Design supportive modelling of constructed wetlands for combined sewer overflow treatment – experiences from Europe

Constructed wetlands for combined sewer overflow treatment have proven to be highly efficient in reducing negative impacts on receiving water bodies. Due to varying loading regimes, the design and dimensioning process of these filters is strictly linked to the use of sewer system simulation tools. Until now, the surface specific annual hydraulic load is the main design criterion but an enhanced approach based on removal process evaluation could be helpful for improved design and operation. Thus, a knowledge-based, design supportive model called RSF_Sim - to be used independently or integrated into sewer system models - was developed in order to estimate long-term treatment performances.

The model RSF_Sim combines simple basic approaches with detailed descriptions. RSF functions for main parameters like COD fractions and NH4-N could be well displayed in their long-term behavior and critical single events. The number of input parameters was kept very small, and initial numbers are available from literature. Limits of application can be found due to irregular operational conditions.

Results of calibrating simulation outputs on measurement data from Germany show that simple mass and volume balances with only few input parameters can be sufficient for the given purpose. In France and Italy there are less data so far, but current research projects aim to adapt and improve existing techniques of CSO-CWs. The existing model RSF_Sim has proven to be generally applicable, but minor changes are in progress. Beyond the mentioned, more and more countries (like USA or UK) started to develop their own CSO-CWs approaches, and the given model could be supportive.

The original German RSF_Sim is a personal property of the main authors. Tob are willing to share their experience for scientific purposes or commercial applications.