The remaining liquid, known as thin stillage, still contains some solids, a variety of organic compounds from corn and fermentation as well as enzymes. Because the compounds and solids can interfere with ethanol production, only about 50 percent of thin stillage can be recycled back into ethanol production. The rest is evaporated and blended with distillers dried grains to produce distillers dried grains with solubles.
The researchers added a fungus, Rhizopus microsporus, to the thin stillage and found it would feed and grow. The fungus removes about 80 percent of the organic material and all of the solids in the thin stillage, allowing the water and enzymes in the thin stillage to be recycled back into production.
The fungus can also be harvested. It’s a food-grade organism that’s rich in protein, certain essential amino acids and other nutrients. It can be dried and sold as a livestock feed supplement. Or it can be blended with distillers dried grains to boost its value as a livestock feed and make it more suitable for feeding hogs and chickens.
Van Leeuwen said all of that can save United States ethanol producers a lot of energy and money at current production levels:
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Eliminating the need to evaporate thin stillage would save ethanol plants up to $800 million a year in energy costs.
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Allowing more water recycling would reduce the industry’s water consumption by as much as 10 billion gallons per year. And it allows producers to recycle enzymes in the thin stillage, saving about $60 million per year.
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Adding value and nutrients to the livestock feed produced by ethanol plants would grow the market for that feed by about $400 million per year.
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And the researchers’ fungal proc
ess would improve the energy balance of ethanol production by reducing energy inputs so there is more of an energy gain.
Van Leeuwen estimated it would cost $11 million to start using the process in an ethanol plant that produces 100 million gallons of fuel per year. But, he said the cost savings at such a plant could pay off that investment in about six months.
Van Leeuwen and the other researchers developing the technology – Anthony L. Pometto III, a professor of food science and human nutrition; Mary Rasmussen, a graduate student in environmental engineering and biorenewable resources and technology; and Samir Khanal, a former Iowa State research assistant professor who is now an assistant professor of molecular biosciences and bioengineering at the University of Hawai‘i at M?noa – recently won the 2008 Grand Prize for University Research from the American Academy of Environmental Engineers for the project.