The overall goal of the proposed work is to demonstrate the feasibility of extractive fermentation of volatile products using a compressed or supercritical solvent. The project will focus on the efficient continuous recovery of ethanol from biomass fermentation by the fibrolytic thermophilic bacteria, Clostridium thermocellum. This organism is capable of producing considerable amounts of ethanol directly from fibrous biomass, but is inhibited by the presence of relatively dilute ethanol. The Principal Invertigators' (PIs) hypthesis is that a compressed solvent is capable of efficiently extracting product so as to reduce product inhibition and thereby increase the fermentation rate and yield. Supercritical fluid extractive fermentation would have the advantages of gas-like mass transfer properties, solvent strength tunability, and ease of solvent regeneration and product recovery through depressurization. The specific objectives are to: (i) characterize effects of compressed solvents on the growth and metabolism of Clostridium thermocellum in the presence of soluble and insoluble carbohydrates; (ii) demonstrate in situ ethanol removal using a compressed fluid and evaluate the metabolic activity of Clostridium thermocellum as a function of extraction conditions; and (iii) develop a mathematicl model which will facilitate the design and analysis of compressed extractive fermentation processes. This award is made by NSF as part of the joint NSF/EPA Program on Technologies for a Sustainable Environment.
