Effects of Bacterial Density on Growth Rate and Characteristics of Microbial-Induced CaCO3 Precipitates: Particle-Scale Experimental Study

Citation

Y. Wang, K. Soga, J.T. Dejong and A.J. Kabla

J. Geotech. Geoenviron. Eng. 147:04021036 (2021)

Abstract

Microbial-induced carbonate precipitation (MICP) has been explored for more than a decade as a promising soil improvementtechnique. However, it is still challenging to predict and control the growth rate and characteristics of CaCO3 precipitates, which directlyaffect the engineering performance of MICP-treated soils. In this study, we employ a microfluidics-based pore-scale model to observe theeffect of bacterial density on the growth rate and characteristics of CaCO3 precipitates during MICP processes occurring at the sand particlescale. Results show that the precipitation rate of CaCO3increases with bacterial density in the range between 0.6×10^8 and 5.2×10^8 cells/mL.Bacterial density also affects both the size and number of CaCO3crystals. A low bacterial density of 0.6×10^8 cells/mL produced 1.1×10^6 crystals/mL with an average crystal volume of 8,000 μm^3, whereas a high bacterial density of 5.2×10^8 cells/mL resulted in more crystals(2.0×10^7 crystals/mL), but with a smaller average crystal volume of 450 μm^3. The produced CaCO3 crystals were stable when the bacterialdensity was 0.6×10^8 cells/mL. When the bacterial density was 4–10 times higher, the crystals were first unstable and then transformedinto more stable CaCO3 crystals. This suggests that bacterial density should be an important consideration in the design of MICP protocols.

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