Fermentation of Bioenergy Crops Into Ethanol Using Biological Abatement for Removal of Inhibitors

Authors: Nichols, Nancy; Dien, Bruce; Cotta, Michael

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2010
Publication Date: 6/1/2010
Citation: Nichols, N.N., Dien, B.S., Cotta, M.A. 2010. Fermentation of Bioenergy Crops Into Ethanol Using Biological Abatement for Removal of Inhibitors. Bioresource Technology. 101(19):7545-7550.

Interpretive Summary: This research discovered that a specially selected microbe may be used to improve the conversion of perennial crops — switchgrass, reed canarygrass, and alfalfa stems — to ethanol by removing inhibitory compounds. Herbaceous energy crops have great potential for conversion to fuels or chemicals. In order to convert the crop biomass to valuable products, however, the material must first be subjected to harsh physical or chemical treatments to free sugars from the fibrous biomass. The severe treatment results in a mixture that, rather than containing pure sugars for fermentation, also has compounds released from the plant material and formed from breakdown of sugars. These side-products are toxic for microbes used to carry out fermentations. Use of a unique microbe to remove the inhibitory compounds yields sugars that can be efficiently converted to ethanol by fermentation.

Technical Abstract: Conversion of biomass to fuels or chemicals is hampered by the presence of inhibitory compounds contained in sugar streams derived from lignocellulosic biomass. Biological abatement is a promising method for removing these inhibitors because it neither consumes chemicals nor generates wastes. In this study, biological abatement was used to remove inhibitors from hydrolysates prepared by dilute acid pretreatment of three perennial herbaceous crops that are potential bioenergy crops: switchgrass, reed canarygrass, and alfalfa stems. Fungal isolate Coniochaeta ligniaria was inoculated into the hydrolysates to metabolize and remove inhibitory compounds prior to yeast fermentation of glucose. Biomass samples were pretreated with dilute acid (at 10% w/w loading of switchgrass, reed canarygrass, and alfalfa stems) and subjected to bioabatement with strain NRRL30616 to prepare the material for simultaneous saccharification of cellulose and fermentation by Saccharomyces cerevisiae. Bioabatement eliminated the extended fermentation lag times observed for the unconditioned biomass hydrolysates. However, prolonged incubations with the bioabatement microbe resulted in consumption of some glucose and reduced production of ethanol.