## 3 Results and Discussion
### Effluent Characterization at Optimal Conditions
#### 3.4.3 Evolution of Organic Matter Using UV-VIS and FTIR Spectra  
Using UV-VIS spectroscopy, it was possible to monitor the aromatic structures of the generated effluents. The absorbance at 254 nm (ABS\({}_{254}\)) was considered an indirect measure of the degree of aromaticity [20]. The EC process reduced ABS\({}_{254}\) by 35% (4.9 AU to 3.6 AU) and the EO process reduced the value by 43% (4.9 AU to 3.1 AU). It could be established that, in both processes, there was a reduction in aromaticity, as confirmed by the decreases in COD and DOC values, as well as the decrease in humic fractions indicated in Section 3.4.1. A decrease in the ABS\({}_{254}\) value in treated leachates has been confirmed in other studies [98, 99, 100]. The decrease in ABS\({}_{254}\) also led to a decrease in color, owing to the high coloring power of HA. The UV-VIS spectra of the analyzed samples are included in the Supplementary Materials section (Figure S1).  
The FTIR spectra allowed the identification of functional groups in the organic matter present in the evaluated sample, providing information on its evolution in the treatment system. In the FTIR spectra shown in Figure 10, a change in the functional groups associated with the removal of organic matter generated by the treatment processes was observed. The peak at 1650 cm\({}^{-1}\) could be related to the presence of the C=C bond by an isolated torsion vibration, indicating the presence of aromatic compounds [101], since the matrix under study was leached. This peak was directly related to the presence of humic substances. When evaluating the samples, it was observed that this peak was eliminated by the treatment system, indicating the effectiveness of electrochemical treatments in the degradation of recalcitrant compounds. This could be confirmed by the increase in biodegradable COD in the effluents, as well as the increase in BI. The peaks at 1440 cm\({}^{-1}\) and 1380 cm\({}^{-1}\) could be associated with the presence of -CH\({}_{2}\) and -CH\({}_{3}\) bonds caused by deformation vibration [101], indicating the presence of aliphatic compounds in simple bonds. The samples showed an increase in these peaks with the proposed treatment system from zero presence in the raw leachates to very pronounced peaks in the effluents of EC and EO. The effectiveness of the proposed system in the degradation of recalcitrant organic matter was confirmed. The peak at 1110 cm\({}^{-1}\) was due to the presence of the C-0 bond caused by the stress vibration of single-chain aliphatic compounds [102, 103]. In the effluents evaluated, an increase in this peak was observed from a very small peak in the raw leachate to a very pronounced peak in the EO effluent. The increase in this peak indicated the degradation of recalcitrant organic matter. The peak at 880 cm\({}^{-1}\) could be related to the C-H bond of flexion in aliphatic compounds. It was observed that the treatment generated an increase in this peak, starting from a zero peak in the raw leachate to a pronounced peak in the EO effluent. This confirmed the degradation of recalcitrant compounds to compounds with simpler structures [104]. Finally, the peak at 610 cm\({}^{-1}\) could have had two distinct origins. The first was the vibration of O-H with an out-of-plane flex [102] or a vibration that was twice degenerated by the presence of CO\({}_{2}\). CO\({}_{2}\) is a linear molecule that does not rotate around the molecular axis, generating two equivalent normal vibrations, which would be stretching vibrations that would have the same frequency of vibration, precisely causing double degenerate vibration. A possible source of this CO\({}_{2}\) in the samples was the presence of air in the samples and, at the time of measurements, there were several people in the laboratory. Although the background spectrum was measured to eliminate residual peaks, this situation occurred.