Environmental Engineering Faculty Papers' Chosen as Best of 2008
02/26/2009
Two research papers, published by Yale School of Engineering & Applied Science Environmental Engineering faculty members, Menachem Elimelech and Thomas Graedel, were chosen as “Best Papers of 2008” by Environmental Science & Technology.
“Transport of Single-Walled Carbon Nanotubes in Porous Media: Filtration Mechanisms and Reversibility,” published by Elimelech, Roberto C. Goizueta Professor of Chemical and Environmental Engineering, and his research team of Deb P. Jaisi, Navid B. Saleh, and Ruth E. Blake, was awarded the Top Paper in Environmental Technology, First Runner-Up, for their examination of mechanisms that would affect single-walled carbon nanotubes, or SWNTs, belowground and if they could reach groundwater.
Elimelech’s paper compares squeezing a single-walled nanotube through the pores of typical sandy sediment as trying to thread a pencil through the spaces of a room packed tightly with basketballs.
“Take any other nanoparticles and you will find typical aggregation or transport behavior in aquatic environments,” Elimelech says, but carbon nanotubes have extremely long aspect ratios, meaning they are like skinny long straws, at a nanometer or two wide by thousands of nanometers long. “We suspected [that SWNTs] would have different transport behavior,” he adds, atypical of the average colloidal particle or related fullerene nanoparticles.
Elimelech’s team took commercial SWNTs, sonicated them to break up the aggregated clumps, and then ran them through sand columns in the lab using different ionic solutions. The researchers found that the long tubes would disperse, only to cling to sand particles in the right salty setting or be caught in pore spaces too tight to let them pass.
The more salt, the more the SWNTs stuck, they found. However, the SWNTs could be washed away in less ionic water. Less-ionized water is similar to rain, meaning that even though SWNTs might aggregate or stick to soil particles, they might also be remobilized in surface soils during heavy rains, the team hypothesized. The next step, says Elimelech, will be to examine the interaction between these nanomaterials and real soils outside of the lab by investigating the root zones of plants and the changes that SWNTs might cause in soil microbial communities.
“In-Use Stocks of Metals: Status and Implications,” published by Michael Gerst, Yale Environmental Engineering alum and Graedel, Clifton R. Musser Professor of Environmental Engineering and Center for Industrial Ecology, School of Forestry & Environmental Studies, was awarded the Top Paper in Environmental Policy, First Runner-Up, for their paper on in-use stock metals.
Gerst and Graedel evaluated the current and historical circulation of certain materials, such as metals, that are significant for societies throughout nine world regions and looked at what is exported and imported, what is mined and recycled, and what is currently being used in a variety of products such as electrical transmission lines, cars, and buildings.
By using historical analysis, the authors found that society has mined more metal in the past 50 years than it has since the beginning of time. If humans continue consuming metals at this rate, metal resources will be depleted. However, once a tally is made of the metals in products (considered in-use stock), decision makers can predict how today’s in-use stock can be used for tomorrow’s products. “We want to preserve the availability of the full spectrum of metals at a sufficiently modest cost so that we don’t have to transfer our technology solely because of a scarcity” of metals, Graedel says.
“This paper covers critically important work that is needed to understand our opportunities and vulnerabilities when it comes to the uses and supplies of the metals so essential to our economy and our society,” adds Paul Anastas, director of Yale’s Center for Green Chemistry & Green Engineering.
In their ES&T paper, Gerst applied his historical data to a scenario in which less-developed countries acquire the same amount of per capita in-use metal stock as today’s more-developed countries. The conclusion? “The amount of global in-use metal stocks required would be 3−9 times those existing at the present,” Gerst writes.
Environmental Science & Technology (ES&T), published by the American Chemical Society, is an authoritative source of information for professionals in a wide range of environmental disciplines. The journal combines magazine and research sections and is published both in print and online.
