Until 1991 when it was outlawed, California rice farmers had collected leftover straw into heaps and set it on fire, creating significant volumes of smoke. Today, the USDA Agricultural Research Service's (ARS) Western Regional Research Center in Albany, Calif., is developing the right formula—through process chemistry and enzyme treatments—to turn the agricultural residue that has caused disposal problems for the state into ethanol.
"[This process] is going to require more infrastructure and some good partnerships with people that are willing to try the engineering out … and we are just getting into that," said William Orts, bio-product chemistry and engineering research leader at the ARS. "We've been working on the enzymes and the chemistry for years, but we are just now working with folks who are starting to scale that up and put out ethanol." Orts said Cargill was among the major partners with the USDA in the private sector, but he said that several participants in the project wished to remain anonymous.
Currently, there are more economic than scientific challenges when it comes to making rice straw a legitimate and successful production feedstock. "The biggest one is getting the straw to a single place and how big that [facility] needs to be because straw farmers don't want to drive more than 50 or 100 miles … and every mile they go adds to the energy cost," Orts said. "That is one component that doesn't track well if oil prices are going up. Then the price to move the straw is going up as well."
The annual California planting for rice production is approximately 600,000 acres. Each acre of rice produces about 2.25 tons of rice straw. Of the 1.35 million tons of California rice straw produced, approximately 3 percent to 4 percent is used in commercial applications.
Rice-straw-to-ethanol conversion through hydrolysis has been proven in the lab, Orts said, but obstacles still remain. "Now it is a matter of calculating the economics," he said. "As we start to scale it up, we have to look at everything from glass to stainless steel, which are really going to be issues. We have to find partners that are willing to build those proto-plants and take those risks. There is a financial risk involved in building these things and hoping that the chemistry in the lab will scale up."
In late August, Colusa Biomass Energy announced that it had selected a site for a 10 MMgy straw-to-ethanol refinery. The 15-acre site is part of an existing industrial park in Colusa, Calif., a prime rice-producing area of the Sacramento Valley. The plant is based on patented and proprietary technologies that convert biomass into ethanol.
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