| In recent years,rapid development of township and village industries,urban and rural populations continue to gather,making the water environment and aquatic ecosystems have been a certain degree of damage,the amount of sewage production also continue to increase.The serious water pollution is one of the difficult problems in our country to realize the sustainable development and utilization of water resources.Therefore,in order to protect water resources and promote sustainable economic development,how to effectively control wastewater pollution has become the key problem to be solved.At present,China's various methods for the treatment of water pollution in an endless stream.Such as widely used artificial wetland system processing technology,has a very broad application prospects,although the technology has received a large number of test data and empirical parameters,the technology still exists many problems in the actual engineering project,such as covering Large area,easily affected by the hydraulic load and water distribution methods,producing clogging and saturation,etc.Therefore,this research is aimed at the main problems existing in constructed wetlands,utilizing the combination of aeration engineering and artificial wetlands,proposing artificial aeration ecological purification system.Based on the research materials and experimental results in domestic and overseas.This research simulating the artificial ecological micropore aeration project in Yizhuang River of Jiaxing Shijiuyang ecological wetland demonstration project by numerical simulation method based on computational fluid dynamics(CFD),analyzing and coupling the turbulence model of liquid-solid two-phase mixture and activated sludge model 2,establishing a turbulence kinetic model of liquid-solid two-phase in the aeration channel.By modeling for each pollutant,achieving the simulation of water quality concentration distribution in the river,verifying the accuracy of the model based on the actual measurement data,discussing the evolution of the velocity field around the aerator and its multiphase flow Aeration process,considering the influence of dissolved oxygen concentration to the system combined with the velocity vector figure,the gas volume fraction distribution cloud figure and so on,providing the theory basis and technical support for further optimization direction and the best craft parameter to the system.The following main achievements have been obtained:(1)Aiming at the main problems existing in the constructed wetlands,utilizing the artificial ecological micropore aeration project in Yizhuang River of Jiaxing Shijiuyang ecological wetland demonstration project,proposing artificial aeration ecological purification system,analyzing its structure,purification mechanism and hydraulic characteristics.(2)The brief introduction of the installation background of the project is made,and the aeration model of this project is simplified to a certain extent.(3)By analyzing and coupling the turbulence model of liquid-solid two-phase mixture and activated sludge model 2,establishing a turbulence kinetic model of liquid-solid two-phase in the aeration channel,obtaining the common points of each source term in Fluent,modeling for each pollutant,achieving the simulation of water quality concentration distribution in the river,verifying the accuracy of the model based on the actual measurement data.Although the simulated and measured results have some deviations in comparison,the simulation results of this model can reflect the general characteristics of water quality concentration with time and space,and can be further optimized.(4)Through the simulation of water quality under steady-state influent condition,it can be seen that there is a good aerobic and anoxic alternate environment in the aeration channel.The nitrification and denitrification proceeded smoothly,the water quality of ammonia nitrogen and total phosphorus increased by one class.The total nitrogen removal effect is obvious,but its water intake absolute value is too high to achieve the goal of raising a category,it's also shows the aeration project is running well in the river,with a certain impact load capacity.The simulated values of each model are higher than the measured values,and the relative error is less than 10%except ammonia nitrogen;Through the simulation of water quality under dynamic influent condition,the results of the distribution of the mean value of the concentration at different points on the same cross section and the comparison of the simulated and measured values of the water quality concentration at different positions are obtained.It can be seen that the simulation results were consistent with the actual measured values in time and space although there were still some deviations.The concentration of COD,TP and NH3-N in the areas close to the aeration pipes have relatively apparent decline except TN.According to the vertical distribution characteristics of pollutants,The concentration of pollutants in the aeration area is generally higher in the depth of 0-50cm,it's gradually decreased below the surface layer and decreased significantly in the depth of 50-100cm,followed by small fluctuations in concentration.(5)Using the same simplified model as the coupled model,exploring the results of the liquid-gas two-phase flow model which applied to the simulation of the system.The liquid-gas two-phase flow model was established on GAMBIT and FLUENT software platform.Through the analysis of the change of the pressure field,velocity field and gas volume distribution in different sections,reflecting the changes in the water flow field caused by the artificial ecological aeration project(for example,the turbulence of the water around the pipe aerator is more intense,Gas volume fraction gradually decreases with increasing depth in the vertical direction,etc.),providing a feasible method to further explore the internal influence and connection of the structural factors on the system,a basis for further improve the efficiency of the system. |
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