Abstract: To seek for new floating bed plants which can efficiently purify eutrophic water, three kinds of terrestrial plant with medicinal value and greening effect, Rumex acetosa, Ophiopogon bodinieri and Ophiopogon japonicus were selected as the floating-bed plants for outdoor experiments. The self-designed ecological floating-bed was used as the plants carrier. The eutrophic waste water which consisted of lake water and a certain amount of nutrients was put under treatment for 40 d. The growth of the plants and the purification effect were compared . The results show that all three plants can survive, and that Rumex acetosa grows faster and its biomass increases more, but its growth period is short, while Ophiopogon bodinieri and Ophiopogon japonicus are the evergreen plants. At the end of the experiment, the removal rate of total phosphorus by Rumex acetosa is 90%, while that of the other two plants is about 40%. The purification rate of ammonia nitrogen by Rumex acetosa is higher than that of Ophiopogon bodinieri and Ophiopogon japonicus. As time goes by, the ammonia nitrogen removal rate by the three plants can reach about 90%; the removal rate of total organic carbon by Rumex acetosa is 80%, while the removal rate by Ophiopogon bodinieri and Ophiopogon japonicus is 60%~70%. It has been shown in this paper that Rumex acetosa, Ophiopogon bodinieri and Ophiopogon japonicas can be used as floating bed plants, and that they can be selected according to different ecological conditions and the degree of water pollution. This has important practical significance for the development of new varieties of floating bed plants.

Key words: ecological floating bed, plant selection, eutrophication, water pollution；waste water treatment