Investigating Microplastic Resuspension in Environmental flows: Experimental and Numerical Approaches

Rivers serve as a big pathway for microplastics (MPs) to reach the oceans. This transport exhibits seasonality, while microplastics tend to deposit on sediment beds and riverbanks during dry seasons, heavy rainfall directly increases the resuspension rate of microplastic particles. The turbulence intensity during such events plays a significant role in particle resuspension. The detachment of MPs embedded in a sediment bed containing other granular phases with a contrasting density ratio remains a complex process that deserves further research. This study aims to investigate the micromechanical effects of microplastic resuspension through a combined experimental and numerical campaign. An experimental closed-loop channel facility is being constructed to analyze the mobilization of millimeter-sized MPs particles from a sediment bed composed of glass beads and polymer pellets of the same diameter. An ultrafast X-ray computed tomography system will be used to scan three-dimensional opaque sediment bed, allowing the mapping of the entrapped polymer MPs particles in space and time for different flow conditions. Additionally, the individual particles crossing two measurement planes will be recorded with this system using a temporal resolution of 1000 samples per second. Thus, the velocity distribution of the MPs particles will be measured in both the sediment bed and the core flow. The experimental study is supplemented with grain-resolving Direct Numerical Simulations (DNS) to replicate the idealized conditions of the experimental setup. This approach allows for a detailed exploration of the hydrodynamic forces acting on particles and permits an investigation of details beyond the experimental capabilities. The findings of this combined experimental and numerical study will contribute to a better understanding of the mechanisms of microplastic resuspension in environmental flows and guide mitigation strategies to limit plastic pollution in aquatic environments.