VOA常速英语:喝到嘴里的水是如何被“洗”干净的

Whether you are treating for a population of 3000 or for 3 million this process is going to look a lot like this.
不管供水的人口是三千还是三百万，水处理过程都类似下面这样。

It’s called conventional water treatment and it makes lake and river water safe to drink.It starts with a chemical that attracts and binds together the stuff you want to take out.
这叫做常规水处理，它能使湖水和河水变成饮用水。一开始先加化学试剂使废物结块沉淀并被清除掉。

We add those coagulant and it’s positively charged while most of the dirt and bacteria are the negative charge.
我们加的沉淀剂是带正电荷的，而泥土和细菌是带负电荷的。

It’s a crucial if temporarily backward step.
这是水暂时性回流的重要一步。

When we added our coagulant it actually made the water dirtier.We created these flocks but now as we are going, all those flocks are settling out.
当加了沉淀剂之后，水更浑浊了，因为废渣都聚合到了一起，不过这一步，就该把它们分离掉了。

This process sedimentation makes the things you don’t want to drink sink,a key step in creating cleaner water for you and for the rivers.
沉淀作用让废料下沉，不管是为了你，还是为了河流水质，这都是一个获得清洁水的重要步骤。

This is all part of the process that diverts those salads should be returned to the river and put beneficial usage instead.
这步是使需要回到河流里的混合物被分流回去，并使它们派上用场。

In this case the solids will coat a landfill. Now back to the drinking water.
然后这些固体物将会填充泥土填筑池。回到正题上，接着说饮用水。

There are some small fine particles that can float on that aren’t removed by gravity settling and here is where we remove those small particles.
有些微小颗粒用刚刚的重力沉淀法没有去除干净，现在我们看到的就是去除这些微粒的方法。

The technical name is dual media filtration which means that within any one filter,water flows through both coal and sand in case you wonder how they clean those filters: backwash.
这个技术名叫双向过滤法，意思是在一个过滤器中，水流从煤块和沙子两边一起进行清洗，如果你纳闷如何清洗过滤器，那就是“反流法”。

In the next step, filtered water is disinfected by adding chlorine.Each step is lab-tested something important in times of erratic weather.
下一步骤，氯将被用来为过滤水消毒。每一步都是实验室检测过的，确保能跟着变幻不定的天气走。

If you’ve got a lot of rain in the watershed it can stir up dirt and debris and carry that into the river.When that’s taken into a water treatment plant,you need to increase your coagulant dose to account for that higher amount of solids in the river.
如果雨水很多的时候，就会有多余的泥土残渣被冲到河里，所以当这种水被排入水处理厂中时，就要相应的多加沉淀剂，确保固体沉淀的量也相对增加。

Engineers at this cutting edge treatment plants say modern technology can keep today’s drinking water cleaner and safer than any other point in history.
尖端污水处理厂的工程师说，现代污水处理技术处理过的饮用水比历史上任何一个时期的水都要干净。

Arash Arabasadi, VOA News, Washington.
美国之音，Arash Arabasadi华盛顿报道。