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Microbial-induced calcite precipitation (MICP) is a promising, sustainable, and environmentally friendly ground improvement technique. This study examined the effectiveness of molasses (MS) as a broth medium compared to nutrient broth (NB). Sporosarcina pasteurii was used in a 0.5 M cementation solution with pore volumes (PV) of 0.50, 0.75, and 1 PV in biotreatment cycles of 9 and 18 days. Mechanical properties of biotreated samples were assessed through unconfined compressive strength (UCS) and split tensile strength (STS) tests, while calcite content, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to interpret biocementation. NB-treated samples exhibited significantly higher strength and calcite content than MS-treated samples. The durability of biotreated samples under 6, 12, and 18 freeze-thaw (FT) cycles revealed that the FT cyclic process affects the mechanical and physical characteristics of biotreated samples. Samples treated with higher PV and for a longer duration exhibited higher strength and durability. The mass losses in NB and MS samples were 7–14.5% and 15–32%, respectively, after 18 FT cycles. Overall, NB samples exhibit higher strength and durability than MS samples. While MS proved less effective as a broth medium compared to NB for the MICP process, its cost-effectiveness and abundant availability make it a promising choice for the MICP process. [ABSTRACT FROM AUTHOR]

Discarded disposable face masks can easily cause environmental pollution, and microbial-induced calcium carbonate precipitation (MICP) technology can lead to soil brittleness. This article attempted to combine discarded disposable face masks with MICP technology by adding the shredded face mask (SFM) with six different percentages (0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight) to ISO standard sand. The test results showed that the optimal content of SFM was 0.2%. Compared with the sand samples without SFM, the water absorption rate decreased by 26.99%, the dry and saturated unconfined compressive strengths (UCS) increased by 145.11% and 252.38%, respectively, and the failure strain increased by 127%, and the calcium carbonate content increased by 20.1%. Meanwhile, 0.2% SFM fiber can form a three-dimensional network structure, which restricts the displacement and deformation of sand particles, improves the brittleness of the sand samples, and enhances the strength of the sand samples. This study provides an effective method for recycling discarded disposable face masks while promoting the application of fiber-reinforced MICP-treated sand in geotechnical engineering. [ABSTRACT FROM AUTHOR]

Microbial-induced calcite precipitation (MICP), which leverages ureolytic microorganisms, has received significant attention during the past decade as a promising method for sustainable building and geoenvironmental applications. However, transitioning from lab-scale experimentation to volumes suitable for practical use poses challenges. This study addresses these obstacles by screening and analyzing over 50 strains sourced from (i) a natural environment in the canton of Ticino in Switzerland; (ii) microorganism banks; and (iii) an industry-scale bioreactor. Several ureolytic Sporosarcina species have been identified in the natural environment, and their ureolytic potential has been compared with that of other strains. A reference, banked microorganism yielded the highest ureolysis rate. When this latter strain was inoculated in 900 L batches and continuously cultivated at 5400 L, no contamination issues were observed, and the reference strain remained the dominant species. The produced culture, obtained under an optimized medium composition involving the circular valorization of NH4+, was subsequently used to induce the biocementation of a 650 kg column of 0–1 mm sand. The results reveal the successful stabilization of the whole mass, with undrained Tresca strength values ranging from 90 to 140 kPa. This research lays the groundwork for scalable MICP production, which is capable of meeting the demands of real-world building and geoenvironmental projects. [ABSTRACT FROM AUTHOR]

The complex and diverse nature of coal mining sites, including different landforms and working conditions, presents challenges for rehabilitation efforts. To address this, we conducted a comprehensive experimental study focusing on microbially induced calcium carbonate precipitation (MICP) remediation, considering the fracture characteristics of coal mining sites. The MICP-restored samples were subjected to confined/unconfined compressive strength, uniaxial/triaxial permeability, and souring tests to assess their restoration efficacy. The results showed that under similar mining conditions, the average depth of parallel fractures was 0.185 m for loess ridges, 0.16 m for the valley, and 0.146 m for the blown-sand region, while the average depth for boundary fractures was 0.411 m for loess ridges, 0.178 m for the valley, and 0.268 m for the blown-sand region. Notably, parallel fractures showed negligible filling in all landforms, whereas boundary fractures in the blown-sand region were completely filled with wind-deposited sand. The valley landform was filled with alluvium and wind-deposited sand, whereas the loess landform was filled with wind-deposited sand and loess. MICP-restored soil samples in all landforms achieved a strength comparable to remolded fracture-free soil samples. Across all landforms, the maximum permeability coefficient of MICP-restored soil samples closely matched that of remolded fracture-free soil samples. Under similar topographic and rainfall conditions MICP restorations scoured 31.3 g on blown-sand region, 19.3 g on loess ridges, and 17.6 g on valleys. These research findings provide an experimental foundation for MICP repair of coal mining ground fractures. [ABSTRACT FROM AUTHOR]

