Treatment of aged leachate by a three-dimensional electrochemical system with biochar as particle electrodes

Aged landfill leachate is a type of refractory wastewater containing high concentrations of humic substances and ammonia nitrogen (NH3-N). A new three-dimensional electrocatalytic oxidation (3D-ECO) system was constructed to treat aged leachate using a composite-loaded metal electrode as the anode, a titanium plate as the cathode, and coconut shell biochar (CBC) as particle electrodes. The conditions for the electrochemical reaction were first optimized, and the pollutant removal effects of the two-dimensional (2D) and 3D systems were compared under optimal conditions. Finally, the electrochemical degradation mechanism was analysed. The results showed that when the initial pH was 5, the current density was 30 mA/cm², the particle addition was 7 g/L, and the electrode plate spacing was 4 cm, the pollutant removal efficiency in the leachate was the highest. At then the removal rates of COD and NH3-N were 90.2% and 30.4%, respectively, while under the same conditions, they in the 2D system were only 41.1% and 17.4%, respectively. The introduction of CBC has increased the removal rate of organic pollutants in leachate by 49.1% and reduced energy consumption by 57.2%. Various active substances such as hydrogen peroxide, hydroxyl radicals, and singlet oxygen played a major role in the degradation of leachate pollutants. The synergy between the anode and the third electrode (75%) enhanced the overall effect of electrochemical degradation of organic pollutants in leachate. Therefore, the introduction of CBC can effectively improve the level of pollutant removal, and the 3D-ECO process is a promising technology for treating aged landfill leachate.