Dissolved air flotation A 2-dimensional CFD model of a small pilot DAF tank

Other conference contribution, 2007

Dissolved Air Flotation, DAF, is an effective treatment process for drinking water and wastewater treatment. The advantages are a short start-up time, high hydraulic loading and more compact sludge. Air-saturated water is injected, under high pressure, into the flocculated main water stream. The decrease in pressure results in the formation of microscopic air bubbles. The flocs attach to the bubbles and rise to the surface where they form a foam layer. It is removed by scrapers at the surface and the clear water is let out at the bottom of the tank. The paper presents a two-dimensional one-phase model of a pilot DAF tank that has been developed with the CFD software FLUENT 6.3. The flow simulations are compared to experimental flow measurements. The results show the difficulties encountered when transforming a three-dimensional flow into a two-dimensional model. The design of the outlets influence the results and the effect of three-dimensional movements cannot be taken into account. In future studies the one-phase model will be extended to a two-phase model and considerations should be put on extending the two-dimensional model into three dimensions.