BioCycle May 2010, Vol. 51, No. 5, p. 42
Initiative charts the economic feasibility of producing fertilizer pellets in a regional facility with organic residuals from wastewater treatment plants, CAFOs, meatpackers and other generators.
Diane Greer

IN Brown County, Wisconsin, a public-private partnership is working on aggregating and processing organic wastes into saleable, nutrient-rich fertilizer products. The Brown County Waste Transformation Initiative (BCWTI), a stakeholder group comprised of industrial, agricultural and municipal entities, was formed in 2008 to determine if a regional facility could be developed to manage the county’s various streams of organics.
Biosolids produced at the Green Bay Metropolitan Sewage District are incinerated and the residual ash is landfilled. Currently wastes generated by meat packers, dairy farms and related industries are land applied. “In the last 15 years, Brown County has experienced significant urbanization and with that urbanization came a loss of rural space which was used to land spread these materials,” explains Brad Holtz, agronomist with the Brown County Land and Water Conservation Department in Green Bay. At the same time the dairy industry has grown.
The county is currently home to 15 CAFOs (confined animal feeding operations) with permits pending for several more. Less available land and more generation are increasing economic pressures on all waste producers, requiring them to travel further and pay more to dispose of their residuals. “In some ways waste is a cap on how much these industries can grow,” says John Katers, associate professor at the University of Wisconsin, Green Bay. “A cap on the agricultural industry has an impact on the meat industry and right on down the line.”
As volumes grow, so, too, do environmental problems. Land application is contributing to ground and surface water contamination, air pollution and farm odors. Excess nutrient runoff is causing algae blooms in the Lower Fox River and the Bay of Green Bay, Holtz says. In 2009, more than 100 wells were polluted with parasites and bacteria from agricultural runoff in the Town of Morrison.

POOLING RESIDUAL STREAMS
The Waste Transformation Initiative has brought together a group of diverse stakeholders to evaluate aggregating and converting organic wastes into pelletized fertilizer. Katers notes that the ability to aggregate residuals to create products is critical since no single generator has enough volume to support a fertilizer plant. Materials considered for aggregation include 12,000 dry tons/year of municipal biosolids, 3,500 dry tons of meatpacker wastes comprised of wastewater sludge, paunch manure and barn waste, and manures from agricultural operations. The total dry volume of this quantity is about 28,700 cubic yards/year
Stakeholders in the group include the Brown County Land Conservation Department; the University of Wisconsin at Green Bay; the Green Bay Metropolitan Sewage District (GBMSD); the De Pere Wastewater Treatment Plant (DWTP); the City of Appleton; two meat packing facilities, the American Food Group and JBS Packerland; Sanimax, an animal rendering company; Ag Venture, LLC.; FEECO International (FEECO); ENCAP and Daanen & Janssen, Inc. The first step in the project was to characterize the various waste streams. “We looked at solid content, moisture content, the nutrient value of the materials and a number of physical characteristics that were important in terms of making [fertilizer] granules,” Katers explains.
Samples of eight different waste streams, sewage sludge from the Green Bay and De Pere treatment facilities, wastewater sludge from the two meat packing facilities as well as barn manure and paunch, were analyzed and tested by FEECO to determine the best way to make fertilizer pellets out of these feedstocks. FEECO manufactures agglomeration and thermal processing equipment for converting raw materials into pelletized fertilizers. “We blended the waste streams in the proportion of how they are being generated to create the pellets,” explains Lee Hoffman, vice president and general manager at FEECO. “Then we did physical property testing – crush strength, bulk density and size, to name a few.”

