PNNL

Abstract

Microbial biofilms are ubiquitous within porous media, and their dynamics of growth interact and influence surface and subsurface flow patterns which impact the physical properties of porous media and large-scale transport of solutes. A two-dimensional pore-scale numerical model was used to evaluate the impact of biofilmm-induced flow heterogeneities on conservative transport. Our study integrates experimental biofilm images of Paenibacillus 300A strain in a micro fluidic device packed with cylindrical grains in a hexagonal distribution, with mathematical modeling. Biofilm is represented as a synthetic porous structure with physical properties varying locally that honors the local impact of biofilm on the porous medium locally varying physical properties. We find that biofilm play a major role in shaping the observed conservative transport dynamics by enhancing anomalous transport. More specifically, when biofilm is present we observe enhanced solute spreading in breakthrough curves that exhibit extreme anomalous slope at intermediate times and very marked late solute arrival due to solute retention. The efficiency of the solute retention by the biofilm is controlled by the transport regime which can extend the tailing in the concentration breakthrough curves. These results indicate that solute retention by the biofilm exert a strong control on conservative solute transport at pore-scale, a role that to date has not received enough attention.