Efficiency And Mechanism Of Uptaking And Removing Nitrogen From Eutrophicated Water Using Aquatic Macrophytes

Due to rapid industrial development and growth of population, water resources are becoming scarce, and water contamination is appearing to be a serious problem. One of main water pollution is eutrophication. Eutrophication is mainly induced by too much nutrients load to water ecosystem, which makes algae proliferation that can produce toxic matter such as microcystin. Water eutrophication is harmful to people health. The key issue is how to rehabilitate polluted groundwater (including river, lake and reservoirs) in an economic and effective way.Our research focused on the use of plants such as macrophytes that can absorb nitrogen, to assess their ability to purify nitrogen polluted water in microcosms. The main purpose was to understand abilities of different macrophytes species to rehabilitate eutrophicated water. Our main research work and conclusions were as follows:1. By phsico-biological engineering, we compared five macorophytes species (Eichhornia crassipes, Jussiaen repens, Alternanthera philoxeroides, Hydrocharis dubia and Trapa quadrispinosa) to test their nitrogen removal capacities. In microscoms containing polluted water (2 m deep) with total N concentration of 2.0 mg L^-1, nitrogen-to-phosphrous ratio 2-5:1, five macrophytes speices can decrease total N by 60-70% in 80 days, mainly by removing nitrate nitrogen in water. The total nitrogen removal capacity ratio was: Jussiaen repens 72% > Eichhornia crassipes 63% > Trapa quadrispinosa 52% > Alternanthera philoxeroides 44%. Jussiaen repens had the best effect on removing nitrogen and Eichhornia crassipes had the largest capacity on improving water transparency. In this experiment it was documented that macrophyte can efficient at decreasing total N in water, but are less efficient at decreasing phosphorus and CODMn. We concluded that Jussiaen repens and Eichhornia crassipes were the effective species on purifying nitrogen polluted water at low to moderate levels.2. We used Eichhornia crassipes to rehabilitate low nitrogen-polluted microcosms in summer. Our results showed that the plant system had good effect on rehabilitating polluted water. In the first 15 days of growth, Eichhornia crassipes absorbed nitrogen from water quickly, the cover area length from 10.0 m increased to 46.7 m; and at 44...