The Department of Civil Engineering, The University of Hong Kong, HKSAR, China.
The Department of Civil Engineering, The University of Hong Kong, HKSAR, China.
Water Res. 2022 Jun 30;218:118476. doi: 10.1016/j.watres.2022.118476. Epub 2022 Apr 19.
Microplastics fibers are abundant in aquatic environments and are an emerging environmental threat. Understanding how fibers are transported in aquatic environments is essential for identifying pollution hotspots and developing remediation strategies. Over recent years, an increasing number of drag models have been proposed to describe the transport of microplastics in aquatic environments. However, none of the proposed models consider secondary motions, which are responsible for non-vertical settling motions. To investigate the role of secondary motions, an experimental setup with an image processing technique was developed to capture the spatial-temporal kinematics of microplastic fibers settling in quiescent water. A new drag model, which adopts the crosswise sphericity to consider the effects of secondary motions of a microplastic fiber and the Aschenbrenner shape factor to account for the unique morphology of the microplastic fiber, was proposed and evaluated. Secondary motions of microplastic fibers have profound effects on their settling trajectories and deposited positions. The settling motion and drag coefficient of a microplastic fiber is an orientation-dependent process. Moreover, the secondary motion is strongly dependent on the fiber dimension and density. The here-proposed drag model is proven to more accurately characterize the settling motion of microplastic fibers compared to existing models that neglect secondary motions. The methodology and model from this study can be used to progress towards improved and realistic predictions of the transport of microplastic fibers in aquatic environments.
微塑料纤维在水生环境中大量存在，是一种新出现的环境威胁。了解纤维在水生环境中的迁移方式对于识别污染热点和制定修复策略至关重要。近年来，越来越多的阻力模型被提出，用于描述微塑料在水生环境中的迁移。然而，提出的模型都没有考虑二次运动，而二次运动是导致非垂直沉降运动的原因。为了研究二次运动的作用，开发了一个带有图像处理技术的实验装置，以捕捉在静止水中沉降的微塑料纤维的时空运动学。提出并评估了一种新的阻力模型，该模型采用横向球形度来考虑微塑料纤维二次运动的影响，采用 Aschenbrenner 形状因子来考虑微塑料纤维独特的形态。微塑料纤维的二次运动对其沉降轨迹和沉积位置有深远的影响。微塑料纤维的沉降运动和阻力系数是一个与方向有关的过程。此外，二次运动强烈依赖于纤维的尺寸和密度。与忽略二次运动的现有模型相比，所提出的阻力模型被证明能够更准确地描述微塑料纤维的沉降运动。本研究的方法和模型可用于改进和实现对微塑料纤维在水生环境中迁移的现实预测。
