S120: Utilization of By-products from Dry-grind Ethanol Plants for Succinic Acid Production

Fermentation of glucose by the yeast Saccharomyces cerevisiae produces ethanol and carbon dioxide in approximately equal quantities. Some of the carbon dioxide is captured and sold, for example, to bottling companies, whereas the rest is allowed to escape to the atmosphere. There has been strong interest in developing technologies for conversion of this green-house gas to useful products, thus preventing it from contributing to the global warming. Succinic acid, which is a platform chemical that can be used as precursor for production of many industrial chemicals and consumer products, can be produced by Escherichia coli strains having a CO₂-fixing enzyme in its biosynthetic pathway. It has been demonstrated that the CO₂ produced in an ethanol fermentor could be sparged directly into an adjacent succinic acid fermentor to increase succinic acid yield. Alternatively, the CO₂ produced in an ethanol fermentor could be absorbed into a strong base solution and the resultant carbonate solution used for pH control of succinic acid fermentation. Another by-product of dry-grind ethanol plants is DDGS, which traditionally is sold for animal feed formulations. Recent increase in corn oil extraction could lower demand and result in surplus DDGS, which can be biologically converted to useful products because of high carbohydrate contents. Destarched DDGS was pretreated by soaking in aqueous ammonia and hydrolyzed with commercial cellulase to produce fermentable sugars, which subsequently were used for succinic acid production. The results on use of CO₂ from ethanol fermentation and DDGS-derived sugars for succinic acid production will be discussed.