Enhanced removal of nutrients and diclofenac by birnessite sand vertical flow constructed wetlands

The application of constructed wetlands (CWs) in organic micropollutants elimination is receiving increasing attention worldwide. However, acclimatization periods of CWs were long due to uncontrollable biotic factors and external conditions. In this study, manganese oxide was applied to enhance the simultaneous removal of nutrients and diclofenac (DFC) in CWs. To evaluate the treatment performance, two vertical up-flow CWs (VFCWs), with/without (experimental/control) birnessite-coated sand VFCW, were set up to treat synthetic secondary effluent of the wastewater treatment plant. The removal performance of ammonia was significantly higher in experimental VFCW than that of control during the first 80 d, indicating that experimental VFCW could maintain a stable NH4+-N treatment performance (over 60%) when wastewater contained DFC. After 200 d of operation, the removal efficiency of DFC was achieved 98.5% in experimental VFCWs. The application of birnessite sand increased 12.8% of nitrogen load in the substrate, while phosphorus removal performance was enhanced by 10.0% on account of plant uptake. Though the final nutrients treatment performance was equivalent in experimental and control VFCWs, micro-environments at the middle layer were diverse for microbial communities. This work presents birnessite sand as the potential substrate of VFCWs for treating DFC as well as nitrogen and phosphorus pollutants.