The Stormwater Experts

Measures for combined systems


Combined sewer systems are systems that are designed to collect storm water runoff, domestic sewage, and industrial wastewater in the same pipe and bring it to the treatment facilities. During rain events, when storm water enters the sewers, the capacity of the sewer system may be exceeded and the excess water could be discharged directly to a waterbody (rivers, streams, estuaries, and coastal waters).

Main possibilities for reducing water pollution by CSOs


To address the above-mentioned disadvantages of the combined sewer overflows 5 different ways exist for optimization:

  • Storage tanks to hold overflow during storm event
  • Green infrastructure to reduce stormwater flows into combined sewer system
  • Expansion of waste treatment capacity
  • Reduction of rain water content in the mixed water by surface decoupling
  • Reduction of high concentrations in the mixed water drain through temporary waste water retention

In order to reduce water pollution in Germany, almost exclusively caching recourses are used. Although the DWA worksheet A128 calls to consider various options in the preamble areas, construction of rainwater overflow basins and storage sewers are mostly practiced. Retention soil filter for the treatment of combined sewer overflows have a huge potential.

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