## 3 Results and Discussion
### Characterization of Raw Leachates
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Value** & **\%** & **Parameter** & **Value** & **\%** \\ \hline COD & 3400 \(\pm\) 100 & - & HyL (COD) & 880 \(\pm\) 40 & 24 \(\pm\) 1 \\ BOD\({}_{5}\) & 320 \(\pm\) 20 & - & HA (DOC) & 850 \(\pm\) 30 & 59 \(\pm\) 2 \\ BI & 0.094 \(\pm\) 0.003 & - & FA(DOC) & 330 \(\pm\) 10 & 23 \(\pm\) 1 \\ DOC & 1200 \(\pm\) 50 & - & HyL (DOC) & 260 \(\pm\) 10 & 18 \(\pm\) 1 \\ NH\({}_{3}\)-N & 660 \(\pm\) 30 & - & CODnb & 2500 \(\pm\) 100 & 74 \(\pm\) 1 \\ Cl\({}^{-}\) & 6700 \(\pm\) 200 & - & CODs & 1800 \(\pm\) 100 & 52 \(\pm\) 1 \\ Color & 3200 \(\pm\) 100 & - & CODp & 1600 \(\pm\) 100 & 48 \(\pm\) 1 \\ Eh & 240 \(\pm\) 10 & - & CODsb & 900 \(\pm\) 30 & 49 \(\pm\) 1 \\ HA (COD) & 1900 \(\pm\) 100 & 55 \(\pm\) 3 & CODnb & 900 \(\pm\) 20 & 50 \(\pm\) 1 \\ FA (COD) & 800 \(\pm\) 40 & 22 \(\pm\) 1 & pH & 8.4 \(\pm\) 0.2 & \\ \hline \hline \end{tabular} The results were expressed in mg L\({}^{-1}\), except for BI, Eh (mV), and pH. COD—chemical oxygen demand; BOD\({}_{5}\)—biochemical oxygen demand; BI—biodegradability index; DOC—dissolved organic carbon; NH\({}_{3}\)-N—ammonical nitrogen; N\({}_{7}\)–N—total nitrogen; Cl\({}^{-}\)—chlorides; Eh—oxidation/reduction potential; HA—humic acids; FA—fatvic acids; H\({}_{7}\)—hydrophilic fraction; COmb—non-biodegradable COD; CODB—soluble COD; CODB—particulate COD; COObs—soluble biodegradable COD; CODsub—soluble non-biodegradable COD.  
\end{table} 
Table 3: Results of characterization of raw leachates. tion of volatile fatty acids and the depletion of the leaching force during the methanogenic phase [66; 67]. The BI value obtained for raw leachates was 0.094 \(\pm\) 0.003. BI values are commonly used to provide information on the biodegradability of leachates. Young leachates have a BI of 0.4-0.6 or even more [68] and stabilized leachates have low BI values between 0.05-0.2 [69]. It was confirmed that the sampled leachate belonged to the stabilized type. This was to be expected, given that Stage III of the Bordo Poniente landfill has been closed since 1994, with an age well above 10 years. A BI below 0.1 is a sign of a high content of stabilized and recalcitrant organic matter [30]. This was confirmed by the obtained value of 74% CODnb. Generally, it is recommended that young leachates undergo biological treatment [70]. The low biodegradability of stabilized leachates indicates that physicochemical options are recommended for biological processes [30; 71]. Therefore, the choice of the electrochemical treatment for this project was successful. The raw leachate had a color value of 3200 \(\pm\) 100 Pt-Co U. The color of leachates can be associated with the presence of stabilized organic substances, such as humic substances, mainly HA and FA [60; 72; 73]. Darker leachates are associated with a higher content of humic substances; therefore, the organic matter content can be determined according to the color of the leachate [74]. A decrease in color in the treated leachates implies a reduction in the humic substance content (see Section 3.4.1). Hydrogen sulfide (H\({}_{2}\)S) and NH\({}_{3}\)-N give raw leachates a mild unpleasant smell [75; 76]. A total of 660 \(\pm\) 30 mg L\({}^{-1}\) of NH\({}_{3}\)-N was detected. The biological breakdown of amino acids and other nitrogenous organic materials in MSW results in the presence of NH\({}_{3}\)-N in leachates [30]. Because NH\({}_{3}\)-N is the longest-lasting component of leachate and has a high degree of stability under anaerobic conditions, it is used to assess the contamination risk in landfills [77]. Eutrophication, which is caused by high NH\({}_{3}\)-N values, causes a decrease in dissolved oxygen. The treatment of biological leachates may be halted owing to the toxicity of NH\({}_{3}\)-N [31; 56]. It was possible to verify that the electrochemical treatment options chosen in this study were appropriate. The % of CODp was 48, indicating that the colloidal materials were amenable to EC. CODsnb accounted for 50 percent of the total soluble material.