## 3 Results and Discussion
### Operation and Performance of the CW with the Studied Substrates  
The variations in COD concentrations in both the influent and effluent, as well as the system's efficiency during the non-vegetated phase (Phase I) and the vegetated phase (Phase II), are presented in Figure 2. The system demonstrated similar removal efficiencies for organic matter in terms of COD across both phases, with percentages of (94.0 \(\pm\) 1.1)% in the vegetated phase and (91.0 \(\pm\) 3.8)% in the non-vegetated phase. Statistical analysis confirmed no significant difference between the two phases (\(p\) = 0.38; \(p\) > 0.05). The concentrations of COD in the treated effluent were (50.0 \(\pm\) 10.8) mg/L for the vegetated phase and (74.8 \(\pm\) 29.8) mg/L for the non-vegetated phase. In the vegetated phase, the presence of plants likely contributed to enhanced treatment efficiency through the development of microbiota on the plant roots, which aids in organic matter assimilation and increases bed oxygenation, promoting degradation by aerobic and facultative microorganisms [20]. Conversely, the non-vegetated system showed greater variability in COD concentrations, ranging from 40.0 mg/L in the 5 th cycle to 132.0 mg/L in the 6 th cycle, whereas the vegetated phase had a narrower range from 38.0 mg/L in the 9 th cycle to 65.5 mg/L in the 14 th cycle. This suggests that vegetation may stabilize and improve the consistency of treatment performance. Table 2 presents the removal efficiencies of organic matter reported in various studies on greywater treatment using vertical flow wetlands across different cycle times. The average removal of organic matter, as measured by COD, was higher than the 88.4% achieved by [PERSON] [7] in a similar wetland system operated on a pilot scale with the same 7-day cycle time for greywater treatment, despite the slightly lower temperature in our study compared to [PERSON]'s [7] pilot system (25-30 \({}^{\circ}\)C). This suggests that _Echinodorus subalatus_ used in both systems is not adversely affected by the lower temperatures in  
Figure 2: COD removal efficiency in the system during the non-vegetated phase (Phase I) and the vegetated phase (Phase II). the controlled environment (~24 \({}^{\circ}\)C) of this study, nor by the temperature fluctuations in [PERSON] et al. 's research [7], which lacked temperature control. Though there are high organic matter concentrations in greywater, as compared with other waters, CW has demonstrated effective performance with their treatment. For instance, [PERSON] et al. [21] reported successful treatment of laundry greywater using a vertical flow wetland with a sand bed and vegetated with _Zantedeschia aethiopica_, operating with varying hydraulic loads (15.9 to 63.7 mm/day) in 24 h cycles. The authors reported removal efficiencies between 92.0% and 97.0%, noting that while the highest hydraulic load reduced efficiency, optimal performance was achieved at a hydraulic load of 15.9 mm/day, resulting in a 97.0% removal. The laundry water had an organic matter concentration varying from 500.0 to 2500.0 mg COD/L, depending on the operational phase. [PERSON] et al. [22] also achieved a high COD removal rate of 96% in greywater treatment using CW, and this removal was similar regardless of the plant used. On the other hand, [PERSON] et al. [23] obtained removal efficiencies that ranged from 46.7% to 55.4%, and the fluctuation in removal percentages was likely due to the type of macroophyte used, with the best efficiency using _Hymenopteracallis littoralis_ and the worse with _Plragmites australis_. Notwithstanding the lower removal percentages compared to other studies, it is important to note that the cycle time was only 0.5 days (Table 2). Interestingly, the concentration of TDS and EC increased from influent to effluent. TDS values were (680 \(\pm\) 33.3) mg/L (Phase I) and (719 \(\pm\) 14.0) mg/L (Phase II) in the influent, and (904 \(\pm\) 46) mg/L (Phase I) and (920 \(\pm\) 2.0) mg/L (Phase II) in the effluent.