Engineers with the USDA Forest Products Laboratory in Madison, WI, are investigating ways to create building and packing materials out of recycled manure. The laboratory works to conserve and extend U.S. forest resources by researching efficient, sustainable uses for wood. As part of that mission, John Hunt, research general engineer, investigates ways to create composite materials from bio-based materials that can either be combined with, or even replace wood while creating a useful finished product.

Speaking at the recent Midwest Manure Summit in Green Bay, WI, Hunt explained the methods and equipment necessary to produce a composite material out of manure biosolids.

When the manure digestion process is complete, the remaining manure fibers can be substituted for all or a part of the wood fiber commonly used in some composite materials. Manure’s cellulosic fiber is similar to what is found in wood. “The fiber characteristics of the manure change during the digestion process and you need to understand what you have at the end. The percentage of lignin and crude protein increases, while the starch decreases,” he explains.

Hunt reinforces to livestock producers that what goes in really does come out. For this reason, a cattle operation where animals are fed more roughage means more fiber-based manure is produced. Pigs, on the other hand, are not fed as much fiber, so the prospect of making building materials from swine manure doesn’t work, he says.

“You need to pay attention to what you feed and the duration (of the manure) in the digester in order to get out the type of fiber that you want,” he continues. “If you plan to make consistent products, then you also need to think about the output from the digestate, which begins with the input.”

Hunt showed sample boards made from manure-based composite material collected from a dairy farm that feeds cotton seed meal to their cows. The cotton seeds were clearly visible as small, black specks embedded in the product. Refining is often necessary to reduce seed hulls and long fiber bundles in the digested manure.

It is important that the manure is well-digested to ensure no odor emanates from the final product. “When the manure is well-digested, the boards smell somewhat like corn, but less-well-digested manure results in a board that smells more manure-like,” he explains. When using manure-based products, it is also important to make sure the material meets area building codes.

In spite of some challenges, Hunt says there is potential for manure-based products to be used as particleboard for office furniture, shipping palates or flooring material in homes. He even tried making manure-based paper postcards, but met with some difficulties in meeting postal regulations. The idea of producing a packaging product from manure is not as new as one might think. According to Hunt, a process for producing manure-based plant pots received a U.S. patent in 1877. “There are a whole host of opportunities out there,” he says.

“Production of a composite panel is not the tail that wags the dog; milk production is still the main goal,” Hunt reminds. “But, we have to think about the possibilities.”

He urges interested producers to focus on value-added products for better return on investment. Try to partner with someone in the manufacturing business that already has existing market distribution channels or niche markets, he suggests.

Learn more about the Forest Products Laboratory online at