Reduction of carbon dioxide into acetate in a fully biological microbial electrolysis cell

A microbial electrolysis cell (MEC) was operated in continuous-flow condition to obtain cathodic CO2 reduction into acetate and methane along with COD anodic oxidation. Under steady-state conditions, most of the electron equivalents produced by COD anodic oxidation (866 mgCOD/Ld) were diverted into current rather than microbial growth, with an average Coulombic efficiency of 95 ± 8 %. In the cathodic chamber, acetate and methane formation from CO2 reduction accounted for 76% of the equivalents generated in the anodic oxidation reaction. Because a spill of cathodic liquid phase was necessary in order to counterbalance osmotic diffusion across the PEM, it was also possible to spill from the cathodic chamber a concentrated stream of acetate (248 ± 16meq/L). Moreover, as an additional effect, cation transport across the proton Exchange membrane (PEM) and the consequent alkalinity generation made it possible to accumulate ammonium nitrogen (242 ± 19 mgN/L) and bicarbonate (22.49 ± 1.45 gHCO3-/L). Hence, the MEC combined COD and CO2 removal in addition to nutrients and energy recovery from an anodic influent that simulated an urban wastewater.