Biogeochemical simulation of microbially induced calcite precipitation with Pararhodobacter sp. strain SO1

Abstract

Biogrouting is a ground improvement technique, which utilizes microorganisms. The numerical simulation of biogrouting is important to ensure efficient operation and to assess the applicability to the target ground. In this study, we compared syringe-scale biogrouting with biogeochemical simulation. Parameters suitable for practical applications were included. The rate constant and half-saturation constant of the reaction rate law in ureolytic bacteria Pararhodobacter sp. strain SO1, obtained from the simulation based on the urease activity test, were 1 × 10⁻⁸ mol/mg/s and 0.635 M, respectively. To achieve the same mineral precipitation in measurement and simulation, a setting in which only the calcite precipitated was used. In the sequential simulation of the solidification test, a variation in discharged Ca²⁺ concentration was reproduced by introducing an “adjustment index”, which considers the microbial biomass contributing to the reaction. Moreover, for the re-injection test, in which microbes were injected again to further improve the biogrout strength, the settings were validated by the sequential simulation followed by predictive simulation on different injection dates. The results indicate that by conducting a biogeochemical simulation of calcite precipitation for biogrouting using ureolytic bacteria, the strength of biogrout can be predicted and managed.