Which plants are needed for a French vertical-flow constructed wetland under a tropical climate?

Plants are essential in the functioning of constructed wetlands. When setting up systems in tropical areas, Phragmites australis is not always a good choice because of its invasiveness. In vertical-flow constructed wetlands (VFCWs) fed with raw wastewater, the main role of plants is their mechanical action, which helps prevent clogging of the deposited organic matter. Various species have already been used in some tropical climate studies, but generally not for such systems, and no attempt has been made to screen large numbers of alternative species. Here we describe a method to select species among a hundred studied, along with promising plants tested in batches, and at full scale. Species of the order Zingiberales showed good adaptation to the main stresses generated by VFCWs. They have long vegetative cycles, which may require weed growth control after plantation, but low harvesting frequency. Root systems with long rhizomes such as Heliconia psittacorum should take priority to ensure even growth and avoid clumps. To limit the phytosanitary risk with Musaceæ (banana tree), Canna indica or Canna glauca are preferable. Species of the genus Cyperus also demonstrate good adaptation, and could be of interest, especially when a high stem density is required (e.g. planted sludge drying beds).