title: Simultaneous saccharification and fermentation of cellulosic biomass to acetic acid.
abstract: A strain of Clostridium thermoaceticum (ATCC 49707) was evaluated for its homoacetate potential. This thermophilic anaerobe best produces acetate from glucose at pH 6.0 and 59 degrees C with a yield of 83% of theoretical. Enzyme hydrolysis of two substrates, a-cellulose and a pulp mill sludge, yielded 68% and 70% digestion, respectively. The optimum conditions for the simultaneous saccharification and fermentation (SSF) were substrate dependent: 55 degrees C, pH 6.0 for alpha-cellulose, and 55 degrees C, pH 5.5 for the pulp mill sludge. In the SSF with alpha-cellulose, the overall yield of acetate was strongly influenced by the enzyme loading. In a fed-batch operation of SSF with alpha-cellulose, an overall acetic acid yield of 60 wt% was obtained. Among the factors limiting the yields were incomplete digestion by the enzyme and the end-product inhibition. In the SSF of pulp mill sludge, inhibitors present in the sludge severely limited bacterial action. A large accumulation of glucose developed over the entire process, changing the intended SSF operation into a separate hydrolysis and fermentation operation. Despite a long lag phase of microbial growth, a terminal yield of 85% was obtained with this substrate.
authors.affiliation: Department of Chemical Engineering, Auburn University, AL 36849, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Borden
authors.forename: Y Y
authors.initials: YY
authors.lastname: Lee
authors.forename: H H
authors.initials: HH
authors.lastname: Yoon
mesh_terms: D019342:Acetic Acid; D000693:Anaerobiosis; D018533:Biomass; D002480:Cellulase / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D003013:Clostridium / Q000502:physiology*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D014934:Wood
chemical_list: D002482:Cellulose; D002480:Cellulase; D005947:Glucose; D019342:Acetic Acid