| WASTE WATER TREATMENT. |
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It is important to clean our waste water because even though it may
not be clean enough to drink, we can stop the large amounts organic material
from ending up in our lakes and seas, where it can cause the lake or the
sea to die.
The first step is to remove the large visible objects (toilet paper,
condoms, etc.). This is done by leading the water through a grating. The
next step is to remove the sand and fatty subsatances, which can be done
by letting the water settle and therby the sand will fall to the bottom
and the fatty substances wil float to the surface. This can now be
removed to a decaytank by using pumps.
The water will still be unclear because of dissolved organic matter.
Some of this can be removed by means of adding a compound containing iron.
This compound will be bound to phosphate causing it to precipitate on the
bootom of the tank. Some small particles will also kling to the chemical
and thereby precipitate too. This precipitate will also be pumped to the
decaytank.
Biological cleaning is a way of cleaning the water by using the advantage of organisms (bacteria) that use the organic materials of the waste water to live and reproduce them selves. This can be done in two ways. In both cases you add oxygen to the water so that the organisms(bacteria) can perform respiration. One way of doing this is by letting the water pass through many fistsized. On these stones the organisms (bacteria) will grow in layers until they will fall off into the water. This is called a stone filter. The other method is to pump atmospheric air into the waste water where organisms(bacteria) will practically eat the organic materials, the dead organisms will precipitate and pumped to the decaytank too.
Nitrogen removal is the last step of the waste water treatment. This tank contains the nitrate decomposing bacteria which require an anaerobic milieu to perform this. These bacteria harness the chemical energy from supplied organic material. In this step, the waste water is almost free from chemical substances, and it can be necessary to add some untreated water. By respiration these bacteria make use of the oxygen in the nitrate molecules. In that way the nitrate is transformed into atmospheric nitrogen, which can be led out in the atmosphere.
These described treatments will not remove poisonous compounds. However, these compounds should not have ended up in the waste water in the first place. Disease germs is also present and you can remove them by adding cloride to the water. However, cloride is also harmfull to the animals and plants that live in the habitates where the waste water ends up.