Transport of Emerging Contaminants in Porous Media

Abstract

Miscible-displacement experiments were conducted to investigate the transport of two emerging contaminants of interest: graphene nanoparticles and perfluorooctanesulfonic acid (PFOS), a representative per and polyfluoroalkyl substance (PFAS). The study of graphene transport focuses on the effect of different factors such as surfactant type, soil type, flow rate, pristine/oxidized form on graphene transport. Breakthrough occurred at 1 pore volume, coincident with a nonreactive tracer and consistent with standard colloid transport theory. The effluent concentrations plateaued at levels lower than the input concentration, indicating irreversible attachment to the solid surface. The observed increasing relative concentration plateau indicated the existence of colloid blocking phenomenon. Greater retention was observed for SDBS-dispersed graphene versus Tween 80-graphene, in Vinton soil versus in sand, at a lower flow rate, and for pristine graphene. Both experiments and mathematical model simulations were used to investigate PFOS transport in two soils and three aquifer sediments. The breakthrough curves exhibited nonideal transport behavior, with asymmetry and extended tailing. The widely used two-domain sorption kinetics model provides good simulations for the experiment with standard input and elution time but cannot fit the long tailing with extended time. A continuous-distribution multi-rate model that has a better resolution for the pore/grain-scale can provide good simulations for the extended elution tailing.