Hydraulic behaviour in an activated denitrifying sludge tank

Kjellstrand, R.
University College of BorĂ¥s / Chalmers University of Technology

Hydraulic behaviour in an activated denitrifying sludge tank was investigated by fullscale tracer tests and computational fluid dynamics (CFD) modeling, using FEMLAB 3.1.

A theoretical model of the hydraulic behavior in the tank was made with FEMLAB 3.1 using the 3D kε turbulence model. Outlet concentrations of the tracer from this model was also plotted in a RTD curve (figure 3). Curve values generated from the CFD model were plotted as velocity weighted mean concentrations based on the overall outlet area. The velocity profile obtained show the main flow just passing straight through the upper part of the tank, above the supporting beams. Below the beams the water seem to be slowly transported backwards. The six mixers, which are installed to avoid settling in the bottom of the tank, are obviously not able to impact the short circuiting stream.

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