Application of Microbial-Induced Carbonate Precipitation for Soil Improvement via Ureolysis

Abstract

The challenges to develop or strengthen the weak soil always prompted the need for further research investigation to develop a new, eco-friendly, and sustainable method of ground improvement. The MICP (microbially induced carbonate precipitation) technique is one such method in which metabolic pathways of microorganism are utilized to form calcite precipitation inside the soil matrix leading to improve the engineering properties of soil. Ureolysis or urea hydrolysis is the most efficient process among all MICP methods of carbonate generating reaction, as it has the potential to produce large amount of calcite (CaCO₃) within a short period of time. This study aims to investigate the effectiveness of MICP technique on fine grained soil as clayey sandy silt or loam in improving its shear strength. In this study, three species of urease positive, alkaliphelic aerobic bacteria, namely Sporosarcina pasteurii, Bacillus megatarium, and Morganella morgani were used for ureolysis and microbially induced calcite precipitation. Quantitative analysis of calcite precipitation in the soil samples was done by Piper method. The target soil was mixed with each microorganism individually before it was compacted into the mould. In the experimental programm, four different treatment conditions were considered for each types of microorganism such as (1) untreated, (2) treated with cementation reagent (mixture of 0.5 M CaCl₂ and 0.5 M urea), (3) treated with bacteria only and (4) treated with both bacteria and cementation reagent. These experiments revealed that all these three types of microorganism can induce sufficient amount of calcite precipitation that can result in measurable improvement of the strength of soil.