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| Aggregation and sedimentation behavior of microplastics in turbulence |
| Received:October 17, 2024 |
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| KeyWord:microplastics;turbulence;sediment;aggregation;sedimentation |
| Author Name | Affiliation | E-mail | | YIN Fuyu | College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, China | | | LI Wang | College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, China | | | ZU Bo | College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, China | zubo@cqjtu.edu.cn | | CHEN Wei | China Merchants EcoEnvironmental Protection Technology Co., Ltd., Chongqing 400067, China | | | WANG Mei | China Merchants EcoEnvironmental Protection Technology Co., Ltd., Chongqing 400067, China | | | ZHANG Zhongjie | China Merchants EcoEnvironmental Protection Technology Co., Ltd., Chongqing 400067, China | | | CHEN Xin | China Merchants EcoEnvironmental Protection Technology Co., Ltd., Chongqing 400067, China | | | LI Haowen | China Merchants EcoEnvironmental Protection Technology Co., Ltd., Chongqing 400067, China | |
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| Abstract: |
| This study aims to investigate the aggregation and sedimentation characteristics of microplastics in sand-carrying turbulence and to reveal the underlying mechanisms. By employing a self-developed isotropic uniform turbulence device and particle tracking velocimetry（PTV）method, the aggregation and sedimentation behavior of microplastics were analyzed. The results indicated that an increase in water flow shear strength could promote the aggregation of microplastics, but excessively high shear strength might disrupt the structure of aggregates, limiting their further enlargement. Concurrently, the presence of sediment in turbulent flow could facilitate the formation of larger microplastic aggregates. As the shear rate increased, the overall structural fractal dimension of particles in water increased, while the surface morphological fractal dimension decreased, and these trends gradually slowed down with further increases in shear rate. In sand-carrying turbulence, both types of fractal dimensions of particles were slightly higher than those in clear water turbulence. In clear water turbulence, the overall settling velocity of microplastic particles first increased and then decreased with increasing shear rate, whereas in sand-carrying turbulence, the overall settling velocity increased with increasing shear rate. Regardless of the presence of sediment, the minimum settling velocity of microplastic particles was directly proportional to particle size, while the maximum settling velocity was inversely proportional to particle size. Smaller microplastic particles exhibited poorer settling stability in turbulence and were more significantly affected by turbulence. The study demonstrates that turbulence has a dual effect on the aggregation of microplastics and can also cause changes in the structure and surface morphology of aggregates. The sedimentation behavior of microplastics is closely related to particle size, and the presence of sediment not only promotes the aggregation of microplastics but also alters their sedimentation behavior. |
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