Microbial electrosynthesis of methane in an up-scaled zero-gap cell

Area of Science:

• Biotechnology
• Electrochemistry
• Environmental Science

Background:

• Microbial electrosynthesis (MES) is a promising technology for converting carbon dioxide (CO2) into valuable products.
• Low energy efficiency and challenges in scaling up are significant obstacles for MES implementation.

Purpose of the Study:

• To develop and assess an up-scaled zero-gap MES reactor for enhanced energy conversion and methane production.
• To investigate the impact of applied voltage on reactor performance and microbial community dynamics.

Main Methods:

• An up-scaled zero-gap MES reactor with a 30-cm flow path was designed and operated.
• Applied voltages were varied to evaluate current density, methane production, coulombic efficiency, and energy efficiency.
• In-situ hydrogen generation was simulated to understand its role in electron transfer.
• Microbial community analysis was performed along the reactor's flow path.

Main Results:

• Increasing cell voltage from 2.3 V to 2.7-2.8 V boosted current density by 131% to 17.5 A m-2.
• Methane production increased from 1.4 to 6.9 L/L-d with high coulombic efficiencies (>95%).
• A peak energy efficiency of 45.2% for methane synthesis was achieved at 30 °C.
• Simulations confirmed hydrogen's crucial role in electron transfer for methane production.
• Microbial analysis showed stable dominance of Methanobacterium, indicating consistent functionality.

Conclusions:

• The up-scaled MES reactor demonstrates effective CO2-to-methane conversion with high energy efficiency.
• Optimized operational parameters and in-situ hydrogen generation are key for successful scale-up.
• MES technology is viable for industrial applications without compromising efficiency or microbial synergy.