Calcite Production Research Articles

Exploring fungal potential for microbial-induced calcite precipitation (MICP) in bio-cement production

IntroductionMicrobial-induced calcite precipitation (MICP) involves various microorganisms, such as bacteria, fungi, and algae. This study focuses on producing bio-cement using fungal species and selecting potential candidates isolated from alkaline soil of different regions of Punjab, namely, Majha, Malwa, and Doaba.MethodsThe selection of fungi isolates capable of bio-cement production involves several tests, including a urease assay and calcium precipitation. Isolates having high urease enzyme production and the ability to perform calcite precipitation are selected for instrumental analyses such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). The isolates selected for further analysis are S1 (3) with 8.879 ± 2.94 µg/ml, S1 (18) with 8.421 ± 0.13 µg/ml, and S4 (1) with 10.057 ± 0.45 µg/ml urease activity and least free calcium ions that are 2.337 ± 0.5 µg/ml, 3.339 ± 0.5 µg/ml, and 4.074 ± 0.1 µg/ml respectively.Results and discussionCalcite precipitation is confirmed through XRD and field emission scanning electron microscopy (FESEM). XRD images showing calcite precipitation with sharp crystalline peaks for S1 (3), S1 (18), and S4 (1) are shown. The calcite precipitation is evident in the micrographs of FESEM. These combined results confirm the potential of urease-positive fungi to facilitate calcite production, which could lead to bio-cement development in future research.

Bhargavaea beijingensis a promising tool for bio-cementation, soil improvement, and mercury removal

Microbially Induced Calcite Precipitation (MICP) has emerged as a promising technique for bio-cementation, soil improvement, and heavy metal remediation. This study explores the potential of Bhargavaea beijingensis, a urease-producing bacterium, for these applications. Six ureolytic bacteria were isolated from calcareous bricks mine soil and screened for urease and calcite production. B. beijingensis exhibited the highest urease activity and calcite precipitation. Urease activity, calcite precipitation, sand solidification, heavy metal removal efficiency, and compressive strength were evaluated. It showed significant heavy metal removal efficiency, particularly highest for HgCl2. Mortar blocks treated with B. beijingensis or its crude enzyme exhibited improved compressive strength, suggesting its potential for bio-cementation. Crack remediation tests demonstrated successful crack healing in mortar blocks using the bacterium or its enzyme. This study identifies B. beijingensis as a novel and promising MICP agent with potential applications in bio-cementation, soil improvement, and heavy metal remediation. Hence, B. beijingensis diversified abilities prove superior performance compared to commonly used strains like Bacillus subtilis and Shewanella putrefaciens in bio-cementation applications. Its high urease activity, calcite precipitation, and heavy metal removal abilities make it a valuable candidate for sustainable and eco-friendly solutions in various fields.

Integrated study on CO2 enhanced oil recovery and geological storage in tight oil reservoirs

Carbon utilization, and sequestration (CUS) in tight oil reservoirs stands as a pivotal strategy for enhancing oil recovery and mitigating CO2 emissions. Research on CUS mainly focuses on the calculation of overall displacement efficiency and the total sequestration amount. However, the primary control and sequestration mechanisms throughout the life cycle of CUS, as well as the contribution of each mechanism at different development stages and under various injection and production parameters, are not clear, which limits effective guidance for oilfield development. Therefore, this paper studies the entire life cycle of tight oil reservoirs, from water flooding to CO2 flooding and CO2 sequestration after reservoir abandonment. The contribution degree changes of dissolution, structural, residual gas and mineralized sequestration mechanisms during the whole life cycle are analyzed. The results show that the main sequestration mechanism during CO2 flooding stage and injection sequestration stage after shutting down production wells is structural sequestration, which accounts for 84.75%. In the 2000 years following the cessation of CO2 injection, the proportion of structural sequestration gradually decreases, with a cumulative decrease of 12.41%, and it is mainly converted to the other three sequestration modes, with the largest increase in mineralization sequestration, reaching 8.81%, mainly due to the reaction of dicalcium silicate with CO2 to produce more stable calcite. When the injection pressure was increased from 23 MPa to 44 MPa, the sequestration efficiency increased by 18.45%. An interesting finding is that the solubility of CO2 in water in the target reservoir reaches its lowest point at 80 °C, and both warming and cooling at this point are conducive to the dissolution and sequestration of CO2. The initial pH value of formation water mainly affects mineralization and sequestration. The rate of calcite production and the contribution of CO2 dissolution and sequestration are positively correlated with water saturation. The findings underscore the importance of understanding dynamic contributions of various sequestration mechanisms and optimizing conditions to enhance CO2 sequestration efficiency.

Visualizing the Internal Nanocrystallinity of Calcite Due to Nonclassical Crystallization by 3D Coherent X-Ray Diffraction Imaging.

The internal crystallinity of calcite is investigated for samples synthesized using two approaches: precipitation from solution and the ammonium carbonate diffusion method. Scanning electron microscopy (SEM) analyses reveal that the calcite products precipitated using both approaches have a well-defined rhombohedron shape, consistent with the euhedral crystal habit of the mineral. The internal structure of these calcite crystals is characterized using Bragg coherent diffraction imaging (BCDI) to determine the 3D electron density and the atomic displacement field. BCDI reconstructions for crystals synthesized using the ammonium carbonate diffusion approach have the expected euhedral shape, with internal strain fields and few internal defects. In contrast, the crystals synthesized by precipitation from solution have very complex external shapes and defective internal structures, presenting null electron density regions and pronounced displacement field distributions. These heterogeneities are interpreted as multiple crystalline domains, created by a nonclassical crystallization mechanism, where smaller nanoparticles coalescence into the final euhedral particles. The combined use of SEM, X-ray diffraction (XRD), and BCDI allows for structurally differentiating calcite crystals grown with different approaches, opening new opportunities to understand how grain boundaries and internal defects alter calcite reactivity.

Improving properties of Engineered Cementitious Composite (ECC) using Bacillus subtilis immobilized in silica gel

This study investigates the impact of incorporating Bacillus subtilis immobilized in silica gel (BS+SG) on various properties of Engineered Cementitious Composites (ECC). Silica gel serves as the immobilization medium to sustain bacterial viability in the challenging environment of ECC mixtures. The study explores bacterial content ranging from 5 % to 15 % of water content. Results reveal a significant enhancement in compressive strength for ECC with 5–15 % BS+SG, showing increases of 11.9–18.8 % at 28 days of water curing as compared to ECC without bacteria. This improvement becomes more pronounced at 56 days, attributed to silica gel’s protective role in preserving bacterial activity, leading to calcite production that effectively fills pores during extended curing. The positive impact extends to tensile strength and strain capacity. Additionally, BS+SG contributes to reduced porosity and water absorption even after prolonged curing, thus enhancing the durability of ECC. This study highlights the potential of BS+SG in advancing the properties of ECC, with emphasis on its role in improving compressive strength, strain capacity, and durability.

Bio-cementation practice on electric-arc steel slag and comparison with natural sand

In construction projects in Khuzestan province in Iran, electric-arc steel slag (EASS) materials are used as fill materials. In this research study, bio-cementation practice on EASS materials is examined and compared with that on natural sand. For this purpose, direct shear, unconfined compressive strength (UCS) and constant head permeability tests, together with scanning electron microscopy images obtained using an instrument equipped with an energy-dispersive X-ray spectroscope, were used to analyse and compare untreated and treated materials. The results showed that despite higher urease activity and higher calcite production of EASS materials compared with natural sand, the latter showed slightly higher UCS, higher cohesion intercept enhancement and higher permeability decrease after bio-cementation treatment.

Encapsulating immobilized ureolytic bacteria yields self-healing concrete apropos sustainable transportation materials: A review

Transportation networks must be resilient to withstand the effects of climate change and natural calamities. Concrete infrastructure must endure extreme weather, flooding, and seismic catastrophes better than many other types of construction to guarantee the sustainability of transportation services. Self-healing concrete is unquestionably the material of the future that could address these issues. Researchers have discovered a self-healing process in automatic repairing the concrete cracks up to 1.8 mm width. This is made possible by ureolytic and non-ureolytic microorganisms from Bacillus family that cause bacterial precipitation and production of calcite that seal cracks, which could extend the serviceability of concrete. Concrete structures can be restored, and damage prevented through different self-healing mechanisms, such as microvascular healing, bacterial healing, capsule-based healing, and autogenous repair. Research reveals that concrete's capacity to repair itself is greatly enhanced by a mixture of self-healing mechanisms. Moreover, the encapsulation of immobilized bacteria with expanded clay, calcium alginate beads, or other porous materials that can hold onto nutrients and bacteria for an extended period resulted in a considerable improvement in the healing ratio. The main objective of this study is to enumerate all the potential challenges and limitations of the recent studies in self-healing concrete to draw a viable conclusion which is necessary for establishing rules and testing procedures for up-scale implementation.

Harnessing microbes for self-healing concrete – A review

This review explores the burgeoning field of microbially enhanced construction materials, with a special focus on self-healing concrete, through the lens of microbial biotechnology. Central to this discourse is the innovative use of bacteria, particularly Bacillus species, to address the pervasive issue of microcracks in concrete, a fundamental material in the construction industry. Traditional remedies, such as chemical admixtures and fiber reinforcements, offer partial solutions; however, self-healing concrete represents a paradigm shift, harnessing the natural calcite-precipitating ability of bacteria to autonomously repair cracks, thereby augmenting structural durability and longevity. Delving into the mechanics, the bacteria, embedded within the concrete matrix, remain dormant until crack formation triggers their metabolic pathways, leading to calcite production that effectively seals the fissures. This bio-mediated repair mechanism not only enhances the structural integrity of concrete but also aligns with sustainable construction practices by minimizing maintenance requirements and material wastage. The review extends beyond self-healing phenomena, encompassing broader applications of microbial technology in construction, including bio-concrete, bio-cement, and soil stabilization methods. These applications underscore the versatility of microbes in enhancing material properties such as compressive strength, tensile resilience, and water impermeability. Empirical evidence underscores the necessity of optimizing bacterial dosages and curing conditions to maximize the self-healing efficiency. Future research trajectories should aim to elucidate the complex interactions between microbial agents and concrete matrices, assess long-term performance, and evaluate the environmental and economic sustainability of microbial interventions in construction. The integration of microbial technology in construction materials heralds a new epoch of innovation, offering robust, sustainable, and resilient solutions to enduring challenges in the industry.

Direct Air Capture: Effects of Low-Purity CO2 and Geological Depths on Post-Capture Compression Energy and Storage

Phreeqc software has been successfully employed to study the behaviour of the gypsum rock-water system under different conditions and various levels of impurities present in the injected CO2 stream. The dissolution of gypsum leads to the increase in water quantity because of release of hydration water molecules. Under the conditions at 1km geological depth, an anhydrite (CaSO4) produced remained dissolved in the solution while the pH slightly drops owing to sulphate ions generation. As the pressure and temperature increase at 1.5km depth, more gypsum dissolves until at 2.5km depth where excess rise in temperature inhibits gypsum dissolution. The injection of pure CO2 leads to the production of calcite in the solution, which continues to grow as more CO2 is injected. But, the presence of impurity such as N2 in the CO2 stream inhibits formation of calcite, owing to continuous dissolution/ionization of calcium. Other carbonate crystals were similarly affected while the pH continues to drop drastically. It is inferred that the presence of impurities such as N2 in the CO2 stream complicates carbonation mechanisms and inhibits formations of the carbonate crystals.

