A new upgraded biogas production process: Coupling microbial electrolysis cell and anaerobic digestion in single-chamber, barrel-shape stainless steel reactor

•CH4 content in excess of 98% was achieved from microbial electrolysis cell and anaerobic digestion coupled process.•COD removal rate was increased 3.0 times and carbon recovery was increased by 56.2%.•Reactor made of stainless steel was used for anaerobic digestion as well as the MEC cathode for H2 gas evolution.

Production of upgraded biogas is required to remove as much carbon dioxide as possible. It was found that by coupling microbial electrolysis cell (MEC) and anaerobic digestion (AD) in a single-chamber, barrel-shape stainless steel reactor, compared with common anaerobic digestion (control), CH4 content in excess of 98% was achieved and CH4 yield was increased 2.3 times. Meanwhile, the COD removal rate was tripled and carbon recovery was increased by 56.2%. In this new process, unwanted CO2 was in situ converted into CH4 on anode by the dominant microbes, hydrogenotrophic electromethanogens (e.g. Methanospirillum). These microbes could utilize hydrogen gas generated at the inner surface of stainless steel reactor, which itself served as cathode of MEC through small voltage addition (1.0 V). The overall energy efficiency was 66.7%.

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