Migration, Distribution and Influencing Factors of Microplastics at the Confluence of Pipe and Channel

Sewage pipes are important conduits for microplastics into the natural environment, but previous studies have paid little attention to the hydraulic characteristics of the confluence of pipe and channel, and the distribution of microplastics at the confluence. This study compared the effects of varying flow rates and particle sizes (Including 500 mu m, 700 mu m, and 900 mu m) on microplastic migration and distribution at the confluence of pipe and channel using experimental measurements. The results obtained using flotation method indicate that flow proportions and particle sizes influence the capacity of flow to transport microplastics. Larger microplastic accumulation occurs in scour holes and separation zones characterized by lower flow velocities, while deposition decreases in acceleration zones characterized by higher flow velocities. Increasing the flow rate of the branch pipe influences the volume of each zone at the pipe-channel confluence. The elongated shape of the scour hole and the acceleration zone facilitate the downstream migration of microplastics. Moreover, the hydrophilic nature of microplastics increases after aging, and it is more likely to migrate to downstream with the water flow, making the downstream microplastics account for more proportion. These results provide valuable insights into the migration and distribution of microplastics at the confluence of pipe and channel, with practical implications for microplastic treatment strategies at these confluences.