Holistic Management of Manure

by: Sara Goudarzi

Holistic management of manure could result in sustainable and energy independent farms, according to new research.

Animal farms have to deal with an abundance of manure. Manures are rich in nitrogen, phosphorus, and potassium (NPK), and are similar to fertilizers that one picks up for the yard. The traditional method to treat manure is to spray the waste onto fields under some type of manure management plan. Typically, these fields grow grasses capable of absorbing some of the nutrients present in manure.

However, researchers are looking at two processes—anaerobic digestion and thermo-chemical processes—to treat manure to produce bio-energy products that farms could utilize for energy independence.

"My research is specifically looking at hydrolysis, high temperature, high pressure conversion processes, to treat the manure and generate different types of bio-energy products—whether it's via gas that you could burn or a char product that you could either put in the ground as a soil amendment or use for combustion," says Kerri Cantrell of the US Department of Agriculture in Florence, South Carolina.

Kerri is working with soil scientists to come up with ways to use the nutrients in the char product to make them more plant available and ready to use as a fertilizer substitute.

"What we're finding is you basically concentrate your phosphorus and potassium in that solid char product from the original material," she says. "We've just done some greenhouse studies with rye grass and phosphorous is very plant available—you could almost substitute it one for one for a traditional commercial phosphorous fertilizer."

Cantrell's work is detailed in an upcoming special topic issue "Low-Carbon Society For A Green Economy II" in the Journal of Renewable and Sustainable Energy.

Thermochemical conversion not only converts all the carbon and biomass, into either an off gas or biochar but also gets rid of the pathogens and breaks down any pharmaceutically active compounds, like antibiotics, hormones and anything else that might come into a waste treatment system.

In addition to hydrolysis, Cantrell's colleagues are looking at a biochemical conversion platform—anaerobic digestion, a mature technology that's utilized in parts of the world.

"Europe has done a very big push, especially in Denmark and Germany for anaerobic digestion," Cantrell says. "They have thousands of small farms and centralized biogas plants, and so they've got the anaerobic digestion and biogas utilization down well—they're getting into cleaning up that methane and liquefying it and converting it into vehicle fuel."

There aren't, however, many farm scale systems that are using thermochemical conversion. Many of those in existence are just small demonstrations to prove that the technology could work.

"If we can target specific sectors—whether it's agriculture or specific sectors in industry—and say alright what does it take to get that group energy independent, it could have a huge impact," Cantrell says.

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