In this research, the microbial‐induced carbonate precipitation (MICP) technique combined with cement was proposed to improve the physical and mechanical properties of silt. A series of comparative experiments of the MICP technique combined with cement treatments on silt (MICP‐reinforced soil‐cement) were conducted. The unconfined compressive strength (UCS), internal friction angle, cohesive force, and ultrasonic velocity of the silt treated with the MICP technique combined with cement were higher than those treated with cement. The X‐ray diffraction (XRD) and scanning electron microscope (SEM) tests showed that the cement hydration products cemented the silt into agglomerates and formed a skeleton, and the calcite produced by the MICP process covered the surface of the agglomerates and filled the silt pores and cemented the particles, which played a role in increasing the strength of the specimens. In addition, the products and reactants of MICP accelerated the hydration reaction of the cement and played a role in the curing system consistent with carbonate‐based and alkaline earth metal–based early‐strengthening agents. The results of this study will provide basic theoretical and experimental data for the research and application of microbe‐based treatment approaches for silt. [ABSTRACT FROM AUTHOR]

To efficiently heal large-aperture cracks in the sandstone cultural relics, a microbially induced magnesia carbonation (MIMC) method was introduced in combination with sandstone grains. A series of MIMC samples and sandstone–MIMC composite samples were meticulously prepared, incorporating different initial water content and magnesia content variations. The mechanical behavior was evaluated by three-point bending test. The results showed that fractures consistently occurred on the MIMC side of the sandstone–MIMC samples, indicating superior bonding compatibility with sandstone. The interfacial bonding strength of sandstone–MIMC samples had a maximum value of 675 kPa, while MIMC samples had a maximum value of 1200 kPa. X-Ray diffraction (XRD) analysis confirmed that brucite with low crystallinity was the predominant cementing product at the interface, and the degree of carbonation showed a stepwise increase with distance from the interface. The bonding between MIMC and sandstone can be attributed to mechanical interlocking of hydration/carbonation products with the sandstone surface and the chemical reaction between brucite and silica. Microstructural examination revealed that there were layered structures near the interface namely interfacial transition zone (ITZ), including the diffusion layer, strong bonding layer and weak bonding layer. The diffusion and strong bonding layers positively enhanced the bonding strength, while numerous microcracks in the weak bonding layer provided a negative effect. This study provides valuable insights into the bonding mechanism of the interface, contributing to the understanding of how MIMC interacts with rock in the context of healing large-aperture cracks in sandstone cultural relics. Highlights: Microbially-induced magnesia carbonation (MIMC) is a promissing biomineralization technology for sandstone cultural relics ceack healing. The interfacial bonding strength of MIMC to sandstone is up to 675 kPa. Low-crystallinity brucite is the predominant cementing product at the interface. There is a layered structure in the interfacial transition zone near the interface. Weak bonding layer is the zone where failure occurs. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) is a geotechnical solution with a low ecological footprint. Conducting MICP inside a porous medium can be used for biocementation. Despite many models and tools being published for simulating MICP, a computationally light, easy-to-use, and freely-available simulation tool is lacking. In this work, we present a reactive transport model using the native capabilities of the Phreeqc software (a free and open-source geochemical solver). We model MICP inside a column packed with sands and inoculated with bacteria. Our model is a one-dimensional representation of the column that accounts for the kinetics of precipitation and ureolysis as well as porosity change. We verify our model by simulating previously published MICP experiments to show our model gives reasonably well predictions. Sensitivity analysis of our model's input parameters and discussions around their range are presented. Additionally, we calculate the supersaturation of calcite as a function of space and time—a feature that could be important for precipitation, but it is commonly ignored in MCIP modeling. Our scripts developed for running simulations are accessible publicly. Due to the low computational effort required for the simulations, our Phreeqc scripts can be used to design and test different treatment recipes for conducting MICP. [ABSTRACT FROM AUTHOR]

