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Cellulosic energy research

Because Arkansas is “prime real estate” for bioenergy crops, the recent announcement of a joint U.S. Department of Energy/University of Arkansas research effort is most welcome, says Chuck West.

“I see biomass crops directed to land areas that don’t reliably produce profitable food crops,” says the professor with the University of Arkansas Department of Crop, Soil, and Environmental Sciences. “There’s a lot of land like that all over the state — for example, the foothills along the Arkansas River Valley. And some of the underutilized pastureland throughout the state is suitable for biomass crops.”

Arkansas researchers (including those at Arkansas State University in Jonesboro working on making cellulosic feedstocks more accessible to fermentation enzymes and sequestration of soil carbon) are collaborating with counterparts in other states on bioenergy research and Extension programs supported in part by a nearly $2 million grant from the DOE. Mark Cochran, director of the Arkansas Agricultural Experiment Station, is coordinating the Mid-South/Southeast BioEnergy Consortium, which includes projects in Arkansas and Georgia.

“Arkansas is well-positioned for bioenergy production with large areas of cropland and forests and an innovative processing industry for agricultural and forest products,” Cochran said. “We are working to support the state’s fledgling biodiesel industry and develop the information infrastructure that will allow our farmers and entrepreneurs to move rapidly into the use of cellulosic technology when it comes online.”

While several Arkansas companies are producing biodiesel using soy oil and other vegetable oils and animal fats as feedstock, the big prize would be to make cellulosic biofuel an economically viable alternative. When treated with acids or enzymes, sugars bound in the cellulose of stems and leaves are released. Those sugars can then be fermented to make fuel. While current processing costs are too expensive, cellulosic feedstocks are plentiful and cheap in the Mid-South.

“In the short-term, the biomass material that might be most quickly put to use will be forest residue,” says West, who along with University of Arkansas-Monticello researchers, is evaluating production systems for switchgrass, several sorghum varieties and cottonwood as cellulosic feedstock. “Wood often gets short shrift. People will talk about corn ethanol, soy diesel and switchgrass and forget about forestry residue and fast-growing trees. We already have a huge land area, millions of acres, that’s growing a biomass crop — it’s called forest.”

In terms of perennial grasses, Arkansas is also well set up. “What we have yet to get a handle on is how physically concentrated the grass biomass production areas have to be to support a bio-refinery. In other words, how many miles can these crops be transported to a refinery in an economical manner? True, we have a lot of land area available — but we need a concentrated land area to minimize transport costs. It would be difficult to make the industry run with a patch of biomass here and another one 30 miles away. This is a major issue that will have to be tackled in the future.”

Like West, Julie Carrier says Arkansas’ vast commercial forests — particularly the understory — could be utilized for biofuel production.

“I wouldn’t want to go so far as to say to the pine plantations, ‘We’ll have another use for your biomass’” says the University of Arkansas professor and agricultural engineer. “Forget the actual forest. The understory, instead of just being a problem to contend with, actually would have a viable use and revenue possibility.”

In her project research — often in conjunction with professor Matt Pelkki at University of Arkansas-Monticello — Carrier is focusing only on pure sweetgums. “We must understand the system first. If we try to work with the mixed understory, we’ll get nowhere fast. Instead, we’re breaking up the problem into many smaller pieces.”

The DOE money won’t finish out the research story on sweetgums. However, it will “allow us to do compositional analysis in conjunction with the National Renewable Energy Lab in Golden, Colo. That means the sweetgums will be broken into bark and core components and deconstructed into sugars. Eventually we will be able to ferment those sugars into ethanol, butanol, or whatever product we’re aiming for.”

Carrier says the sweetgum breakdown work will likely take two or three years. The DOE funds, granted on an annual basis, are “simply providing a kick-start for the research.”

Phytochemicals (plant-derived chemical compounds often cited as having health-promoting properties) in sweetgums are also a target of Carrier’s studies. The deconstruction of sweetgums is done with water — “we’re working on a water-dilute acid process at temperatures between 130 centigrade and 180 centigrade. Before doing the sugar deconstruction process, can we extract the value-added phytochemicals with water below 130 degrees?”

If so, the researchers could wash the biomass while extracting phytochemicals and then move on with deconstructing the sugars for fuel.

Back-of-the-envelope calculations show a 50-million-gallon ethanol plant would need 2,000 dry tons of biomass daily. That means a 365-day operation would require roughly between 700,000 and 800,000 tons of biomass per year.

The Arkansas forest understory could produce about 2 million tons annually, says Carrier. “Roughly, we’d have enough biomass to support three ethanol plants from woody feedstock alone, not from herbaceous biomass. If we can get the systems up and running, get the economics right, this could certainly promote the use of woody feedstock for biofuel production.”

West’s research group is aiming for “a sustainable ligno-cellulosic feedstock production practice for energy crops.” The group’s four objectives are:

• Improve weed control and establishment practices for switchgrass.

• Assess diseases potentially limiting switchgrass and sorghum production.

