Parameter Analysis in Simulating Transport of Metformin in a Sandy Medium

An anti-diabetic drug and personal care product emerging pollutant, metformin, is being reported for its ubiquitous presence in different environmental compartments. Meanwhile, there is a high possibility for metformin travelling into soil and groundwater compartments during groundwater recharging. In order to investigate the transport process of metformin in the sandy vadose zone, static batch tests and sand column experiments were conducted, and an inverse method embedded in HYDRUS-1D was applied to identify essential transport parameters of metformin while supporting future environmental management practice. According to the static experiment, the Freundlich isotherm can describe metformin's adsorption in the medium. The two-site nonequilibrium model is suitable to describe the adsorption of metformin in the investigated sandy columns. The type-1 sorption fraction values (f) in all three sandy columns are 0.505, 0.355 and 0.236, respectively, indicating type-2 nonequilibrium adsorption is the primary metformin adsorption process in the sandy medium. In this case, when transporting in such a medium with a relatively higher adsorption intensity, metformin's long-range transport potential is likely to be weakened, which might lead to local environmental impact.