Crop Biotech Update

Fungus Reduces Energy Costs in Dry-Grinding Process for Corn-Ethanol Production

May 30, 2008
Scientists from Iowa State University and the University of Hawaii (both in the United States) have harnessed a fungus called Rhizopus microporus, to clean up the waste residue from dry-milling corn ethanol plants, and allow recycling with energy cost savings. The dry-grinding/milling process for corn ethanol process roughly involves the following steps: (1) grinding the corn kernels with the addition of water and enzymes (to convert the starches in corn into simple sugars), (2) fermentation of the sugars to ethanol by yeasts, (3) distillation of the fermentation broth to evaporate the ethanol, and (4) condensing the ethanol vapor into liquid ethanol. The liquid residue from distillation (called “thin stillage”) contains organic matter, solids and enzymes from the first step which can be recycled back to the process. However, because the solids and the organic matter in thin stillage can adversely affect ethanol fermentation, only 50% of the waste residue is recycled. The remaining portion is thermally processed and blended with distiller’s dried grains to produce a solid residue called “distiller’s dried grains with solubles”. In the new process, the Rhizopus microporus is added to the thin stillage and the organism cleans off the solids and organic matter. The “clean thin stillage” can then be completely recycled back into the system, without the need for the thermal processing step of “distillers dried grains with solubles”. The fungal biomass can also be processed into nutrient-rich animal feed supplement. According to Iowa State University Professor and Project Leader, Hans van Leeuwen, energy cost can be reduced by as much as one-third. The research won the 2008 Grand Prize for University Research, given by the American Academy of Environmental Engineers..