The feedback interaction between biomass accumulation and heterogeneous flow in porous media: Effect of shear stresses

Bioclogging, resulting from excess biomass growth in porous media, can influence flow, solute transport, and biogeochemical reactions in natural and remedial subsurface systems. In this study, we investigated bioclogging in heterogeneous porous media using a reactive-transport model, with a focus on the effect of shear stresses on the spatial changes of biomass accumulation and hydraulic properties. The results show that, when the shearing-induced detachment was negligible, the accumulation of biomass was mainly controlled by substrate transport. Newly generated biomass was then accumulated in the regions with high hydraulic conductivity due to the fast substrate supply, resulting in a homogenization of hydraulic conductivity. When the shearing-induced detachment was significant, newly generated biomass was less accumulated in the flow paths with higher hydraulic conductivity, and more in the pore regions with relatively low hydraulic conductivity, resulting in the increase of heterogeneity in hydraulic conductivity. The results were then used to establish a macroscopic correlation between the reduction of porosity and the reduction of hydraulic conductivity as a result of biomass growth, and to identify factors controlling such a correlation. A correlation was established and was found to be significantly affected by flow velocity and shearing-induced biomass detachment. Overall, this study indicated that flow-induced shearing is important in understanding bioclogging and its effect on hydraulic conductivity and water flow in porous media.