Enzyme study shows DDGS dewatering applications

By Holly Jessen | November 22, 2011

A one-month plant trial showed a commercial enzyme could help extract water from distillers grains, saving natural gas, electricity and water used in the ethanol process. More work needs to be done, said David Johnston, a sustainable biofuels and co-products food technologist for the USDA Agricultural Research Service, adding that now that the idea is out there, ethanol plants can start testing the idea internally. “I think that there would be some other process benefits that we couldn’t tell in a one-month trial,” he said. “The enzyme does something that should actually help in some of the unit operations, as far as maintenance and that sort of thing, but it’s something that you would really need to do in the long run to show and prove.”

The study was conducted at Center Ethanol Co. LLC, a 54 MMgy ethanol plant in Sauget, Ill. For the study, one pound of an enzyme supplied by Genencor was added for each 1,000 pounds of corn. Similar products from other ethanol enzyme makers could also be used, Johnston said. The enzyme, which typically is used as a cellulose preparation, was added as an additional enzyme during fermentation with no added equipment necessary.

As a result, scientists found that the natural gas usage for the dryer was reduced by 14 percent because the enzyme boosted water extraction in the centrifuge. “The enzyme is believed to disrupt that physical structure that the water is binding to, basically it makes it so it doesn’t hold on to the water as tightly,” he said. Using an existing economic model of ethanol production, researchers found that using the enzyme to dewater the stillage resulted in a reduction of natural gas usage by 12 percent and a reduction of electricity consumption by 2.4 percent. Water recycling opportunities can also be increase because more suspended solids are removed during the decanter centrifuge operation, Johnston added. In all, researchers calculated a 10 percent water reduction with the use of the enzyme for dewatering.

Making these reductions in natural gas, electricity and water use adds up to a reduction in greenhouse gas (GHG) emissions equivalent to about 8,000 tons of CO2 yearly for a 50 MMgy ethanol plant. “If we had a greenhouse reduction mandate, the enzyme would be worth a lot more,” Johnston said. “Environmentally it would be a great thing to do right now but economically, you’ve got to have both in order for it to be actually applied.”

The research, which was published in the scientific journal Industrial Biotechnology, was lead by Johnston and Andrew McAloon at the ARS Eastern Regional Research Center in Wyndmoor, Pa. Additional members on the team were Milorad Dudukovic, a professor at Washington University in St. Louis, and graduate student Ana Beatriz Henriques. "The production of grain ethanol is a key component in our nation's efforts to increase the supply of transportation fuels derived from renewable plant resources," said ARS administrator Edward B. Knipling. "The results from this investigation give us new tools for increasing the efficiency of grain ethanol production and for protecting our natural resource base."