CAREER: The Impact of Extracellular Polymeric Substances on Particle Transport in Aquatic Environments

Predicting and managing the transport of particles in aquatic environments are critical components of strategies to treat drinking and wastewater, to monitor sediment movement, to predict pollutant transport, and to understand effects of the global ocean carbon cycle on climate change. The transport of particles is often affected by the presence of extracellular polymeric substances (EPS) in aquatic environments. EPS are biopolymers that are secreted in high quantities from algae and bacteria and are known to promote aggregation of particles and influence the physical properties of the aggregates. This CAREER project comprises several experiments to quantify the influence of EPS on particle aggregates. The results of the research will improve predictions of particle transport through aquatic environments by explaining how EPS influence the formation of particle-to-particle bonds during aggregation, by demonstrating the roles EPS play in defining aggregate physical properties, and by tracking how these properties ultimately govern aggregate breakup and settling in turbulent fluid flows. Integrated educational activities will advance career-strengthening opportunities for undergraduate and graduate students as well as promote environmental science and engineering to underrepresented high school student groups.Experiments conducted under this CAREER award will measure the chemical makeup, surface energy, and interaction energy of EPS from aquatic algae and bacteria to determine how EPS form aggregates that incorporate naturally occurring particulate matter, sediment particles, and microplastic pollutants. A theoretical framework will be formulated to predict the deformability of EPS aggregates based on cohesion properties, experimental data for aggregate deformation in hydrodynamic shear, and fundamental principles for colloidal gels and viscoelastic droplets. Finally, three-dimensional flow experiments will link aggregate cohesion and deformability to breakup and settling characteristics of EPS in turbulence. The results generated in this research will fill several knowledge gaps for aggregation and disruption of EPS aggregates and transform the way aquatic EPS aggregates are modeled. The results will help understand aggregation processes that are crucial to quantifying the ocean carbon cycle and refining environmental protocols for anthropogenic pollutants. The project will provide collaborative career-development opportunities for diverse undergraduate and graduate students and an integrated Research Experience for a Teacher opportunity that focuses on environmental research in engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.