The first experiments aimed at the possibility of wastewater treatment by wetland plants were
undertaken by Käthe Seidel in Germany in the early 1950s at the Max Planck Institute in Plön [3].
Seidel then carried out numerous experiments aimed at the use of wetland plants for treatment of
various types of wastewater, including phenol wastewaters [4], dairy wastewaters [5] or livestock
wastewater [6]. Most of her experiments were carried out in constructed wetlands with either
horizontal (HF CWs) or vertical (VF CWs) subsurface flow, but the first fully constructed wetland was
built with free water surface (FWS) in the Netherlands in 1967 [7]. However, FWS CWs did not
spread substantially in Europe where subsurface flow constructed wetlands prevailed in the 1980s
and 1990s [2].