Consumers’ corner : The Technical Director explains the process of water purification
What is water purification all about ?
Hubert ABEGA ABEGA : First of all, it is important to make it clear: water in its natural state is not necessarily pure. It contains many materials such as: suspended solids, dissolved materials and gases. These elements are dangerous to human beings. The aim of water treatment is to remove these materials.
Talking about water, there are two types: ground water and surface water, that is, water found in rivers, lakes etc. In surface water, there are lots of suspended solids, but also, dissolved materials, gases and many other materials. For these two types of water, there are usually two treatment procedures. One is aimed at removing suspended coarse particles -like a tree trunk. In pumping stations, railings are usually installed to filter these coarse particles. But once coarse particles are removed, fine particles remain and it is difficult to agglomerate them because, they have the same electric charge. This electric charge causes them to repel each other so, it is necessary to neutralize them so as to ease their agglomeration. We will either agglomerate them to the bottom of the water or cause them to float on the water and after remove them..
What do the second and third phases of water purification consist in ?
Hubert ABEGA ABEGA :The second phase is that of coagulation. It consists in injecting a substance that will fix positive and negative charges and ease the agglomeration of fine particles which are not necessarily visible to the naked eye. The following step is that of flocculation. Since coagulated particles are not heavy enough, another product is added in a machine found in water treatment plants and which is called “mix tank”. After that, particles are introduced into the settling tank which makes them heavier, so that they can fall at the bottom. They will finally be collected and expelled for treatment. Thus, clarified water is collected on the surface. At this level, water is not yet potable because all the work done before is for suspended particles. However, some of these particles are still present in the water. During the next phase, water is introduced in a sand filter which retains fine particles which could have escaped settling. After that comes the step of disinfection which consists in injecting a disinfectant that will neutralize dissolved particles, dangerous for man’s health and hygiene. Once the disinfectant -generally calcium hypochlorite or bleach in normal proportions- has been injected, water is considered potable. But problems of acidity and neutrality remain, and we all know that drinking water is not supposed to be acid because it can attack surfaces with limestone for example, and neither should it be incrusting, it should be neutral. Thus, a product is injected into the water for it to lose acidity and incrusting property. Generally, at this stage, calcium hydrate is used, thereafter, water is considered potable .
And the smell that is sometimes noticed when we drink water, what is it ?
Hubert ABEGA ABEGA : First of all, we should point out the fact that potable water can lose its potability if it gets in contact with other dangerous particles, bacteria and other contaminants. To solve this problem, a disinfectant and a residual product are injected to allow water to hold for a certain period in the pipeline before reaching the consumer. That is why you can smell a beat of chlorine when it reaches you. This chlorine is a good sign because, it shows that the necessary residual dose was left in the water in order to keep is potability when circulating in the pipeline. Now you know how surface water is treated.For underground water, since it contains no suspended solids, we are only concerned with dissolved particles and the neutrality of water. So, we inject only a disinfectant and calcium hydrate to correct its neutrality. Because of the presence of gases in the two types of water, it is necessary to put it in contact with oxygen. Thus, water is oxygenated in order to eliminate some particles or mineral salts. In short, water purification consists in removing suspended and dissolved particles.