Influence of Polyethylenimine (PEI) in enhancement of microstructure and surface morphology of recycled construction and demolition waste aggregate in concrete by carbonation

This investigation explores the influence of Polyethylenimine (PEI) on the improvement of carbon dioxide (CO2) uptake, surface texture, and pore structure of construction and demolition waste (CDW) through carbonation. The study focuses on the coarser fraction of CDW (10 mm), which is pre-treated with varying concentrations of PEI before being carbonated. The resulting changes in pore structure, mineralogical composition, physical properties, and surface morphologies of the CDW are characterized using various techniques. The study also evaluates the impact of carbonated CDW on compressive strength. The results indicate that PEI modification of CDW enhances carbonation efficiency by reducing pores more effectively than non-treated CDW. This microstructural refinement is possible due to the formation of calcite and its products, facilitated by PEI adsorption into CDW, enhanced CO2 uptake, and formation of calcite products through carbonation. Additionally, PEI modification results in the formation of undulated plate-like structures that enhance surface morphology and compressive strength when used in concrete. The carbonation behavior of PEI-modified CDW in concrete was also investigated by analyzing carbonation depth and pH value. The results reveal that the optimal PEI concentration for enhancing the performance of CDW is 0.2. Overall, the study highlights the potential of PEI modification as an effective approach to improve the properties of CDW and its potential as a sustainable construction material.

Bioconsolidation of Damaged Construction Calcarenites and Evaluation of the Improvement in Their Petrophysical and Mechanical Properties.

Bioconsolidation treatment using bacterial carbonatogenesis has been proposed as an environmentally friendly strategy for the efficient preservation of damaged stones, particularly suitable for carbonate stones. The study presented here deals with the evaluation of the performance of this treatment, applied to damaged carbonate stones in two historical buildings in Spain. The methodology applied in this research serves as a reference for future similar studies. Results showed significant improvement in the petrophysical and mechanical properties of the damaged stone following the treatment through the production of calcite and vaterite by the abundant carbonatogenic bacteria inhabiting the stone. These bacteria were able to effectively consolidate weathered areas if an adequate nutritional solution was employed, thereby augmenting the stone's resistance, as evidenced by the Drilling Resistance Measurement System (DRMS). FESEM images showed calcified bacteria and calcified exopolymeric substances (EPS) consolidating stone minerals without blocking their pores. In addition to consolidation, this biotreatment improves the stone's behavior against water absorption and increases the contact angle of water droplets without significant modifications in the pore size or diminishing vapor permeability. No color changes are observed. Overall, these results show that the application of the nutritional solution (M-3P) for in situ consolidation of different types of porous carbonate building stones is a highly effective conservation method, with no modification of the chemical composition of the treated materials.

Understanding the CO2 utilisation potential of various cementitious materials through review and analytical modelling

Carbon dioxide sequestration in cement-based materials has emerged as a promising avenue for utilising captured carbon dioxide (CO2) and reducing the carbon dioxide footprint of the concrete industry. This article presents a comprehensive review of various studies conducted in this domain with a particular emphasis on factors affecting the carbon dioxide uptake potential of various concrete types and the effect of carbonation on the critical properties of concretes. Studies conducted on the micro-mechanical analysis of carbon sequestered concrete show that carbonation significantly improved the microhardness of the concrete samples, thereby increasing the strength and reducing the cement intake requirement. Further, keeping two parameters, namely water/solid (w/s) ratio and carbonation reaction time, in focus, the carbon dioxide uptake capacity in concrete slurry waste (CSW) was evaluated using non-linear regression analysis. It was observed that CSW paste had a maximum carbon dioxide uptake with an intermediate w/s ratio of 0.2 due to carbon dioxide reaction hindrances during diffusion at a higher w/s ratio and lack of hydration at a lower w/s ratio. On the contrary, for belite-rich cement, a higher w/s ratio led to higher carbon dioxide uptake owing to belite phase consumption leading to increased calcite production. Additionally, comparing the maximum carbon dioxide uptake capacity of CSW at a particular condition with various other cement-based materials, it was observed that belite-rich cement had the ability to sequester the maximum amount of carbon dioxide compared to the other cement-based materials considered in this study.

