Intermittent electrical stimulation as a selective enrichment strategy for electrotrophic methanogens in CO2-to-CH4 microbial electrosynthesis

Artikel i vetenskaplig tidskrift, 2026

Biogas derived from anaerobic digestion (AD) has emerged as a compelling renewable energy carrier with carbon-neutral characteristics, but the high CO2 content and low calorific value in raw biogas lower the energy density of the fuel and limit its direct connection to natural gas pipelines. Microbial electrosynthesis (MES) offers an electrochemically driven pathway for recycling endogenous CO2 into CH4, thereby enhancing the energetic value and the economic viability of AD systems. The slow acclimation of electroautotrophic microbial communities on biocathodes, often requiring several months, remains a critical bottleneck that necessitates the development of effective enrichment strategies for practical MES implementation. This article presents an intermittent applied potential (IAP) strategy that leverages the selective enrichment of electrotrophic methanogens, predominantly Euryarchaeota-affiliated hydrogenotrophic genera such as Methanobacterium and Methanobrevibacter, to drive efficient CO2-to-CH4 bioconversion. The IAP-implemented MES system operating at −1.0 V (vs. Ag/AgCl) showed exceptional upgrading performance, achieving 97 ± 1% CH4 purity, a volumetric productivity of 8.34 ± 0.2 L m⁻²cat day⁻¹, and an energy efficiency of 48 ± 3% with a faradaic efficiency of 91 ± 1.2%. The application of IAP substantially accelerated system start-up, reducing the initiation period to less than 10 days across diverse inocula, including food waste and mixed wastewater. The developed IAP strategy establishes a robust and scalable approach for accelerating MES start-up and maximizing biomethane production from AD effluents.