Abstract: Transport of adhesive colloidal particles and bacteria in biological and industrial porous systems is of importance to several applied sciences including human health, food science, and environmetal remediation. This work tries to elucidate the role of the heterogeneous nature of adhesive (particle) mechanisms at the pore scale. Brownian dynamics simulations are used to research these transport phenomena on individual colloid/bacteria movement (rather than biofilm growth) so results apply to low concentrations/coverage. Bacteria motility and reversible/irreversible attachment/detachment are incorporated with a numerical laminar flow solver. The case of a narrow channel (as in Taylor dispersion) is considered first. When a particle hits the boundary, a waiting time occurs, before it returns to the mobile (aqueous) phase. This waiting time can be finite (reversible) or infinite (irreversible) and it represents the time elapsed during biochemical interactions occurring at the boundary. An alpha stable distribution for these waiting times captures different time scales of the biochemical interactions with just a few (2 to 4) parameters. It is shown that under this assumption, biochemical heterogeneity at the wall induces anomalous dispersion.
Then convective velocity fields analyzed are based on different pore geometries consistent with a microflow cell of variable cross sectional area that correspond to an ongoing microflow cell experimental study. Two interrelated aspects of bacterial transport are the focus of this study: wall attachment/detachment (reversible/irreversible adsorption), and the role of convective (shear flow) and pore geometry in adhesion.
New avenues to model these processes at the Darcy scale are discussed in light of the complexities found at the pore scale. In particular fractional advection difussion models that have attracted attention lately are addressed