Chemical Oxygen Demand, Nitrogen, and Phosphorus Removal by Vegetation of Different Species in Pilot-Scale Subsurface Wetlands

Abstract

To assess the removal characteristics of different wetland plants, gravel-based pilot-scale subsurface wetlands vegetated by monoculture vegetation of Salix babylonica, Phragmites australis, Typha angustata, Zizania latifolia, and Lythrum salicaria with stem densities of 20, 1,010, 135, 105, and 58 stem m−2 were used to treat artificial sewage characterized by chemical oxygen demand, total nitrogen (TN), and total phosphorus (TP) pollution. It was revealed that chemical oxygen demand, TN, and TP removal loads of S. babylonica, P. australis, T. angustata, and Z. latifolia vegetation reached 0.112–0.172, 5.7–7.1, and 0.0674–0.152 g m−2 day−1, respectively, accounting for 24.5–37.6%, 34–42%, and 36.1–81.4% of that of the unvegetated control wetland. Moreover, there were exponential relationships between TN removal and evapotranspiration rate in wetlands vegetated by T. angustata, L. salicaria, and S. babylonica, whereas there were linear relationships between TP removal and evapotranspiration rate in wetlands vegetated by P. australis, T. angustata, Z. latifolia, and L. salicaria. After harvest, the N and P standing stocks of all the five kinds of vegetation were only 4.3–9.6 g P m−2 and 2.2–23.9 g N m−2 because both the above-ground biomass and the N and P contents of wetland vegetation harvested in late autumn were low.