Primary education treatment of water

The Water resources soft of surface as the rivers provide a rough Eau which enormously contains Pollution S which make it nondrinkable; they thus should be eliminated. To this end water will undergo a certain number of treatments necessary to make it drinkable. The primary education treatment of water is composed of the following operations:

Cleaning is the first stage of a die of treatment, which consists in retaining all large waste such as the pieces of wood, plastic the bottles, the quills… With this intention, one sets up a system of grids, whose spacing is of approximately 50 Misters As soon as the grids are encumbered by waste, a scraper (called rake more simply) goes up along the grids and makes fall this waste in a bucket which once full goes obviously to the discharge.

Flocculation

After having undergoes the treatment of coagulation, water will be transferred in another basin. It is in this basin where will begin truly accretion. Indeed nothing is then any more opposed to the gathering neutralized colloids. An agitation thus should be maintained slow to support accretions. This one is accelerated by the addition of a Polymère i.e. of a large molecule consisted the repetition of a basic reason which imprisons the agglomerated colloidal matters and thus forming bulky flakes which settle by gravity. It is the floc. It is also accelerated by a regulation of an optimum pH to obtain the best possible precipitation of the whole of the metal hydroxides which have just appeared thanks to the reaction of coagulation. One makes use of calcium hydroxide Ca (OH) ₂ also called extinct lime or whitewash and of sulphuric acid H₂SO₄ to control this optimum pH which ranges between 8.45 and 8.9.

Decantation

After having gathered the various small particles in much larger, it now will be necessary to make elutriate all this. In a motionless water body the suspended particles heavier than water are subjected to their apparent weight (actual weight less pushed of Archimedes). They fall slowly to accumulate on the bottom: it is the decantation. Their falling speed obeys the law of Stokes:

One of the simplest techniques concerning the decantation is the static decantation for example with a vertical decanter. The food is done by bottom, the particles forms a deposit and can be recovered at the bottom of the cone, while treated water is evacuated by the top, by overflow. The sedimentation test is unfortunately generally low. It is thus necessary to call upon the dynamic decantation thanks to which one can act on the trajectory to separate uninterrupted from the particles of different size and density. This type of decanter is also called decanter with plates . It improves the speed of decantation considerably. The decanters currently used are in small installations of the horizontal plate decanters but for very large installations, one will prefer decanters to him functioning thanks to this principle but with an operation still a little more optimized. After this very important stage of the decantation, it still remains to still eliminate the smaller particles thanks to a filtration.

Filtration

The first principles of filtrations had been inspired by the natural filtering of water by the various layers of the Earth which water crossed before reaching of the “underground tanks”. Unfortunately this process was too much slow for large quantities of water to treat. It should nevertheless be noted that this process is on the other hand excellent on the level of filtered water quality.

One now uses batteries of filters according to the treatment which subitl' water has before arriving at this stage. For a station of traditional treatment of water, the various treatments have summers: mix fast with a coagulant, flocculation, decantation, filtration.

Filtration necessary after all these treatments is a fast filtering called mono or double-layered conventional filtration. The materials of filtration met in the water treatment of consumption are numerous. They must have following qualities: they must be insoluble, nonfriable, and do not have to salt out any substance likely to deteriorate water qualities.

The three materials most employed are:

sand: The sand used in filtration is a natural material, containing silica, coming from rivers, natural layers, dunes or obtained starting from marine rollers. Its true density is approximately 2.5. to 2.7.

crushed sand is obtained by a flint crushing of career or rollers of sea, follow-up of operations of washing, drying and sifting. It presents angular grains, favorable to the retention of the particles during filtration.
round sand is a natural sand, filtered after washing and drying. Contrary to crushed sand, it has particles rounded, and exists in ranges of granulometry i.e. of more restricted size of sand.

the Anthracite: it is a material containing carbon, obtained by calcination of vegetable material such as wood or the peat. It is appeared as hard and angular grains. Its true density is of about a 1,45 to 1,75.

the Activated carbon is also a material containing carbon, obtained by calcination and activation of wood, coal, peat or coconut.

For a traditional filtration the most current materials are sand and anthracite. Sand is employed as full-course or is only associated with anthracite in the double-layered filters. The supports of biological filtration (deferrization, demanganization, nitrification, denitrification) are sand and the activated carbon in grains.

See too

The Coagulation-flocculation

Random links: