Enhancing proton-coupled electron transfer drives efficient biomethane generation from multiphase anaerobic environments

The enhancement of electron or proton transfer between syntrophic microbes has been widely recognised as a means for improving methane generation through syntrophic metabolism. However, the uncoupled supplementation of electrons and protons in the multiphase environment hinders the balanced uptake of electrons and protons in the cytoplasm of methanogens, limiting methanogenesis efficiency. Herein, the cooperation of a proton-conductive material (PM) and an electron-conductive material (EM) was conducted for enhancing proton-coupled electron transfer (PCET) to drive efficient methanogenesis in anaerobic digestion (AD). The cooperation of the PM and EM significantly increased methane production and the maximum methane generation rate in AD by 76.9% and 103.5%, respectively, compared with the sample without the PM and EM, indicating enhanced methane generation efficiency. Analysis of the physicochemical properties, biochemical components, and microbial dynamics throughout the AD process revealed that the cooperation of the PM and EM improved the metabolism of syntrophic microbes, which was critically dependent on electron and proton transfer. This enhancement was primarily due to the improvement in PCET, as supported by hydrogen/deuterium kinetic isotope effect measurements and genome-centric metatranscriptomic analysis. In conclusion, our findings suggest that the PCET enhancement stimulated efficient membrane-bound enzymatic reactions related to electron-driven proton translocation and facilitated electron and proton supply for CO2 reduction to realise high-efficiency methane generation.