A Comprehensive Optimization Study of Microbially Induced Carbonate Precipitation for Soil Strength Enhancement: Impact of Biochemical and Environmental Factors

Microbially induced carbonate precipitation (MICP) represents a technique for biocementation, altering the hydraulic and mechanical properties of porous materials using bacterial and cementation solutions. The efficacy of MICP depends on various biochemical and environmental elements, requiring careful consideration to achieve optimal designs for specific purposes. This study evaluates the efficiency of different MICP protocols under varying environmental conditions, employing two bacterial strains: S. pasteurii and S. aquimarina, to optimize soil strength enhancement. In addition, microscale properties of carbonate crystals were investigated and their effects on soil strength enhancement were analyzed. Results demonstrate that among the factors investigated, bacterial strain and concentration of cementation solution significantly influence the biochemical aspect, while temperature predominantly affects the environmental aspect. During the MICP treatment process, the efficiency of chemical conversion through S. pasteurii varied between approximately 80% and 40%, while for S. aquimarina, it was only around 20%. Consequently, the CaCO3 content resulting from MICP treatment using S. pasteurii was significantly higher, ranging between 5% and 7%, compared to that achieved with S. aquimarina, which was about 0.5% to 1.5%. The concentration of the cementation solution also plays a pivotal role, with an optimized value of 0.5 M being critical for achieving maximum efficiency and CaCO3 content. The ideal temperature span for MICP operation falls between 20°C and 35°C, with salinity and oxygen levels exerting minor impact. Furthermore, although salinity influences the characteristics of formed carbonate crystals, its effect on unconfined compressive strength (UCS) values of MICP-treated soil remains marginal. Samples subjected to a one-phase treatment, adjusted to pH values between 6.0 and 7.5, exhibit roughly half the UCS strength compared to the two-phase treatment. These findings hold promising potential for MICP applications in both terrestrial and marine environments for strength enhancement.