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Arundo Is Better than Switchgrass for Biomass Power Generation

Arundo donax, the ancient species of Giant Reed that may have hidden Moses along the Nile River more than 3500 years ago, could also go a long way in solving the U.S.' 21st century biomass to energy needs. That is, if it can overcome regulatory hurdles and environmentalists bent on characterizing this tall grass as an "out of control" invasive species.

In the U.S., Arundo’s biggest challenge remains whether the Environmental Protection Agency (EPA) will ultimately grant the Giant Reed a Renewable Identification Number (RIN).  A RIN would enable biofuel refiners and fossil fuel blenders to receive credits for complying with the 2005 federally-mandated Renewable Fuels Standard (RFS).

“The EPA hasn’t announced a timetable for RIN approval,” said Wil Glenn, communications director for the Biofuels Center of North Carolina.  “But the agency has already recognized the Giant Reed (Arundo donax) as a crop that can reduce Greenhouse Gas (GHG) emissions by up to 80 percent.”

However, environmentalists note that Arundo has already transformed a significant amount of native southern California riparian habitat into pure stands of this weed-like grass.  In fact, it’s estimated that tens of thousands of acres of Arundo now line southern California drainage systems, after being intentionally introduced nearly two hundred years ago as a hedge against soil erosion.

Originally, native to the grasslands and wetlands of East Asia, its hollow, bamboo-like stems can reach heights of more than 25 feet producing 20 dry tons of biomass per acre.  That’s compared to Switchgrass, which only averages up to 8 tons an acre annually. 

But although fast growing and drought-tolerant, Arundo’s seeds are sterile.  Thus, its stems and underground bulb-like rhizomes only propagate via cultivation or movement by forces of nature like hurricanes and flooding.

Despite such cultivation challenges, Arundo’s potential as a biofuel feedstock is already recognized in Europe.

Since late last year, Beta Renewables, whose partners are Chemtex, Novozymes and TPG, has been operating a 20-million gallon a year ethanol production facility in Crescintino, Italy using Arundo donax and wheat straw as feedstock.

“In Italy, we use enzymatic hydrolysis fermentation,” said Delane Richardson, a chemical engineer at Chemtex in Medina, Ohio.  “You extract the sugar from the biomass and the enzymes take the long chain sugars and cut them into digestible C5 and C6 sugars that are then exposed to a patented ethanologen microorganism to produce ethanol.  We want a facility just like it in North Carolina.”

Although the EPA has yet to get onboard, the North Carolina Dept. of Agriculture recently decided against putting Arundo on the noxious weed list, leaving the door open to cultivation.

Richardson says Chemtex would like to build a biomass to ethanol plant in Clinton, North Carolina that would operate on a combination of Arundo, Switchgrass, Fiber Sorghum, Miscanthus, and Rye at a delivered aggregate biomass feedstock cost of $50 or less per dry ton.  However, the largest single component would be 100,000 tons of Arundo, which would account for 7 million gallons (or at least a third) of the Clinton facility’s annual ethanol production. 

If the plant’s local biomass supply chains were firmed up, Richardson says the North Carolina facility could be operational by mid-2015.  

Richardson says that while the conversion process uses the Arundo’s sugars, as much as 60 percent of the harvested reed is leftover.  It’s this leftover lignin that is generally converted to electricity.  Richardson notes that Beta Renewables’ Italian facility has enough converted electrical power to supply its own needs as well as sell a portion to local utilities.  Chemtex hopes to do something similar with its planned North Carolina facility.

On the other side of the country, however, Portland General Electric (PGE) is running a study to determine whether Oregon’s Boardman coal-fired electric plant can be converted to a total biomass facility after the year 2020.  That’s the deadline for the plant to meet a regulatory ultimatum dictating that the facility cease burning coal.

If it successfully makes the transition to biomass, the 585 MW Boardman plant, which already provides PGE with 15 percent of its electricity, or some 65 percent (374 MW) of the plant’s output, would become the U.S.’ largest biomass-fueled electric generator.

But to do so, PGE would have to have some 8,000 tons of biomass for every day the biofuel generator was operational.  An Arundo test crop, being grown on 90 acres of Morrow County, Oregon farmland, will be harvested, pulverized and then torrefied in a charring process before the Boardman plant actually tests the crop in its facility next year. 

“The goal in the test burn is to determine whether it’s feasible to convert this coal-fired power plant to [biomass],” said PGE spokesman Steve Corson.  “Arundo would only be only one of several feedstocks for such a biomass plant.”

Still, it’s estimated that Arundo would produce about 10,000 Btu/lb compared to 8500 Btu/lb for Boardman’s coal operations.

As for the risk of invasiveness in Oregon?

Tim Butler, a weed scientist at the Oregon Dept. of Agriculture, says mitigation control against Arundo invasivity would include strict monitoring of fields; restrictions on how close it could be planted to water; and attention in cleaning farm equipment leaving its fields. 

The Giant Reed has been sold in Oregon as an ornamental for decades, says Butler, and thus far, the state appear to be free of wild Arundo stands.

However, Lauren Quinn, an invasive plant ecologist at the University of Illinois at Urbana-Champaign, says that every Weed Risk Assessment (WRA) published for Arundo has indicated high risk.  “We worry about extreme climatic events such as hurricanes moving rhizomes out of cultivation [areas] and about abandonment of plantations after leases expire or if the industry fails,” said Quinn.  She notes there is also a risk of escape via transportation of rhizomes to production fields or bio-refineries.   

As weed scientist Joe DiTomaso at the University of California at Davis notes, Arundo is the “weediest” of all the plants being considered for biofuel and, as such, has taken over a lot of stream banks.  Its root fragments can also can spread down river corridors via flooding events, where they eventually create new Arundo colonies.

But when planted on farmland, DiTomaso says Arundo is easy to manage because it doesn’t produce any viable seeds.  Because its only means of spreading are via stem nodes and rhizomes, he says when planted in confined areas away from water, it remains at low risk of invasivity.

“The good news is that Arundo is one of the few crops that meets the yield threshold that we believe is going to make it attractive for farmers to plant,” said Richardson.  “The bad news is that a hundred years ago it was mishandled and became invasive in some environments.” 

But at this point, without the RIN, Richardson says the economics for Chemtex’ North Carolina project don’t look promising.  Even so, Richardson says Chemtex is looking at other potential Arundo biofuel plant locations in the Southeast including Virginia, Kentucky and Georgia.  The idea is to target former strip-mining areas, as well as low-production agricultural lands, such as former tobacco-growing areas for Arundo acreage.

“Arundo can be grown on very contaminated soils without herbicides or pesticides and a minimal amount of fertilizer,” said Richardson.  “Plant it once and it lasts 15 years.  That’s versus a corn crop where you’re pushing a tractor through a field five times a year.

Arundo is a win, win, win.”   

Lead image: Arundo Donax by Bouba at fr.wikipedia (photo by Bouba) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 via Wikimedia Commons

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