Calcite seed-assisted microbial induced carbonate precipitation (MICP)

Seeding improves the strength of bio-tiles grown with microbially induced calcium carbonate precipitation

Bio-tiles are a biobased alternative to conventional tiles that utilise a promising technology called microbially induced calcium carbonate (CaCO3) precipitation (MICP). This technology has low energy requirements and also sequesters carbon. Bio-tiles have been made in previous work using a submersion method, however, the process required additives such as 0.3 M magnesium chloride to achieve bio-tiles that meet international standards. The current study aimed to improve the bio-tile strength properties with CaCO3 crystal seeding and a pumping method instead of the use of magnesium that also increases ionic strength. With this technique, cementation solution containing the required calcium and urea for the MICP reaction was pumped through a sealed mould in a series of programmed treatments. The highest concentration of ureolytic Sporosarcina pasteurii with an effective urease activity of 40 mmol NH4-N/L·min was found to be most beneficial to the breaking strength of the bio-tiles, as were the shortest retention times of 1 h between treatments. Seeding with CaCO3 crystals offered significant benefit to the MICP process. Pre-seeding of the geotextiles was explored and the mass of seeds initially present on the geotextiles was found to have a direct improvement on the breaking strength of 21-82 %, increasing with seed loading. The highest CaCO3 seed loading tested of 0.072 g seeds/cm2 geotextile resulted in bio-tiles with a breaking strength of 940 ± 92 N and a modulus of rupture of 16.4 ± 1.7 N/mm2, meeting international targets for extruded tiles with 6-10 % water absorption. When a seed loading of 0.021 g/cm2 was used instead, bio-tiles meeting targets for tiles with a water absorption of >10 % were produced at 628 ± 18 N and 10.5 ± 1.1 N/mm2.

Microfluidic study in a meter-long reactive path reveals how the medium's structural heterogeneity shapes MICP-induced biocementation

Microbially induced calcium carbonate (CaCO₃) precipitation (MICP) is one of the major sustainable alternatives to the artificial cementation of granular media. MICP consists of injecting the soil with bacterial- and calcium-rich solutions sequentially to form calcite bonds among the soil particles that improve the strength and stiffness of soils. The performance of MICP is governed by the underlying microscale processes of bacterial growth, reactive transport of solutes, reaction rates, crystal nucleation and growth. However, the impact of pore-scale heterogeneity on these processes during MICP is not well understood. This paper sheds light on the effect of pore-scale heterogeneity on the spatiotemporal evolution of MICP, overall chemical reaction efficiency and permeability evolution by combining two meter-long microfluidic devices of identical dimensions and porosity with homogeneous and heterogeneous porous networks and real-time monitoring. The two chips received, in triplicate, MICP treatment with an imposed flow and the same initial conditions, while the inlet and outlet pressures were periodically monitored. This paper proposes a comprehensive workflow destined to detect bacteria and crystals from time-lapse microscopy data at multiple positions along a microfluidic replica of porous media treated with MICP. CaCO₃ crystals were formed 1 h after the introduction of the cementation solution (CS), and crystal growth was completed 12 h later. The average crystal growth rate was overall higher in the heterogeneous porous medium, while it became slower after the first 3 h of cementation injection. It was found that the average chemical reaction efficiency presented a peak of 34% at the middle of the chip and remained above 20% before the last 90 mm of the reactive path for the heterogeneous porous network. The homogeneous porous medium presented an overall lower average reaction efficiency, which peaked at 27% 420 mm downstream of the inlet and remained lower than 12% for the rest of the microfluidic channel. These different trends of chemical efficiency in the two networks are due to a higher number of crystals of higher average diameter in the heterogeneous medium than in the homogeneous porous medium. In the interval between 480 and 900 mm, the number of crystals in the heterogeneous porous medium is more than double the number of crystals in the homogeneous porous medium. The average diameters of the crystals were 23-46 μm in the heterogeneous porous medium, compared to 17-40 μm in the homogeneous porous medium across the whole chip. The permeability of the heterogeneous porous medium was more affected than that of the homogeneous system, while the pressure sensors effectively captured a higher decrease in the permeability during the first two hours when crystals were formed and a less prominent decrease during the subsequent seeded growth of the existing crystals, as well as the nucleation and growth of new crystals.

