The prerequisite for the best separation of activated sludge is among others an optimal zeta potential.

The charge balance of the sludge or the zeta potential can indicate the ideal flocculation point and thus optimize the addition of coagulants such as iron or aluminum salts. This can minimize the formation of voluminous hydroxides.

Theoretically, the attraction and thus the flaking of particles is greatest when the zeta potential at the shear surface is zero. One then speaks of the isoelectric point.

Many years of experience show that activated sludges with a low sludge index and excellent flocculation properties have a zeta potential of -6 to -10 mV.
If the zeta potential lies outside this range, the flake formation is worse and the sludge index is higher. The flake's shear stability decreases. The flake disintegrates in turbulent flow.
If there is a large deviation from the zeta potential of -6 to -10 mV, the flakes may self-decay. Microorganisms are then no longer incorporated into the flake, causing clouding in the course of the clarification.


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