CSF-MODULE is based on the principle of solids contact unit which create convey a larger mass of sludge into the flocculation area. This unit involves the recirculation of sludge.

CSF-MODULE is an external recirculation unit based on the lamellae settling principle. It is a fast, compact and adaptable unit, unaffected by variations in raw water composition and flow rate. The unit reduce the volume of settled sludge, which can than be dewatered without further thickening.

CSF-MODULE has three main components: flocculator, presettler-thickener, lamella settling. Flocculator provides rapid flocculation with mixing by an axial-flow impeller that recirculates the flow within the reactor and plug-flow conditions prevail to allow slow flocculation. In the Presettler-thickener zone most of the flock settles. The thickened sludge is drawn off through a pipe from the central sludge hopper. Part of the sludge is recirculated to the raw water inlet pipe, thereby ensuring optimum sludge concentration in the reactor at all times. The excess sludge is drained by gravity or pumped away. The sludge is thick enough to be transported to the dewatering system without any additional thickening. Lamellae settling removes the residual flock. The settled water is recovered by a system of collection troughs. The sludge is collected by gravity extracted in and recycled to the head of the reactor. To keep the CSF-MODULE effluent at a fairly, constant quality sand filtration was added to this unit. Filtration is brought in to raise the quality of the final effluent and to keep the quality of this effluent as constant as possible.