Rejected watermelons -- those with misshapen, scarred or discolored rinds -- may soon be the newest ethanol feedstock, according to new research released this week.
Agriculture Department scientists have shown that watermelon juice can be efficiently fermented into ethanol.
That's good news for watermelon farmers, who routinely leave 20 percent to 40 percent of their crop in the field because of rind defects. Estimates say 360,000 tons of watermelons were wasted in 2007 because of blemished rinds.
"It's not that there's anything wrong with the melon on the inside, but our only method of judgment is the outside," said Wayne Fish, a research chemist at USDA's Lane Research Center in Oklahoma and lead author of the study, published this week in Biotechnology for Biofuels. "You and I as consumers wouldn't buy it in store. ... So it has to be left."
But leaving a fifth to nearly half of a watermelon crop to be tilled back into the soil results in major losses for farmers and isn't worth the value of the nutrients added back to the soil.
So for the past three years, Fish and his colleagues have been studying the viability of producing ethanol from concentrated watermelon juice tapped from the leftover crop.
"It's like in 'Field of Dreams,' the saying, 'If you build it, they will come.' In technology development ... it's 'If you don't build it, they certainly won't come,'" Fish said. "We're testing the feasibility to get the numbers out there to be able to do fairly accurate calculations about whether this might be economically feasible."
He added, "After all, we are basically losing 20 percent of the cropping expenses, and we certainly don't get that back in plant nutrients that go back into the ground."
Fish's team and watermelon farmers aren't the only ones interested in the idea. A small biofuels company in College Station, Texas, is planning to build a vehicle that could begin traveling next summer to watermelon fields and producing ethanol on-site.
"We're trying to assemble the equipment at this time, and as you know, the crop year for watermelons is on right now, so we're in good shape for next season," said Jim Rausch, president of Common Sense Agriculture.
Rausch said the traveling ethanol plant will be capable of producing up to 200,000 gallons of fuel annually.
Rausch said using watermelon juice as an ethanol feedstock has other perks, as well -- besides the ready availability of hundreds of thousands of rejected melons each year.
"Watermelon uses very little nutrients out of soil, it doesn't deplete the soil, and it uses a small amount of water," Rausch said. He added that the energy input -- the amount of fertilizer and water put in -- is significantly lower for growing watermelon than for other potential feedstocks.
But corn and cellulosic ethanol producers needn't worry about the competition just yet. Both Rausch and Fish said they envision the watermelon-ethanol industry as a localized operation, with mobile or small-scale plants being installed at or near watermelon fields to process the leftover fruit and produce ethanol on the spot for use in farm equipment or in other applications that don't require long-distance transport.
In fact, watermelon ethanol could be produced anywhere in the United States.
"Watermelons are grown from Alaska to Florida and Hawaii to Maine," Rausch said. "Those [perks of widespread watermelon production} are all very positive."
Click here to read the study in Biotechnology for Biofuels.
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