Settling velocity of submillimeter microplastic fibers in still water

Chenlong Dai; Fangyang Yuan; Dongxiang Wang; Xinjun Yang; Jiyun Du; Wei Yu; Cheng Zhang

doi:10.1016/j.scitotenv.2023.168054

Settling velocity of submillimeter microplastic fibers in still water

Sci Total Environ. 2024 Jan 10:907:168054. doi: 10.1016/j.scitotenv.2023.168054. Epub 2023 Oct 28.

Authors

Chenlong Dai¹, Fangyang Yuan², Dongxiang Wang³, Xinjun Yang¹, Jiyun Du¹, Wei Yu¹, Cheng Zhang⁴

Affiliations

¹ Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment & Technology, Wuxi 214122, China; School of Mechanical Engineering, Jiangnan University, Wuxi 214122, China.
² Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment & Technology, Wuxi 214122, China; School of Mechanical Engineering, Jiangnan University, Wuxi 214122, China. Electronic address: fyyuan@jiangnan.edu.cn.
³ Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment & Technology, Wuxi 214122, China; School of Mechanical Engineering, Jiangnan University, Wuxi 214122, China. Electronic address: dxwang@jiangnan.edu.cn.
⁴ School of Environment and Civil Engineering, Jiangnan University, Wuxi 214122, China.

PMID: 37898197
DOI: 10.1016/j.scitotenv.2023.168054

Abstract

Microplastic fibers (MPFs) are one of the most important MP contaminants of aquatic environments. However, little research has been conducted on the movement of submillimeter MPFs in water. Herein, the settling of 519 submillimeter MPFs in still water was measured and the settling velocity was analyzed. Observations of the settling velocity of MPFs with lengths of 300, 500, and 600 μm showed that most MPFs settled individually or in pairs. The sedimentation of a single fiber could be divided into three patterns, that is, horizontal, inclined, and vertical. The average settling velocity increased with an increase in the MPFs length and orientation angle. As the MPFs length increased, the probability of inclined settlement decreased but that of horizontal settlement increased. The horizontal velocity of single fibers also was investigated, and the horizontal and vertical settling of MPFs exhibited minimal horizontal velocity. Because of the considerable difference between the calculated drag coefficients from existing drag coefficient models and experimental values, a drag coefficient model was developed with a deviation of <3 %. Four settling patterns were identified for two fibers, that is, X shaped, inverted-T shaped, cross shaped, and overlapping. The average velocity of the overlapping settlement of two fibers was considerably higher than that of the other three settling patterns. The average settling velocity of 600-μm two fibers was 1.47 times that of single fibers, indicating that their corresponding drag coefficient was ~46 % that of a single fiber.

Keywords: Drag coefficient; Horizontal velocity; Microplastic fiber; Settling orientation; Settling velocity.