Electric Field-Driven Direct Interspecies Electron Transfer for Bioelectrochemical Methane Production from Fermentable and Non-Fermentable Substrates

Abstract

The bioelectrochemical methane production from acetate as a non-fermentable substrate, glucose as a fermentable substrate, and their mixture were investigated in an anaerobic sequential batch reactor exposed to an electric field. The electric field enriched the bulk solution with exoelectrogenic bacteria (EEB) and electrotrophic methanogenic archaea, and promoted direct interspecies electron transfer (DIET) for methane production. However, bioelectrochemical methane production was dependent on the substrate characteristics. For acetate as the substrate, the main electron transfer pathway for methane production was DIET, which significantly improved methane yield up to 305.1 mL/g chemical oxygen demand removed (CODr), 77.3% higher than that in control without the electric field. For glucose, substrate competition between EEB and fermenting bacteria reduced the contribution of DIET to methane production, resulting in the methane yield of 288.0 mL/g CODr, slightly lower than that of acetate. In the mixture of acetate and glucose, the contribution of DIET to methane production was less than that of the single substrate, acetate or glucose, due to the increase in the electron equivalent for microbial growth. The findings provide a better understanding of electron transfer pathways, biomass growth, and electron transfer losses depending on the properties of substrates in bioelectrochemical methane production.

Electrostatic Fields Promote Methanogenesis More than Polarized Bioelectrodes in Anaerobic Reactors with Conductive Materials

“…5,31 The redox peak potentials for EEB and EMA are known to be in the range −0.20 to 0.41 V versus Ag/AgCl and −0.07 to −0.41 V versus Ag/AgCl, respectively. 5,34,36 For AC, the oxidation peak was 0.01 V versus Ag/AgCl, and there were two reduction peaks at 0.17 and −0.38 V versus Ag/AgCl. The oxidation peak and the second reduction peak appeared to be the activities of EEB and EMA, based on their reported potential ranges (Figure 2a).…”

“…This confirms that cDIET is advantageous over IIET in kinetics and thermodynamics for methane production. 5,35,36 Polarized Bioelectrode-driven DIET. In ACPB, the cumulative methane production increased over time in a pattern similar to that in AC (Figure 1a).…”

“…The redox peaks of the CV indicate electrochemically active substances that include biotic and abiotic redox substances. 32,36,37,43 EEB and EMA belong to the biotic redox substances, and there are several types of abiotic substances, including flavins, quinones, and humic substances. 5,31 The redox peak potentials for EEB and EMA are known to be in the range −0.20 to 0.41 V versus Ag/AgCl and −0.07 to −0.41 V versus Ag/AgCl, respectively.…”

“…Clostridium quinii was an abundant bacterial species in AC and ACEF and is a commonly observed EEB species in bioelectrochemical systems. 5,36 In archaeal groups, a clear difference in the dominant groups appeared at the genus level. Genus Methanocorpusculum was the predominant group in control.…”

“…34,35 It indicates that electrostatic fields enrich the bulk medium with EAM, and drive bDIET for methane production. 36 The electrostatic field-driven DIET in the bulk medium is not proportional to the electrode surface area, with fewer electrode-related issues.…”