Quantifying turbulence-burst-induced PFASs release across the sediment-water interface: 3D coupled computation of the...

Turbulence bursting induced by hydrodynamic forcing within the boundary layer is a dominant driver of PFASs release and transport. Existing models rarely account for the vortex structures generated during bursting events, leading to incomplete quantification of burst-driven release processes. To address this gap, a coupled numerical model was developed to simulate PFASs release from sediments under turbulence-burst forcing, including PFASs transport through pore water, and subsequent transfer across the sediment-water interface into the overlying water. The model employs a Detached Eddy Simulation approach to resolve boundary-layer vortex structures and incorporates a hydrodynamic effect factor to enhance PFASs release responsiveness. Velocity threshold, determined by comparing release depths, was used to define the effective range. By jointly resolving the overlying water and pore water domains, the model provides a more accurate characterisation of boundary-layer processes. The simulations reproduce pore-water PFASs gradients and align with measured residual sediment concentrations (R² = 0.84). The model captures the relationship between PFASs release and vortex intensity under three flow situations. Notably, short-chain PFASs exhibit greater downward penetration under high-intensity vortical structures. Localised high-concentration enrichment zones were observed within the sediments under weak vortex-driven conditions. The results demonstrate that vortex evolution during turbulence bursting significantly influences PFASs release dynamics. This model provides a valuable framework for understanding the micro-scale processes governing PFASs release at the sediment-water interface.