Microbially Induced Calcium Carbonate Precipitation Research Articles

Influence of bacterial biomineralization conditions on the microstructural characteristics of cement mortar

Bacterial concrete is considered an effective self-healing material due to its capacity to repair damages such as cracks autonomously throughout microbially induced calcium carbonate precipitation (MICP). This study aimed to evaluate the direct incorporation of bacteria into mortar within the framework of concrete damage repairing technol-ogy. Sporosarcina pasteurii, a bacterium capable of surviving in alkaline conditions and inducing biomineralization by precipitating calcium carbonate, was selected for this purpose. Cement mortars with and without bacteria were prepared, and these samples were cured in different solutions to examine bacterial reactivity: a media solution for bacterial growth and calcium carbonate precipitation, a urea solution for calcium carbonate precipitation, and normal water. Mechanical properties and microstructural characteristics were investigated using various approaches. The out-comes revealed that the calcium carbonate precipitated by bacteria in cement mortar exhibited varying phases, such as calcite and vaterite, depending on the specific curing solutions employed. Particularly, the presence of properly precipitated calcium carbonate was found to significantly enhance the durability and mechanical properties of the cement mortar.

Influence of biochar in the calcite precipitation of sandy soil using sporosarcina ureae

The microbially induced calcium carbonate precipitation (MICP) technology is an emerging novel and sustainable technique for soil stabilization and remediation. MICP, a microorganism-mediated biomineralization process, has attracted interest for its potential to enhance soil characteristics. The inclusion of biochar, a carbon-rich substance formed by biomass pyrolysis, adds another degree of intricacy to this process. The study highlights the impact of the combination of biochar and MICP together, using a bacterium, Sporosarcina ureae, on soil improvement. This blend of MICP and biochar improved the soil in terms of its geotechnical properties and also enabled the sequestering of carbon safely. It was observed that addition of 4% biochar significantly increased the soil's shear strength parameters (c and φ) as well as its stiffness after 21 treatment cycles. This improvement was because the calcium carbonate precipitate, which acts as a crucial binding agent, increased significantly due to microbial action in the soil-biochar mixture compared to the pure soil sample. The excess carbonate precipitation on account of biochar addition was verified through SEM-EDAX analysis where the images showed noteworthy carbonate precipitation on the surface of particles and increment in the calcium mass at the same treatment cycles when compared with untreated sand. The collaboration between MICP and biochar effectively increased the carbon sequestration within the sand sample. It was observed that at 21 cycles of treatment, the carbon storage within the sand sample increased by almost 3 times at 4% biochar compared to sand without any biochar. The statistical analysis further affirmed that strength depends on both biochar and the number of treatment cycles, whereas carbon sequestration potential is primarily influenced by the biochar content alone. This strategy, as a sustainable and environmentally friendly approach, has the potential to reform soil improvement practices and contribute to both soil strength enhancement and climate change mitigation, supporting the maintenance of ecological balance.

The Application of Microbially Induced Calcium Carbonate Precipitation (MICP) Technology in Building Materials and its Contribution to Waste Resource Utilization

Abstract: In many countries around the world, waste generation has become an increasingly pressing issue, particularly in urban areas experiencing rapid population growth and industrialization. The volume of waste produced by human activities continues to rise, posing significant challenges to the environment, economy, and public health. Improper waste management can lead to air and water pollution, soil degradation, and the spread of diseases. Additionally, waste generation consumes substantial natural resources and energy, exacerbating resource depletion and contributing to greenhouse gas emissions.To address these challenges, sustainable waste management practices are essential to reduce waste generation and promote resource recovery and recycling. In this context, the development of innovative technologies, such as Microbially Induced Calcium Carbonate Precipitation (MICP) in building materials, offers an effective means of converting waste into valuable and sustainable applications. MICP is an environmentally friendly biogeochemical technique that employs microorganisms and chemical agents in biological processes to produce carbonate minerals, providing an energy-efficient, cost-effective, and sustainable solution to environmental and engineering challenges.Recent research indicates that waste streams can substitute for several MICP chemical components in microbial and cementitious agent growth media. MICP technology has been found not only to be effective in handling hazardous waste streams but also to be a cost-effective and sustainable solution applicable to various waste media. This comprehensive review aims to provide insights into the environmental advantages and engineering applications of MICP technology, with a particular focus on the potential contributions of waste streams. It also offers guidance for researchers on identifying and overcoming challenges associated with using waste streams for MICP technology applications.

