High-rate biogas production from cattle manure in an integrated microbial electrolysis cell and anaerobic reactor system

The aim of this study was to investigate the biogas production performance of an integrated microbial electrolysis cell and anaerobic reactor system (MEC-AR) treating cattle manure at different applied voltages and hydraulic retention times (HRT) ranging from 6 days to 1 day. The MEC-AR system was operated in semi-continuous mode under various voltage applications of 0.3, 0.6, and 1.0 V and organic loading rates (OLR) ranging from 5 g VS/L/d to 30 g VS/L/d. The MEC-AR system presented 25 to 62% higher biogas production and 10 to 21% higher organic removal rates compared to the control reactor, until the control reactor deteriorated at the HRT of 3 days. As the HRT was decreased further, biogas production of the MEC-AR system increased depending on the applied OLR and voltage. Maximum biogas productions, 4.88 L/L/d (CH4: 76%) and 5.10 L/L/d (CH4: 77%), were observed at HRT of 2 days and OLR of 30 g VS/L/d in MEC-AR(0.6 V) and MEC-AR(1.0 V), respectively. Higher applied voltages (MEC-AR(0.6 V) and MEC-AR(1.0 V)) resulted in higher biogas production (16 to 21%) and organic removal rates (9 to 21%) compared to lower applied voltage (MEC-AR(0.3 V)) especially at high OLRs (22.5 and 30 g VS/L/d). As a result, MEC-AR system can be operated efficiently at challenging operational conditions (as low as 1 and 2 days; OLR of 15-30 g VS/L.d.) that conventional anaerobic reactors cannot withstand.