Fuel ethanol and high protein feed from corn and corn–whey mixtures in a farm‐scale plant

Abstract

Distiller's wet grain (DWG) and 95% ethanol were produced from corn in a farm-scale process involving batch cooking-fermentation and continuous distillation-centrifugation. The energy balance was 2.26 and the cost was $1.86/gal (1981 cost). To improve the energy balance and reduce costs, various modifications were made in the plant. The first change, back-end (after liquefaction) serial recycling of stillage supernatant at 20 and 40% strengths, produced beers with 0.2 and 0.4% (v/v) more ethanol, respectively, than without recycling. This increased the energy balance by 0.22-0.43 units and reduced costs by $0.07-$0.10/gal. The DWGs from back-end recycling had increased fat. The second change, increasing the starch content from 17-19% to 27.5%, increased the ethanol in the beer from 10.5-14.9% at a cost saving of $0.41/gal. The energy balance increased by 1.08 units. No significant change was seen in DWG composition. The third change, using continuous cascade rather than batch fermentation, permitted batch-levels of ethanol (10%) in the beer but only at low dilution rates. Both the cost and energy balance were decreased slightly. The DWG composition remained constant. The last change, replacing part of the corn and all of the tap water in the mash with whole whey and using Kluyveromyces fragilis instead of Saccharomyces cerevisiae during fermentation, resulted in an energy balance increase of 0.16 units and a $0.27/gal cost reduction. Here, 10% ethanolic beers were produced and the DWGs showed increased protein and fat. Recommendations for farm-scale plants are provided.

Intermediate-Scale, Semicontinuous Solid-Phase Fermentation Process for Production of Fuel Ethanol from Sweet Sorghum

“…The estimated PF credit for sweet sorghum (Table 3) is higher than those for corn and fodder beets (3,5,6,22).The credit of nearly $0.12/liter of ethanol ($0.45/gal) brings the net feedstock cost to $0.17/liter, compared with our previous estimates of $0.16/liter for corn and $0.17/liter for fodder beets. Valuation of the sweet sorghum by-product was based on the protein content of the raw feedstock (1.98% protein in fresh weight sorghum).…”

“…Preliminary estimates of costs (net of the PF credit) for ethanol produced from sweet sorghum in a farm-scale plant are approximately $0.47/liter ($1.78 to $1.80/gal) ( Table 3). This can be compared with our estimates for ethanol production from corn and fodder beets (3,5,6,22). Ethanol derived from corn by using our baseline method of plant operation costs $0.47/liter ($1.78/gal) when corn costs are $2.50 per bushel ($2.50/25.2 kg), and other prices are at 1981 levels.…”

Development of a low-cost medium for production of nisin from Lactococcus lactis subsp. lactis

“…However, nisin titers were limited due to the low glucose concentration. CCS normally contains less than 10 g glucose/l (Westby and Gibbons 1982;Gibbons and Westby 1983), and we only supplemented with an additional 10 g glucose/l. Thus, if additional glucose or other suitable carbohydrates were added to CCS, it would not only be higher yielding than cheese whey, but could also produce higher concentrations of nisin at higher yield coefficients.…”

“…Removing this large amount of water consumes a tremendous amount of energy, and therefore using CCS or thin stillage as a nutrient source for a secondary fermentation is a desirable option (Bock et al 1997;Smith et al 2008). This material contains corn nutrients as well as yeast hydrolysate (Westby and Gibbons 1982;Gibbons and Westby 1983). In prior research with Clostridium thermoaceticum (Bock et al 1997) and Rhodospirillum rubrum (Smith et al 2008) we have shown that CCS can be a very effective replacement for yeast extract.…”

Effects of Inoculum Size on Solid-Phase Fermentation of Fodder Beets for Fuel Ethanol Production

“…During conventional submerged fermentation of corn and other grains, fermentation is generally initiated by the addition of a quantity of yeast inoculum broth equal to 1 to 3% (wt/wt) of the saccharified mash (5,12,14,15). This results in initial yeast concentrations ranging from 2 x 105 to 5 X 106 cells per g (3-5, 11, 15).…”