Anomalous Transport of Microplastic Fibers in Porous Media

The diffusion and transport of elongated and deformable particles—such as fibers and filaments—through microstructured porous media have wide-ranging applications in environmental and biological systems. In this study, we examine the applicability of classical diffusion and transport models to microplastic fibers and investigate how their deformation, motion, and localization are influenced by the medium’s morphology and local flow features arising from fluid–particle–solid interactions at the pore scale.

Numerical simulations using the Immersed Boundary Method (IBM), complemented by analytical solutions, are employed to analyze microfiber trajectories and accumulation hotspots within both periodic and random porous structures. Our results reveal that the elongated particle geometry and the disordered medium structure induce anomalous transport features, including breakthrough curve tailing and long-time memory effects.

To quantify these behaviors, we develop a generalized probabilistic framework based on the Continuous Time Random Walk (CTRW) model, enabling the upscaling of pore-scale dynamics to macroscopic transport equations. The effective transport parameters—including mean velocity, dispersion coefficients, and transition-time distributions—are extracted from direct numerical simulations. Additionally, the Mean First Passage Time (MFPT) is derived using both Monte Carlo and analytical approaches.

This work provides new insight into the coupling between particle deformation and porous media heterogeneity, advancing predictive modeling of microfiber and microplastic transport in natural and engineered systems.