The capacity of autopurification of the natural environment has been overcome by the great quantity of spillages of waste water that generates the human activity. Therefore, to support the ecological balance is necessary the purification of this waste water, as step before the spillage to seas, rivers, lakes or any another mass of water. The purification consists of treating the waste water by physical, chemical or biological procedures, in order to make alike the possible maximum thing, in its physical and chemical characteristics, to the waters before any human intervention.
