(Anomalous) Transport of Microplastic Fibers in Porous Media

The diffusion and transport of elongated and deformable particles, such as fibers, filaments, or threads, through micro-structured media in an extra dilute form has wide range of applications in various fields, including environmental science. In this talk, I will present our ongoing work to examine the applicability of classic diffusion and transport models to the elongated microplastic particles, microfibers: How the deformation, motion, and localization of the microfibers are affected by the medium's morphology and local flow features originating from the fluid - particle - solid interactions taking place at pore scale. Numerical simulations, using Immersed Boundary Method (IBM), and analytical solutions are employed to study the connection between microfiber transport dynamics and the periodic or random arrangement of solid grains mimicking the structure of a porous medium.

The trajectories of microfibers, as well as hotspots of their accumulation within both periodic and randomly structured media, are analyzed. We show that the randomly structured media gives rise to anomalous transport features, such as breakthrough curve tailing. A generalized probabilistic framework based on the Continuous Time Random Walk (CTRW) model is utilized to describe the upscaled transport behavior and to capture non-Fickian transport characteristics and memory effects. The upscaled model parameters, including effective velocity, dispersion coefficients, and transition time distributions, are extracted from direct numerical simulations. The particles Mean First Passage Time (MFPT) is derived using both Monte Carlo simulations and analytical solutions.

Speaker: Mojdeh Rasoulzadeh, University of Alabama