Reversible Bio-Sorption and Solute Transport in Floating Vegetated Wetlands

Floating vegetated wetlands play a vital role in improving water quality by filtering pollutants and mitigating eutrophication in lakes, rivers, and wastewater systems. Within these systems, solute transport is strongly influenced by the interaction between hydrodynamics, vegetation structure, and reactive processes such as biosorption; however, the mechanisms governing such interactions remain poorly understood. This study develops a novel mathematical model to elucidate the dispersion of reactive solutes in flows containing floating vegetation, incorporating reversible adsorption–desorption dynamics at the vegetation–water interface. The governing equations are upscaled using Mei’s homogenization technique to derive an effective dispersion coefficient that accounts for multiscale interactions between flow and reaction processes. Three key dimensionless parameters, namely the vegetation factor (α), partition coefficient (θ), and Damköhler number (Da), are identified as primary controls on the effective dispersion behavior. Results indicate that vegetation density modulates flow heterogeneity and mechanical dispersion, with sparse vegetation (α < 1) promoting molecular diffusion-dominated transport, while dense vegetation (α > 1) induces recirculation zones that suppress dispersion. Additionally, increasing Da enhances solute localization via faster reactions, whereas higher θ intensifies retention within the biofilm phase. The interplay among α, θ, and Da defines distinct transport regimes, revealing optimal combinations that balance mixing and reaction for efficient contaminant removal. These findings provide a mechanistic framework for designing and optimizing floating vegetated wetlands, enabling improved control of solute fate under varying hydrodynamic and biochemical conditions.