Hydraulic Conductivity of Mine Waste Treated Using Enzyme-Induced Calcite Precipitation Method Under Various Curing Conditions

The hydraulic conductivity of mine waste soil is considered moderately high attributed to the high percentage of pore spaces. One of the risks associated with this poor property ispossibleintrusion of contaminated acid drainage into the groundwater or river. Biocementation using enzyme-induced calcite precipitation is a relatively new, more inventive, and environmentally sustainable method compared to the other techniques in improving soil properties. However, limited available data on how this method can be applied in improving heavy-metal contaminated mining wastes. This paper summarizes the effectofthis treatment,includingdifferent cementation concentrations, degree of compaction, curing temperatures and curingdurations in reducing the hydraulic conductivity of mining waste. Results obtained indicate a greater effect of 1.0M compared to 0.5Mconcentration, a degree of compaction of 80% compared to 70%,acuring temperature of 25 °C compared to 15 °C and 5 °C, and immediate reaction effect after 1then slowed down after 3 and 7-day curing. When compared to control samples, the reduction in hydraulic conductivity ranged from75.66to 97.14%. The positive result is attained due to the production of calcite, CaCO3that biocemented the soil particles together and reduced the pore spaces, indicated by their content obtained,ranging from 2.0-5.15% in the treated soil. Visualimages through SEM and spectra of x-ray diffraction confirmed the presence of CaCO3in soil particles. This work contributedsignificantly to the study of the properties of copper mine tailings in Ranau, Sabah, including the first study on biocementation of copper mine tailings. The method couldbe used to reduce the hydraulic conductivity of mining waste soils contaminated with heavy metals. Various scenarios such as curing temperature, duration, cementation concentration and degree of compaction have been proposed to optimize the effectiveness of the treatment.

Application potentials of conch shell powder as a bacterial carrier for enhancing the Micro-Mechanical performance of biogenic gypsum plaster

Microbial-induced calcite precipitation (MICP) is a relatively novel technology that can improve the strength and durability of gypsum plasters. This present study seeks to explore the application potential of three different bacterial species (Bacillus subtilis, Bacillus sphaericus, and Sporosarcina pasteurii) on the mechanical strength, durability, and microstructure of the gypsum plaster. The use of porous conch shell powder (CSP) as a bacterial carrier through immobilization approach is also proposed in this work. The effect of vacuum impregnation of bacteria in the CSP with and without nutritional coating was attempted, and the results suggested the plaster mixes displayed higher performance with vacuum impregnation and the compressive strength was raised by around 7% over the ordinary plaster. The developed plaster indicated greater strength with fewer pores and improved durability by displaying increased water tightness, and the process of calcite production was evident for a period of up to 28 days through UPV monitoring. As SEM and XRD studies showed, microbial calcite precipitation plugged up the pores, making the microstructure dense and more durable.

Use of bacterial binder in repair mortar for micro-crack remediation.

Micro-cracks are one of the types of stone deterioration which can propagate and lead to surface detachments and larger cracks in the long run. The present study developed a sustainable and environmentally friendly infill material-biological mortar (BM), as an alternative to conventional approaches. Using a biomineralization approach, this BM was explicitly designed for healing micro-cracks (less than 2 mm) in historic travertines. To this end, the mortar was prepared using a calcifying Bacillus sp. isolated from thermal spring water resources in Pamukkale Travertines (Denizli), stone powder gathered from travertine quarries in the vicinity, and a triggering solution specifically designed to set off calcium carbonate precipitation reaction. After setup, BM was applied to micro-cracks of artificially aged test stones for testing. Scanning electron microscopy revealed calcium carbonate-coated Bacillus sp. bodies in the BM matrix, optical microscopy showed secondary calcite minerals throughout the BM applied micro-cracks, and stereomicroscopy and nanoindentation analyses demonstrated bonding of BM with stone due to microbial calcification activities. Furthermore, BM and original material contact showed a continuous and coherent structure in all samples. Within this context, BM could be considered a promising and alternative approach for the remediation of micro-cracks of historic stones. KEY POINTS: A binder was produced by the MICP of Bacillus sp. Pamukkale. Physical, mineralogical, and nanomechanical characterization demonstrated microbial calcite precipitates in BM. A significant bond was determined between the grains and matrix of BM due to Bacillus sp. calcite production activities.

