## 3 Results and Discussion
### Industrial Water Treatment  
The most common parameter to be monitored for nontoxic wastewater is COD. The treatment efficiency of the different processes was determined by studying the CODs of wastewater and treated water. The main characteristics of paint-industrial wastewater were a pH value of around 9 and a high value of COD 60 g/L.  
Two dilution ratios (1:1 and 1:3) of industrial wastewater and two different working electric currents (20 A and 30 A) were tested. As a result, four different types of treated wastewater were obtained. In all cases, the COD values were rapidly reduced; however, lower values were obtained when the dilution ratio was 1:3 (\(V\):\(V\)) for working electric current 20 A and 30 A, respectively. The reduction in CODs is shown in Figure 3. The COD was reduced by between 95% and 99% in both systems. The reduction in the COD values reflects that the system worked with a higher working electric current, 30 A, which was more advantageous because the COD values have been reduced from 60 g/L to 0.63 g/L. The COD values of the untreated diluted effluents were evaluated. The COD has been reduced thanks to the dilution into the values of 21.8 g/L and 33.5 g/L for dilution ratio 1:3 (wastewater:deionized water, \(V\):\(V\)) and 1:1 (wastewater:deionized water, \(V\):\(V\)), respectively.  
The most commonly used method for paint-industrial wastewater treatment is the physicochemical treatment method; however, COD removal efficiency is lower in comparison with the hybrid electrothermochemical method, and it depends on the sample  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Analytes** & **Retention Time [min]** & & **Ions [m/z]** & & **LOD [\(\mu\)g/L]** & **Correlation Coefficient** \\ \hline Toluene & 1.330 & 91 & 92 & 65 & 0.19 & 0.9978 \\ Chlorobenzene & 1.593 & 112 & 77 & 114 & 3.22 & 0.9902 \\ Ethylbenzene & 1.627 & 106 & 91 & 78 & 2.07 & 0.9935 \\ Xylenes & 1.700, 1.721 & 105 & 106 & 91 & 4.02 & 0.9921 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The retention times of the identified compounds, the selected fragment ions (m/z), and basic validation parameters.  
Figure 3: The reduction in the COD values using the different parameters during the wastewater treatment process. TW1—dilution 1:1 (treated water 1: deionized water \(V\):\(V\)), working electric current: 20 A; TW2—dilution 1:1 (treated water 2: deionized water \(V\):\(V\)), working electric current: 30 A; TW3—dilution 1:3 (treated water 3: deionized water \(V\):\(V\)), working electric current: 20 A; TW4—dilution 1:3 (treated water 4: deionized water, \(V\):\(V\)), working electric current: 30 A.  
pH and the type of coagulants and flocculants [35; 36; 37]. In paint-industrial effluent treatments, electrochemical methods are also very popular and starting to replace traditional processes. However, in the case of COD removal, they are less effective than the combined hybrid electrothermochemical wastewater treatment with COD removal between 66% and 81% [38; 39; 40]. The new hybrid electrothermochemical wastewater treatment technology provides a similar COD removal, such as [PERSON]'s oxidation process at 99.5% [41]. The comparison of the different treatment processes in the case of COD removal efficiency is shown in Table 2.