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In order to reduce the concentration of coal dust in open-pit coal mines, reduce and prevent the harm of coal dust, based on the microbial induced calcite precipitation solidification dust technology, the influence of environmental factors（temperature, pH） on the growth of Bacillus pasteuri was explored, and the effects of bacterial concentration, cement concentration and nutrient solution concentration on the solidification effect were evaluated by measuring the production of CaCO3. Through the experiment, the matrix analysis method was used to optimize the proportion of Bacillus pasteuri microbial dust suppressant and a new type of high-efficiency and environmentally friendly microbial dust suppressant for mining was proposed. The results show that the suitable culture conditions of Bacillus pasteuri are 30 ℃-35 ℃, pH 7.5, and the microbial dust suppressant is suitable for opencast coal mines under high temperature and moderate alkaline environment; there was a positive correlation between the concentration and the bacterial concentration. With the increase of cement concentration (urea, calcium chloride), the generation amount of CaCO3 increases and then decreases; Bacillus pasteurelli microbial dust suppressant has good permeability, strong wind resistance, water retention, rain resistance and other comprehensive properties; the optimization scheme of the composition ratio of Bacillus pasteuri microbial dust suppressant is: the OD600 value of Bacillus pasteuri bacteria solution is 1, the cementing solution （urea, calcium chloride mixed solution）is 0.5 mol/L, and the nutrient solution is 2 g/L.

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.

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.

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.

Currently, coastal sandy soils face issues such as insufficient foundation strength, which has become one of the crucial factors constraining urban development. Geotechnical engineering, as a traditional discipline, breaks down disciplinary barriers, promotes interdisciplinary integration, and realizes the green ecological and low-carbon development of geotechnical engineering, which is highly important. Based on the "dual carbon" concept advocating a green and environmentally friendly lifestyle, Bacillus spores were utilized to induce calcium carbonate precipitation technology (MICP) to solidify coastal sandy soils, leveraging the rough-surface and low-permeability characteristics of silty soil. The mechanical-strength variations in the samples were explored through experiments, such as calcium carbonate generation rate tests, non-consolidated undrained triaxial shear tests, and scanning electron microscopy (SEM) experiments, to investigate the MICP solidification mechanism. The results indicate that by incorporating silty soil into sandy soil for MICP solidification, the calcium carbonate generation rates of the samples were significantly increased. With the increase in the silty-soil content, the enhancement range was 0.58–3.62%, with the maximum calcium carbonate generation rate occurring at a 5% content level. As the silty-soil content gradually increased from 1% to 5%, the peak deviator stress increased by 4.2–43.2%, enhancing the sample shear strength. Furthermore, the relationship between the internal-friction angle, cohesion, and shear strength further validates the enhancement of the shear strength. Silty soil plays roles in adsorption and physical filling during the MICP solidification process, reducing the inter-particle pores in sandy soil, increasing the compactness, providing adsorption sites, and enhancing the calcium carbonate generation rate, thereby improving the shear strength. The research findings can provide guidance for reinforcing poor coastal sandy-soil foundations in various regions. [ABSTRACT FROM AUTHOR]

Bio-cementation through microbially induced calcite precipitation (MICP) has the potential to overcome several technical and environmental limitations of conventional cement-based soil improvement techniques. While a significant amount of research has been directed towards better understanding and controlling MICP processes, there is still a lack of multiphysical formulations that can be used for the design of real geotechnical applications in which both the treatment extent and its strength and deformability need to be evaluated. This paper presents the development and application of a comprehensive bio-chemo-hydro-mechanical model that can be used for designing MICP treatments with the finite element method. To overcome the limitations of current approaches based on elasticity, the formulation involves an elastoplastic constitutive model based on Mohr–Coulomb that can predict the strength increase of MICP-improved soils. The model can easily be calibrated with existing experimental results. The scope of model application is demonstrated through the case of a 2D shallow foundation strengthening. Results reveal that the questions of what level of cementation to target and how to distribute cementation efficiently are of equal importance to ultimately serve the needs of specific geotechnical problems, such as those of bearing capacity. [ABSTRACT FROM AUTHOR]

