ISU scientists identify process to make pig waste less noxious
Scientists at Illinois State University in Normal have developed a method for processing massive quantities of hog excrement that removes so much of the nasty odor and pollution potential, it even has a cute name — Swine Waste Economical and Environmental Treatment Alternatives, or SWEETA.
The process is designed for use on large-scale factory farms, where hogs spend their lives in confined feeding areas built on slatted floors suspended above containment pits. The SWEETA process provides a way to separate the "slurry" from those pits into solid and liquid waste, turning the former into compost and the latter into fertilizer that farmers can spray on crops.
There's nothing new about the separation process — it mimics what municipal wastewater-treatment plants have been doing for decades. The breakthrough at ISU is the development of a separation system that costs as little as $100,000 — cheap enough that large-scale farmers can afford it.
"All the technology is available commercially from other companies. We have taken other companies' technology and developed them into a systems approach," says Paul Walker, professor of animal science and coordinator of ISU's livestock and urban waste research team.
SWEETA separates solid waste through a combination of mechanical screens and a polymer flocculent, which attracts and binds smaller particles of organic matter. Walker likens this part of the process to the way Ivory soap attracts particles of dirt. "If you look at dirty suds in the bathtub, that's what a flocculent is," he says.
The solids can then be composted, mixed with landscape waste, and turned into mulch that can be sold on the retail market or used as an agronomic fertilizer, Walker says. The remaining liquid is aerated and can be used on farmland where corn or soybeans are grown, at much higher concentrations than the untreated slurry that many farmers now use. The SWEETA process removes more than 90 percent of phosphorus — the surface-water pollutant associated with the creation of algae blooms.
At ISU's 40-acre test site, researchers used
25,000 gallons of SWEETA-treated liquid effluent per acre instead of the
5,000 to 8,000 gallons of slurry that's the traditional per-acre
dose. "We were still phosphorus-deficit for what the corn plant
needed," Walker says. "We have eliminated the pollution
potential for phosphorus with this method."
At this stage, however, phosphorus and noxious odors are the only hazards reduced by the SWEETA process. It isn't designed to address such contaminants as pesticides, parasites, and hormones.
Furthermore, this new system isn't yet in use anywhere other than ISU's test farm. Walker has hosted workshops for extension specialists and is planning a "field day" for producers, but so far no one has bought it.
"We're still trying to make the process
more economical," Walker says. "We've got several folks
interested — just no one has chosen to do it yet."
Contact Dusty Rhodes at firstname.lastname@example.org.