Hybrid electron donors of ethanol and lactate stimulation chain elongation in microbial electrosynthesis with different inoculants

Microbial electrosynthesis (MES) is a new technology that uses electrically driven biocatalysts to convert CO₂ into valuable chemicals. However, C2 as the primary product limits the development of MES. To address this issue, ethanol and lactate as additional electron donor (ED) were introduced into MES systems with different inoculants (anaerobic sludge and sediment) for chain elongation. The hybrid EDs in MES with sediment can produce the highest concentrations of butyrate (6.30 g/L) and caproate (1.60 g/L), and the corresponding total electron recovery efficiency reached the maximum value (94.51 ± 1.04%). Hybrid EDs not only provided sufficient reducing force, but also enhanced the gas mass transfer rate by releasing CO₂ from lactate in situ. Metagenomic analysis showed that reverse β-oxidation pathway and fatty acid biosynthesis pathway were the main pathways. This study demonstrated that the addition of ethanol and lactate is promising method for improving the performance of MES.