Granular Carbon-Based Electrodes as Cathodes in Methane-Producing Bioelectrochemical Systems

Area of Science:

• Bioelectrochemical systems
• Renewable energy conversion and storage
• Microbial electrochemistry

Background:

• Methane-producing bioelectrochemical systems (BESs) utilize microorganisms to convert carbon dioxide into methane using electricity.
• These systems offer a promising avenue for renewable electricity conversion and storage.
• Key challenges include achieving high methane production rates and ensuring stable performance under intermittent electricity supply.

Purpose of the Study:

• To investigate the impact of electrode materials (granular activated carbon - GAC, and graphite granules - GG) on methane production rate and stability in BESs.
• To evaluate the performance of biocathodes under various intermittent electricity supply conditions.
• To compare the electrochemical properties and microbial communities associated with GAC and GG biocathodes.

Main Methods:

• Utilized galvanostatic control to operate biocathodes with GAC and GG electrode materials.
• Assessed methane production rates and current-to-methane efficiencies under continuous and intermittent current supply.
• Employed electrochemical measurements to determine overpotentials and 16S rRNA gene sequencing to analyze microbial community composition.

Main Results:

• Achieved methane production rates of approximately 65 L CH4/m2catproj/d at 35 A/m2catproj, a significant increase compared to previous studies.
• Demonstrated stable current-to-methane efficiencies around 60% at 10 A/m2catproj under intermittent current supply, with rapid recovery of performance.
• GAC biocathodes exhibited lower overpotentials (-0.52 V vs. Ag/AgCl) compared to GG biocathodes (-0.92 V vs. Ag/AgCl) at 10 A/m2catproj.
• Identified *Methanobacterium* as the dominant methanogen, with GAC showing a higher abundance of proteobacteria.

Conclusions:

• Both GAC and GG show potential as effective cathode materials for methane-producing BESs.
• The studied electrode materials facilitate high methane production rates and stable operation under intermittent electricity supply.
• Further research into GAC and GG may lead to practical applications in renewable energy conversion and storage.