Industrial-grade nitrogen sources modulate CaCO3 polymorphs and strength in MICP-cemented sand: A structure-property...

Area of Science:

• Geotechnical Engineering
• Microbiology
• Materials Science

Background:

• Microbially induced carbonate precipitation (MICP) shows potential for soil stabilization.
• High costs associated with laboratory-grade yeast extract (YE) limit large-scale MICP applications, accounting for over 70% of cultivation medium expenses.
• Alternative nitrogen sources are needed to reduce MICP costs.

Purpose of the Study:

• To evaluate industrial yeast extract (IYE) and soy peptone (SP) as cost-effective replacements for YE in Sporosarcina pasteurii cultivation.
• To assess the impact of these nitrogen sources on urease activity, bio-cemented sand performance, and CaCO3 precipitation.
• To determine an optimal blending strategy for enhanced MICP performance and cost reduction.

Main Methods:

• Cultivation of Sporosarcina pasteurii using YE, IYE, and SP in various combinations.
• Measurement of bacterial urease activity.
• Assessment of bio-cemented sand columns using unconfined compressive strength (UCS), CaCO3 content analysis, and mineralogical/microstructural examination.

Main Results:

• A blend of 5 g/L pure YE + 10 g/L IYE achieved ~80% of control urease activity and a UCS of 4.27 MPa, 9% higher than the control.
• This YE-IYE blend reduced nitrogen source costs by 65.53% and resulted in predominant calcite formation (~95.57% of CaCO3).
• Soy peptone substitution led to lower UCS despite high CaCO3 content, indicating that mechanical performance is influenced by polymorph composition and microstructure, not just CaCO3 quantity.

Conclusions:

• Partial substitution of YE with IYE is a viable strategy for cost-effective MICP soil stabilization.
• The optimal YE-IYE blend enhances bacterial urease activity, significantly increases UCS, and promotes calcite precipitation with a dense microstructure.
• This approach offers a practical solution for achieving lower-cost, higher-performance MICP applications in geotechnical engineering.