Induced Calcium Carbonate Precipitation Research Articles

Experimental Study on Structural Behavior of Self Healing Concrete

The Cracking of concrete is a common phenomenon without immediate and proper treatment, cracks in concrete structures tends to expand further and eventually require costly repairs. Even though it is possible to reduce the extent of cracking by available modern technology, remediation of cracks in concrete has been the subject of research for many years. Cracks and fissures are a common problem in building structures, pavements, and historic monuments. Cement mortar durability is the function of its internal pore structure and distribution, porosity, and its permeation properties. Research has shown that some specific bacterial species isolated from soil can tolerate harsh and challenging alkaline environment and can be used in remediating cracks in cement mortar structures. This state-of-the-art microbial based crack healing mechanism is one such phenomenon on which studies were carried out to investigate the role of calcite mineral precipitation in improvement of durability in bacteria integrated cement mortar. The primary goal of this study is to explore the potential of biomineralization microbial calcium carbonate deposition in cement mortar, to develop sustainable construction materials. The idea has led to the conception of energy efficient and sustainable construction material called ‘Bacterial Cement mortar’. This paper primarily focuses on the studies related to the characterization of bacteria produced calcium carbonate crystals using various nano characterization techniques such as Scanning Electron Microscope (SEM), X-ray diffraction (XRD), and Thermo gravimetric analysis (TGA) to validate that cracks/pore were sealed up by calcite crystals grown due to complex metabolic mechanism of nitrogen cycle by Bacillus subtilis JC3. In concrete, cracking is a common phenomenon developed due to relatively low tensile strength. High tensile strength may be developed in concrete due to external loads, imposed deformations, plastic shrinkage, plastic settlement and expensive reaction. Proper and immediate treatment should be done to prevent expansion of cracks which may eventually be of higher cost. For crack repair, a variety of traditional repair systems are available which possess several disadvantages aspect such as different thermal expansion coefficient, environmental and hazards of health. Bacterially induced calcium carbonate precipitation has been proposed as an alternative and environmentally friendly crack repair technique. It is found that microbial mineral precipitation as a result from metabolic activities of favorable bacteria in concrete improved the overall behavior of concrete. It is expected that further development of this technique will result in a more durable, sustainable, and crack free concrete that can be used efficiently for construction in wet atmosphere where corrosion of reinforcement affects the durability, permeability, and strength of concrete.

Microbes in bioconcrete technology: exploring the fundamentals and state-of-the-art findings for advancing civil engineering

ABSTRACT The bioconcrete technology on cementitious composites over the past years has brought us the application of microbes on concrete materials with self-healing ability. Certain microbes, such as bacteria, algae, and fungi, have been identified as able to enhance the strength of concrete and other properties, including durability, resistance, self-healing, and others. The key ability of those microbes is their capability to induce calcite biomineralization, which is also known as microbiologically induced calcium carbonate precipitation. This ability allows microbes to produce calcites under specific biochemical reactions comparable with the bonding material in cement concrete, thus enhancing concrete properties and healing microcracks before further propagation occurs. However, each microbe has its own characteristic that brings certain challenges and benefits to its application, considering the reactants, products, availability, survivability, sustainability, etc. Although many studies have been done in this field, the microbes, cultivations treatments, testing methods, and obtained outputs vary between one finding and another. This paper discloses both the fundamental and state-of-the-art bioconcrete findings for different types of microbes.

Steerable artificial magnetic bacteria with target delivery ability of calcium carbonate for soil improvement.

