| A combining enhanced sewage treatment and in-situ sludge reduction system(abbreviate for A2MO-M system), is a novel simultaneous wastewater treatment and sludge reduction integrated system, designed to reduce excess sludge and remove the nutrients from waste water at the same time. Through the gradient conditions of dissolved oxygen in grading aeration tank and the micro-oxygen conditions in sludge holding tank, A2MO-M reactor has cultivated more abundant microbial species and reaching the strengthening effect of wastewater treatment and in-situ sludge reduction. Therefore, researching the fluid mechanics and optimizing the flow regime can improve the performance of A2MO-M reactor. In this paper, the fluid field characteristics of grading aeration tank and sludge holding tank was simulated and researched, by using computational fluid dynamics.By analyzing the original classification aeration tank simulation result, fluid dynamics design defects were found. Through simulation of the improvement of the single cell, the optimized scheme is obtained. The results show that the length and width ratio of the single cell in the grading aeration tank has a great influence on the whole flow field. 2:1, 3:2 and 1:1 three kinds of long and wide ratio are simulated and the ratio of 1:1 is optimal, which has the largest average flow velocity and the most uniform velocity distribution. Stirring is the main way of mixing in microoxygen cell, and three kinds of distance from the stirring to the bottom were simulated. When the distance is 5cm, the average flow velocity of the upper micro-oxygen cell change little and the gas phase can be fully mixed with the liquid phase, which is conducive to the uniform micro oxygen condition. Reducing the size of aeration devices, increasing aeration sites, and two uniform configurations and one near wall configuration also has been consideration to research the flow regime. In the case of the same effective aeration area, reducing the size of aeration devices and increasing aeration sites is conducive to the uniform flow field. 4-4 near wall configuration which has the largest average flow velocity, leave enough space between aeration sites, making the liquid phase flow down and formed a cyclic flow field in the reactor.The retention time distribution of the original micro-oxygen sludge retention tank was tested, and the RTD test was simulated by CFD. T he hydraulic characteristics of the sludge retention tank are obtained, and the CFD model is verified. The results show that the average residence time of RTD was 420 min and the stagnation region was 22.22%. It was necessary to simulate sludge retention tank by using CFD. The CFD model can simulate the flow pattern of the sludge in the tank, the maximum error is 14.7% and the average error is 7.8%. Comparison four types of stirring blade, double blade axial compression each other the height of the circulation area, the formation of vortex, bad for mixing and mass transfer; Oblique leaf blade can effectively in the region of the rotating downward axial flow, promotes the mass transfer of oxygen, gas phase dispersion effect is better. Therefore, oblique leaf blade for the optimal choice. The influence of different number of the blade flow field. With the increase of blade under piece number, mixed liquid axial and radial average rate fell slightly, gas distribution results consistent with the results o f radial average speed. Under the condition of the same liquid mixture average rate, increase the number of blade can reduce the speed, effectively reduce the mixing area at the center of the flow rate, the overall velocity distribution more uniform. Comprehensive consideration, four inclined propeller for anaerobic sludge retention pond is optimal choice. |
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