Constructed Wetlands treating Urban Runoff Contaminated with Nitrogen

The aim of this research project was to assess the role of the macrophyte Phragmites australis (Cav.) Trin. ex Steud. in experimental, mature and temporarily flooded vertical-flow wetland filters treating simulated urban runoff rich in organic matter. During the experiment, ammonium chloride was added to sieved concentrated road runoff (i.e. gully pot liquor) to simulate primary treated urban runoff contaminated with nitrogen. The five days @ 20degC N- Allylthiourea biochemical oxygen demand (BOD) and chemical oxygen demand removal efficiencies were relatively lower for planted than unplanted filters. Moreover, there was no significant difference for BOD removal for all filters under fluctuating inflow concentrations of sulfate. The nitrogen removal performances of planted filters were more efficient and stable throughout the seasons compared to those of unplanted filters. A substantial load of nitrogen (approximately 500 mg per filter (diameter of 10 cm) at the end of the growing season) was removed by harvesting P. australis. Plant uptake was the main removal mechanism for nitrogen during high concentrations (approximately 10 mg/L) of ammonia-nitrogen in the urban runoff.