene sequencing. This strain was identified as Bacillus velezensis. Guar gum—a natural polymer, was used as a sole carbon source to enhance the MICP process. It was observed that the isolated strain was able to breakdown the guar gum into simple sugars resulting in two-fold increase in calcium carbonate precipitate. Major bio-chemical activities of isolated strain pertaining to MICP such as ammonium ion concentration, pH profiling, and total reducing sugar with time were explored under four different concentrations of guar gum (0.25%, 0.5%, 0.75% and 1% w/v). Maximum ammonium ion concentration (17.5 μg/ml) and increased pH was observed with 1% guar gum supplementation, which confirms augmented MICP activity of the bacterial strain. Microstructural analysis of microbial precipitation was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, which confirmed the presence of calcium carbonate in different phases. Further, XRD and SEM based studies corroborated that guar gum supplemented media showed significant increase in stable calcite phase as compared to media without guar gum supplementation. Significant diverse group of nitrogenous compounds were observed in guar gum supplemented medium when subjected to Gas Chromatography–Mass spectrometry (GC-MS) profiling.

Coral sand with microbial-induced calcite precipitation (MICP) is a promising material for practical engineering. This study attempts to improve the precipitation efficiency by using a modified bio-cement method based on MICP and sodium alginate (SA). It was found that adding an appropriate amount of SA in the bacterial solution could greatly improve the ability of immobilising bacteria, thus achieving an effective precipitation of calcium carbonate on the aggregate surfaces. As the SA content increased, the weight increment and unconfined compressive strength of each sample after MICP cementation initially increased and then decreased. Three main failure modes were observed, i.e., the particle unbroken failure, stepped failure, and steep drop failure. Owing to the macro pores of coral sand, the specific loss of calcium carbonate crystals produced by MICP had a significant effect on the cementation performance, while prolonging the single soaking time could favourably reduce the crystal loss. The calcium carbonate crystals occupied part of the pores between sand aggregates, but did not change the compression strength of a single aggregate significantly.

A biotechnological approach for suspended solids removal in biogas slurry via microbially induced calcite precipitation (MICP)

Wind erosion of aeolian sandy soil can cause serious land degradation and other environmental problems, and thus its prevention and control is very important. However, there has not been a very effective way to prevent this severe wind erosion until now, and traditional measures such as mechanical methods, chemical sand‐fixing methods, and agronomic methods also have many disadvantages. The main objective of this study is to evaluate feasibility of microbially induced calcite precipitation (MICP) as a novel soil‐strengthening technique, to cement aeolian sandy soil, and reduce wind erosion risk. For this purpose, aeolian sandy soil was cemented withSporosarcina pasteuriithrough MICP technique, and the physical and mechanical properties and wind erosion resistance of cemented aeolian sandy soil were tested. The results show that wind erosion resistance of aeolian sandy soil can be effectively improved by sprayingS. pasteuriisolution and cementing solution (equal concentration of urea and calcium chloride mixture) into it from the surface, and the cemented aeolian sandy soil had good wind erosion resistance. Finally, morphology of precipitated CaCO3crystals was studied using scanning electron microscope, optical microscope, and X‐ray diffraction. The calcium carbonate crystals produced in aeolian sandy soil were calcite, and the calcium carbonate crystals had polyhedral, spherical, or flower clusters crystal morphology. The results of this study demonstrate an effective way to use MICP technology to cement aeolian sandy soil and prevent wind erosion, and provide a new way for wind erosion prevention.

Migration of fine particles within internally unstable granular soils under water seepage flow (suffusion) is one of the most common causes of earth infrastructures’ failure. To assess the ability of Microbial Induced Calcite Precipitation (MICP) to prevent the segregation in an internally unstable soil, internal erosion tests were conducted upon soil samples treated by bacteria and cementation solutions. MICP experiments were carried out with concentrations of urea/CaCl2 equal to 1.4 M. Volumes of injected bacteria solutions were equal to the volumetric water content corresponding to different tested degrees of saturation (Sr): 30, 60 and 80%. Cementation solutions were injected three times for each sample. Biochemical properties of MICP were examined to predict bacterial movement through soil matrices as a function of Sr. The amount of the CaCO3 produced was examined depending on Sr. Following their treatment, samples were saturated and submitted to increment of hydraulic gradients varying from 0.1 to 10. Eroded fine particles masses, seepage flow rates and effective hydraulic gradients along samples were measured throughout the experiment. The results of our study pointed out that MICP stabilized internally unstable granular soils as the critical gradient went from 0.7 for untreated samples to 5 for biocemented samples.