Removal of cadmium through biomineralization using halophilic and ureolytic bacteria under saline conditions

Heavy metal pollution poses an immense challenge to humanity owing to its severe toxic effects on living beings. This study investigates the bioremediation potential of the urease-hydrolyzing and halophilic bacterium Bacillus paramycoides- MSR1 to reduce the toxicity of cadmium (Cd) in the environment under salt stress through microbially induced calcium carbonate precipitation (MICCP). The enzymatic activity of urease and calcium carbonate (CaCO3) precipitation was studied under different concentrations of salt stress (0%, 3.5%, 5%, 7.5%, 10%, 15%) and maximum urease activity of 735.7 U/ml was recorded at 5% salt stress. The urease activity and CaCO3 precipitation decreased with increasing Cd toxicity (0, 10, 20, 30, 40, 50, and 60 μM). The maximum concentration of Cd endured by bacteria was determined by IC50 value and the minimum inhibitory concentration of Cd was recorded as 9.86 μM under 5% stress. Atomic absorption spectroscopy results revealed that Cd removal was as high as 90.3% under 5% salt stress. Microstructural analysis through FE-SEM revealed the surface topography of carbonate crystals as rhombohedral, whereas EDS confirmed the presence of CaCO3 and Cd in the bio-precipitates. These results suggest that MICCP is a potential, environmentally safe, low-cost technique and an excellent alternative to conventional heavy metal removal strategies from the environment.

Microbially mediated rock fine fracture mineralization sealing: Evolution of flow channels and the resulting transmissivity reduction

The sealing of fine aperture fractures in geological repositories is an important consideration for long-term sealing integrity. Common grouting materials have some disadvantages, such as low sealing efficiency, environmental pollution, etc. Microbially induced calcium carbonate precipitation (MICP) has been proposed as a potential solution for sealing fine fractures. In this paper, the microbially mediated fine fracture mineralization sealing process was investigated by using a designed visual test device. The flow channel evolution and fracture transmissivity reduction during the sealing process were systematically monitored and analysed. Based on the experimental results, a sealing pattern of microbially mediated rock fracture mineralization was proposed. In addition, the influence of biomineralized floc particles formed by different bacterial concentrations on the critical sealing threshold of fracture was discussed. The results show that the sealing pattern can be divided into four stages: (a) flow channel formation; (b) preferred channel blocking; (c) finer channel blocking; (d) filtration zone formation. The four sealing stages correspond to different fracture transmissivity reduction trends, and the majority of transmissivity reduction occurs in stage III. However, the transmissivity decreases rapidly only after the preferred channels are blocked, which indicates that the critical threshold of sealing fracture is reached. The critical sealing threshold is mainly attributed to two factors: biomineralized floc particle size and fracture aperture. Larger floc particles and finer aperture are more likely to reach the critical sealing threshold, improving the sealing efficiency of fractures. It is crucial to further study the interaction between the biomineralized floc particle sizes and the fracture aperture at the critical sealing threshold to optimize the application of MICP-grouting in rock fine fractures.

