Elucidating the impacts of voltage application on construction of extracellular electron transfer in semi-continuous anaerobic digestion of kitchen waste

The application of direct current voltage in anaerobic digestion systems facilitates the establishment of extracellular electron transfer (EET) networks, which foster synergistic interactions among microorganisms. In this study, a semi-continuous anaerobic digestion system for kitchen waste was operated under 0.6 and 1.0 V direct current electrical stimulation. The data indicated that at high organic load ratios (OLR = 4.22 gVS/L/day), the 1.0 V system achieved superior stability and methane yield (661.8 ± 25.7 mL/gVS/day), representing a 179.2% increase versus the control (369.4 ± 111.1 mL/gVS/day). Theoretical calculations further indicated that cathodic electron transfer accounted for only 3.38–3.55% of total methane production and 6.99–11.12% of the methane enhancement in the 1.0 V system, suggesting that indirect voltage-mediated regulation dominated the performance gain. Microbial community analysis revealed that applied voltage enhanced microbial interactions, as evidenced by the synchronized enrichment of electroactive microorganisms (Geobacterium) and methanogens (Methanobacterium and Methanosarcina). Functional prediction further indicates the stimulation of methanogenic modules in both electrode surfaces and digestate slurry, with particular enhancement of the CO2-reducing methanogenesis pathway. Notably, distinct spatial heterogeneity was observed: electrode surfaces showed concurrent enrichment of electrogenic bacteria and methanogens, whereas the digestate slurry exhibited selective proliferation of methanogens without corresponding increases in electroactive populations. These findings provide critical insights into voltage-driven methanogenic regulation in kitchen waste anaerobic digestion.