Study On Factors Affecting Sediment Flocculation And Phosphorus Adsorption And Release Characteristics

Sedimentation and water environment problems have been widely concerned.For the reservoir area,the water flow rate is low.A large amount of sediment is deposited after entering the reservoir area due to changes in water conditions,and these sediments will adsorb nutrient salts in the water body during the continuous deposition process,causing the sediment of each reservoir to become a storage pool of nitrogen and phosphorus,so that the water source pollution increases.These changes will not only affect the navigation of the lake and the water transfer and flood control capacity of the reservoir,but also have a negative impact on the water quality of the lake and the ecological environment of the waters.In order to study the influencing factors of sediment flocculation and the adsorption/release characteristics of phosphorus and other pollutants,the sediment samples of the typical curved section?Zhongxian section?of the Three Gorges reservoir area were taken,the flocculation characteristics and the adsorption/release of phosphorus in the Three Gorges reservoir area under various factors were studied by laboratory experiments.The following conclusions were drawn:?1?The shear rate value has a great influence on the particle size distribution of the sediment flocs.As the shear rate increases(35.5s^-1255.8s^-1),the particle size distribution curve shifts to the left,and the large particle size fraction significantly reduced,the small particle sediment volume fraction gradually increased.When the shear rate G value is high,the curve is obviously widened,the peak value is decreased,and the fine particles are increased greatly,which indicates that the sediment particles are obviously dispersed.The high turbulent shear rate reduces the content of large particle sediment flocs and increases the distribution of fine particle sediment.?2?The flocage grades of the particles under different sediment concentrations are significantly different after flocculation equilibrium.With the increase of sediment concentration,the collision efficiency of sediment particles can be increased,the particle size distribution range is reduced,the proportion of large particle flocs increases,and the degree of sediment flocculation increases.The particle size also has a great influence on flocculation.The flocculation of the particles was studied by the change of the flocculation degree F_n with the characteristic particle size d_n,it is found that as the particle size increases,the flocculation degree of the sediment particles decreases continuously,that is,the smaller the particle size of the sediment particles,the better the flocculation effect of the sediment particles.The flocculation degree F_n has a significant correlation with the characteristic particle size d_n,with the increase of the characteristic particle size dn,the flocculation degree F_n decreases exponentially.The results of flocculation experiments show that with the increase of organic matter concentration,the proportion of fine particles is significantly reduced,while the proportion of large particles is increased.It is indicated that organic matter can promote the bridging effect between particles.As the content of organic matter increases,the flocculation effect between particles increases.?3?The adsorption and release of phosphorus by sediment is obviously fast and slow.The higher the sediment concentration,the greater the total adsorption of phosphorus on the sediment,Moreover,with the increase of sediment concentration,the adsorption tends to reach equilibrium earlier,but the phosphorus adsorption amount per unit sediment decreases with the increase of sediment concentration,that is,there is“solid concentration effect”.In addition,the higher the sediment concentration,the higher the total release of phosphorus,but as the sediment concentration increases,the phosphorus release per unit sediment decreases,It is believed that at low sediment concentration,the unit sediment has a larger adsorption capacity and stronger adsorption performance to hinder the release of phosphorus carried by itself.There is a significant positive correlation between the equilibrium adsorption amount and the disturbance intensity.As the disturbance increases,the sediment adsorption/release capacity becomes stronger,and the equilibrium adsorption/release amount and the maximum adsorption/release capacity increase.The presence of organic matter can affect the surface morphology and microporous properties of the sediment particles,thereby affecting the amount of phosphorus adsorbed by the unit sediment particles.The higher the organic matter content,the higher the unit sediment adsorption capacity,and the longer the adsorption time,the more obvious the difference,but it was found in the release experiment and the phosphorus release amount decreased with the increase of organic matter content.Whether it is the Pseudo-first-order,Pseudo-second-order,Elovich model used to simulate the dynamic process,or the Langmuir,Freundlich,Tempkin models used to simulate the isothermal adsorption process,they all can better model the process of adsorption/desorption of phosphorus by sediment particles,and estimate the maximum adsorption capacity and equilibrium adsorption capacity of sediment particles.However,there is a difference between the judgments of the reaction trends and the end point estimates between the models.