Startup of Electromethanogenic Microbial Electrolysis Cells with Two Different Biomass Inocula for Biogas Upgrading

The performance and biomass enrichment of the biocathode of a pair of lab-scale two-chambered microbial electrolysis cells (MEC) were assessed for 95 days as a technology for upgrading the biogas produced in anaerobic digesters, converting CO2 into CH4 through the electromethanogenic process. Two different inocula were compared: (i) a mixture of biomass from the anode of a MEC and anaerobic granular sludge (BC1); (ii) biomass enriched in a methanol-fed upflow anaerobic sludge blanket reactor (UASB) (BC2). Quantitative and qualitative microbial community assessment of the enrichment process on the biocathodes was performed by means of high-throughput sequencing of 16S rDNA- and 16S rRNA-based massive libraries as well as RT-qPCR of 16S rRNA and mcrA genes. Although BC2 had a faster increase in current density than BC1, there were no significant differences neither in the average CH4 production (0.23 ± 0.01 and 0.22 ± 0.05 L m–3 day–1 for BC1 and BC2, respectively) nor in the cathodic methane recovery effic...