Due to the fact that there is very little difference between the density of water and activated sludge, turbulences and energy inputs in secondary sedimentation tanks impair the sedimentation behaviour of the sludge particles. Consequently, all measures that reduce turbulence can be said to be positive and, thus, desirable. Bearing this in mind, a new type of secondary sedimentation tank has been developed. As hydraulic energy is predominantly introduced via the inflow, it is recommendable to feed the sludge/water mixture directly into the sludge layer on the bottom of the tank. In addition, sludge and water should, if possible, flow in the same direction. If these principles, which can be applied to both rectangular and circular secondary sedimentation tanks, are taken into account, the tanks can be designed more cost-effectively and efficiently.

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