Stick an Orange in Your Gas Tank! Stick an Orange in Your Gas Tank!
by Jan Suszkiw
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An apple a day keeps the doctor away, but an orange-load could keep your car on the road. That’s if Florida chemist Karel (pronounced “Carl”) Grohmann’s idea ever bears fruit: making ethanol, a natural “biofuel,” from the peels, pulp, and other wastes of processed oranges.
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He first came up with the idea about six years ago at the Citrus and Subtropical Products Research Laboratory in Winter Haven, Florida. The lab is part of USDA’s Agricultural Service. Grohmann’s idea may sound wacky until you learn that oranges and their peels are chock-full of many different kinds of sugars, like fructose. These sugars can be fermented by microscopic yeasts to make a type of alcohol called ethanol.
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Most ethanol is now made out of fermented corn sugars. Today, ethanol is used in about 11 percent of all automotive fuel blends sold in the U. S. In some states, ethanol is regularly sold to help hold down air pollution from cars, trucks, and buses because the oxygen it adds to petroleum-based fuels like gasoline helps neutralize carbon monoxide.
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Until recently, no one has tried making this natural biofuel from orange peels or other citrus waste. In Grohmann’s view, Florida, the Sunshine State, was the perfect place to start. Juice makers and other food processors generate millions of pounds of citrus waste there each year. This waste is dried, pressed, and sold as animal feed. But citrus growers and processors don’t earn much from such waste. It usually sells for less than five cents a pound.
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Grohmann figured he could squeeze more value out of the industry’s citrus castaways. He knew that yeasts could partially ferment orange sugars into ethanol, also called ethyl alcohol. But he knew that certain natural oils in orange peels keep the yeasts from finishing the job. Grohmann, therefore, decided to get extra help from another microbe, a bacterium called Escherichia coli KO11. This one-celled assistant came from the lab of two University of Florida scientists with whom Grohmann teamed up. They gave the bacterium special genes for fermenting the leftover sugars.
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When grown in a batch of citrus waste, KO11 quickly ferments the sugars that the yeast passed up. It takes the hardworking bacterium only about two days to convert the unfermented sugars into ethanol, acetic acid, and carbon dioxide.
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Ethanol isn’t the only valuable product from the bacterium’s efforts, Grohmann says. The carbon dioxide, for example, can be captured and frozen into dry ice, which keeps perishable items cold during shipping and storage. Acetic acid is used in many industrial products—from organic solvents to food items such as vinegar and flavorings. All this from oranges! And you thought they were just for eating, and the peels only good for throwing away.
Public Domain
According to the passage, what is the biggest challenge Grohmann faced in his attempt to make ethanol from citrus wastes?
a. determining why yeast was unable to ferment all parts of an orange peel
b. developing a bacterium that could aid yeasts in breaking down sugars
c. convincing growers that citrus wastes can be used for something other than animal food
d. finding a large quantity of inexpensive orange wastes for his experiments