The microbial-induced carbonate precipitation (MICP) has acquired significant attention due to its immense potential in sustainable engineering applications, particularly in soil improvement. However, the precise control of microbial-induced calcium carbonate precipitation remains a formidable challenge in engineering practices, owing to the uncertain movement paths of bacteria and the nonuniform distribution of soil pores. Taking inspiration from targeted therapy in medicine, this paper presents novel research on the development and validation of magnetically responsive bacteria. These bacteria demonstrate the ability to target calcium carbonate precipitation in a microfluidic chip, thereby promoting an environmentally friendly and ecologically sustainable biomineralization paradigm. The study focuses on investigating the migration of magnetite nanoparticles (MNPs) in aqueous solutions and enhancing the stability of MNP culture liquids. A specially designed microfluidic chip is utilized to simulate natural sand particles and their pores, while an external magnetic field is applied to precisely control the movement path of the artificial magnetic bacteria, enabling targeted precipitation of calcium carbonate at the micron-scale. Verification of the engineered artificial magnetic bacteria and their ability to induce calcium carbonate precipitation is conducted through SEM-EDS analysis, microfluidic chip observations, and the application of the K-means algorithm and ImageJ software to analyze calcium carbonate formation. The influence of the concentration of magnetic nanoparticles on the calcium carbonate production rate was also studied. The results confirm the potential of the artificial magnetic bacteria for future engineering applications. KEY POINTS: • Sporosarcina pasteurii is first time successfully engineered into artificial magnetic bacteria. • The artificial magnetic bacteria show excellent performance of targeted transportation and directional deposition of CaCO3 in microfluidic chip. • The emergence of artificial magnetic bacteria promotes paradigm shift of next generation environmentally friendly biomineralization.

Microbially Induced Calcium Carbonate Precipitation by Sporosarcina pasteurii: a Case Study in Optimizing Biological CaCO3 Precipitation.

Current production of traditional concrete requires enormous energy investment that accounts for approximately 5 to 8% of the world's annual CO2 production. Biocement is a building material that is already in industrial use and has the potential to rival traditional concrete as a more convenient and more environmentally friendly alternative. Biocement relies on biological structures (enzymes, cells, and/or cellular superstructures) to mineralize and bind particles in aggregate materials (e.g., sand and soil particles). Sporosarcina pasteurii is a workhorse organism for biocementation, but most research to date has focused on S. pasteurii as a building material rather than a biological system. In this review, we synthesize available materials science, microbiology, biochemistry, and cell biology evidence regarding biological CaCO3 precipitation and the role of microbes in microbially induced calcium carbonate precipitation (MICP) with a focus on S. pasteurii. Based on the available information, we provide a model that describes the molecular and cellular processes involved in converting feedstock material (urea and Ca2+) into cement. The model provides a foundational framework that we use to highlight particular targets for researchers as they proceed into optimizing the biology of MICP for biocement production.

Mechanical Properties of Eolian Sand Solidified by Microbially Induced Calcium Carbonate Precipitation (MICP)

Eolian sand is widely distributed in desert areas, and can easily trigger sandstorms under the combined effects of wind and thermal conditions. In this paper, an eolian sand solidification test via microbially induced calcium carbonate (CaCO3) precipitation (MICP) was conducted to explore prospective applications of MICP in the field of dust prevention and sand fixation. A bacterial growth test and a MICP mineralization reaction test were performed based on the response surface method and an orthogonal experiment. Based on eolian sand solidification test, the effects of cementation number and dry density on the permeability and strength characteristics of solidified eolian sand, as well as the content of CaCO3 generated were analyzed. The results showed that the bacteria grew best at a temperature of 35 °C, a pH of 9, and a shaking frequency of 170 rpm. Both urease activity and bacterial concentration increased as the temperature and pH increased but showed a trend of rising before falling as the shaking grew faster. The optimal conditions for MICP mineralization were a bacterial concentration of OD600=1.5, a consolidating fluid concentration of 1 mol/L, a reaction time of 16 h, a pH of 9, and a temperature of 25 °C. The permeability coefficient of solidified eolian sand decreased as the dry density and the number of cementations increased, whereas the CaCO3 content increased with the number of cementations. As the number of cementations increased, the unconfined compressive strength (UCS) of eolian sand initially rose before stabilizing and then increasing again. The CaCO3 content had a positive relationship with UCS, which with the correlation coefficient reached 0.80.

