Efficiency and Characteristics of MICP in Environments with Elevated Salinity, Diminished Oxygen, and Lowered Temperature: A Microfluidics Investigation

Abstract

Microbially induced carbonate precipitation (MICP) shows significant potential for improving soil strength, but environmental factors greatly influence its mechanisms and effectiveness. The feasibility of using MICP in demanding conditions, such as the soil around piles in shallow seabeds during winter, known for their elevated salinity, diminished oxygen, and lowered temperature, remains uncertain due to limited research in this area. To address this gap, microfluidic techniques and advanced measurement tools, including Raman spectroscopy and scanning electron microscope (SEM), were utilized to investigate the impact of high salinity, low oxygen levels, and cold temperatures on bacterial growth, calcium carbonate crystallization, and porous medium permeability through MICP. The findings revealed that cold temperatures notably hinder bacterial growth, whereas high salinity and low oxygen levels also play significant roles. Low oxygen levels particularly reduce bacterial attachment. Additionally, in seawater environments, high salinity and cold temperatures have a more pronounced effect on calcium carbonate crystal shape and type, whereas the impact of low oxygen levels is relatively minor. Specifically, high salinity has minimal effect on average crystal diameter but reduces crystal number by 20.2%; in contrast, low oxygen levels increase average diameter (20.3%) but decrease crystal quantity (50.9%). Furthermore, cold temperatures decrease average diameter (36.9%) with little impact on crystal quantity. After six injections of the cementation solution, the chemical transformation efficiency of MICP-treated samples under combined marine conditions (high salinity, low oxygen levels, and cold temperatures) was 20.6% of deionized (DI) water, atmospheric oxygen levels, and 20°C, with cold temperatures being the primary contributor to this reduction (40.1%). An exponential decline in permeability with increasing calcium carbonate content was also observed. Based on the location of calcium carbonate generation within the percolation channel, it can be categorized into two types: fast decay and slow decay. Overall, this study provides valuable insights for optimizing mineralization processes in challenging marine conditions and opens new avenues for stabilizing shallow seafloors using MICP. Additionally, this study highlights the induced nature of MICP, illustrating how bacterial activity, along with environmental factors, impacts its performance, thus posing challenges for its application in engineering projects with varying environmental conditions.