Turbulent-Induced Transport of Microplastic Contaminants: A Numerical Study

Drastic increase in global plastic production has resulted in a proportional up-surge in plastic input to the aquatic environment. Microplastic (MP) pollution has detrimental effects on aquatic ecosystem health. Understanding the fate and transport of aquatic these contaminants can help their pollution mitigation. The transport and distribution of MPs in the aquatic environment are influenced by various factors. MPs have diverse physical characteristics, including density, shape, and size, due to their different origins and exposure to weathering processes. Additionally, transport mechanisms such as biofouling and turbulent-induced mixing, generated by factors such as temperature gradient, wind, and sudden changes in topography, can alter the gravity-driven transport of MPs. This numerical study uses a hybrid Lagrangian–Eulerian model to investigate the entrainment and distribution of MPs in a fully developed turbulent flow. Based on our observations, MP particles exhibit a wide range of particle Reynolds numbers, with some falling in the linear Stokesian regime and others in nonlinear transient regimes. The fate of MPs depends on both the hydrodynamic characteristics of the ambient flow and the particle characteristics. Here we used the settling parameter, Stokes number, and the radius of eddy trapping to characterize the distinct transport and mixing behaviour of heavy MPs of different sizes and shapes. Our findings suggest that the shape and size of the MP can affect the trajectory of the particles and, consequently, the instantaneous ambient flow characteristics. Thus, the relative velocity of the particle with respect to the ambient flow, and the drag-driven transport is dominated by the size and shape of the particle.