On hydraulic and pollution effects of converting combined sewer catchments to separate sewer catchments

Abstract

The overall objective of this paper is to contribute to the standing debate concerning the advantages of separate sewer systems compared to traditional combined sewer systems. By a case study this investigation reveals that transformation of part of a town from being serviced with combined sewer systems to become serviced with separate sewer systems decreases the volumes of storm water and pollutants diverted to the waste water treatment plant and discharged as combined sewer overflow. This happens at the expense of an increase in volumes of storm water and pollutant loads diverted to local receiving waters when detention ponds are not built-in the new separate sewer systems. It is concluded that consequences can be fatal for receiving waters, if no retention of pollutants is integrated into the system.

Keywords::

• combined sewer systems vs. separate sewer systems
• MOUSE LTS simulations
• historical rainfall time series
• annual discharge statistics, storage basins

Acknowledgement

The authors are very grateful to the Municipalities of Aalborg for making the Frejlev catchments and sewer system data available for this investigation - as well as DHI Water & Environment for making their software freely available for investigations of this kind.