Microfluidic study in a meter-long reactive path reveals how the medium’s structural heterogeneity shapes MICP-induced biocementation

Abstract

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is one of the major sustainable alternatives to the artificial cementation of granular media. MICP consists of injecting the soil with bacterial- and calcium-rich solutions sequentially to form calcite bonds among the soil particles that improve the strength and stiffness of soils. The performance of MICP is governed by the underlying microscale processes of bacterial growth, reactive transport of solutes, reaction rates, crystal nucleation and growth. However, the impact of pore-scale heterogeneity on these processes during MICP is not well understood. This paper sheds light on the effect of pore-scale heterogeneity on the spatiotemporal evolution of MICP, overall chemical reaction efficiency and permeability evolution by combining two meter-long microfluidic devices of identical dimensions and porosity with homogeneous and heterogeneous porous networks and real-time monitoring. The two chips received, in triplicate, MICP treatment with an imposed flow and the same initial conditions, while the inlet and outlet pressures were periodically monitored. This paper proposes a comprehensive workflow destined to detect bacteria and crystals from time-lapse microscopy data at multiple positions along a microfluidic replica of porous media treated with MICP. CaCO3 crystals were formed 1 h after the introduction of the cementation solution (CS), and crystal growth was completed 12 h later. The average crystal growth rate was overall higher in the heterogeneous porous medium, while it became slower after the first 3 h of cementation injection. It was found that the average chemical reaction efficiency presented a peak of 34% at the middle of the chip and remained above 20% before the last 90 mm of the reactive path for the heterogeneous porous network. The homogeneous porous medium presented an overall lower average reaction efficiency, which peaked at 27% 420 mm downstream of the inlet and remained lower than 12% for the rest of the microfluidic channel. These different trends of chemical efficiency in the two networks are due to a higher number of crystals of higher average diameter in the heterogeneous medium than in the homogeneous porous medium. In the interval between 480 and 900 mm, the number of crystals in the heterogeneous porous medium is more than double the number of crystals in the homogeneous porous medium. The average diameters of the crystals were 23–46 μm in the heterogeneous porous medium, compared to 17–40 μm in the homogeneous porous medium across the whole chip. The permeability of the heterogeneous porous medium was more affected than that of the homogeneous system, while the pressure sensors effectively captured a higher decrease in the permeability during the first two hours when crystals were formed and a less prominent decrease during the subsequent seeded growth of the existing crystals, as well as the nucleation and growth of new crystals.

Microfluidic chips for microbially induced calcium carbonate precipitation: Advantages, challenges, and insights

“…While microfluidics was originally developed for different applications, its precision and control over fluid dynamics have made it a valuable tool for investigating complex processes, such as MICP. Researchers have adopted microfluidic systems to simulate and analyze the intricate mechanisms of MICP in controlled laboratory settings [33,34]. These microscale platforms offer a unique advantage for studying how microorganisms interact with calcium ions, urea hydrolysis, and carbonate precipitation [35][36][37].…”

“…Within microfluidic channels, researchers can observe and record MICP processes as they unfold at the microscale level. This dynamic visualization not only offers valuable insights into the temporal and spatial aspects of MICP but also enables the monitoring of microbial activity, mineral nucleation, and growth [34,43,44]. Microfluidic systems inherently operate at the microscale, aligning with the dimensions of MICP processes.…”

“…For practical reasons, microfluidic studies may use simplified microbial populations or monocultures, which can neglect the complex interplay among microorganisms, potentially leading to deviations in MICP behavior. Microfluidic devices often simplify [34] the complexity of natural MICP environments. Soil properties, such as grain size distribution, mineral composition, and porosity, can vary widely in natural settings.…”

New non-ureolytic heterotrophic microbial induced carbonate precipitation for suppression of sand dune wind erosion

“…MICP is a natural biological process associated with various microbial activities and chemical processes, during which calcium carbonate precipitation occurs as a result of microbial metabolic products such that carbonate ions react with calcium ions in the environment 18 , 19 . MICP involving nitrogen cycle by the degradation of urea (ureolytic MICP) is the most common type of microbial-induced carbonate precipitation, in which the urease enzyme generated by the bacteria catalyzes the hydrolysis of urea 20 – 27 , described by the following reactions: …”

Enhanced Oil Recovery through Microbially Induced Calcium Carbonate Precipitation

“…Microfluidic platforms, paired with optical microscopy, offer an opportunity to study the fundamental pore-level interactions between microbes and reservoir fluids in confined rock environments to understand and control MICP-enabled hydrocarbon recovery. While microfluidics have been used previously to investigate the impact of MICP on pore morphology, these studies rely on the use of artificial porous media comprised of simple channel geometries (i.e., linear or cylindrical flow geometries) fabricated using polymeric materials [e.g., poly­(dimethylsiloxane), PDMS] that fail to replicate the representative pore geometry and surface chemistry of geologic formations. − Recent developments in geochemical microfluidics enable the direct visualization of pore-scale (∼μm) phenomena in real time (∼ms) to resolve complex multiphase transport dynamics within geomaterials. − For example, Song et al introduced calcite-based and carbonate-functionalized micromodels to investigate the reactive transport mechanisms underlying carbonate dissolution to assess the security of geologic carbon sequestration. , …”