## 4 Conclusions  
The leachate sampled at the Bordo Poniente landfill was of the stabilized type, with BI values of 0.094, COD, DOC, color, and NH\({}_{3}\)-N of 3400 \(\pm\) 100 mg L\({}^{-1}\), 1200 \(\pm\) 50 mg L\({}^{-1}\), 3200 \(\pm\) 100 Pt Co U, and 660 \(\pm\) 30 mg L\({}^{-1}\), respectively.  
The optimal operating conditions for the EC and EO processes were established to maximize COD removal. DOC, COD, color, and NH\({}_{3}\)-N removal efficiencies of 69%, 63%, 94%, and 50%, respectively, were achieved in the EC process under optimal conditions (I: 4.3 A, agitation: 120 RPM, and pH: 7). For the EO process the removal efficiencies of 86%, 82%, 99%, and 81% for DOC, COD, color, and NH\({}_{3}\)-N, respectively, were achieved under the best conditions (NaCl: 1.0 g L\({}^{-1}\), distance between electrodes: 0.75 cm, I: 2 A, and pH: 7).  
The proposed treatment improved the biodegradability of the effluent. CODb increased from 26% to 39% in the EC process, resulting in 58% CODb in the effluent from the EO process. As anticipated, the EC process eliminated more HA than FA (69% and 63%, respectively). A total of 40 and 55 percent of HA and FA, respectively, were eliminated during the EO process.  
The EC process eliminated the interference of colloidal species in the leachates; it proved to be a suitable alternative to the first stage of treatment. Recalcitrant organic matter could be effectively converted into biodegradable materials and CO\({}_{2}\) using EO.  
Owing to the low reactivity of recalcitrant compounds, the rate at which organic matter is degraded to CO\({}_{2}\) is limited by reaction kinetics.  
Figure 10: FTIR spectra of leachates and effluents at optimum conditions. AU—absorbance units.  
Recalcitrant organic matter undergoes EC and EO processes that alter its chemical structure, changing the absorption characteristics of the electromagnetic spectrum at various wavelengths, including ultraviolet, visible, and infrared.  
Using coupled EC-EO processes as part of the treatment process, this study helped to better understand the variability in the evolution of organic matter.  
The optimal conditions proposed in this investigation were applicable to sampled leachates. If leachates of other origins are to be treated, further experimental tests would need to be carried out because of the variability in leachate composition due to the particular conditions of each landfill.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13095605/s1](https://www.mdpi.com/article/10.3390/app13095605/s1)]([https://www.mdpi.com/article/10.3390/app13095605/s1](https://www.mdpi.com/article/10.3390/app13095605/s1)), Figure S1: the UV-VIS spectrum of raw leachates and effluents was included as supplementary material under optimal conditions of EC and EO processes.  
Conceptualization, A.M.-C. and M.N.R.-V.; methodology, A.M.-C. and M.N.R.-V.; validation, M.N.R.-V.; formal analysis, M.N.R.-V.; investigation, A.M.-C.; resources, M.N.R.-V.; writing--original draft preparation, A.M.-C.; writing--review and editing, M.N.R.-V.; supervision, M.N.R.-V.; project administration, M.N.R.-V.; funding acquisition, M.N.R.-V. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the UNAM project. Project No. R-275, Name of the project \"Investigation Lines under Dr. [PERSON]\".  
Not applicable.