The purpose of the tertiary treatments is to eliminate the organic residual load and those other pollutant substances not eliminated in the secondary treatments, for example, the nutrients, phosphorus and nitrogen.
These processes belong to biological nature or physicist chemistry, being the most used unitary process the treatment physicist - chemist. These consist of a coagulation, floculation and a decantation.
Other processes used as tertiary treatments are the resins of exchanges of ions, the adsorption in active coal, the ultrafiltration, the inverse osmosis, etc.
IONIC EXCHANGE
It is an operation in which there is in use a material, habitually named resins of ionic exchange, which is capable of retaining selectively on its surface the solved ions in the water, keeps them temporarily joined the surface, and yields them opposite to a solution with a regenerated. The habitual application of these systems, is for example, the elimination when they are in low concentrations.
ADSORTION
It defines the property of material (adsorbents) certain in fixing in its surface organic molecules extracted from the liquid phase in which they are. The process of adsorption consists of the captation of soluble substances of the surface of the solid one. A fundamental parameter is this case it will be the specific surface of the solid one, provided that the soluble compound to eliminating has to center in the surface of the same one.
There is in use for eliminating phenols, aromatic hydrocarbons nitrated, chlorinated derivatives, etc, as well as to eliminate smell, colour and flavour. The adsorbent most used in the water treatment is the active coal.
MICROFILTRATION AND ULTRAFILTRATION
The principle of the micro and ultrafiltration is the physical separation. It is the size of pore of the membrane what it determines up to what point there are eliminated the solved solid and the microorganisms. The substances of major size that the pores of the membrane are retained totally. · Microfiltration: have the membranes used for the microfiltration a size of pore of 0.1 to 10 µm. The microfiltration can be applied to many types different from water treatments when it is necessary withdraw from a liquid the particles of a diameter superior to 0.1 mm. Ultrafiltration: it allow to retain molecules which size ranges between 0.001 to 0.1 µm.
Consists of applying to the concentrated dissolution a pressure superior to the osmotic one, producing the waters down from the dissolution most concentrated to most diluted up to reaching a new balance. Using this technology, most of the content is eliminated in the water.
