Microbial dynamics with the introduction of brewery waste in a long‐term chain elongation process for caproate production

Abstract

BACKGROUND: The long-term cultivation of sewage sludge in a chain elongation process was performed, and brewery wastewater (BW) was gradually introduced as ethanol source for medium-chain carboxylate (MCC) production. RESULTS:The results showed that the introduction of BW promoted ethanol utilization and electron recovery efficiency of the system. The improvement was mainly due to the readily available organics, such as yeast cells and leftover grain biomass, supplied along with BW as feedstock. In addition, the microbes introduced from BW and long-term cultivation facilitated the enrichment of MCC-forming microbes and the enhancement of microbial diversity. Microbial analysis revealed that the supply of BW was correlated with acetate-and butyrate-forming Proteiniclasticum, ethanol-oxidating Desulfovibrio, as well as biofilmforming Pseudomonas, which are beneficial to the chain elongation reactions. Further metabolic pathway analysis suggested that, other than reverse ⊎-oxidation, fatty acid biosynthesis was identified as the primary pathway for MCC formation in this system. Also, the introduction of BW promoted the chain elongation process by stimulating the rate-limiting steps involved in the conversion of ethanol to acetyl-CoA and the circular fatty acid biosynthesis pathway, thereby enhancing MCC formation.CONCLUSION: Generally, the enhancement of MCC production with BW was attributed to the microbes and organics leftover introduced from BW.