Microbial‐induced calcite precipitation (MICP) is regarded as environmentally friendly, partly due to the storage of carbon as carbonates. Although CO2 emissions during MICP have been reported, quantification of its environmental impact regarding total greenhouse gas fluxes has not yet been thoroughly investigated. In particular, N2O fluxes could occur in addition to CO2 since MICP involves the microbially mediated nitrogen cycle. This study investigated the greenhouse gas fluxes during biostimulation of MICP in quartz sand in incubation experiments. Soil samples were treated with MICP cementation solution containing calcium concentrations of 0, 20, 100 and 200 mM at a fixed urea concentration of 100 mM to offer a range of carbonation potential and/or mitigation of CO2 emissions. Greenhouse gas (CO2, CH4 and N2O) measurements were determined by gas chromatography during incubations. Soil total inorganic carbon and the isotopic composition of precipitated and emitted CO2 were determined by isotope ratio mass spectrometry. CO2 emissions (0.52 to 4.08 μg of CO2–C h−1 g−1 soil) resulted from MICP, while N2O and CH4 fluxes were not detected. Increasing Ca2+ with respect to urea resulted in lower CO2 emissions, lower solution pH, similar carbonate precipitation and urea hydrolysis inhibition. The highest urea‐to‐calcium ratio (1:0.2) emitted roughly two times the amount of CO2 (112 μg of CO2–C g−1 soil) compared to the 1:1 and 1:2 ratios (47 to 58 μg of CO2–C g−1 soil) and five to six times more than samples that did not receive Ca2+ (1:0) (~18 μg of CO2–C g−1 soil). Precipitated CaCO3–C was tenfold higher than cumulative emitted CO2–C, and isotopic analysis indicated both emitted and precipitated carbon were of urea origin. Both emitted and precipitated carbon accounted for a very low percentage of total carbon applied in the system (<0.35 and <4.5%, respectively), presumably due to limited urea hydrolysis which was negatively affected by increasing the Ca2+ concentration. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) is a promising process with applications in various industries, including soil improvement, bioremediation, and concrete repair. However, comprehensive bibliometric analyses focusing on MICP research in hydrodynamics are lacking. This study analyses 1098 articles from the Scopus database (1999–2024) using VOSviewer and R Studio, identifying information on publications, citations, authors, countries, journals, keyword hotspots, and research terms. Global participation from 66 countries is noted, with China and the United States leading in terms of contributions. The top-cited papers discuss the utilisation of ureolytic microorganisms to enhance soil properties, MICP mechanisms, concrete deterioration mitigation, soil and groundwater flow enhancement, biomineral distribution, and MICP treatment effects on soil hydraulic properties under varying conditions. Keywords like calcium carbonate, permeability, and Sporosarcina pasteurii are pivotal in MICP research. The co-occurrence analysis reveals thematic clusters like microbial cementation and geological properties, advancing our understanding of MICP's interdisciplinary nature and its role in addressing environmental challenges. [ABSTRACT FROM AUTHOR]

To explore the effects of the introduction order of calcium sources and the bacteria-to-calcium ratio on the microbially induced calcium carbonate precipitation (MICP) product CaCO3 and to achieve the regulation of CaCO3 crystal morphology, the mineralisation products of MICP were compared after combining bacteria and calcium at ratios of 1/9, 2/9, 3/9, 4/9, 5/9, and 6/9. A bacterial solution was combined with a urea solution in two calcium addition modes: calcium-first and calcium-later modes. Finally, under the calcium-first addition method, the output of high-purity vaterite-type CaCO3 was achieved at bacteria-to-calcium ratios of 2/9 and 3/9; under the calcium-later addition method, the output of calcite-type CaCO3 could be stabilised, and the change in the bacteria-to-calcium ratio did not have much effect on its crystalline shape. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitation (MICP) stands as a potent technique for remediating soils contaminated with heavy metals. However, the lack of efficient methods to detect the efficacy of MICP necessitates the use of electrical resistivity as an indicator. Consequently, an empirical model was devised to assess the strength and lead curing rate of the remediated soil. Through resistivity tests and microscopic experiments, it became evident that water content and lead contamination concentration exerted an influence on the electrical resistivity of the soil. Remarkably, the MICP technology led to a significant increase in the electrical resistivity of the remediated soil. This phenomenon can be attributed to the immobilization of lead ions within the contaminated soil, which consequently alters the soil's pore structure, thereby resulting in noticeable modifications in electrical resistivity. The empirical model further revealed a linear correlation between the strength of the remediated soil and its electrical resistivity. As the electrical resistivity increased from 1.09 to 8.71 Ω m, the strength of the soil improved from 175 to 1070 kPa. Additionally, a multifactor linear framework elucidated the interrelation between the lead curing rate and water content, primary lead contamination concentration, and electrical resistivity. The rate of lead solidification showed a positive correlation with water content but exhibited a negative correlation with both the initial concentration of heavy metal pollutants and the electrical resistivity. Notably, the highest rate of lead curing rate, reaching 90.89%, was observed at a water content of 16.1%, a pollutant concentration of 100 mg/kg, and an electrical resistivity of 1.54 Ω m. These findings firmly establish electrical resistivity as an effective means of evaluating the remediation effect of MICP, thereby providing a theoretical foundation for assessing the impact of MICP technology in the field. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) is an eco-friendly bio-remediation technology. The unconfined compressive strength (UCS) of MICP cemented soil is an important indicator of repair effectiveness. This study proposes a machine learning technique utilizing the Sine Cosine Algorithm (SCA) to optimize the regularization coefficient C and kernel width γ of the kernel extreme learning machine (KELM) to predict the UCS of MICP cemented soil. To evaluate the performance of the proposed models, a dataset containing 180 groups of the UCS of MICP cemented soil was obtained. The results obtained by SCA-KELM were compared with those obtained by the Random Forest algorithm (RF), Support Vector Machine (SVM), and KELM. The performance of these models was evaluated by the scores of MAE, RMSE, and R2. The results indicate that the SCA-KELM algorithm exhibits optimal prediction performance (Total score: 21). After optimizing KELM with SCA, the total score improved by 110%, suggesting that SCA significantly enhances the KELM performance. After model development, the optimal population size for SCA-KELM was determined to be 50. Based on the mutual information test, an innovative method was developed for categorizing factor sensitivity by employing importance scores as the partitioning criterion. This method categorizes the influencing factors into three tiers: high (importance score: 8.03–11.14%), medium (importance score: 5.93–7.25%), and low (importance score: 3.23–5.18%). These results suggest that the proposed SCA-KELM algorithm can be regarded as a powerful tool for predicting the UCS of MICP cemented soil. [ABSTRACT FROM AUTHOR]

