## 3 Results and Discussion
### Operation and Performance of the CW with the Studied Substrates
Similarly, EC rose from (1256 \(\pm\) 67) \(\mu\)S/cm (Phase I) and (1452 \(\pm\) 23) \(\mu\)S/cm (Phase II) in the influent to (1807 \(\pm\) 93) \(\mu\)S/cm (Phase I) and (1842 \(\pm\) 49) \(\mu\)S/cm (Phase II) in the effluent. This increase in TDS and EC may be attributed to ions released from the bed materials, such as carbonate, bicarbonate, chloride, and calcium, among others [24]. Calcium carbonate present in shells and bricks can gradually leach into water over time, resulting in an increase in calcium ion concentration and, consequently, water hardness [24; 25], as observed in this study. The total hardness measured in the influent exhibited similar values across both phases: in the phase non-vegetated phase (Phase I), hardness in the influent ranged from 100.0 mg/L to 175.0 mg/L, with a mean of (125.5 \(\pm\) 23.8) mg/L, and, during the vegetated phase (Phase II), it ranged from 100.0 to 160.0 mg/L, with a mean of (135.7 \(\pm\) 23.9) mg/L. Regarding the effluent, hardness values were also close across both phases, ranging from 400 to 505 mg/L in the non-vegetated phase with a mean of (457.1 \(\pm\) 37.3) mg/L, and from 400 to 505 mg/L, with a mean of (444.3 \(\pm\) 31.7) mg/L in the vegetated phase. Elevated hardness and EC values can compromise the performance of these systems. High EC indicates increased salinity, which can stress macrophytes [13; 26]. Increased \begin{table}
\begin{tabular}{c c c c c} \hline
**Reference** & **Colonizing Species** & \begin{tabular}{c} **Influent COD** \\ **(mg/L)** \\ \end{tabular} & \
\begin{tabular}{c} **Cycle Time** \\ **(Days)** \\ \end{tabular} &
\begin{tabular}{c} **Efficiency** \\ **(\%)** \\ \end{tabular} \\ \hline This study & _Echinodorus subalatus_ & 843.7 & 7 & 94.0 \\ \hline [PERSON] [7] & _Echinodorus subalatus_ & 1851.7 & 7 & 88.4 \\ \hline [PERSON] et al. [21] & _Zantedeschia aethiopica_ & 500–2500 & 1 & 92.0–97.0 \\ \hline [PERSON] et al. [22] & _Pittsoporum tobira_ & & & \\  & _Polygala myrtifolia_ & 350 & 7 & 96.0 \\  & _Hedera helix (ivy)_ & & & \\ \hline [PERSON] et al. [23] & _Hymenopteracallis littoralis_ & & & 55.4 \\  & _Phragmites australis_ & 143.3 & 0.50 & 46.7 \\  & _Canna indica_ & & & 52.5 \\  & _Colocasia esculenta_ & & & 50.6 \\ \hline \end{tabular}
\end{table} 
Table 2: Organic matter removal efficiency, measured as COD, reported in the literature for vertical flow wetlands operated at various cycle times for greywater treatment. hardness, driven by higher calcium concentrations, can impact aquatic organisms by reducing epithelial permeability, affecting nutrient availability, and altering biogeochemical processes in wetlands. This reduction in permeability can hinder passive diffusion and increase the energy required for osmoregulation [27]. The increase in Ca++ and Mg++ can also influence the pH of the environment, as these ions can neutralize acids and bases present in the environment, especially in closed systems like CW [28]. However, in this study both influent and effluent showed stability in pH values throughout the operational cycles, with average values of 6.93 and 7.02, respectively, in the non-vegetated phase and 6.83 and 6.98 in the vegetated phase, respectively, in the vegetated phase, remaining very close to neutral conditions. It is considered ideal for pH to remain between 6.50 and 8.00 to favor nitrification and denitrification processes [29; 30]. Additionally, the final effluent complied with the pH limits set by Brazilian legislation CONAMA N\({}^{*}\) 430/2011 [31], which is between 5.0 and 9.0 for discharge into receiving water bodies. In Phases I and II, the system demonstrated an ammonium nitrogen removal efficiency of (32.4 \(\pm\) 9.7)%, with the average ammonia concentration decreasing from 56.8 \(\pm\) 2.4 mg/L in the influent to (38.4 \(\pm\) 5.4) mg/L in the effluent.