Nitrate, Phosphate, and Salt Removal from a Pilot-Scale Hybrid Constructed Wetland with Planted Phragmites Australis

This study was carried out to investigate the feasibility of using Constructed Wetland (CW) systems in removing nitrate and phosphate pollutants and salts from agricultural runoff. For this purpose, two Subsurface-Flow Constructed Wetlands (SFCW) were used in series; one with horizontal flow and another with vertical flow.  These wetlands were first filled with gravel (2-3 mm in size) as a bed material with a height of  0.1 m (according to EPA recommendations). The drain pipes were then covered with a 0.2 m layer of 70:30 gravel–zeolite-clinoptilolite mixture. The systems were studied with and without planted phragmites australis (common reed), and their performance were investigated in terms of pollutant removal efficiency using agricultural runoff containing 12 dS.m-1 salinity, 80 mg.L-1 nitrate and 10 mg.L-1 phosphate. It was found that as pollutants continue to pass through the beds, the removal efficiency is reduced in wetlands with and without planted reed. The final efficiencies of hybrid HF–VF CW, VF–HF CW, VSFCW, and HSFCW models were calculated to be 69.39, 65.81, 73.57, and 94.75% in the wetland with planted reeds and 60.40, 57.16, 55.58, and 53.91% in the wetland without planted reed, respectively. Finally, it is concluded that the hybrid HF–VF CW with the presence of reed plant and with higher efficiency offers an acceptable level of nitrate, phosphate, and salt removal.