4　Artificial Media

Recently,researchers in china have been improving the ecological floating bed to achieve better removal effect,mainly by adding microbial biofilm,filler,etc,to the floating bed system and forming a compound ecological floating bed where artificial media,plants and microorganism coordinate.The experimental research about the combined ecological floating bed composed of aquatic plants(lower),aquatic animals(middle)and artificial media(upper),and invented by Li and Song et al.(2007),clearly show that the artificial media is the main subject for removing nitrogen and phosphorus.FCEFB(framebent compound ecological floating bed)of Fan and Chou et al.(2011),developed by using symbiosismechanism,where zeolite is hung on the framework and submerged and plants are grown in the planting apparatus,optimizes the ecological floating bed system and obviously has better denitrification effect than the ordinary system.

Generally,artificial media adopt inorganic materials,porous and highly adsorptive,which can absorb some particulate pollutants and gather efficiently indigenous microorganism in the sewage.Additionally,porous media have the characteristic of huge surface area which can provide attachment points for microbial growth,which is beneficial for the biodegradation of contaminants,especially macromolecular hard-degraded organics.

The studies about constructed wetlands show that mature plants can gradually supply adequate carbon source for denitrification,which can increase the removal ratio of nitrogen.Whereas,phosphorus removal ability descends with the decline in the absorption capacity of the soil matrix(2009;1996),the absorption plays a remarkable role in the wetlands when removing phosphorus.However,in the ecological floating bed system,developed roots can extend to deep underwater where,owing to these roots,contaminants absorbed by the artificial media are mostly degraded,then the released pore is available to maintain the removal effect.If allowed,in order to achieve better purifying effects,managers need to regularly regenerate the artificial media.It is also crucial to select artificial media according to pollutant characteristics.