Multi-scale simulation of the effect of microbial growth on the permeability of porous media

In this study, a novel algorithm coupling the flow at the pore and representative elementary volume (REV) scales was developed to analyze the effect of microbial growth at the pore scale on the permeability decay of porous media at the REV scale. This provides a new method for investigating microbial clogging in porous media. At the pore scale, an immersed boundary-lattice Boltzmann model was used to simulate the flow field and solute transportation in porous media, and the cellular automata (CA) model was employed to investigate microbial growth. According to Ergun's empirical relationship, the equivalent porosity change at the pore scale caused by microbial growth was calculated and used in a generalised seepage model describing the fluid flow in the porous medium at the REV scale. First, the microbial growth experiments were conducted to validate the coupling al-gorithm. Second, the spatial and temporal characteristics of microbial growth at the pore scale were analyzed. Third, we investigated the effects of nutrient inlet concentrations and pH on microbial growth at the pore scale and the macroscopic permeability properties of porous media. The main results are as follows. (1) Microbial growth changes the local porosity and dominant flow path. Spatial non-uniformity in microbial growth depends on the availability of nutrients in the dominant flow path. (2) The discrepancy in microbial growth under different nutrient inlet concentrations was gradually amplified from the pore scale to the REV scale. (3) The microbial clogging period was the shortest at a pH of 6.7. When the pH was >6.7, the microbial clogging period slightly increased at a rate of 6.1 h/pH. When the pH was <6.7, the microbial clogging period increased significantly with decreasing pH at a rate of 20.0 h/pH. (4) A linear relationship was observed between the microbial clogging periods at the REV and pore scales, which enriches the theory about microbial clogging in porous medium.