Papers by Two Environmental Engineers Chosen Among the Year’s Best

Will the materials we use in everyday products end up in our water supply? How much metal does the developed world use in computers, cars and skyscrapers? These questions were at the heart of two research papers written by Yale environmental engineers last year, and the answers were good enough to earn them each a top spot in the journal Environmental Science & Technology’s selection of the best environmental research papers of 2008.

Impact of nanomaterials

Menachem Elimelech’s paper “Transport of Single-Walled Carbon Nanotubes in Porous Media: Filtration Mechanisms and Reversibility,” published in October, was chosen as the first runner-up in the environmental technology category. It focuses on single-walled carbon nanotubes — an emerging nanomaterial used in a wide range of products, from fuel cells and drug delivery systems to bicycles and golf clubs.

But despite the increasing use of this material, no one had thought much about what happens to the nanotubes once all of these products are thrown away and whether they could eventually seep through the soil and make their way into the groundwater, lakes and rivers. Elimelech and his team, led by postdoctoral fellow Deb Jaisi, set out to study how easily the nanotubes move through the type of soil they’re likely to encounter before reaching groundwater.

The team found that the nanotubes — which are very long, thin structures — don’t move easily through sandy soil, which is made up of tightly packed sand grains. In fact, the straw-like nanotubes tend to get stuck in the sand and stick to the sand particles.

But that may keep the materials clear of the groundwater, there’s another potential problem, the researchers realized. Earlier on, Elimelech and his team discovered a surprising feature of the nanotubes: They have inherent anti-bacterial properties.

“Bacteria play a very important role in soil, and these are beneficial bacteria, so killing them isn’t a good thing,” says Elimelech, chair of chemical engineering and director of the environmental engineering program. It’s these kinds of surprising results, notes Elimelech, that make understanding just how these new materials behave in a broader environmental context so important.


Metal shortages

Thomas Graedel is another Yale engineer interested in the relationship between the environment and one of the most common materials used by humans. He and his former graduate student, Michael Gerst, were interested in how much metal humans employ in everything from the computers we use to the cars we drive to the office buildings we work in.

Their paper “In-Use Stocks of Metals: Status and Implications,” published last September, won first runner-up in the environmental policy category for Graedel, the Clifton R. Musser Professor of Industrial Ecology and director of Yale’s Center for Industrial Ecology, and Gerst, who is now a research associate at Dartmouth College.

The two gathered the existing data about in-use stocks of metals - i.e., metal that is currently in use in the world — to get a big picture view of the developed and developing world’s total metal use.

They found good data for five of the most common metals: iron, aluminum, copper, lead and zinc. They calculated that there are between 10 and 15 tons of those metals in use for every person in the developed world. In fact, humans have mined more metal in the past 50 years than in all of previous human history, Graedel says — a staggering fact that he believes could have major implications for the environment.

“We have the attitude that we can go out and dig a hole in the ground and mine what we need, then use something once and throw it away,” Graedel says. “That’s really not a very smart or sustainable way to do things.”

To help reach a more sustainable way of processing and manufacturing, he continues, engineers will need to start designing products while keeping sustainability in mind. Today, only about 40% of the most common metals in use are recovered; for less common ones, the number is much lower.

“We need to get better at reusing and repurposing what we already have,” Graedel says. “Non-renewable resources are going to be much less available in the future than people have assumed.”

— By Suzanne Taylor Muzzin

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Suzanne Taylor Muzzin: suzanne.taylormuzzin@yale.edu, 203-432-8555