# Kinetics and Thermodynamics of Efficient Phosphorus Removal by a Composite Fiber
## 3 Results and Discussion
### Adsorption Kinetics at Different Temperatures
#### 3.1.3 Influencing Factors  
Effect of Adsorbent Dosage on Phosphorus Removal  
The more the fiber was dosed, the higher the phosphorus removal rate, but the lower the adsorption capacity (Table 5). When the fiber dosage increased, the usable surface area of the fiber increased. More \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Temperature (\({}^{\circ}\)C)**} & \multicolumn{3}{c}{**Pseudo-First-Order Kinetic Model**} & \multicolumn{3}{c}{**Pseudo-Second-Order Kinetic Model**} \\ \cline{2-7}  & \(Q_{e}\) & \(K_{1}\) & \(R^{2}\) & \(Q_{e}\) & \(K_{2}\) & \(R^{2}\) \\ \hline
15 & 0.666 & 0.097 & 0.9956 & 0.831 & 0.119 & 0.9949 \\
25 & 0.759 & 0.122 & 0.9706 & 0.918 & 0.147 & 0.9976 \\
35 & 0.819 & 0.135 & 0.9687 & 0.976 & 0.159 & 0.9954 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Kinetics of phosphorus removal by ZSFB composite fiber at different temperatures. Figure 5: Adsorption kinetic curve of ZSFB composite fiber at different temperatures. adsorption sites for phosphorus exist, and the phosphorus was more easily combined with the active sites and hence was removed; however, since the total amount of phosphorus in the solution was constant, the amount of phosphorus adsorbed per unit mass of the composite fiber decreased as the dosage of the composite fiber increased. When the dosage was small, the removal rate of phosphorus increased rapidly. For example, the removal rate of adding 1 g of the composite fiber was 14.71% higher than that of adding 0.5 g. When continuing to increase the dosage, the positive effect on removal rate gradually decreased until it stopped as the phosphorus was completely removed. When the dosage was 3.5g, the residual phosphorus concentration was 0.327 mg/L, which met the class A demands of \"discharge standard of pollutants for municipal wastewater treatment plant\" (GB18918-2002) with an adsorption capacity of 0.276 mg/g. Therefore, the ZSFB composite fiber can be applied to the advanced phosphorus removal, and it can be considered that the optimum dosage is 3.5 g at a phosphorus concentration of 10 mg/L. However, for the difference in phosphorus concentration in different sewage treatment plants, it is necessary to conduct experiments to determine the optimal dosage for each plant. The phosphorus removal performance was best when the pH level was 4 with a removal efficiency of 90%, and the phosphorus removal performance at pH 10 was slightly better than that at pH 7 (Figure 6). Therefore, we can conclude that in the range of pH 4 to 10, the acidic condition is beneficial to improve the phosphorus removal performance of the composite fiber, and the alkaline condition has little effect on that. This is because under acidic conditions, the composite fiber releases more metal ions, such as Fe\({}^{3+}\) and Ca\({}^{2+}\), which combine with the phosphate to form precipitates, and the phosphorus is removed. Under alkaline conditions, although the release of metal ions is inhibited, Fe\({}^{3+}\) combined with the modified adsorption substrates easily forms Fe(OH)\({}_{3}\) flocculant on the surface of the fiber, which is beneficial to the adsorption and precipitation of phosphate. Moreover, the activity of the alkali-activated adsorption substrates will be improved, so the overall performance of the composite fiber is slightly improved under alkaline conditions [25]. Therefore, compared with the neutral condition, the acidic or alkaline conditions (\(4\leq\mathrm{pH}\leq 10\)) did not reduce the phosphorus removal effect of the composite fiber. It can be seen that the composite fiber performed well under both acidic and alkaline conditions.