Performance of Treating Synthetic High-Strength Wastewater by Hybrid Vertical-Subsurface Flow Constructed Wetlands in Response to Various Two-Stage Combinations of Vertical Up-Flow and Down-Flow

The performance and temporal variation of hybrid vertical-subsurface flow constructed wetlands (VFCWs) in response to two-stage combinations of vertical up-flow (VUF) and vertical down-flow (VDF) were tested in order to treat non-point sources of pollution wastewater. The effect and seasonal variation of four kinds of two-stage combinations VFCWs (VUF-VUF, VDF-VDF, VUF-VDF and VDF-VUF) were analyzed by synthetic high organic/N loading wastewater. Furthermore, the impact of loading variation treatments, combination patterns, season variation and their interaction on treatment performance were calculated. Four kinds of two-stage combinations VFCWs all showed high nutrient removal efficiencies under high organic/N loading treatments and the optimum two-stage combination was VDF-VUF VFCWs. During the experimental period, the relatively higher nutrient removal efficiency was achieved in late summer (July and August) and early autumn (September) and the highest value was obtained in August. Chemical oxygen demand and total nitrogen removal efficiencies under high organic/N loading treatments were only significantly affected (p < 0.05) by season, system variation and the combined effect of season and system variation, while the total phosphorus removal efficiencies were not significantly affected (p > 0.05) by any factors.