Although microplastics are an emerging pollutant of global concern, little is known about the environmental behavior of microplastic in sediments. This study investigated the occurrence and seasonal variation of microplastics in the sediments of Liangfeng River, China with a fluorescence staining method, and then explored the transfer of microplastics at the water and sediment interfaces during resuspension . The results showed that smaller microplastics were detected in the sediments, which were concentrated in the size range of 50–500 μm. Microplastic abundance in the sediments in the dry season were slightly higher than those from the rainy season, and the rainy season promotes the accumulation of smaller microplastics in the sediment along the river-flow direction but not for the dry season. The shape of microplastics were predominantly fibers, followed by fragments and films. Polyethylene was the most abundant polymer, accounting for more than 50% of the total. Microplastics in the surface sediment move both to the overlying water and deeper sediment during the disturbance process. Disturbance-induced resuspension and vertical transport have significant effects on small-sized microplastics (50–500 μm). Small-sized microplastics can potentially migrate and redistribute via resuspension at different temporal and spatial scales, as some extent of resuspension is occurring in most river systems, especially in urban areas with boat traffic.
The resuspension of deposited nanoparticles within a boiling fluid is a nanoparticle behavior that may mitigate or even avoid the degradation of nanofluids, which is of great significance to the long-lasting heat transfer enhancement of nanofluids. In this study, the nanoparticle resuspension behavior during pool boiling was investigated experimentally and theoretically. Visualized pool boiling experiments were conducted for the nanoparticle-deposited surfaces which were prepared by boiling nanofluids. Various methods were employed to capture the resuspension phenomenon and characterize the morphology of nanoparticle deposition layer. The nanoparticle resuspension ratio was measured for various boiling durations, deposition area densities, and heat fluxes to elucidate the effects of these factors on the resuspension behavior. It was found that a part of deposited nanoparticles were resuspended to the bulk of the boiling liquid and then migrated with the internal flow during pool boiling, and the porous structure of nanoparticle deposition layer played a key role in the occurrence of resuspension. The measurement showed that heat flux was a main influential factor, and increasing heat flux can lead to a dramatical increase of resuspension ratio. A semi-theoretical model was developed to predict the resuspension ratio, which agreed well with the experimental results.
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