Physical-chemical treatment plants systems allow the removal of poorly biodegradable pollutants present in the water, particularly in the industrial waste water, such as heavy metals, surfactants, mineral oils, suspended solids and settleable solids.
These systems involve the use of chemical additives, commonly called “reagents”, which in particular conditions of pH, react with the pollutants, making them insoluble and favoring the abatement by coagulation, precipitation and / or neutralization.
This process is divided in two stages: in the first phase (flocculation), the slurry is mixed with the reagents (a pH corrector, a primary coagulant and / or an auxiliary coagulant) that cause the agglomeration in flakes of contaminants; in the second phase (clarification), the flakes are separated from the water by sedimentation or flotation and removed in form of mud.
If the clarified water has an excessive residual pollution, typically due to the presence of micropollutants that are beyond the chemical treatment, prior to discharge it proceeds to a refinement by filtration through sand filters and activated carbon.
The most important elements in order to obtain an efficient system of chemical purification are the physico-chemical characteristics of the water to be treated, the choice of the chemical reagents to be used, the quantity to be dosed and the timing of the reaction