Contamination issues in a continuous ethanol production corn wet milling facility
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ORIGINAL PAPER
Contamination issues in a continuous ethanol production corn wet milling facility Esha Khullar • Angela D. Kent • Timothy D. Leathers Kenneth M. Bischoff • Kent D. Rausch • M. E. Tumbleson • Vijay Singh
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Received: 13 October 2012 / Accepted: 18 December 2012 / Published online: 25 December 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract Low ethanol yields and poor yeast viability were investigated at a continuous ethanol production corn wet milling facility. Using starch slurries and recycle streams from a commercial ethanol facility, laboratory hydrolysates were prepared by reproducing starch liquefaction and saccharification steps in the laboratory. Fermentations with hydrolysates prepared in the laboratory were compared with plant hydrolysates for final ethanol concentrations and total yeast counts. Fermentation controls were prepared using hydrolysates (plant and laboratory) that were not inoculated with yeast. Hydrolysates prepared in the laboratory resulted in higher final ethanol concentrations (15.8 % v/v) than plant hydrolysate (13.4 % v/v). Uninoculated controls resulted in ethanol production from both laboratory (12.2 % v/v) and plant hydrolysates (13.7 % v/v), indicating the presence of a contaminating microorganism. Yeast colony counts on cycloheximide and virginiamycin plates confirmed the presence of a contaminant. DNA sequencing and fingerprinting studies also indicated a number of dissimilar communities in samples obtained from fermentors, coolers, saccharification tanks, and thin stillage.
E. Khullar K. D. Rausch M. E. Tumbleson V. Singh (&) Agricultural and Biological Engineering, University of Illinois, Urbana, IL 61801, USA e-mail: [email protected] A. D. Kent Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801, USA T. D. Leathers K. M. Bischoff National Center for Agricultural Utilization Research, ARS, USDA, Peoria, IL 61604, USA
Keywords
Contamination Wet milling Ethanol
Introduction The US ethanol industry continues to grow with 53 9 109 L (13.9 9 109 gallons) produced in 2011 (RFA 2012). Ethanol production has supported economic growth alongside rural development by adding value to commodities produced by farmers. With the goal of producing 136 9 109 L (36 9 109 gallons) of ethanol by 2022, the Renewable Fuels Standard (RFS) has provided incentives to increase ethanol production using starch and non-starch feedstocks. In the US, corn is the major feedstock for ethanol production. In 2011, 127 9 109 kg (5 9 109 bushels) of corn, representing 40 % of annual production, was converted to ethanol and coproducts for animal food. Dry grind and wet milling are the two processes used for producing ethanol from corn starch. To reduce grain size, the dry grind process employs hammer mills followed by addition of water to produce slurry. The slurry is treated with enzymes; sugars released are fermented to ethanol using yeast. Contrary to dry grind, wet milling involves soaking corn kernels with sulfur d
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