The Experiment And Numerical Simulation Study On Aeration Tank Of Active Sludge Treatment

In recent years, along with the environmental protection getting more value, there are many new sewage treatment craft appeared, but the active sludge treatment is still the first choice for the large-scale sewage treatment plant, however, the aeration tank is the core part of this craft. By aerating, it makes oxygen, activated sludge and nutrient mix fully, makes the sludge in the state of suspending, so that the microorganism has enough oxygen to carry on substance metabolism. From the view of fluid dynamics, all of these processes are realized by the flow of gas-liquid two-phase. So from this point, it is meaningful to make deep understand to the characteristic of flow field and grasp the influence of gas spreading way and aeration speed to flow field. And also it is helpful in practical running and the way of aerating optimization design.A plug flow aeration tank is designed which can treat 5580m3/d by sludge load method, and according to the request of different aeration way, a plain plug flow aeration and a circumvolve plug flow aeration which aerate in bottom are chosen for comparing. According to the theory of similitude, an experimental structure is set up for simplification in proportion of 1:20. In the same conditions, the effect of two aeration ways and different aeration velocities for one of aeration ways is gained. For further understand the characteristics of two-phase flow in aeration tank, the paper adopts CFD (computational fluid dynamics) software to simulate. Gas is selected as the primary-phase, and liquid is selected as the secondary-phase. Three-dimension steady incompressible mixture model is picked up for simulating. By solving the Continuity Equation for the Mixture, Momentum Equation for the Mixture, Volume Fraction Equation for the Secondary Phases and Relative Velocity formula, two-phase flow field of two kinds plug flow aeration tank and different aeration velocities flow field for one aerate way are simulated.Comparing with real engineering, analyze the experiment and simulation results, the conclusion is that the mixture model can simulate the flow field of gas-liquid two-phase well; the effect of plain plug flow aeration is better than circumvolve plug flow aeration's; for the same plug flow aeration , the effect of 20m/s aeration is better than 10m/s's and 30m/s's.