Recently, the ability of microbial-induced calcium carbonate precipitation (MICP) to remediate heavy metals has been widely explored. Sporosarcina pasteurii was selected to remediate heavy metal-contaminated solution and aged refuse, exploring the feasibility of Sporosarcina pasteurii bioremediation of heavy metals and analyzing the changes in heavy metal forms before and after bioremediation, as well as the mechanism of remediation. The results showed that Sporosarcina pasteurii achieved remediation rates of 95%, 84%, 97%, and 98% for Cd, Pb, Zn, and Cr (III) in contaminated solution, respectively. It also achieved remediation rates of 74%, 84%, and 62% for exchangeable Cd, Pb, and Zn in aged refuse, respectively. The content of exchangeable Cr (III) before bioremediation was almost zero. The content of heavy metals with exchangeable form and carbonate-bounded form in aged refuse decreased after bioremediation, while the content of heavy metals with iron–manganese oxide binding form and residual form increased. Simultaneously, the presence of Fe and Al components in aged refuse, as well as the precipitation of calcium carbonate produced during the MICP process, jointly promotes the transformation of heavy metals into more stable forms. [ABSTRACT FROM AUTHOR]

Biocementation is an innovative and sustainable technique with wide-ranging applications in slope stabilization, watershed management, and erosion control. Despite its potential, comprehensive evaluations of its use in hydrology and geotechnical engineering are limited. This study addresses this gap through a bibliometric analysis of 685 articles (2013–2023) from the Scopus database, employing VOSviewer and RStudio to explore global research trends, key contributors, and emerging themes. The analysis reveals that China, the United States, and Japan are leading contributors to this field, with significant advancements in microbial-induced (MICP) and enzyme-induced calcium carbonate precipitation (EICP) techniques. These methods have demonstrated effectiveness in improving soil strength, reducing erosion, and enhancing hydrological properties such as infiltration, runoff control, and water retention. Co-occurrence analysis identifies interdisciplinary connections between geotechnics and hydrology, highlighting research clusters focused on biomineralization, erosion resistance, and durability. The findings underscore biocementation's pivotal role in addressing sustainability challenges by providing environmentally friendly alternatives to traditional soil stabilization techniques. This study not only maps the current research landscape but also offers valuable insights into the practical implications of biocementation for slope stability and hydrological management, laying the foundation for future advancements in sustainable engineering practices. [ABSTRACT FROM AUTHOR]

Saline soil is widely distributed in China and poses significant challenges to engineering construction due to its harmful effects, such as salt heaving, dissolution collapse, and frost heaving. The Microbial-Induced Calcite Precipitation (MICP) method is an emerging environmental-friendly modification that can reduce or eliminate the environmental and engineering hazards of saline soil. To verify the feasibility of the MICP method for improving the properties of saline soil, laboratory tests were conducted to study the effects of salt content, activated carbon content and freeze-thaw cycles on the compression and water retention behavior of MICP modified saline soil. The following conclusions were drawn: calcium carbonate produced from the MICP can cement the soil particles of the modified soil structures, which resists the expansion damage caused by salt frost heaving and reduces soil compressibility. Additionally, calcium carbonate particles can fill pores of the soil structures, which improves the water retention capacity of the modified saline soil. The addition of activated carbon can enhance the MICP reaction leading to further reduction in compressibility and enhancement in water retention capacity of MICP modified saline soil. [ABSTRACT FROM AUTHOR]

In the course of pipe jacking construction, the carrying-soil effect frequently arises, influenced by factors such as excavation unloading, ongoing disturbance from successive pipe sections, and the progressive accumulation of soil adhesion. The pipe jacking slurry serves as a critical agent for friction reduction and strata support, essential for the secure advancement of the construction process. This study introduces the Microbial-Induced Calcium Carbonate Precipitation (MICP) technology into the realm of pipe jacking slurry, aiming to enhance its friction-reduction capabilities and the stability of the soil enveloping the pipe. An optimal MICP-slurry formulation was determined using the uniform design approach. Subsequent model tests were carried out to assess the friction-reducing efficacy of the MICP-slurry, while the mechanism by which the MICP-slurry reinforces strata stability was investigated through soil mechanics and scanning electron microscopy (SEM) analyses. The findings indicate that the optimal MICP-slurry composition is as follows: bentonite: sodium carboxymethyl cellulose: soda ash: polyacrylamide: xanthan gum = 12%: 0.31%: 0.36%: 0.25%: 0.54%. The MICP-slurry achieves a 42.2% reduction in the friction coefficient between the test block and the sand. In comparison with the untreated sample, the cohesion of the MICP-treated sample is enhanced by 38.12%, and the internal friction angle increases by 14.01%. SEM examination reveals that the calcium carbonate crystals precipitated by the MICP-slurry within the soil populate the pores, increase the inter-particle bite force, and bolster the soil's mechanical characteristics. [ABSTRACT FROM AUTHOR]

