## 3 Results and Discussion  
### Physicochemical Parameters of Leachate Landfill in Pilot-Scale CW Units  
The temporal variation and statistics of the physicochemical parameters of the inflow and outflow of the pilot-scale CW units are presented in Figure 2 and Table 3, respectively. The temperature of the landfill leachate at the inlet of the pilot-scale CW units ranged between 7.0 \({}^{\circ}\)C and 36.2 \({}^{\circ}\)C and did not show a remarkable difference from that at the outlet of the units, which ranged between 7.0 \({}^{\circ}\)C and 36.1 \({}^{\circ}\)C (Figure 2a, Table 3). In general, the variation in the leachate temperature in all units showed the same pattern as that of the air temperature during the experimental period. The mean DO concentration in the effluent of the five pilot-scale CW units ranged from 4.27 mg/L to 5.14 mg/L and was higher than that in the influent (3.24 mg/L), probably due to the dissolution of atmospheric oxygen in the landfill leachate (Table 3). In the planted units, the average concentration of DO was higher than that in the unplanted unit (Figure 2b), a fact attributed to the action of plants, which transfer oxygen from the atmosphere to the wetland in the root zone [36]. The mean pH value at the inlet of the CW units was 8.11, while at the outlet of all the units it was slightly lower, ranging from 7.53 (W5 FGZ-R unit) to 7.91 (W2 FG-U unit) (Figure 2c, Table 3). Lower pH values were measured in the planted units, likely due to the interaction of the porous media and the biofilm that develops on the plant root system. According to [PERSON] and [PERSON] [36], the plant life cycle generates organic compounds that are a source of natural acidity. Additionally, the nitrification process that occurs in CWs produces hydrogen ions that contribute to the reduction in pH. Similar results for the reduction in pH in CWs have been reported in other studies [35; 40; 43]. \begin{table}
\begin{tabular}{l l c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{**Influent**} & \multicolumn{6}{c}{**Effluent**} \\ \cline{3-8}  & & & **W1 FG-R** & **W2 FG-U** & **W3 FG-R** & **W4 FG-C** & **W5 FGZ-R** \\ \hline \multirow{4}{*}{T (\({}^{\circ}\)C)} & mean & 21.5 & 21.0 & 20.8 & 20.7 & 21.1 & 21.1 \\  & SD (n) \({}^{1}\) & 6.4 (106) & 6.4 (106) & 6.6 (106) & 6.6 (106) & 6.8 (106) & 6.7 (106) \\  & min & 7.0 & 7.0 & 7.1 & 7.0 & 7.2 & _7.7_ \\  & max & 36.2 & 35.8 & 36.1 & 33.5 & 34.8 & 34.3 \\ \hline \multirow{4}{*}{DO (mg/L)} & mean & 3.24 & 4.49 & 4.27 & 4.50 & 4.41 & 5.14 \\  & SD (n) & 1.18 (106) & 1.40 (106) & 1.10 (106) & 1.39 (106) & 1.49 (106) & 1.19 (106) \\  & min & 0.33 & 1.66 & 1.78 & 0.57 & 1.37 & 2.13 \\  & max & 5.01 & 8.58 & 6.91 & 7.65 & 7.74 & 8.14 \\ \hline \multirow{4}{*}{pH} & mean & 8.11 & 7.73 & 7.91 & 7.70 & 7.65 & 7.53 \\  & SD (n) & 0.87 (106) & 0.71 (106) & 0.81 (106) & 0.71 (106) & 0.61 & 0.66 (106) \\  & min & 6.11 & 6.11 & 6.11 & 6.11 & 6.23 & 5.98 \\  & max & 9.47 & 8.68 & 8.77 & 8.57 & 8.47 & 8.45 \\ \hline \multirow{4}{*}{EC (mS/cm)} & mean & 7.37 & 9.80 & 6.04 & 10.45 & 9.61 & 10.38 \\  & SD (n) & 0.88 (106) & 4.71 (106) & 1.05 (106) & 5.55 (106) & 4.50 (106) & 6.31 (106) \\ \cline{1-1}  & min & 4.05 & 4.04 & 3.69 & 3.54 & 3.56 & 3.12 \\ \cline{1-1}  & max & 9.50 & 27.70 & 9.48 & 25.80 & 24.50 & 27.00 \\ \hline \hline \end{tabular}  
* SD = standard deviation, n = number of measurements.  
\end{table} 
Table 3: Statistics of the physicochemical parameters in each pilot-scale CW unit. In the planted units, the mean effluent EC value was higher than that in the influent, in contrast to the unplanted unit, where the average effluent EC value was lower than that in the influent (Figure 2d, Table 3). In addition, higher EC values were measured in the planted units during the warmer months when evapotranspiration was higher. Therefore, evapotranspiration is an important factor affecting the EC value due to the condensation of leachate [44].