Research drives improvements in biofuel processing

Paul Boughton

Growing a fungus in some of the leftovers from ethanol production can save energy, recycle more water and improve the livestock feed that's a co-product of fuel production, according to a team of researchers from Iowa State University and the University of Hawaii.

“The process could change ethanol production in dry-grind plants so much that energy costs can be reduced by as much as one-third,” said Hans van Leeuwen, an Iowa State professor of civil, construction and environmental engineering and the leader of the research project.

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's now an assistant professor of molecular biosciences and bioengineering at the University of Hawaii at Manoa – recently won the 2008 grand prize for university research from the American Academy of Environmental Engineers for the project (Fig. 1).

“Those chosen for prizes by an independent panel of distinguished experts address the broad range of modern challenges inherent in providing life-nurturing services for humans and protection of the environment,” according to a statement from the academy. “Their innovations and performance illustrate the essential role of environmental engineers in providing a healthy planet.”

The Iowa State project is focused on using fungi to clean up and improve the dry-grind ethanol production process. That process grinds corn kernels and adds water and enzymes. The enzymes break the starches into sugars. The sugars 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 per cent 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 per cent 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 pigs and chickens.

Van Leeuwen said all of that can save US 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 US$800 million a year in energy costs.

Allowing more water recycling would reduce the industry’s water consumption by as much as 10 billion gallons/y. And it allows producers to recycle enzymes in the thin stillage, saving about US$60 million/y. Adding value and nutrients to the livestock feed produced by ethanol plants would grow the market for that feed by about US$400 million per year. In addition, the researchers’ fungal process 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 US$11 million to start using the process in an ethanol plant that produces 100 million gallons/y of fuel. However, he added that the cost savings at such a plant could pay off this investment in about six months.

The researchers have filed for a patent on the technology and are looking for investors to commercialise the invention. And while the process needs to be proven at larger

Biomass-to-gas grant

Meanwhile, the University of has been awarded US$1 million from the US Department of Agriculture and the US Department of Energy to develop rapid solar- thermal chemical reactor systems for the conversion of biomass material such as switchgrass and algae to synthesis gas.

The three-year award was made to a team led by Alan Weimer, professor of the university’s chemical and biological engineering department. The team will use concentrated sunlight to heat biomass like grass, sorghum, corn stalks and leaves, wood waste and algae to more than 2000ºF for just fractions of a second. The process will produce an intermediate syngas – a mixture of carbon oxides and hydrogen – that can be easily converted into hydrogen or liquid fuels, he said.
The university will subcontract out to NREL to provide a high-flux solar furnace for the research and to CSU to study switchgrass growth and supply quantities of the tall prairie grass to the researchers for conversion. The CSU collaboration will be led by CSU horticulture professor Yaling Qian, while the NREL collaboration will be led by Carl Bingham at NREL's high flux solar furnace.

Weimer said he envisions a totally renewable technology, in which a significant fraction of the nation’s fuel supply is provided using solar-thermal processing in marginal lands where the farming of crops such as switchgrass and algae can provide the needed biomass. “Since the process is driven by sunlight and converts biomass to fuels, the end result is a process that is ‘carbon negative’,” Weimer said. “This provides an opportunity to substantially reduce greenhouse gases in the atmosphere without impacting the food supply.”

The Colorado University grant was part of a new USDA/DOE award package to spend up to US$18.4 million to fund 21 biomass R&D demonstration projects over three years. The projects are aimed at addressing barriers to making the production of biomass more efficient and cost-effective, according to the USDA and DOE.

“The University of Colorado at Boulder has been working in the area of solar-thermal chemical processing for more than ten years and is the largest academic research team in this area in the world,” said chancellor GP ‘Bud’ Peterson. “This award recognises the university's expertise in the field and provides professor Weimer and his team with an opportunity to move this process closer to commercial reality.”

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