The removal of nitrogen compounds in constructed wetlands in Poland

More than 100 constructed wetlands are in operation in Poland. Most of them are one-stage wetland systems with horizontal Subsurface flow. Constructed wetlands ensure efficient removal of organic matter (BOD5, CODCr) and suspended solids, but efficiency of nitrogen compound removal in many cases is insufficient. From 1995 to 2001 a study on the removal of contaminants in 11 individual pilot households as well as 4 local community plants equipped with one-stage horizontal flow bed and 4 local community equipped with hybrid reed wetland systems composed of HF-CW and VF-CW filters were carried out. The hybrid constructed wetlands ensure more stable removal rates of nitrogen in comparison with one stage systems. The removal of nitrogen takes place in VF beds and HF beds (denitrification) applied as the second and third stage of primary hybrid treatments. The removal of nitrogen was limited by efficiency of the nitrification process in VF beds in wetland systems.