## 3 Results and Discussion
### Evaluation of the As(V) Removal Capacity of the Ion-Exchange Fabric
The ion-exchange capacity of the IEF was compared with commercial ion-exchange fibers supplied by Kaneka Co. (Table 2); the characteristics of these ion-exchange fibers were presented in our previous studies [13; 14]. The IEF was synthesized by combining SA1 ion-exchange fibers on a polyethylene/polypropylene base; its adsorption capacity was around one-third of those of the commercial ion-exchange fibers. The adsorption capacity of an IEF can generally be regenerated using NaCl, NaOH, and HCl, with the regeneration rate depending on the solution conditions and ion-exchanger properties [15]. As shown in Figure 4d, the regeneration rate with 0.1 M NaCl solution averaged around 95% and decreased slightly as the number of regenerations was increased. The regeneration rate with 0.1 M HCl solution was similar to NaCl (94%) during the first regeneration cycle but decreased significantly compared to NaCl, with an increase in the number of regeneration cycles. On the other hand, the NaOH solution was not able to regenerate the As(V) adsorption capacity of the IEF at all. Figure 4: Effects of (**a**) solution pH (Dose = 2 g/L, initial concentration = 10 mg/L, reaction time = 6 h), (**b**) contact time (Dose = 2 g/L, initial concentration = 10 mg/L), and (**c**) initial As(V) concentration (Dose = 2 g/L, reaction time = 6 h) on As(V) removal by the ion-exchange fabric. (**d**) Regeneration efficiency during 3 reuse cycles with various regeneration solutions (Reaction time = 6 h, regenerant concentration = 0.1 M, regeneration time = 3 h). Removal of Heavy Metals As(V) and Zn(II) and Turbidity According to Solution pH Using the Hybrid Ion-Exchange Fabric/Ceramic Membrane System  
The removal efficiency of the hybrid ion-exchange fabric/ceramic membrane system was evaluated with contaminated solutions of heavy metals and turbidity. First, the variation in flow rate and the Zn(II) removal rate from a Zn + Kaolin solution according to solution pH is shown in Figure 5. Unlike the ceramic filter, the hybrid ion-exchange fabric/ceramic membrane system was able to remove some Zn(II) even at solution pH values of 4 and 6. This is because Zn(II) ions can be chemically bonded with the amine groups on the surface of the ion-exchange fabric under the given pH conditions [26]. However, Zn(II) was not stably removed at solution pH values of 4 and 6, while it was almost completely removed at solution pH values of 8 and 10 during the hybrid process. The removal of Zn(II) at solution pH values of 8 and 10 was caused by the ceramic membrane; the flow rate was stable at pH 8 but changed severely at pH 10. It is well known that the solution pH affects both foulant and the membrane surface, thereby altering the membrane performance significantly [27,28]. The decreased flow rate could be recovered through the backwashing process under all conditions. \begin{table}
\begin{tabular}{c c c} \hline \hline
**adsorbent** & **Conditions** & \(q_{e}\)\({}^{*}\) \\  & & **(mg/g)** \\ \hline KC31 & Initial concentration = 500 mg/L; pH = 8.6; contact time = 360 min & 47.16 \\ SA1 & Initial concentration = 500 mg/L; pH = 8.6; contact time = 360 min & 47.19 \\ SA2 & Initial concentration = 500 mg/L; pH = 8.6; contact time = 360 min & 38.05 \\ IEF & Initial concentration = 500 mg/L; pH = 8.63; contact time = 360 min & 13.29 \\ \hline \hline \end{tabular} \({}^{*}\): \(q_{e}\), equilibrium adsorption capacity.  
\end{table} 
Table 2: Comparison between the As(V) adsorption capacities of the commercial ion-exchange fibers and the novel ion-exchange fabric (IEF). Figure 5: Effect of solution pH on the flow rate and Zn(II) removal rate during the hybrid ion-exchange fabric/ceramic membrane process in Zn + Kaolin solution: (**a**) pH 4, (**b**) pH 6, (**c**) pH 8, and (**d**) pH 10. The variation of flow rate and As(V) removal rate according to solution pH in As + Kaolin solution was also examined (Figure 6). The removal rate of As(V) by the hybrid ion-exchange fabric/ceramic membrane system was higher than that of the ceramic membrane alone.