Understanding the importance of endosporulation methods for generating endospores that can resist harsh conditions and produce calcite in bio self-healing of concrete

Vegetative cells used for the concrete bio self-healing process often face threatening environmental conditions such as extreme temperature, pH, salinity, shear stress, and starvation during the hardening process and the service life of the concrete. These conditions can eventually lead to cell death. Since endospores are likely to remain dormant for prolonged periods and can survive, germinate, and grow under inhospitable conditions, they are a suitable bacterial phenotype to introduce into concrete for microbial-inducing calcite precipitation. This study investigated how different endosporulation methods affect the endosporulation ratio (i.e., the fraction of vegetative cells that are converted to endospores during endosporulation), as well as the germination ratio (i.e., the fraction of endospores that are converted to vegetative cells following germination) and the microbial-induced calcite precipitation (MICP) performance of germinated endospores after facing harsh conditions of concrete, specifically, freeze and that cycling. Results from this study show that thermal shock followed by cell incubation in alkaline conditions leads to increased sporulation and germination ratios. It was also observed that freeze and thaw cycling had negligible effects on calcite production by endospores, while exposure of vegetative cells to these harsh conditions led to not only less biomass and calcite production but also to a lower mass of calcite produced per mass of cells, as determined by thermogravimetric analysis (TGA). The results from this study provide key insights into improving methods for endosporulation and germination to effectively use them for bio self-healing applications in concrete.

Application of technical grade reagent in soybean-crude urease calcite precipitation (SCU-CP) method for soil improvement technique

Soybean crude urease-calcite precipitation (SCU-CP) is a potential method as a sustainable and economical soil improvement technique. This method begins with developing the bio-cementation method that has successfully increased soil strength. The use of laboratory-grade material is high-cost for large-scale. The applicability of original soybean material combined with technical grade reagent in SCU-CP was discussed, considering its relevance for a larger scale treatment. The hydrolysis rate, test-tube experiment, and X-Ray Diffraction (XRD) test were conducted to evaluate the entire material's potential for the calcite precipitation method considered for precipitation materials. This study shows that low-cost soybean material and technical-grade reagents have a good level of effectiveness for calcite production. The low-cost material of soybean 20 g/L produced the highest hydrolysis rate of 331.701 u/g. Technical-grade reagent with a concentration of 1 mol/L was proven effective compared to laboratory-grade with a precipitation ratio of 114.44%. XRD results showed that the highest calcite formation was in technical-grade samples using soybean Gasol with a crystallinity of 40.25%. Unconfined compressive strength (UCS) results showed that the original soybean has a higher value than other solutions, which is 66.18 kPa in 14 days. Therefore, technical-grade materials are more economical with 100% cheaper than laboratory-grade. The result of this study elucidated that SCU-CP has a high potential to be an economical, sustainable and effective soil improvement technique.

Controls on the accumulation of Early Cretaceous organic-rich fine-grained deposits in a mixed marine siliciclastic-carbonate distal settings of the Neuquén Basin, central-western Argentina

