Hydraulic experiments and numerical simulation of microplastics migration in aquatic environments
LI Yu-xuan1, DOU Ming1,2, LI Gui-qiu2, WANG Zhen2, ZHOU Yu-ze2, XING Ao-qi1
1. College of Ecology and Environment, Zhengzhou University, Zhengzhou 450001, China; 2. College of Water Conservancy and Transportation, Zhengzhou University, Zhengzhou 450001, China
Abstract：The migration behavior of microplastics in aquatic environments is governed by complex interactions among hydraulic, physical, and material-specific factors. This study integrates hydraulic experiments and force analysis to identify the critical hydraulic parameter thresholds influencing state transitions of different microplastic types in freshwater systems. A Lagrangian particle tracking method is then employed to develop a migration model grounded in well-defined physical principles. This model simulates microplastic trajectories, predicting their ultimate movement states and environmental fate. The model is validated using field data from the urban section of the Jialu River in Zhengzhou, China. Results indicate that 66.79% of microplastics in this section have particle sizes smaller than 0.5mm, with fragmented (31.1%) and fibrous (29.2%) shapes being predominant. Polypropylene (PP) migrates as floating debris with the highest velocity, while polystyrene (PS) and polyamide (PA) particles smaller than 0.5mm migrate as suspended load. In contrast, polyethylene terephthalate (PET) and PA particles larger than 0.5mm migrate as bedload or remain stationary on the riverbed. Under flow rates of 14m3/s and 20m3/s, retention rates of microplastics over 36hours were 43.79% and 47.85%, respectively, with PA and PET constituting the major retained microplastic types. These findings provide valuable insights into the hydrodynamic behavior and environmental fate of microplastics, offering guidance for pollution management in freshwater systems.
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