Pore-scale lattice Boltzmann modeling of solute transport in saturated biochar amended soil aggregates

Biochar has been increasingly used as an amendment to enhance soil structure and improve soil hydraulic properties. Nevertheless, there are very limited physically based studies to investigate solute transport in biochar-amended soils at pore scale. In this study, for the first time, synchrotron-based X-ray micro-computed tomography (SR-μCT) was used to obtain high-resolution pore geometries of two clayey soils and their biochar amended samples, then the three-dimensional lattice Boltzmann (LB) method was implemented to simulate solute transport using the pore structure information. By using the innovative method of combining SR-μCT and LB simulation, we found that biochar amendment reduced the spatial variability of pore water velocity and increased the dispersion coefficient by one order of magnitude. In addition, we observed that anomalous dispersion was more likely to occur in soils with biochar amendment. Furthermore, soils after biochar amendment had relatively higher thresholds of both the transition zone and advection-dominated zone for the dispersion coefficients. These results are crucial in understanding nutrient transport processes and contaminant migration occurring at pore scale.