Biological formation of caproate and caprylate from acetate: fuel and chemical production from low grade biomass

TLDR

This study presents a mixed‑culture fermentation method for anaerobic digestion of low‑grade biomass to recover valuable products. The mixed‑culture fermentation converts organic waste streams into caproate and caprylate, precursors for biodiesel or chemicals. Acetate was elongated to medium‑chain fatty acids, producing 8.17 g L⁻¹ caproate and 0.32 g L⁻¹ caprylate under methanogenesis‑suppressed conditions, achieving a peak rate of 25.6 mM C caproate day⁻¹ and a yield of 0.6 mol C mol C⁻¹, with both ethanol and hydrogen donors usable and a stable community dominated by Clostridium kluyveri relatives.

Abstract

This research introduces an alternative mixed culture fermentation technology for anaerobic digestion to recover valuable products from low grade biomass. In this mixed culture fermentation, organic waste streams are converted to caproate and caprylate as precursors for biodiesel or chemicals. It was found that acetate, as the main intermediate of anaerobic digestion, can be elongated to medium chain fatty acids with six and eight carbon atoms. Mixed microbial communities were able to produce 8.17 g l−1 caproate and 0.32 g l−1 caprylate under methanogenesis-suppressed conditions in a stable batch reactor run. The highest production rate was 25.6 mM C caproate per day with a product yield of 0.6 mol C per mol C. This elongation process occurred with both ethanol and hydrogen as electron donors, demonstrating the flexibility of the process. Microbial characterization revealed that the microbial populations were stable and dominated by relatives of Clostridium kluyveri.