July 2008, Vol. 20, No.7

Research Notes

Research Notes

Concentration of Nanoparticles in Water Depends on Solution Properties

The ability of municipal filtration systems to remove carbon-based nanoparticles from drinking water depends on the solution properties of the water carrying the particles, according to a new study by researchers at the Georgia Institute of Technology (Georgia Tech; Atlanta).

The study found that clusters of Carbon 60 (C60) tend to adhere tightly to soil or filtration system particles in slightly salty water but tend to flow easily where natural organic compounds or chemical surfactants serve as stabilizers in water. Movement of C60 was found to be very sensitive to solution conditions.

“Our work shows that you cannot directly apply traditional clean-bed filtration theory to describe C60 nanoparticle transport and deposition in quartz sands,” said Kurt Pennell, a professor in the School of Civil and Environmental Engineering at Georgia Tech. “[Our] studies are unique in that we actually measured the C60 retention profile with distance and showed that one needs to modify the traditional approach, using rate-limited attachment kinetics and a maximum retention capacity to accurately describe C60 nanoparticle transport and retention.”

The study, funded by the U.S. Environmental Protection Agency, was deemed necessary because little is known about the toxicity and persistence of C60 nanoparticles in the environment, Pennell explained. This study increases knowledge about these nanoparticles and will soon be built upon with additional studies by Pennell and his collaborators at Georgia Tech that look at transport issues in real soil and other nanoparticles.

“In this study, we focused on C60 nanoparticles, and varied the sand grain size, flow rate, and electrolyte conditions,” Pennell said. “In future work, we will look at quantum dots, paramagnetic iron, and some metal-based nanoparticles.”

Pennell’s research team filled glass columns with either glass microbeads or sand, and saturated the columns with water. A “pulse” of water containing C60 nanoparticles was sent through the columns and followed by additional water that did not contain nanoparticles.

Measurements of nanoparticles that emerged from the columns, that were retained in the sand and glass beads, and that were retained in the columns, resulted in up to 77% of nanoparticle mass retained by the sand, and between 8% and 49% of nanoparticle mass retained by the glass beads. The study showed that the nanoparticles retained by the sand or beads could only be removed by changing the pH of the water.

In the sand, the particles were distributed evenly throughout the column, which suggests that under those circumstances, there is a limited retention capacity because of filtration, Pennell said. He added that once that capacity is reached, the particles pass through until they are retained by other grains of soil or sand.

The study also found that preparation of the solutions containing the C60 dramatically affected retention of the particles. When no salt was added to the solution, the particles flowed through the columns like water. This sensitivity to solution characteristics means that local conditions may play a key role for municipal drinking water filtration, Pennell said.

For more information, contact Pennell at kpennell@ce.gatech.edu.

WERF Offers Improved Stormwater BMP Database

Stormwater professionals now have an improved tool to help evaluate best management practices (BMPs).

The International Stormwater BMP Database, www.bmpdatabase.org, was unveiled by the Water Environment Research Foundation (WERF; Alexandria, Va.) and its partners to enable better BMP searches, data collection and uploading, and access to BMP performance analyses.

With the recent addition of 65 new BMP studies, the database now includes more than 300 studies, according to a WERF press release. In addition, the database includes a new analysis that identifies how different types of BMPs performed in removing a variety of pollutants. The performance descriptions assess achievable effluent concentrations, determine the effects of BMPs on total loadings, and identify the frequency of potential exceedances of water quality criteria or other targets.

Data entry has been simplified with new Excel-based spreadsheets, the press release says.

WERF is working with large data providers on this project to open up the database to additional BMP study submissions. Several large data providers are using or adapting the database as their data storage tool and regularly providing information to the database. Anyone interested in submitting data should contact Jane Clary at clary@wrightwater.com.

The U.S. Environmental Protection Agency (EPA) has collaborated with WERF by using the BMP database as a resource link on the agency’s Urban BMP Performance Tool Web site, which provides information about urban BMPs. The site is accessible at cfpub.epa.gov/npdes/stormwater/urbanbmp/bmpeffectiveness.cfm.

The BMP database provides scientific information that various disciplines in the stormwater industry can use to improve the design, selection, and performance of BMPs. Partners in the program include WERF, EPA, the Environmental and Water Resources Institute of the American Society of Civil Engineers (Reston, Va.), the Federal Highway Administration, and the American Public Works Association (Kansas City, Mo.). For more information, contact Jeff Moeller at jmoeller@werf.org.