The performance improvement by the planted units has already
been reported [e.g., 39,40], but with no statistically significant differences;
on the contrary, significant differences were observed for
the effluent concentrations in the present study. Taking also into
account the limited nitrogen uptake by plants (Table 2), it seems
that nitrification is the major ammonia removal process. Increased
effluent concentrations of oxidized nitrogen (nitrate and nitrite)
confirmed this, indicating that the intermittent loading of the beds
ensures adequate aeration. The lack of statistical significance for
phosphorus effluent concentration implies that sorption onto the
substrate is the main removal mechanism, which is limited due
to short contact time. Additionally, the type of plant species does
not affect the system performance of vertical systems, contrarily to
what was found in HSF [23] and FWS [32] CWs.