Influence of pore property and alkalinity on the bio-deposition treatment efficiency of recycled aggregates

Microbial induced calcium carbonate precipitation (MICP) technology has been successfully used to enhance the properties of recycled concrete aggregates. However, the complex source and varied physical and chemical properties of recycled aggregates may have influence on the modification efficiency since microbes are often sensitive to the surroundings. In this study, two representative types of recycled aggregates, recycled concrete aggregates (RCA) and recycled brick aggregates (RBA), were subjected to two kinds of MICP treatments, basic MICP treatment and sodium alginate (SA) aided MICP treatment. The absorption and desorption of bacteria in/on aggregates during MICP treatments were quantified. The physical and chemical properties of aggregates after the bio-treatments were tested, and the influence of alkalinity and pore structure of aggregates under various MICP treatment methods on treatment efficiency were detailed investigated. Results indicated that, when the aggregates were subjected to the basic MICP treatment, the treatment efficiency was more remarkable in RBA, because of its high porosity and moderate pH (around 8–9), which facilitated the absorption of bacteria in/on aggregates and urease activity respectively. While under SA-aided MICP treatment, the influence of pore structure and alkalinity of aggregates on the treatment efficiency was not significant compared with that under the basic MICP treatment, especially the mass of CaCO3 on the aggregates. The biogenic CaCO3 generated by SA-aided MICP treatment not only plugged micropores, but also distributed all over the entire surface of the aggregates, resulting in a sufficient repair of microcracks. Meanwhile, the surface repair may reduce the influence of pore structure and pH of aggregates on the precipitation process, thereby reducing the impact of varied physical and chemical properties of aggregates on the treatment efficiency, which was conducive to the widely unified application of SA-aided MICP treatment in the modification of recycled aggregate based on construction solid waste.

Degradation of tetracycline based on activated persulfate by microbial-induced calcium carbonate precipitation as templates modified sludge biochar

The template method is capable of enhancing the catalytic sites by controlling the size and properties of the material. However, the integration of the template and biological methods requires further development. In this study, an environmentally friendly modified sludge biochar (TBC) was successfully synthesized by modifying sludge with biosynthetic calcium precipitation as a template. TBC effectively activated peroxydisulfate (PDS), achieving a tetracycline (TC) removal efficiency of 95.07 %. Active species identification and electrochemical analyses confirmed that the main mechanism for TBC to activate PDS in degrading TC involved the non − radical pathway, including singlet oxygen (1O2) production and direct electron transfer. The CO functional group was the main active group to produce 1O2. Additionally, the adsorption of TBC also played a role in TC removal. Experimental results indicated that TBC exhibits significant stability and reusability. This study offers novel insights into utilizing the template method for PDS activation to degrade TC and presents a viable approach for the rational disposal of sludge.

A Numerical Bio-Geotechnical Model of Pressure-Responsive Microbially Induced Calcium Carbonate Precipitation

The employment of Microbially Induced Calcium Carbonate Precipitation (MICP) is of increasing interest as a technique for environmentally sustainable soil stabilisation. Recent advancements in synthetic biology have allowed for the conception of a pressure-responsive MICP process, wherein bacteria are engineered to sense environmental loads, thereby offering the potential to stabilise specific soil regions selectively. In this study, a 2D smart bio-geotechnical model is proposed based on a pressure-responsive MICP system. Experimentally obtained pressure-responsive genes and hypothetical genes with different pressure responses were applied in the model and two soil profiles were evaluated. The resulting model bridges scales from gene expression within bacteria cells to geotechnical simulations. The results show that both strata and gene expression–pressure relationships have a significant influence on the distribution pattern of calcium carbonate precipitation within the soil matrix. Among the evaluated experimental genes, Gene A demonstrates the best performance in both of the two soil profiles due to the effective stabilisation in the centre area beneath the load, while Genes B and C are more effective in reinforcing peripheral regions. Furthermore, when the hypothetical genes are utilised, there is an increasing stabilisation area with a decreased threshold value. The results show that the technique can be used for soil reinforcement in specific areas.

