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.

Calcite seed-assisted microbial induced carbonate precipitation (MICP).

Microbial-induced calcium carbonate precipitation (MICP) is a biological process inducing biomineralization of CaCO3. This can be used to form a solid, concrete-like material. To be able to use MICP successfully to produce solid materials, it is important to understand the formation process of the material in detail. It is well known that crystallization surfaces can influence the precipitation process. Therefore, we present in this contribution a systematic study investigating the influence of calcite seeds on the MICP process. We focus on the changes in the pH and changes of the optical density (OD) signal measured with absorption spectroscopy to analyze the precipitation process. Furthermore, optical microscopy was used to visualize the precipitation processes in the sample and connect them to changes in the pH and OD. We show, that there is a significant difference in the pH evolution between samples with and without calcite seeds present and that the shape of the pH evolution and the changes in OD can give detailed information about the mineral precipitation and transformations. In the presented experiments we show, that amorphous calcium carbonate (ACC) can also precipitate in the presence of initial calcite seeds and this can have implications for consolidated MICP materials.

Microbial-induced calcium carbonate precipitation: an experimental toolbox for in situ and real time investigation of micro-scale pH evolution.

Concrete is the second most consumed product by humans, after water. However, the production of conventional concrete causes more than 5% of anthropogenic CO2 emissions and therefore there is a need for emission-reduced construction materials. One method to produce a solid, concrete-like construction material is microbial-induced calcium carbonate precipitation (MICP). To get a better understanding of MICP it is important to be able to follow local pH changes in dissolution and precipitation processes of CaCO3. In this work we present a new method to study processes of MICP at the micro-scale in situ and in real time. We present two different methods to monitor the pH changes during the precipitation process of CaCO3. In the first method, the average pH of small sample volumes is measured in real time, and pH changes are subsequently correlated with processes in the sample by comparing to optical microscope results. The second method is introduced to follow local pH changes at a grain scale in situ and in real time. Furthermore, local pH changes during the dissolution of CaCO3 crystals are monitored. We demonstrate that these two methods are powerful tools to investigate the pH changes for both MICP precipitation and CaCO3 dissolution for knowledge-based improvement of MICP-based material properties.