Evaluation of Calcium Carbonate Precipitation by Bacillus spp. Isolated from Stingless Bee Products

Microbiologically Induced Calcium Carbonate Precipitation (MICCP) through urea hydrolysis is the most effective way to precipitate a high concentration of calcium carbonate (CaCO3) within a short time. The MICCP process is used to remediate the micro-crack in the concrete. However, limited research has been conducted to determine CaCO3 precipitation by bacteria, especially in Malaysia. Here, Bacillus spp. isolated from the Malaysian stingless bee products were evaluated for CaCO3 precipitation. Bacillus spp. were selected for further study according to their ability to produce urease enzymes. The urease-positive Bacillus spp. were screened for CaCO3 precipitation by culturing on both CaCO3 precipitation agar and broth media. The survivability of the urease-positive Bacillus spp. in various temperatures, pH values, and NaCl concentrations were tested. Seven out of 11 Bacillus spp. were found as ureolytic bacteria. Among the ureolytic bacteria, bacteria belonging to the Bacillus subtilis species complex group showed the highest number of bacteria (36.4%) that are capable of precipitating CaCO3. Bacillus stratosphericus PD6 and B. aryabhattai BD8 exhibited the largest CaCO3 precipitation zones (15 mm). Bacillus stratosphericus PD6 also precipitated the highest amount of CaCO3 (65 mg) and urease activity (0.197 U/mL). All the urease-positive Bacillus spp. were able to grow at 45 °C, pH (8 to 12), and 5% NaCl. Only B. subtilis BD3 can withstand high temperatures up to 55 °C and 15% NaCl concentration. In conclusion, Bacillus spp. isolated from stingless bee products showed the ability as the CaCO3 precipitating bacteria; suggesting its potential application in self-healing concrete.

Crack healing in cement mortar using enzyme induced calcium carbonate precipitation

The current study highlights a breakthrough approach to crack healing by harnessing the potential of plant-based urease enzymes derived from urease-rich seeds. In this investigation, pulverized watermelon seeds (Citrullus lanatus) served as a valuable source of urease, which facilitated the production of calcium carbonate for crack repair in cement mortar. The healing process involved introducing a specialized suspension, consisting of urea, watermelon seeds’ urease, and calcium hydroxide, into the existing cracks of the specimens. Prior to treatment, the cracked mortar specimens exhibited a substantial 35% reduction in compressive strength as compared to the control specimens. The application of the biocementing suspension led to complete repair of the cracks, resulting in an impressive recovery of approximately 90% of the compressive strength on 7th day, comparable to the control specimens. The UPV results clearly indicated that the crack was healed on the 7th day thus confirming that the proposed biocementing suspension was able to repair the crack completely within 7 days of application. Moreover, the treated i.e experimental specimens demonstrated significant improvements in water tightness, indicating remarkable effectiveness of this crack healing methodology.

A potential sustainable technique to entrap contaminants against rill erosion based on MICP

Health risks due to toxic metals (TM) contamination is a global concern. Toxic metals could be release to the environment due to soil erosion. The present study was aimed to prove the synergistic mechanisms of microbially induced calcium carbonate precipitation (MICP) on improving the strength properties of soil particles toward rill erosion, as well as immobilizing toxic metals into stable crystals. Hence, laboratory batch studies were conducted to evaluate the rill erosion stability as well as Cd, Pb and Zn removal ability based on bioprecipitation through MICP, using urease producing bacteria. Results revealed that the application of the strain Bacillus pasteurii PTCC1645 in MICP process of test model treated with 500 mM cementation solution showed a great potential to decrease sand lost to below 20% with the flow rate of 15 ml/min with highest strength (131 KPa) and the highest calcium carbonate content (0.84%). Moreover, the immobilization of the toxic metals in biotreated test models above 50 mM under the flow rate of 3 ml/min showed the efficiency of Pb, Zn and Cd ions by 100%. SEM proved the presence of calcite among the sand particles which could be attributed to the effectiveness of the strain. Energy-dispersive X-ray spectroscopy(EDS) analysis revealed the presence of toxic metals, while were transformed into carbonates by MICP of PTCC1645. Hence, toxic metals have stronger stability encountered with rill erosion and low toxicity compared with metal ions. The present study illustrated that the carbonate-biomineralization can offer an effective and eco-friendly approach to immobilize soluble toxic metals and that MICP may play an important role in metal bioconservation during rill erosion.

