## 3 Results and Discussion
### Removal of Ammonium, MEA, and TMAH by Various Processes (Synthetic Wastewater)  
Removal results for ammonium, MEA, and TMAH by the processes examined in this study (GAC, MnCe-GAC, O\({}_{3}\), H\({}_{2}\)O\({}_{2}\), GAC/O\({}_{3}\), GAC/H\({}_{2}\)O\({}_{2}\), MnCe-GAC/O\({}_{3}\), MnCe-GAC/H\({}_{2}\)O\({}_{2}\), GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\), and MnCe-GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\)) are shown in Figure 3 (pH 11, C\({}_{0}\) = 100 mg/L, V = 0.5 L, solid 1g, 0.25 mmol O\({}_{3}\)/min, 0.125 mmol H\({}_{2}\)O\({}_{2}\)/min, 30 min). In general, the removal efficiencies of ammonium and MEA by these processes were better than that of TMAH. For example, the removal efficiencies of ammonium, MEA, and TMAH by MnCe-GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) were 92.3, 71.6, and 42.0%, respectively. This result is in agreement with Lei et al. [11]. They reported that the degradation rate of MEA was significantly higher than that of TMAH. In addition, the ozone processes (O\({}_{3}\), GAC/O\({}_{3}\), and MnCe-GAC/O\({}_{3}\)) had slightly better removal efficiencies (40, 50, and 64% for ammonium removal, respectively) than the H\({}_{2}\)O\({}_{2}\) processes (H\({}_{2}\)O\({}_{2}\), GAC/H\({}_{2}\)O\({}_{2}\), and MnCe-GAC/H\({}_{2}\)O\({}_{2}\); 28, 38, and 61% ammonium removal, respectively) (Figure 3). The removal of ammonium and MEA by the MnCe-GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) process was slightly better than that observed for the GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) process. However, the removal of TMAH by the MnCe-GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) process (42%) was significantly greater than that observed for  
Figure 2: SEM images of (**a**) GAC and (**b**) MnCe-GAC. the GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) process (29%) (Figure 3). The addition of H\({}_{2}\)O\({}_{2}\) could improve the removal of pollutants in wastewater in ozonation processes and it might be due to the formation of \(\bullet\)OH radicals by the conjugated base of H\({}_{2}\)O\({}_{2}\) with ozone [16; 22; 23; 24; 25]. In addition, an overdose of H\({}_{2}\)O\({}_{2}\) might act as a scavenger and react with \(\bullet\)OH instead of ozone. Therefore, the overall removal efficiency might be hindered by the overdose of H\({}_{2}\)O\({}_{2}\). Therefore, the ratio of H\({}_{2}\)O\({}_{2}\)/O\({}_{3}\) applied in the process is important. The stoichiometric molar ratio of H\({}_{2}\)O\({}_{2}\)/O\({}_{3}\) being 1/2 [16] was applied in the study to ensure high efficiency of the treatment processes. As shown in Figure 3, MnCe-GAC/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) had the highest removal efficiencies among these processes for ammonium, MEA, and TMAH removal. This result indicated that the removal mechanism of the process is a combination of adsorption and degradation via catalysis/oxidation. The addition of H\({}_{2}\)O\({}_{2}\) could improve the removal of pollutants in wastewater in ozonation processes. Therefore, this process was used in the subsequent experiments. The solution pH played a significant role in these processes. A higher solution pH (pH 11) had a better ammonium removal than those of pH 3 and pH 7 (Figure 4). For example, the removal of  
Figure 3: Removal of (**a**) Ammonium, (**b**) Monoethanolamine (MEA), and (**c**) Tetramethylammonium hydroxide (TMAH) by various processes (pH 11, C\({}_{0}\) = 100 mg/L, V = 0.5 L, solid 1g, 0.25 mmol O\({}_{3}\)/min, 0.125 mmol H\({}_{2}\)O\({}_{2}\)/min, 30 min). ammonium at pH 3, 7, and 11 by the MnCe-GAC/O3/H2O2 process were 34, 61, and 92%, respectively (C\({}_{\text{o}}\) = 100 mg/L, V = 0.5 L, solid 1g, 0.25 mmol O3/min, 0.125 mmol H2O2/min, 30 min). Similar results were obtained for the removal of TMAH by these processes (Figure 5). The solution pH had a significant impact on the removal of TMAH. In general, the order of removal efficiencies of TMAH is as follows: pH 11 \(>\) pH 7 \(>\) pH 3. At high pH values, ozone decomposes into nonselective hydroxyl radicals which oxidize organic pollutants.