Separation system

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With the separation system ( separation process ) in drainage technology , separate pipe and sewer systems are created for the drainage of wastewater and rainwater .

For this purpose, the rainwater from the roof and traffic areas is collected separately from the remaining domestic wastewater and, if possible, channeled into a nearby body of water. Since significant floods can enter small bodies of water after heavy rain events, efforts are being made, especially for newer systems, to build structures to store part of the precipitation in rainwater retention basins or in rainwater retention ditches . Rainwater infiltration is particularly sensible from an ecological point of view , if possible in open trenches, as it not only temporarily stores the water but also cleans it.

The separation system has the advantage that relatively lightly polluted rainwater does not have to be sent through the sewage treatment plants . This allows wastewater treatment to be carried out much more thoroughly and also more cost-effectively. The wastewater channel can also be made smaller. For this reason, new building areas are now almost exclusively developed using the separation system, but wastewater is also increasingly separated in the old town drainage system. However, all lines must be duplicated.

Since streets, roofs and squares can be polluted with leaves or animal droppings, for example, the rainwater is also often polluted - albeit significantly less. As a rule, however, there is no treatment of the wastewater with rainwater, which is why the receiving water is polluted by the rainwater discharge. In water protection areas today at least one oil separator is interposed.

Even with a carefully designed separation system, clean extraneous water can penetrate the wastewater channel. This gets into the sewer through the manhole cover , incorrect connections, or in the case of leaky sewers through the groundwater. Therefore, even with new sewers, a 100% surcharge for the extraneous water is expected, which in this dimension only occurs with heavy rainfall.

Situation in Germany

While in the past the lower operating and installation costs of mixing systems were often decisive for the decision against a separation system, the trend today is towards separation systems, mainly due to the relatively high water pollution from untreated wastewater in mixing systems. In 1991, the share of separation systems in the total municipal sewer system in Germany was 25% and by 1998 had increased to 30% of the total length of all drainage channels.

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