CA2166402C

CA2166402C - A device for aiding the solubilization of gases in liquids

Info

Publication number: CA2166402C
Application number: CA 2166402
Authority: CA
Inventors: Arthur F. Isbell
Original assignee: ISBELL AERATION LLC
Current assignee: ISBELL AERATION LLC
Priority date: 1993-05-03
Filing date: 1994-05-02
Publication date: 2001-02-06
Anticipated expiration: 2014-05-02
Also published as: WO1994025403A1; AU6822294A; CA2166402A1

Abstract

An apparatus and method are disclosed for rapidly and efficiently dissolving gases in a liquid. A diffuser, including a closed top hollow device, preferably a hollow conical, shaped frustum having a plurality of openings around the perimeter near the closed top is submerged in the liquid and rotated at relatively high speeds creating a centrifuge-pump. When the rotating diffuser is located near the surface of the liquid, no additional gas is required in the dissolution process. When the device is submerged substantially below the surface or if a gas other than oxygen is to be dissolved, then additional gas must be pumped into the bottom opening of the rotating diffuser. This device can be used in oxygenating treated sewage water, removing impurities from liquids, and for oxygenating horticultural ponds to increase production.

Description

A DEVICE FOR AIDING THE SOLUHILIZATION
OF GASES IN LIQUIDS
BACKGROUND OF THE INVENTION

1. Field of the Invention This invention pertains to the dissolution of gases in liquids and more specifically to a device for introducing large numbers of microbubbles of the gas into the liquid to greatly increase the gas/liquid contact, facilitating rapid dissolution.

2. Description of the Prior Art.

The ability to rapidly and efficiently dissolve gases and liquids is required in several different, fields in several different applications. Soluble gases are relatively easily and rapidly dissolved in liquids, especially under the application of elevated pressure. However, less soluble the gases are more difficult to dissolve in liquid economically and efficiently.

Additional difficulties are encountered when attempting to dissolve one gas of a gas mixture, such as dissolving i j oxygen in water from an air mixture that is approximately 20%

oxygen and 80~ nitrogen. It is well known that the rate of solubility of the gases in the liquid is directly proportional to the concentration of the gases in the mixture. Thus, it will take oxygen in air about five times as long to dissolve in water than it would take a 100% oxygen gas to dissolve in water. However, many times it is desirable to dissolve oxygen .

in a fluid and typically air is the desired source of oxygen due to the availability.
i I

W'O 94125403 PCTIUS94I04758 ~16fi402 Frequently, it is desirable to dissolve oxygen in water.

Oxygen, however, is relatively insoluble in water. For example, at 32C the solubility of oxygen in water in contact with air at one atmosphere of pressure is only 7.3 mg./liter or 7.3 parts per million (p.p.m). Solubility increases with the decrease in temperature - at OC the solubility is approximately 14.6 p.p.m.

Many applications exist which require the dissolution of large amounts of oxygen into a large volume of liquid. For example, it is necessary to oxygenate commercial fish ponds to enhance production and to oxygenate treated sewage or process water from industrial plants and mills to purify the liquid.

Oxygenation of commercial fish ponds is necessary for the following reasons. For example, aquatic organisms, including both animals and plants require at least a minimum amount of dissolved oxygen in water to survive. The amount of required dissolved oicygen varies between different aquatic organisms.

For example, cold water fish such as trout and salmon require much more dissolved oxygen than warm water organisms, such as catfish or crawfish. Currently, aquatic animals such as crawfish, shrimp, catfish, trout, salmon, and abalone are being raised in horticultural ponds. In order to sustain maximum production in these ponds, a minimum amount of dissolved oxygen is required. The more oxygen dissolved in the pond water, the more animals that can be raised.

