Experimentally constructed wetlands for wastewater treatment in Estonia

This work presents preliminary results from two constructed wetlands for municipal wastewater treatment in Estonia: (1) a free water surface constructed wetland (a cascade of 4 serpentine ponds in which Typha latifolia and Phragmites australis have been planted (total area about 1.2 ha, mean depth of the ponds 0,5 m) for secondary treatment of waste water from the town of Poltsamaa with about 5,000 inhabitants and from a food processing factory, and (2) a two-chamber horizontal-flow sand-plant filter (two chambers, 30x6.25x1.0 m, each) filled with coarse sand, one planted with Typha latifolia, and the other with Iris pseudacorus and Phragmites australis, receiving a septic tank effluent of about 40 population equivalents in Kodijarve. The horizontal flow sand-plant filter showed satisfactory purification efficiency in terms of BOD, and phosphorus (66-95% and 63-96%, respectively). However, nitrogen removal was relatively low, varying from 12 to 85%. In the cascade of free water surface wetlands, the most critical parameter is phosphorus retention. Mean purification efficiency observed was about 73% for nitrogen, 68% for BOD7 and 24% for phosphorus. Purification efficiency in both wetland systems did not decrease during the cold season.