The Decision Support System (DSS) is an innovative tool for the sustainable operation of the integrated sewer network and wastewater treatment plant (WWTP). It is based on a series of level and flow sensors within the sewer network, WWTP operation data and accurate flow forecast at the inflow of the WWTP (solution 11). Goal of the DSS is to optimize treatment capacities, pumping strategies and in-sewer flow allocation to make the best use of existing infrastructure for stormwater handling.


Sharper environmental and economic regulations, constantly growing cities and the general need for adaptation to climate change put pressure on utilities to find new ways to optimize the sewer system across its many shareholders. Integrated urban water management is an imperative in this context to reduce adverse impacts on surface waters and minimize future investment costs. In particular, real-time control provides a range of alternative strategies for the integrated management of sewer networks and wastewater treatment plants. It can support the reduction of flooding and environmental impacts and enhance the treatment capacity of the treatment plant by defining different operation schemes for dry and wet weather situations. Real-time control relies mainly on the availability of reliable flow forecast in order to optimize the operation of wastewater treatment plant and manage in-sewer retention capacities.

Limitations of current practices

Integrated real-time control has already been successfully tested in several EU utilities to mitigate CSO, environmental contamination, energy consumption and flood risk. The resilience of sewer networks and WWTP can highly benefit from a fully integrated management of the infrastructures.

However, in practice the potential of real-time control is often hampered by the lack of interoperability between systems and stakeholders so few utilities have fully implemented real-time control strategies for the management of the integrated water cycle, namely sewer, WWTP and rivers.

Several solutions exist for monitoring and controlling WWTP processes including specific measures for stormwater control. Existing commercial systems focus on WWTP only but are not fully interoperable with sewer management systems and do not allow real-time integrated control of both sewer and WWTP processes.


The DSS provides a fully interoperable platform including WWTP and sewer system data and models. It develops advanced real-time control strategies for the WWTP and sewer system under different operational conditions, such as switching between dry and wet weather flow operation of the WWTP based on short-term inflow forecasts and management of in-sewer retention capacity and emptying of retention basins based on long-term inflow forecasts. The solution supports decision making taking into account sensors and modelling uncertainties. It is available in both online (real-time) and offline versions.

City tests

The sewer flow forecast toolbox is deployed in Copenhagen in the catchment to the WWTP Damhusåen, covering an area of approximately 55 km² and six municipalities (Copenhagen, Frederiksberg, Gladsaxe, Herlev, Rødovdre and Hvidovre). The catchment’s sewer system is mainly combined (85%), with ca. 160,000 m³ established storage volume and ca. 86 combined sewer overflows across the catchment, representing 45% of all overflows in the BIOFOS catchment area (ca. 350 km²). The utilities in charge of operating the sewer system are HOFOR, NOVAFOS and Frederiksberg, while BIOFOS is in charge of operating the WWTP. Runoff in the catchment is primary transported gravitational and control options are limited. Inflow to the WWTP can be as high as 28,000 m³/ hour while the plant’s biological treatment capacity is limited to 10,000m3/ hour. This leads to frequent bypass events, in average more than 75 times per year, with untreated sewerage spilled to the surface waters.

Contact solution

DHI – Copenhagen – Sten Lindberg :
BIOFOS – Carsten Thirsing :
BIOFOS – Barbara Greenhill :
BIOFOS – Dines Thornberg :

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