Nitrogen removal in constructed wetlands of vertical and horizontal flow

Constructed wetlands (CW) are considered as one of principal wastewater treatment methods containing plant and soil filters. CW may be of subsurface vertical flow (VF) and horizontal flow (HF). The objective of the studies was to estimate N-removal efficiency differences In CW of vertical and horizontal flow. To evaluate nitrogen (N| removal efficiency, the database of the studies on both construction ofCW collected within the period of 1995-2005 was used. Horizontal filter systems characterize for a 1.6 times higher N-removal efficiency than vertical filters. Generally, N-removal efficiency depends on the load of filters. When filter load was 1.5 g m-2 d-1 according to TN, N-removal efficiency is 39.6 and 24.0% in HF and VF systems respectively. Considering the seasons of the year, no significant difference was observed in N-removal efficiency in HF and VF systems during cold and warm periods of the year. N contained in water after the treatment process in filters is detected in different forms. NH,-N is prevailing in HF, while in VF systems NO3-N is dominant. It was also observed that NH3-N in the effluent during the initial operation of VF after the construction works in the first two months in the warm and in four months during their operation in the cold period of the year was prevailingVytauto Didžiojo universitetasŽemės ūkio akademij