This study investigates the influence of two fundamental soil properties—Cation Exchange Capacity (CEC) and Specific Surface Area (SSA)—on the efficiency of Microbially Induced Calcite Precipitation (MICP) in mitigating the swelling potential of expansive clayey soils. While previous research has explored biological and environmental factors affecting MICP, the role of soil physico-chemical properties, particularly CEC and SSA, has not been comprehensively studied. Six clayey soils from diverse geographic locations in the United States were collected, classified, and treated with MICP solutions. The impact of MICP treatment was assessed through one-dimensional (1D) swelling tests, carbonate content determination, and microstructural analyses using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The results demonstrated that MICP treatment significantly reduced the swelling potential of all tested soils, with the most substantial reductions observed in the MA and NTP soils, which have the highest clay content (96% and 73%, respectively). The analysis of CaCO₃ precipitation revealed a strong positive correlation between SSA and CEC with the amount of biogenic calcium carbonate formed, suggesting that these soil properties could serve as reliable indicators for predicting MICP efficiency. Additionally, soils with higher initial inorganic carbonate (SIC) content exhibited lower CaCO₃ precipitation post-MICP treatment, likely due to a pre-existing carbonate film that reduced available reaction sites. The study further revealed a distinct influence of Soil Organic Carbon (SOC) on the efficiency of MICP, with increased SOC levels correlating with decreased CaCO₃ precipitation, indicating competitive interactions between organic matter and carbonate formation. SEM and XRD analyses confirmed that post-MICP CaCO₃ predominantly precipitated in the form of agglomerated rhombohedral calcite crystals, with occasional vaterite formations. In high-clay soils, precipitated CaCO₃ manifested as a discontinuous film coating clay particles, a morphology that likely contributes to enhanced soil stabilization. These findings highlight the critical role of soil chemical and physical properties in optimizing MICP for expansive soil stabilization and suggest that SSA and CEC should be considered in pre-treatment assessments for field applications.

This study investigates the influence of two fundamental soil properties—Cation Exchange Capacity (CEC) and Specific Surface Area (SSA)—on the efficiency of Microbially Induced Calcite Precipitation (MICP) in mitigating the swelling potential of expansive clayey soils. While previous research has explored biological and environmental factors affecting MICP, the role of soil physico-chemical properties, particularly CEC and SSA, has not been comprehensively studied. Six clayey soils from diverse geographic locations in the United States were collected, classified, and treated with MICP solutions. The impact of MICP treatment was assessed through one-dimensional (1D) swelling tests, carbonate content determination, and microstructural analyses using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The results demonstrated that MICP treatment significantly reduced the swelling potential of all tested soils, with the most substantial reductions observed in the MA and NTP soils, which have the highest clay content (96% and 73%, respectively). The analysis of CaCO₃ precipitation revealed a strong positive correlation between SSA and CEC with the amount of biogenic calcium carbonate formed, suggesting that these soil properties could serve as reliable indicators for predicting MICP efficiency. Additionally, soils with higher initial inorganic carbonate (SIC) content exhibited lower CaCO₃ precipitation post-MICP treatment, likely due to a pre-existing carbonate film that reduced available reaction sites. The study further revealed a distinct influence of Soil Organic Carbon (SOC) on the efficiency of MICP, with increased SOC levels correlating with decreased CaCO₃ precipitation, indicating competitive interactions between organic matter and carbonate formation. SEM and XRD analyses confirmed that post-MICP CaCO₃ predominantly precipitated in the form of agglomerated rhombohedral calcite crystals, with occasional vaterite formations. In high-clay soils, precipitated CaCO₃ manifested as a discontinuous film coating clay particles, a morphology that likely contributes to enhanced soil stabilization. These findings highlight the critical role of soil chemical and physical properties in optimizing MICP for expansive soil stabilization and suggest that SSA and CEC should be considered in pre-treatment assessments for field applications.