Growing bio-tiles using microbially induced calcium carbonate precipitation

Using the biomimetic process known as microbially induced calcium carbonate precipitation (MICP), the growth of bio-tiles was investigated as an alternative to conventionally fired ceramic tiles which require operating temperatures above 1000 °C, therefore adding to global carbon emissions. The ureolytic activity of Sporosarcina pasteurii was controlled by centrifuging and dilution with fresh yeast extract media. The bio-tiles were grown using a novel submersion method in which custom moulds were placed in exact positions within the bio-reactor and each was mixed individually from beneath. Five parameters were optimised to achieve bio-tiles (dimensions of 100 × 100 × 10 mm) of breaking strength comparable to conventional tiles of equivalent thickness. By optimising ureolytic activity (4.0 mmol/L·min), the cementation solution concentration (0.3 M), the particle size distribution (D10 = 312 μm; D50 = 469 μm), the volume of cementation solution, as well as the addition of supplemental magnesium (0.3 M), bio-tiles with a breaking strength 637 N ± 60 N and a modulus of rupture of 13.0 N/mm2 ± 2.3 N were produced. These parameters exceed the conventional standards of breaking strength and modulus of rupture of 600 N and 8 N/mm2, respectively, the standards set for tiles with a water absorption above 10 %. This is also the first time that an optimum CaCO3 precipitation rate constant has been identified (0.11–0.18 day−1) for producing bio-tiles that meet the strength properties of conventional extruded ceramic tiles. The tile manufacturing technique described in this study is easy to operate and scale since multiple bio-tiles can be produced in larger cementation tanks. This natural tile making process also benefits the environment by operating at room temperature.

Microbially induced calcium carbonate precipitation in fossil consolidation treatments: Preliminary results inducing exogenous Myxococcus xanthus bacteria in a miocene Cheirogaster richardi specimen

This research paper proposes Microbially Induced Calcium Carbonate Precipitation (MICP) as an innovative approach for palaeontological heritage conservation, specifically on deteriorated carbonate fossils. Due to its efficiency in bioconsolidation of carbonate ornamental rocks, Myxococcus xanthus inoculation on carbonate fossils was studied in this research.Treatment was tested on nine fossil samples from decontextualized fragments of Cheirogaster richardi specimens (Can Mata site, Hostalets de Pierola, Catalonia, Spain). The main objective was to evaluate whether treatment with Myxococcus xanthus improved fossil surface cohesion and hardness and mechanical strength without significant physicochemical and aesthetic changes to the surface. Chemical compatibility of the treatment, penetration capacity and absence of noticeable changes in substrate porosity were considered as important issues to be evaluated.Samples were analysed, before and after treatment, by scanning electron microscopy, weight control, spectrophotometry, X-ray diffraction analysis, water absorption analysis, pH and conductivity control, Vickers microindentation and tape test. Results show that hardness increases by a factor of almost two. Cohesion also increases and surface disaggregated particles are bonded together by a calcium carbonate micrometric layer with no noticeable changes in surface roughness. Colour and gloss variations are negligible, and pH, conductivity and weight hardly change. Slight changes in porosity were observed but without total pore clogging.To sum up, results indicate that Myxococcus xanthus biomineralisation is an effective consolidation treatment for carbonate fossils and highly compatible with carbonate substrates. Furthermore, bacterial precipitation of calcium carbonate is a safe and eco-friendly consolidation treatment.

Optimization of growth medium for microbially induced calcium carbonate precipitation (MICP) treatment of desert sand

Optimization of growth medium for microbially induced calcium carbonate precipitation (MICP) treatment of desert sand

Multi-scale analysis of the mechanism of microbially induced calcium carbonate precipitation consolidation loess.

Microbial-induced calcium carbonate precipitation (MICP) treatment of consolidated loess has the advantages of high efficiency and environmental protection. In this study, changes in the microscopic pore structure of loess before and after MICP treatment were compared and quantified, combined with test results at different scales, to better understand the mechanisms of MICP-consolidated loess. The unconfined compressive strength (UCS) of MICP-consolidated loess is significantly increased, and the stress-strain curve indicates improved strength and stability of the loess. X-ray diffraction (XRD) test results show that the signal strength of calcium carbonate crystals is significantly enhanced after loess consolidation. The microstructure of the loess was determined by scanning electron microscopy (SEM). The loess SEM microstructure images are quantitatively analyzed using comprehensive image processing methods (including gamma adjustment, grayscale threshold selection, median processing). The changes in microscopic pore area and average pore sizes (Feret diameter) of the loess before and after consolidation are described. More than 95% of the pores consist of pores with a pore area of less than 100 μm2 and an average pore size of less than 20μm. The total percentage of pore numbers with pore areas of 100-200 and 200-1000 μm2 decreased by 1.15% after MICP consolidation, while those with 0-1 and 1-100 μm2 increased. The percentage of pore numbers with an average pore size greater than 20μm decreased by 0.93%, while the 0-1, 1-10, and 10-20μm increased. Particle size distributions revealed a significant increase in particle size after MICP consolidation, with an increase of 89μm in D50.

