Experimental Study on the Permeability of Microbial-Solidified Calcareous Sand Based on MICP

Abstract

In the construction of artificial islands in distant seas, calcareous sand has been widely used as a foundation filler due to its excellent mechanical properties and extensive availability in the marine environment. How to store more fresh water on the artificial islands by reducing its permeability is currently a great challenge. Microbial-induced carbonate precipitation (MICP) has always been considered as a great potential method to improve the cemented properties of calcareous sand, but the effect of grain gradation on the permeability of MICP-improved calcareous sand remains unclear. In this research, a self-made device was developed to conduct MICP grouting and permeability tests, where the permeability coefficient (k) under different grain gradations (curvature coefficient (Cc) and uniformity coefficient (Cu)) was measured. A CT scan was conducted to investigate the variation in the porosity (n) of sand samples before and after MICP treatment. The weighting method was adopted to measure the content of induced calcium carbonate (M). A scanning electron microscopy (SEM) technique was used to further study the micromechanism of the MICP treatment. Finally, the correlations between the k of MICP-treated sand and Cu, as well as Cc, were semiquantitively analyzed. The results show that the magnitude of M, k and n changes are closely related to Cc and Cu. The reduction amount of k and n increased with the rise in Cc and Cu, and the increased amount of M increased with the rise in Cc and Cu. The SEM results show that the particle surface became rough due to the coating effect of CaCO3 crystals, and the pore spaces were reduced because of the partially filling effect of the crystals, which was responsible for the decrease in permeability and porosity. Furthermore, k fitted well with Cu and Cc, respectively, and the fitting curve reveals that larger Cu (Cu ≥ 6.0) and smaller Cc (2.0 > Cc > 0.5) were more suitable for MICP treatments and lead to a large reduction in permeability. The above results indicate that the grain gradation of calcareous sand had a significant influence on its permeability improved by MICP.

Unlocking the Potential of Microbially Induced Calcium Carbonate Precipitation (MICP) for Hydrological Applications: A Review of Opportunities, Challenges, and Environmental Considerations

“…Previous research on MICP-treated sands has consistently shown that the hydraulic conductivity decreases significantly as the cementation level increases even up to 10 orders of magnitude. This reduction in hydraulic conductivity was reported in several studies [51,76,79,[82][83][84][85][86][87][88]. However, there was an exception noted in the study by Whiffin et al [3], where the measured hydraulic conductivity showed little change after treatment.…”

“…This was confirmed by other studies in which the hydraulic conductivity of cemented sand was found to be influenced also by its grain gradation in a similar manner. The reduction in the hydraulic conductivity coefficient during each MICP treatment cycle increased with higher values of the uniformity coefficient (C u ) and the curvature coefficient (C c ) [86].…”

“…Even though the findings are in good agreement, there is room for further research to examine the combinations of factors and their effects on the resulting hydraulic conductivity. Figure 8 presents the data concentrated from the available references that measured hydraulic conductivity [3,22,51,53,67,76,79,[82][83][84][85][86][87][88][89][91][92][93][94][95][96][97][98][99][100][101]. The y-axis is in a log scale.…”

“…The literature contains few studies with this fundamental requirement and are presented in Table 3. The generation of artificial islands in distant seas with the deposition of sand within the sea is one such application [86], where the use of calcareous sand as a foundation filler is common due to its mechanical strength and wide availability. A key challenge in this application is to reduce permeability to store more fresh water on these islands.…”

Effect of Calcium and Magnesium Ions on Microbial Urease Activity in Landfill Leachate Treatment

“…5. Inhibitory effect of calcium and magnesium ions mixed pollutants on urease activity: a) when the proportion of calcium ions in mixed pollutants is 0.2, b) when the proportion of calcium ions in mixed pollutants is 0.5, c) when the proportion of calcium ions in mixed pollutants is 0.8. low the proportion of calcium ions) magnesium ions react with negatively charged functional groups on the surface of microorganisms [20,21], calcium ions react with carbon dioxide or carbonate ions in wastewater to form precipitates on the surface of microorganisms, which together inhibit the metabolic activities of microorganisms, and the interaction between the two ions is synergistic. When the concentration of calcium ions in mixed pollutants is increasing, more calcium carbonate crystals will be generated, while the existence of magnesium ions will hinder some calcium ions from precipitating, and the synergistic effect between the two ions will decrease.…”