## 3 Results and Discussion
### Operation and Performance of the CW with the Studied Substrates
The increase in effluent hardness, associated with the wear of seashells, may also indicate the formation of calcium precipitates. Figure 3: Variation in (**a**) ammonium nitrogen (N-NH\({}_{4}\)+) and (**b**) total phosphorus (P) concentrations, along with their removal efficiency over time during the phases without vegetation (Phase I) and with vegetation (Phase II). Indeed, in most of the CW systems, phosphorus removal efficiency remains relatively low, but performance may be enhanced through the use of alternative substrates, particularly those rich in calcium, iron, and aluminum, which can form insoluble complexes with phosphorus [36]. Materials with high adsorption capacities can further optimize wetland performance. For instance, [PERSON] et al. [37] demonstrated that a vertical flow wetland using a dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)) bed achieved a 21% increase in phosphorus removal compared to one with a sand bed, underscoring the significance of substrate selection for improving treatment efficiency. Other materials with high phosphorus adsorption capabilities, such as expanded clay, aluminum sludge, and oyster shells, have also been suggested [38; 39]. The use of adsorbent materials as substrates typically plays a more pivotal role than biological absorption in phosphorus removal within constructed wetlands [40; 41]. While vegetated wetlands generally exhibit enhanced phosphorus absorption, achieving permanent nutrient removal and contributing to efficiencies ranging from 4.72% to 59.6% [38; 42], this study found no significant difference in phosphorus removal between the vegetated phase (40.17 \(\pm\) 0.15)% and the non-vegetated phase (34.42 \(\pm\) 3.07%) (\(p\) = 0.6586; \(p\) > 0.05). Similarly, no significant statistical difference was observed in the removal of the anionic surfactant between phases I and II (\(p\) = 0.2500; \(p\) > 0.05), with removal efficiencies of (71.9 \(\pm\) 14.1)% and (60.0 \(\pm\) 9.5)% in the non-vegetated and vegetated phases, respectively. In Phase I (without vegetation), the final effluent anionic surfactant concentrations ranged from 0.7 to 2.3 mg/L, with a mean of (1.4 \(\pm\) 0.7) mg/L, and, in Phase II (with vegetation), ranged from 0.9 to 2.8 mg/L, with a mean of (1.8 \(\pm\) 0.6) mg/L. The removal efficiency observed in the unplanted systems suggests that physical processes such as adsorption or biofilm formation on the gravel surface play a significant role in LAS removal. The overall average removal efficiency of (64 \(\pm\) 16.9)% indicates that the system effectively removed this substance. Interestingly, [PERSON] [7], while operating two pilot-scale CW with 7-day cycles and vegetated with _Echinodorus subulatus_ in a bed composed of sand, shells, and bricks, achieved a 94.1% removal of LAS despite a significantly 100 times higher influent concentration. Adsorption onto the media was the primary mechanism for LAS removal. This discrepancy in removal efficiency compared to the current study may be attributed to the use of pure surfactant in this research, whereas [PERSON] [7] used shampoo and liquid soap as the source of the surfactant. [PERSON] et al. [42] reported a 90% removal of 83.0 mg/L of LAS using agave fiber as a substrate in a CW vegetated with _Schoenoplectus americanus_ and operated under continuous flow with an HRT of 15 days. They attributed the primary removal mechanism to the adsorption of LAS onto the filter bed material. Similarly, [PERSON] et al. [43] achieved a 95% removal of LAS from an influent concentration of 10 mg/L in a CW system treating domestic wastewater. This system was vegetated with _Pragmites australis, Thypha latifolia, Salix vitimalis, Iris_, and _Juncus effusus_ in a gravel bed, and operated an HRT of 13.8 days. The study also highlighted adsorption onto the filter bed as the principal removal pathway.