Effect of Concentrations of Biocementation Solution on Enzyme Induced Calcium Carbonate Precipitation (EICP)

Abstract: The need to accommodate a growing global population has become major concern in many societies and has pushed human inventiveness to new levels. There is an increase in need for engineering technologies to improve the mechanical properties of the ground. Mostly soil strengthening is done by applying cement or chemical products to enhance the mechanical properties of soil. However, the usage of those products can possibly disturb improved soil and the production process of cement and chemical products can create harmful products. Enzyme Induced Calcium Carbonate Precipitation (EICP) is one sustainable method where calcium carbonate precipitation occurs via hydrolysis of urea (ureolysis) catalysed by plant-extracted urease enzyme for soil improvement . This study analysed the effect of different concentrations of urea- CaCl2 (0.5M, 1M, 1.5M) and urease enzyme (5 g/l) which forms the biocementation solution on the mechanical properties of soil. Direct Shear test is done to analyse the shear strength parameters. The optimum EICP treatment solution was obtained as urea- CaCl2 (1 M) at urease enzyme (5 g/l). It was observed that there was an increase in cohesion (0.16kg/cm2 ) and angle of internal friction (35º) at 7 days was to cohesion(0.18kg/cm2 ) and angle of internal friction (36º) at 14 days .

Elucidating factors governing MICP biogeochemical processes at macro-scale: A reactive transport model development

Microbial Induced Calcium Carbonate Precipitation (MICP) influenced by biofilm metabolism in the subsurface can be exploited for a variety of engineered applications encompassing geotechnical ground improvement, environmental bioremediation, and hydraulic barriers. A reactive transport model was developed to determine the effects of controlling factors in terms of treatment protocols and experimental methods. Six column tests were calibrated and a range for the key parameters was determined. Fifteen key parameters of MICP reactive transport model were assessed in four categories (microbial activity and attachment, sample preparation, treatment protocol, and experiment dimensions). The results emphasized the effects of three main factors of microbial activity, microbial attachment process, and number of treatment (among all 15 assessed parameters) on the calcium carbonate (CaCO3) precipitation content and distribution. An increase in specific ureolysis rate (Ku) and attachment rate coefficient (Kat) by two orders of magnitude improves average CaCO3 by up to 13% and 6%, respectively with non-uniformity (COV) increase of 16%. Higher flow rates and solution concentrations contribute to more uniform CaCO3 distribution. The constant attachment rate model is useful to yield the CaCO3 precipitation profiles but more accurate models are needed to capture exact distribution. Post-treatment hydraulic conductivity, porosity and attached biomass were assessed.

Biogenic material design by stone waste treatment with biologically induced mineralization

One of the most widely studied branches of biologically induced mineralization (BIM) processes, microbially induced calcium carbonate precipitation, also known as microbially induced calcite precipitation, can be used as a method for the reinterpretation of waste natural stone particles into a sustainable material. By overcoming the need for synthetic adhesives or energy-consuming firing or sintering procedures for regaining such wastes, a natural and sustainable solution is proposed through certain biological treatment processes. The aim of this study was to determine the main processing variables affecting microbially induced biocement production using waste stone as a scaffold material. Bacillus pasteurii bacteria were used for biological induction of calcite precipitation. A custom-made reactor was designed for controlled incubation and medium injection into the waste stone scaffold. The parameters examined were the particle size of the waste stones, the effect of the stone type on cementation, the urease activity of the bacterial culture, temperature, the pH and flow rate of media, the mechanical strength of cemented scaffolds and water absorption capacity. This research demonstrated a potential solution to the waste generation problem of the global natural stone industry through the treatment of such wastes with BIM for creating a sustainable and biogenic material.

