Metabolism-Induced CaCO₃ Biomineralization during Reactive Transport in a Micromodel: Implications for Porosity Alteration

The ability of Pseudomonas stutzeri strain DCP-Ps1 to drive CaCO₃ biomineralization has been investigated in a microfluidic flowcell (i.e., micromodel) that simulates subsurface porous media. Results indicate that CaCO₃ precipitation occurs during NO₃^- reduction with a maximum saturation index (SI_calcite) of ∼1.56, but not when NO₃^- was removed, inactive biomass remained, and pH and alkalinity were adjusted to SI_calcite ∼ 1.56. CaCO₃ precipitation was promoted by metabolically active cultures of strain DCP-Ps1, which at similar values of SI_calcite, have a more negative surface charge than inactive strain DCP-Ps1. A two-stage NO₃^- reduction (NO₃^- → NO₂^- → N₂) pore-scale reactive transport model was used to evaluate denitrification kinetics, which was observed in the micromodel as upper (NO₃^- reduction) and lower (NO₂^- reduction) horizontal zones of biomass growth with CaCO₃ precipitation exclusively in the lower zone. Model results are consistent with two biomass growth regions and indicate that precipitation occurred in the lower zone because the largest increase in pH and alkalinity is associated with NO₂^- reduction. CaCO₃ precipitates typically occupied the entire vertical depth of pores and impacted porosity, permeability, and flow. This study provides a framework for incorporating microbial activity in biogeochemistry models, which often base biomineralization only on SI (caused by biotic or abiotic reactions) and, thereby, underpredict the extent of this complex process. These results have wide-ranging implications for understanding reactive transport in relevance to groundwater remediation, CO₂ sequestration, and enhanced oil recovery.