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参与翻译: 郜黎帆 (4)

引言

我们总是想当然地认为水都是干净的。我们习惯于在渴的时候喝喷泉或者水龙头的水,但你是否知道世界上十亿以上的人口无法获得干净的水呢?其中一部分原因是干净(或纯净)水是很难获取的。你不仅需要去除其中的灰尘以及其他杂质,还必须处理掉所有可能使人生病的看不见的细菌和微生物。在本文的活动之中,我们将探索一些清洁水的方法,并了解当您口渴时确保水可以安全饮用的步骤。

 

第 1 段(可获 1.55 积分)

背景

净化水的过程复杂且昂贵,然而,这个过程可以划分为五个基本步骤:曝气,混凝,沉淀,过滤和消毒。第一步,曝气。将空气注入水中,同时向水中添加氧气,使得其他气体得以逸出。第二部,混凝。将污垢和其他固体颗粒附在一起,当它们附着在一起时,污物会凝结(形成较大的团块),这样在整个过程的后续步骤中污垢就更容易过滤掉。第三步,沉淀。我们要让重力为我们工作。重力将沉重的污块吸入水底,使其与表面的清洁水进一步分离,并准备好进行下一步过滤。 过滤包括从水中分离污垢和其他固体颗粒。最后(也许是最重要的步骤)第五步是消毒。 用化学品以及/或者热处理水来消毒水,从而除去可能使我们生病的细菌和其他不安全的微生物。

第 2 段(可获 2.18 积分)

您可以通过测试您自己的几个水过滤系统来探索其中的几个步骤。 下次你从水龙头接水喝时,记住要确保饮用水的干净、安全!

材料

  • 两片咖啡过滤纸
  • 三个透明塑料水瓶
  • 一杯生米或生豆子
  • 五个透明塑料或玻璃杯
  • 两张白纸
  • 一支钢笔或铅笔
  • 四杯水
  • 一杯松土
  • 一个带盖的大型塑料容器(用来盛放混合水和土)
  • 尺子
  • 剪刀或美工刀
  • 一位成年助手
  • 橡皮筋
  • 定时器或时钟
  • 量杯(至少是半线量杯)
  • 半茶匙明矾
  • 一把勺子
第 3 段(可获 1.55 积分)

准备工作

将水和泥土在大塑料容器中混合起来,摇晃容器确保泥土和水均匀混合。

比着标尺用笔在纸上划四行两列,将一张纸均匀分割成八个部分。在第一行中按如下所示标记每一列:列1-“控制”; 列2-“咖啡过滤器”; 列3-“米和咖啡过滤器”; 列4-“米,咖啡过滤器,明矾”(注意:如果您用的是豆子,请在表格中用“豆”代替“米”)。

让你的成年帮手把水瓶的底部剪下来,并使瓶身和瓶口保持完好。

第 4 段(可获 1.3 积分)

