Combined sewer systems are designed to transport stormwater surface run off in addition to the dry weather flows up to defined limits. In most European countries, hydraulic loads greater than the design flow are discharged directly into receiving water bodies, with minimal treatment (screening, sedimentation), or with no treatment at all. One feasible solution to prevent receiving waters from strong negative impacts seems to be the application of vertical flow constructed wetlands. In Germany, first attempts to use this ecological technology were recognized in early 1990s. Since then, further development continued until a high level of treatment performance was reached. During recent years the national “state-of-the-art” (defined in 2005) was adapted in other European countries, including France and Italy. Against the background of differing national requirements in combined sewer system design, substantial developmental steps were taken. The use of coarser filter media in combination with alternating loadings of separated filter beds allows direct feedings with untreated combined runoff. Permanent water storage in deep layers of the wetland improves the system’s robustness against extended dry periods, but contains operational risks. Besides similar functions (but different designs and layouts), correct dimensioning of all approaches suffers from uncertainties in long-term rainfall predictions as well as inside sewer system simulation？tools.
References
[1]
EC (European Commission). Water Framework Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 Establishing a Framework for Community Action in the Field of water Policy; Official Journal of the European Community: Brussels, Belgium, 2000.
[2]
Bratieres, K.; Fletcher, T.D.; Deletic, A.; Zinger, Y. Nutrient and sediment removal by stormwater biofilters: A large-scale design optimisation study. Water Res. 2008, 42, 3930–3940, doi:10.1016/j.watres.2008.06.009.
[3]
Welker, A. Occurrence and fate of organic pollutants in combined sewer systems and possible impacts on receiving waters. Water Sci. Technol. 2007, 56, 141–148.
[4]
Brunner, P.G. Regenwasserbehandlung in Bodenfilterbecken (in German). Wasserwirtschaft 1995, 85, 134–138.
[5]
Frechen, F.-B.; Schier, W.; Felmeden, J. The Plant-covered retention soil filter (RSF): The mechanical and biological combined sewer overflow (CSO) treatment. Eng. Life Sci. 2006, 6, 74–79, doi:10.1002/elsc.200620109.
[6]
Meyer, D.; Dittmer, U.; Schmitt, T.G. Modelling CWs for CSO treatment—Reasonable balancing between detailed description and practicable handling. In Proceedings of 11th International Conference on Wetland Systems for Water Pollution Control, Indore, India, 1–7 November 2008.
[7]
DWA (Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall). Empfehlungen für Planung, Konstruktion und Betrieb von Retentionsbodenfilteranlagen zur weitergehenden Regenwasserbehandlung im Misch- und Trennverfahren (in German); Merkblatt M 178; DWA: Hennef, Germany, 2005.
[8]
Uhl, M.; Dittmer, U. Constructed wetlands for CSO treatment—An overview of practice and research in Germany. Water Sci. Technol. 2005, 51, 23–30.
[9]
Geiger, W.F. Combined sewer overflow treatment—Knowledge or speculation. Water Sci. Technol. 1998, 38, 1–8.
[10]
Dittmer, U.; Schmitt, T.G. Purification processes in biofilter systems for CSO treatment. In Proceedings of 12th International Conference on Urban Drainage, Porto Alegre, Brazil, 11–15 September 2011.
[11]
Green, M.B.; Martin, J.R.; Griffin, P. Treatment of combined sewer overflows at small wastewater treatment works by constructed reed beds. Water Sci. Technol. 1999, 40, 357–364.
[12]
Gamerith, V.; Bertrand-Krajewski, J.-L.; Mourad, M.; Rauch, W. Implications of long-term stormwater quality modelling for design of combined sewer infrastructure. Urban Water J. 2011, 8, 155–166, doi:10.1080/1573062X.2011.581295.
[13]
Dotto, C.B.S.; Mannina, G.; Kleidorfer, M.; Vezzaro, L.; Henrichs, M.; McCarthy, D.T.; Freni, G.; Rauch, W.; Deletic, A. Comparison of different uncertainty techniques in urban stormwater quantity and quality modelling. Water Res. 2012, 46, 2545–2558, doi:10.1016/j.watres.2012.02.009.
[14]
Illgen, M.; Harting, K.; Schmitt, T.G.; Welker, A. Runoff and infiltration characteristics of pavement structures—Review of an extensive monitoring program. Water Sci. Technol. 2007, 56, 133–140.
[15]
Langergraber, G.; ？imunek, J. Reactive transport modeling of subsurface flow constructed wetlands. Vadose Zone J. 2012, 11, doi:10.2136/vzj2011.0104.
[16]
Dittmer, U.; Meyer, D.; Langergraber, G. Simulation of a subsurface vertical flow constructed wetland for CSO treatment. Water Sci. Technol. 2005, 51, 225–232.
[17]
Henrichs, M.; Langergraber, G.; Uhl, M. Modelling of organic matter degradation in constructed wetlands for treatment of combined sewer overflow. Sci. Total Environ. 2007, 380, 196–209, doi:10.1016/j.scitotenv.2006.11.044.
[18]
Henrichs, M.; Welker, A.; Uhl, M. Modelling of biofilters for ammonium reduction in combined sewer overflow. Water Sci. Technol. 2009, 60, 825–831, doi:10.2166/wst.2009.397.
[19]
Langergraber, G.; Giraldi, D.; Mena, J.; Meyer, D.; Pe？a, M.; Toscano, A.; Brovelli, A.; Korkusuz, E.A. Recent developments in numerical modelling of subsurface flow constructed wetlands. Sci. Total Environ. 2009, 407, 3931–3943, doi:10.1016/j.scitotenv.2008.07.057.
[20]
Molle, P.; Liénard, A.; Boutin, C.; Merlin, G.; Iwema, A. How to treat raw sewage with constructed wetlands: An overview of the French systems. Water Sci. Technol. 2005, 51, 11–21.
[21]
Fournel, J.; Millot, Y.; Grasmick, A.; Molle, P. Treatment performances of vertical flow constructed wetland treating urban runoff: Design comparison. In Proceedings of 13th International Conference on Wetland Systems for Water Pollution Control, Perth, Australia, 25–29 November 2012.
[22]
Balbo, A.; Bresciani, R.; Conte, G.; Zanieri, L.; Masi, F. Feasibility of CWs to provide treatment to CSO in the Lombardy Region, Italy. In Proceedings of 12th International Conference on Wetland Systems for Water Pollution Control, Venice, Italy, 4 October 2010.
[23]
Born, W. Enhanced stormwater treatment by a constructed wetland within a retention basin. In Proceedings of 8th International Conference on Urban Drainage, Sydney, Australia, 30 August–3 September 1999.
[24]
Wo？niak, R.; Dittmer, U.; Welker, A. Interaction of oxygen concentration and retention of pollutants in vertical flow constructed wetlands for CSO treatment. Water Sci. Technol. 2007, 56, 31–38.
