# Evaluation and Utilization of Aged Bacteria in MICP Technology

## TL;DR

This paper explores how aged bacteria can still be effectively used in microbial-induced calcite precipitation (MICP) technology to produce carbonate for soil stabilization.

## Contribution

The study introduces a method to estimate precursor-carbonate and viable bacterial density using depth-based carbonate measurements in soil.

## Key findings

- Aged bacteria can produce more carbonate than the initial calcium chloride amount.
- Carbonate depth distribution in soil correlates with microbial adsorption properties.
- Formulas linking precursor-carbonate, viable bacteria density, and apparent viability are validated.

## Abstract

As a response to aging of cultured urease-producing microorganisms, the blending method was examined to obtain the required carbonate production amount using the apparent viability (Rcv) based on previous research. As a result, a significantly higher carbonate content than the amount of CaCl2 2H2O used was produced. Since this trend has been obtained in previous studies, it was judged that carbonate hydrate was formed. As a next step, a penetration test of soil–biocement–liquid (BCS) was conducted to investigate the properties and behavior of the BCS system, taking into account the microscopic properties of the BCS response. The depth distribution of carbonate content (C) was measured by the acid dissolution method of soil sampled from the specimen. It was assumed that the C-profile was formed by adsorption based on the diffuse double layer of microorganisms. It was shown that the amount of precursor-carbonate (precursor CPR), the optical density (OD) of viable bacteria, and the physical amount of soil adsorbed at that position can be estimated from C obtained at the various depths. In addition, the previously obtained formulas among CPR, viable OD, and Rcv shown are briefly explained in this paper.