Coarse solids can be discharged into the pre-clarifier in the form of suspended or floating matter during the relief process. In order to prevent this, relief structures were equipped with baffles which were given the task of retaining floating matter (e.g. oils and greases) and solid matter (e.g. sanitary products such as toilet paper, sanitary towels, etc.). However, conventional baffles are only suitable for this purpose to a restricted degree since the efficiency of baffles decreases with increasing volumetric flow and the reinforced suction effect resulting from this.
The unwanted discharge of coarse matter can have various causes. On the one hand, floating matter passes the area between the threshold and the baffle without any obstructions. On the other hand, solid matter does not exclusively float on the surface of the water but can also take the form of suspended matter which is swept away by the suction effect of the overflow in case of a relief.
The modern, environmentally friendly operation of a sewer system should aim at retaining these residues according to the current state of the art in as far as possible.