Floccculants play an important role in the removal of impurities in drinking, industrial and waste water. Both suspended, emulsified and solute substances can be removed. Solutes must be converted into a water-insoluble form by means of a precipitation reaction, which can proceed simultaneously with flocculation.
The flocculated substances are separated by sedimentation, flotation or filtration.
The following substances can be removed from the water in this way:
Organic substances (hydrocarbons, humic acids, oils, fats, emulsions of all kinds, etc.)
Heavy metals (iron, manganese, copper, cadmium, mercury, etc.)
Inorganic substances (water hardness, phosphates, mineral turbidity, etc.)
Many organic substances that are lighter than water are removed from the polluted waters by flotation processes, whereas mineral substances can usually be separated by sedimentation.
Metal salts such as aluminium sulphate or iron chloride can be used to destabilise colloids, agglomerate them and convert them into separable particles. With the help of adsorbents, such as bentonites or activated carbon, even substances that are difficult to separate can be removed. In order for the resulting solids to settle quickly, flocculants based on polyacrylamide are used, which forms large, rapidly sedimenting flakes with the solids.