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 yieldwas 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%.