Enhanced performance of pilot-scale hybrid constructed wetlands with A/O reactor in raw domestic sewage treatment

The aim of this study was to improve the nutrient removal efficiency by optimizing aeration time, hydraulic loading rate (HLR) and combination type in hybrid constructed wetlands (HCWs) with anoxic/oxic (A/O) reactor. The results showed that, the highest removal percentages of TN, NH₄–N, TP, PO₄–P and COD were 87.9%, 98.1%, 86.1%, 85.3% and 95.2%, respectively, in horizontal subsurface flow (HF) – surface flow – vertical subsurface flow CW with A/O reactor at 0.1 m/d HLR and 2 h aeration. HLR, aeration time and combination type had a significant impact on the removal of nutrients, though plant diversity did not have any significant influence. Presence of the A/O reactor improved the removal of TN in the HCWs by reducing influent loading and changing influent characteristics, thereby affecting the role of nitrification, anammox, and denitrification processes. The anammox process was the dominant pathway in the 1^st HF CWs during the aeration period, where the highest removal of phosphorus was observed.