Wastewater purification is the removal of the contaminant content. It is the first step to return it to the environment with minimal ecological risks, or for other uses.

This treatment is carried out through a combined set of unit processes that result in the desired purpose. This particular sequence of unit processes is reflected below in an easy way:


  1. Tributary Control: comprehensive knowledge of the water that reaches the treatment plant by controlling certain parameters.
  2. Smoothing down/Refining: thick solid separation through grilles or screens.
  3. Sand-filtering and degreasing: the filtering of the sand is to draw out the dirty water, gravel, sand and more or less fine mineral particles in order to avoid deposits in the channels, conduits, and to protect pumps and other equipment against abrasion. Sand-filtering and degreasing is used to remove floating oils via sandblasting by using a small quantity of air through compressors.

Primary settling (filtering): this aims to achieve maximum particle separation and settling solids from waste water by gravity into a settling tank.

Biological treatment: lbiological processes remain the treatment of choice for their reliability and simplicity of operation. The most widespread is the activated sludge reactor with biological nutrient removal (nitrogen and phosphorus). The biological denomination is the result of the process taking place, i.e. the removal of organic matter present in the wastewater through the intervention of microorganisms (bacteria, protozoa, etc.).

Secondary sedimentation: This consists in the separation of biological sludge and treated water by gravity.

Sludge Treatment: All solids filtered in the primary sedimentation process, pass to a sludge thickener by gravity and secondary sedimentation via a flotation sludge thickener.

Once thickened, the sludge is extracted and mixed, and is then fed to an anaerobic digester. This digestion process removes much of the organic sludge. Once it is extracted from the digester, it is passed through a sludge centrifuge process to separate water from sludge solids so as to remove it as dry as possible, to then take it to a specialized treatment plant, or to be used as fertilizer for agricultural purposes.


The treated water which is not used is returned to the river or sea through special pipes or underground ducts, trying to change the natural systems as little as possible.