Voltage application and biomass retention increased biogas production in a combined microbial electrolysis cell and anaerobic digestion system treating chicken manure

This study investigates the effect of the voltage application and biomass retention on the biogas production performance of a combined microbial electrolysis cell and anaerobic digestion (MEC+AD) reactor operated at different organic loading rates (OLR). The chicken manure (CM) with a content of 6 % VS was fed to the reactors as substrate at various hydraulic retention times (HRT) ranging from 3 to 20 days. It was observed that the conventional anaerobic digestion (AD) reactor collapsed due to the overloading at the HRT of 5 days. On the other hand, due to the voltage application and biomass retention on the electrodes of the combined reactors, (MEC+AD)C without a voltage application and (MEC+AD)0.3 with a voltage application of 0.3 V presented the highest methane production of 1.98 +/- 0.19 and 2.37 +/- 0.32 L/LR/d, respectively. Organic removal rates of the combined reactors were similar to each other; however, in terms of biogas production, (MEC+AD)0.3 presented superior performance at all sets due to the voltage application and microbial community on the electrodes. Methanosarcina had a dominance of 5 % at the cathode of (MEC+AD)0.3 at the genus level, which affected the results. The highest methane yield obtained in this study was 373 +/- 72 mL CH4/g VS at (MEC+AD)0.3, which was 30 % higher than that of (MEC+AD)C due to the voltage application and the genus Methanosarcina on the cathode.