Effect of intermittent operation on contaminant removal and plant growth in vertical flow constructed wetlands: A microcosm experiment Original Research Article

The influences of intermittent operation and different length of drying time on contaminant removal as well as wetland plant growth in vertical flow constructed wetlands (VFCWs) were investigated in this study. Microcosm wetlands planted with Phragmites australis were subjected to a 4-month experiment involving different operations (continuously and intermittently flood) and time ratios of flood to drain (F/D) with the hydraulic loading of 0.10 m3/m2/batch. It was found that the intermittent operation promoted a lower level of COD and TP removal. The intermittent operation caused more oxidizing conditions in the microcosm wetlands and thus greatly enhanced the removal of ammonium, and the removal efficiency was more than 90%. However, the intermittent operated wetlands had lower TN removal efficiencies the flooding system. With different lengths of drying time, the COD and TP removal were similar. The removal of ammonium was enhanced at a lower level with the prolongation of drying time. Contrarily, the TN removal was lower at F/D = 1:2 (46.86%) than at F/D = 2:1 (56.32%). The detected results of photosynthetic rate of Phragmites australis showed that the intermittent operation had no harmful effect on the wetland plant and the plant could grow normally.