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Researchers explore ultrasound's potential in river sediment cleanup

Ohio Sea Grant researchers are continuing to work on a method to remove contamination from Lake Erie rivers and streams, using ultrasound and chemical agents that bind to contaminants and render them inactive on the river bottom. The eventual goal is to treat contaminated sediments right where they are, instead of having to dredge them up for treatment or disposal.

Researcher Linda Weavers and her team at The Ohio State University have built a basic model of a river cross-section in their lab, and are moving from experiments where the contaminated sediment samples are mixed into water to one where the sediment has settled into the bottom of a glass column, closer to how they would find contamination in an actual river or lake. Weavers is a professor in the Department of Civil, Environmental and Geodetic Engineering at Ohio State.

The ultrasound treatment creates cavitation bubbles in the water around sediment particles that carry contaminants. As those bubbles form and collapse, the tiny shockwaves produced in the process act a little like a pressure washer, pushing heated water against the sediment particles and removing stuck-on contaminants. In addition, the pressure waves created by the ultrasound also spread apart the sediment particles.

“When we looked at our bromide tracer in the water, we saw it spread through the sediment more with ultrasound than without,” said Weavers. “So if you think about the bigger picture, if we look at our contaminants, we have a better ability to reach more spaces within the contaminated sediment and are able to affect a larger area.”

Currently, Weavers and her students are working on sediment samples that were provided by the Ohio Environmental Protection Agency (OEPA). Those samples contain polycyclic aromatic hydrocarbons (PAHs, for short), which are a major problem for Lake Erie and its tributaries.

“We have these contaminated sediments from a former creosote facility, which is one of the sources of PAH contamination,” Weavers said. “If you think of wood telephone poles, they don’t decay even though they’re made of wood, and that’s because they’re treated with creosote, which is heavy in PAHs.” Another example of creosote compounds is the black tarry sealant used on many driveways.

More information, including details on a potential way to inactivate contaminants once they’re removed from the sediment particles, is available in the Winter/Spring 2017 issue of Ohio Sea Grant’s Twine Line magazine, available at ohioseagrant.osu.edu/products/twineline.

Ohio State University’s Ohio Sea Grant College Program is part of NOAA Sea Grant, a network of 33 Sea Grant programs dedicated to the protection and sustainable use of marine and Great Lakes resources. For more information, visit ohioseagrant.osu.edu.

written by Christina Dierkes, Ohio Sea Grant