Methanothrix enhances biogas upgrading in microbial electrolysis cell via direct electron transfer

Area of Science:

• Environmental Science
• Biotechnology
• Electrochemistry

Background:

• Biogas upgrading via bioelectrochemical conversion of carbon dioxide (CO2) to methane (CH4) increases biogas calorific value.
• Methanogens, including hydrogenotrophs and acetoclastic methanogens, are key players in these systems, capable of direct electron transfer (DET).

Purpose of the Study:

• To investigate the enhancement of biogas upgrading through bioelectrochemical CO2 conversion to CH4 using a microbial electrolysis cell (MEC).
• To analyze the microbial communities and metabolic pathways involved in enhanced methane production.

Main Methods:

• Operation of a microbial electrolysis cell (MEC) at -500 mV (vs. SHE) for biogas upgrading.
• Analysis of biogas composition changes.
• Enrichment of microbial communities on the cathode.
• Transcriptomic analysis to determine metabolic pathways of methanogens.

Main Results:

• Methane content in biogas increased from 71% to over 90%.
• 8.2% of CO2 was converted to methane.
• Methanothrix (acetoclastic methanogen) and Azonexus (electrogen) were enriched on the cathode.
• Transcriptomics confirmed Methanothrix utilized CO2 reduction on the cathode and acetate decarboxylation in bulk sludge.

Conclusions:

• Direct electron transfer (DET) stimulation in MECs significantly enhances biogas upgrading processes.
• MEC technology effectively converts CO2 to CH4, improving biogas quality.
• Understanding microbial pathways is crucial for optimizing bioelectrochemical systems.