Food waste holds significant untapped potential to drive the production of sustainable bioproducts that displace fossil fuels and bolster electrification. This study presents a novel single-stage electro-fermentation (EF) reactor designed to convert complex food waste compounds into valuable medium-chain carboxylates (MCCs) such as caproic acid. The reactor incorporates particle-electrode architectures and a diverse microbiome capable of hydrolysis, acidogenesis, and chain elongation in a single unit process, eliminating the need for multistage reactors. EF performance was evaluated under voltages ranging from −0.8 to +0.8 V vs Ag/AgCl. Under −0.8 V, a particle-fluidized (PF) reactor achieved the highest caproic acid selectivity (68.25%) of any EF study using complex substrates. Chemical analyses suggest that hydrolysis rate and H2 pressures likely influenced carbon flux toward MCCs. Biofilm imaging and genomic analyses revealed the enrichment of chain-elongating taxa such as Clostridium (∼24%, relative abundance) under reducing conditions in PF reactors, indicating that extracellular electron transfer mechanisms vary across voltage and reactor configuration. These results demonstrate that particle-electrodes, voltage, and chain-elongating microbiomes can be leveraged to direct metabolic flux toward MCC production. Altogether, this work provides a new single-stage strategy for converting waste streams into high-value bioproducts, offering a roadmap for future EF reactor design and operation.
Yang et al. (Wed,) studied this question.