Impact of Packed Bed Microscale Geometry on PFAS Adsorption

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent water contaminants that can often be removed using packed beds of granular activated carbon (GAC). In this study, we present a particle-resolved simulation framework to investigate how the packed bed microscale geometry can be designed to improve PFAS adsorption. The model explicitly resolves individual particles and solves species transport in both the solid adsorbent particles and the pore spaces between them. This allowed us to study how different polydisperse bed configurations could impact the bed’s breakthrough behavior. For the microporous adsorbent particles considered, the intraparticle diffusion was treated as the rate-limiting mechanism, while the adsorption equilibrium was described using the Langmuir isotherm. A unique attribute of the proposed approach is that it can capture the nonuniform nonconcentric PFAS loading inside the particles, which is not available in the conventional reduced-order models. Our simulation results were compared with the experimental data from the literature for a monodisperse packed bed of carbon particles, and good agreement was observed. The simulations indicated that breakthrough curves for bidisperse packed beds composed of coarse and fine particles fall between those of the monodisperse packed beds made of the same particles. Comparing the fully blended and layered particle configurations, it was observed that the blended configuration better delays the breakthrough, followed by the layered configuration in which the coarse particles were placed on the upstream side.