# A Three-Dimensional Electrochemical Process for the Removal of Carbamazepine
## 3 Results and Discussion
### 3.3D Experiments
#### 3.3.4 Effect on Energy Consumption, Current, and Electric Efficiencies  
[PERSON] et al. (2018) proposed standard figures of merit for the comparison and evaluation of advanced oxidation technologies, based on electric energy consumption and providing a direct link to the electric efficiency (lower values meaning higher efficiency), independently of the nature of the system, and therefore allowing direct comparison of different treatments (Figure 13). The current efficiency was higher in the 3D process (0.21% for all the particulate electrodes) in comparison with the 2D process (0.18%) (Figure 13A). The energy consumption of the 3D process (Figure 13B) was lower when using the biochar TN 1-2 mm (390 Wh/g), followed by the biochar TN \(<\) 75 \(\upmu\)m (394 Wh/g) and SARATECH\({}^{\circled{B}}\) activated carbon (401 Wh/g). The 2D process presented the highest energy consumption (418 Wh/g). The electric energy per order can be defined as the electric energy (kWh) required to degrade a contaminant by one order of magnitude in a unit volume (m\({}^{3}\)) of contaminated water ([PERSON] et al., 2018). Figure 13C shows that the 3D process, mainly using the biochars (2237 and 2709 kWh/m\({}^{3}\) for biochar TN \(<\) 75 \(\upmu\)m and biochar TN 1-2 mm, respectively), reduced the electric energy per order (EEO) when compared with the 2D process (7507 kWh/m\({}^{3}\)). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Processes**} & \multicolumn{2}{c}{**3D**} & \multicolumn{2}{c}{**2D**} \\ \hline \multirow{2}{*}{**adsorbent**} & **Biochar TN** & **Biochar TN** & \multirow{2}{*}{**SARATECH\({}^{\circled{B}}\)**} & \multirow{2}{*}{**None**} \\  & **\textless{} 75 \(\upmu\)m** & **1-2 mm** & & \\ \hline \multirow{2}{*}{\% CBZ removal} & 95.9 & 99.5 & 99.1 & 86.7 \\ \cline{2-5}  & R\({}^{2}\) & 0.9994 & 0.9731 & 0.9991 & 0.9835 \\ \cline{2-5}  & k\({}_{1}\), s\({}^{-1}\) & 0.00112 & 0.00199 & 0.00167 & 0.000635 \\ \cline{2-5}  & Half-life, min & 10.5 & 5.8 & 6.8 & 19.3 \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Second-order \\ model \\ \end{tabular} } & R\({}^{2}\) & 0.9009 & 0.7298 & 0.8387 & 0.9952 \\ \cline{2-5}  & k\({}_{2}\), L/(mol.s) & 237 & 2050 & 1045 & 59.5 \\ \cline{2-5}  & Half-life, min & 1.8 & 0.2 & 0.4 & 6.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: CBZ removal efficiency, regression coefficient, rate constant, and half-life as a function of 3D and 2D processes. Figure 13: Effect of the particulate electrode on the removal of CBZ, represented by bars, and on energy consumption (**A**), current efficiency (**B**), and electric energy per order (**C**), represented by the black lines, and comparison between the 2D and the 3D process (operational conditions: j = 6.67 mA/cm\({}^{2}\); NaCl = 0.1 M; CBZi = 10 mg/L; pH = 7; reaction time = 45 min; interelectrode distance = 7.5 cm; particulate electrode = 1 mg/mL solution; cathode = STS; anode = MMO). [PERSON] et al. [34] reported a maximum current efficiency of 0.7% for the removal of CBZ in the 2D process (using 7.0 mA/cm\({}^{2}\) current density, 5 mg/L initial concentration of CBZ, 500 mg/L NaCl concentration, 60 min reaction time, and aluminum electrodes) and 16% for the 3D process (same experimental conditions except 0.5 g/L of activated carbon and a 10 min reaction time). The removal efficiency was 30 and 90% for the 2D and 3D processes, respectively. The calculated energy efficiency (evaluated through the electric energy per order) was 133,000 and 2520 kWh/m\({}^{3}\) for the 2D and 3D processes, respectively. Considering the obtained results, the 3D process allowed efficient removal of CBZ after a shorter period when compared with the 2D process, decreasing the energy consumption with higher current efficiency. The particulate electrode that presented the best performance when considering the energetic factors, kinetics, removal efficiency, and reaction time was the biochar TN 1-2 mm.