Coastal erosion is a global environmental concern, threatening infrastructure, human livelihoods and ecosystems. Recently, microbial‐induced calcite precipitation (MICP) has emerged as a promising ground improvement technique. The present study examined the effects of adding three different fibre reinforcements, namely carbon, basalt and polypropylene, on the physical and mechanical properties of coastal soil through MICP. The fibre content used was 0.20%, 0.40% and 0.60% of soil weight. A comprehensive biotreatment investigation was conducted using Sporosarcina pasteurii (S. pasteurii) in a 0.5 molar cementation solution. The samples prepared for this study had aspect ratios of 2:1 and 1:1. These samples were subjected to biotreatment, consisting of a 24‐h cycle for 9 and 18 days. Unconfined compressive strength (UCS), split tensile strength (STS) and ultrasonic pulse velocity (UPV) tests were conducted on the biotreated samples to evaluate the effect of fibre reinforcement on the mechanical properties of the biotreated samples. The amount of calcite precipitation, scanning electron microscope (SEM) and energy dispersive X‐ray spectroscopy (EDS) were used to interpret biocementation. Results suggest that adding fibres to the MICP process enhances the mechanical properties of coastal soil. The optimum fibre content for carbon and basalt fibre was 0.40%, whereas, for polypropylene, it stood at 0.20%. The maximum UCS, STS, UPV and average CaCO3 were observed in a basalt fibre‐reinforced biotreated sample with a fibre content of 0.40%, subjected to 18‐day biotreatment. Conversely, the sample without fibre‐reinforcement, biotreated for 9 days, exhibited the lowest values for these parameters. Samples subjected to 18 days of treatment have higher values of UCS, STS, UPV and CaCO3 content than 9‐day‐treated soil samples. SEM revealed the presence of CaCO3 precipitates on the surfaces of soil grains and their contact points, and the EDS spectrum corroborated this observation. [ABSTRACT FROM AUTHOR]

Microbial-Induced Calcium Carbonate Precipitation (MICP) is an environmentally friendly, efficient, and sustainable new soil reinforcement technology. For this study, Bacillus pasteurii were domesticated and cultured in a natural seawater environment with multiple gradients and used for coral reef calcareous sand reinforcement, comparing the mineral composition of the generated precipitates and the reinforcement strength under different domestication gradient conditions. The results revealed that, while the natural seawater environment inhibits the growth of Bacillus pasteurii, the gradient domestication method allows the bacteria to gradually adapt to the natural seawater environment. Notably, their shape becomes thin and long under the seawater environment. Furthermore, the MICP mineralisation reaction rate is faster in the natural seawater environment and, with an increase in the domestication gradient, the mineralisation reaction precipitates increased. At the same time, in the seawater environment, a small amount of mineral components were generated in addition to C a C O 3 , such as M g x C a y (C O 3 ) z , and the M g 2 + mineral content increased with an increase in the domestication gradient. When comparing the curing effect under different gradients in the natural seawater environment, it was found that the Bacillus pasteurii can effectively enhance the curing effect of the calcareous sand after multi-gradient domestication in the seawater environment, with the curing effect increasing with an increase in the domestication gradient. The results of this study provide new ideas for the application of MICP technology in seawater environments for the reinforcement of calcareous sand in the construction of South China Sea islands and reefs. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) is an emerging solidification method characterized by high economic efficiency, environmental friendliness, and durability. This study validated the reliability of the MICP sand solidification method by conducting a small-scale wind tunnel model test using aeolian sand solidified by MICP and analyzing the effects of wind velocity (7 m/s, 10 m/s, and 13 m/s), deflation angle (0°, 15°, 30°, and 45°), wind erosion cycle (1, 3, and 5), and other related factors on the mass loss rate of solidified aeolian sand. The microstructure of aeolian sand was constructed by performing mesoscopic and microscopic testing based on X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). According to the test results, the mass loss rate of solidified aeolian sand gradually increases with the increase in wind velocity, deflation angle, and wind erosion cycle. When the wind velocity was 13 m/s, the mass loss rate of the aeolian sand was only 63.6%, indicating that aeolian sand has excellent wind erosion resistance. CaCO3 crystals generated by MICP were mostly distributed on sand particle surfaces, in sand particle pores, and between sand particles to realize the covering, filling, and cementing effects. [ABSTRACT FROM AUTHOR]

