Influence of calcium carbonate precipitation on the flow behavior in a gravel layer of leachate collection system: A pore-scale analysis

Prolonged operation of leachate collection systems (LCS) often leads to calcium carbonate precipitation within the gravel layer, which can result in clogging and compromised system performance. Understanding the impact of calcium carbonate deposition on the hydraulic behavior of LCS is crucial for optimizing their design and mitigating potential clogging issues. In this study, a pore-scale numerical model was developed using the Navier-Stokes-Brinkman (NSB) equation to simulate fluid flow in regions of the gravel layer affected by calcium carbonate precipitation as well as in open pore regions. The model was validated against relevant experimental data. A geometrical model of the porous network, based on realistic particle size distributions observed in LCS, was employed to capture the actual conditions within the system. This model was used to investigate the spatial and temporal variations in the flow field, pressure distribution, porosity, and concentrations of calcium ions and acetic acid under different particle size characteristics. The results indicate that, over time, the flow path increasingly favors preferential flow pathways, resulting in a significant rise in the pressure difference between the inlet and outlet, as well as a gradual decrease in porosity, particularly along the preferential flow paths. Additionally, calcium ion and acetic acid concentrations were found to be more concentrated along these preferential paths, decreasing in concentration downstream. Notably, the medium particle model exhibited higher flow rates compared to the coarse particle model, with calcium carbonate precipitation and pore-clogging being more pronounced in the medium particle system. These findings provide valuable insights into the biochemical clogging process in LCS at the pore scale and can inform future strategies for optimizing LCS design to mitigate the impacts of calcium carbonate precipitation and ensure the long-term effectiveness of waste management systems.