Over compliance through real time control. Sewerflex – sewer network optimisation

Hestbæk, T. K.1 , Sørud, M. 1 , Poulsen, T. S.1 , Grum, M.1 , Moelbye, N. and Joergensen, A. T.1 1 Krüger A/S, Denmark



Sewerflex focuses on advanced Real Time Control (RTC) of sewer networks. The main focus is to reduce Combined Sewer Overflow (CSO) events by utilising the existing storage volume in an optimised way and to reduce capital investment within new sewer infrastructure.

The core of Sewerflex is a Dynamic Overflow Risk Assessment that uses a Generic Algorithm to minimise the total expected impact on the receiving waters. Setpoints for pumps and gates are communicated through the existing SCADA system. The system works on radar-based flow forecast, online measurements from the sewer system and an advanced algorithm.

Two different case studies are presented. One case is regarding the city of Copenhagen, capital of Denmark, where the number of CSO events was reduced by 75% by utilisation of the existing sewer system. The other case is from Kolding, a town of about 60,000 citizens, where capital investments were reduced by 22% by implementation of RTC, which brought the City in compliance with the CSO requirements.

This paper also lends focus to a review on how advanced RTC can be approached in at step-by-step way giving important value to the city along the way.

Sewerflex is part of the product suite STAR Utility Solutions™, an intelligent software for wastewater facilities.

Keywords Overflow compliance, sewer network optimisation, Real Time Control (RTC), radar-based flow forecast, overview, Sewerflex, SewerView, PREACT, STAR Utility Solutions™, reduce CSO events.


In most old cities, rainwater is handled in combined sewer systems that are vulnerable to overflow events. A Combined Sewer Overflow (CSO) will occur when the rain intensity/volume exceeds a given threshold.

50 years ago it was not considered a problem discharging untreated sewage water to the surrounding water bodies. These days things are different, the utilities have to comply with increasing restrictions on discharge to receiving waters, e.g. the annual number of CSOs or annual discharge volume.

These new demands regarding handling of sewage water has inspired utilities to look into alternative solutions on how to handle sewage water in the most optimal way.

For most utilities there are two main reasons for looking into global, real time wastewater control.

  • A desire to optimise the utilisation of the existing wastewater system and network
  • A desire to minimise the needed expansion (capital investments) of the existing wastewater system in complying with the environmental requirements.

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