Washington, May 28 : A team of researchers has used fungus to clean up and improve the dry-grind ethanol production process.
The researchers included Hans van Leeuwen from Iowa State University and Samir Khanal, a former Iowa State research assistant professor, along with colleagues Anthony L. Pometto III and Mary Rasmussen.
The dry-grind ethanol production process grinds corn kernels and adds water and enzymes. The enzymes then break the starches into sugars, which are fermented with yeasts to produce ethanol.
The fuel is recovered by distillation, but there are about six gallons of leftovers for every gallon of fuel that's produced. Those leftovers, known as stillage, contain solids and other organic material.
Most of the solids are removed by centrifugation and dried into distillers dried grains that are sold as livestock feed, primarily for cattle.
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.
According to Van Leeuwen, all of that can save United States ethanol producers a lot of energy and money at current production levels.
Eliminating the need to evaporate thin stillage would save ethanol plants up to 800 million dollars a year in energy costs.
Allowing more water recycling would reduce the industry's water consumption by as much as 10 billion gallons per year, and allow producers to recycle enzymes in the thin stillage, saving about 60 million dollars per year.
The researchers' fungal process would also improve the energy balance of ethanol production by reducing energy inputs so there is more of an energy gain.
"We will be saving ethanol producers money and energy," said Pometto. "That's the bottom line," he added.