Influence of biofilm growth on permeability evolution in gravel layers of leachate collection system: A pore-scale analysis using Darcy-Brinkman-Stokes approach

•A pore-scale model for LCS permeability change due to biofilm growth was developed.•The model was validated against both experimental and numerical results.•Biofilm permeability and porosity both affected permeability decline in the LCS.•Fine particle group exhibited a pronounced effect on permeability reduction of LCS. Biofilm formation within the gravel layer of leachate collection systems (LCS) poses a significant challenge by reducing permeability, potentially leading to clogging. Understanding the impact of biofilm growth on the hydraulic performance of LCS is essential for optimizing gravel layer design. This study utilized the Navier-Stokes-Brinkman equations to develop a numerical model that describes fluid flow at the pore scale within both biofilm-covered and open pore regions of the LCS gravel layer. The model was validated using previous experimental and numerical results. A geometric model of a porous network composed of randomly packed spherical particles, reflecting actual particle sizes in LCS, was then established. This model was used to investigate the evolution of the flow field and changes in permeability under varying conditions of particle size, biofilm thickness, and permeability characteristics. The results showed that increasing biofilm thickness reduced channel cross-sectional area, elevated flow velocity, increased pressure drop, and caused an exponential decrease in permeability. The study also confirmed that the permeability and porosity of the biofilm significantly influenced the extent of permeability reduction in the LCS gravel layer. Additionally, smaller particle size combinations had a more pronounced effect on permeability reduction. These findings provide valuable insights at the pore scale, helping to predict the impact of biofilm growth on gravel layer permeability in LCS and offering essential guidance for future design and management strategies.