Heterogeneous Flow Field in Presence of Biofilms and its Impact on Solute Transport and Retention

Biofilm images of Paenibacillus 300A strain obtained from two-dimensional micromodel experiments were integrated with pore-scale numerical models to evaluate the impact of biofilm-induced flow heterogeneities on conservative solute transport. The micromodels were designed with hexagonal packing of equal diameter grains to simulate a pore network environment with simple parabolic flow profiles. The biofilms were modeled as porous microstructures with locally varying physical properties. The inclusion of these microstructures in the numerical model produces local velocities orders of magnitude slower than those found in the main channels of the micromodel. This flow heterogeneity leads to enhanced solute spreading in the breakthrough curves that exhibit extreme anomalous slopes at intermediate times and very marked late solute arrival times due to retention imparted by low velocity and stagnation zones. The efficiency of solute retention by the biofilms is manifested in the long tailing of the breakthrough curves. The study shows that solute retention by biofilms exerts a strong control on conservative solute transport at the pore-scale, a role that has not received enough attention in the past.