Vacuum Type Units

This process consists of saturating the wastewater with air by aerating in a tank, or by permitting air to enter on the

FIG. 7.16.2 Flotation unit with skimmers. A. Flotation unit; B. Pressure flotation unit.

suction side of the waste transfer feed pump. Under vacuum the solubility of air in the waste is decreased and air is released in minute bubbles. The rising air bubbles attach themselves to the solid particles in the waste, carrying them to the surface.

Because of the fairly high vacuum levels involved (9 in Hg vacuum), this type of flotation unit requires an expensive, airtight construction. Grease removal of up to 50%; suspended solid removal of 35 to 55%; BOD removal of 17 to 35% may be achieved at surface loadings of 4000 to 6000 gpd per ft2. The air requirement is 2.5 to 5 ft3 per 100 gallons.

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