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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Cell Wall Biology and Utilization Research » Research » Publications at this Location » Publication #309431

Title: Improving ethanol production from alfalfa stems via ambient-temperature acid pretreatment and washing

Author
item ZHOU, SHENGFEI - University Of Wisconsin
item Weimer, Paul
item Hatfield, Ronald
item RUNGE, TROY - University Of Wisconsin
item DIGMAN, MATTHEW - Kuhn North America, Inc

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2014
Publication Date: 8/9/2014
Citation: Zhou, S., Weimer, P.J., Hatfield, R.D., Runge, T.M., Digman, M. 2014. Improving ethanol production from alfalfa stems via ambient-temperature acid pretreatment and washing. Bioresource Technology. 170:286-292.

Interpretive Summary: While corn has always been separated into grain and stover fractions at harvest, the whole alfalfa plant is harvested for hay or haylage. But alfalfa is a crop that produces large amounts of protein (30% of dry matter) in the leaves and a high-fiber fraction in the stems (< 10% protein, but high in carbohydrate). ARS researchers are currently working on a system that would separate the leaves from the stems at harvest. The stem fraction could be used as a biomass source for cellulosic ethanol production. This study looked at an on-farm treatment of alfalfa stems with acid during ensiling and found that it improved subsequent ethanol production, especially when a wash step was included to remove soluble ash components after neutralization of the acid. This system has the potential to add value at the farm level and to bring more alfalfa into rotation with corn, thus improving soil health, reducing soil erosion, and reducing the amount of nitrogen fertilizer needed to grow corn.

Technical Abstract: The concept of co-production of liquid fuel (ethanol) along with animal feed on farm was proposed. The strategy of using ambient-temperature acid pretreatment, ensiling, and washing to improve ethanol production from alfalfa stems was investigated. Alfalfa stems were separated and pretreated with sulfuric acid at ambient temperature after harvest. The ensiled stems were subjected to simultaneous saccharification and fermentation (SSF) for ethanol production. Ethanol yield was improved by the sulfuric acid pretreatment before ensiling, and by washing before SSF. It was theorized that the acid pretreatment at ambient temperature partially degraded hemicellulose and lignin and altered cell wall structure, resulting in improved cellulose accessibility. Washing removed soluble ash in substrates which could inhibit the SSF. The pH of stored alfalfa stems can be used to predict ethanol yield, with a correlation coefficient of +0.83 for washed alfalfa stems.