In natural state, granite residual soils have high shear strength. It is prone to disintegration when exposed to water environment. To investigate the influence of various reinforcement technologies on the disintegration resistance of granite residual soil and the corresponding solidification mechanism, a series of granite residual soil samples solidified by cement, lime and microbial induced calcium carbonate precipitation (MICP) are prepared. Direct shear test, disintegration test, and microscopic observation test are conducted on these solidified samples to evaluate the solidification effect of different reinforcement technologies. The results show that: (1) cement, lime and MICP treatment are effective in improving the shear strength and disintegration resistance of granite residual soil; (2) when cement and lime content is larger than 2%, and the MICP treatment of mixing + grouting is conducted, the solidified granite residual soil samples do not disintegrate within 3d, while their untreated counterparts completely disintegrates within 10 min; (3) the granite residual soil samples solidified by the MICP treatment of mixing + grouting produced a certain amount of colloidal calcium carbonate precipitates, which are capable of effectively cementing the soil particles and aggregates and fill the pores in the sample. This is the microscopic mechanism for the disintegration resistance improvement of the MICP-solidified granite residual soil. [ABSTRACT FROM AUTHOR]

In recent years, microbial mineralization has aroused attention in soil reinforcement. However, most studies focus on soil and coast on land, and the consolidation of seafloor sediments is rarely reported. In this paper, the hydrate reservoir sediments in different sea areas are strengthened, which provides a new method to solve the formation settlement problem in hydrate exploitation. In this study, the microorganisms were cultivated using both fresh and seawater, and hydrate sediments of varying particle sizes (fine sand and silty sand) were consolidated. Triaxial tests and calcium carbonate content tests were conducted to characterize the consolidation effect and detect calcium carbonate content. X-ray diffraction was used to analyze the crystal form and mineral composition of calcium carbonate generated. SEM was employed to observe the microscopic characteristics of the consolidated samples. X-ray computer tomography (X-ray CT) was utilized to analyze changes in pore throat size and the distribution of calcium carbonate in different samples and environments. The experimental results indicate that the consolidated samples exhibit higher strength, particularly in a seawater environment. Fine sand sediment samples primarily demonstrate increased cohesion, from 3.7 kPa initially to 42.3 and 86.8 kPa after consolidation, with the friction angle increasing by less than 2°. While silty sand sediment samples exhibit a greater increase in friction angle after cementation, from 22 to 24.9° and 27.6°, and the cohesion increased by only about 6%. Additionally, it was discovered that the increase in sample strength is not only related to the calcium carbonate content but also to the crystal form and distribution of calcium carbonate within the samples. Under identical sample conditions, those treated in a seawater environment exhibit a more uniform distribution of calcium carbonate and a greater abundance of calcium carbonate crystal forms, such as calcite and vaterite. Furthermore, after consolidation, among the samples treated with fresh water, the porosity of the fine sand sample decreased from 46.38 to 18.26%, and that of the silty sand sample decreased by 25.62%, indicating that fine sand and silty sand samples still possess connecting pores that are not completely obstructed by calcium carbonate. This provides a pathway for improving grouting cycles and gas release following hydrate decomposition. [ABSTRACT FROM AUTHOR]

Pore structure is a fundamental parameter in determining the hydrocarbon storage capacity and flow characteristics of a reservoir. Mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) are two commonly utilized techniques for characterizing rock pore structures. However, current studies indicate that disparities in testing methodologies due to distinct physical characteristics lead to a partial misalignment in pore size distributions. We conducted MICP (dynamic) and NMR (static) experiments on eight tight sandstone and eight shale samples and proposed a method to utilize information from the differences in MICP and NMR pore size distributions, aiming to enhance the accuracy of rock quality analysis. We observed that in rock cores where large pores are interconnected with smaller pore throats, MICP tends to overestimate the proportion of these smaller pores and underestimate the larger ones. Furthermore, we integrated information from both dynamic and static experimental processes based on physical significance and found that the fitting accuracy of the newly proposed method is superior to the Winland r35 equation. Compared to the Winland r35 equation, our new method significantly improves fitting accuracy, increasing the R-squared value from 0.46 to 0.93 in sandstones and from 0.80 to 0.87 in shales. This represents a potential high-precision, comprehensive tool for rock quality analysis, offering a new perspective for an in-depth understanding of rock properties. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitation (MICP), as an eco-friendly and promising technology that can transform free metal ions into stable precipitation, has been extensively used in remediation of heavy metal contamination. However, its depressed efficiency of heavy metal elimination remains in question due to the inhibition effect of heavy metal toxicity on bacterial activity. In this work, an efficient, low-cost manganese (Mn) elimination strategy by coupling MICP with chitosan biopolymer as an additive with reduced treatment time was suggested, optimized, and implemented. The influences of chitosan at different concentrations (0.01, 0.05, 0.10, 0.15 and 0.30 %, w/v) on bacterial growth, enzyme activity, Mn removal efficiency and microstructure properties of the resulting precipitation were investigated. Results showed that Mn content was reduced by 94.5 % within 12 h with 0.15 % chitosan addition through adsorption and biomineralization as MnCO3 (at an initial Mn concentration of 3 mM), demonstrating a two-thirds decrease in remediation time compared to the chitosan-absent system, whereas maximum urease activity increased by ∼50 %. Microstructure analyses indicated that the mineralized precipitates were spherical-shaped MnCO3, and a smaller size and more uniform distribution of MnCO3 is obtained by the regulation of abundant amino and hydroxyl groups in chitosan. These results demonstrate that chitosan accelerates nucleation and tunes the growth of MnCO3 by providing nucleation sites for mineral formation and alleviating the toxicity of metal ions, which has the potential to upgrade MICP process in a sustainable and effective manner. This work provides a reference for further understanding of the biomineralization regulation mechanism, and gives a new perspective into the application of biopolymer-intensified strategies of MICP technology in heavy metal contamination.

