Floating Treatment Wetlands: an Innovative Option for Stormwater Quality Applications

Floating Treatment Wetlands (FTWs) are an innovative variant of the more traditional constructed wetland and pond technologies that offer great potential for treatment of urban stormwaters. FTWs employ rooted, emergent macrophytes (similar to those used in surface and subsurface flow wetlands) growing on a mat floating on the surface of the water rather than rooted in the sediments. Thus, they can tolerate the wide water depth fluctuations typical in stormwater systems, without the risk of the plants becoming inundated and stressed. In many aspects, FTWs are a hybrid between a pond and a wetland; they behave hydraulically similar to a stormwater detention pond, whilst imparting similar treatment processes to that of a wetland. The plant roots hang beneath the floating mat and provide a large surface area for biofilm growth which forms an important part of the treatment reactor. This paper provides a review of the FTW concept, structure and function, and discusses some of the potential advantages of this emerging technology for stormwater applications. T. R. Headley*, C.C. Tanner** * Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, D-04318 Leipzig, Germany (E-mail: [email protected]) ** National Institute of Water and Atmospheric Research (NIWA), PO Box 11-115, Hamilton, New