PELLET PRODUCTION, CROP TRIALS
FEECO’s process for creating pellets starts by mixing the wet feedstock with two parts of dry materials in a paddle mixer. Materials from the paddle mixer go into the rotary dryer after going through a machine that forms the mixture into
pellets. “You can’t run them right into rotary drying when they are received,” Hoffman adds. “They tend to stick to the shelf and you expose yourself to the potential for a fire.”
Once dried, the materials go up a bucket elevator to a double deck screen, which separates the appropriately sized pellets from the oversized and fine streams. The oversized granules are crushed, mixed with the fine stream and returned to the paddle mixer as the dry recycle material that gets added to the wet feedstock at the beginning of the process. Meanwhile the product stream from the screening process goes to a cooler.
Initial testing found that four of the eight materials, the barn manure and paunch from each of the meat packing houses, were not practical. “There were very fibrous,” Hoffman says. “They needed to be ground down, which is a very expensive process, before they could come into the program.”
The team decided to run field tests on the pellets made from the four remaining waste products, municipal biosolids from two waste-water treatment plants and wastewater sludge from two meat packing facilities. FEECO produced 6,000-lbs of pellets, dubbed the “4-blend,” for the trials, funded with a $30,000 grant from the University of Wisconsin (UW) Systems Solid Waste Research Council. The trials were conducted during the 2009 growing season at five sites. Two small plots growing corn and alfalfa were established at the UW Research Farm in Arlington by a soil scientist, Richard Wolkowski. Three test plots were located on farms in Brown County where the fertilizer was applied in field length strips. For these tests, Wolkowski worked with Holtz and his team at the Brown County Land and Water Conservation Department.
On-farm testing at the five sites looked at blending the pellets with urea to reduce the need for straight urea in the field, Wolkowski explains. The idea is to obtain 10 to 25 percent of the total corn nitrogen requirement from the pellets. “Our yields looked pretty good,” he says. “Results tended to show that, at least for the conditions we had last year, most of the test sites were able to substitute up to 25 percent.”
Wolkowski hopes to obtain funding to repeat the tests this year. Testing of this type is best done over a three-year period to take into account different conditions. “It looked real promising but I hesitate to make a full- scale endorsement unless we know much more about it,” he adds.

EVALUATING A DIGESTER
The team is currently considering anaerobic digestion for the materials eliminated from the initial testing. These materials are very fiberous. “A digester could effectively pretreat these materials, and make them more amenable to a fertilizer product,” Hoffman says. After digestion, the separated solids from the digestate could be combined with the other materials in the process and pelletized. “We think it is a viable economic solution.”
Biogas produced by the process could assist in drying the materials. “A digester would also allow us to increase revenues on the front side by taking in other waste streams that would be high in BOD (biological oxygen demand) and maybe too high in moisture content to dry down into fertilizer,” Holtz says. There are a number of cheese processors, candy makers and malting facilities in the regions that could supply codigestion feedstock for the process.
A market study and preliminary financial analysis of the project look favorable. The financial plan found that project economics are sensitive to the selling prices for the pellets and energy costs. “At a selling price of $150/ton the project is generally viable,” Katers says. “At $100/ton, some level of energy cost reduction is required.”
The primary challenge now is to determine an ownership structure for the entity producing the products. “A recent survey of the stakeholder group indicated that they would like the GBMSD, Brown County or a combination of the two entities to step up to the plate and take ownership by the horns,” Holtz says. GBMSD recently completed a biosolids management plan that was looking at four alternative processes. Two of the four options incorporate some variation of the fertilizer facility. Ultimately, anaerobic digestion with further thermal processing was selected; it includes production of fertilizer pellets, as well as energy recovery.
For its part, FEECO is looking into better ways to process the paunch and cow manures not included in the original product tests. They are also providing support to the engineering company that is helping GBMSD with its biosolids study. “We have been doing some drawings and are trying to integrate the digester in the process as well,” Hoffman explains.
The plant FEECO is designing would produce 17,500 tons/year of dry fertilizer pellets. “That is as small as you can go to make the economics work,” he adds, noting that the concept has applicability in other regions. “There are a whole host of places where this can work across the country. It is just a matter of getting enough materials in one location to justify putting in a fertilizer plant. Economies of scale come into play, so aggregation of materials is really the key.”

Diane Greer is a Contributing Editor to BioCycle.