The calcium precipitation activity (CPA) of bacterial strains can vary in response to shifts in ambient conditions. When these conditions become unsuitable, the CPA of bacterial cells may decrease noticeably, potentially compromising the self-healing process. Nonetheless, the synergistic behavior of various bacterial strains can present additional crystallization sites for calcium precipitation and adapt to diverse ambient conditions, thus enhancing microbial-induced calcium precipitation (MICP). In this article, we delve into the interconnected mechanisms involving forty-one bacterial strains, assessing their initial spore concentration ratios and nutritional needs in relation to CPA. Based on CPA considerations, DSM6307 and B6, were selected and combined. Subsequent investigations were carried out to determine the efficacy of self-healing concrete exposed to co-cultured bacterial strains. The mineralization capacity of these combined strains was bolstered using starch and ammonium nitrate as carbon/nitrogen sources, with the ideal initial spore concentration ratio between B6 and DSM6307 established as 4:6. Through visual assessments confirmed that the synergistic effect of B6-DSM6307 can yield repair efficiencies nearing 100% for crack widths between 0.02 mm and 0.2 mm. Furthermore, water permeability and capillary absorption tests on the sample block demonstrated that the repair compound, derived from the composite spore dry powder B6-DSM6307, effectively seals cracks and binds securely. A microstructural evaluation using scanning electron microscope emphasized the prominent presence of calcite crystals, attributed to the metabolic actions of the introduced composite strains within the cracks. The findings presented in this research pave the way for subsequent studies focusing on the incorporation of co-culture bacterial strains into CPA-based engineering strategies.

In this study, native ureolytic bacteria were isolated from copper tailings soils to perform microbial-induced carbonate precipitation (MICP) tests and evaluate their potential for biocement formation and their contribution to reduce the dispersion of particulate matter into the environment from tailings containing potentially toxic elements. It was possible to isolate a total of 46 bacteria; among them only three showed ureolytic activity: Priestia megaterium T130-1, Paenibacillus sp. T130-13 and Staphylococcus sp. T130-14. Biocement cores were made by mixing tailings with the isolated bacteria in presence of urea, resulting similar to those obtained with Sporosarcina pasteurii and Bacillus subtilis used as positive control. Indeed, XRD analysis conducted on biocement showed the presence of microcline (B. subtilis 17%; P. megaterium 11. 9%), clinochlore (S. pasteurii, 6.9%) and magnesiumhornblende (Paenibacillus sp. 17.8%; P. megaterium 14.6%); all these compounds were not initially present in the tailings soils. Moreover the presence of calcite (control 0.828%; Paenibacillus sp. 5.4%) and hematite (control 0.989%; B. subtilis 6.4%) was also significant unlike the untreated control. The development of biofilms containing abundant amount of Ca, C, and O on microscopic soil particles was evidenced by means of FE-SEM-EDX and XRD. Wind tunnel tests were carried out to investigate the resistance of biocement samples, accounted for a mass loss five holds lower than the control, i.e., the rate of wind erosion in the control corresponded to 82 g/m2h while for the biocement treated with Paenibacillus sp. it corresponded to only 16.371 g/m2h. Finally, in compression tests, the biocement samples prepared with P. megaterium (28.578 psi) and Paenibacillus sp. (28.404 psi) showed values similar to those obtained with S. pasteurii (27.102 psi), but significantly higher if compared to the control (15.427 psi), thus improving the compression resistance capacity of the samples by 85.2% and 84.1% with respect to the control. According to the results obtained, the biocement samples generated with the native strains showed improvements in the mechanical properties of the soil supporting them as potential candidates in applications for the stabilization of mining liabilities in open environments using bioaugmentation strategies with native strains isolated from the same mine tailing.

