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Biological oxidation and flotation apparatus and method
| Details |
Inventors: Fullerton, Donald Griswold; Kyrias, Gilbert Mowder; Weber, Richard Baxter;
Assignee: FMC Corporation (Chicago, IL)
Primary Examiner: Hart; Charles N.
Assistant Examiner: Spitzer; Robert H.
Attorney, Agent or Firm: Dressler, Goldsmith, Clement, Gordon & Shore, Ltd.
Biological oxidation and flotation apparatus and method are disclosed for use in the treatment of sewage or other aqueous waste material by the activated sludge process. A treatment and flotation chamber is provided in which both biological oxidation and flotation take place. In some forms of the method and apparatus, a separate biological oxidation tank is also used prior to the treatment and flotation chamber. The treatment and flotation chamber includes a quiescent zone at the top of the chamber that extends horizontally through at least the downstream part of the chamber, and extends downward at least about three inches blow the surface of the contents of the chamber. The contents of the chamber below the quiescent zone are continuously recirculated, for example by pumps whose inlets lie below the quiescent zone and which transfer a part of the aqueous material under treatment to the bottom of the chamber to be employed as the shearing liquid in a bubble shearing apparatus. The entire contents of any part of the treatment and flotation chamber over which the quiescent zone does not extend are also continuously recirculated, as are the entire contents of any separate biological oxidation tank. Oxygen-containing gas bubbles are introduced into the system to provide oxygen for biological treatment of the aqueous material in any separate biological oxidation tank and in the treatment and flotation chamber, and to provide bubbles (supplemented by carbon dioxide and nitrogen, absorbed from the liquid medium) which attach themselves to suspended solid particles to form a float in the quiescent zone at the top of the treatment and flotation chamber. Substantially all of the oxygen-containing gas bubbles introduced below the quiescent zone in the treatment and flotation chamber are no larger than about 500 microns in diameter, with the bubble size measured under certain specified conditions. A maximum bubble size of about 200 microns produces improved results, 100 microns produces still better results, and a 50 micron maximum bubble diameter is preferred. The oxygen-containing bubbles are introduced into the treatment and flotation chamber from gas in the free state, at a pressure, measured adjacent the outlet orifices of the bubble forming devices employed, that is approximately equal to the hydrostatic pressure of the liquid at that point. |
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DETAILED DESCRIPTION OF METHOD AND APPARATUS The apparatus shown in FIGS.
1-5 and 7-13 is designed for use in a sewage treatment plant employing the activated sludge process.
Three embodiments are illustrated.
SINGLE TREATMENT AND FLOTATION CHAMBER In the apparatus shown in plan view in FIG.
1, treatment and flotation chamber 20 has an upstream part 21 and a downstream part 22.
The apparatus is adapted for the withdrawing of "float" over downstream end wall 24 of chamber 20, but both the float and the withdrawal means are omitted from FIG.
1 for clarity.
Aqueous waste material to be treated in this apparatus is introduced into treatment and flotation chamber 20 through inlet 26, located in the central section of upstream end wall 27.
The aqueous waste material may be introduced as raw sewage in an untreated state, or if desired, it may be pretreated by removal of grit, large solids, grease or similar materials.
As explained below, activated sludge -- either in the form of floated sludge skimmed off from chamber 20 itself or settled sludge from the settling tank that follows the treatment and flotation chamber -- may also be introduced at inlet 26.
Materials moving from left to right in FIG.
1 pass at about region 28 from upstream part 21 of chamber 20 into downstream part 22.
As is seen, "mixed liquor," containing soluble waste material and suspended solid particles that have been "activated" by the biological oxidation treatment in upstream part 21 as well as return activated sludge from farther downstream, moves through area 28 into downstream part 22 of chamber 20.
The preferred location for aqueous waste material inlet 26 is as shown in FIG.
1, at one end of treatment and flotation chamber 20, with the mixed liquor outlet at the other end of the chamber.
However, if desired, there may be more than one inlet, which may be located in various parts of the chamber so long as the chamber has one or more outlets spaced a substantial distance from the inlets.
Biological Oxidation Gas diffusing means 32 are positioned adjacent the bottom of the upstream part of chamber 20 for dispersing a quantity of oxygen-containing gas bubbles through the body of liquid contained therein
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