Research on the Effect of Natural Seawater in Domesticating Bacillus pasteurii and Reinforcing Calcareous Sand

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 CaCO3, such as MgxCay(CO3)z, and the Mg2+ 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.

Identification and extraction of cementation patterns in sand modified by MICP: New insights at the pore scale.

Microbially induced calcium carbonate precipitation (MICP) is an environmentally friendly technology that improves soil permeability resistance through biocementation. In this study, 2D microscopic analysis and 3D volume reconstruction were performed on river sand after 24 cycles of bio-treatment based on stacked images and computed tomography (CT) scanning data, respectively, to extract biocementation patterns between particles. Based on the mutual validation findings of the two techniques, three patterns in the biocemented sand were identified as G-C-G, G-C, and G-G. Specifically, 2D microscopic analysis showed that G-C-G featured multi-particle encapsulation and bridging, with a pore filling ratio of 81.2%; G-C was characterized by locally coated particle layers, with a pore filling ratio of 19.7%; and the G-G was marked by sporadic filling of interparticle pores, with a pore filling ratio of 11.7%. G-C-G had the best cementation effect and permeability resistance (effective sealing rate of 68.5%), whereas G-C (effective sealing rate of 2.4%) had a relatively minor contribution to pore-filling and flow sealing. 3D volume reconstruction showed that G-C-G had the highest pore filling rate, followed by G-G and G-C. The average filling ratios of area and volume for G-C-G were 83.979% and 77.257%, respectively; for G-G 20.360% and 23.600%; and for G-C 11.545% and 11.250%. The analysis of the representative element volume (REV) was conducted, and the feasibility and reliability of the micro-scale pattern extraction results were confirmed to guide the analysis of macro-scale characteristics. The exploration of the effectiveness of cementation patterns in fluid sealing provides valuable insights into effective biocementation at the pore scale of porous media, which may inspire future research.

Genome Sequence Analysis of Calcifying Bacteria Bacillus paranthracis CT5 and Its Biomineralization Efficacy to Improve the Strength and Durability Properties of Civil Structures.

Bacteria producing urea amidohydrolases (UA) and carbonic anhydrases (CA) are of great importance in civil engineering as these enzymes are responsible for microbially induced calcium carbonate precipitation (MICCP). In this investigation, genomic insights of Bacillus paranthracis CT5 and the expression of genes underlying in MICCP were studied. B. paranthracis produced a maximum level of UA (669.3 U/ml) and CA (125 U/ml) on 5th day of incubation and precipitated 197mg/100ml CaCO3 after 7days of incubation. After 28days of curing, compressive strength of bacterial admixed and bacterial cured (B-B) specimens was 13.7% higher compared to water-mixed and water-cured (W-W) specimens. A significant decrease in water absorption was observed in bacterial-cured specimens compared to water-cured specimens after 28days of curing. For genome analysis, reads were assembled de novo producing 5,402,771bp assembly with N50 of 273,050bp. RAST annotation detected six amidohydrolase and three carbonic anhydrase genes. Among 5700 coding sequences found in genome, COG gene annotation grouped 4360 genes into COG categories with highest number of genes to transcription (435 genes), amino acid transport and metabolism (362 genes) along with cell wall/membrane/envelope biogenesis and ion transport and metabolism. KEGG functional classification predicted 223 pathways consisting of 1,960 genes and the highest number of genes belongs to two-component system (101 genes) and ABC transporter pathways (98 genes) enabling bacteria to sense and respond to environmental signals and actively transport various minerals and organic molecules, which facilitate the active transport of molecules required for MICCP.

