## 4 Conclusions  
According to this study, natural zeolite--both coarse- and fine-grained--has a much greater capacity to adsorb ammonium and phosphate than gravel, which makes it a great option for CWs. Specifically, it achieved up to 96.49% ammonium removal and up to 12.81% phosphate removal, outperforming gravel by a wide margin. The adsorption of ammonium and phosphate on the three substrates studied followed the pseudo-second-order model, indicating chemisorption as the main removal mechanism, except for the adsorption of ammonium on coarse gravel, which followed the pseudo-first-order model. Phosphate  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Substrate** & **T (K)** & \(\mathbf{K_{d}}\) & \(\Delta\)**G (k/mol)** & \(\Delta\)**H (k/mol)** & \(\Delta\)**S (k/mol K)** \\ \hline \multicolumn{6}{c}{Ammonium} \\ CG-Z & 283 & 5.41 & \(-\)4.00 & 0.54 & 0.016 \\  & 298 & 5.48 & \(-\)4.18 & & \\ \hline \multirow{2}{*}{FG-Z} & 283 & 4.84 & \(-\)3.71 & 2.81 & 0.023 \\  & 298 & 5.14 & \(-\)4.06 & & \\ \hline \multirow{2}{*}{CG-G} & 283 & 1.10 & \(-\)0.22 & \(-\)16.79 & \(-\)0.059 \\  & 298 & 0.77 & 0.66 & & \\ \hline \multirow{2}{*}{CG-Z} & \multicolumn{4}{c}{Orthophosphate} \\ CG-Z & 283 & 0.94 & 0.15 & 6.69 & 0.023 \\  & 298 & 1.08 & \(-\)0.20 & & \\ \hline \multirow{2}{*}{FG-Z} & 283 & 0.87 & 0.34 & 4.34 & 0.014 \\  & 298 & 0.95 & 0.13 & & \\ \hline \multirow{2}{*}{CG-G} & 283 & 0.56 & 1.36 & 20.09 & 0.066 \\  & 0.86 & 0.37 & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Thermodynamic parameters of ammonium and orthophosphate adsorption on coarse-grained zeolite (CG-Z), fine-grained zeolite (FG-Z) and coarse-grained gravel (CG-G).  
adsorption fits the Freundlich model better, indicating multilayer adsorption on heterogeneous sites, but ammonium adsorption was best represented by the Langmuir model, indicating monolayer coverage on homogeneous surfaces, according to isotherm modeling. Zeolites performed better than gravel in the removal of both ammonium and phosphate, and the adsorption mechanisms were impacted by temperature, substrate type, and interactions specific to the pollutant. These results demonstrate the remarkable effectiveness and sustainability of natural zeolite as a substrate for the removal of both ammonium and phosphorus nutrients from wastewater in constructed wetlands. According to the results, zeolite-based systems can greatly improve wastewater treatment efficiency while remaining economically and ecologically friendly. However, the method should be tested using natural wastewater containing both nutrients. Furthermore, future studies should examine potential synergies between zeolite substrates and microbial communities and focus on long-term performance evaluations in full-scale operating wetland systems. In addition, although zeolite addition to CW substrates can promote plant-microhe interactions, enhance nitrogen removal, and increase microbial diversity, excessive addition may affect redox dynamics and substrate regeneration, requiring careful optimization.  
Conceptualization, G.D.G.; methodology, G.D.G.; formal analysis, G.D.G., P.P. and N.C.; investigation, G.D.G., P.P. and N.C.; resources, G.D.G.; writing--original draft preparation, G.D.G., P.P. and N.C.; writing--review and editing, G.D.G., P.P. and N.C.; visualization, G.D.G.; supervision, G.D.G. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data supporting the research findings of this study are available from the corresponding author upon request.  
The authors declare no conflicts of interest.