問題詳情


(B) The world’s population is ever rising. And the more people there are, the more need there is forclean drinking water. Now, researchers have come up with a new way to remove many pollutants fromwater, including salt: They __31__ it.The oceans hold about 97 percent of Earth’s water. Its salt content makes it undrinkable. Other waterthat is pumped from underground often has minerals dissolved in it. So this water, too, can be undrinkable(or at least not tasty). Scientists have developed many methods to remove impurities from water. Butthose methods often take lots of energy. And that makes them costly.But Martin Bazant and his teammates have come up with a new method that could lower the cost.Bazant works at the Massachusetts Institute of Technology in Cambridge. And as a chemical engineer, heuses chemistry to solve problems related to the production of food, fuel and other products. Many of themethods now used to separate fresh water from salty substances use some sort of barrier, __32__ a filter.Those barriers often are designed to let water pass through, but __33__ larger atoms, such as sodium andchlorine. (Those two elements are what make up table- and sea salts.)Bazant’s group instead made a system that doesn’t use physical barriers. It __34__ the fact thatsodium and chlorine particles have an electrical charge. Charged particles are called ions. And the newsystem uses electricity to steer the ions dissolved in water in a particular direction. This separates themfrom a stream of fresh (unsalty) water.Here’s how it worksThe MIT team pushes the water they’re trying to purify through a porous material. That means itcontains many tiny __35__. (For its tests, the team built a system small enough to sit on a bench in alaboratory. They used a material made of tiny glass particles. Those tiny bits were fused together to makea solid object that looked somewhat like a sponge.) Then, they place that material between a positive anda negative electrode and send an electric current through it. That current separates the water flowingthrough the material into two different zones. One part of the stream contains sodium and chlorine ions.So this water becomes __36__ salty. The other part of the stream contains fresh water. On thedownstream side of the porous material, a simple divider channels the fresh water into a separate area.The new system can work nonstop, says Bazant. And its materials are cheap, so making larger__37__ should be easy and quite affordable. That makes the system practical, he says. One added benefit:英文科教師甄試-5Electricity passing through the water might kill bacteria even in the zone that remains polluted, Bazantsays.The system only steers charged particles. So it won’t remove pollutants that have no electric charge.And the now extra-salty (or polluted) portion of the water will need to be treated as a __38__.Particularly __39__ its inexpensive materials, the new system “opens up a whole range ofpossibilities,” says Maarten Biesheuvel. He’s an environmental engineer at the European Center ofExcellence for Sustainable Water Technology. That’s a research institute in Leeuwarden, TheNetherlands. There, scientists and engineers study how to develop water-cleanup methods that are (amongother things) easier on the environment.Biesheuvel __40__ the system could be used to pull salt out of seawater. It might also help removesalts from groundwater. He says it even might be used to remove the dissolved salts from the fluids leftover from the hydraulic fracturing (fracking) of rocks to extract gas and oil.Plus, Biesheuvel adds, the new study will likely lead to even more research. For example, scientistsand engineers will want to figure out how to make the systems larger and more efficient. “I expect thatthis discovery will be a big ‘hit’ in the academic field,” he says.
31.
(A) zap
(B) zip
(C) zigzag
(D) zoom

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