This study systematically examined the effect of different microbial electrolysis cell (MEC) components (i.e., anode, cathode, and suspension) on CH4 production in MEC-anaerobic digestion (MEC-AD) system. The impact of pre-enriching the anode with Geobacter sulfurreducens and the cathode with hydrogenotrophic methanogens was evaluated. CH4 production was 14 ± 4 % higher in reactors with pre-enriched electrodes (PEE) than virgin electrodes (VE) under both open and closed-circuit conditions, demonstrating the advantages of electrode pre-enrichment. Closed circuit reactors (PEE-CC & VE-CC) exceeded open circuit reactors (PEE-OC & VE-OC) in CH4 production by 16.5 ± 2 %, underscoring the importance of bioelectrochemical processes. VE-OC reactors produced 12 ± 2 % more CH4 than AD without electrodes (AD-NE), which recorded the lowest CH4 production (306 ± 5 ml), highlighting the role of biomass retention. The suspension contributed most significantly to CH4 production in all MEC-AD reactors (43–62 %), followed by the cathode (21–32 %) and the anode (7–19 %). G. sulfurreducens and D. acetexigens dominated the anodes of PEE-CC and VE-CC reactors, respectively, while Methanobacterium was prevalent on the cathode. The detection of 19 diverse methanogen species underscores the metabolic diversity of the system. These results highlight the synergistic effects of electrode pre-enrichment, bioelectrochemical processes, and biomass retention in enhancing AD performance by improving system stability and robustness.