Adsorption And Desorption Characteristics Research Of Suspended Sediment To Ammonia Nitrogen In Lanzhou Section Of The Yellow River

Suspended sediment distribute very widely in the Yellow River, they have a hugespecific surface area because of the small particles, and a large number of active substancesare attached in the gap because of the uneven surface, thereby, which show strong adsorptionfor much pollutants entering the river, and become the carrier of pollutant migration andtransformation, they are the important part of the Yellow River self purification. In view ofthis, for rational developing and protecting of the existing water resources and waterenvironment in Lanzhou section, and providing the basis for water environment to assess andimprove the quality of the water environment for the Lanzhou section of the Yellow River, ithas extremely important practical significance to launch the research on sediment adsorptionof pollutants. At the same time, the Yellow River is an important source of water supply forLanzhou city, the study that suspended sediment adsorb and desorb pollutants has a certaininfluence and role for city water purification process. This paper summarizes on the basis ofthe results of much experience, suspended sediment of Lanzhou section of the Yellow Riverare used as test sand, and the water of the Yellow River as the test water, ammonia nitrogen isselected as the representative pollutants which pollutes serious in Lanzhou section, by usingthe test method for kinetics and isothermal equilibrium, mechanism of sediment adsorption onammonia nitrogen were studied, and sediment concentration, particle size, initialconcentration of ammonia nitrogen and sediment turbulence and other factors were analyzed,and conduct preliminary study on the saturated sediment desorption by similar methods. Themain contents and results of this study mainly includes:(1) Access to relevant data of water quality, the paper analyzes the water pollution statusand pollution index of Lanzhou section of the Yellow River, and determines the test programwith ammonia as the research object; sorts out and analyzes the physicochemicalcharacteristics, the particle size distribution, mineral composition and chemical compositionof the suspended sediment; points out the difference on suspended sediment between thissection and other section in the Yellow River; determines three sediment that median particlesize are15.721μm,43.660μm and67.188μm as the test sand, and associated method forpreparing the pretreatment.(2) According to related theories of sediment adsorption of pollutants, the paper analyzesthe interaction between sediment and water of the Yellow River, points out the reasons forsediment suspension has a strong adsorption degradation of pollutants, emphasizes thesignificance of suspended sediment adsorption and desorption for pollutants; introducessome related content of common water quality model such as Langmuir and Freundlichisotherm model, Quasi-one and Quasi-two kinetic models, and their characteristics and datafitting method.(3) By designing a dynamic test of sediment adsorption to ammonia with the sediment concentration and the initial concentration of ammonia as variables, the Quasi-one andQuasi-two model of sediment adsorb ammonia was established to investigate the mechanismof sediment effects on adsorption rate, adsorption equilibrium time and the amount ofammonia adsorption. Results show that: under certain conditions, the equilibrium adsorptioncapacity to per unit mass of silt on ammonia nitrogen with sediment concentration andparticle size was negatively correlated, and positively correlated with the initial concentrationof ammonia; the process of sediment adsorbs ammonia in2-4h to reach equilibrium,adsorption rate slows with increasing sediment concentration, and accelerates with increasingthe ammonia concentration; Quasi two model can better describe on the adsorption behaviorof sediment under two conditions; the sediment maximum adsorption capacity of ammoniapositive correlation with two variables, the characteristics has important significance to waterself-purification on ammonia and water environmental capacity of the river.(4) It investigated the impact on initial concentration of ammonia and sedimentconcentration to the ammonia adsorption capacity and adsorption isotherms for the unit massof sediment in isothermal equilibrium adsorption experiment. The results show that: theequilibrium adsorption capacity to per unit mass of silt on ammonia nitrogen positivelycorrelated with the initial concentration of ammonia and negatively correlated with sedimentconcentration; the initial concentration of ammonia can affects the distribution of ammonia inwater and sediment surface and the adsorption capacity of the sediment; Langmuir andFreundlich isothermal model are similar on the fit and have a higher correlation coefficient;reducing sediment particle size can effectively change the adsorption capacity to ammoniaand can promote the degree of spontaneous reaction.(5) Sediment adsorbs ammonia is not only affected by sediment concentration and initialconcentration of ammonia, but also restricted in many external conditions. The test doescorrelation analysis for sediment grain size and the degree of turbulence and sediment, thefollowing conclusions: the particle size have a significant impact on ammonia adsorption perunit mass of sediment, which shows a significant negative correlation trends with ammoniaadsorption capacity, meanwhile explains that the vast majority of suspended sediment ofLanzhou section of the Yellow River was strongly adsorbed component; The degree ofturbulence of sediment influenced by the oscillation speed, when the oscillation speed in thevicinity of200r/min, sediment turbulence will not precipitate by slow, also won’t collisionrelease by rapid, At this point of there is a peak for sediment balance adsorb ammonia.(6) Sediment desorption tests found: sediment desorption laws is similar to adsorption,desorption process make up by the physical and chemical desorption, mostly of ammonia thatadsorbed on the surface of sediment are chemical adsorption type, while mostly of ammoniathat desorbed are physical adsorption type; ammonia desorption rate of sediment increaseswith the sediment concentration increases, ammonia desorption amount of same particle sizesediment is negative correlation with sediment concentration, ammonia desorption amount ofthe same sediment concentration are negative correlation with sediment particle size; the proportion of desorption expressed as coarse sand>middle sand>fine sand, and positivecorrelation with sediment concentration; equilibrium desorption of ammonia nitrogen ispositively correlated with the initial concentration of ammonia, and negatively correlate withparticle size and sediment concentration.