Making ethanol ‘lemonade’ out of bruised peaches and orange scraps
Posted on August 14th, 2008By Sara Goodman
Climatewire: The self-proclaimed “Tastier Peach State,” otherwise known as South Carolina, may be on the cusp of taking its luscious, plentiful resource and putting a form of it into your car’s gas tank.
South Carolina harvests more than 200 million pounds of peaches a year. But about 10 percent — 20 million pounds — are discarded because they are bruised or damaged in some way. Researchers at Clemson University decided to try to tap this waste and have discovered a way that rotten peaches can be turned into a biofuel.
Peaches are full of sugar, which makes them ideal to convert into hydrogen, according to lead researcher Caye Drapcho, with Clemson’s BioSystems Engineering. Using a microorganism that can convert carbons to hydrogen gas, Drapcho and others are hoping their discovery will provide an easy alternative to fossil fuels.
“When you use a biological organism, it becomes a renewable resource, and it gets us away from our dependence on fossil fuels,” Drapcho said.
High gasoline prices, the quest for U.S. energy independence and the simmering controversy over turning food into fuel have sent people to an unlikely place to look for alternative technology: the local landfill where the bruised peaches and other wastes would otherwise decay into methane, a global warmer 20 times more powerful than carbon dioxide.
The energy law signed by President Bush last December expanded the overall biofuels mandate to 36 billion gallons annually by 2022, with corn ethanol peaking at 15 billion gallons and the rest coming from “advanced” biofuels like cellulosic ethanol that do not come directly from food crops.
U.S. biofuels are made primarily from corn, along with other grains like sorghum and wheat and oilseeds from plants like soybeans. DOE and other federal agencies are working on developing diverse, non-food feedstocks that require less water and fertilizer than corn (Greenwire, Aug. 7).
While one much-discussed option in the Corn Belt — making ethanol out of corn stalks — requires some high technology applications to break down the stalk and its complex sugars, fruit waste offers some less difficult targets and researchers are looking at peaches, oranges, lemons and watermelons.
Thermotoga loves peaches
The South Carolina Peach Council first approached Drapcho in 2003 because it was looking for a useful way to deal with the millions of pounds of peach waste it was left with each year. For Drapcho, the solution seemed obvious.
“We were pretty confident,” Drapcho said. “[This microbe] is ideal for peaches.”
The microbe she is using — Thermotoga neapolitana — successfully breaks down the peach’s sugars, which are primarily fructose, sucrose and glucose, to produce gas byproducts that contain between 25 percent and 30 percent hydrogen. Peaches are about 10 percent sugar, though; the rest is water. Because of this, the waste from one year’s peach season, which is about four months long, will power about 188 homes, Drapcho estimated.
There are ways to put this technology to work year-round. Drapcho suggested one option would be to have a factory that takes in peaches for the three or four months they are harvested, then other fruits throughout the rest of the year.
Another option would be to focus on fruit processors, Drapcho suggested, pointing to a company that cuts up fresh fruit and vegetables for fruit trays and packages. This company hauls away fruit and vegetable wastes such as rinds and peels, getting about 10,000 gallons of juice a week. Because those fruits and vegetables are likely to contain similar amounts of sugar, Drapcho said the microbe would be able to convert that waste to hydrogen, as well.
Moving this technology into application is the next step, Drapcho said. The goal is to launch a small pilot program by this fall, she said. To do that, the ideal location would be a peach packing facility where farmers bring their produce to one location to be packed for shipping. That way, after the sorting and discarding, the technology to produce hydrogen would be on site.
A blend of fruits running your car
In Florida, researchers using technology developed at the U.S. Department of Agriculture’s Agricultural Research Service laboratory in Winter Haven are working on taking citrus waste — primarily the peel — and converting it into ethanol.
“Citrus waste is abundant in Florida,” said David Stewart, president of Citrus Energy LLC, which is developing a process to convert citrus waste to ethanol using an enzyme cocktail that processes the sugar from the waste.
Florida grows between 7 million and 8 million tons of citrus annually, resulting in about 4 million tons of waste, according to Bill Widmer, a USDA Agricultural Research Service scientist. As with peaches, that waste makes citrus fruits prime candidates for conversion.
“It has a big advantage over other feedstock because it’s already collected, which means we don’t have any financial cost or carbon footprint associated with growing, collecting or harvesting it,” Stewart said. “That makes it financially attractive, and in the energy and carbon balance, it also has a big advantage over corn ethanol because it doesn’t interfere with the human food supply.”
Stewart is working on commercializing his technology, which was developed by USDA about 15 years ago. At that time, the enzyme cocktail was not economically viable, but as gas prices have increased and the cost of the enzymes has decreased, that equation shifted about four years ago, according to Widmer. Stewart, who became involved with the USDA/ARS technology about five years ago, formed Citrus Energy a couple of years later.
The Florida Department of Agriculture recently granted another company, Southeast Biofuels LLC, a $500,000 grant to expand its work on converting citrus waste to cellulosic ethanol.
Hunting for the sweet spot in orange juice wastes
Widmer said he believes this technology is primarily geared toward Florida because the state processes 90 percent of the oranges it grows into juice. This means about half of the fruit — the peel, pulp, segment membrane and seeds — is waste. In California, in comparison, the majority of the fruit grown goes to the fresh market, leaving little waste.
Florida’s citrus waste can yield between 30 million and 60 million gallons of ethanol, making it a local energy solution, not a national one, Widmer said.
“The amount of ethanol we can produce from citrus processing waste is not going to solve the energy problem in the United States,” he said. “You can’t really grow corn economically in Florida, so here’s a local waste biomass that could be utilized to make ethanol for a local market.”
Stewart said he is hoping he will be able to break ground on a pilot facility by the end of this year.
Despite these advances in converting fruit waste into biofuels, Widmer said the future of converting wastes into biofuels is in the development of economically viable cellulosic biofuels.
“In order for waste biomass to really make a significant dent into our fuel needs, the cellulosic biomass process has to be made economical,” Widmer said. “There’s a tremendous amount of biomass out there, and then we’ll be able to produce a significant amount of ethanol. They’re close, but they’re not quite there yet.”