A new bioslurry-induced restoration method via biomineralization for fragmented ceramic cultural relics

This study presents a new restoration method for fragmented ceramic cultural relics using bioslurry-induced biocementation via a microbially induced calcium carbonate precipitation (MICP) process. Bioslurry is highly urease active calcium carbonate crystals, which serve as filling and cementitious material with newly induced calcite precipitation when supplying cementation solution (urea and calcium source). With the pre-filling of bioslurry and newly induced calcite crystals, the fragmented ceramic can be connected and the gap along the fracture surface can be sealed. Due to the high urease active bacteria cells embedded in bioslurry, the ceramic restoration can be completed in 24 h with the optimal concentration of cementation solution of 1.6 M. Taking the advantage of bonding effect gained from newly induced calcite precipitation, the tensile strength was improved up to 0.92 MPa through a customized tensile strength test. This is satisfactory to ensure the stability and integrity of fragmented ceramic after bioslurry-induced restoration. A demonstrative restoration has been completed on fragmented ceramics from Ming Dynasty. With the good bonding strength and high stability of bioslurry-induced calcite precipitation, the proposed bioslurry-induced restoration method contributes valuable insights to the conservation of ceramic cultural relics. Other prospective applications include the restoration of masonry relics and bone relics.

Generation of enhanced endospores for microbially induced calcium carbonate precipitation (MICCP) via thermal shock for concrete self-healing

Endospores are desirable phenotypes in Microbially-Induced Calcium Carbonate Precipitation (MICCP) for their durability in challenging environments. This study investigates the impact of various endosporulation methods on endospore morphology and their subsequent performance under harsh conditions. Results revealed that the Thermal Shock (TS) method produced larger endospores, possibly due to multi-layer encasement. Notably, endosporulation and germination ratios, besides MICCP effectiveness, achieved via TS-produced endospores surpass that of the Carbon Starvation method, both in vitro and within a cement-paste setting under freeze and thaw cycling. This outcome underscores the pivotal role of utilizing TS-produced endospores for concrete self-healing, particularly in cold areas.

Applying Microbial-Induced Calcium Carbonate Precipitation Technology to Improve the Bond Strength of Lightweight Aggregate Concrete after High-Temperature Damage

High temperatures and external force can easily lead to a decline in the bond strength of reinforced concrete components. Microbial-induced calcium carbonate precipitation (MICP) technology has considerable potential for repairing concrete. Given this, this study utilized MICP technology to improve the bond strength of heat- and pull-damaged lightweight aggregate concrete (LWAC). The specimens of a control group (Group A) and two experimental groups (Group B and Group C) were prepared. The experimental group was prepared using lightweight aggregates (LWAs) that had been immersed in a nutrient solution and a bacterial solution. The control group was prepared using LWAs that were not immersed in a nutrient solution or bacterial solution. These specimens healed themselves in different ways after exposure to high temperatures (300 °C and 500 °C) and pull-out damage. Groups A and B adopted the same self-healing method; that is, their specimens were placed in a computer-controlled incubator at 40 °C. Group C used different self-healing methods. The specimens in this group were soaked in a mixed solution of urea and calcium acetate at 40 °C for two days and then taken out and placed in an incubator at 40 °C for two days. A cycle took four days until the expected self-healing age was reached. After being exposed to 300 °C and self-healed for 90 days, the residual bond strengths of the secondary pull-out tests in Groups A, B, and C were 20.63, 22.13, and 25.69 MPa, respectively. Moreover, compared with Group A, the relative bond strength ratios of the secondary pull-out tests in Groups B and C increased by 5.8% and 20.3%, respectively. This demonstrates that MICP technology could effectively improve the bond strength of LWAC after high-temperature and pull-out damage.

Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO₃ vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water.

