Numerical Simulation Of Two-phase Flow In Oxidation Ditch And Hydrolytic Acidification Tank

The development of industry and agriculture has brought a large amount of convenience for human beings. However, it also leads to a series of environmental pollution problems, such as water pollution and air pollution. In recent years, the engineering technology of sewage treatment has been improved rapidly, aiming to protect the water resources and control the water pollution. The oxidation ditch and hydrolytic acidification tank are widely utilized as techniques of sewage treatment due to their efficiency and practicability. During the process of sewage treatment, the fluid motion in the reactor can directly influence the mixing effect, and thence it is of importance to study the characteristic of flow field in the reactor aiming to improve the efficiency. In this context, the dissertation, focusing on the oxidation ditch and the sewage reactor of hydrolytic acidification tank, uses Gambit to establish the geometric model and Fluent to perform the numerical simulation and finally determines the deposition zone and the floating zone of sewage sludge. The main method and conclusion are as follow:According to the structural characters of oxidation ditch, the three-dimensional numerical model is established by applying the knowledge of computational fluid dynamics and the normal k ?? turbulent model and then applied for computation. Firstly, the model is used to simulate the condition when one turntable operates in clean water and combine the simulation value of flow velocity to the measured one. The calculation results shows that the simulation is quite in coincidence with the practical situation, which can reflect the characteristics of the flow field in oxidation ditch. Thus, the model established has been proved to be accurate. After that, trials for different conditions with different number of turntables and content of sludge are repeated to detect the distributions of both the flow field and the concentration of sludge. Through analyzing the mixed state of water and sludge, the deposition or floating zone can be easily identified. Comparing the results of one turntable and two turntables, it shows that when the two turntables operate together, the flow velocity is higher while circulation frequency is faster, and thence the mixing effect becomes better.Furthermore, this study selects a large-scale hydrolytic acidification tank of the sewage treatment plant in Jilin Province, in which the tank has been severely silted up owing to the corrosion of blender. The flow field of the original snakelike tank and its sludge deposition is simulated and validated by the site observation data, comparing with its modification scheme up-flow hydrolytic acidification tank. The result demonstrates that the modified one is more capable to meet the technological requirements that could sufficiently improve the efficiency of sewage treatment.The above-mentioned results demonstrate that the model proposed in this dissertation is reasonable for sludge simulation in oxidation ditch and hydrolytic acidification tank. The achievements is expected to provide scientific basis for practical application of these sewage treatment techniques, and give proper guidance for related water treatment reactor in its designation, operation and optimization.