Methane-driven microbial fuel cells recover energy and mitigate dissolved methane emissions from anaerobic effluents

Abstract

The effluents of mainstream anaerobic treatment processes such as anaerobic membrane bioreactors (AnMBRs) contain dissolved methane that represents a large fraction of the available energy (approximately 50% at 15 °C) and a significant greenhouse gas (GHG) emission if released to the atmosphere. Microbial fuel cells (MFCs), which rely on exoelectrogenic microorganisms to generate electricity from organic or inorganic matter, could be used to recover energy and prevent GHG emissions from dissolved methane. Two replicate air-cathode, single-chamber MFCs and one dual-chamber MFC were constructed and operated in continuous mode on a synthetic, methane-saturated medium at 20 °C and hydraulic retention times of 4, 8, and 16 h. Up to 85% dissolved methane removal was achieved, resulting in the generation of 0.55 ± 0.06 V. Geobacter, a common exoelectrogen, and methanotrophs were identified in anode biofilm samples by Illumina sequencing targeting the 16S ribosomal RNA (rRNA) and 16 rRNA gene. Activity quantification of key microbial populations via reverse transcription-quantitative polymerase chain reaction (RT-qPCR) indicated that methane removal and voltage production results from a consortium of aerobic methanotrophs enriched in a cathode biofilm that produce intermediate metabolites (e.g., formate and acetate) that serve as substrates for Geobacter in the anode biofilm.