Dark material at bottom of sample
vial held by chemist Aprel Ellison is calcium phosphate that has settled out
from the wastewater. (Image courtesy M. Vanotti, ARS)
separation module. Click here for larger view
and more details. (Image courtesy M. Vanotti, ARS)
Process Developed by USDA Scientists Makes
Swine Wastewater Environmentally Friendly By
January 24, 2003
WASHINGTON, Jan. 24--Agriculture Secretary Ann M. Veneman
announced today that USDA scientists have
developed a process that can remove phosphorus from swine production wastewater
and turn it into a solid, marketable fertilizer, while converting the leftover
effluent into a liquid crop fertilizer that is more environmentally friendly
"This technology is a good example of how agricultural research
can provide benefits to everyone through environmental protection and
improvement," said Veneman. "This research provides an opportunity to help
farmers better protect the environment and enhance the soil they use for
The process was developed by soil scientists Matias Vanotti,
Ariel Szogi and Patrick Hunt at the Coastal Plains Soil, Water and Plant
Research Center, operated by USDA's Agricultural Research Service in Florence,
S.C. ARS is the chief scientific research agency of USDA.
The new process has several positive implications. Removing
phosphorus from wastewater can cut down on any excess phosphorus that may run
off into streams and rivers. Excess amounts of phosphorus can lead to oxygen
depletion in water bodies.
During processing, hydrated lime precipitates most of the
phosphorus in the wastewater as a solid and converts it into a marketable
phosphate fertilizer. This phosphorus could be a boon to the fertilizer
industry, because world reserves of the nutrient are limited. Another benefit
is that the high pH achieved by the process destroys disease-causing pathogens
present in the leftover liquid.
Meanwhile, the effluent contains a nitrogen-to-phosphorus ratio
greater than 12 to 1--ideal for crop irrigation, which requires an 8-to-1
ratio. Regular manure offers a nitrogen-to-phosphorus ratio of 4 to 1. This
higher nitrogen-phosphorus ratio translates into less excess phosphorus on land
on which the treated wastewater is applied.
The scientists had previously succeeded in separating ammonia
nitrogen from wastewater, a necessary step in completing the new process.
A patent application has been submitted for the combined
nitrogen- and phosphorus-removal processes, which will be tested through next
summer at a full-scale demonstration facility that opened earlier this month in
Duplin County, N.C.