Grass: It's Not Just for Grazing
We know cows like it-and by eating certain varieties, they give more milk. So do these grasses' higher sugar content also mean greater ethanol output?
Could we use it for transport fuel?
That idea is under consideration in several places around the world, including Wales-and in Wales, cows in fact may be a guide for researchers studying cellulosic ethanol.
Steve Kelly, a molecular biologist at Swansea University in Wales, is one scientist working on a process that may eventually let motorists tank up on "grassohol" from the very meadows past which they drive on their next holiday.
Kelly's is a two-step process, using high-sugar, low-lignin, highly digestible variants of ryegrass. These grasses were developed at the Institute of Grassland and Environmental Research at Aberystwyth University in Wales through conventional crossbreeding techniques, particularly with the AberDart and AberMagic varieties (see sidebar on page 33).
Researchers have deliberately avoided the laboratory techniques of genetic modification, which directly alter the genetic makeup of the plants, because it is controversial in Europe. Among the concerns is that genetically modified (GM) crops will spread into the natural ecosystem. Grass is wind-pollinated, and the scientists don't want to risk gene transfer to non-GM plants.
The first step for Kelly and colleagues is processing the grass to extract a water-soluble "juice" that contains fructans (fructose oligomers and polymers). Kelly's team has cloned genes for enzymes that can hydrolyze these fructans. They insert the fructans into the fermenting yeast to optimize the process.
The second step is fermenting the relatively dry, stable lignocellulose fraction residue. This involves use of enzymes that can break down the plant cell walls.
Iain Donnison, leader of the bioenergy and biorenewables program at the Aber Bio Centre at Aberystwyth University and one of Kelly's main collaborators, says preliminary calculations suggest ryegrass could be as good as or better than wheat or sugar beets as a source of ethanol.
Swansea's Kelly is well-schooled. He studied molecular biology with Nobel Prize winner Sir Paul Nurse, who shared the 2001 prize for work on key regulators of the cell cycle. That positions Kelly to push forward a genomic approach in meeting the challenges of producing ethanol from biomass.
Wales, on England's west, is famous for its grassy landscapes. No surprise, it is trying to build its biofuels involvement in part on all that grass. The Welsh government is funding a planned Centre of Excellence in Biorefining at the universities of Aberystwyth, Bangor and Swansea, with additional funding from the European Union.
In a region where mining once drove the economy but has since diminished in importance, the purpose of the centre is to provide research and guidance for businesses to create new employment and preserve existing jobs. Backers seek commercial partners as well. "This," says Kelly hopefully, "is a good time to invest in this area of science."
He pushes ahead with his work on ryegrass to establish a better understanding of the grasses and the key microbes associated with processing them.
Ryegrass represents an important prospective source of biomass because it is present on two-thirds of agricultural land in the U.K. At the same time, EU efforts to reform agricultural subsidies encourage farmers to decrease the number of animals grazing on their land. "So, farmers are wondering what they can do with this excess of grass." Donnison says.
Cows Like It
Grass stands out from other prospective perennial feedstocks for its high soluble carbohydrate (sugar) content. Indeed, IGER has bred ryegrasses from varieties such as AberDart and AberMagic to select for this high-sugar content, originally because cattle grazing on high-sugar grasses gave a higher milk and meat yield. Now it appears that the same grasses can also provide a high potential ethanol yield.
Donnison's team is scaling up. "We believe ethanol from grass could be comparable in yield to wheat and beets," Donnison says, "and the key advantage is that it could be low-input, as it is a perennial crop. If it is grown with clover, which fixes nitrogen, then not much fertilizer is needed."
The work tracks research published earlier this year showing the economic feasibility of producing ethanol from switchgrass. Researchers at the USDA and the University of Nebraska-Lincoln carried out field trials on 10 plots of 15 acres to 20 acres each on marginal cropland on 10 farms in the U.S. Midwest. Measuring inputs, biomass yield, estimated ethanol output, greenhouse gas emissions and net energy, researchers found that switchgrass produced more than six times the renewable energy compared with nonrenewable energy consumed. Researchers also calculated that emissions of greenhouse gases from switchgrass ethanol would be 94 percent lower than regular gasoline.
Meanwhile, back in the U.K., Richard Dinsdale of the University of Glamorgan in Pontypridd, Wales, has found another use for grass. Collaborating with IGER researchers, Dinsdale is working at producing hydrogen.
Using anaerobic organisms-mainly Clostridium cultures-to produce hydrogen and methane, Dinsdale and colleagues are now working on a variety of techniques to improve hydrogen yield from grass stocks.
Biogas can include both methane and hydrogen, depending on the nature of the fermentation process. It can be piped off, compressed and used as a transportation fuel.
Dinsdale's figures suggest that, as a transport fuel, biogas can produce three times more mileage than either ethanol or biodiesel per unit of land. He and his colleagues are currently building two pilot plants to establish key engineering parameters and seeking funding to extend the work beyond 2009.
Biogas is already used in Germany, Austria, Sweden and Italy-but not yet much in the U.K. or the United States. Dinsdale believes biogas ought to have a big future as a transportation fuel in the U.K. However, existing liquid-fuel infrastructure inhibits its development.
In any case, researchers say that 30 acres can fuel a London bus for a year. If true, evidently the cows knew it first.
Susan Aldridge is a London-based freelance writer and editor specializing in biotechnology, medicine, health and chemistry.