"Super Socks" Help Stem Pollution Runoff
Perry July 23, 2010
Agricultural Research Service
(ARS) scientists and their collaborators have improved on an existing method
for removing contaminants from storm water runoff. These findings could provide
surface waters additional protection against runoff containing pollutants from
point sources such as construction sites, storm waters and other urban
"Filter socks" containing compost tucked into mesh tubes are used to
capture some of the silt, heavy metals, fertilizers and petroleum products
washed from compacted surface areas into nearby streams and rivers.
A group of scientists from the ARS Animal and Natural Resources
Institute in Beltsville, Md., teamed with researchers from Filtrexx
International, which manufactures the socks, to see if adding flocculation
agents to the socks improved their performance. The ARS team included
agronomist Eton Codling, microbiologist Dan Shelton and soil scientists Yakov
Pachepsky and Ali Sadeghi. Their Filtrexx International partners were Britt
Faucette and Fatima Cardoso-Gendreau.
Wastewater treatment plants use flocculation agents to help sediments
and pollutants form clumps large enough to be filtered out of the water, even
when the substances are in a dissolved state. The team added flocculation
agents to compost socks and then ran laboratory tests to see how well the socks
trapped sediment, coliforms, nitrates, E. coli bacteria, heavy metals
and petroleum products in runoff after simulated "rain events."
The scientists found that compost socks alone removed the majority of
clay and silt particles that contribute to suspended solids in surface waters.
The socks also removed 17 percent of ammonium nitrogen, 75 percent of E.
coli bacteria, and from 37 percent to 72 percent of the heavy metals. In
addition, runoff levels of diesel fuel dropped 99 percent, levels of motor oil
dropped 84 percent, and gasoline levels dropped 43 percent.
However, socks with flocculation agents removed even more of the
pollutants from runoff, including 27 percent of the ammonium nitrogen, 99
percent of E. coli bacteria, 99 percent of the motor oil, 54 percent of
the gasoline and from 47 percent to 74 percent of the heavy metals.
Results from this research were published in the Journal of
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.