In this study, the microbiologically-induced calcium carbonate precipitation (MICP) method was employed to examine its potential for repairing cracks in concrete. In addition, specific gravity and porosity values were measured to examine the effect of calcite formations on concrete surfaces and microstructures. Bacteria-supplemented concrete repaired cracks up to 0.4 mm wide by filling them with CaCO3. Furthermore, this study not only examined the healing of the width but also the length of cracks. However, as the width of the treated cracks decreased, their length increased. This indicated that the MICP treatment is more effective in a limited crack range. Specific gravity values increased, and porosity values decreased in concrete supplemented with calcifying bacteria. SEM analyses showed that calcite is a bacterial product that forms a very tight bond with a cement gel and that calcite fills visible cracks and voids and creates more of a void-free and undamaged concrete structure.

Microbially induced calcite precipitation (MICP) is an environmentally conscious ground-improvement method that can enhance the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO3) on soil particle surfaces and contacts. Although numerous studies have shown the ability of biocementation to improve the liquefaction resistance of loose sands, the effects of light cementation levels on undrained cyclic behaviors have remained relatively unexplored. A series of undrained monotonic and cyclic direct simple shear tests were performed to examine the effect of light biocementation (ΔVs

The aim of this study is to present the effect of treatment with ureolytic bacteria (Sporosarcina pasteurii) on the compressibility parameters of mineral and anthropogenic soils. In the presence of the urease enzyme, secreted by a strain of Sporosarcina pasteurii bacteria, urea hydrolysis occurs, allowing CaCO3 to be precipitated. The literature suggests applying the Microbially Induced Calcite Precipitation (MICP) method to non-cohesive soils. In order to determine whether the biomineralization process occurs in other soil types, cohesive and anthropogenic soils were tested in the laboratory. Compressibility tests were carried out in the laboratory on MICP-treated and untreated soils as reference samples. The process of biocementation in the soil is made possible by the introduction of bacteria into the soil and subsequent activation by a cementation solution (consisting of urea and calcium ions Ca2+). This paper presents the methodology for introducing bacteria into the soil, as well as the effect of the biomineralization process on the deformation parameters of the tested materials.

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) can improve the shear strength of soil via biocementation while reducing its porosity and hydraulic conductivity. The purpose of this study was to evaluate the effect of the addition of bacterial metabolites and montmorillonite on the crack healing and biocementation of sandy soil during the MICP process. Cracks were generated by drying wet soil samples in Petri dishes, after which they were sprayed with one of four treatments: deionized water, a cementation solution, bacteria mixed with the cementation solution, and bacterial metabolites mixed with the cementation solution. After five cycles of this spray treatment, the surface crack ratio was observed to decrease by about 71% when living cells were used and by about 80% when microbial metabolites were added. However, the crack reduction ratio was relatively low when treated with water (28%) and the cementation solution alone (48%). To investigate the effect of adding a phyllosilicate to improve the strength of sandy soil, MICP was induced in sand mixed with 0–30% montmorillonite (MMT). As a result, the soil strength increased with higher levels of MMT, indicating that MMT contributed to soil stabilization as a colloid for CaCO3 precipitation and via adhesion between sand grains. Therefore, for the crack healing and stabilization of sandy soil, the addition of bacterial metabolites and montmorillonite may enhance the effectiveness of the MICP process. [ABSTRACT FROM AUTHOR]

Due to coastal storm surge and wave or man-made activities, widespread coastal erosion events are emerging. In this study, the feasibility of bio-carbonation of reactive magnesium cement (RMC) to mitigate coastal erosion was investigated by conducting laboratory-scale wave erosion tests. The accumulative erosion volume (V), erosion resistance duration (Dre), and volume erosion rate (VIS) were calculated to evaluate the erosion resistance of sand dunes with the different cement thickness (T = 3 mm, 4 mm, and 5 mm) and RMC content (R = 1%, 1.5%, and 2%). The surface penetration resistance and the cementation product content (brucite/hydrated magnesia carbonates (HMCs)) were also measured to assess the effectiveness of bio-carbonation in sand dunes. Results show that in comparison with RMC hydration, the VIS decreased by 77%, Dre increased by 333%, and peak penetration resistance increased by 42% after the bio-carbonation treatment of sand dunes. Further improvements in these results were obtained with increasing T or R. Given varying T or R, we identify two types of erosion process responses under wave action. For bio-carbonation treatment with higher T or R, the erosion process response follows four phases. In contrast, for hydration treatment, or bio-carbonation treatment with lower T or R, Phase II does not exist because of small crust thickness or weak bond. The presentation of Phase II effectively delays the slope failure depending on larger erosion volume (V ≥ 93 cm3) and turns sudden into flexible failure. Scanned electron microscopy observations further revealed that HMCs formed by RMC bio-carbonation provided better filling and cementation effects than brucite formed by RMC hydration, however, massive amounts of HMCs concentrated in the shallow surface layer, causing hindered penetration and reducing the number of cementation products at higher depths. [ABSTRACT FROM AUTHOR]