Research status and development of microbial induced calcium carbonate mineralization technology

In nature, biomineralization is a common phenomenon, which can be further divided into authigenic and artificially induced mineralization. In recent years, artificially induced mineralization technology has been gradually extended to major engineering fields. Therefore, by elaborating the reaction mechanism and bacteria of mineralization process, and summarized various molecular dynamics equations involved in the mineralization process, including microbial and nutrient transport equations, microbial adsorption equations, growth equations, urea hydrolysis equations, and precipitation equations. Because of the environmental adaptation stage of microorganisms in sandy soil, their reaction rate in sandy soil environment is slower than that in solution environment, the influencing factors are more different, in general, including substrate concentration, temperature, pH, particle size and grouting method. Based on the characteristics of microbial mineralization such as strong cementation ability, fast, efficient, and easy to control, there are good prospects for application in sandy soil curing, building improvement, heavy metal fixation, oil reservoir dissection, and CO₂ capture. Finally, it is discussed and summarized the problems and future development directions on the road of commercialization of microbial induced calcium carbonate precipitation technology from laboratory to field application.

Natural Biomaterials from Biodiversity for Healthcare Applications

Natural biomaterials originating during the growth cycles of all living organisms have been used for many applications. They span from bioinert to bioactive materials including bioinspired ones. As they exhibit an increasing degree of sophistication, natural biomaterials have proven suitable to address the needs of the healthcare sector. Here the different natural healthcare biomaterials, their biodiversity sources, properties, and promising healthcare applications are reviewed. The variability of their properties as a result of considered species and their habitat is also discussed. Finally, some limitations of natural biomaterials are discussed and possible future developments are provided as more natural biomaterials are yet to be discovered and studied.

Biomineralization Induced by Cells of Sporosarcina pasteurii: Mechanisms, Applications and Challenges

Biomineralization has emerged as a novel and eco-friendly technology for artificial mineral formation utilizing the metabolism of organisms. Due to its highly efficient urea degradation ability, Sporosarcina pasteurii(S. pasteurii) is arguably the most widely investigated organism in ureolytic biomineralization studies, with wide potential application in construction and environmental protection. In emerging, large-scale commercial engineering applications, attention was also paid to practical challenges and issues. In this review, we summarize the features of S. pasteurii cells contributing to the biomineralization reaction, aiming to reveal the mechanism of artificial mineral formation catalyzed by bacterial cells. Progress in the application of this technology in construction and environmental protection is discussed separately. Furthermore, the urgent challenges and issues in large-scale application are also discussed, along with potential solutions. We aim to offer new ideas to researchers working on the mechanisms, applications and challenges of biomineralization.

A sample cell for the study of enzyme-induced carbonate precipitation at the grain-scale and its implications for biocementation

Biocementation is commonly based on microbial-induced carbonate precipitation (MICP) or enzyme-induced carbonate precipitation (EICP), where biomineralization of [Formula: see text] in a granular medium is used to produce a sustainable, consolidated porous material. The successful implementation of biocementation in large-scale applications requires detailed knowledge about the micro-scale processes of [Formula: see text] precipitation and grain consolidation. For this purpose, we present a microscopy sample cell that enables real time and in situ observations of the precipitation of [Formula: see text] in the presence of sand grains and calcite seeds. In this study, the sample cell is used in combination with confocal laser scanning microscopy (CLSM) which allows the monitoring in situ of local pH during the reaction. The sample cell can be disassembled at the end of the experiment, so that the precipitated crystals can be characterized with Raman microspectroscopy and scanning electron microscopy (SEM) without disturbing the sample. The combination of the real time and in situ monitoring of the precipitation process with the possibility to characterize the precipitated crystals without further sample processing, offers a powerful tool for knowledge-based improvements of biocementation.