Hybrid CWs (HF þ VF, VF þ HF) look for effective nitrification
and denitrification through the combination of anaerobic/anoxic
and aerobic conditions which can be provided by the different
types of CW units, depending on its relative surface area and
operating conditions. On the other hand, multi-step systems consisting
of the same type of units (HF þ HF, VF þ VF) rely on
simultaneous nitrification and denitrification in some parts of the
units, depending mainly on the SLR applied. Beside this considerations