Assessment of effect on water quality by hybrid constructed floating treatment wetlands in the low flow urban rivers

In this study, the effect of hybrid constructed floating treatment wetlands (FTWs) in a low-flow urban river was evaluated, and the influence radius on dissolved oxygen (DO), ammonia nitrogen (NH4+-N), and total phosphorus (TP) under different flow conditions was quantified. It was found that DO considerably increased and NH4+-N and TP decreased at the outlet after treatment with hybrid constructed FTW. The NH4+-N removal rate continued to increase to 72.03%, whereas that for TP decreased to 63.16% with fluctuation. The cloud picture of the influence radius showed that when DO <= 3 mg/L, R-flow approximate to 5 m, R-still approximate to 3 m, and when DO > 3 mg/L, R-flow = R-still approximate to 8 m. For NH4+-N under flow conditions, R-flow approximate to 8 m, whereas under still conditions when NH4+-N <= 7 mg/L, R-still approximate to 5 m, and when NH4+-N > 7 mg/L, the concentration changes were not considerable. When TP <= 0.4 mg/L, R-flow approximate to 5 m, and when TP > 0.4 mg/L, R-flow approximate to 8 m; while under still conditions, when TP <= 0.8 mg/L, R-still approximate to 5 m, and when TP > 0.8 mg/L, the concentration changes were not remarkable. Various water quality parameters and water flow affected the radius of influence of FTW on DO, NH4+-N, and TP at the spatial level. For the same water quality parameter, the influence radius in the flow state was larger than that in the still state (R-flow >= R-Still). This study evaluated treatment efficiency of the hybrid constructed FTW in urban rivers and provided guidance and support for FTW deployment in future.