# Regeneration of Activated Carbons Spent by Waste Water Treatment Using KOH Chemical Activation
## 3 Results and Discussion
The total of analysis resulted in the chemically activated ACs were similar with S-AC and H-AC, but the C-AC-A differed (Table 3). The elements without nitrogen, carbon, hydrogen, sulfur, and oxygen could be assumed to be ash. Approximately 14% of total of C-AC-A increased compared to C-AC-W, meaning that ash was reduced by the acid treatment. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{4}{c}{**Surface Concentration (from C 1 s Peak) of (\% at.):**} \\ \hline \multirow{2}{*}{**B.E. (eV) (Assign)**} & **283.6–284.2** & **284.6–284.8** & **285.5–285.6** & **286.7–286.8** & **288.8–289.0** & **290.6–291.1** \\ \cline{2-7}  & **(C-H)** & **(C-C)** & **(C-O/C-O-C)** & **(C=O)** & **(O-C=O)** & **(n-\(\pi\))** \\ \hline \multirow{2}{*}{**S-AC**} & 20.14 & 42.70 & 14.46 & 10.39 & 7.41 & 4.89 \\  & 21.13 & 39.57 & 18.69 & 8.85 & 6.55 & 5.21 \\
**C-AC-W** & 58.51 & 10.69 & 7.86 & 9.32 & 8.42 & 5.21 \\
**C-AC-A** & 16.01 & 39.25 & 14.20 & 10.60 & 9.87 & 10.08 \\ \hline \end{tabular}
\end{table} 
Table 2: Relative concentration of different groups in C 1 s peak based on X-ray photoelectron spectroscopy. Figure 3: X-ray photoelectron spectroscopy analysis of (**a**) S-AC, (**b**) H-AC, (**c**) C-AC-W, and (**d**) C-AC-A. The ash removal was also confirmed by the proximate analysis as shown in Figure 4. The ash content of S-ACs was 30%, which was slightly reduced through the thermal treatment and chemical activation. In particular, the ash content of C-AC-A was sharply reduced. The contents of C-AC-A was similar to the commercial ACs (especially coal-based ACs) [29]. Therefore, this suggests that the most physical properties of C-AC-A were recovered as fresh ACs. The ashes usually were generated from metal ions in the waste water. The S-ACs were collected in the final process of WWTP. During this process, the various metal ions were adsorbed on the AC surfaces, so the water was purified. The adsorbed metal ions were not evaporated during both thermal treatment and chemical activation, and remained on the carbon surface and pores. The metal ions were converted into the ashes, which blocked the pores and covered the active carbon surface [17]. They reduced the surface area and also prohibited the utilization of ACs. The adsorbed metal ions were analyzed by XRF (Figure 5; Table 4). The Ca, Si, and Fe ions were mainly occupied on the S-ACs. In the H-ACs and C-AC-W, the metal composition was not significantly different. However, the composition and amount of metals changed in C-AC-A. In particular, Ca and Si were reduced compared to the others groups. Acetic acid (CH\({}_{3}\)COOH) could dissolve metal ions, including Ca and Si, changing the metal composition and reducing ash content as shown in Figure 5. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Elemental Analysis (wt. \%)**} \\ \cline{2-7}  & **Nitrogen** & **Carbon** & **Hydrogen** & **Sulfur** & **Oxygen** & **Total** \\ \hline
**S-AC** & N.D. & 69.98 & 0.38 & N.D. & 2.27 & 72.64 \\
**H-AC** & N.D. & 73.43 & 0.33 & N.D. & 0.84 & 74.60 \\
**C-AC-W** & N.D. & 71.30 & 0.34 & N.D. & 3.47 & 75.12 \\
**C-AC-A** & N.D. & 86.26 & 0.11 & N.D. & 2.30 & 88.68 \\ \hline \hline \end{tabular} Analysis condition: dry basis. N.D.: not detected.  
\end{table} 
Table 3: Elemental analysis (EA) of prepared ACs. Figure 4: Proximate analysis of the ACs of S-AC, H-AC, C-AC-W, and C-AC-A. The regeneration of S-ACs using the KOH chemical activation increased the specific surface area, which was comparable to the fresh ACs. However, the metal ions present during the water purification process were adsorbed on the ACs and then converted to ashes. The generated ashes were not eliminated through the thermal treatment and chemical activation, leading to the negative effects. The ash removal was essentially required, and the acid washing shown in this study would be suggested.