Influence of the applied external voltage on anaerobic digestion with integrated microbial electrolysis cell

Abstract

An external microbial electrolysis cell (MEC) was integrated into the ethanol stillage anaerobic digestion reactor (AD). The AD-MEC system is a promising technology for enhancing biogas production. It accelerated methane production and stabilized the process. A change in applied external voltage could change microbial metabolism and affect substrate degradation rate, volatile fatty acid (VFA) generation and biogas production. The effect of applied external voltage on biodegradability, VFA and methane content in produced biogas was studied. Four values of external voltage were selected - 0.6, 0.8, 1.0 and 1.2 V. The kinetics of biogas production for 15 days was monitored. Methane yields increased to 84, 88 and 82 % (“vol.) at 0.6, 0.8 and 1.0 V voltages of the microbial electrolysis cell, respectively. Higher voltage (1.2 V) did not increase the methane content vs AD-only process (75 %, vol.). The best biodegradability was achieved at low voltages (0.6 and 0.8 V) - reduction of chemical oxygen demand by 88-89 % and purification of ethanol stillage from sulfates. Acetic acid decreased by 96 % at 0.6 V, 95 % at 0.8 V, 74 % at 1.0 V and 65 % at 1.2 V.