| Urban sewage is a kind of potential water resources. Purifying and reusing urban sewage, it can not only reduce water contamination and improve the ecological environment, but also solve the problem of urban water shortage. Immobilized microorganism technology has become a hot point in the field of sewage treatment and environmental protection because of its unique advantages. However, the existing immobilized microbial reactors are not applicable to purifying dispersive and hard-collected urban sewage in some shallow waters like pond and Pool.In view of the water treatment project about biological oxidation pond in Guangxi Zhuang autonomous region Ningming country Aidian village, it has been tried to design a new circle push-flow microbial reactor in this thesis, including reactor cylinder design, immobilized microorganism carriers selection and aeration system design. The fluid mechanics behavior of flow field in the reactor is very complex. It contributed to determining which design parameters impact the reactor performance by analyzing the simplification of gas-liquid-solid phase model, the form of gas-liquid phase flow, oxygen transfer between gas and liquid and the circulation flow principle, then providing the basis for further improvement and optimization about the structure of reactor. Three plans named A, B, C was designed for different structures of reactor according to different installation heights of aerator:650 mm,750 mm,850 mm. The internal flow field of reactor has been numerically simulated by Fluent 6.3. Through analyzing fluid velocity contours, velocity vector and outlet velocity distribution, the results showed that there was a big whirlpool above aerator affecting circulation effect in plan A, and liquid velocity was less than 0.25 m·s-1; in plan C, the axial force caused by aerator was not big enough to drive the water up because of short distance between aerator and outlet. Besides, the liquid velocity in half area of outlet was less than 0.05 m·s-1; in plan B, it had not only sufficient lift for the oxygen transfer from air to water, but also a high liquid velocity to ensure fluid circulation. Judging from above, The optimal plan realizing liquid circulation was the plan B, that is, the best installation height of aerator was 750 mm. Through simulating the different aeration quantity in plan B, D, E by the same method, the result was that in plan E, when aeration quantity was equal to 0.5 kg-h-1, liquid velocity was biggest, which was good to fluid circulation. An Experiment Scheme was been designed to verify the accuracy and reliability of numerical simulation results:using clear water as tested subject, Na2SO3 as reductant to relieving oxygen and CoCl2 as catalyst. In the line graph of DO changes about different installation heights of aerator, it could be seen that oxygenating rate in plan B was faster than that in plan A and plan C. In the line graph of DO changes about different aeration quantity, it could be seen the oxygenating rate in plan E was faster. The experimental results were consistent with that of numerical simulation.When the optimized reactor was running in the oxidation pond, testing the water quality for 30days, the result showed that chemical oxygen demands in water concentration (COD) falled from 58 g·m-3 to 14 g·m-3 and the total phosphorus concentration dropped from 0.76 g·m-3 to 0.19 g·m-3. Although ammonia nitrogen concentration fluctuated slightly, the overall trend declined from 11 g·m-3 to 7 g·m-3. In the oxidation pond, the phenomenon of fish widespread death disappeared, foul smells dissolved, the situation of spreading algae was solved and the biosphere of water system was improved, which contributed to enhance the self degradation ability of oxidation pond. |
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