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On the vertical structure of non-buoyant plastics in turbulent transport

Lofty, James ORCID:, Valero, Daniel, Moreno-Rodenas, Antonio, Belay, Biruk S., Wilson, Catherine ORCID:, Ouro Barba, Pablo ORCID: and Franca, Mário J. 2024. On the vertical structure of non-buoyant plastics in turbulent transport. Water Research 254 , 121306. 10.1016/j.watres.2024.121306

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Plastic pollution is overflowing in rivers. A limited understanding of the physics of plastic transport in rivers hinders monitoring, the prediction of plastic fate and restricts the implementation of effective mitigation strategies. This study investigates two unexplored aspects of plastic transport dynamics across the near-surface, suspended and bed load layers: (i) the complex settling behaviour of plastics and (ii) their influence on plastic transport in river-like flows. Through hundreds of settling tests and thousands of 3D reconstructed plastic transport experiments, our findings show that plastics exhibit unique settling patterns and orientations, due to their geometric anisotropy, revealing a multimodal distribution of settling velocities. In the transport experiments, particle-bed interactions enhanced mixing beyond what established turbulent transport theories (Rouse profile) could predict in low-turbulence conditions, which extends the bed load layer beyond the classic definition of the bed load layer thickness for natural sediments. We propose a new vertical structure of turbulent transport equation that considers the stochastic nature of heterogeneous negatively buoyant plastics and their singularities.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Publisher: Elsevier
ISSN: 0043-1354
Date of First Compliant Deposit: 12 March 2024
Date of Acceptance: 10 February 2024
Last Modified: 14 Mar 2024 14:46

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