An indigenous bacterium with enhanced performance of microbially-induced Ca-carbonate biomineralization under extreme alkaline conditions for concrete and soil-improvement industries

A quantitative, high-throughput urease activity assay for comparison and rapid screening of ureolytic bacteria

Microbially induced carbonate precipitation (MICP) has proven to be an effective method for soil reinforcement. Sporosarcina pasteurii is widely used due to its high urease activity. However, being an alkaliphilic bacterium, its limitations in acidic soil environments tend to be overlooked. This study isolated a native urease-producing bacterial strain Bacillus aryabhattai with acid tolerance, and comparative analysis of the growth characteristics of B. aryabhattai and S. pasteurii. The grouting and spraying techniques were employed to reinforce granite residual soil by the B. aryabhattai and the S. pasteurii, and the reinforcement mechanisms were systematically investigated. Experimental results indicated that despite exhibiting slightly lower urease activity and growth, the indigenous urease-producing bacterium B. aryabhattai demonstrated superior environmental resilience in terms of both environmental temperature and pH range. The soil samples reinforced by grouting with B. aryabhattai and S. pasteurii exhibited increases in ultrasonic wave velocity, unconfined compressive strength, cohesion, and cumulative disintegration rate to varying degrees compared to the untreated soil samples. Meanwhile, the resistance value of the soil samples reinforced by spraying with B. aryabhattai and S. pasteurii decreased by 84.39% and 79.79%, respectively. Additionally, the calcium carbonate content in the upper section of soil reinforced with B. aryabhattai was comparable to that of S. pasteurii; however, while in the lower section, it exhibited a 36.22% higher precipitation rate than the S. pasteurii-treated soil. Overall, the indigenous strain B. aryabhattai demonstrated remarkable reinforcement effectiveness, attributed to its rapid adaptation to weakly acidic soil conditions and moderate urease activity, which promoted a homogeneous distribution of calcium carbonate. These findings provide significant insights for soil reinforcement applications through MICP.

Strengthening effect of nano-SiO2 on microbial induced carbonate precipitation (MICP) solidified sediment: Macro- and micro-analysis

Microbially Induced Carbonate Precipitation (MICP) is currently viewed as one of the potential prominent processes for field applications towards the prevention of soil erosion, healing cracks in bricks, and groundwater contamination. Typically, the bacteria involved in MICP manipulate their environment leading to calcite precipitation with an enzyme such as urease, causing calcite crystals to form on the surface of grains forming cementation bonds between particles that help in reducing soil permeability and increase overall compressive strength. In this paper, the main focus is to study the MICP performance of three indigenous landfill bacteria against a well-known commercially bought MICP bacteria (Bacillus megaterium) using sand columns. In order to check the viability of the method for potential field conditions, the tests were carried out at slightly less favourable environmental conditions, i.e., at temperatures between 15-17°C and without the addition of urease enzymes. Furthermore, the sand was loose without any compaction to imitate real ground conditions. The results showed that the indigenous bacteria yielded similar permeability reduction (4.79 E-05 to 5.65 E-05) and calcium carbonate formation (14.4–14.7%) to the control bacteria (Bacillus megaterium), which had permeability reduction of 4.56 E-5 and CaCO3 of 13.6%. Also, reasonably good unconfined compressive strengths (160–258 kPa) were noted for the indigenous bacteria samples (160 kPa). SEM and XRD showed the variation of biocrystals formation mainly detected as Calcite and Vaterite. Overall, all of the indigenous bacteria performed slightly better than the control bacteria in strength, permeability, and CaCO3 precipitation. In retrospect, this study provides clear evidence that the indigenous bacteria in such environments can provide similar calcite precipitation potential as well-documented bacteria from cell culture banks. Hence, the idea of MICP field application through biostimulation of indigenous bacteria rather than bioaugmentation can become a reality in the near future.

The microbial induced mineral precipitation can be used to modify and improve the performance of construction materials and can partially replace ordinary Portland cement. Microbially induced carbonate precipitation (MICP) mainly uses the urease secreted during the growth of urease-producing bacteria (UPB) to hydrolyze urea produce CO32- and reacts with Ca2+ to form CaCO3. Microbially induced struvite precipitation (MISP) mainly uses the urease to decompose urea to produce NH4+. In the presence of hydrogen phosphate and magnesium ions, the struvite can be precipitated. The elemental composition and chemical composition of the precipitates produced by the MICP and MISP processes are analyzed by energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction analysis (XRD). The morphology of the precipitates can be observed by scanning electron microscope (SEM). Compared with the initial porosity, the MICP method can reduce the initial porosity of the sand column by 2.98% within 90 min. However, the MISP is only 1.45%. The permeability coefficient of the sand column can be effectively reduced in the MICP process. The total content of cementitious materials is 27.71g and 13.16g in MICP- and MISP-cemented sand columns, respectively. The MICP technology can improve the strength of alkali-activated mortars under different pH values of the UPB solution.

