Direct Interception of Particles by a Vegetation Stem With Varying Adhesive Forces

Abstract

The direct interception of particles by vegetation stems has been reported in field studies of saltmarsh platforms as a major cause for removing suspended particles and pollutants. Laboratory observations and numerical models reported in the literature have computed the attachment efficiency under the assumption that particles stick and do not move when they collide with the surface of the collector (i.e., perfect attachment). This study was aimed at lifting this assumption using a Discrete Element Model (DEM) with varying adhesive contact forces coupled with Computational Fluid Dynamics (CFD). The CFD-DEM model considers the stickiness of the collector through a surface energy parameter. Model predictions showed good agreement with laboratory observations. The final configuration of particles on the collector's surface and the attachment efficiency changed when the collector's surface energy was varied. In some cases, the attachment efficiency was twice that under the perfect attachment assumption, indicating that modeling studies with perfect attachment may underestimate suspended particle removal. As biofilms are considered the main cause of the adhesiveness of stems, our study shows that any biofilm formation that could create a surface energy as low as 0.01 $\text{mJ}/m^2$ could lead to attachment of particles on a single saltmarsh stem.