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Coagulation / Flocculation

In coagulation/flocculation, a chemical (flocculant) is added to the water to remove fine suspended particles which cannot normally be removed directly by sedimentation, flotation or sand filtration. Coagulation is the process in which, by the addition of chemicals (e.g. trivalent iron), the repulsion between the suspended (colloidal) particles is reduced so that they are able to clump together (intensive mixing of water and chemicals is required and a short retention time).

The flocs that arise due to coagulation are small and can only grow further if the colloidal mixture is slowly stirred. This process, known as flocculation, therefore requires slow mixing and a prolonged retention time. Flocculents, such as polyelectrolytes (PE), can be added to improve the flocculation process.
The coagulation/flocculation process takes place in tanks, the mixing energy and retention time requiring considerable attention. If PE are used, the retention time required for flocculation has a less significant role (pipe flocculators can also be used).

Pipe flocculators

A pipe flocculator guarantees that mixing is effective and that the retention time of the water and the mixing energy released are constant (plug flow). In this way, the particles in the water and the chemicals to be dosed (coagulant, flocculant, etc.) undergo identical treatment so that the effluent of the pipe flocculator is of a constant quality with regard to floc size, etc.

The big advantage of using a pipe flocculator is that it makes mixing equipment superfluous and takes up much less space than a coagulation and flocculation tank.  
The coagulant is dosed at the beginning of the pipe flocculator. After a period of x hours (to allow the charge of the particles to stabilise), a flocculant is dosed further up in the flocculator. The optimum injection point must be determined on a laboratory scale by means of a beaker test. The pipe flocculator is equipped with sampling points and has an optional pH meter, in the event that pH correction is also carried out.