Natural Removal Effect Of Nitrogen And Phosphorus In River And Ditch

The method of natural purification has the advantages of simple performance, low investment, less dissipation of energy and cheap operation cost, so that has a prosperous future in application in the most area of our country. In recent years there is a lot of research on water quality models of pollutant in a wide dimension river in and out of the country, and little research is studies on cleaning efficiency and removal mechanism of different dimension river and ditch in the nature.Based on experiments on the point of monitoring nitrogen and phosphorus of water body, soil and aquatic plants in the different dimension river and ditch in the nature in the Dapu town of the Yixing city, the paper analyses cleaning efficiency and affecting facts of nitrogen and phosphorus in the different dimension river and ditch, discusses the method of using natural river and ditch environmental capacity rationally, and provides experiment data for calculating nitrogen and phosphorus flux running into the lake for reference only. The main contents includes: (1) Survey on variety, density and quantity of aquatic plants and algae; (2) Comparative study on cleaning efficiency of TN, TP, NH₄⁺-N and NO_x^--N(involving NO₃^- and NO₂^-) in water body of four river and ditch; (3) Comparative study on retention effect of TN and TP in soil and aquatic plants of four river and ditch; (4) Discussion on removal mechanism and main effecting facts of nitrogen and phosphorus in different dimension river and ditch.The results show that: (1) The concentrations of NH₄⁺-N, TN and TP are decreased after input to different dimension river and ditch with rain runoff and fields drainage. It means that ditch wetland have the ability of rentention and purification of non-point source pollutants. The concentrations of NO_X^--N are in increase in small dimension ditch, such as Mao ditch, Lin ditch and Longhua river, and is decreased in wide dimension, such as Xixi river. But the concentration of NO_X^--N is never exceeded 2.0mg/L, there is no pollution potential of it in river and ditch. The decomposition of hydrophytes residua led to high concentration of NH₄⁺-N, TN and TP in winter. (2) In condition of resemble variety and density of aquatic plants, current velocity and inflow concentration, geometricdimension of river and ditch is more wide, cleaning efficiency of nitrogen and phosphorus is better. (3) The quantity of aquatic plants is key facts effecting cleaning efficiency of river and ditch. Higher density of aquatic plants is higher, higher the removal rate in the same river and ditch. (4) The current velocity is another facts relating to purification efficiency of river and ditch. Higher current velocity, lower the removal rate in the same river and ditch. (5) Cleaning function of nitrogen and phosphorus in river and ditch also relates to temperature, pH, algae, water depth, width and area of ditch wetlands and type of sludge and soil, and etc.