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Electrochemical treatment of mature landfill leachate using Ti/RuO2–IrO2 and Al electrode: optimization and mechanism

Today, improving the elimination of refractory pollutants in landfill leachate through electrochemical oxidation technology has attracted considerable attention. In this study, a combination of anodic oxidation and cathodic coagulation process using Ti/RuO2–IrO2 and Al electrodes, was adopted to treat the mature landfill leachate with a very low biodegradability ratio (BOD5/COD) of 0.12. The effects of current density, pH, and the chloride ion concentration on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH3–N) were investigated by response surface methodology (RSM). The optimum condition of 83.7% COD and 100% NH3–N removal was achieved with a current density of 0.1 A cm−2 and a pH of 6.37, the chloride ion concentration 6.5 g L−1, and an electrolytic time of 150 min. In addition, heavy metals were partly removed. A main degradation mechanism of the pollutants, including oxidation, coagulation and precipitation, was elucidated by gas chromatography-mass spectrometry (GC-MS), environmental scanning electron microscopy coupled with energy dispersive spectrometer (ESEM/EDS) and Fourier transform infrared spectroscopy (FT-IR) analysis of organic components in landfill leachate and sludge generated at the cathode. These results indicated that the electrochemical processes could be a convenient and efficient method for the treatment of landfill leachate.