At the same time, humans have a responsibility to cooperate with this system so that it can work without undue interference. Self-Purification System The heat from the sun evaporates water from the surfaces of the oceans, lakes and other bodies of water, as well as from damp surfaces. This evaporation lifts tremendous amounts of water vapor into the atmosphere every day. Even if these waters or surfaces happen to be dirty or salty, the vaporized water is almost pure.
In time, this water returns to the earth as rain (or snow). At the same time it helps to purify the air by taking with it dust and other substances. When it reaches the ground, it gives a cleansing rinse to the vegetation and other surfaces. Some of the water flows into rivers, and some soaks into the ground. Yet, when you draw up groundwater from a good well, it is not dirty. It has become good, pure drinking water!
What has happened to make it that way? When the water soaks into the ground, it is first of all purified mechanically, in that the soil acts as a filter. Solid particles that were in the water remain in the soil as the water passes through it.
However, in water there are also organic impurities and other ones that are not removed by the filtering action of the soil. But the purification of water from these also has been arranged.
Biological Purification The impurities that are not removed from water by filtering through the soil are handled by biological purification. In this process, countless different microorganisms in the soil go to work on the impurities.
As the water slowly soaks into the ground, bacteria and other organisms use the various impurities in the water as food. Their digestive system breaks down the impurities into matter that vegetation can use as nourishment. As the water is being purified in this way, it absorbs various beneficial minerals from the soil.
These also serve to improve its taste as drinking water. So this is why the groundwater in many places is good drinking water without any further purification. There is also a similar, wonderfully designed water purification process taking place in the rivers, lakes and oceans.
The greater part of the solid impurities sink to the bottom of such waters, and the biological process takes care of other impurities. Rainwater washes into the bodies of water great amounts of nutrients from the soil. This includes various nitrogen and phosphorous compounds, as well as countless different substances. Microorganisms in the rivers, lakes and oceans work on these substances, breaking them up into nutrients that the water plants can use for food.
When bodies of water get these nutrients adequately, balance is preserved and the water remains sufficiently pure. Too, when water plants get sunlight they produce oxygen in the water. Microorganisms and fish need this oxygen in order to live. Thus, the entire arrangement is a marvel of order, cooperation and efficiency.
Man-made Problems Nature’s self-purification system worked well without any problems for thousands of years. But gradually people began to come together in ever-expanding cities, causing problems with the balance of nature. In early times, drainage systems were constructed in cities.
These discharged untreated sewage and waste directly into bodies of water. It could be said that this was the beginning of water pollution. In time, the natural purification process was overwhelmed.
Thus, many of the rivers flowing through cities gradually became foul-smelling, open sewers. What happens when too much waste is discharged into a body of water? At first, microorganisms multiply quickly, as do plants.
So the water begins to get muddy. In order to produce oxygen in the water, the plants need sunlight. But the muddiness of the water prevents the light from penetrating below the surface.
Thus, the plants that are deeper under the water begin to die and decompose. The decomposition of the plants uses the oxygen in the water faster than the living plants can produce it. Gradually the oxygen supply is exhausted.
This, in turn, means that the microorganisms and fish that are dependent on oxygen die. Increasing population and the growth of industry have led to problems like this in many places. Due partly to ignorance and partly to indifference, vast amounts of waste and poisons have been discharged into the water.
The natural purification process cannot neutralize these quickly enough. As a result, some very dangerous substances have found their way into plants, fish, birds and humans. Gradually, the need for laws governing the handling of waste became evident.
And when action has been taken to improve a polluted body of water, a marked improvement has resulted. But how is this accomplished? Waste Water Treatment The treatment of waste water has been the key factor.
The methods used take advantage of the natural biological purification process. Let us take a look at what happens to waste water as it goes through a typical treatment plant. Since there are large solid substances in waste water, it is first filtered through a screen to strain out these large solids.
Then the water flows slowly through a small basin where the heavy substances, such as sand, sink to the bottom, from where they are cleared away. This basin is called a grit chamber. Next the water flows into a large sedimentation basin, where it moves slowly for one or two hours.
Here the dirt or sludge in the water sinks to the bottom, from where it can be pumped out. At this point, however, there are still a lot of organic substances in the waste water. So the water is next channeled into the biological stage for “high-powered treatment” by microorganisms.
In large treatment plants this is generally done by adding a concentration of microorganisms to the waste water when it comes into the aeration tank. As the tank’s name suggests, air or plain oxygen is blown into the water.
The microorganisms now have an abundance of both oxygen and food in the waste water. So they multiply rapidly and effectively break down the impurities. After this, a clarification tank is needed to separate the microorganisms from the purified water.
They sink to the bottom in this tank and the relatively clean water can now be discharged into the lakes or rivers. However, such water may still contain much bacteria, some of which could cause disease.
For that reason this water is usually disinfected with, for example, chlorine or ozone to kill dangerous bacteria. Improved Purification In the past few years many countries have been trying to improve their treatment of waste water. Their goal is to remove phosphorous and nitrogen compounds from the water more effectively.
Human excreta and many detergents contain a lot of phosphorus, of which only about a third is removed by biological treatment. Phosphorus would cause the growth of algae in the water unless it was removed. So a chemical that precipitates or attaches to itself more than 90 percent of the phosphorus in water is added after the biological treatment has been carried out. Then it can be gathered as sediment from the bottom of the tank.
Aluminum sulphate or iron sulphate, which are waste products from industry, can be used for this purpose. Other chemical-physical methods also have been adopted in order to achieve a greater degree of purity. Among these are absorption on activated carbon or other absorbents, reverse osmosis, ion exchange, and distillation.
It is clear that the building of plants for treating waste water, and the treatment itself, are quite costly. But it is part of the price that must be paid for the concentration of population and industrialization.
Realizing how valuable pure water is, most people will no doubt be willing to sacrifice something so that the natural cycle of this vital liquid can continue relatively undisturbed.
