Study On Migration Law Of Pollutants In Wetland Sediment And Its Influencing Factors

With the development of economy,a large amount of sewage and wastewater are discharged into natural water,and pollutants are partially deposited in the sediment after entering the water body.Under certain conditions,the pollutants deposited in the sediment under the influence of environmental factors and hydrodynamic factors,re-enter the water body causing secondary pollution of the water body.Nowadays,sediment pollution has become one among the key issues in water environment.Most of research on sediment in China is concentrated in Huaihe River,Taihu Lake and other rivers and lakes,while less research has been done on peaty sediment in the north.Due to the different geographical locations of different sediment and the different depositional environments,the results of the same research method are different when the same research method is chosen to investigate different sediment.Therefore,this paper takes Longfeng wetland sediment in Daqing City as the research object to investigate the migration law of pollutants in sediment under static and hydrodynamic conditions and their influencing factors,to provide scientific basis and reference for endogenous prevention and control in Longfeng wetland.In this paper,based on the detection of the physicochemical properties and pollution contents of the sediment,overlying water,interstitial water of wetland,correlation analysis of different pollutant contents in the wetland was conducted;Through static simulation experiments,the static migration patterns of pollutants in sterilized and unsterilized sediment in natural state and the influence of environmental factors on pollutant migration were investigated.The regression model was constructed based on the response surface method to predict the most unfavorable and optimal migration conditions of sediment;The migration law of sediment pollutants under different soil-water ratio,disturbance intensity and resuspension-settlement conditions was investigated by shaking bed and force multiplier.The main research results are as follows:The contents of various indicators of the overlying water in the Longfeng wetland all exceed the level V of the Surface Water Environmental Quality Standard.The concentration difference between the overlying water and the interstitial water is about 2 times,and the pollutants are prone to diffusion behavior.The comprehensive pollution index of the sediment is evaluated as moderate and heavy pollution level.The organic pollution index is evaluated as still clean and organic nitrogen pollution level.The correlation of each pollutant content among overlying water,interstitial water and sediment was high,and there was frequent material exchange between interstitial water and overlying water.In addition,the pollutant content in the water body was influenced by the pollutant content in the substrate to a certain extent.The concentration of NH₃-N,SRP,and COD in the unsterilized sediment in the water phase increased firstly,then decreased with the increase of time,and finally stabilized.The concentrations of NH₃-N,SRP and COD in the water phase of the sterilized sediment were stable on the 14th,10th,and 12th days,and their stable values were 0.63mg/L,0.42mg/L,114.56mg/L.The migration amounts and rates of NH₃-N,SRP and COD increased with the increase of temperature and decreased with the increase of dissolved oxygen concentration.Based on the response surface method optimization,the optimal migration condition temperature of NH₃-N,SRP,COD is 7.68℃,the dissolved oxygen is 6mg/L,and the coefficient is 0.983.At this time,the pollutant migration is the minimum value.The most unfavorable migration condition temperature is 20℃,dissolved oxygen is 2mg/L,and the acceptable coefficient is 0.985.At this time,the migration amount of pollutants takes the maximum value.Under hydrodynamic conditions,the smaller the soil to water ratio,the more pollutants are migrated per unit mass of sediment.When the soil-water ratio is 1:10 and 150r/min rpm,the migration amount of organic matter needs 6h to reach saturation.The greater the rotation speed,the greater the resuspension concentration of sediment.When disturbed for 10 minutes,at the sediment-water interface,the concentration of suspended matter in water body of180r/min is 1.22 times that of water body of 60r/min,and the migration of pollutants to the water body is accelerated.In the process of resuspension-sedimentation of the sediment,the particle pollutants occur adsorption bridging and agglomeration,resulting in faster settling of large particles,but the high stability of small particles continues to stay in the overlying water,so that the water body to restore clarification time is extended.