One apparatus of the above-mentioned type is known. It is arranged as a stationary structure at the edge of a settling tank. The collecting basin is constructed as a trough with a V-shaped cross section, one V-leg being shorter than the other one and the shorter leg providing the waste water an access to the trough. At the base of the trough there is a conveying device in the form of a pipe having bores. The pipe terminates in an upwardly extending sludge return pipeline. An injector for supplying compressed air is provided in the pipeline, with the help of which compressed air sludge in the pipeline is conveyed and discharged.
A floating overflow receptacle for the cleared waste water is provided in the region of the water surface and is connected through a flexible waste water pipe to a stationary waste water pipeline.
In general, the conventional apparatus operates reliably. As desired, the sludge which settles in the collecting basin is concentrated and is then removed by the conveying device. The cleaned water can discharge through the overflow receptacle and the floating arrangement of the overflow receptacle ensures that, during water level variations, the selected discharge rate is not changed.
The conventional apparatus is, however, a stationary structure and therefore requires space outside or at the edge of the basin. It must be constructed relatively strongly, for example of concrete, since such structures are intended for long periods of use without repairs. Therefore, the expense in manufacturing the conventional apparatus is considerable, and appropriate considerations must be made during construction and dimensioning of the apparatus to ensure that it withstands the pressure of the earth and the lift caused by ground water, waste water, etc.
In some cases, particularly where in-ground basins are used, a concrete construction is not at all possible in consideration of the soil.
The greatest disadvantage of stationary systems, however, is that these systems are not flexible. If the settling tank is to be enlarged, a larger final clearing apparatus would have to be available in order to process the accumulating sludge and the waste water. In this case, the stationary clearing apparatus must be enlarged, insofar as this is possible with respect to the space available.
Therefore, the basic purpose of the present invention is to produce an apparatus of the above-mentioned type which is more economical to manufacture and more flexible during use than conventional systems.