Synergistic effects of microencapsulated bacterial spores and superabsorbent polymer on self-healing performance in mortar

This study explores the feasibility of utilizing a superabsorbent polymer (SAP) to improve the self-healing performance of microbial-induced calcium carbonate precipitation (MICP) in cement-based materials. The amount of microencapsulated bacterial spores was varied from 0.25–1 % by cement weight. The SAP content was set to either 0 or 4 % by cement weight. As additives, the impact of SAP and MICP bacteria on mortar properties, including flowability and compressive strength, was assessed. The self-healing performance was evaluated based on crack-healing percentage and water permeability recovery. Microstructural analyses, including thermogravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), were performed to investigate the microstructural and chemical changes during the healing process. The findings revealed that specimens exclusively mixed with 4 % SAP exhibited a slightly lower crack-closure efficiency compared to those mixed exclusively with 1 % MICP bacteria. However, the SAP-containing specimens exhibited a higher degree of permeability recovery. Meanwhile, in the binary additive system with 0.5 % MICP bacteria and 4 % SAP, the specimens exhibited the highest crack-closure percentage of 91 % and a final water discharge rate of 15 mL/min after 45 days of healing. In contrast, specimens mixed exclusively with 1 % MICP bacteria showed a crack-closure percentage of 76 % and a final water discharge rate of 59 mL/min. These results suggest that incorporating SAP into the MICP system enables a reduction in MICP bacterial content without compromising self-healing performance.

Effect of nanoparticle-enhanced biocementation in kaolinite clay by microbially induced calcium carbonate precipitation

Microbially induced calcium carbonate precipitation (MICP) is a nature-based technique that has been developed over the past two decades for soil stabilization. However, the use of MICP for clay stabilization has received limited attention in the literature. On the other hand, the utilization of nanomaterials, such as nano-silica (nano-SiO2), for soil stabilization has been explored in numerous studies in the literature. This paper investigates the effect of nano-CaCO3 and nano-SiO2 on MICP stabilization in kaolinite clay. Nanoparticle-enhanced bio-cementation is introduced to effectively improve the strength of kaolinite clay at high water contents. Unconfined compressive strength (UCS) tests were conducted to evaluate the impact of the nano-bio-treatment (mixture of nano-additives and MICP) on soil strength. Additionally, the microstructure of the treated soils was examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray diffraction (XRD) analyses. The results indicate that the MICP stabilization method is effective in enhancing the strength of kaolinite soil through a mixing approach. The study of UCS in the treated samples revealed that the use of nano-CaCO3 and nano-SiO2 can have either detrimental or beneficial effects on the MICP method, depending on the degree of saturation of the treated samples. The highest UCS observed for the MICP method at a target water content of 0.25 was more than three times that of untreated soil at the same moisture content. Furthermore, the increase in UCS for the samples treated with MICP was 2.5 times that of the untreated soil at a 30% target water content. The most significant finding, however, is that, at a 30% target water content, the samples improved with MICP+ 1.5% nano − SiO2 exhibited UCS values that were six and fifteen times greater than those of the untreated and MIC-treated samples, respectively. SEM images illustrated that the addition of nano-SiO2 with the MICP method led to an agglomerated soil texture, and the formation of calcium carbonate attached to the clay minerals. This results in an increase in soil strength.

Biotrapping Ureolytic Bacteria on Sand to Improve the Efficiency of Biocementation.

Microbially induced calcium carbonate precipitation (MICP) has emerged as a novel technology with the potential to produce building materials through lower-temperature processes. The formation of calcium carbonate bridges in MICP allows the biocementation of aggregate particles to produce biobricks. Current approaches require several pulses of microbes and mineralization media to increase the quantity of calcium carbonate minerals and improve the strength of the material, thus leading to a reduction in sustainability. One potential technique to improve the efficiency of strength development involves trapping the bacteria on the aggregate surfaces using silane coupling agents such as positively charged 3-aminopropyl-methyl-diethoxysilane (APMDES). This treatment traps bacteria on sand through electrostatic interactions that attract negatively charged walls of bacteria to positively charged amine groups. The APMDES treatment promoted an abundant and immediate association of bacteria with sand, increasing the spatial density of ureolytic microbes on sand and promoting efficient initial calcium carbonate precipitation. Though microbial viability was compromised by treatment, urea hydrolysis was minimally affected. Strength was gained much more rapidly for the APMDES-treated sand than for the untreated sand. Three injections of bacteria and biomineralization media using APMDES-treated sand led to the same strength gain as seven injections using untreated sand. The higher strength with APMDES treatment was not explained by increased calcium carbonate accrual in the structure and may be influenced by additional factors such as differences in the microstructure of calcium carbonate bridges between sand particles. Overall, incorporating pretreatment methods, such as amine silane coupling agents, opens a new avenue in biomineralization research by producing materials with an improved efficiency and sustainability.