• Generate information on the management, productivity and quality of sweet sorghum for sugar and biomass.

• Establish hybrid, giant miscanthus for future biomass research.

Hybrid miscanthus is a plant native to Asia. It grows very tall — “12 feet tall, easily” — and densely with a lot of stems and leaves. In other states, hybrid miscanthus has produced two or three times more biomass per acre than switchgrass. It’s already being cultivated as a biomass crop in Europe.

“This is a plant that, as far as we can tell, does better than switchgrass in cooler, moister environments. But since Arkansas is a hot, sometimes drought-stressed, environment, switchgrass may hold its own here. Switchgrass is generally more heat- and drought-tolerant than miscanthus.

“So we want to do the research and find out how the two compare in the state. Part of the DOE project is to provide money to establish the beginnings of that research. We’ll be getting some rootstock from Mississippi State University and establish those plants here in Fayetteville for use in future trials.”

Few know that hybrid miscanthus doesn’t produce fertile seeds. “You have to use cuttings, like sprigging bermudagrass. That means it’s more labor-intensive than when planting the seeds of switchgrass.”

Miscanthus is a perennial and will come back from the rootstock every year. Following establishment, it should provide crops for a long time, says West.

What about sweet sorghum? “Sweet sorghum is sort of an odd duck. We mainly grow it for the sugar content. The idea is it would serve Arkansas in the same way sugarcane serves Louisiana. The sorghum contains sucrose — table sugar — that can be fermented quite easily to make ethanol. What’s left over — the stems and so forth — can be burned to provide heat for the fermentation and distillation process.”

West compares miscanthus to biomass sorghum (also known as forage sorghum) which is grown for its biomass, not sugar. “They should have comparable yields. However, the biomass sorghum is an annual and so would require yearly planting. That replanting would be done from seed, though, which is easy to get and economical, and a large acreage can be planted quickly.”

The advantage to the yearly planting is a farmer isn’t locked into a specific energy crop and can make cropping decisions yearly. That isn’t the case with perennials like miscanthus. “If he plants miscanthus, a farmer will want it for a long time. It’s expensive to establish and is a tough plant — it’s tough to kill.

Best case scenario, what is the nation looking at in terms of getting a viable, cellulosic energy industry up and running?

It largely depends on the economy and oil prices, says Carrier. “Even now, (the National Renewable Energy Lab) can produce cellulosic ethanol for approximately $2.29 per gallon. A decade ago, the cost was $4 per gallon. I’m sure engineers will be able to bring the cost of cellulosic ethanol down even more.

“But you’ve got to remember that ethanol has a third less of the energy content of gasoline. A gallon of ethanol won’t take you as far as a gallon of gasoline. So, if gasoline is less than $2 per gallon at the pump, cellulosic ethanol is certainly not competitive.”

West says such a viable cellulosic energy industry is “closer to 10 years than five. There is so much left to do.”

First, says West, investors must be convinced that oil prices will remain high. Right now, with lower oil demand in a severe economic recession it will be more difficult to bring investors in.

It also remains to be seen if there will be a consistent government policy that provides incentives for the biomass energy industry to develop. And that policy must be stable enough so that investors can justify long-term commitments for long-term returns.

Part of that government incentive has to include carbon credits, insists West. There must also be incentives not only for investors but for the landowners and farmers.

“For a farmer to say, ‘I’m going to grow switchgrass instead of soybeans,’ takes a lot. They must be able to point to consistent financial returns.”

One way to accomplish that is through carbon storage in the soil. “Switchgrass, we know, is good at that — deep, thick root systems. Farmers should be able to take advantage of that if they commit to growing switchgrass for a decade.”

Asked the most pressing issue for the energy crops he’s studying, West says it is “definitely” weed control. “Establishment of switchgrass is rather dicey. It’s hard to do in a consistently successful manner. The main problem: weeds. And there are few herbicides that are legally labeled for use on switchgrass. The choices for weed control are very narrow, and the ones we’ve looked at don’t do a very good job. The products just aren’t reliable — some years they work, some they don’t.”

During research “we’ll be looking at some other types of herbicides — different rates, different formulations — that could potentially be labeled. We’ll also be looking at the possibility of no-till seeding into old pastures. We want to know how easy it would be to convert an old pasture into switchgrass without plowing. A crop like switchgrass wouldn’t be used on prime cropland but on soils that are more sloped and erosion-prone. We don’t want to lose the nice cover of grass already on those sensitive lands. Say the pasture is in bermudagrass, can we kill that and then drill right into it and produce switchgrass?”

As for diseases, the energy crops don’t have any serious problems. However, “we also don’t have any large-scale plantings of switchgrass or biomass sorghum. That’s why we don’t see the diseases and don’t know which potential diseases biomass sorghum or switchgrass could face. Once acreage jumps up, disease outbreaks become more probable.”

The plant pathologists in West’s group will be doing surveys to check which pathogens are in evidence. They may be at very low numbers, but “we want to know what could become sources of outbreaks. There’s actually very little known about switchgrass diseases.”


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