Researchers at North Carolina State University (Raleigh, North Carolina) recently found that black sludge growing in a water treatment site could have redeeming benefits.
In this case, black sludge had coated water pump components at a U.S. Environmental Protection Agency (Washington, DC) Superfund cleanup site in Raleigh. Generally, the presence of such material is believed to “gum up” the facility’s primary task of cleaning fouled water, says Owen Duckworth, an associate professor of soil science at North Carolina State and author of a paper describing the study on black sludge and its characteristics.
On the whole, black sludge at a water treatment facility is still mostly something to be avoided, rather than encouraged, he says. But when researchers used microscopic and x-ray techniques to closely examine the sludge, they found that it contained manganese oxides—potentially offering benefits.
“Manganese oxides have low toxicity and are of technological interest because they suck up metals and cause chemical reactions that chew up organic matter,” Duckworth says. “So they’re used in things like water treatment to get micro-pollutants out of water.”
The manganese oxides at the site are small, but they have large affinities for metal, the researchers explain. They are thousands of times smaller than the width of a human hair, and shaped like dinner plates—with holes in the middle.
“Metals like zinc, copper, and lead, for example, will sit in the holes of the plates or stick to the edges,” Duckworth says. “And the naturally occurring manganese oxides have more holes than those grown in a lab setting, making them even more effective in sucking up metals.”
During their testing, the researchers found that manganese was oxidized by a fungal catalyst.
“Unlike iron, which oxidizes when exposed to air, manganese needs a catalyst to oxidize,” Duckworth said. “In this case, we found evidence of a fungal catalyst.”
Moreover, the researchers found that the manganese oxides in the treatment plant, which appeared to grow naturally, are similar to what scientists would grow in a lab setting to test the oxides’ utility in environmental remediation.
“There is great interest in passive treatment systems in which naturally occurring components, like the manganese oxides at this water treatment site, could serve a useful function,” Duckworth says. “In essence, we would use the fruits of this site to help clean up other sites, because we’re never going to run out of metal-contaminated sites.”
Before attempting to use fungal manganese oxides in remediation efforts, though, Duckworth says he will continue to track how the black sludge grows in different conditions, how it binds to different metals, and how it reacts to organic matter.
The research was supported by the U.S. National Science Foundation’s (Arlington, Virginia) environmental chemical sciences program and the U.S. Department of Energy’s (Washington, DC) offices of science and basic energy sciences. Researchers from North Carolina State and the University of Minnesota (Minneapolis, Minnesota) co-authored the paper.
For more information, visit North Carolina State’s web site.