IRONING OUT THE WATER SHORTAGE PROBLEM

ASEE Prism, Nov 2003

We've all heard the lament of Samuel Taylor Coleridge's ancient mariner: "Water, water every where, nor any drop to drink." It now seems as if the 19th-century poet's "rime" was quite prescient. In a world nearly covered in water, only a mere .05 percent of it is, in fact, potable. Nearly all of the rest is saltwater, although snowfields and glaciers comprise about 2.5 percent. And the share guzzled by humans has been increasing; global freshwater consumption quadrupled over the last half century.The U.N. estimates that within 25 years, two thirds of the world's population will be scrounging for scarce freshwater. Clearly, it would help matters if more of the water polluted by society could be cleansed and put back into circulation. The burgeoning science of nanotechnology is being enlisted in that effort.

Researchers at Lehigh University have had promising results using synthesized nanoparticles of iron to scrub polluted water. Iron chips, each about a millimeter in size, have long been used to clean dirty water. Iron corrodes in water, of course, and in the process it turns harmful wastes into benign hydrocarbons. But the Lehigh researchers say the process can be made more efficient using iron particles slightly less than 50 nanonmeters in diameter, which is smaller than bacteria.Team leader Weixian Zhang, an associate professor of civil and environmental engineering, notes that because the minuscule particles have a larger surface area they react more quickly with water. Moreover, he adds,"in an environmental cleanup, it's important that materials can move around."Larger iron filings tend to settle; nanoparticles go with the flow. Cleanups that would take months or years using current methods could be conducted within hours or days using iron particles, he estimates.The process works on a variety of toxins, including pesticides, PCBs, some fertilizers, and some heavy metals, such as lead and mercury.