Enhancing concrete resilience and sustainability through fly ash-assisted microbial biomineralization for self-healing: From waste to greening construction materials

This study presents a pioneering approach that enables remarkable crack closure up to 0.8 mm through stimulated biomineralization aiming to enhance the self-healing capacity of concrete. The innovative synergy tackles the pressing environmental challenges head-on investigates the intriguing germination process of endospores in a cementitious environment and underscores the function of calcareous fly ash in promoting Microbially Induced Calcium Carbonate Precipitation (MICP) by providing additional Ca2+ ions, that are converted into carbonate phases through bacterial metabolic processes. These phenomena are thoroughly examined using an in-situ model particularly concerning MICP in bio-concrete, and thermodynamic modelling is performed to forecast the influence of fly ash on the quantity of Ca-bearing (carbonation sensitive) phases present in the hydrated phases of fly ash-blended cement system. Incorporating 30 % class C fly ash significantly amplifies the biomineralization activity, with 6.5 % calcium carbonate deposition in bio-concrete leds to significant healing activity. Concurrently, MICP contributes to a significant reduction in pore sizes, thereby enhancing the overall durability of concrete. Beyond structural improvements, this innovative bio-concrete formulation showcases an impressive 39 % reduction in CO2 emissions, aligning with sustainability goals. Additionally, repurposing fly ash, typically consigned to landfills, seamlessly adheres to the tenets of a circular economy, despite incurring a 7 % rise in the initial production cost. That promising advanced methodology can deliver transformative environmental benefits, ushering in a paradigm shift in sustainable construction practices, and finding the synergistic interplay between microbial activity and calcium-dependent fly ash.

The optimized microbial-induced calcium carbonate precipitation process to fabricate underwater superoleophobic mesh for efficient oil-water separation

Microbial-induced calcium carbonate precipitation (MICP) is an environmentally-friendly and easy operation technique for separating oil-water mixtures. However, the effect of environmental factors on the wettability and oil-water separation performance of MICP remains unclear. In this study, three primary factors including mineralization solution (MS) concentration, bacterial suspension (BS) concentration, and temperature were carefully investigated. Under these varying conditions, stainless steel meshes (SSM) were chosen as the substrates for the growth of CaCO3 precipitations. Experimental results demonstrate a strong dependence of the morphology and wettability of CaCO3 precipitations on these factors. Higher MS concentration and temperature contribute to enhanced hydrophilicity of CaCO3 coatings due to the increased surface roughness. The water flux of MICP-coated SSMs decreases with the increase of BS concentration, MS concentration, and temperature. The MICP-coated SSM obtained with MS concentration of 0.15 M, BS concentration of 0.1 × 108 cells/mL, and mineralization reaction at 25 ℃ for 24 hours demonstrated the optimal comprehensive performance, exhibiting underwater superoleophobicity with an underwater oil contact angle (UWOCA) exceeding 151°, an ultra-high oil intrusion pressure (> 3.0 kPa), ultrahigh flux (28,644 L m−2 h−1), and a preferable oil rejection rate (> 99.9%). Additionally, the as-prepared mesh exhibited superior anti-oil-fouling property and reusability, while concurrently demonstrating excellent chemical and thermal stability. This work contributes to advancing our knowledge of the influence of various environmental factors on the wetting characteristics of MICP and provides a feasible solution for the highly efficient and low-cost preparation of oil-water separation membranes based on the MICP process.