# A Three-Dimensional Electrochemical Process for the Removal of Carbamazepine
## 3 Results and Discussion
### 2D Electrochemical Process Operational Conditions
#### 3.1.2 Effect of Interelectrode Distance, Reaction Time, and Current Density on CBZ Removal  
To assess the effect of interelectrode distance on CBZ removal, two different distances were tested (3.5 and 7.5 cm). It can be seen in Figure 2 that 3.5 cm resulted in a higher CBZ removal rate. When the interelectrode distance was 7.5 cm, the CBZ removal was 80% after 45 min, while at d = 3.5 cm, CBZ was completely removed after 10 min. This might be due to the short distance, which favored the mass transfer [45]. Thus, an interelectrode distance of 3.5 cm was chosen to continue the work.  
Figure 1: Effect of the anode material on CBZ removal in aqueous solutions (operational conditions: current density = 6.67 mA/cm\({}^{2}\); inter-electrode distance = 3.5 cm; NaCl = 0.1 M; CBZi = 10 mg/L; pH = 5; reaction time = 10 min; cathode = STS).  
The effect of the reaction time on CBZ removal can be analyzed using Figure 2. With the increase of the reaction time, the production of strong oxidizing substances in the reactor rose, causing an increase in the CBZ removal rate [45]. However, an increase of the reaction time corresponded to an increase of the hydraulic retention time in continuous operation, and consequently larger reactors and higher energy consumption. Therefore, it was most appropriate to select the minimum reaction time that allowed a high removal efficiency, which was 10 min for 100% removal in the studied system.  
As stated by [PERSON] et al. [46], current density (j) is an important parameter that can be directly controlled during the electrochemical oxidation process. Therefore, different j values were tested, placing the anode and cathode at different distances, and the results (Table 2) showed that an increase in j had a positive impact on the removal of CBZ. A higher current density resulted in a higher cell potential, and consequently a higher energy consumption for the same reaction time (10 min). Considering the degradation efficiency and energy consumption, using a 3.5 cm interelectrode distance, the optimum j for the 2D process should be 6.67 mA/cm\({}^{2}\). These results also highlighted the fact that an increase in potential does not translate into greater efficiency removals.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**j (mA/cm\({}^{2}\))**} & **Interelectrode Distance (cm)** & **CBZ Removal (\%)** & **Potential (V)** & **ECon (Wh/g)** \\ \hline \multirow{2}{*}{6.67} & 3.5 & 96.4 & 5.40 & 68.7 \\ \cline{2-5}  & 7.5 & 80.2 & 8.20 & 118 \\ \hline \multirow{2}{*}{13.30} & 3.5 & 99.3 & 7.70 & 91.2 \\ \cline{2-5}  & 7.5 & 99.1 & 16.5 & 193 \\ \hline \multirow{2}{*}{26.70} & 3.5 & 99.9 & 13.6 & 158 \\ \cline{2-5}  & 7.5 & 99.2 & 25.8 & 301 \\ \hline \end{tabular} \({}^{\text{O}}\)Operational conditions: NaCl = 0.1 M; conductivity = 13.6 \(\pm\) 0.2 mS/cm; CBZi = 10 mg/L.  
\end{table}
Table 2: Current density, interelectrode distance, CBZ removal (%), potential, and energy consumption for the 2D electrochemical removal of CBZ from aqueous solutions using an MMO anode and an STS cathode.  
Figure 2: Effect of interelectrode distance on the removal of CBZ from aqueous solutions (operational conditions: j = 6.67 mA/cm\({}^{2}\); NaCl = 0.1 M; CBZi = 10 mg/L; pH = 5; reaction time = 45 min; cathode = STS; anode = MMO).