## 2 Materials and Methods
### Case Study
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**1 st Stage French Reed** & & & **2 nd Stage HF CWs** & **HF 1** & **HF 2** \\ \hline n\({}^{\circ}\) of FRB parallel line & 3 & & n\({}^{\circ}\) of parallel sectors & 1 & 3 & \\ \hline Total surface area FRB & 1197 & m\({}^{2}\) & Total surface area of HF & 480 & 504 & m\({}^{2}\) \\ \hline Surface area of each & 399 & m\({}^{2}\) & Surface area of each VF line & 480 & 168 & m\({}^{2}\) \\ \hline Feeding period per each sector & 3 & h & Total height of the filter media & 80 & cm \\ \hline Feeding resting period & 6 & h & Width of the HF sector & 16 & 14 & m \\ per each sector & 85 & cm & Length of the HF sector & 16 & 12 & m \\ \hline FRB filter media layers & & & Bottom slope & 1\% & \\ (from the bottom) & & & & & \\ \hline Coarse gravel—\(\mathcal{O}\) & 25 & cm & Designed hydraulic conductivity & 500 & m/d \\ \hline Gravel—\(\mathcal{O}\) 5–20 mm & 20 & cm & Designed porosity & 0.35 & \\ \hline Fine gravel—\(\mathcal{O}\) 2–8 mm & 40 & cm & Designed minimum hydraulic retention time & 2.4 & d \\ \hline Freeboard height & 50 & cm & & & \\ \hline Minimum organic & 160 & g\({}_{\text{COD}}\)/m\({}^{2}\)/d & & & \\ loading rate (70 m\({}^{3}\)/d) & 230 & g\({}_{\text{COD}}\)/m\({}^{2}\)/d & & & \\ \hline Minimum Hydraulic & 60 & L/m\({}^{2}\)/d & & & \\ loading rate (70 m\({}^{3}\)/d) & 80 & L/m\({}^{2}\)/d & & & \\ \hline Batch feeding time & 16 & min & & & \\ (maximum) & 9.7 & m\({}^{3}\) & & & \\ \hline HLR flush & 2.4 & cm & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specifications of the Cecchi CW WWTP: HF 1, refurbished bed from 2001 CW WWTP; HF 2, bed built during the 2009 upgrade. The technical specifications of HF 2 nd stage are resumed in Table 1. The HF 2 nd stage was built realizing four parallel sectors. The first sector was placed in a single bed and has a surface of 480 m\({}^{2}\); it was realized when refurbishing the HF bed of the CW WWTP of 2001 (hereinafter referred to as HF 1). The other 3 parallel HF sectors were realized in a single bed (hereinafter referred to as HF 2), hydraulically separated into three sectors. The sectors were designed with a length-to-width ratio proximal to 1:1 to limit the clogging risk at the cross-sectional area. Effluent of HF 2 nd stage is sent by gravity to the FWS 3 rd stage. The HF beds are planted with _Phragmites australis_. The FWS 3 rd stage was recovered from the CW WWTP of 2001 and has a total surface area of 850 m\({}^{2}\). The FWS 3 rd stage was designed with five cells in series. The first four FWS cells have an average water depth of 0.4 m, while the last FWS cell has an average depth of 1.0 m. The designed hydraulic retention time of the FWS is 3.3 days with an influent hydraulic load of 100 m\({}^{3}\)/d. Variable water depth was designed in each cell in order to place different autochthonous aquatic plants (_Typha latifolia_, _Myriophyllum spicatum_, _Phragmites australis_, _Eledea Canadensis_, _Certophyllum demersum_, _Lythrum salicaria_, _Iris pseudacorus_, _Epilobium hirsutum_, _Alisma plantago aquatica_, and _Butumus umbellatus_). Effluent from the FWS 3 rd stage can be either sent the optional sand filier with a pumping system or discharged by gravity in the Gena river. The CW WWTP was designed to respect the water quality targets fixed by the Italian legislation for the discharge of industrial wastewater in water body: pH 5.5-9.5; COD 160 mg L\({}^{-1}\); BOD\({}_{5}\) 40 mg L\({}^{-1}\); N-NH4+ 15 mg L\({}^{-1}\); TSS 80 mg L\({}^{-1}\); TP 10 mg L\({}^{-1}\); N-NO2- 0.6 mg L\({}^{-1}\); N-NO3- 20 mg L\({}^{-1}\); MBAS 2.0 mg L\({}^{-1}\).