经济学人下载:清洁水源 生命的银丝带

Science and Technology
科技

Clean water
清洁水源

Silver threads of life
生命的银丝带

A water filter that kills bacteria, rather than just removing them
新滤水器能够消灭细菌，而不单单是排除细菌

MORE than a billion people lack clean water-and in most cases the lack is just of cleanliness, rather than of the water itself.
超过十亿人口缺少饮用水，并且在绝大多数情况下缺少的只是纯净的水，而不是水本身。

The result is disease, particularly diarrhoea. This kills millions of children a year and stunts the growth of millions more.
其结果是给人们带来了疾病，特别是每年夺取数百万儿童性命并使更多的儿童生长发育受阻的腹泻。

Better water filters, then, could save many lives and improve many others, and Yi Cui of Stanford University thinks he has come up with one.
所以更好的滤水器就能挽救许多生命，提高人们的健康水平。而来自斯坦福大学的崔毅教授认为他已经研制出了这样的滤水器。

Traditional filters work by forcing water through pores to weed out bacteria.
传统的滤水器使水流流过微孔从而排除细菌。

That needs power, as well as frequent changes of the filter element as the pores fill up with bugs.
这需要消耗电力，而且由于微孔上积满了细菌，滤水器元件也需经常更换。

Dr Cui's filter, though, does not screen the bacteria out. It kills them.
但是崔教授研制的滤水器并不是将细菌排除出去，而是将其消灭。

The filter element he and his team have designed is a mesh of tiny carbon cylinders, known as nanotubes, and silver wires laid on top of a thin strip of cotton cloth.
崔教授及其团队所设计的滤水器元件采用微小的碳圆柱形网状物，也就是碳纳米管。

Silver is well known to kill bacteria, so Dr Cui conjectured that forcing bugs to pass close to the metal without actually trapping them might lead to their destruction.
薄薄的棉布覆盖着碳纳米管一端，并用银丝固定。金属银因能够杀死细菌而为人所知。崔教授据此推测将细菌引至银丝附近而不是使其进入微孔，即可消灭细菌。

He also suspected that running an electric current through the silver might help the process, because electrical fields have the ability to break down the membranes that surround bacterial cells.
他同时猜测，使银丝接通电流，将有助于整个过滤工序，因为电场具有穿透细菌细胞膜的特性。

Though silver is a good conductor, carbon is cheaper, and the nanotubes provide the extra electrical conductivity needed.
因此虽然银是良好导体，碳也很便宜，但是纳米管却可以额外提供必需的导电性。

To make their new filter, the team first dipped strips of woven cotton into "ink" containing nanotubes. They then used pipettes to drop the silver wires, which were suspended in methanol, on to the surface of the strips.
制作新型滤水器，首先把棉布条浸入含有碳纳米管的"墨水"中，然后用吸管将浸泡在甲醇中的银丝滴在棉布条的表面。

Once dried, the new filters were ready to try.
置干后，新的滤水器就可以工作了。

To do that Dr Cui connected them to a battery and ran water containing E. coli, a common bacterial contaminant of water, through them.
崔教授将这些碳纳米管与电池相连接，并使含有导致水污染的一种常见细菌——大肠杆菌的水流经其中。

A few drops of the filtered water from each experimental run were then scattered on an incubation plate to see what was left to grow.
随后每次过滤实验得到的几滴水被放在孵化盘中用以观察水中剩余物质的状况。

As they report in the latest edition of Nano Letters, Dr Cui and his team found that when the filter was operated at -20 volts it killed 89% of the bacteria and that at +20 volts it killed 77%.
正如在最新一期《纳米快报》中报道的一样，崔教授与其团队发现滤水器在-20伏的电压下工作时，可消灭89%的细菌，在+20伏的电压下工作时，可消灭77%的细菌。

At zero volts, most of the bacteria survived.
而在不通电的情况下，大部分细菌都得以存活。

In a follow-up experiment, in which contaminated water was run through three of the new filters in sequence, 98% of the bacteria were killed.
在进一步的实验中，受污染的水依次流经三个新型滤水器，结果98%的细菌被消灭了。

Using silver this way might sound expensive, but it is not.
如此使用银乍听起来十分昂贵，实则不然。

The amount involved is minuscule, as is the quantity of electricity needed to keep the filter charged (a small solar panel would be sufficient to supply it).
银的使用量非常小，与维持滤水器运转所需电量（一小块太阳能电池板就足够了）一般。

And the filter itself would be expected to last indefinitely.
此外，滤水器本身还可望永久使用。

The next test, then, is to see if the new device kills the full range of dangerous bacteria found in polluted water.
随后的测试将证明这种新型滤水器是否能消灭在受污染的水中所发现的各种有害细菌。

If it does then potable water, one of the necessities of life, may become easier for many people to obtain.
如果确实如此，那么许多人就可以更容易获得生活的必需品——纯净的饮用水了。