The Study On Purification Of Irrigation Return Flow By Floating-beds In Ningxia Irrigation Region

As planting stuff on floating-beds, crops, such as swamp morningglory, lettuce and rice were studied about their growth in the irrigation return flow. The materials of floating-beds were plant straw and Polystyrene. The purpose was to choose kinds of plant straws which suit to produce floating-beds, and took it as the carrier that can plant three kinds of crops on irrigation return flow surface, which can form a good aquatic landscape without conventional measure such as irrigation and fertilization. As plants were grown on the surface of the water, they had well-developed root system,and roots were large enough for microbes to live. Plants and microbes had the advantages to purify the irrigation return flow which rich in N and P. And plants could also get some productions. Therefore, some mechanisms of purification were studied in this paper.This experiment was divided into two parts: one was the selection of the plant material for floating-beds; another was the effects of purification of the irrigation return flow.The selection of the plant material for floating-beds showed that: straws of rice, wheat, reed and typha angustifolia would absorb waters when they were immersed in water. Ph and DO had a tendency of drop. Straws released NH4+-N,NO3--N and some other ions to the water, so the tendency of EC raise. Compared various influences of straws to water qualities, reed had a minimum affect to the water during a short time immersed. When immersed the reed at a long time, the concentration of organic compounds and EC would drop, at the same time, DO had a tendency of rise. Reed can improve the quality of water, so it is better to choose as the material of floating-beds.The effects of purification of the irrigation return flow showed that: Plants could cultivate on floating-beds which were made by plant straw and Polystyrene. Floating-beds, especially the one made by reed, could provide enough O2 for root systems, so the root could grow steadily and the function of the root could bring into play. Compared with plants growing in floating-beds made by Polystyrene, the plant growing in floating-beds made by reed was better. Plants growing in floating-beds could reduce N in the irrigation return flow. Both floating-beds had good removal efficiency to NH4+-N, but floating-beds made by reed had a better efficiency to NO3--N than floating-beds made by Polystyrene. Rice growing on floating-beds could reduce P in the irrigation return flow very well. The removal efficiency of swamp morningglory growing in floating bed was little difference from the net effect. In experiment, cultivating rice has the best removal efficiency of nutrients, and the efficiency of cultivating lettuce was the worst. Plants can get some biological yields. During three kinds of plant,rice grew better than swamp morningglory and swamp morningglory grew better than lettuce. Ether production or quality, plants growing in floating-beds made by reed are better than they growing in floating-beds made by Polystyrene. Purification of irrigation return flow by plants growing in floating-beds is a comprehension of physical,chemical,vegetal and micro organic effects. The absorbing and used of nutrients by plants and microbes are the most important and direct aspect, pH, DO play roles by affecting the activities of plants and microbes.