| Agricultural non-point source pollution caused by the soil erosion posed a serious threat to the protection of water sources, and slope catchment area is crucial to make sure water sources security safety. As the ditch, pond, wetlands and other single ecological treatment technology is no absolute advantage for removal of nitrogen and phosphorus, therefore, in this paper, based on the National Science and Technology Major Project on water quality security of Hubei Han reservoir catchment basin in the middle route of the South to North Water Transfer Project----the research of multistage ditch-pond-wetland combined system for reduction of nitrogen and phosphorus load in slope drainage, a combined technology of multistage ditch-pond-wetland for purifying the pollutant in slope drainage was developed with the goal of reducing nitrogen and phosphorus discharge from slope farmland and ensuring safety of water quality of the Danjiangkou reservoir by the methods of construct of rainstorm runoff erosion effect experiments and simulating slope ditch drainage test.The main conclusions in this paper are as follows:(1) Test results showed that there is obvious first flush effect of the slope land under storm condition. Loss of particulate nitrogen, phosphorus is higher than that of the dissolved nitrogen and phosphorus. Moreover, nitrogen, phosphorus and other nutrients have enriched obviously in the soil loss.(2) Based on the first storm flush effect to determine the runoff coefficient, combined with catchment time and catchment area, this study determined the initial runoff and the reasonable capacity of ditches and ponds.(3) The test results of simulating slope ditch drainage show as follows:In the flow conditions, structure of ditches, vegetation in ditches, the flow and other factors have obvious influence on the interception and removal of pollutants. The removal rate of nitrogen and phosphorus increased as the residence time prolonged in the condition of ditches under water logging. And in the drawdown conditions and in different soil profile, ammonia nitrogen, nitrate nitrogen and phosphorus showed different change patterns.(4) The raw water of the interception and purification test was the flow state drainage from the pond under the maximum flow and test conditions. The main results are as follows:The total nitrogen and total phosphorus, ammonia nitrogen removal efficiency of the cushion pond were higher than 60% and higher than 88%, respectively. There are discrepancies in N and P removal efficiency by different vegetation ponds.Therefore, it is obvious that the rational disposition of vegetation in ecological pond can give full play to the function of all kinds of vegetation and making effective use of nitrogen and phosphorus and the maximum cut.(5) This research invented constructed wetland sewage treatment system with wind energy and negative pressure ventilation reaeration, named as replaceable phosphorus adsorbent matrix. Verification test of two years demonstrated that constructed wetlands with the design can effectively strengthen the reaeration of the system and improve the removal efficiency of nitrogen and phosphorus under different influent concentrations and different types of vegetation.(6) The preliminary research results are applied to the demonstration project of Research of multistage ditch-pond-wetland combined system technology on nitrogen and phosphorus load reductions in slope drainage According to the running results of the ecological treatment system on sloping fields flow of 157mm hypo-rainfall, the various indexes of discharged water are up to the grade III of the Environmental quality standards for surface water (GB3838-2002). With the popularization and application of this engineering technology, good social economic and environmental benefits will be got. |
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