The demand for ground improvement of marine sediments has been risen in construction of offshore infrastructures, including wharves, embankments and breakwaters. In recent years, microbially induced carbonate precipitation (MICP) has developed rapidly and become an alternative technology for increasing soil strength and limiting soil erosion. Silty sand is widely distributed in offshore areas throughout the world. The high salinity of seawater may have an impact on the bacterial activity, while the fine particles in silty sand would affect the transportation of cementation solution and the formation of carbonate precipitation. In this study, attentions are paid to the application of MICP on improvement of marine silty sand properties, as well as the factors influencing the hydraulic conductivity and strength of the bio-cemented soil. Multi-gradient domestication tests on Sporosacina pasteurii were carried out to ensure the bacterial and urease activities in seawater environment. It was found that the bacterial concentration and urease activity after five-gradient domestication in seawater reached 98.5% and 92.8% of those in the deionized water environment, respectively. The permeability, unconfined compressive strength (UCS) and content of carbonate precipitation of bio-cemented specimens were measured. The MICP treatment on silty sand with seawater resulted in an increase of UCS to 700 kPa and a reduction of permeability by an order of magnitude, corresponding to a carbonate content of 8%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to investigate the types and distributions of carbonate crystals. The results indicated the formation of calcium carbonate and magnesium carbonate crystals due to the interaction between carbonate ions and calcium and magnesium ions in seawater. The precipitations were distributed on the surfaces of soil particles and near particle contact points, affecting the soil microstructure and thus the strength and permeability. The influences of concentration and injection rate of cementation solution on the efficiency of MICP were demonstrated and the recommended values were given. This study may provide a possible solution for improvement of engineering properties of marine silty sand foundations.

In recent years, traditional material for coastal erosion protection has become very expensive and not sustainable and eco-friendly for the long term. As an alternative countermeasure, this study focused on a sustainable biological ground improvement technique that can be utilized as an option for improving the mechanical and geotechnical engineering properties of soil by the microbially induced carbonate precipitation (MICP) technique considering native ureolytic bacteria. To protect coastal erosion, an innovative and sustainable strategy was proposed in this study by means of combing geotube and the MICP method. For a successful sand solidification, the urease activity, environmental factors, urease distribution, and calcite precipitation trend, among others, have been investigated using the isolated native strains. Our results revealed that urease activity of the identified strains denoted as G1 (Micrococcus sp.), G2 (Pseudoalteromonas sp.), and G3 (Virgibacillus sp.) relied on environment-specific parameters and, additionally, urease was not discharged in the culture solution but would discharge in and/or on the bacterial cell, and the fluid of the cells showed urease activity. Moreover, we successfully obtained solidified sand bearing UCS (Unconfined Compressive Strength) up to 1.8 MPa. We also proposed a novel sustainable approach for field implementation in a combination of geotube and MICP for coastal erosion protection that is cheaper, energy-saving, eco-friendly, and sustainable for Mediterranean countries, as well as for bio-mediated soil improvement.

This narrative review evaluates green reinforcement technologies for peat soil based on the synergistic mechanism of microbially induced carbonate precipitation (MICP), magnesium-rich synthetic gypsum (MRSG) and concrete waste (CW). A systematic search of Scopus, Web of Science and Google Scholar from 1997 to 2025 using keywords related to peat stabilisation, MICP, MRSG and CW identified 67 experimental studies. The review first summarises the distribution and engineering characteristics of peat soils and the limitations of conventional physical and chemical improvements. It then explains MICP ureolysis and factors influencing calcite precipitation. The reviewed studies demonstrate substantial strength enhancements in treated peat soils. Ureolytic MICP treatment elevated the unconfined compressive strength (UCS) of tropical peat from approximately 5 kPa to about 82 kPa. Treatment with 5% Mg-rich synthetic gypsum (MRSG) by weight resulted in a fourfold increase in UCS, from about 15 kPa to 59 kPa. A notable synergistic effect was observed in a combined treatment incorporating 10% MRSG and 10% concrete waste aggregate (CW), which yielded the most significant gain by elevating the UCS from 36 kPa to 144 kPa. The microstructural analysis revealed calcite, ettringite, and C–S–H gel. The synergy arises because MRSG and concrete waste supply Ca 2+ /Mg 2+ and alkalinity, accelerating bacterial ureolysis and carbonate precipitation. Considering the environmental impact, urea hydrolysis produces NH 4 + , and excessive CaCl2 or high pH values can inhibit bacteria, posing a risk. Overall, MICP–MRSG–CW technology offers a promising, low-carbon alternative for stabilising peat soils.

