Comparison of biomineralization kinetics induced by bacteria, bacterial enzyme, and soybean enzyme

Bacteria (BS), bacterial enzymes (BE), and soybean enzymes (SE) have been used to induce CaCO₃ precipitation for soil stabilization. While the performance of these three urease sources has been widely studied, the underlying mechanisms have not been thoroughly explored. In this study, we conducted solution tests, followed by mathematical analysis, to investigate bacteria/enzyme degradation, urea hydrolysis rate, and CaCO₃ precipitation rate across different reaction phases. Microfluidics tests were also conducted to visually observe the precipitation process. Our results indicated that both urea hydrolysis and CaCO₃ precipitation intensified the degradation of the urease sources. Bacteria exhibited the most stable urease activity, followed by soybean enzymes, and then bacterial enzymes. The microfluidics tests revealed a lag period before CaCO₃ nucleation across all conditions, with the longest duration for BS, followed by SE, and then BE. Bacteria proved to be more effective urease producers, maintaining adequate urease levels without acting as heterogeneous nucleation sites. Additionally, SE contained significant impurities, which may contribute to the higher strength observed in SE-stabilized soil compared to BS-stabilized soil. The current work offers a fundamental approach for practical biocement grouting design through mathematic analysis and provides new insights into biocementation processes.