Mutual effects of CO₂ absorption and H₂-mediated electromethanogenesis triggering efficient biogas upgrading

Area of Science:

• Environmental Biotechnology
• Biochemical Engineering
• Renewable Energy

Background:

• Anaerobic digestion coupled with bioelectrochemical systems (BES) offers low-energy biogas upgrading.
• Alkalinity generation during electromethanogenesis is often overlooked but can aid CO2 removal.
• Dissolved inorganic carbon (DIC) formation is a key aspect of CO2 transformation.

Purpose of the Study:

• To propose and investigate a novel bioelectrochemical CO2 conversion method in methanogenic BES.
• To leverage active CO2 capture and in-situ microbial utilization for enhanced biogas upgrading.
• To explore the role of alkalinity generation in CO2 removal and methane production.

Main Methods:

• Development of a bioelectrochemical system (BES) with a stainless steel/carbon felt hybrid biocathode (BES-SSCF reactor).
• Application of a 1.0 V applied voltage to drive electromethanogenesis and CO2 conversion.
• Analysis of biogas composition (CH4, CO2), methane yield, production rate, and microbial community structure.

Main Results:

• The BES-SSCF reactor achieved a CH4 yield of 0.33 ± 0.03 LCH4/gCODremoval, a 28.3% increase in CH4 production rate compared to a BES-CF reactor.
• Upgraded biogas reached 93.1% CH4 content, with CO2 content below 3%.
• A high CO2 to CH4 conversion rate of 82.3% was achieved, with CO2 and DIC accounting for only 12% of total carbon.

Conclusions:

• The hybrid biocathode effectively generates alkalinity, enhancing CO2 capture as bicarbonate and subsequent microbial reduction to CH4.
• Enrichment of specific methanogens (Methanobacterium, Methanosarcina) in the cathodic biofilm facilitated H2-mediated electromethanogenesis.
• This study presents an innovative CO2 utilization mechanism integrating CO2 absorption and H2-mediated electromethanogenesis for efficient biogas upgrading.