The microbial electrolysis cell combined with anaerobic digestion for high salinity landfill leachate treatment: Operation parameter optimization, microbial analysis and degradation pathways

The high salinity of landfill leachate can enhance electron transfer and salt tolerance within the MEC-AD system. The influence of various operational parameters, including applied voltage, electrode spacing, and cathode area were investigated under high salinity conditions. Orthogonal experiments determined that the primary factors influencing COD removal during intensive MEC-AD treatment of landfill leachate were electrode spacing, applied voltage, and cathode width, in descending order of impact. The optimal parameter combination was identified as R3 (applied voltage = 0.6 V, electrode spacing = 2.5 cm, cathode width = 8 cm), achieving a 51.3 % COD removal efficiency. The structure of heterocyclic aromatic hydrocarbons was broken down into conjugated unsaturated bonds before further degradation, leading to improved metabolism of proteins and humus-related substances. GC-MS analyses demonstrated the MEC-AD system's capacity to degrade long-chain alkanes and ester organics present in landfill leachate. After electrical stimulation by electroactive bacteria and then degraded by anaerobic bacteria, including norank_f_norank_o_SBR1031, norank_f_A4b, and Pseudomonas (with enrichment percentages of 5.8-31.8 %, 2.3-8.6 %, and 1.2-18.5 %, respectively). The biodegradation of landfill leachate was enhanced by the synergistic effect of the two bacteria.