Study On The Reduction Effect Of COD And Nitrogen Runoff In Different Types Of Green Space

Urban stormwater runoff carrying the large amount of solid particles, nutrients, organic matter, Oils and heavy metals pollutants by rain erosion, the initial concentration of pollutants in runoff over poor V, the urban rainfall runoff to become the second largest of non-point source pollution, urban runoff pollution control and management is imperative.Green space as an important part of the urban area, it can not only beautify the environment, purify the air, but also effectively reduce the rainfall runoff, is considered to be an important measure of urban non-point source pollution.The paper selected two types of green space, study on the nitrogen and COD of sunken lawn and grassland in the runoff reduction effect by simulated rainfall experiment.In order to explore the reduction rules of urnoff pollutant of nitrogen and COD in sunken green space,The paper explores the influence of repetition period of rainfall, rainwater inlet height, vegetation type and influent pollutant concentration and other parameters on green cut pollutant runoff by the sunken green space lab experiment and artificial preparation of road runoff. The results showed that: (1)When the rain nozzle height is 4cm, the rainfall duration is 2h, and the rainfall intensity is 22-36mm/h, the reduction rate of runoff in the sunken green space was 77.40%-91.30%,the concentration reduction rates of COD, ammonia nitrogen, nitrate nitrogen and total nitrogen in the runoff were 25.95%～36.35%,18.34%～30.12%,17.98%-27.73%,9.24%-10.66%.The total reduction rates of COD, ammonia nitrogen, nitrate nitrogen and total nitrogen in the runoff were 68.92%-84.74%, 68.12%～85.31%,66.27%～81.27%,64.17%～82.33%. (2)Reduction rate of simulated road runoff pollutants by the sunken green space were decreasing with rainfall intensity and water pollutant load increased. At the same time, because the device is not large, the runoff in the green space of the residence time is short, so that the sunken green space for runoff pollutant concentration removal rate is low, so the influent pollutant load has less influence on the pollutant reduction rate.In order to explore the reduction rules of urnoff pollutant of nitrogen and COD in grassland, through artificial rainfall simulation experiments, study the nitrogen and COD output process of Tall Fescue and Bermuda grass grassland and bare land runoff, under the different rainfall intensities (30mm/h,50mm/h,65mm/h,100mm/h) and slope (0°,5°,10°). The results showed that:(1)Runoff reduction rate of Bermuda grass and tall fescue grass were 55.8%～100%,49.9%～100%,And under the same conditions, runoff reduction effect of Bermuda grass is better than tall fescue.And with the increase of rainfall intensity and slope, the runoff reduction rate of the two kinds of grassland showed a downward trend.(2)When the slope gradient is 0-10 degree, the rainfall intensity is 30～100mm/h,the reduction rates of COD, ammonia nitrogen, nitrate nitrogen and total nitrogen in the runoff by Bermuda grassland were 43.2%-100%,29.2%～100%,31.3%～100%,23.5%～100%, the reduction rates of COD, ammonia nitrogen, nitrate nitrogen and total nitrogen in the runoff by tall fescue grassland were 51.2%-100%,34.1%～100%,30.1%～100%,28.6%～100%.