Deposition of black shales occurred under specific conditions that need to combine in a precise way the rate of production and the rates of destruction and dilution of organic matter. Whereas good progress has been made in the determination of the role of production and destruction of organic matter, the role of dilution of the organic components still remains comparatively understudied. In mixed siliciclastic-carbonate marine systems, the dilution of organic matter by non-organic components could be detrital and/or biogenic in origin, adding more complexity to the understanding of these particular types of black shales. In the present contribution, we studied the mixed siliciclastic-carbonate distal deposits of the late Hauterivian Agua de la Mula Member (Agrio Formation) in the Neuquén Basin. Through a combination of sedimentological, petrographic, SEM, and geochemical analyses we define the origin of the fine-grained components, reconstruct the environmental evolution, and determine the role of the production, preservation, and dilution of the organic matter. The results indicate that the unit is predominantly composed of calcite (>47%), whereas illite is the major component among the clay minerals. Thin sections and SEM studies suggest that the carbonate fraction is dominantly composed of nannofossils, i.e. biogenic in origin, and subordinately micarbs (diagenetic, but with a potential biogenic precursor). Thus, the composition of the distal deposits is mostly controlled by the input of detrital illite. The organic geochemistry and XRF data reveal that the most appropriate conditions for the accumulation of organic matter are the transgressive intervals, near the base, with a predominant effect of the rate of the production over the preservation. On the other hand, the dilution of organic matter is mainly driven by the rate of production of biogenic calcite. Interestingly, previous studies showed that in more proximal settings (but still offshore to basin realms) the dilution is controlled by siliciclastic components. Finally, organic geochemistry suggests that most of the organic matter produced is marine in origin (type II), but towards the top of the section it switches to mixed marine and terrestrial (type III to IV), likely related to a progradation of the shallower system and the consequent increase in the input of terrestrial-derived components.

Research on plugging characteristics of microorganism induced calcite precipitation in sandstone environment

Microorganism-induced calcite precipitation (MICP) has been proposed to increase crude oil recovery for more than two decades. It is only recently that mine trials have emerged. The present study was conducted to advance the application of MICP for enhanced crude oil recovery. The changes of core permeability and bacterial biomass on permeability reduction rate during MICP treatment were investigated by core blocking experiments and reverse unblocking experiments. The permeability conditions for biomass and calcite production blocking were explored. Based on this, the changes in mechanical properties of the cores by MICP were explored by unconfined pressure experiments. Finally, the mineral composition and mineral phases were analyzed by XRD and SEM. Our study shows that MICP is much less effective at permeabilities less than 66mD. The decrease in permeability presented in the experiment comes from the blocking effect of the injection end of the core on the bacteria. The compressive strength of the MICP-treated cores was increased by 10.05% and was more resistant to brittle damage. Also calcite is attached to the sandstone matrix. The characteristic peaks of calcite were observed in the cores treated with MICP by SEM and XRD. In addition, under the same culture conditions, the mineral morphology in the sandstone environment is quite different from that in the shake flask. In the sandstone environment, calcite is tightly adsorbed on the sandstone matrix, showing a typical rhombic hexahedral structure, and in the shake flask environment, it is more Spherical or spherical aggregates. Based on the above study, the blocking mode of MICP is proposed. The free agglomerated calcite particles form a physical seal in the pore throat and the biofilm mineralizes directly in the sandstone matrix together to seal the sandstone cores. The results of this study report a new mineral morphology difference in MICP. It is also a theoretical support for further improving the MICP for enhanced oil recovery.

Variation in biogenic calcite production by coccolithophores across mesoscale eddies in the Bay of Bengal

Coccolithophore calcite production (CP) was investigated for the first time in the Bay of Bengal. Against expectation, calcite production was not fueled by the nutrient-enriched cold eddy because of the reduced light penetration. CP rate was observed to be higher at the anticyclonic eddy possibly benefited from rare species production. The adjoining river-induced shallow mixed-layer depth and eddy activity co-influenced CP rate. On average, the integrated CP rates were 0.04, 0.15, and 0.07 mmol C m−2 h−1 for the cyclonic eddy, anticyclonic eddy, and outer area, respectively. In the upper photic waters, CP rates showed a strong correlation with primary productivity (PP). However, a decoupling of CP and PP was observed in the lower photic zone due to differential light and nitrogen preferences in calcification and carbon fixation. Our findings could help to understand the biogenic response of eddy and inorganic-organic carbon association in the pelagic biogeochemical cycles.