## 3 Results and Discussion  
### Adsorption Removal  
The removal of NH\({}_{4}\)-N and PO\({}_{4}\)-P due to adsorption in the three porous media (i.e., CG-Z, FG-Z, and CG-G) is presented in Figure 1. The experimental findings showed that the type of porous medium and the duration of contact had a significant impact on the removal efficiency of orthophosphate and ammonium from the aqueous solutions. It is clearly seen that for both ammonium and orthophosphates, zeolite achieves greater removal rates compared to gravel. Specifically, Figure 1a shows that 65.33% of the ammonium was removed due to adsorption in CG-Z and FG-Z in the first 3 h. Then the ammonium removal rate gradually decreased until 48 h, with the removal reaching 96.23% and 96.34% for CG-Z and FG-Z, respectively. From this time point until 144 h, there was essentially an equilibrium, as there was no change in the concentration of NH\({}_{4}\)-N in the aqueous solution. The average removal rate at equilibrium was 96.20% and 96.49% for CG-Z and FG-Z, respectively. Regarding coarse gravel (CG-G), on the other hand, ammonium removal gradually increased from 5.65% in the first 3 h to 15.48% at 24 h. It then remained almost constant at these levels until 144 h (in equilibrium state), finally achieving an average ammonium removal rate of 16.84%. Furthermore, the removal efficiencies in this study are comparable to those of [PERSON] et al. [50], who, using an integrated system with zeolite and lime, achieved ammonium removal efficiencies of approximately 98%. The removal of orthophosphates from the aqueous solution by adsorption in the studied porous media was much lower and occurred at a slower rate compared to that of NH\({}_{4}\)-N (Figure 1b). The removal rate in the first 6 h was 1.72%, 4.79%, and 2.31% for CG-Z, FG-Z, and CG-G, respectively. Equilibrium was reached after 96, 192, and 96 h for CG-Z, FG-Z, and CG-G, respectively, with an average removal rate of 11.46%, 12.81%, and 6.70%, respectively, until 288 h (Figure 1b). These results are in agreement with those reported by [PERSON] et al. [51]. In both ammonium and orthophosphate removal, fine-grained zeolite generally performed better than the other substrates, highlighting the importance of material type and particle size in adsorption efficiency. Despite being frequently utilized in constructed wetlands, gravel showed only a slight ability to retain any pollutant under the conditions evaluated. More specifically, these results show that zeolite adsorbs approximately six times more NH\({}_{4}\)-N and twice as much PO\({}_{4}\)-P compared to gravel. Also, there was no significant difference in the removal of both ammonium and orthophosphate between CG-Z and FG-Z. Therefore, when designing constructed wetlands for wastewater treatment, for ammonia and orthophosphate removal, the total or partial replacement of the filling material, which is usually gravel [52], with zeolite would improve the performance of the system. Furthermore, using a coarser material as the filling material in the CW (i.e., CG-Z instead of FG-Z) had a minimal effect on contaminant removal while improving the hydraulic conductivity and avoiding clogging, as finer materials contribute more to clogging and related hydraulic problems [53]. According to the adsorption mechanisms documented in the literature, the experimental results clearly show differences in adsorption efficacy between zeolite and gravel substrates. The higher ammonium removal by zeolites (96.20-96.49% efficiency) is consistent with earlier research showing that clinoptiolite's remarkable cation exchange capacity is caused by its negatively charged surface and aluminosilicate structure [31]. According to [PERSON] et al. [26], the quick initial adsorption phase (65.33% removal in 3 h) is caused by easily accessible exchange sites on zeolite surfaces. The low ammonium uptake by gravel (16.84%) is in line with research by [PERSON] et al. [19], who highlighted the poor ion exchange characteristics of gravel-based built wetlands and observed comparable low removal rates.