Mixing model of an aeration tank: Calculation of mixing process and complete mixing time

What is it about?

The biochemical degradation reaction of organic pollutant must be conducted in a complete mixing state, while an aeration tank operates in Continuous Stirred Tank Reactor (CSTR) mode. Here, a two-dimensional mixing model of an aeration tank was developed to analyze the mixing state. The feasibility was verified and the entrainment coefficient µ of bubble plume for calculation of diffusion coefficient was calibrated. Numerical solutions for the mixing process of instantaneous point-source of tracers in a square aeration tank with a symmetric flow field could be computed with the model and the two-dimensional mixing process and complete mixing time analyzed. Further, the mixing state and complete mixing time of the rectangular aeration tank could be approximated and analyzed according to the spatial scale of mixing, based on the calculation of the square aeration tank. The model calculation showed that the spatial mixing scale of the aeration tanks dominated the mixing processes. The rectangular aeration tanks could operate in the complete mixing state and CSTR mode by taking smaller mixing spatial scale or longitudinal mixing length, minimal spatial and mixing time in the square aeration tank.

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Photo by Zdeněk Macháček on Unsplash

Photo by Zdeněk Macháček on Unsplash

Why is it important?

The two-dimensional mixing model facilitates the assessment of mixing process in an aeration tank for ensuring that the biochemical reaction of organic pollutants was conducted in complete mixing state and CSTR mode, and optimization of tank layout and mixing structure.

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