Groundwater provides drinking water to more than half of all Americans, but much of the nation’s groundwater is contaminated, say scientists, and clean-up could cost hundreds of billions of dollars and take several decades.

    Wei-xian Zhang, associate professor of civil and environmental engineering, has developed a technology that is dramatically more effective than traditional groundwater-cleanup methods and could significantly reduce the nation’s total clean-up bill.  Zhang and Dan Elliott, a Ph.D. candidate in environmental engineering, recently tested and verified the technology at an industrial site owned by Trane Inc. in Trenton, N.J.  Because his method can reduce biological and chemical agents quickly, Zhang says, it also holds promise for preventing attempts by bioterrorists to contaminate drinking water. And, he adds, it might offer a safer, cheaper way to clean up nuclear waste and Superfund sites.
     Traditional “pump and treat” clean-up requires groundwater to be pumped out, treated, then disposed of. Nanoparticle technology enables water to be treated in the ground. Using nanoparticle technology, a  $20-million clean-up project could cost $5 million or less.
     The new technology involves pumping nanoparticles – minute, iron-based particles measuring 100 to 200 nm – into the groundwater. The nanoparticles, which are 99.9 percent iron and less than 0.1 percent palladium, have a large relative surface area and a high rate of reactivity, and they race through groundwater. When applied to water or soil contaminated with carcinogenic solvents used in dry cleaning and industrial processes, the nanoparticles remove the chlorine and convert the solvents to harmless hydrocarbons and chlorides commonly found in table salt.
     Trane Inc., which makes air-conditioning systems, has been investigating a toxic trichloroethene (TCE) plume for several years. Trane put the nanoparticles to work at its Trenton manufacturing plant in a field demonstration in 2000. Water samples taken from monitoring wells 12 hours after the nanoparticles had been injected showed that as much as 96 percent of the TCE was reduced to harmless ethylene and ethane.
     “This is the first technology we have found that has the potential to clean up the thousands of sites in many industries in the U.S., where currently nothing is happening,” says Chang Tai, environmental and safety engineer for Trane.
     Zhang has a patent pending for his remediation method and has licensed the technology to two environmental remediation companies. He also recently received a grant of $300,000 from the U.S. Environmental Protection Agency to explore the potential for using nanoparticles to treat hazardous waste.
     Elliott left an environmental engineering job in industry to work with Zhang on the technology.
     “Nanoparticles have been used in chemical processing and electrical engineering for years, but as far as I know, we are the first to use them for groundwater cleanup,” says Zhang.
     “The potential for nanoparticle technology is unlimited,” says Elliott. “Our interest is environmental, but there are a host of industrial applications in which small magnetic particles could be useful. We’re applying for grants to scale up our production of nanoparticles. Quite frankly, we can’t make them fast enough. We can’t even come close.”
     Zhang and Elliott published the results of their Trenton site tests in November 2001 in an article titled “Field Assessment of Nanoscale Bimetallic Particles for Groundwater Treatment” in the journal Environmental Science and Technology.
     Their work was also featured in the Dec. 17, 2001, issue of Chemical and Engineering News in the “Science and Technology Concentrates” section.
     “Generally, colloidal or particulate additives, such as microscale iron particles, have low mobility in aquifers and so don’t perform optimally,” said the C&E News article. “To reduce the mobility problem, Elliott and Zhang determined the optimum particle size.”
     The two engineers are scheduled to test their remediation method this year at several more chemically contaminated groundwater sites. They are also exploring the use of nanoparticles to neutralize explosives and treat nuclear waste sites.