Prediction of the settlement of submillimeter microplastic fibers in still water

It is imperative to acknowledge the pervasive issue of microplastic pollution in aquatic environments. A significant proportion of these pollutants can be attributed to microplastic fibers shed from synthetic textiles. Microfibers differ from microplastics derived from other sources in that they possess both porous and hygroscopic qualities. A numerical model was constructed using the lattice Boltzmann method to simulate the free settling of a single microfiber in still water. The results were validated by experimental data. The settling wake flow and relaxation time were analyzed, as well as the size and density effects of microplastic fibers on terminal settling velocity. It was found that Stokes law can predict the drag coefficient of settling submillimeter microplastic fibers. A new drag model was proposed, taking into account the effect of orientation to more accurately predict the settlement of heterogeneous or irregularly shaped microfibers in water. • Investigated settling motion of microplastic fibers (MPFs). • The microfiber orientation remains unchanged under a small Reynolds number. • Stokes law can predict the drag coefficient of microfibers settling horizontally. • A C D model specifically designed for MPFs settling with different orientations was introduced.