Microbially Induced Calcite Precipitation Employing Environmental Isolates

A Study on Bio-Stabilisation of Sub-Standard Soil by Indigenous Soil Urease-Producing Bacteria

Sub-standard soils are of great concern worldwide due to diverse economic losses and the possibility of severe environmental hazards ranging from catastrophic landslides, building collapse, and erosion to loss of lives and properties. This study explored the potential of urease-producing bacteria, <i>Bacillus cereus</i> and <i>Bacillus paramycoides</i>, to stabilise sub-standard soil bio-stabilisation. The maximum urease activity measured by <i>B. cereus</i> and <i>B. paramycoides</i> was 665 U/mL and 620 U/mL, respectively. <i>B. cereus</i> and <i>B. paramycoides</i> precipitated 943 ± 57 mg/L and 793 ± 51 mg/L of CaCO₃ at an optical density (425 nm) of 1.01 and 1.09 and pH 8.83 and 8.59, respectively, after 96 hours of incubation. SEM microstructural analysis of the precipitated CaCO₃ revealed crystals of various sizes (2.0–23.0 µm) with different morphologies. XRD analysis confirmed that the precipitated CaCO₃ comprised calcite and aragonite crystals. SEM analysis of the microstructure of organic and sandy clay soils treated with <i>B. cereus</i> and <i>B. paramycoides</i> showed the formation of bio-precipitated calcium carbonate deposits on the soil particles (biocementing soil grains), with <i>B. cereus</i> precipitating more CaCO₃ crystals with a better biocementing effect compared to <i>B. paramycoides</i>. Overall, the experimental results attributed CaCO₃ formation to bacterial-associated processes, suggesting that soil ureolytic bacteria are potentially useful to stabilise sub-standard soil.

Highlighting Bacteria with Calcifying Abilities Suitable to Improve Mortar Properties

Biomineralization, the use of microorganisms to produce calcium carbonate, became a green solution for application in construction materials to improve their strength and durability. The calcifying abilities of several bacteria were investigated by culturing on a medium with urea and calcium ions. The characterization of the precipitates from bacterial cultures was performed using X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The formation of carbonate crystals was demonstrated by optical and scanning electron microscopy. Water absorption and compressive strength measurements were applied to mortars embedded with sporal suspension. The efficiency of the supplementation of mortar mixtures with bacterial cells was evaluated by properties, namely the compressive strength and the water absorption, which are in a relationship of direct dependence, the increase in compressive strength implying the decrease in water absorption. The results showed that Bacillus subtilis was the best-performing bacterium, its introduction into the mortar producing an increase in compressive strength by 11.81% and 9.50%, and a decrease in water absorption by 11.79% and 10.94%, after 28 and 56 days of curing, respectively, as compared to standards. The exploitation of B. subtilis as a calcifying agent can be an interesting prospect in construction materials.

Smart soil grouting using innovative urease-producing bacteria and low cost materials

AIMS

Calcium carbonate is a biomineral whose precipitation could be mediated by ureolytic bacteria and contributes in strengthening of sandy soils. The type of bacteria and grade of reagents have significant influence on microbially induced calcite precipitation (MICP). In the present study, factorial experiments based on these two factors were designed to determine their potential on MICP process, taking into consideration the economic advantages while giving quality results as well.

METHODS AND RESULTS

For the first time, Alkalibacterium iburiense strain EE1 (GenBank accession no. MF355369.1) is reported for its biogrouting activity. Optimum growth conditions for MICP treatments were pH (9·56 ± 0·021), EC (44·7 ± 0·057 mS cm^-1 ), OD₆₀₀ (2·04 ± 0·015), NH₄ ⁺ concentration (487·06 ± 1·021 mmol l^-1 ), and urease activity (20·0 ± 0·75 mmol l^-1 urea hydrolysed min^-1 ) after 72-h incubation. Statistical analysis comparing the growth in technical-grade medium prepared in tap water and analytical-grade medium prepared in deionized water showed no significant differences (P = 1·0) in biomass and urease activity. In contrast to previous studies, the current approach could reduce the bacterial culture and cementation solution ratio by about 50%, using a simple surface percolation method with staged injection instead of parallel injection to treat different sand columns. Using fixation solution could immobilize the bacteria over the full length of columns for better strength improvement. The unconfined compressive strength ranged between 0·64 to 2·11 kg cm^-2 , and the corresponding CaCO₃ contents 5·7-38·5%. The scanning electron microscope images indicated that the precipitated CaCO₃ by bacteria was stable calcite.

CONCLUSIONS

Alkalibacterium iburiense and technical-grade reagents under nonsterile conditions are satisfactory consolidating agents for sandy soils.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach is considered eco-friendly and cost-effective for future scale-up applications in various geotechnical engineering.

Biocementation of soil by calcite/aragonite precipitation usingPseudomonas azotoformansandCitrobacter freundiiderived enzymes

Microbial geotechnology is the use of microorganisms and/or their derivatives to alter engineering properties of soil for improving its stability, strength and stiffness.