Cracks in cement-based materials are a common issue to be solved in construction and civil engineering. Although in the last 20 years microbiologically induced carbonate precipitation (MICP) has been investigated successfully to recover and improve the physical properties of cracked concrete, the assessment of the effectiveness of treatments is a very important challenge to solve. In this article, a non-destructive methodology is reported to monitor the progress of crack sealing and calcium carbonate (calcite) deposition during MICP. An ureolytic bacteria was applied to treat mortar specimens for 30 wk, in which the effectiveness of calcite precipitation was evaluated. For this, two-dimensional X-ray tomography was used to characterize the calcite filling progress, showing that the MICP treatment had a higher CaCO3 filling effect when compared to control. It was estimated that MICP activity allowed to fill mortar holes with CaCO3 by 18–27%, after 8 wk. As a comparison indicator during repair treatments of cement-based materials using microorganisms that perform MICP, a Relative Treatment Effect (RTE) index was proposed. It is concluded that X-ray tomography can be used as an effective non-destructive technique to track the progress of MICP during calcite deposition and crack repair. An experimental study was carried out to monitor progression of mortar healing by ureolytic bacteria by non-destructive methods. X-ray tomography technology was feasible to monitor mortar healing in real time. Relative effect (RTE) is proposed as a comparison index in the repair treatments of cement-based materials by Microbiologically Induced Carbonate Precipitation (MICP). [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) technology has gained significant traction as an eco-friendly, cost-effective, and intelligent self-healing method for concrete cracks. The harsh service environment and high alkalinity of cement matrices have posed a significant challenge to the survival and growth of bacteria, which is crucial for the success of MICP technologies in concrete components. This article aims to present an up-to-date overview of the current research status of self-healing concrete cracks utilizing MICP technology. Specifically, it comprehensively reviews the selection of mineralization repair systems, encompassing repair mechanisms, effects, processes, nutrient addition sequences, and carrier selection. Furthermore, various characterization methods for evaluating the self-healing ability of concrete are explored, accompanied by an in-depth analysis of practical applications of self-healing concrete. Finally, this paper highlights the pressing issues facing this technology while outlining promising directions for future advancement. [ABSTRACT FROM AUTHOR]

Mining waste represents a global issue due to its potential of generating acidic or alkaline leachate with high concentrations of metals and metalloids (metal(loid)s). Microbial-induced calcium carbonate precipitation (MICP) is an engineering tool used for remediation. MICP, induced via biological activity, aims to precipitate calcium carbonate (CaCO3) or co-precipitate other metal carbonates (MCO3). MICP is a bio-geochemical remediation method that aims to immobilize or remove metal(loid)s via enzyme, redox, or photosynthetic metabolic pathways. Contaminants are removed directly through immobilization as mineral precipitates (CaCO3 or MCO3), or indirectly (via sorption, complexes, or inclusion into the crystal structure). Further, CaCO3 precipitates deposited on the surface or within the pore spaces of a solid matrix create a clogging effect to reduce contaminant leachate. Experimental research on MICP has shown its promise as a bioremediation technique for mining waste. Additional research is required to evaluate the long-term feasibility and potential by-products of MICP-treated/stabilized waste. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) presence and bioavailability in soils is a serious concern for cocoa producers. Cocoa plants can bioaccumulate Cd that can reach humans through the food chain, thus posing a threat to human health, as Cd is a highly toxic metal. Currently, microbiologically induced carbonate precipitation (MICP) by the ureolytic path has been proposed as an effective technique for Cd remediation. In this work, the Cd remediation potential and Cd resistance of two ureolytic bacteria, Serratia sp. strains 4.1a and 5b, were evaluated. The growth of both Serratia strains was inhibited at 4 mM Cd(II) in the culture medium, which is far higher than the Cd content that can be found in the soils targeted for remediation. Regarding removal efficiency, for an initial concentration of 0.15 mM Cd(II) in liquid medium, the maximum removal percentages for Serratia sp. 4.1.a and 5b were 99.3% and 99.57%, respectively. Their precipitates produced during Cd removal were identified as calcite by X-ray diffraction. Energy dispersive X-ray spectroscopy analysis showed that a portion of Cd was immobilized in this matrix. Finally, the presence of a partial gene from the czc operon, involved in Cd resistance, was observed in Serratia sp. 5b. The expression of this gene was found to be unaffected by the presence of Cd(II), and upregulated in the presence of urea. This work is one of the few to report the use of bacterial strains of the Serratia genus for Cd remediation by MICP, and apparently the first one to report differential expression of a Cd resistance gene due to the presence of urea. [ABSTRACT FROM AUTHOR]