j Oxygen is introduced into commercial fish ponds by a 1 variety of mechanisms where the natural air-to-water contact i is insufficient to reach the desired oxygen level. As previously stated, when water is in contact with air, the maximum concentration or saturation point of oxygen in water i i at 32C and one atmosphere of pressure is approximately 7.3 p.p.m. Typically, it is desirable to maintain the oxygen concentration in the fish pond as close to saturation point as possible to enhance production. The rate of solution increases as wind and wave action increase because of PATENT
increased air-to-water contact. However, even on windy days the rate of solution is slow.
One source of oxygen in the outdoor commercial ponds is green plants. Any green plant that engages in photosynthesis utilizes some of the dissolved oxygen, but normally produces significantly more photosynthetic oxygen than it uses. However, in darkness no photosynthetic oxygen is produced, yet the plant organism is using some of the dissolved oxygen. Therefore, typically in a fish pond the dissolved oxygen decreases during the night to its lowest value at daybreak, unless there is considerable night wave action. On the other hand, many commercial fish ponds are inside, requiring photosynthesis producing light sources.
Many attempts have been made at trying to raise the oxygen content of the water in commercial fish ponds. Most techniques are targeted at improving the gas-to-water contact, including: pumping pond water over rocky waterfalls; squirting water from fountains in the air;
turning paddle wheels on surface of the ponds; and pumping water/air mixtures at very high pressures and velocities into the pond surfaces at various angles. All of these techniques require large amounts of energy primarily because of the large amount of energy required to lift 8.3 lb./gallons (1 kilogram/liter) of water above the pond surface.
French Patent No. 2,466,271 ("Brandin") discloses a different type of aeration device. Specifically, the device is comprised of a vertical tube, an injector joined to the interior part of the tube, a centrifugal pump wheel that turns in the interior of a diffuser located below the injector, and an electric motor for turning the centrifugal pump wheel. The entire device is submerged into the liquid to be aerated. Although not as much energy is required to aerate the liquid, the aeration process is relatively c~166402 P~a'1'EidT
inefficient. In addition, the device is structurally comulex.
An alternate means of introducing more oxygen into the water is the use of a simple stack of wire screens placed in the water with the screen mesh fines decreasing from bottom to top. A stream of air is then pumped into the water below the screen stack.- This technique requires little energy, but the bubbles coming through the screens are still relatively large and at shallow depths a-rWthe to efficiency is very poor.
Another oxygen introducing means is the use of spinning air nozzles beneath the water. The nozzles are somewhat more efficient than the other schemes, because they are capable of producing small bubbles. However, the devices are unsymmetrical and require considerable energy to spin. Venturi tubes and porous diffuser stones are also used, but are not efficient, particularly at shallow depths.
U. S. Patent No. ~,~22,766 ("Sunada") discloses a gas liquid contacting device that includes a rotor consisting of a hollow inverted closed bottomed cone. The rotor is either partially or entirely submerged in a liquid and then rotated so that the liquid adheres to the outer periphery of the rotor and is projected outward in a substantially continuous thin film to be spread in the form of a film . comprising fine particles. This device does not require a great deal of energy to rotate. However, this device is inefficient in that only the amount of water that adheres to. the side of the rotor will be projected outwardly.
Oxygen is also used in water treatment applications.
For example, government regulation requires sewage treatment plants to dissolve oxygen in effluent prior to releasing the effluent into rivers, lakes, or oceans. The spillage of any organic substance into a body of water 3~ causes the fairly raid loss of dissolved oxygen, because of the oxidative destruction of the organic material. The AMEI~DcD Si-#E~I

.-1 s64a2 pl~.'1'ErIT
amount of dissolved oxv en required to decompose the or gap is sewage by bac ter a~ xida tion is grea tly i~ excess of the amount of dissolved oxygen that must be added to the effluent prior to release. Reduction of oxygen causes death in fish and aquatic plants. The devices used in the sewage treatment plants are very costly and require a great deal of power to run, just as those described above.
Oxygen can also be used to clean process water fron industrial plants, such as chemical plants, paper mills, and many other similar operations.. However, again the dissolution process is very costly.
Just as oxygen is used to remove undesirable products in water, so too is ozone. ozone is a form of oxygen having three oxygen atoms per molecule rather than twc.
Ozone is a much better oxidizing agent than oxygen because ozone is a much more energetic molecule. The ozone is used for oxidatively destroying organic compounds in the liquid.
Organic destruction using ozone requires only seconds to minutes, as opposed to the hours to days reauired to destroy the organic compound using oxygen. an acrueous solution of ozone decomposes within about 15 minutes, leaving no undesirable product. Ozone is very fast acting at very low concentration which makes it invaluable for removing undesirable bacteria, viruses, and contaminating organic matter from drinking water, spas, swimming pool . water, and industrial water. However, there are very few efficient means for producing ozone.
The problems of producing ozone from oxygen and the inefficient methods currently available for dissolving it make the ozone purification of water more expensive than chlorine treatment. Even so, it is now being recognized as superior because any excess ozone decomposes within about 25 minutes, leaving no bad taste, bad odor or toxic products, as is true for chlorine. Chlorine does not destroy organic contaminants but does react with them to produce substances that are now recognized as carcinogens.