Biocementation of coral sand under seawater environment and an improved three-stage biogrouting approach

Introduction
 Ground source heat pump (GSHP) or shallow geothermal energy systems are gaining attention for helping combat global warming and the negative effects of urbanisation caused by human activities. In recent decades, energy geo-structure techniques have developed by using subsurface infrastructures to exchange heat with the ground. These techniques can provide space heating and cooling while still preserving the primary structural function. As a result, they have become a valuable part of geothermal energy systems. Researchers have developed an understanding of incorporating ground heat exchangers into foundation piles, retaining walls, and tunnel linings with modest additional cost [1-4]. Pavements are also structures in contact with the ground that have the potential to be used as energy geo-structures (i.e., geothermal pavements), yet, their use has not been extensively studied [5-8].
 Soil thermal conductivity is an important factor influencing the efficiency of geothermal pavements since heat transfer in soils occurs primarily by conduction [9]. Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is an innovative technique for strengthening sandy soils by coating and binding soil grains with calcium carbonate crystals. The distribution and arrangement of the CaCO3 within the pore spaces play a crucial role in determining the resulting strength of the treated sand. In addition, these crystals can act as thermal bridges to enhance the soil's thermal conductivity [10]. Combining geothermal pavements with MICP sand is still nascent, and the limited number of studies that exist mainly focus on the associated thermal property changes [11]. However, since the principal function of pavements is transmitting (dynamic) loads to the subbase and the underlying soil, the thermal conductivity of the MICP-treated pavement may vary as a result of the applied mechanical loads (e.g., due to the partial or total loss of thermal bridges and/or particle rearrangement). This research thus investigates the changes in the thermal conductivity of MICP-treated sands as they are subjected to quasi-static triaxial compression. The experimental results collected can deepen our understanding of the thermo-mechanical behaviour of MICP-treated sands and provide practical insights for using MICP to reinforce the subbase or underlying soil of geothermal pavements.
 Methodology
 This research performed a series of quasi-static triaxial tests on MICP-treated Houston sand, fine-grained, high-purity silica sand. Sporosarcina pasteurii (strain designation DSM 33) was used for the MICP treatment of the soil specimen. To study the effect of CaCO3 content on the thermo-mechanical performance of MICP-treated sand, three cementation solution treatment cycles were applied, yielding theoretical CaCO3 contents of 0.6%, 1.6% and 2.7% by weight, respectively. Details on the MICP treatment of the samples can be found in [12]. Samples for triaxial testing were treated in cylindrical tubes of 50mm inner diameter and 100mm height. To investigate the influence of the CaCO3 content on the soil thermal conductivity, MICP-treated specimens were air-dried prior to triaxial testing Triaxial tests were subsequently conducted in dry conditions to isolate the effect of the MICP and avoid the influence of water content on soil thermal conductivity (λ). Furthermore, a new miniaturised transient sensor was embedded in the triaxial samples to monitor the λ changes during the sharing phase [12].
 Results
 An example of the evolution of the deviatoric stress with axial strain under 50kPa confining stress (σ3) in the triaxial cell is shown in Figure 1a. Compared to the untreated sand, MICP-treated samples lead to higher peak strength and stiffness. Importantly, λ changes during triaxial testing for different CaCO3 contents are summarised in Figure 1b. Results indicate that the increase in CaCO3 content can significantly improve λ, and that λ rapidly decreases post-peak strength due to dilation and CaCO3 bond breakage. Once the samples reach its ultimate state, λ remains unchanged.

A novel strategy for reinforcing cementation process coupling microbially induced carbonate precipitation (MICP) with cross-linked silk fibroin

Improving the thermal-mechanical performance of bio-treated backfill materials by addition of magnetic iron oxide nanoparticles (nano-Fe3O4)

Effect of Microbially Induced Carbonate Precipitation (MICP) in the Highly Saline Silty Soil of the Cold Plateau Area of the Qinghai-Tibetan Plateau

Mechanical properties and repairing mechanism of recycled cement stabilized macadam for road base based on microbial induced carbonate precipitation technology

Whole-cell evaluation of urease activity of Pararhodobacter sp. isolated from peripheral beachrock