Research On The Desorption Laws Of Pollutants To Bottom Sediment In Channel Dredging

The three gorges dam in Yangtze river is a cross-century and extra-large sized hydro-power project, and it has also brought remarkable benefits in flood control, power generation as well as navigation since its establishment. But the eco-system and environmental-system in the three gorges reservoir area has suffered great change after it became a reservoir. On one hand, it is due to the eutrophication in some branches caused by the decrease of velocity of flow. On the other hand, over99%of the sediment are deposited in the regular backwater reachof the reservoir. And most of sediment are deposited in the form of a point. Over70%of the sediment are deposited in25%of the reaches, and large amount of sediment has imposed severe impacts on the construction of high-grade waterway in the backwater area. Besides, it’s quite likely to cause secondary pollution during the channel dredging, which is also an environmental problem that can’t be ignored.On the basis of previous research, bottom sediment in three gorges reservoir area was taken as the object of the paper. And the impacts of the grain size, concentration, temperature and disturbance of the sediment on the desorption of ammonia-nitrogen and COD were further studied in the paper as follows:①Summarizes the basic principle of desorption sediment contaminants, andsediment characteristics and environmental factors on pollutant desorption, in-depth study of the status quo of pollutants in sediment desorption model, provides a theoretical basis for the test.②How the desorption amount varying as the grain size and concentration of the sediment changes was revealed on the basis of desorption experiments of ammonia-nitrogen and COD. Under the condition of the same grain size and different concentrations, the desorption amount had decreased as the concentration increased. The desorption rate had also increased, and the desorption equilibrium had been reached in shorter time as well. While under the condition of the same concentration and different grain sizes, the desorption amount had decreased as the grain size increased.③The desorption process of ammonia-nitrogen and COD can be well fitted by the langmuir model. And it was fitted better with higher concentration of the sediment. Meanwhile, the value of k had generally increased as the concentration increased. Also the time for the desorption equilibrium was shorter.④The temperature experiment showed that the amount of ammonia-nitrogen and COD had increased as the temperature increased. And the desorption rate was even faster so that the desorption equilibrium can be reached in an even shorter time.⑤The disturbance experiment showed that with faster rotating speed, ammonia-nitrogen and COD in the floating flow had increased, the amount of desorption had also increased. But the desorption rate had decreased and it had taken longer for the desorption to reach equilibrium. While with same rotating speed, the concentration of the sediment had increased as the flow got deeper. And when it reached the liquid equilibrium, the concentrations of ammonia-nitrogen and COD had increased. The amount of the desorption had decreased and thus it was easier to reach desorption equilibrium.