Experimental Study of MICP-Solidified Calcareous Sand Based on Ambient Temperature Variation in the South China Sea

With the continuous advancement of the construction of the Hainan Free Trade Port and Island Reef Project, deploying Microbial Induced Calcium Carbonate Precipitation (MICP technology) for related research on the temperature range in this area would be of great significance. MICP technology is an innovative and sustainable new soil reinforcement technology that uses the metabolic activity of specific bacteria to produce calcium carbonate precipitation (CaCO3) to connect loose soil. A few previous studies reporting on the applications of MICP technology in different temperature environments drew different conclusions. Therefore, this study involved MICP sand column reinforcement tests at ambient temperatures of 20 °C, room temperature, 30 °C, and 40 °C. The reinforcement effect was evaluated using indicators such as CaCO3 generation rate, Ca2+ conversion rate, bacterial adhesion rate, water absorption rate, and unconfined compressive strength, providing a reference basis for the future applications of MICP technology to island and reef engineering construction. The results showed that, with an increase of temperature from 20 °C to 40 °C, the CaCO3 production rate, Ca2+ conversion rate, and unconfined compressive strength showed a trend of first increasing and then decreasing; the UCS was 548 KPa at 20 °C and 2276.67 KPa at 30 °C; the water absorption rate at 20 °C was 25.32, which decreased continuously with increasing temperature, and reached 21.49 at 40 °C; and the bacterial adhesion rate also continued to rise in the range of 20 °C to 40 °C, from 10.91 to 28.44. The increase in temperature had an impact on the physiological state of bacterial cells. A scanning electron microscope test shows that CaCO3 crystal forms generated under different temperature environments were different, and the CaCO3 mineral deposits generated during MICP reinforcement at 30 °C were denser. Fewer gaps were present between adjacent sand particles, and the bond was tight, which served better as a bridge. The strength of the solidified sample was also higher. The annual average temperature of the South China Sea is about 30 °C. The findings of this experiment provide feasibility and sustainable development for MICP project reinforcement in the South China Sea.

Experimental study of synergistic reinforcement of silty clay with glutinous rice paste and MICP.

The use of microbially induced calcium carbonate precipitation (MICP) technology can improve the mechanical properties of silty clay, and glutinous rice paste can enhance microbial activity, improve the conversion rate of CaCO3 precipitation, and help increase soil strength. An MICP solidification test of silty clay was carried out by adding different concentrations of aged glutinous rice slurry and cementing liquid, and unconfined compressive strength tests and scanning electron microscope analysis of the solidified samples were carried out. The strength growth mechanism of the glutinous rice paste was investigated, and the results revealed that glutinous rice slurry can improve the enzymatic activity of microorganisms, that is, the microorganisms can produce more urease to decompose urea, and as the amount of urease increases, the concentration of the cementing solution increases, and the calcium carbonate generated by the MICP precipitates. When the concentration of the added cooked glutinous rice slurry was 5%, the unconfined compressive strength of the soil was the largest. In addition, the scanning electron microscope analysis revealed that cooled glutinous rice slurry can be used as a bridge to generate a large amount of ineffective carbonic acid. Calcium atoms are connected together to form effective calcium carbonate, which fills in the pores of the soil as a whole, increasing the compactness of the soil and greatly improving its macroscopic mechanical strength.

Bacterial communities shift and influence in an acid mine drainage treatment using barium carbonate disperse alkaline substrate system

