## 3 Results
### Removal of Ammonium and Phosphate in PAP Systems  
The removal efficiency during a typical rainfall for NH4+-N and TP was shown in Figure 4. A declined trend was observed in the effluent water quality in the PAP system as the duration of rainfall was prolonged. The effluent water quality order with the whole rainfall event processing was MZP-PM > zeolite bedding > limestone bedding. The results showed that the collective removal of nutrients by zeolite (33.7-62.7%) was slightly higher than that of limestone (26.3-56.4%) (Figure 4) whilst the heights of zeolite applied in the PAP system were the same. The amounts of nutrients removed by the limestone PAP system were much lower. It may be due to the higher adsorption potential of the zeolite of the Langmuir model (Table 1). On the other hand, the removal was insufficient because the high concentrations of nutrients in the effluent would adversely affect the aquatic \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Pollutants**} & \multicolumn{4}{c}{**Langmuir**} & \multicolumn{4}{c}{**Freundlich**} \\ \cline{3-8}  & & **Qmax (mg/g)** & **R2** & **K\({}_{\text{L}}\) (L/mg)** & **K\({}_{\text{F}}\) (mg/g (L/mg)\({}^{1\text{In}}\)** & **1/n** & **R2** \\ \hline \multirow{2}{*}{Limestone} & NH4+-N & 1.31 & 0.992 & 0.053 & 0.11 & 0.71 & 0.917 \\  & TP & 0.55 & 0.997 & 0.103 & 0.17 & 0.59 & 0.981 \\ \multirow{2}{*}{Zeolite} & NH4+-N & 3.34 & 0.986 & 0.036 & 0.32 & 0.43 & 0.956 \\  & TP & 0.42 & 0.994 & 0.112 & 0.14 & 0.63 & 0.954 \\ \multirow{2}{*}{MZP-PM} & NH4+-N & 9.72 & 0.972 & 0.028 & 0.91 & 0.39 & 0.923 \\  & TP & 1.23 & 0.965 & 0.32 & 0.23 & 0.49 & 0.946 \\ \hline \hline \end{tabular} K\({}_{\text{L}}\) and K\({}_{\text{F}}\) are the correlation constants of Langmuir and Freundlich models respectively, n is an empirical constant reflecting the adsorption capability, R2 is the correlation coefficient in the fitting process.  
\end{table} 
Table 1: [PERSON] and [PERSON] model parameters for NH4+-N and TP adsorption in zeolite, limestone and MZP-PM, and coefficients of determination for the models fits the data (R2). Figure 3: Adsorption isotherms of NH4+-N (**a**) and TP (**b**) at pH 6.5 for zeolite, limestone and MZP-PM. (C\({}_{\text{e}}\) is the equilibrium concentration of pollutants, mg/L; qe is the adsorption capacity at equilibrium, mg/g). organisms and plants in the urban rivers [30]. The post treating with a horizontal filter column packed with MZP-PM gave greater removal of nutrients (82.2% NH4\({}^{*}\)-N and 81.9% TP). An additional amount of nutrients was removed by MZP-PM, equivalent to 4.2% of the volume of zeolite and limestone, which was considerable. It is due to the extremely elevated adsorption ability of MZP-PM (Langmuir adsorption capacities of 9.72 and 1.23 mg/g for NH4\({}^{*}\)-N and TP (Table 1) compared with zeolite and limestone in the range of 1.31-3.34 mg/g for NH4\({}^{*}\)-N and 0.42-0.55 mg/g for TP). The adsorption capacity of MZP-PM was 3-8 times greater than that of zeolite and 2-3 times greater than that of limestone. Batch adsorption data in Table 1 showed that MZP-PM had a higher adsorption capacity to NH4\({}^{*}\)-N than that of TP. It had been reported that modified zeolite adsorbents exhibited higher adsorption capacity [19; 26]. However, in the PAP system, the mixture of nutrients with MZP-PM had a higher adsorption capacity for TP because of the lower influent concentration of TP (1.2 mg/L) than NH4\({}^{*}\)-N (5.2 mg/L). Nevertheless, both the NH4\({}^{*}\)-N and TP were almost completely removed by MZP-PM in the initial stages of the rainfall event (Table 2). The removal efficiency of MZP-PM to NH4\({}^{*}\)-N and TP decreased from 90.6% to 74.5% and from 92.6% to 72.9% as the duration of the rainfall event (Figure 4). This result was because of a permanent number of adsorption sites on the MZP-PM surface for a fixed dose. As the rainfall event was enhanced, the adsorption among nutrients would decrease so that the adsorption efficiency becomes reduced.