Pore-scale quantification of colloid transport in saturated porous media.

It is currently not clear how to quantifiably relate pore-scale observations of colloid transportto larger scales, so,we proposed a geometric theory showing that pore-scale-derived rate constants may be appropriate to model a larger scale system. This study considered three different types of colloids: latex microspheres, Escherichia coli, and microspheres made of poly lactic acid (PLA). Colloid attachment and detachment rate constants were calculated using digital microscope images, taken in rapid (1 s) sequences, from which rates of attaching and detaching colloids were readily observed. Average rate constants from >1000 images per colloid-type were used to model Darcy-scale colloid transport breakthrough curves. The modeled and observed breakthrough curves agreed well for all three types of colloids. However, for latex and PLA microspheres, the model systematically under predicted the breakthrough curves' rising limb, which may indicate that the rate "constants" are actually dependent on the amount of attached colloids. Insights into these sorts of complexities are best addressed by research that considers both pore-scale phenomena and larger-scale transport responses.