The influence of the outlet position and substrate on the nitrogen purification of vertical flow constructed wetlands

Abstract

Abstract To investigate the influence of outlet location on nitrogen removal in Vertical Flow Wetlands (VFWS), three VFWS, that were, wetland H (planting Pennisetum Hydridum), wetland X (planting Pennisetum purpureum Schum.) and wetland CK (no planting) were constructed. High, medium and low water outlets were set in each wetland, namely A, B and C. The main results were as followed: TN (total nitrogen) removal efficiency of A, B, C in H wetland was 61.3%, 55.4%, 53.2 %, and variance analysis was 100.2, 137.1, 177.8. A, B, C in X wetland was 58.3%, 56.6%, 50.2%, and variance analysis was 55.6, 68.8, 116.4. A, B, C in CK wetland was 53.1%, 51.5%, 50.2%, and variance analysis was 131.9, 188.7, 275.4, respectively. The content of nitrogen and urease activity in the substrate decreased with increasing of substrate depth. These results indicated that planting Pennisetum Hydridum and Pennisetum purpureum Schum. In VFW and appropriately raising outlet position could help improve nitrogen removal efficiency and obtain relatively stable effluent quality, and the upper substrate (0-10 cm) was the main site for nitrogen interception and purification. It can provide theoretical basis for the scientific construction and management of VFW.