IMPROVING BIOCHEMICAL PROCESSES FOR THE PRODUCTION OF SUSTAINABLE FUELS AND CHEMICALS
Location: Renewable Product Technology Research Unit
Title: Troubleshooting fermentation in corn wet milling ethanol production
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 8, 2011
Publication Date: June 8, 2011
Citation: Khullar, E., Kent, A.D., Leathers, T.D., Bischoff, K.M., Rausch, K.D., Tumbleson, M.E., Singh, V. 2011. Troubleshooting fermentation in corn wet milling ethanol production. Proceedings of the Seventh International Starch Technology Conference. p. 140.
To convert starch to ethanol, continuous fermentation processes are employed by corn wet milling plants all over world. Contaminations by bacterial microorganisms like Lactobacillus and wild yeasts like Brettanomyces are common and result in lower ethanol yields (Abbott and Ingledew 2005, Skinner and Leathers 2004). Contaminants compete with inoculated yeast for nutients and produce inhibitory end products, leading to stuck fermentations and expensive down times required for cleaning unit operations (Skinner and Leathers 2004).
Low ethanol yields and poor yeast viabilities in continuous fermentations for ethanol production were investigated. For hydrolyzate preparation, starch liquefaction and saccharification steps at a commercial ethanol facility were reproduced in the laboratory. Fermentation with hydrolyzates prepared in the laboratory were compared with plant hydrolyzate for final ethanol concentrations and total yeast counts. Fermentation controls were prepared using hydrolyzates (plant and laboratory) but were not inoculated with yeast. Hydrolyzates prepared in the laboratory resulted in higher final ethanol concentrations (15.8% v/v) than plant hydrolyzates (13.4% v.v). Controls resulted in ethanol production from both laboratory (12.2% v/v) and plant hydrolyzates (13.7% v/v), indicating the presence of a contaminating microorganism. Upon further experimentation, involving yeast colony counts on cycloheximide and virginiamycin plates, we confirmed the presence of a contaminant. DNA sequencing and fingerprinting studies conducted also were indicative of a number of dissimilar communities in samples obtained from fermenters, coolers, saccharification tanks and then stillage.