Barley Distillers Dried Grains with Solubles (DDGS) as Feedstock for Production of Acetone, Butanol and Ethanol

Distillers dried grains with solubles (DDGS) represent important co-product from commercial yeast fermentations, including bioethanol, from grains. In view of the current expansion of the bioethanol fermentation process, with the concomitant increase in production of DDGS, alternative applications to their main current use as animal feed are being explored. In this study, DDGS from a bioethanol facility which uses barley as feedstock have been characterized and used as feedstock for biobutanol production. These DDGS contained, per kg of dry matter, 250 grams of protein and 390 grams of sugars, being glucose, xylose and arabinose the main sugar components. DDGS were hydrolyzed by alkaline pre-treatment followed by enzymatic hydrolysis resulting in the solubilization of approx. 80 % of the sugars in the feedstock and contained 57 g/L total sugars. The fermentation of 20 % (w/v) DDGS suspensions and of the hydrolysate of DDGS by two acetone, butanol and ethanol (ABE)-producing bacterial strains is described. Both strains utilized the sugars in these suspensions and in the hydrolysate to produce ABE. In these cultures, the strains only utilized soluble mono- or oligosaccharides. The hydrolysate was fermentable without addition of extra nutrients, being C. acetobutylicum the best-performing strain, producing 8.3 g/L ABE. In addition, DDGS were used as nutrient for the fermentation of wheat straw hemicellulosic syrup (C5-syrup) with low nutrient content. This C-5 syrup was a side stream obtained from steam-exploded wheat straw, and was subjected to overliming to make it fermentable. The supplementation of the C5-syrup with DDGS eliminated the need for addition of nutrients for the fermentation