Microfluidic study in a meter-long reactive path reveals how the medium's structural heterogeneity shapes...

Area of Science:

• Geotechnical Engineering
• Environmental Science
• Biotechnology

Background:

• Microbially induced calcium carbonate precipitation (MICP) offers a sustainable alternative for soil cementation.
• MICP performance depends on bacterial growth, solute transport, reaction kinetics, and crystal formation.
• The influence of pore-scale heterogeneity on MICP processes remains poorly understood.

Purpose of the Study:

• To investigate the effect of pore-scale heterogeneity on MICP.
• To analyze spatiotemporal evolution, chemical reaction efficiency, and permeability changes during MICP.
• To compare MICP performance in homogeneous versus heterogeneous porous media.

Main Methods:

• Utilized two meter-long microfluidic devices with homogeneous and heterogeneous porous networks.
• Employed real-time monitoring and time-lapse microscopy to track bacteria and crystal formation.
• Measured inlet/outlet pressures to assess permeability evolution under imposed flow.

Main Results:

• Calcium carbonate (CaCO3) crystals formed within 1 hour, with growth completing in 12 hours.
• Heterogeneous networks exhibited higher average crystal growth rates and greater crystal diameters (23-46 μm) compared to homogeneous ones (17-40 μm).
• Heterogeneous media showed higher chemical reaction efficiency (peak 34%) and more significant permeability reduction than homogeneous media.

Conclusions:

• Pore-scale heterogeneity enhances MICP efficiency by promoting faster crystal growth and larger crystal formation.
• Heterogeneous porous media are more effectively cemented by MICP, leading to greater strength improvements.
• Understanding heterogeneity is crucial for optimizing MICP applications in geotechnical and environmental engineering.