Physical experiment and pore-scale investigation of the clogging of polydisperse particles in saturated porous media during artificial groundwater recharge

•Colloidal particle clogging is caused by both deposition and aggregation.•Rough concave surfaces play a dominant role in particle deposition.•Surface clogging is the ultimate type of clogging if recharge time is unlimited. Groundwater recharge engineering practices are usually accompanied by the migration and deposition of polydisperse particles. Solid particles may be retained in the pore space leading to clogging of the porous media and reducing groundwater recharge efficiency. However, the mechanism behind this clogging phenomenon remains poorly understood. Specifically, the relation of particle clogging at pore-scale and macroscale is unclear. Here, the influence of polydisperse particle size on clogging development patterns was studied utilizing a series of laboratory-scale column experiments in conjunction with pore-scale scanning electron microscopy (SEM) experiments. Particles with median particle sizes (dp50) of 0.66, 4.05, 11.83 μm were injected separately into the sand column to simulate particle clogging that occurs during groundwater recharge. SEM was used to directly observe particles deposition on porous media grain surface after the column experiments. By counting the size distribution of the particles on the media grain surface, the response of the particle deposition to the surface morphology of the media grains was analysed. Compared to dp50 of 4.05 and 11.83 μm, the spatial distribution of particles deposited in the sand column was more uniform at dp50 of 0.66 μm. The smallest particles (dp50 = 0.66 μm) used in the experiments ultimately formed mixed clogging, which was the result of the combined effects of particle deposition and aggregation. The particle deposition with dp50 = 4.05 and 11.83 μm ultimately exhibited hyper-exponential distribution and formed mixed and superficial clogging, respectively. At the same time, the concave region of the media grain surface played a dominant role in particle deposition. For dp50 = 4.05 μm, 69.41 % of the particles were deposited in the concave region, and for dp50 = 11.83 μm, the proportion was 90.1 %. The results help to better manage particle clogging in groundwater recharge and other engineering applications (e.g., groundwater source heat pump, and filtration project). In addition, these findings provide a theoretical reference for the development of numerical models to help recognize the probability of particles of different sizes to be captured in porous media.