Converting food losses into fuel and profit gains

Switchgrass can yield almost twice as much ethanol as corn, estimates Geneticist Ken Vogel, who is conducting breeding and genetics research on switchgrass to improve its biomass yield and its ability to recycle carbon as a renewable energy crop.

What could be more beneficial to a grower than eliminating crop waste? Perhaps nothing, but since that’s an unlikely scenario, the second best thing may be creating lucrative products from what sometimes rots in the fields.

As interest and demand for alcohol fuel or ethanol continues to build, scientists are finding that more and more spoiled crop varieties are suitable for conversion. Better still, they are developing methods for producing both ethanol and other high-value byproducts from the same waste, while refining processing techniques for greater efficiency.

These findings open more doors for growers to branch into the biomass fuel market, without regard for the food vs. fuel debate.

The basics of converting waste to alcohol fuel

Almost any food containing sugar or starch can be converted into alcohol, according to David Blume, permaculture expert and alcohol fuel advocate. In addition to many fruits and vegetables, stale doughnuts and other garbage and contaminated products are suitable feedstocks. Author of “Alcohol Can Be a Fuel” (, he says foods are converted into alcohol fuel in the same way that alcoholic beverages such as wines are produced.

The feedstock is cooked to form a sugary solution to which yeast is added. Depending upon the material used, fermentation takes one to three days. The result is one-half alcohol and one-half carbon dioxide, which Blume says can be marketed for greenhouse use. The solution is distilled, extracting the 96 percent that is in alcohol form; the remainder is water.

Disadvantages of this method can be high production costs and excess liquid waste. The costs can be mitigated if additional valued-added products are created.

Sugar beet (Beta vulgaris).Leaf beets were originally domesticated in the Mediterranean, whereas sugar beets and other beet varieties were developed mainly in northwestern Europe. For biofuel use, raw sugar beets are processed to obtain refined sugar, which is then converted to ethanol.

Citrus peel has potential as energy

Researchers at the Agricultural Research Service (ARS) Citrus and Subtropical Products Laboratory in Winter Haven, Fla., and its partner Renewable Spirits, LLC of Delray Beach, Fla., are developing a method for efficiently converting citrus peels into ethanol.

Florida alone produces between 3 million and 5 million tons of wet peel waste annually, which is typically dried as cattle feed. But the value of the feed is so low that this form of disposal often represents financial loss. Converting citrus peel into sugar for fermentation into alcohol also is costly, but researchers are finding ways to make it profitable.

First, scientists modified the process to substantially reduce the amount of enzyme required to convert the citrus waste carbohydrates to sugars and ethanol. Then they developed a way to produce limonene, used in cosmetics and cleaning products, as an additional marketable commodity. Together, these innovations offer citrus growers a profitable way to dispose of waste.

New praise for watermelons

Packed with lycopene, watermelons are more popular than ever, but about 20 percent of the juicy fruits never leave the fields due to poor cosmetic quality. ARS scientists in Lane, Okla., say those 800 million pounds of melon are fine for ethanol production.

After valuable nutraceutical compounds lycopene and citrulline are extracted from the waste, ethanol can be produced from the remaining sugars. In addition to those marketable products, benefits include helping to defray the sewage treatment costs of harvesting lycopene and citrulline. Scientists believe rotating crops such as annual ryegrass and sorghum with melons to produce a year-round biomass supply may be possible.

Tons of distiller’s dried grains are stored at the ethanol plant in West Burlington, Iowa.

The list of crop waste and nonfood plants that may fill your tank in the future is seemingly endless. Today, corn kernels are the most common feedstock, but new technology can convert cobs and stalks. Africans are putting banana skins, leaves and stems to fuel use. Blume says almond and walnut husks and carrot peels also have potential. He is in favor of northern Californians returning to beet production, as the crop makes quality fuel and dairy feed. Sweet sorghum is ideal, as it can generate more than 1,000 gallons of alcohol per acre; corn only yields 250 gallons per acre.

Innovations in production

ARS scientists aren’t the only parties helping to make ethanol production fiscally efficient. Novozymes (, a Danish biotechnology firm, has developed an enzyme for creating so-called second-generation biofuel, which is cellulosic ethanol produced from nonfood plant sources. The enzyme breaks down the biomass for fermentation. The new product cuts the enzyme cost by one-half. The company expects to offer commercially viable enzymes next year, when the Renewable Fuel Standard requires suppliers to blend 100 million gallons of cellulosic ethanol into gasoline.

In work that can go a long way in making biomass ethanol production viable, a mobile crop residue machine has been developed in Canada. The new method breaks down material thermally through a pyrolysis (heating) process and much more rapidly than enzyme-based techniques; 10 tons can be processed daily.

In addition to the bio-oil, comparable to crude oil, that it yields, the machine also produces byproducts such as bio-char (ash-like leftovers) and light gases such as methane. Still in the development phase, the portable pyrolysis machine will be produced by the Canadian firm Agri-THERM ( The firm envisions a system through which it could be transported from farm to farm to collect waste.

Systems and infrastructure

Of the 170 commercial U.S. ethanol plants operating in 27 states as of January, the majority are located in the Midwest, reflecting the feedstock most commonly used, corn kernels; 24 plants are under construction.

As the obstacles to ethanol production from crop waste are being eliminated, the race to establish suitable plants is on. Twenty-six facilities are in the works, distributed more evenly across the nation, and feedstocks vary by region. Plants in Idaho, Iowa, Kansas, Kentucky, Montana, Nebraska, South Dakota and Tennessee will use corn waste, while California and Florida operations will work with post-sorted municipal solid waste. Woody biomass, construction debris and sugarcane are additional feedstocks.

Establishing an alcohol fuel plant

Constructing a small on-farm ethanol plant can be done quickly and inexpensively, according to Blume. By recycling a tank and other materials, a plant capable of generating 200 gallons a day could be built for about $2,000 with a few months’ part-time work.

In general, it costs about $1 per gallon of annual production; a 100,000-gallon plant would run about $100,000. Blume says most supplies are sold to oil companies, where they are blended into gasoline. He suggests that investing about $100,000 to open an above sground tank and pump and selling the fuel to the local community may be another viable option. With a production cost estimated at 50 cents per gallon, such a venture could be profitable.

For growers interested in selling their waste to second-generation ethanol plants or entering the business themselves, federal and state tax credits, loans and other incentives may be available. Oregon, for example, offers tax credits for up to 50 percent of a plant’s construction cost and for using alcohol fuel. California gives producers a cash payment of 45 cents per gallon made and tacks on an extra dime for plants yielding less than 60 million gallons annually.

For more information:
The U. S. Department of Energy:
The U.S. Department of Agriculture:
The Renewable Fuels Association:

Based in Greensboro, N.C., the author writes articles about horticulture, landscaping, agriculture and travel. She has been a contributor to Moose River Media publications for three years.