Effect of chloride ions on the simultaneous electrodialysis and electrochemical oxidation of mature landfill leachate

An attempt has been made to improve the treatment efficiency of mature landfill leachate prior to the existing biological treatment. In this study, electrochemical oxidation (EO) was applied as a pre-treatment to remove organic contaminants and was simultaneously combined with electrodialysis (ED) to remove ionic constituents, such as ammonium and phosphate. A laboratory-scale electrochemical reactor was designed by utilizing a carbon graphite anode and a stainless steel cathode and separated by an anion exchange membrane (AEM) and cation exchange membrane (CEM), creating a three-compartment reactor. The oxidation of the organic pollutant would occur in the anodic compartment, while the targeted ammonium and phosphate ions would be migrated and accumulated in the central compartment. The treatment process was performed in a batch recirculation time of 12 h at a constant supplied current of 0.25 A and evaluated by means of the initial leachate pH (i.e., original pH value of 7.85; adjusted pH value of 5.50 and 8.50) and three different initial chloride concentrations. The higher the chloride concentration in the leachate, the higher the removal efficiency, except for total phosphate. The highest chemical oxidation demand (COD) removal was 86.2% (0.88 g W⁻¹ h⁻¹), at an initial leachate pH value of 7.85 with the addition of 2 g L⁻¹ of NaCl. Furthermore, under the same conditions, the ammonium, total phosphate, and chloride removals were 85% (0.44 g W⁻¹ h⁻¹), 89% (0.08 g W⁻¹ h⁻¹), and 83% (0.69 g W⁻¹ h⁻¹), respectively. Also, the concentrated ionic compounds in the central compartment can lower the energy consumption and can possibly be further treated or managed.