A whole stillage sieving process to recover fiber for cellulosic ethanol production

•Sieving was effective to recover fiber from whole stillage.•Samples recovered by sieving have potential to be a bioethanol feedstock.•Enhanced DDGS exhibited decreased fiber contents and increased oil contents.•Grinding and sieving whole stillage showed higher sugar yields than sieving alone.•More DDGS is produced after grinding and sieving than sieving alone.

A sieving step was developed to recover corn fiber from whole stillage of a dry grind process as a cellulosic ethanol feedstock, and to reduce fiber contents in distillers dried grains with solubles (DDGS). Several processes have been developed to recover fiber in the dry grind process, such as wet fractionation, dry fractionation and elusieve process. Wet fractionation and dry fractionation recover fiber before liquefaction, but addition of these steps to existing plants requires considerable modifications with high capital costs. The elusieve process recovers fiber from DDGS, but it requires drying of DDGS. To simply integrate fiber recovery to current dry grind plants with less operating and capital costs, sieving was applied to whole stillage. Commercial whole stillage samples were ground, incubated with protease or with a surfactant, and sieved. Sieving was effective to recover neutral detergent fiber (NDF), and NDF contents in retentate samples were increased by 45–101%. In addition, permeate samples, called enhanced DDGS, exhibited decreased fiber contents and increased oil contents. Among treatments, grinding before sieving was more effective to recover fiber with high NDF contents and low protein and oil contents. Fiber recovered from whole stillage and ground whole stillage were hydrolyzed for cellulosic sugars. Whole stillage and ground whole stillage were sieved in a scaled-up (15×) vibrator shaker. The retentate samples were pretreated with dilute acid followed by hydrolysis. Ground whole stillage showed higher sugar yields than whole stillage. After hydrolysis, glucose, xylose and arabinose yields from ground whole stillage were 90.78, 92.93 and 76.99%, respectively. Grinding before sieving produces more eDDGS, and could potentially increase downstream ethanol yields.