Leveraging viscoelastic flow instabilities for remediation of soiled porous media

The increased pollution of groundwater aquifers necessitates safe and efficient remediation strategies. One proposed solution involves the injection of viscoelastic fluids into the subsurface environment; however, how exactly viscoelasticity of the displacing fluid may influence soil removal in a 3D, spatially complex environment remains largely unexplored. Here, we investigate flow-induced removal of microplastics from a porous medium by injection of a dilute polymer solution. We use confocal microscopy to directly visualize the pore-scale dynamics of soil removal under imposed fluid flow. Under flow-controlled conditions, we find that the polymer solution flow—above a threshold flow rate—achieves greater removal efficacy than an equivalent flow of a viscous Newtonian solvent. We hypothesize that this results from two mechanisms: (1) additional hydrodynamic forces arising from polymeric elastic stresses, and (2) an elastic flow instability that produces chaotic spatiotemporal flow fluctuations. These in turn collectively enhance soil removal compared to viscous drag-dominated removal for Newtonian flows. Our work thus provides insight into the in situ removal dynamics of microplastics in geometrically-complex environments and highlights the potential for using viscoelastic fluid flows towards remediation of contaminated porous media.