Bioelectrochemically assisted anaerobic digestion system for biogas upgrading and enhanced methane production

The objective of this study was to evaluate the effect of biofilm and external voltage on the performance and microbial community composition of batch-fed, combined anaerobic digestion-bioelectrochemical cell (AD-BEC) systems under different operational conditions. A dextrin/peptone mixture was fed at a range of organic loading rates (0.34 to 1.37g COD/L-d). The hybrid system with both suspended biomass and biofilm without any external potential application achieved a substantially higher initial soluble COD consumption (53.7±2.3% vs. 39.7±3.7) and methane (CH₄) production (331 vs. 225mL) within one day of feeding than the conventional AD system (suspended biomass only). Compared to the conventional AD system, the hybrid systems had higher resilience to shock organic loadings. A range of external potential (0.5 to 2.0V vs. Ag/AgCl) was applied to AD-BEC reactors, developed with two different start-up procedures. A potential of 2.0V resulted in water electrolysis leading to a higher CH₄ production rate (105 vs. 84mL/L-d) and biogas CH₄ content (88.5±1.4 vs. 64.5±1.9%) in the AD-BEC reactor (closed vs. open circuit condition, respectively). Application of external potential enriched putative exoelectrogens at the anode biofilm and hydrogenotrophic methanogens at the cathode biofilm, which may have contributed to the observed enhanced CH₄ production in the AD-BEC system. A phylotype related to Methanobacterium formicicum, a hydrogenotrophic methanogen, dominated the archaeal community in the AD-BEC cathode biofilm.