The proposed project will identify fundamental processes governing two phenomena that are ubiquitous in colloid and microbial transport in porous media: 1) apparent decreases in attachment rate with increased distance of transport; and 2) detachment in the absence of macroscopic perturbations. Elucidation of the contributing processes will lead to improved understanding of the transport of biological and non-biological colloids, and improved models for decision making in a number of societal contexts including: protection of water resources from pathogens; bioaugmentation; filtration for the purpose of drinking water treatment; and maintenance of well dispersed flow and reaction during heap leaching operations despite confounding effects from colloid mobilization. Three direct-observation technologies will be utilized in the proposed investigation: 1. X-ray microtomography (XRMT) will be used for exact characterization of the pore domain. Flow in the pore domain will be simulated using a Lattice-Boltzmann algorithm to obtain the three-dimensional fluid velocity field. A 3-D particle tracking model will be developed to simulate the colloid transport in the three-dimensional flow field. Neutrally-buoyant microspheres visible to XRMT will be utilized to allow in-situ characterization of microsphere deposition locations within the pore domain using XRMT. 2. A simple shear flow cell will be combined with a total internal reflection fluorescence microscope (Flow-TIRFM) to allow direct observation of colloid attachment-detachment dynamics. This system will allow direct determination of the relevance of detachment mechanisms such as hydrodynamic collision and erosion, as well as determination of the effects of asperities and rear stagnation points on the surface coverage attained by attached colloids. 3. Colloid-surface interaction and adhesion forces will be measured directly using AFM with total internal reflection fluorescence microscopy (TIRFM-AFM) to relate contact area to adhesion force. These measurements will greatly increase the accuracy of interaction and adhesion force estimations, thereby improving estimation of the barrier to attachment and the resisting moment for detachment. The proposed project will provide support for two graduate students, as well as partial support for a post-doctoral researcher, two research professors, and the P.I.s. Undergraduate researchers will be involved in the proposed work, and supplemental funding will be pursued to further facilitate their involvement. Mentoring responsibilities will extend to all levels below the rank of an individual. Hence, mentoring of undergraduates will involve all superceding levels, from graduate student to P.I.s. Women will be active at all ranks within the research group (post-doc, graduate, and undergraduate).
