y the evaluated treatments is significant. The T8 and T12 treatments were the ones that obtained the highest percentage of removal, however, the difference between these two removal percentages was not significant, therefore, the T12 treatment was taken (j = 22 mA/cm2, pH = 6) as the best due to the fact that it operated under conditions closer to neutrality, unlike the T8 treatment that operated with a pH value of 4.5 (Figure 3).
Under the operating conditions of the T12 treatment, a 68% removal of the initial COD was achieved, which generated an effluent with 297 mg/L COD.
Figure 3. Analysis of variance between treatments.
Authors such as Norma et al. ,and Ukundimana  have reported greater efficiencies in COD removal (75% - 92%) when applying anodic oxidation on pretreated leachates. However, both studies used BDD electrodes as cathode and anode, which are more expensive and require a more delicate handling. The use of graphite electrodes in pretreated leachate was reported by Feki et al. ,but with a low COD removal (22%), far removed from that achieved in the present study (68%). Obtaining better removal efficiencies at a greater j can be explained by the increase in the diffusion flow of organic matter from the anode, allowing a more efficient oxidation of organic compounds . Whereas, authors such as Chiang et al. ,point out that larger j increases the generation of oxidizing chlorine species, which further favor the elimination of pollutants.
Regarding Color removal, Figure 4 shows that during the five hours of reaction under the conditions of the T12 treatment, color was reduced by 90%, obtaining a final effluent with 158 Pt-Co. This decrease can be related to the degradation of humic and fulvic acids that gives color to leachates and are susceptible to oxidation by hydroxyl radicals produced in anodic oxidation . In addition, although maximum color removal was achieved with the higher pH value, it still remained acidic (pH = 6), and according to Anglada ,acidic conditions in the treatment of wastewater by anodic oxidation favors the release of certain oxidants such as Cl, Cl2 or HOCl− in the anode, which can act directly on the species that give color to the leachate, resulting in better efficiencies in color removal. In general terms, after five hours of electrolysis, and by increasing j from 7 to 22 mA/cm2, the removal rate increased from 30% to 68% in COD and from 76% to 91% in Color.
Anodic Oxidation using graphite electrodes as cathode and anode was effective in removing recalcitrant organic matter present in pretreated leachate, reaching 68% in COD and 91% in color, representing a quality in the final effluent of 271 mg/L and 151 Pt-Co in COD and color, respectively, where the best removal conditions were achieved at a j of 22 mA/cm2 and pH of 6.
Figure 4. Color removal efficiencies at 5 hours of reaction.
According to the results obtained, anodic oxidation can be a viable and economical alternative with the use of graphite electrodes, as a stage of purification in the final treatment of pretreated leachates.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.
Cite this paper
Sánchez-Sánchez, T.J., Nájera-Aguilar, H.A., Gutiérrez-Hernández, R.F., García-Lara, C.M., Araiza-Aguilar, J.A., Bautista-Ramírez, J.A. and Castañón- González, J.H. (2020) Application of Anodic Oxidation with Graphite Electrodes in Pretreated Leachates. Open Journal of Applied Sciences, 10, 69-77. https://doi.org/10.4236/ojapps.2020.103006
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