Does Size Matter? Nanoparticles in Our Wastewater

by Mika Pringle Tolson

Sharon Walker and her research group at UC Riverside have found a better way to remove nanoparticles from water

Particles less than ten millionths of a meter are appearing in consumer products everywhere from pharmaceuticals, cosmetics, clothing, electronics, and even washing machines to control odor. These nanoparticles can solve engineering and technological problems, but they end up in our waste stream.

"We need to be thinking about where these particles go and what damage they might do in the environment," says Sharon Walker, Assistant Professor of Chemical and Environmental Engineering at UC Riverside.

Walker received a Collaborative Research Grant from the TSR&TP to investigate which properties of nanoparticles influence their interactions with water and how to remove them.

Before her TSR&TP grant, Walker studied the movement of pathogens in aquatic systems. "The UC Toxics call was an impetus to get really involved with nanomaterials," says Walker. "There are very few systematic studies of the fate of these particles. I was interested because my training and background in colloid transport apply very well in nanosystems."

Walker is working with Nosang Myung, an electrochemist and fellow professor at UCR, to make nanoparticles to order for her experiments. "The ability to work with someone who can make particles in a controlled way was an important part of my study," she explains. Nanoparticles are notoriously unstable, particularly in aquatic systems. Scientists are still sorting out how these particles behave.

"The experiment may all just depend on the pH of the day," says Walker. "None of the published work on nanomaterials to date is truly reproducible."

Using the finely tuned particles they synthesized, Walker's group has been able to get reproducible data on how nanoparticles break through the sand of a filter. "We can get reproducible trends under a realistic range of aquatic conditions," says Walker. "We're really excited about these transport studies." They can make the particles, characterize them, and repeat the process with the same results.

The ultimate goal is to be able to filter these particles out. Walker and her group have made good progress. "We can do some predictions on ability to filter them out based on electrostatic and magnetic properties." This knowledge can help engineers design better wastewater treatment processes.

The research has also led to surprising results. "We've learned that these particles we've been synthesizing may have some remediation applications," explains Walker. Out of curiosity, her postdoctoral fellow, Yongsuk Hong decided to put their particles through a remediation model system and found improved rates of reduction. The group is putting together a manuscript on this work for an environmental journal.

As a result of her TSR&TP work, Walker was one of two faculty from UC Riverside asked to participate in the newly awarded UCLA Center for Environmental Implications of Nanotechnology. Her enthusiasm is catching. "When we got involved with TSR&TP this was a new area for me," says Walker. "We got enough momentum that this will be an important part of my research. We will continue to study the fate and transport of nanoparticles in the future."

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