An integrated ecological floating-bed employing plant, freshwater clam and biofilm carrier for purification of eutrophic water

Planted floating-beds can be used for treating eutrophic water in a simple and cost-effective manner, the performance of which is, however, unavoidably restricted by the growth rate and limited stand biomass of the plant. A novel approach is reported here to enhance the performance of traditional planted floating-bed by introduction of filter-feeding bivalve and biofilm carrier. The objective of the present study was to prove that the co-existence of the three key components of the ecological floating-bed is necessary for the integrated ecological floating-bed (IEFB) and for the evaluation of the influence of the water exchange period on the water purification efficacy of IEFB. The mesocosm experiments were carried out at the shore of Meiliang Bay, north part of Lake Taihu, China. The IEFB concurrently employing plant (Ipomoea aquatica), freshwater clams (Corbicula fluminea) and biofilm carrier (an artificial semi-soft assembly medium) performed better than the other two kinds of floating-beds, one of which was constructed with freshwater clams and biofilm carrier, while the other one consisted of plant and biofilm carrier. Moreover, percentage reductions of pollutants increased with extended water exchange period. With a water exchange period of 7 d, the removal efficiencies of IEFB for total nitrogen (TN), ammonium nitrogen (NH4+-N), total phosphorus (TP), total organic carbon (TOC), chlorophyll-a (Chl-a), total microcystin-LR and extracellular microcystin-LR were 52.7%, 33.7%, 54.5%, 49.2%, 80.2%, 77.4% and 68.0%, respectively.