Fates of selected pharmaceuticals in a large recirculated mesocosm with a pond and bank filtration

Abstract

Pharmaceuticals such as carbamazepine (CBZ), sulfamethoxazole (SMX) and diclofenac (DCF) are detected at a high frequency in the aquatic environment. The fates of these compounds in bank filtration (BF), a nature-based water treatment system, have been extensively studied, mainly in batch and laboratory column studies. This study, for the first time, investigated the fates of CBZ, SMX and DCF in a large recirculated mesocosm with a pond and subsequent BF. Changes in dissolved organic carbon (DOC) in the pond and bank filtrate were also observed. The averaged spiking concentration of CBZ, SMX and DCF was 1 μg/L at the pond influent and the hydraulic retention time of surface water in the pond was 15 days to reach at the bank. The infiltrated surface water travelled through two parallel subsurface layers and a combined effluent (from both layers) was collected (35 m from the bank) and recirculated as an influent of the pond. The redox conditions in both layers were significantly different (p < 0.05) and correlated with temperature (R2 = 0.91, p < 0.05). The results revealed that CBZ was persistent in the surface water and groundwater passage, SMX was persistent in surface water and removed entirely through BF within 50 days of operation. DCF was completely removed after infiltration and groundwater passage (within 2 m). The DOC in the surface water showed insignificant variations between the influent and the bank. A significant reduction of DOC was observed within the first 5 m after infiltration, and the reduction was associated with the removal of biopolymers. This work shows that the selected organic micropollutants in surface water were not affected by sunlight intensity, water chemistry and water depth. In addition, recirculation mesocosm BF confirms the potential environmental risk and predictive concentrations of organic micropollutants in the aquatic environment.