For more than a year, scientists at North Carolina State University have successfully collected hog manure and dried it to produce ethanol, using an under-slat conveyor system in the test laboratory. The project has recently moved to a belt-collection system designed for an existing, partially slatted hog building. It has operated well in its first trial with 120 pigs.
The estimated cost of installing the system in an existing, partially slatted building is less than $8 per pig capacity.
Manure solids are collected on an under-slat polypropylene belt that extends the full width and length of the slatted flooring area. The belt is mounted at a 5 percent crosswise slope so that urine drains into a side gutter that empties into an enclosed tank.
The belt is operated for a few minutes every 48 to 72 hours, allowing the manure to dry. This increases the dry matter content to about 60 percent – fresh manure is typically 30 percent dry matter. On a farm, the belt would deposit the dried manure in a truck so it could be hauled to a centralized gasification facility.
A ton of the dry hog feces is expected to produce 90 gallons of a product that has an octane rating of 140.
“The process destroys pathogens and other bio-active compounds,” says Theo van Kempen, the North Carolina State researcher heading up the project. “This makes the mineral residue safe for use in livestock rations. We plan to conduct trials with animals to evaluate the feasibility of using this ash as a feed ingredient.”
An approximate 80 percent reduction in ammonia and odor is a bonus with the system, he adds.
Concludes van Kempen, “The process of converting hog manure to ethanol is technically successful and appears to be economically feasible. Actual profitability will depend on fuel prices and government incentives.”