April 17, 2008 | General

Redefining Ag Wastes As Coproducts

BioCycle April 2008, Vol. 49, No. 4, p. 42
Once considered products of the waste stream, a nonprofit in Minnesota shows that agricultural residues and coproducts are powering the future.
Dan Lemke

ALAN Doering doesn’t have the word “waste” in his vocabulary. As the scientist heading up the Agricultural Utilization Research Institute’s (AURI) coproduct utilization program, Doering sees crop residue, agricultural processing leftovers and biomass as products with value worth exploring.
“Every leftover or coproduct has a value,” Doering says. “Our goal is to find the best use with the highest value for each of them.”
AURI is a nonprofit corporation based in Waseca, Minnesota that works to develop new uses for the state’s agricultural products and ag processing coproducts. It’s the focus on identifying and developing value-added uses for products with little value that makes Doering’s work unique. That work is also moving those coproducts into some exciting new areas, including renewable energy, fertilizer, environmental products and even animal care.
Between 2001 and 2007, U.S. fuel ethanol production capacity grew 220 percent from 1.9 billion to 6.1 billion gallons. In Minnesota alone, 17 plants produce over 680 million gallons of ethanol from corn each year. Each bushel of corn yields 2.8 gallons of ethanol. In addition to the liquid fuel, that bushel yields 17 pounds of dried distillers grains (DDG) and a thick, heavy liquid called solubles or syrup. In most cases the solubles are sprayed back onto the distillers grains and dried. However, more recently, both the liquid and dry coproducts have garnered attention as valuable products individually.
The distillers grains are golden brown granular remnants of the fermentation process. The DDGs are primarily used as livestock feed for cattle, poultry and hogs. That market is expanding as research underway determines optimal inclusion rates in feed rations for each species.
High in energy value at over 8,400 Btu per pound, the distillers grains are also attractive as a fuel. Doering and AURI have provided assistance to multiple companies working to include DDGs in solid fuel pellets. The grains also have the potential to be cofired with nonrenewable fuels like coal to help reduce emissions.
Two Minnesota ethanol plants have installed gasification equipment, which allows biomass materials such as wood, grasses and distillers grains to displace natural gas. Gasification converts solids into synthesis gas that can be used to produce heat or electricity, offsetting the use of fossil fuels. Central Minnesota Ethanol Cooperative in Little Falls, Minnesota and Chippewa Valley Ethanol Cooperative in Benson, Minnesota have installed gasifiers capable of using the DDGs when the economics are favorable. DDGS are typically more valuable as a feed ingredient, but when prices dip, they can supply the biomass needed to produce syngas.
The solubles are also offering opportunities for adding value. Another Minnesota ethanol plant installed the first-in-the-world fluidized bed biomass incinerator to burn the syrup, making steam that powers the plant. Since introducing the technology in 2005, Corn Plus of Winnebago, Minnesota has reduced its natural gas consumption by more than 50 percent.
It’s not all about energy, though. Since ethanol plants are always looking for ways to add value to their coproducts, Doering wondered about the syrup’s nutritive value. Tests by several independent laboratories revealed high enough levels of nitrogen, potassium and phosphorous to warrant applying the solubles as fertilizer in field trials. One thousand gallons of solubles contained about 73 pounds of total nitrogen – almost 100 percent in the organic form.
“The solubles looked good after the lab analysis, but the only way to find out for sure was to test it in the field,” Doering says. Harvest data showed that the solubles had an effect, though not as much as commercial fertilizer. Ammonium and nitrate forms of commercial fertilizer are almost immediately available to plants. Organic nitrogen, including solubles and livestock manure, take time to mineralize or break down so plants can use them.
Comparing the response rates of solubles and commercial fertilizer, University of Minnesota soil scientist Dr. Gyles Randall found “only about 21 percent of the nitrogen in the syrup was actually available,” compared to 100 percent for fertilizers like urea. Test data revealed that plots spread with 3,000 gallons per acre of solubles yielded about the same harvest as plots with 60 pounds of commercial fertilizer.
While yield results showed modest success, Randall and Doering expect the syrup would provide more available nitrogen if applied, like manure, in the fall and incorporated during postharvest tillage. “There should be better mineralization,” Randall says. “Its potential as a spring applied fertilizer appears limited, but it may be much better fall applied.”
One advantage is the relatively low cost of using syrup as fertilizer. However, transportation and application costs may impact its economic feasibility.
Biodiesel is a growing industry as a vegetable oil-based diesel fuel replacement. In Minnesota, for example, three operating biodiesel plants have a total annual production capacity of about 63 million gallons.
Like the ethanol industry, biodiesel refining creates coproducts. Mixing 100 pounds of soybean oil with 10 pounds of alcohol yields about 100 pounds of biodiesel and 10 pounds of glycerin. The sweet, thick liquid has hundreds if not thousands of uses – from toothpaste, lotions and cosmetics to livestock feed and medicine. As biodiesel production has increased, so has the amount of available glycerin.
Several years ago, crude glycerin sold for over 70 cents a pound – today it may sell for just a few pennies. In some cases, manufacturers are paying to get rid of excess glycerin.
