Effects of applied voltages on electron transfer pathways for bioelectrochemical methane production from maize straw

The electron transfer pathways for CH4 production from maize straw are investigated in the bioelectrochemical anaerobic digestion (BEAD) under different applied voltages of (0.5–12) V, and compared to that of the conventional anaerobic digestion. The CH4 yield is 589.8 mL/g Volatile solid (VS) in BEAD reactor under the applied voltage of 4 V, which is remarkably higher than the 175.7 mL/g VS of the control reactor and the other BEAD reactors of (0.5, 1, 2, 8) V. The CH4 production was mainly improved by the direct interspecies electron transfer (DIET) activated by electroactive microorganisms in the bulk solution, rather than that on the electrode surface, and varied under different applied voltage. The contribution of biological DIET pathway in the bulk solution was 73.5 % of total CH4 production under the applied voltage of 4 V, followed by the indirect interspecies electron transfer pathway (23.1 %), and electrode pathway (3.4 %). These findings provide critical knowledge for the large-scale use of the bioelectrochemical process, and the recycling of maize straw.