Burning rice straw is now a significant issue faced by different regions in India, as its burning releases harmful gases, mainly carbon dioxide. Various techniques are now in trend to utilize the rice straw, e.g., producing compressed natural gas using rice straw, bioethanol, etc., as a substrate for various microorganisms. A high quantity of non-utilized rice husk generates more ideas for its proper utilization. The cellulose, hemicellulose, and lignin found in rice straws can be a fungi growth medium. In this research, the delignification of rice husk is done by acid (2% and 4% H2SO4) and alkali (2% and 4% NaOH) at 121 °C at 103 kPa for 1 h to obtain crude carbon source which is further utilized for biomineralization. The glucose is subjected to qualitative and quantitative analysis using Molisch's and Dinitro salicylic tests. The delignification process showed a positive outcome when 2% H2SO4 is utilized maximum yield of 5.9 ug/ml free sugar concentration. Representing the highest glucose yield compared to the experiment's other acid and base substances used. Various techniques such as field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier transformed infra-red (FTIR) spectroscopy are employed to examine surface and chemical alterations. The 2% H2SO4 pretreated rice husk is utilized for microbial-induced calcite precipitation using fungal isolates S1 (3), S1 (18), and S4 (1). The calcite and vaterite produced by biomineralization are confirmed using XRD for fungal isolates namely, S1 (3), S1 (18), and S4 (1) having percentage crystallinity of 59%, 46.428%, and 62.69% percentage crystallinity respectively. [ABSTRACT FROM AUTHOR]

Biocementation is a promising soil stabilization technology that relies on microbiologically induced calcite precipitation (MICP). The addition of wastepaper was found to enhance the mechanical strength of biocemented soil. This study examined the effects of incorporating wastepaper into biocemented soil, focusing on the use of the ureolytic bacterium Bacillus licheniformis DSMZ 8782 and the yeast-like fungus Scytalidium candidum 3C for soil stabilization. The optimal wastepaper content was determined to be 2%, as it did not disrupt the uniform distribution of CaCO3 and contributed to improved soil strength. The combination of bacteria and fungi significantly increased the unconfined compression strength of samples containing 2% wastepaper (161.1 kPa) compared to untreated soil (61 kPa) and bacteria-only treatments (66.5 kPa), showing improvements of 2.6 and 2.4 times, respectively. Furthermore, we demonstrated that adding fungal biomass without wastepaper significantly improved the compressive strength, achieving a value of 236.6 kPa—nine times higher than untreated soil (26.4 kPa) and four times higher than soil treated with bacteria alone (60.6 kPa). This study identifies the optimal wastepaper content and highlights the potential of combining fungal and bacterial biomass for biocementation in soil stabilization. [ABSTRACT FROM AUTHOR]

[Objective] The aims of this study are to explore the effect of MICP solidified loose Pisha sandstone, and to provide solutions and theoretical basis for reducing soil erosion in Pisha sandstone area. [Methods] The effects of the bacterial solution concentration and curing frequency on the mechanical properties of MICP-cured Pisha sandstone and its resistance to water erosion were investigated at the macro-scale (penetration strength, rainfall erosion, etc), and the mechanism of water erosion resistance of Pisha sandstone-cured soil was revealed at the micro-scale (X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermal analysis). [Results] For the same curing time, when the concentration of the bacterial liquid (OD600) was 0.8, the curing effect was the best, and its strength was increased by 20%～50% compared to the other concentrations. When the optimal concentration of the bacterial liquid was 0.8 and the curing frequency was five times, the Pisha sandstone attained a good strength and water erosion resistance, and the total rain erosion soil loss was reduced to 10% of the amount before curing. When the bacterial liquid concentration was 0.8, the calcium carbonate content was the greatest, and most of the calcite phase occurred as rhombic blocks and were more densely distributed. With increase of curing time, the cementation and filling effects improved. [Conclusion] The bacteria and their extracellular polymeric substances (EPS) in the MICP acted as nucleation sites, were involved in calcium carbonate localization and growth and development, and improved the stability of the calcium carbonate. The EPS, organic matter, calcium carbonate, and Pisha sandstone minerals involved in the formation of the intermolecular hydrogen bonds and other functional groups enhanced the cementation capacity of the calcium carbonate and further improved the strength of the Pisha sandstone and its resistance to water erosion. [ABSTRACT FROM AUTHOR]