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

Abstract

Concrete is the second most consumed product by humans, after water. However, the production of cement, which is used as a binding material in concrete, causes more than 5% of anthropogenic CO 2 emissions and has therefore a significant contribution to climate change and global warming. Due to increasing environmental awareness and international climate goals, there is a need for emission-reduced materials, that can replace conventional concrete in certain applications. One path to produce a solid, concrete-like construction material is microbial-induced calcium carbonate precipitation (MICP). As a calcium source in MICP, crushed limestone, which mainly consists out of CaCO 3 , can be dissolved with acids, for example lactic acid. The pH evolution during crystallization and dissolution processes provides important information about kinetics of the reactions. However, previous research on MICP has mainly been focused on macro-scale pH evolution and on characterization of the finished material. To get a better understanding of MICP it is important to be able to follow also local pH changes in a sample. In this work we present a new method to study processes of MICP at micro-scale in situ and in real time. We present two different methods to monitor the pH changes during the precipitation process of CaCO 3 . In the first method, the average pHs of small sample volumes are 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 CaCO 3 crystals are monitored. We demonstrate that these two methods are powerful tools to investigate pH changes for both MICP precipitation and CaCO 3 dissolution for knowledge-based improvement of MICP-based material properties.

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

“…However, the sample cell additionally has the option to cultivate bacteria and is therefore also suitable for MICP experiments and experiments can also be performed under non-stagnant conditions (flow). We have used a similar sample cell previously to monitor local pH changes during MICP precipitation without additional crystallization surfaces present and for the dissolution of crystals with lactic acid 22 .…”

“…Dissolved chalk solution (DCS) was produced as described previously 22 , and used as a cost-effective calcium source for EICP 13 . Usually, is used in EICP/MICP, however, chloride-ions react fast to form chloride salts and pollute water and can lead to steel corrosion of steel-reinforcement in concrete.…”

“…Local pH changes during the precipitation processes were monitored in real time and in situ on a single crystal level with confocal laser scanning microscopy (CLSM, TCS Leica SP8, objective 40×, NA 1.1) using a method described previously 22 . The pH sensitive fluorescent dye N-(rhodamine 6G)-lactam-ethylenediamine (R6G-EDA, concentration: ) and pH insensitive dye Sulfhorhodamine 101 (SR101, concentration: ) were added to the crystallization solution.…”

Research status and development of microbial induced calcium carbonate mineralization technology

“…Although the optimal pH for the induction of calcium carbonate precipitation by various microorganisms has been reported, the pH during medium precipitation is constantly changing. Therefore, Zehner [115] discovered a rapid increase in pH owing to urea hydrolysis, followed by a decrease in pH due to CaCO 3 precipitation by monitoring the pH change in the solution environment. The higher the pH, the more unstable the calcium carbonate crystals (Fig 4).…”

High level of calcium carbonate precipitation achieved by mixed culture containing ureolytic and nonureolytic bacterial strains

“…1999; Zehner et al . 2020). The most studied MICP process is the urea degradation pathway (Chaparro‐Acuña et al .…”