Research Of Contaminated Sediments Effect On Overlying Water Quality

The research of Polluted sediment impact on the water quality is carried out in this dissertation. Comprehensive treatment and pollution prevention of sediment, resolving this ubiquitous and significant environmental issue in the world, is one of the biggest challenges in lake treatment. Most pollutants entering water system may be stored in sediment resulting in a sediment-containing contaminant layer. A variety of inorganic and organic pollutants in the sediment, under certain circumstance, will release to aquatic environment through chemical react, and physical and biological exchange with water above, which may be the major contamination source of upper water. It is very important to know the laws of release and diffusion of bottom sediment to improve the water quality. Both experimental investigation and numerical simulation are conducted to investigate diffuse of phosphorus from polluted sediment in details.A conservative and a reactive tracer (NaCl and KH2PO4) are respectively used as the contaminant in bed sediment in a laboratory flume. The release mechanism of polluted sediment is studied in detail. The experiment studies the mechanism of pollutants release from sediment in the form of two processes: the static release at the sediment-water interface, and the dynamic release of re-suspension of sediment release. The static release divides into two paths, flow water and still water which the sediment keep rest. In this paper here are three mechanisms in the pollutant release: molecular diffusion at the sediment-water interface, release from pore water release and re-suspended particles. When the sediment is static, only molecular diffusion on sediment-water interface was considered. When the sediment re-suspension occurred, the re-suspend pore water and the re-suspend particle play the most important role.The different effects of cohesive sediment and non-cohesive sediment on the pollutant releasing flux are also studied. The study performed some laboratory experiments using KH2PO4 solution as the adsorbent. The data of isothermal adsorption experiments are analyzed by isothermal adsorption equations. The analyzed results indicate that the adsorption of phosphorous by suspended sediment is in agreement with Langmuir equation. The cohesive sediment adsorbed amount is greater than non-cohesive sediment because of the surface structure of cohesive presents more micro pore. In water body with the same concentration of sediment the amount of phosphorous adsorbed by suspended sediment increases with its initial concentration in water phase. When the initial concentration rose to a certain extent, the equilibrium adsorption capacity growing more slowly, and then reaches the saturation adsorption quantity.In order to study the release of sediment better, a model for contaminant release at sediment-water interface is established in this paper. Distribution of flow field and concentration field are obtained through numerically coupling the flow and concentration fields which is in a good agreement with experimental data. The model is used to study the influences of fluid velocity on release quantity, and the relationship between the amount of release and different flow velocity are obtained.