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As conventional concrete repairs have shortcomings and impact the environment, multiple attempts exist to find alternative sustainable measures to address this issue. Microbial-induced carbonate precipitation (MICP) using microalgae is one of the proven methods that can heal microcracks. In this study, the method used in repairing micro-cracks is by spraying microalgae species, namely, Arthrospira platensis and Synechococcus elongatus, cultured in a high calcium-based medium onto the surface of the cement mortar. The crack healing was evaluated for 14 days after the cracks were induced by applying 65–70% of the maximum threshold load. The results show that the microalgal-treated specimens exhibited a higher strength recovery, crack closure, and less water absorption than the control specimen. It is also observed that over 75–80% (0.26 mm, approx.) of the cracks can be healed within the span of 14 days sustainably using microalgae. This research investigated the healing capacity of cracked cement mortar by applying a microalgal solution on the surface externally. The study proves that microalgae are a better and more eco-friendly way than other external chemical agents to crack repair. A maximum of 67% strength was regained in 14 days of treatment with Arthrospira platensis. Over 75–80% of cracks can heal after spraying microalgae. Comparing SEM and XRD polymorphs, CaCO3 precipitation was identified as Vaterite and Calcite. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) stands as an environmentally friendly and promising technique for enhancing the performance of soil. Bacteria catalyze the hydrolysis of urea, prompting calcium ions to react with carbonate ions, ultimately forming calcium carbonate precipitation as a cement within soil grains. However, studies of using MICP to enhance granite residual soil (GRS) that is recognized as a problematic soil because of its wide grain size distribution are relatively rare. In this present study, bio-cemented GRS samples were prepared through grouting with Sporosarcina pasteurii as the colony and a mixture of urea and calcium chloride as the cementation solution. The effect of cementation–solution concentrations on the mechanical properties of the bio-cemented samples was analyzed through unconfined compression and triaxial shear tests. Furthermore, X-ray computerized tomography, scanning electron microscopy, and X-ray diffraction experiments were performed to reveal the mechanism of MICP from a microscopic perspective. The experimental results indicate that an optimal concentration of 2 mol/L achieved the highest level of cementation, resulting in an impressive 47.15% increase in the unconfined compressive strength of the GRS samples. The triaxial shear strength and stress paths of bio-cemented samples were affected by the cementation level. The variation of porosity indicated that CaCO3 precipitation improves soil densification by filling the macropores among the soil grains. The CaCO3 precipitates from the MICP treatment predominantly exist in the form of calcite crystals, serving to fill, wrap, and cement within the soil structure, thereby enhancing the cohesive and frictional forces exerted by the bio-cemented grains. [ABSTRACT FROM AUTHOR]

Microbial-induced calcite precipitation (MICP) is an innovative technology in civil engineering. However, the high cost of components and the fragility of the treated soil limit its wide use. One of the possible solutions is organic waste incorporation at different stages of the technology. In the present study, we consider the use of spent brewer's yeast (BSY) to produce bacterial inoculates and wastepaper, flax shives and sawdust as reinforcing additives into the soil. We showed that the replacement of expensive components of LB medium by BSY extract increased biomass growth characteristics of Bacillus subtilis K51, B. cereus 4b and Micrococcus luteus 6 strains by 1.4, 1.5 and 1.8 times, respectively, while for B. subtilis 168, they were comparable to LB medium. The urease activities of all strains were not reduced compared to the control. Among the three kinds of cellulose-containing waste, wastepaper incorporation into MICP-treated soil samples led to an increase in compressive strength by 2.1 times and precipitated calcite percentage by almost 1.5 times compared to a sample without additives. Thus, we showed the potential for soil stabilization through MICP using organic waste. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) is an environmentally friendly approach that relies on the production of calcium carbonate by microorganisms to construct or reinforce coastal structures. In order to address the disadvantages of current coastal countermeasures techniques, MICP is a cost-effective solution that can be used to repair and restore coastal habitats damaged by human activities. The resulting structures formed through MICP are strong and durable, providing long-term protection against erosion and flooding caused by storms or rising sea levels. Biominerals, including calcium carbonate or calcium phosphate, are used to create complex composites with organic molecules by combining the strength of inorganic materials with the versatility and biocompatibility of organic macromolecules. It is of the utmost importance to investigate the functionality of MICP and scale up its deployment in various fields in order to thoroughly assess the instrument's application. Coastal erosion has been a severe concern in archipelagic countries. Therefore, this study explored the Miyazaki coast in Japan and the Yogyakarta coastline in Indonesia to minimize coastal erosion using MICP. The bacteria found in Miyazaki (Sporosarcina species) and the Yogyakarta coast (Pseudoalteromonas tetradonis) were used in the experiment. As a result, the sample treated with a gradual injection of the cementation solution achieved about 6 MPa UCS after 21 days of treatment. The objective were investigated the potential biotreatment with original sand materials and to evaluate the long-term durability under saturated conditions. For these purposes, the MICP-treated sand columns were subjected to series of compression tests and wet-drying (WD) durability analysis. [ABSTRACT FROM AUTHOR]