Abstract: Direct interspecies electron transfer (DIET) has a low dependence on diffusive mass transfer. In anaerobic digestion projects of urban organic solid waste with high solid content and ammonia nitrogen stress, DIET can serve as an additional methanogenic pathway. However, electroautotrophic methanogens that are known to participate in DIET lack conductive pili or outer membrane cytochromes, and extracellular electrons must cross the electrically inert cell membrane to enter the cell interior and participate in the CO? reduction process. Studies have shown that low-voltage electrical stimulation can improve the conductivity of membrane-bound proteins, but the effect is mainly concentrated in the biofilm enriched at the cathode, and continuous power supply will lead to excessive energy consumption, which is not conducive to large-scale engineering applications. In this study, granular activated carbon (GAC) was used as a packing material in the electrode coupled with intermittent power supply to investigate its impact on the anaerobic digestion performance of urban organic solid waste. The results showed that the GAC-packed electrode could extend the influence of the electric field from the cathode to its surface, increasing the methanogenic capacity by 26%. Cyclic voltammetry scanning was used in combination with the Randles-?ev?ík equation to calculate the electron transfer coefficient of the microbial film, and it was found that the microbial film on the GAC surface had more than double the electron transfer coefficient compared to the sludge in the reactor. During intermittent power supply, GAC could retain some of the electric field’s influence, and in the closed-circuit operation phase, the biofilm on the GAC surface had a stronger electrical signal response to scanning electrochemical microscopy and electrochemical Fourier transform infrared spectroscopy. Microbial community analysis revealed that adding GAC as a packing material in the electrode could enrich more methanogenic archaea related to DIET, for example, the relative abundance of Methanospirillum on activated carbon (39.86%) was much higher than that of the control group (21.45%). When the GAC was coupled with intermittent power supply, the relative abundance of Methanospirillum decreased from 39.86% to 25.84% during open-circuit operation.

Key words: urban organic solid waste, anaerobic digestion, direct interspecies electron transfer, intermittent power supply, granular activated carbon-filled electrode