Collaborative Research: Retention of Anisotropic Colloids in Porous Media: A Modeling and Experimental Investigation at Multiple Scales

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Collaborative Research: Retention of Anisotropic Colloids in Porous Media: A Modeling and Experimental Investigation at Multiple ScalesAbstractGroundwater is one of the most important components of the hydrologic cycle, serving as the source of about 33 percent of public water supply and providing drinking water to more than 90 percent of the rural population in the United States. Biological (bacteria) and non-biological (soil particles) natural colloids are ubiquitous in groundwater. The transport of pathogens (biological colloids) is relevant to producing safe drinking water, and the transport of heavy metals as facilitated by colloids (non-biological colloids) in groundwater has been widely recognized as a serious public concern. Almost all natural colloids are anisotropic in nature, being non-spherical in shape and possessing varied degrees of heterogeneity in surface charge. This project addresses the limitations of our current understanding of transport and fate of colloidal particles in porous media that stem from approximations of spherical shape and uniform surface charge used in previous studies. An improved understanding of colloid transport and retention in the environment will provide critical knowledge needed for producing safe drinking water and protecting sustainable water resources, essential steps for human health and development. Results from this work will be incorporated into undergraduate and graduate curriculums. Interactive demonstrations on environmental aspects of colloids and nanomaterials will engage middle- and high-school students during a two-week summer camp that encourages interest in STEM disciplines among women and under-represented minorities.This project is a combined experimental and modeling study that integrates considerations of shape anisotropy and surface-charge heterogeneity. The research uses a multi-scale approach to investigate the retention of anisotropic colloids onto flat surfaces, at grain-to-grain contacts, and in complex porous media. Systematic experiments using laboratory-prepared rod-shaped colloidal particles with various aspect ratios and surface-charge heterogeneity will be analyzed in novel ways. Applications of cutting-edge methodologies in microelectronics, high-resolution mass sensing, optical microscopy, and laser-scanning cytometry will enable observations of colloid attachment rates on the surfaces and pore throats of the mineral grains comprising porous media and reveal phenomena appropriate to scaling up observations to aquifers. In parallel, a numerical simulation model that is capable of tracking both the movement and orientation of anisotropic colloids within porous media will be developed. The results of this project provide predictive quantification on how non-spherical shape and surface-charge heterogeneity impact transport and retention of anisotropic colloids.