The experiment was carried out in an intermediate-scale pilot
plant, comprising six horizontal subsurface flow CW (HSSCW)
made of concrete, constructed in a covered outdoor plot at IRTA
in Cabrils (Spain) (41◦ 25 N, 2◦ 23 E). All beds were covered with a
geotextile layer and high-density polyethylene (HDPE) to make the
CW impermeable. A slope of 1% was required in the plot to maintain
the hydraulic gradient of the beds. The inlet zone consisted of a
pipe with 2 L h−1 emitters to regulate the flow (0.24 m3 day−1) per
experimental line (Narváez et al., 2011). Two online instruments to
monitor the CW were connected to one of the six available beds of
the pilot plant at the inflow and outflow pipes (Figs. 1 and 2).