Biocement Fabrication and Design Application for a Sustainable Urban Area

Recently, designers have begun to pursue sustainability through the fabrication of materials from living organisms such as bacteria, fungi, and algae in order to address environmental issues. Based on the potential of materials from living organisms, this study has explored a sustainable design application using biocement formed thorough microbially-induced calcite precipitation (MICP), which produces minerals by bacterial metabolic activity. Since most of the studies on MICP thus far have focused on limited fields such as engineering, biotechnology, and geo-technology, this study has focused more on improving the application of biocement in design. We optimized MICP conditions using two parameters (i.e., concentration of urea-CaCl2 and bacterial cell density) through water percolation testing, compressive strength testing, and X-ray diffraction (XRD) analysis. Then, based on the optimized conditions, material compatibility testing and scalability testing were performed, and design application research was conducted as well. As a result, biocement has been identified as a potential sustainable design material, based on its 40% compressive strength compared to conventional concrete, improved material finish, aesthetic aspects, and environmental impact. This paper contributes to the development of biocement applications in the environmental design field through multidisciplinary research ranging from biological experiments to design applications.

Effect of Temperature, pH, and Reaction Duration on Microbially Induced Calcite Precipitation

In this study, the amount of calcite precipitate resulting from microbially induced calcite precipitation (MICP) was estimated in order to determine the optimal conditions for precipitation. Two microbial species (Staphylococcus saprophyticus and Sporosarcina pasteurii) were tested by varying certain parameters such as (1) initial potential of hydrogen (pH) of urea-CaCl2 medium, (2) temperature during precipitation, and (3) the reaction duration. The pH values used for testing were 6, 7, 8, 9, and 10, the temperatures were 20, 30, 40, and 50 °C, and the reaction durations were 2, 3, and 4 days. Maximum calcite precipitation was observed at a pH of 7 and temperature of 30 °C. Most of the precipitation occurred within a reaction duration of 3 days. Under similar conditions, the amount of calcite precipitated by S. saprophyticus was estimated to be five times more than that by S. pasteurii. Both the species were sensitive to temperature; however, S. saprophyticus was less sensitive to pH and required a shorter reaction duration than S. pasteurii.

Isolation, differentiation and biodiversity of ureolytic bacteria of Qatari soil and their potential in microbially induced calcite precipitation (MICP) for soil stabilization

Biomineralization plays a key role in modifying the geological properties of soil, thereby stabilizing it against wind erosion, especially in areas characterized by harsh weather and harsh soil (calcareous and arid); i.e. Arabic Gulf region. Among soil microorganisms, ureolytic bacteria are capable of modifying soil characteristics and thus, inducing biomineralization. This research investigated the occurrence and diversity of ureolytic bacteria in Qatari soils, specifically to study their acquired potential to adapt to harsh conditions exhibiting ureolytic activity. Soil samples were collected from various locations in Qatar and were used to isolate the indigenous ureolytic bacteria. It was noticed that most of the ureolytic bacteria in Qatari soil belong to the genus Bacillus mainly Bacillus cereus. Identification and differentiation of 18 ureolytic isolates were performed using MALDI-TOF MS techniques while ribotyping (16S rRNA) molecular technique was used mainly for 6 selected strains. This study not only shows the diversity of species of ureolytic bacteria in Qatari soil but also shows the diversity in their protein profiles, which confirms that bacteria have adapted well to the harsh environment. In addition, the strains were evaluated based on a newly modified screening method in this work; i.e. production of arbitrary urease activity (AUA). Thus, the strains showing the highest AUA, exhibited the highest capability to produce urease enzymes induced by urea. Analysis of calcium carbonate precipitation utilizing SEM-EDX showed that the ureolytic bacteria also play a significant role in the precipitation of minerals such as CaCO₃, in the presence of urea in soil. Therefore, this research showed a high occurrence of indigenous Bacillus bacteria in Qatari soil that can perform biomineralization and thus can be helpful, if properly stimulated, in enhancing soil stabilization, and for other local applications as well, since they are adapted to these soil and weather conditions.

Biomineralization plays a key role in modifying the geological properties of soil, thereby stabilizing it against wind erosion, especially in areas characterized by harsh weather and harsh soil (calcareous and arid); i.e. Arabic Gulf region.

Nano-Inclusions Applied in Cement-Matrix Composites: A Review

Research on cement-based materials is trying to exploit the synergies that nanomaterials can provide. This paper describes the findings reported in the last decade on the improvement of these materials regarding, on the one hand, their mechanical performance and, on the other hand, the new properties they provide. These features are mainly based on the electrical and chemical characteristics of nanomaterials, thus allowing cement-based elements to acquire "smart" functions. In this paper, we provide a quantitative approach to the reinforcements achieved to date. The fundamental concepts of nanoscience are introduced and the need of both sophisticated devices to identify nanostructures and techniques to disperse nanomaterials in the cement paste are also highlighted. Promising results have been obtained, but, in order to turn these advances into commercial products, technical, social and standardisation barriers should be overcome. From the results collected, it can be deduced that nanomaterials are able to reduce the consumption of cement because of their reinforcing effect, as well as to convert cement-based products into electric/thermal sensors or crack repairing materials. The main obstacle to foster the implementation of such applications worldwide is the high cost of their synthesis and dispersion techniques, especially for carbon nanotubes and graphene oxide.