Author(s): Camillo De Castro; Siamak Seyfi; Wim S. J. Uijttewaal And Shooka Karimpour
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Keywords: Microplastics settling velocity particle-particle interaction environmental hydrodynamics particle tracking velocimetry
Abstract: With the rise in microplastics (MPs) as an emerging contaminant polluting aquatic environments globally, it is crucial to analyze settling velocity, as it is the fundamental process impacting the mobility of MPs in water. In an aquatic environment, MP particles are exposed to other particles (natural or other MPs) affecting their settling. This study aims to investigate the settling behaviour of MPs (spherical and beyond) under a single-particle condition and when particle-particle interaction becomes prominent. Preliminary settling experiments have been conducted to investigate the settling behaviour of spherical MP particles in quiescent water. Settling experiments for both single MP sphere tests and multiple MP sphere tests of either two, three, or four spheres have been performed in order to study settling velocity as well as particle-particle interaction for multiple spheres. Varying MP types are utilized for these settling experiments, where the selected equivalent diameters and densities cover a large range of particle Reynolds numbers (from nearly 10 to 1000) in the transitional regime. A Particle Tracking Velocimetry (PTV) system is employed to capture frame-by-frame the settling of MP particles and to compute the experimental values of the terminal settling velocity ws, particle Reynolds number Rep, and drag coefficient CD. The results of this study provide fundamental insights into the settling behaviour of single and multiple spherical MP particles in quiescent water, which can improve strategies and models for more accurately predicting the transport and fate of MPs in aquatic environments.
Year: 2025