Hydraulic Characteristics Of Oxidation Ditch And Structural Optimization

The popularity of the Oxidation Ditch is mainly due to its reliability, simplicity of operation and good treatment performance. There are some problems in a sewage treatment plant of Xi’an. To solve these problems, the hydraulic characteristics of Oxidation Ditch and structural optimization is studied. The main study content is showing as follow:(1)Set up a suit of laboratory scale oxidation ditch. The flow field around submersible pump was tested by using particle image velocimetry. The max velocity of the water is in accordance with the theoretical calculation value. Using bits of wood as tracer particles and the C programming language, the surface flow of screen outlet were analysised. Based on the study of the hydraulic characteristics and structural optimization of Oxidation Ditch, the analysis and research of the screen outlet blocking problem of laboratory scale oxidation ditch was conducted. It can be showed that:In practical engineering, the distance between impeller and screen outlet should be less than 7.2 m; By changing the y offset position of impeller could alleviate the screen outlet blocking problem. Keeping the level difference between two pool below 0.72 m, screen outlet blocking problem could be solved completely. Adding baffle near the screen outlet can reduce the blocking problem in a degree. In laboratory scale oxidation ditch, if the level difference between two pool was 20 mm, the max accumulation rate could be decreased from 16% to 3.6%. If the level difference between two pool was 30 mm, the max accumulation rate could be decreased from 31% to 16.8%. If the level difference between two pool was 40 mm, the max accumulation rate could be decreased from 35% to 18%.(2)A 3D flow model in CFD software Fluent was employed to simulate the process in laboratory scale oxidation ditch. The structure optimization of screen outlet blocking problem was conducted. The results can guide the experimental study. The optimal parameters is that: the position change of NO.5 impeller:Y:+20 mm, Z:+20 mm, the angle of baffle:7.5° opening mode of baffle:anticlockwise 45°. Add anticlockwise 45° baffle can change the tangential velocity and reduce the max normal velocity. It can solve the blocking problem in a certain degree.(3) A 3D flow model in CFD software Fluent was employed to simulate the process in a full scale oxidation ditch. The hydraulic characteristics of different section were analyzed. What’s more, the screen outlet blocking problem and energy allocation problems in practical engineering were analyzed. Six kinds of working conditions were designed in order to find the key for adjustment and optimization of energy configuration,. The best condition was that: the distance between the impeller and bend outlet:1.5 m, the distance between the impeller and bend inlet:7.5 m; the position change of impellers:Y:+0.25 m, Z:+0.25 m; the power of impeller:2.3 kW, power allocation:4.84 W/m3.