Modeling the Effect of Microbially Induced Calcium Carbonate Precipitation (MICP) on CO2 Trapping.

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is hypothesized to accelerate mineral and solubility trapping of CO2(g) through bacterial hydrolysis of urea, which increases pH, and hence the solubility of carbonate ions. While previous models of MICP only targeted selected conditions and did not offer modeling of all reaction kinetics, enzyme activities, and buffers in the cultivation media, our model addressed these research gaps and helped to understand the limitations and effectiveness of MICP to enhance CO2(g) solubility and mineral trapping. Results showed the capability of ureolysis to increase solubility trapping, with buffers in the media having a non-negligible influence on the process. However, ureolysis above pH 8.9 decreases the capacity of solubility trapping and ultimately causes CO2(g) outgassing. For the modeled configurations, MICP does not increase CO2(g) mineral trapping, since the pH increase by ureolysis is insufficient to precipitate additional CaCO3 than from C atoms released from urea hydrolysis. However, mineral trapping in actual sedimentary reservoirs is more complex. Thus, MICP might enhance mineral trapping in combination with mechanisms in sedimentary reservoirs, while CO2(g) solubility trapping by ureolysis and bacterial carbonic anhydrase enzymes can act as an important intermediate step for subsequent geochemical reactions, leading to long-term mineral trapping.