Experimental Study On The Adsorption And Biodegradation Of Pollutants In Water Body With Suspended Sediment

As we known, the suspended sediment is distributed widely in natural rivers. Its size is very small and has a huge specific surface area. There are also some active materials on the surface of sediment. Some physical activities, chemical activities and biological ones will take place between the surface of sediment and the pollutants discharged into the water body. So, the sediment is an important media for the transference and transform of pollutants. The pollutants move along with the sediment and have some effects on the zoological environment. These effects are called as environmental effects of sediment. In this paper, after reviewing the previous research works, the author points out that it is important to carry out research works on the adsorption and biodegradation of pollutants in water body with suspended sediment. Then several groups of experiments are designed to carry through a systematic experimental study on the adsorption and biodegradation characteristics of pollutants in water body with sediment. In these experiments, two groups of suspended sediment with different dimension in diameter are used, and a typical nutriment—phosphorus and domestic sewage which includes many kinds of organic pollutants are chosen as the experimental simulated pollutants. This research is magnificent for theoretical analysis and practical application for water quality evaluation and water environment planning of water body with sediment. The main contents of this study and conclusions are as follows: (1) Using filtered natural river water from Yangtze River as experiment water, some experiments are designed to study the adsorption kinetics of phosphorous. The results show that the amount of phosphorous is in dynamic equilibrium in water phase and sediment phase. They reach equilibrium in 10 hours. With the same initial concentration of phosphorous in water phase, the equilibrium time increases with the concentration of sediment. But it has not an obvious law under the condition of different initial concentration of phosphorous in water phase. (2) The isothermal adsorption of phosphorous by suspended sediment is studied by some isothermal adsorption experiments. Some conclusions are drawn: 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. But the value induces in reverse increment increases lightly when the initial concentration of phosphorous reaches up to a certain value. With the same condition of the initial phosphorous concentration, its adsorption amount decreases with the concentration of sediment. This phenomenon also appears in heavy metals adsorption experiments and is named by "sediment adsorption effect". The results also show that the adsorption content increase with the concentration of sediment. This property will contribute to the self-purification and environment capacity. (3) 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 and Freundlich equation. Additionally, the concentration of sediment has insignificant effect on the parameters of isothermal adsorption equation. But the smaller is the sediment size, the more is the extreme adsorption amount of phosphorous. (4) By summarizing present experimental research methods of biodegradation, the author points out that the BOD degradation method and CO2 adsorption method in which the biodegradation process is reflected by the consumption process of dissolved oxygen can exhibit a more actual biodegradation process of pollutants. They are all suitable to the study on the biodegradation of pollutants in water body with sediment. (5) Using diluted domestic sewage as simulated pollutant and adopting BOD degradation method, an experimental study on the biodegradation of lowconcentration pollutant in water body with sediment is carried out. The experimental data are analyzed by one-order and two-order kinetics of DO which is based on the reaction kinetics of organic pollutants. The experiment results indicate that the biodegradation process of organic pollutants can be expressed by one-order reaction kinetics. It also can be seen that the existence of sediment accelerates the biodegradation of organic pollutants. The biodegradation rate of low concentration pollutants in water body with sediment is faster than that without sediment and with the same initial concentration of pollutant. The value of biodegradation rate increases with the sediment concentrations. There is a non-linear function relationship between the biodegradation rate constants due to the influence of sediment and the sediment concentrations. Additionally, the sediment size has little effect on the biodegradation of low concentration pollutants. Moreover, the varying process of DO in clean water with sediment shows that the DO adsorbed by sediment is ignorable. (6) At last, the biodegradation process of high concentration pollution in water body with sediment is investigated preliminarily by experiments. This work is likely to give some primary advices for the renovation of severe organic polluted water body. In these experiments, domestic sewage without dilution is used as simulated pollutant and CO2 adsorption method is adopted. Some primary conclusions are drawn: the turbulence condition has great influence on the biodegradation of high concentration organic pollutants. Its biodegradation rate in continuous stirred water body is higher than that in water body without stirring. The trend of biodegradation in water body with high concentration organic pollutants and sediment is the same as that in water body without sediment. But the sediment speeds up the biodegradation of high concentration organic pollutants. In addition, the sediment size influences slightly on the biodegradation of high concentration organic pollutants. (7)At last, some discussions about water quality models in water body with sediment are carried out based on the above research results.