[Simulation Experiment: Effect of Organic Colloid on Carbamazepine Transport in Porous Media]

The behavior of organic contaminants in subsoil can be affected by their interactions with organic colloids. In order to explore the impact of organic colloids on the mobility of emerging contaminants in porous media, especially pharmaceutical and personal care products (PPCPs), column experiment was conducted to investigate the migration behavior of target compound carbamazepine (CBZ). In the experiments, quartz sand, standard soil and natural field-collected soil were selected as three types of porous media respectively, and organic colloids were prepared with commercial humic acid. The results showed that, the two-site chemical nonequilibrium model in CXTFIT could better describe the migration behavior of CBZ in all soil columns. This results demonstrated that chemical nonequilibrium adsorption happened in CBZ's migration process. After colloid was added to the sand column, results of CBZ's adsorption process had no significant changes, however, desorption hysteresis was weaker. The reason for that can be explained as the formation of colloid-CBZ complexes by the combination of colloid with CBZ. These complexes could not significantly influence CBZ's adsorption process, however, they could accelerate CBZ's desorption process by solubilization. When organic colloids existed, the migration of CBZ in natural soil and standard soil columns was more hysteretic than sand column, indicating that the sorption capacity of soil column was higher than sand column. The soil organic matter and clay should play a crucial role in the transportation: low/high energy adsorption sites in organic matter and clay surface all could bond with CBZ. Compared with standard soil, the magnitude of sorption and desorption hysteresis of CBZ in natural soil was higher. It was mainly because of the higher organic content in natural soil. Based on the migration behavior of the contaminant in this study, a concept model for various interactions during the transport of hydrophobic organic contaminants in porous media in the presence of organic colloids was then proposed.