AMEt~DcD Sk-;EET

-~ 1 s~ ~ 4 0 2 uATENT
In spite of the current greater cost of the ozone purification of water, the drinking water in at least one major United States city is purified with ozone, as is virtually all the drinking water in Europe. The water in virtually all European swimming pools and spas and increasing number of pools and spas in the United States is purified with ozone. Yet, the available methods for dissolving ozone in a liquid are relatively inefficient.
The dissolution of gases in liquids is required in other areas as well. A gas-to-liquid reaction can be used in any chemical process which requires the dissolution of a slightly soluble gas. For example, cleaning and disinfecting agents, like bleach and related products, are produced by dissolving the slightly soluble chlorine gas in a water slurry of lime. Carbon monoxide is a valuable gas for reacting with many organic liquids for producing products of great value such as different types of polymers and pharmaceuticals.
European Patent Application No. 0,151,434 ("Venas") discloses a device for treating and breaking up a liquid, primarily molten metal, with the help of "centripetal force." The device is a rotor having a cylindrical hollow body with holes around the perimeter of the device and.a hole in the bottom of the device. As the rotor is rotated in a liquid, the liquid rises inside the rotor as a result of centripetal force, creating a centripetal pump. A
centripetal pump is a very poor pump for liquids and even worse for gases, because the pumping action is caused by the friction that occurs between the liquid and the inside of the cylinder. In order to throw molten metal, the liquid used in the example described in the Venas specification, out of the holes in the side wall and above the molten metal surface, a significant amount of energy must be expended to overcome the forces of gravity and tie high density of the molten metal.
5a A~~~NDcO Si-3EET

'.
a ~ PATENT
The devices described above are directed to some, but not ail, of the scientific principles involving dissolving soluble gases in liquids. An example of one principle is that the rate of solubility of a gas in a liquid is directly proportional to the area of liquid-gas contact.
Accordingly, a related principle is that the smaller the gas or liquid bubbles that are in contact wi ~.h the other medium, the faster the gas will dissolve. Even though most of the patents :aentioned above attempted to meet these principals, they did so inefficiently.
P.nother scientif is principal is that a liquid has a density that is about 700 times greater than that of gaseous oxygen and, therefore, requires much more energy to lift and pump than is required to lift or pump a gas. This 1~ a major deficiency of the surface aeration devices that spray water into the air mentioned above. For this reason, it is much cheaper and more efficient. to pump and subdivide a gas than a liquid. In addition, a gallon of water, in water, "weighs" nothing, but raising a gallon. of water above tile SLLT'faCe of the water requires the lifting of 8.3 /' pounds (~3~~ilogram) and requires the expenditure of significant energy, depending on how high the water is lifted. Lifting the same volume of gas in the same manner would require only a small fraction of such energy. Thus, 2~ the choice is to move gas rather than liquid and to not move it out of its own medium, if possible. Clearly, the Sunada device is contrary to this principle.
Yet another principal is that air is 53 times less viscous than water. Therefore, it takes less energy to subdivide air than to subdivide water. The Sunada device fails to utilize this principle, because it subdivides water rather than gas. The Brandin device also fails under this principal, because its pumping of large amounts of water causes the gas to be pumped and subdivided along with the water.
5b AltClln~-r, "..__ PATENT
Another principle is that the gas-to-liquid contact must be accomplished with a minimum expenditure of energy for the amount of gas dissolved. The major problem with most of the devices described above is that they expend a great deal of energy to overcome the excessive friction produced during operation due to the complex designs. It is desirable to use a mechanism that is simple, as symmetrical as possible, with no sharp corners (e. g., flanges, paddles) , and with the smoothest possible surfaces to reduce the amount of energy required to overcome friction. The blades, vanes, and paddles of the devices described above create a great deal of friction. For example, the Brandin device is complicated and difficult to construct. The Venas device is designed to function by friction and, thus, as stated above, is very inefficient.
Finally, the mechanism should be of the simplest design so that it might be most easily constructed from cheap and readily available materials and at the lowest possible cost. None of the devices mentioned above successfully meet this principle.
Therefore, it is a feature of the present invention to provide an improved apparatus for inexpensively and efficiently dissolving a gas in a liquid.
It is another feature of the present invention to provide an improved process for oxygenating horticulture ponds to enhance the productions of the ponds.
It is yet another feature of the present invention to provide an improved mechanism for oxygenating sewage water.
5c It is another feature of the present invention to provide an improved process for removing impurities from liquid.
SUMMARY
These and other features and advantages are accomplished by an apparatus including a hollow frustum having a closed top and a bottom opening with the closed top being larger than the bottom opening. A plurality of side openings are located around the circumference of the frustum and preferably nearer to the closed top rather than the bottom opening. The frustum is rotated at sufficient speed to create a pumping action to draw water up through the bottom opening and out through the plurality of openings.
Preferably, the total surface area of the plurality of openings is greater than 20% of surface area of the bottom opening. The hollow frustum is either conical or pyramidal.
This apparatus is used in the processes of oxygenating of horticultural ponds, waste water treatment, and impurity removal from water and an application that requires dissolution of a gas in a liquid.
BRIEF DESCRIPTION OF
THE DRAWINGS
So that the manner in which the above-cited features, advantages and objects of the invention, as well as others which will become apparent, are obtained and can be understood in detail, more particularly a description of the invention briefing summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of the specification. It is to be noted, however, that the impended drawings illustrate only preferred embodiments of the invention and are, therefore, not to be considered limiting of its scope for the invention may admit to other equally effective embodiments.

