The use of natural wetlands for treatment of wastewater has
been practiced for several decades in the past [1]. Since the
1950s, the wetland technology emerged and the use of controlled
wetland environments for wastewater treatment was developed.
Constructed wetlands (CWs) appear nowadays as a reliable, effective
and feasible solution in the field of wastewater treatment [2,3].
They can be classified by the type of plants (free floating, rooted
emergent and submerged systems) or by the type of flow (horizontal
or vertical) [4].
The use of Vertical Flow CW (VFCWs) systems in Europe became
very popular in the 1990s. The adoption of strict disposal limits
for nitrogen favored the application of VFCWs compared to
horizontal systems [1], due to their enhanced ability to oxidize
ammonia nitrogen. In VFCW systems, the wastewater fills periodically
the wetland matrix and then drains completely by gravity. This
way of feeding provides high levels of oxygen transfer within the
substrate, which allows for good treatment performance, especially