Efficacious enrichment of butyrate-oxidizing exoelectrogens upgrades energy recovery in relevant bioelectrochemical systems

Energy recovery via bioelectrochemical systems (BESs) while treating organic wastes has proven to be a promising technology. Organic waste hydrolysates are appealing feedstocks for BESs due to their richness in short-chain fatty acids rather than complex organics. However, butyrate, among the abundant acids in hydrolysates, has been found to particularly hinder the efficiency of BESs. The lack of efficient anodic butyrate-oxidizers appears to be critical; therefore, this study targeted the enrichment of an anodic community to enhance butyrate oxidation efficiency in BESs. We initially tested three different inoculum sources using butyrate as the sole electron donor. Then, through successive transfers of a bioanode piece to fresh anodes, significant improvement in coulombic efficiency (CE) from 9.4 % to 78.6 % was achieved over six transfers. The enriched bioanode was dominated by the bacterial genera Geobacter (72 %) and Sporomusa (16 %), which correlated positively with CE development over transfers. The metagenomic/transcriptomic analyses confirmed the key role of Geobacter in the anodic oxidation of butyrate, while Sporomusa likely displayed a syntrophic interaction, assimilating acetate from CO₂ and excess H₂. The enriched culture was further bioaugmented with Geobacter sulfurreducens and tested with real butyrate-containing hydrolysate, in which CE and maximum current density of 86.9 % and ∼3.5 A/m² were achieved, respectively. Overall, the enriched butyrate-oxidizing culture, bioaugmented with G. sulfurreducens, proves efficient for BESs treating butyrate-rich waste-streams.