Removal of acidic pharmaceuticals by small-scale constructed wetlands using different design configurations

To better understand the performance of constructed wetlands (CWs) to remove acidic pharmaceuticals (APs) in wastewaters in subtropical areas and to optimize CW design criteria, six small-scale CWs under different design configurations were operated. The factors (environmental parameters, water quality, and seasonality) influencing the APs removal were also analyzed to illustrate the removal mechanisms. The results indicated that the best performances of CWs were up to 80-90%. Subsurface flow (SSF) CWs showed high removal efficiency for ibuprofen, gemfibrozil and naproxen, but surface flow (SF) CWs performed better for ketoprofen and diclofenac. The positive relationship between the removal efficiencies of ibuprofen, gemfibrozil, and naproxen with dissolved oxygen and ammonia nitrogen reveals that SSF CWs under aerobic conditions benefit the biodegradation, while the favorable conditions created by SF CWs for receiving solar radiation promote the effective photolysis of ketoprofen and diclofenac. Planted SSF CWs had significantly higher removal efficiencies of ibuprofen and gemfibrozil than the unplanted controls had in all seasons. The removal of all APs was higher in summer and autumn than those in winter. Furthermore, an inverse relationship between removal efficiency and the distribution coefficient (logDow) was observed in SF CWs. Overall, CWs that provide aerobic degradation and photolysis would benefit APs removal in subtropical areas in the south of China.