To assess the influence of the connection of a further 250,000 PE in addition to the 1.85 m PE already served by the combined WWTPs Köhlbrandhöft/Dradenau, a dynamic simulation study was started in 1996. A previous study developing the extension of the WWTP proposed several solutions with costs between €25 million and €100 million euro. Those concepts were examined by a dynamic simulation study for comparison and further optimisation.

The simulation results indicated that with an increased volume for the storage of sludge liquor it would be likely to fulfil the effluent requirements in spite of the increased load. The construction of the additional storage tank was finished at the end of 1999 together with the connection of the additional load to the WWTP. The cost of this concept was less than 1 million euro, which is significantly less than if the plants had been extended in a traditional manner.

The first two years of operation showed that the chosen solution is able to fulfil the requirements. The effluent values can be kept within the required limits. A very good correspondence between the measured and the simulated values could be observed.

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