Procedure

  • Measure one half cup of the dirty water and pour it into one of your plastic cups. Add one half teaspoon of alum to the water and stir gently for three to four minutes. What do you notice about the water as you stir?
  • Set the cup with alum and dirty water aside; let it sit undisturbed for at least 10 minutes.
  • Starting with Bottle 1, cover the mouth of the bottle with a coffee filter. Use a rubber band to secure it in place.
  • Turn the bottle upside down (so the bottle mouth faces downward). Hold the bottle over one of your clear cups.
  • While you hold the bottle, ask your adult helper to carefully pour one half cup of the dirty water into your bottle. Start your timer.
  • Hold the bottle over the cup until all of the water is in the cup. In Column 2 on your paper, next to the square that says “Coffee Filter” write how long it took for all of the water to get into the cup. What do you notice about the water in the cup? Does it look different than it did when you poured it in the bottle? What is left in the bottle?
  • Put the cup with water from Bottle 1 on your paper, in the square where you wrote the time. Use a measuring cup to measure how much water is in the cup. Write this amount next to where you wrote the time. Pour the water back into the cup and leave it on the paper. Did all of the water that you poured into the bottle make it into the cup? If not, where do you think it went?
  • Put Bottle 1 aside.
  • Prepare Bottle 2. Cover the mouth of the bottle with a coffee filter. Use a rubber band to secure it in place.
  • Turn the bottle upside down (bottle mouth downward). Hold the bottle over one of your clear cups.
  • Have your adult helper carefully measure and pour one half cup of rice into Bottle 2. Tap the sides of the bottle so that the rice settles at the bottle mouth.
  • While you hold the bottle, ask your adult helper to carefully pour one half cup of the dirty water into your bottle. Start your timer.
  • Hold the bottle over the cup until the bottle has no water left and all of the water is in the cup. In column 2 on your paper, next to the square that says “Rice and Coffee Filter,” write how long it took for all of the water to get into the cup. What do you notice about the water in the cup? Does it look different than it did when you poured it in the bottle? What is left in the bottle?
  • Put the cup with water from Bottle 2 on your paper, in the square where you wrote the time. Use a measuring cup to measure how much water is in the cup. Write this amount next to where you wrote the time. Pour the water back into the cup and leave it on the paper. Did all of the water that you poured into the bottle make it into the cup? If not, where do you think it went?
  • Put Bottle 2 aside.
  • Prepare Bottle 3. Cover the bottle mouth with a coffee filter. Use a rubber band to secure it in place.
  • Turn the bottle upside down (bottle mouth facing downward). Hold the bottle over one of your clear cups.
  • Have your adult helper carefully measure and pour one half cup of rice into Bottle 3. Tap the sides of the bottle so that the rice settles at the bottle mouth.
  • This time, have your adult helper carefully pour the water from the first steps into Bottle 3. Try to avoid disturbing any sediment that collected in the cup. Start your timer.
  • Hold the bottle over the cup until all of the water is in the cup. In column 2 on your paper, next to the square that says “Rice, Coffee Filter, Alum,” write how long it took for all of the water to get into the cup. What do you notice about the water in the cup? Does it look different than it did when you poured it in the bottle? What is left in the bottle?
  • Put the cup with water from Bottle 3 on your paper, in the square where you wrote the time. Use a measuring cup to measure how much water is in the cup. Write this amount next to where you wrote the time. Pour the water back into the cup and leave it on the paper. Did all of the water that you poured into the bottle make it into the cup? If not, where do you think it went?
  • Measure and pour one half cup of dirty water into your last clear cup. Place this cup on your paper, in the square next to the one that says “Control.”
  • You should now have four cups lined up on your paper. Look at the water in each cup as well as the time and measurements you wrote on your paper. Compare the results of each of your three tests, with the Control cup. Which water is the dirtiest? Which is the cleanest? Which filter system took the most time to filter the water? Which took the least? Which filter system absorbed the most water? Which allowed the most water to pass through it? (Note: Although your water may appear clean—it is not, and you should not drink it. Use it to water your yard or plants instead!)
  • Extra: Try this activity with other household materials such as cotton balls, paper towels, sponges or anything else you think might be a good filter. Did you find one that worked well? Why do you think it worked well—or not?

第 5 段(可获 12.29 积分)

Observations and results

In this activity you tested several different methods for filtering dirty water. Your results may have varied slightly depending on the type of dirt you used in your dirty water. You should have found, however, the water was cleanest when you used the coffee filter, rice and alum all together. This filter did the best job of cleaning the water because it incorporated several different water purification steps. First you added alum to cause coagulation. You should have observed the water coagulating as you stirred the mixture during the first step. Next you allowed the water to sit undisturbed for at least 10 minutes. This resulted in sedimentation, where gravity pulled the coagulated substances to the bottom of the cup, leaving cleaner water at the surface. Finally you filtered the cleaner water through rice and a coffee filter, separating those coagulated chunks from the water.

第 6 段(可获 1.85 积分)

You should have found the coffee filter alone did a fairly good job of filtering the water, however the extra steps you took with the alum yield better results. In addition you probably observed that you had the most water come through the coffee filter. Both the rice and alum absorb some of the water, so less makes it into your cup from the bottle. The coffee filter alone should have been the fastest filtering method of the three you tested, and have taken the least amount of time to empty the bottle.

第 7 段(可获 1.16 积分)

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