Chemical passive treatment systems used to remediate acid mine drainage has been evaluated based mainly on the reactivity of the chemical alkaline reagents, overlooking the activity of the microorganisms that proliferate in these artificial ecosystems. In this study, the bacterial communities of a unique passive treatment system known as BDAS (Barium carbonate Dispersed Alkaline Substrate) were investigated using 16S rRNA gene metagenomic sequencing combined with hydrochemical characterization of the AMD and phenotypic characterization of biogenic precipitates. According to the hydrochemical characterization, the water quality improved as the water progressed through the system, with a drastic increase in the pH (up to alkaline conditions) and total organic carbon, as well as the removal of main contaminants such as Ca2+, SO42−, Fe3+, Al3+, and Mn2+. These environmental changes resulted in an increase in bacterial diversity (richness) after the inlet and in the shift of the bacterial communities from chemoautotrophs (e.g., Ferrovum and Acidiphilum) to chemoheterotrophs (e.g., Brevundimonas and Geobacter). Some of these taxa harbour potential to immobilize metals, aiding in the treatment of the water. One of the mechanisms involved in the immobilization of metals is microbially induced calcium carbonate precipitation, which seems to occur spontaneously in BDAS. The production of biofilm was also observed in most parts of the system, except in the inlet, helping with the removal of metals. However, in the long run, the build-up of biofilm and precipitation of metals could clog (i.e., biofouling) the pores of the matrix, reducing the treatment efficiency. Potential human pathogens (e.g. Legionella) were also detected in BDAS indicating the need for a treatment step at the end of the system to remove pathogenic microorganisms. These findings present a new perspective of the bacterial communities and their effects (both positively and negatively) in a chemical passive treatment system.

Mechanisms of carbonate precipitation induced by two model bacteria

The investigation of microbially induced calcium carbonate precipitation is essential to understanding CO2 fixation, marine carbonate rock formation, and biogeochemical cycling of life-essential elements. In this study, two model bacteria Bacillus subtilis (possess the cell wall of G+ bacteria) and Escherichia coli (possess the cell wall of G− bacteria) were used as representatives to induce carbonate mineralization. The mineralization ability of the two bacteria and carbonate precipitation mechanisms were studied with the biochemical analysis of bacterial fermentation products, mineral characterization, and biomimetic mineralization experiments. The results showed that both bacteria induced biomineral formation by using the cell wall as a template, but B. subtilis was more capable of inducing mineralization than E. coli. Particularly, the percentage of Ca2+ removal from the culture medium by the former reached 36% in 7 days, which induced the formation of vaterite and calcite, while that of Ca2+ removal by the latter reached 28%, and the resulting carbonate was amorphous calcium carbonate. Biomimetic mineralization experiments showed that protein molecules were the key factors inducing the formation of biological vaterite, while polysaccharides tended to bind small vaterite particles to form large organo-mineral aggregates. By comparing the results of inducing calcium carbonate under the same culture conditions, the two types of bacteria with completely different cell wall structures had significant differences in the ability to induce calcium carbonate synthesis, among which that was stronger by Bacillus subtilis (G+) than by Escherichia coli (G−). It was found that factors such as bacterial cell wall structure, extracellular secretions including carbonic anhydrase, pH value, etc. all affect the microbial-induced carbonate precipitation to varying degrees, providing new insights into the theory of bacterial-induced carbonate mineralization.

A comparative study of strength and durability characteristics of concrete and mortar admixture by bacterial calcite precipitation: A review

Frequently used concrete is the second most used material after water worldwide, but it is vulnerable to cracks, leading to decreased durability and service life. Self-healing techniques, including natural processes, polymers, carbonated steel slag, S.C.M.s, biological/chemical, bacteria direct/liquid, and immobilization/encapsulation, have been studied. The most recent technique is Microbially Induced Calcium Carbonate Precipitation (MICCP), which uses ureolytic bacteria of the bacillus family to heal or fill cavities, fissures, and cracks by precipitating CaCO3. Researchers aim to enhance self-healing efficiency in mortar and concrete by non-pathogenic bacteria, such as B. Megaterium, Subtilis, Aerius, Sphericus, Cereus, Pseudoforms, Shewanella, and Sporosarcina pasteurii. Previous studies found that 105 cells/ml was the most effective concentration for concrete, while mortar specimens interacted better with bacteria at various cell concentrations. Bacterial concrete at 105 cells/ml exhibited improved microstructure interaction and densification due to the formation of “C.S.H.” gel and a depletion in C.H. bond with confined pore space. Consolidated bacteria produced a copious volume of minerals that could fill the cracks in the concrete, as observed in SEM and EDS studies. XRD analysis confirmed the increase in calcite composition at the bacteria's concentration level of 105 cells/ml in cement concrete specimens. Bacterial concrete at this concentration level has the potential for sustained and strong concrete properties.