Long-term performance of an integrated constructed wetland for advanced treatment of mixed wastewater

The aim of this study was to investigate long-term performance of a full-scale integrated constructed wetland (CW) system for advanced treatment of sanitary and industrial mixed wastewater. The system consisted of a vertical subsurface flow (VSF) CW, a free water surface (FWS) CW, and a horizontal subsurface flow (HSF) CW in series. Results from six-year operation showed that the system resulted in average removal efficiencies of 70%, 70%, 34%, 52%, 45%, 74%, 21%, 43%, and 98% for COD, NH4-N, NO3-N, TN, TP, TSS, F−, Ni, and E. coli, respectively. Especially, NH4-N was effectively removed by the VSF CW. With relatively high hydraulic loading rates (18.0-43.6 cm d−1) and short hydraulic retention times (1.04-2.51 d), the removal efficiencies of the system were quite stable for most of the water quality parameters, while the removal efficiency of TN increased from 49% to 60% during the six years. The removal efficiencies of the system were generally stable with the change of seasons. This study demonstrates that the VSF + FWS + HSF CW system can be a valuable approach for advanced wastewater treatment to meet the more stringent discharge requirement.