The glycerin in personal care and food products is highly refined. Because of the expense, most biodiesel refineries lack the necessary equipment to further purify glycerin. Finding a large-scale use for crude glycerin will help alleviate growing supplies and give the biodiesel industry a new revenue stream.
Pure glycerin contains about 19,000 Btu energy value per pound, while crude glycerin yields just under 7,000 Btu. Research has been conducted using crude glycerin as a fuel; however, its use is not widespread. Crude glycerin is also being evaluated as an ingredient in livestock feed.
The nation’s first poultry litter-fueled power plant opened in October 2007. Fibrominn is generating enough renewable electricity to serve 40,000 homes. Fibrominn will burn 500,000 tons of poultry manure a year, as well as other biomass. Most of the manure is supplied by central Minnesota turkey producers.
In addition to generating electricity, Fibrominn also produces ash as a coproduct. Ash from the combusted litter is reconditioned for use as a fertilizer. This spring, ash from a number of renewable energy production facilities utilizing a variety of technologies, will be tested for nutrient value and functionality as fertilizers. Test plots will be established to determine the value of the ash.
“As biomass combustion and gasification increases, the availability of ash will also grow,” says Doering. “Like many other ag-based coproducts, there is value left in that ash. In this case it’s as a fertilizer. We want to see just how much value there is, see how available the nutrients are to the plants and compare it to commercial fertilizer.”
The tests will be conducted during the 2008 growing season at the University of Minnesota Southern Research and Outreach Center in Waseca, with results expected in early 2009. Doering says work will also be done on ways to densify the ash so that it can be land applied. Presently, most ash is very light and fine, making application difficult.
Building on Biomass
Growing in popularity among Minnesota’s dairy producers is an innovative cow housing setup that reduces labor inputs, improves cow comfort and also helps solve some manure management issues. Called compost bedded pack dairy barns, the open facilities feature a layer several feet deep of bedding, often sawdust or biomass. Cows lounge on the thick pack, which farmers till or stir several times a day. Microbial activity causes the manure and bedding to compost, creating warmth for the cow and stabilizing the manure. It also reduces pathogens and has a positive effect on cow health.
But rising fuel prices have increased the cost of transporting sawdust and wood shavings, the most commonly used products in compost barns. Tight supplies of those wood products also impact availability and are a limiting factor in managing these barns.
Since wood is only one source of bedding, AURI and the University of Minnesota researchers set out to determine other suitable biomass sources. Scientists evaluated 11 different media for chemical, physical and microbiological characteristics that would indicate they could be used as bedding materials. They tested beet pulp, corn cobs, corn stover, elm chips, flax straw, pine bark, pine chips, soybean hulls, soybean straw, wheat straw and wheat straw screenings. Investigators evaluated the various products for pH levels, water-holding capacity, carbon to nitrogen ratios, phosphorous, bulk density and free air space, which is needed to support microbial activity.
“Because of the growing interest in compost barns and the demand for bedding material, this really provides an excellent opportunity to utilize ag fibers and coproducts,” says Doering. “Not everything we looked at worked, but it helps to narrow down other alternative sources that could be available to dairies.” Four different media are being tested further including sawdust, a blend of sawdust and small wood chips, corn cobs and soybean straw.
Corn stalks are the main ingredient in another animal comfort creation called Compost-A-Mat. These mats are used in hog furrowing and nursery operations as a replacement for rubber mats that are generally reused after each pig litter is weaned. Even though they are disinfected before each use, not all pathogens are completely removed. Compost-A-Mats are single use and biodegradable, offering a comfortable environment, but not harboring pathogens that can lead to disease and higher death rates. Independent tests have shown significantly lower instances of E. coli and other pathogens among litters using Compost-A-Mats. Produced in northern Minnesota, the mats are used by hog producers in 13 states, plus Canada and Australia.
Straws, corn stover and other fibers are being used in Minnesota to battle erosion and fight pollution. Erosion control mats and tubes made from grain straw are the industry standard and are used at construction sites, particularly where runoff could impact surface and groundwater. These natural filters and stabilizers help to keep soil in place.
Liquid hydroseeding mulch containing fiber is another new arena being entered by coproducts. Mixed into slurry using water, plant seeds and ground ag fibers like wood, paper, corn stover or straw, hydroseeding mulch is sprayed onto exposed dirt. As the liquid dries, the fibers and seeds form a blanket that covers the dirt, providing a growing environment that spurs rapid development by the seeds.
“In the past several years, a lot of people have changed their opinions about coproducts,” says AURI’s Doering. “Instead of seeing coproducts as a problem they need to deal with, they’re being recognized as potential new revenue streams.”
Dan Lemke is the Communications Director for the Agricultural Utilization Research Institute (AURI) coproduct program based in Waseca, Minnesota. He can be reached at 507-835-8990, or visit for more info.

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