An analysis of the flow field in final settling tanks is presented. Computer simulations and hydraulic model tests have succeeded in demonstrating the forward flow near the bottom and the resulting backward flow at the surface, as well as in finding their cause. A reduction of the total energy input and consequently a more uniform velocity distribution were achieved by an inflow which is situated relatively low in the tank. By means of energy considerations a major criterion was found to position the inlet baffle. The positive effects of angle bars after the inflow and of a dividing wall in the tank itself to the flow field are explained.

Purification, final settling tank, sludge settling, density current, hydraulic modelling, inlet structure, velocity distribution
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© IWA Publishing 1991
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