Dr. Dongye Zhao: associate professor of civil and enrivonmental engineering, has been developing nanotechnology that will help reduce petroleum contamination. Elizabeth Williams / NEWS EDITOR
Dr. Dongye Zhao, associate professor of civil and environmental engineering, led a research team at Auburn University to develop a new environmental remediation technology for cleaning up contaminated sites, soil and groundwater.
Zhao was invited to Ecuador in June to lead an international workshop for environmental remediation based on his developments in nanotechnology. The lectures explained how to use the technology developed at Auburn and its environment impact. Ecuador has a widespread petroleum contamination problem because of oil fields.
Groundwater contamination is a serious problem in Ecuador. Organic contaminants and heavy metals such as mercury, copper and lead leach into the soil and pollute the drinking water, making crops unable to grow.
Traditional remediation of contaminated soils or sediments requires excavation and landfill. This method is impractical when the contamination is spread over a large area, because it requires digging up the soil.
“You cannot landfill everything because it is too costly and environmentally disruptive,” Zhao said. “The Environmental Ministry of Ecuador wants to do something cheaper, more effective and more environmentally friendly.”
Landfill is not an ultimate solution because contained contaminants sit for many years. According to Zhao, digging up the soil prior to landfill is costly. “Even shallow digging is $700 per cubic yard,” Zhao said.
Using nanotechnology for cleanup often has a savings of 90 percent.
Zhao and his team developed nanoparticles that can be injected into the ground to destroy organic contaminants. “Injection of zero-valent iron nanoparticles to the soil is a way of environmental remediation for some chlorinated organic solvent like TCE,” said Rebecca Zhang, graduate research assistant in Dr. Zhao’s research group.
Trichloroethene, TCE, is one of the most commonly detected organic compounds in soil and groundwater. Sites adjacent to dry cleaners, automobile manufacturers, asphalt processing plants and military bases all contain high concentrations of TCE.
Another common organic chemical is polychlorinated biphenyls, PCB, which is used in electrical transformers.
Different strategies for cleaning up these carcinogens are being studied, but all are based on novel nanoparticles developed in the lab. Both TCE and PCB resist natural degeneration.
Nanoparticles are very reactive. When injected into undisturbed soil, the particles spread out and seek contaminants. When the particle meets with a contaminant, it either destroys or degrades it.
Another group of nanoparticles can be delivered to the soil that affixes to heavy metals and keeps those contaminants from leaching into the groundwater. With metal, the nanoparticle joins in the metal and binds it to the soil matrix so contaminants will not get into the water.
“This idea was proposed about ten years ago, but never got off the shelf because we could not find a way to prepare a real mobile nanoparticle to deliver,” Zhao said. The nanoparticle had to be on a micro scale to be able to move through tiny soil pores.
Because the particles were unstable, they would agglomerate quickly to form larger flocks, called aggregates. Aggregates are big enough to be seen with the human eye. They are not mobile in soil and cannot be injected.
By applying a water-soluble starch, the nanoparticles become stable and unable to agglomerate.
“The particles are mobile in soil so we can inject them,” Zhao said. “That is one technical barrier that we overcame here.”
Nanotechnology is being studied for use in water contamination cleanup also.
Dr. Gwynedd Thomas, associate professor for Polymer and Fiber Engineering, works with developing new nanotechnology. She said professors at Auburn are working with nanotechnology to create water cleanup solutions.
“When there is an oil spill, certain types of nanoparticles can be released into the water,” Thomas said. “The nanoparticles will migrate toward the oil, corral it and migrate away from heavier water concentration.” This keeps the oil from spreading and causing further contamination.
Because the technology is new, there are still some questions about the environmental impact of nanotechnology. Field testing is being done in California and Alabama.
After reacting, the particles become iron oxide, a common mineral. Zhao said they are working to confirm the fate of the particles and their effect on the environment.
Zhao has been asked to return to Ecuador to explain how his nanotechnology is applicable to their situation in further detail.
