Next generation digestion: Complementing anaerobic digestion (AD) with a novel microbial electrolysis cell (MEC) design

Abstract This study determined the effect of incorporating a microbial electrolysis cell (MEC) with an anaerobic digester (AD) in a single chamber. The study evaluated three treatments: a combined AD-MEC operated for 23 days (AD-MEC-23); a combined AD-MEC operated with the MEC running for 5 days followed by no MEC for the subsequent 18 days (AD-MEC-5); and an AD operated for 23 days (AD-only). Food waste was the digestion substrate at an inoculum to substrate ratio of 1:1 (VS basis). Cumulative methane and hydrogen during the batch test in AD-MEC-23 (9.4 L CH4 , 3.39 L H2 , 2.8 L CO2 ) was higher than AD-MEC-5 (7.6 L CH4 , 2.2 L H2 , 4.6 L CO2 ), and AD-only (7.4 L CH4 , 0.2 L H2 , 5.8 L CO2 ). The results also showed that using the MEC continuously inside the digester (AD-MEC treatment) reduced CO 2 concentration to approximately 4% at the end of the experimental period, thereby, increasing the useful gases (CH 4 and H 2 ) concentrations to a maximum of 95.8%, with an average of 71.9% CH 4 , 17.4% H 2 and 10.7% CO 2 over the 23-day digestion period in the AD-MEC-23 reactor. Additionally, the COD removal in AD-MEC-23 was 12% higher than AD-only. The volumetric current was 108.7 A/m 3 based on MEC volume and 17.3 A/m 3 based on total AD-MEC volume, while the current density was 1.35 A/m 2 (cathode surface area). The total energy produced from the AD-MEC-23 (414 kJ) was higher than AD-MEC-5 (325 kJ) and AD-only (295 kJ), with an increase of energy production of over 400% output energy compared to the input energy to power the MEC. The results showed that the novel MEC design incorporated into an AD reactor increased the biogas quality, overall energy production, and waste treatment.