Floating islands or floating treatment wetlands (FTWs) are a technology that was commercialized by a Montana company in 2005. FTWs utilize microbes (biofilm) and to a lesser extent, plants, to improve water quality, provide wildlife and fish habitat, and offer beautification. Over 5200 FTWs have been installed worldwide.
Contaminants such as nitrate, ammonia, phosphorus, TSS, BOD and metals have been removed from wastewater, lakes and ponds. Nitrate removal rates in wastewater lagoons were substantially improved to "control" lagoons without FTWs. I have served as a technical consultant to Floating Island International since 2009.
Floating island at a city park in China
Wastewater lagoon treatment in New Zealand
Wastewater treatment in Montana
Here are two papers by Apex Engineering on nitrate removal using FTWs: