Environmental Dependence of Microbially Induced Calcium Carbonate Crystal Precipitations: Experimental Evidence and Insights

Microbial-induced calcium carbonate precipitation (MICP) is a nature-based and eco-friendly technique that has presented promising applications in various disciplines. Despite the extensive amounts of prior studies about this technique, the impact of environmental conditions on the mineral compositions and cementitious characteristics of calcium carbonate precipitations remains unclear. In this study, we focus on four primary factors including temperature (15°C, 25°C, and 35°C), pH of initial solution (7, 8, 9, and 10), bacteria solution (BS) concentration (OD600=0.24, 0.47, 0.68, and 0.81), and cementation solution (CS) concentration (0.1, 0.25, 0.5, 0.75, 1.0, and 1.25 M). Under these varying conditions, 36 groups of MICP experiments are performed. Material characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and an ultrasonic oscillation test are applied to investigate the morphological features, mineral compositions, and cementitious characteristics of calcium carbonate precipitations, respectively. Experimental results highlight the strong dependence of calcium carbonate precipitations on these factors. The higher temperature contributes to the larger size of calcium carbonate crystal. As the pH of initial solution increases, there is a tendency for mineral composition to change from vaterite into calcite. The decreased BS concentration increases calcite contents and enhances the cementitious characteristics of the precipitation. The CS concentration level influences the size of the calcium carbonate crystal. Through a systematical analysis of how various factors jointly influence the crystal precipitations, this study is expected to improve the current understanding of the MICP process, and contribute to the future optimized design of biomediated soil improvement.