Influence of on-site low-ureolysis bacteria and high-ureolysis bacteria on the effectiveness of MICP processes

TL;DR

This study investigates how native soil bacteria with different ureolysis capabilities affect the efficiency of Microbially Induced Calcium Carbonate Precipitation (MICP), revealing that high-ureolysis bacteria improve MICP outcomes compared to low-ureolysis bacteria.

Contribution

It provides new insights into the distinct impacts of low- and high-ureolysis bacteria on MICP performance and soil stabilization, emphasizing the importance of bacterial activity and pH control.

Findings

High-ureolysis bacteria reduce bacterial activity less than S. pasteurii alone.

High-ureolysis bacteria increase calcium carbonate precipitation and UCS.

Low-ureolysis bacteria significantly decrease bacterial activity and UCS.

Abstract

Microbially Induced Calcium Carbonate Precipitation (MICP) is an eco-friendly technique that enhances soil mechanical properties using urease-producing microorganisms, especially Sporosarcina pasteurii. However, field trials often yield suboptimal results due to the presence of indigenous soil microbes. To evaluate their impact, bacteria from natural soil were classified into two groups: low-ureolysis and high-ureolysis. These were combined with S. pasteurii in experiments using microfluidic chips and sand columns. The analysis covered bacterial populations, urease activity, pH changes, calcium carbonate crystal metrics, and unconfined compressive strength (UCS). Results indicated that mixing low-ureolysis bacteria with S. pasteurii resulted in a 74-84% reduction in bacterial activity and a 60% decrease in chemical conversion rate, leading to a 60% drop in UCS. In contrast, combining high-ureolysis bacteria with S. pasteurii reduced bacterial activity by 49-54%, which was less than the 64% reduction seen with S. pasteurii alone. This combination improved calcium carbonate conversion rates by 9% to 45% and slightly enhanced UCS.The study highlights the distinct effects of low-ureolysis and high-ureolysis bacteria on MICP efficiency, particularly regarding their influence on pH. Low-ureolysis bacteria decrease pH, while high-ureolysis bacteria increase it. Maintaining high bacterial activity and precipitation rates is crucially dependent on pH levels. Future strategies could focus on reducing the presence of low-ureolysis bacteria or sustaining higher pH levels to enhance MICP effectiveness in field applications.