Clemson researcher converting waste fruit into biofuel
Deep in the ocean, in water so hot it’s almost boiling, a little-known type of bacteria that loves to turn sugar into hydrogen thrives, unnoticed—until now.
This exotic microscopic creature has found a home in a laboratory at Clemson University, where researchers are exploring the possibilities of harnessing its creative potential to make energy.
Its sugar source: peaches.
Not the ones that are marketable, but those that are blemished in some way that makes them unsaleable.
It’s not likely to solve America’s dependence on foreign oil, but Biosystems Engineer Caye Drapcho’s work with peaches and the microbe called Thermotoga neapolitana could indeed prove groundbreaking.
The project promises to provide a new way to generate electricity, not only from peaches, but from any waste fruit material that now has little, if any, value.
“In our view, any little contribution you can make is worthwhile,” Drapcho said. “When you think about all the food processing waste from tomatoes or other crops, if that could be converted, it would add up.”
While the process might be applicable to many sources of sugar, it’s the 20 million pounds of peaches that are thrown away by South Carolina growers every year that is the first target.
Ninety percent of that waste is water. The 2 million pounds of peach solids remaining could be converted into enough electricity to power 200 homes for four months, according to Drapcho’s calculations.
South Carolina, second only to California in peach production, grows more than 200 million pounds of the fruit annually. The South Carolina Peach Council is funding the research by Drapcho and Graduate Assistant Abhiney Jain.
Sun-ripened Palmetto State peaches, loaded with sugars, are a perfect source of fuel for the hungry microbes.
“Obviously they like sugar in peaches just like people like sugar in peaches,” Drapcho said.
To the peach blend, she adds nutrients such as nitrogen, phosphorus and micronutrients into the bioreactor with the bacteria. The next phase of the project will be to see how well the process goes without adding nutrients.
In the lab, it takes about 20 hours for the bacteria to convert the sugars into hydrogen. Using the same process on a production scale with a continuous flow of peach sugar into the system, Drapcho’s models show it could take just four hours to make the conversion. The next step will be to set up a pilot plant in a packinghouse to try the process on a larger scale.
“A significant percent of our future energy I think will come from biofuels, and if we look at all the waste resources then we’ll be able to do it effectively, along with solar, geothermal and everything else,” she said.
New bug on the block
While converting plant sugars into fuel that can be burned to produce energy is as old as the distillation of liquor, using that raw material to produce hydrogen rather than a fuel such as ethanol is fairly new.
The bacteria Drapcho is using was only discovered in the mid-1990s. Classed as an extremophile, it flourishes in conditions that would kill most forms of life. It was discovered in mineral-rich, deep-ocean heatvents near volcanoes and requires temperatures of 180 degrees Fahrenheit.
The bacteria is anaerobic, meaning it converts sugar to hydrogen without using oxygen in the process.
Although it typically produces byproducts that contain 25 to 30 percent hydrogen, it can produce up to 80 percent hydrogen out of plant sugars, Drapcho said.
The South Carolina Peach Council was originally interested in converting the waste peaches into methane or ethanol, but bought into Drapcho’s concept for biological production of hydrogen.
The hydrogen used in fuel cells now generally comes from natural gas, so it doesn’t actually save fossil fuel, she said.
A hydrogen fuel cell’s only byproduct is water, which could help reduce overall carbon dioxide emissions into the atmosphere.
“Hydrogen gas is kind of viewed as what our fuel of the future may be,” she said.
One possible application for using the waste peaches would be to provide energy to run the packing plants themselves. It is there where about 10 percent of the harvest is usually culled out because of bruises or other cosmetic defects.
Those wasted peaches are usually discarded in fields, but growers are concerned that state and federal regulators may outlaw that practice.
A 5,000-liter bioreactor, about 10 feet by 10 feet, would be the optimal size for practical application of the hydrogen conversion operation, Drapcho said. It could be connected to a hydrogen fuel cell to convert it to electricity. A setup of that size would be enough to power one home or a small packing plant, she said.
Just as petroleum has many other uses besides making gasoline and diesel fuel, the peach bioreactor process creates useful byproducts as well, she said.
Acetate is one such byproduct. One of Drapcho’s graduate students, Derek Little, is working on a project using acetate leftover from the peach process to generate a small amount of electricity in a microbial fuel cell.
The only reason oil has been relatively cheap in the past is because of all the byproducts that come from it, Drapcho said.
It actually takes more energy to get the oil out of the ground and refine it as the oil generates, she said. Tax breaks to oil companies and the oil byproducts are what make the economics feasible, she said.
The process Drapcho is working with could have much broader applications on all kinds of plant products that are now going to waste.
For example, one vendor has been in touch with her about the possibility of using juice that drains off from the processing of cut fruit for sale in grocery stores. One local chain produces 10,000 gallons a week of juice in this way—Drapcho has already started fermenting some of it.
“Of course the bacteria love that, too,” she said.
Ron Barnett is a freelance writer and has been a frequent contributor to Moose River Media over the years. He resides in Easley, S.C., and is always on the lookout for new and interesting stories in the Carolinas, Georgia and east Tennessee.