## 4 Discussion  
In this paper, we show how a Constructed Wetland, connected to a pyrolysis plant, was able to remediate the wastewater with the aim of contributing to the water reuse in the context of a Circular Economy. Moreover, our results confirm the possible use of CWs, not only for urban wastewater up to 2000 equivalent people, as suggested by the Italian D.lgs 152/06, but also for industrial applications. In our experiment, the pH of PL wastewater was initially acid (Table 1) in the inflow; the effect of the CW treatment provided a pH variation to slightly alkaline. This result is in agreement with [34], who suggested that change of pH to alkaline condition was probably due to the addition of oxygen \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Metal** & **IN** & **OUT** & **u.m.** \\ \hline Fe & \(3.4\pm 1.2\) a & \(1.5\pm 0.8\) a & ppm \\ Ni & \(0.03\pm 0.01\) a & \(0.06\pm 0.04\) a & ppm \\ Zn & \(0.7\pm 0.03\) a & \(0.1\pm 0.01\) b & ppm \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physical and chemical characteristics of PL in inflow and outflow. Different letters indicated that the differences were significant (\(p\)-value \(<0.05\)). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Contaminant** & **IN** & **OUT** & **u.m.** \\ \hline Sulfites & \(11.72\pm 0.1\) a & \(1.66\pm 0.2\) a & mg/L \\ Sulfites & \(55.14\pm 2.1\) a & \(33.41\pm 2.7\) b & mg/L \\ Chlorides & \(10.2\pm 1.3\) a & \(5.46\pm 24\) a & mg/L \\ Fluorides & \(0.45\pm 0.08\) a & \(<\)0.01 b & mg/L \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Contents of sulfites, sulfates and halogenates in wastewater previous and after the CW treatment. Different letters indicate that the differences among the means were significant (\(p\)-value \(<0.05\)). Figure 6: Nitrogen and phosphorus levels before and after phytodepuration. Different letters indicate that the differences among the means were significant (\(p\)-value \(<0.05\)). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & _V. fischeri_ & _P. subcapitata_ & _D. magna_ \\ \hline IN & \(13\pm 2\%\) a & \(78\pm 2\%\) a & \(7\pm 1\%\) a \\ OUT & \(<\)0.1\% b & \(63\pm 1\%\) a & \(<\)0.1\% b \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Ecotoxicological risk assessment of wastewaters before and after the CW treatment. Different letters indicated that the differences among the means were significant (\(p\)-value \(<0.05\)). through dissolution of atmospheric oxygen and photosynthetic activity by the plant. COD and BOD\({}_{5}\) produced by the pyrolysis plant were higher than the limit of the Italian Law; the results obtained after the CW treatment indicate that the CW was able to oxygenate the wastewater to a level that supports the aerobic degradation of the contaminants produced by pyrolysis, as previously observed by [35]. The CW treatment also improved the physical characteristics of the wastewaters, such as color and odor. These results are supported by the chemical analyses that showed a decrease of the evaluated parameters, except for the ammonium source of nitrogen, whose value significantly increased within the limit of the Italian Law. The observed increase could be ascribed to bacterial dissimilatory nitrate reduction to ammonium (DNRA), also known as nitrate/nitrite ammonification, a not very common process that is the result of anaerobic respiration by chemo-organo-heterotrophic microbes. This process could been performed by naturally occurring bacteria [36]. The nitrate source of nitrogen, significantly decreased, according with previous results obtained by using the same biological system on nitrate rich waters [27]. The ecotoxicological risk showed a positive impact of CW due to the efficient removal of almost all the targeted contaminants [37; 38]. These results can be partly explained by the effects induced by AMF on the host plants, as shown by the mesoccosm experiment: while improving the mineral nutrition of the plants, AMF can also increase their tolerance towards some pollutants, either organic or inorganic [39].