Tuesday, May 3, 2011
Fermentation inhibitors arise from lignin, hemicellulose, and degraded sugar during pretreatment of lignocellulosic biomass. Use of a microbe has been explored for abatement of pretreated biomass in which fermentation inhibitors, if left untreated, can complicate microbial conversion of biomass to fuels or chemicals. The fungus Coniochaeta ligniaria NRRL30616 has native ability to metabolize a number of inhibitory compounds, including furan aldehydes and aromatic compounds known to act as inhibitors toward relevant fermenting microbes. C. ligniaria grows in liquid culture with a yeast-like appearance. In this study, C. ligniaria was used to metabolize and remove inhibitory compounds from pretreated rice hull hydrolysates, prior to ethanol fermentation. Rice hulls comprise a readily available agricultural residue rich in glucose (0.32-0.33 g glucan/g hulls) and xylose (0.15-0.19 g xylan/g hulls). Samples were dilute-acid pretreated and subjected to bioabatement with strain NRRL30616. Furfural and 5-hydroxymethylfurfural concentrations in hydrolysates were measured as markers for bioabatement of inhibitors. In fermentations of supernatants from pretreated rice hulls, yeast added to bioabated samples converted glucose to ethanol at 100% of theoretical yield. Simultaneous enzymatic saccharification and fermentation (SSF) of 5% pretreated solids yielded 0.5% (w/v) ethanol from bioabated samples, whereas ethanol was not produced in fermentations of unabated samples. Because conversion of pentoses is relevant for this feedstock, results of ethanologenic E. coli fermentations will also be presented.