Promoting biomethane production from propionate with Fe₂O₃@carbon nanotubes composites

Using a batch anaerobic system constructed with 60 mL serum bottles, potential of a composite material with Fe₂O₃ nanoparticles decorated on carbon nanotubes (CNTs) to enhance biomethane production was investigated. The composites (Fe₂O₃@CNTs) with well dispersed Fe₂O₃ nanoparticles (4.5 nm) were fabricated by a facile thermal decomposition method in a muffle furnace under nitrogen atmosphere. Compared with Fe₂O₃, Fe₂O₃@CNTs showed a large specific surface area and good electrical conductivity. Supplementation of Fe₂O₃@CNTs to the propionate-degrading enrichments enhanced the methane production rate, which was 10.4-fold higher than that in the control experiment without material addition. The addition of Fe₂O₃@CNTs also not only showed a clearly electrochemical response to flavin and cytochrome C, but also reduced the electron transfer resistance when compared to the control. Comparative analysis showed that Fe₂O₃ in Fe₂O₃@CNTs played a key role in initiating electrochemical response and triggering rapid methane production, while CNTs functioned as rapid electron conduits to facilitate electron transfer from iron-reducing bacteria (e.g., Acinetobacter, Syntrophomonas, and Geobacter) to methanogens (e.g. Methanosarcina).