| With the growing shortage of energy, worsening pollution of wastewater and growing complexity of the types of pollutants in the wastewater, anaerobic biological treatment technology have been paid more and more attention to because of its low investment, low energy consumption, available methane, high-load, low-mud, impact-resistant load, and so on. As a new type of highly efficient, highly promising anaerobic reactor, anaerobic baffled reactors (ABR) gain a high degree of attention and a lot of research in recent years. However, these studies focused mostly on the effects of various wastewater treatments with ABR, and little was about the research on hydrodynamic characteristics and flow pattern of ABR. The hydrodynamic characteristics of ABR reactor, decide the mixing degree of matrix and microbial, control the the transmission of materials in ABR, thus the hydraulic characteristics of ABR reactor are important factors that affect its treatment efficiency. The hydraulic characteristics of ABR reactor performance mainly on the condition of fluid flow, the mixing intensity of anaerobic sludge with the matrix, the reactor's capacity utilization and the actual residence time of wastewater in the reactor, and so on. Researchers in our laboratory have studied the effects of ABR to treat dairy farm wastewater, and have achieved good results. On this basis, hydrodynamic characteristics and flow field distribution were studied in this dissertation, so as to provide theoretical bases and guidance for further research.Firstly, with the residence time distribution (RTD) method, NaCl was used as a tracer to research hydrodynamic characteristics of the ABR reactor. The study results in several HRT showed that when the HRT changed from 60 min to 540 min, the dead zone fraction dead was under 0.30, among 0.068 to 0.299. With the increase of HRT, the dead zone decreased, and the extent of mixing decreased. When HRT was around 420 min, the flow pattern in ABR changed sharply. In order to maintain good flow state, HRT should be controlled above 420 min.Secondly, with the method of Computational Fluid Dynamics (CFD), LUENT software was used to simulate the flow field of an ABR reactor. In simulations, turbulence model and laminar model were used respectively, with HRT=60 min and HRT=540 min as examples. The results showed that, when the flow was turbulent, the hydraulic dead zone of the ABR reactor mainly occurred at the bottom corner of the reactor and the middle position of the up-flowing compartments; when the flow was laminar, the hydraulic dead zone reduced significantly. An ABR reactor has its counterpart for the HRT. Excessive small HRT may increase the hydraulic dead zone, and impact its treating efficiency.According to the findings of this study, some factors of ABR design in engineering were discussed. To design an appropriate ABR, the ABR structures, the sizes of the main components and operating conditions should be considered comprehensively, according to the influent quality of wastewater and the discharge standard. Some existing successful engineering projects could be referenced in the design of ABR reactor.As is known to us, the biological reaction between activated sludge and pollutants, and the transfer process through activated sludge have decisive effects to the efficiency of ABR. So it is recommended to go on with the computational simulation in this field and to find out how to verify the simulation results. Although CFD software have there limitations, they have broad prospects in research and design of wastewater treatment equipments. |
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