PATENT
~1 ~~64a~ _ In the Drawings:
FIG. 1 is a side view of a diffuser illustrating a preferred embodiment of the invention.
FIG. 2 is a perspective view of a system used to dissolve gases in a liquid in accordance with this invention.
FIG. 3 is a side view of a diffuser illustrating an alternate embodiment of the invention.
FIG. 4 is a perspective view of an system used to dissolve gases in a liquid in accordance with an alternate embodiment of this invention.
DESCRIPTION OF THE
PREFERRED EMBODIMENTS
Now referring to the drawings and first to FIG. 1, a typical preferred embodiment of the present invention is illustrated. Diffuser 10 includes a hollow frustum 12 and attached to hollow cylindrical member 18. Frustum 12 includes bottom opening 14 and top opening 16.
Cylindrical member 18 is of the same diameter as top opening 16 and has closed top 19 and a bottom opening 21 that aligns with top opening 16, such that when frustum 12 and cylindrical member I8 are attached, one homogeneous unit is created. A plurality of side openings are spaced about the top of the perimeter or circumference of cylindrical member 18. Rotating shaft 22 is positioned in the middle of the closed top 19 of the cylindrical member 18 for rotating diffuser 10 when submerged in a liquid to create a centrifuge-pump.
In the preferred embodiment of this invention, the diameter of cylindrical member 18 and top opening 16 is 2-3/4 inches (70 mm). The overall vertical dimension of diffuser 10 is 3-15/32 inches (88 mm), with the vertical dimension of cylindrical member being 2-3/32 inches (53 mm). The diameter of bottom opening 14 is 1 inch (25 mm), and internal cone angle 24 is 147.5°. Frustum 12 is conical.

PATENT
~,1664fl~
Figure 2 shows a diffuser, such as the one shown in FIG. 1, submerged in reservoir 28 containing liquid 30.
Diffuser 10 is suspended by rotating shaft 22 of motor 34.
Motor 34 spins rotating shaft 22, and thus diffuser 10 at high velocities, at which point the diffuser becomes a centrifuge-pump, wherein liquid is drawn up through bottom opening 14, thrown in an upward direction and out plurality of openings 20.
Pump 36 injects a stream of gas through tubing 38 into bottom opening 14, forming a liquid-gas-mixture that is drawn into the diffuser 10 and ejected through plurality of openings 20. The injections of the gas into diffuser 10 is typically only required when diffuser l0 is submerged substantially below the surface of liquid 30.
When oxygenating a liquid, no gas injection is required if diffuser 10 is submerged in liquid only a small distance below the surface. Preliminary results have shown that the rate of oxygen dissolution into the liquid is much higher when diffuser 10 is located near the surface of the water without the injection of the gas, as opposed to the diffuser being located well below the surface of the liquid with the injection of the gas. When a diffuser of the dimensions described above is placed within three inches of the surface of the liquid in a 40 gallon (151.4 liters) reservoir containing approximately 35 gallons (132.5 liters) of liquid and rotated at approximately 3,450 revolutions per minute (rpm), a violent surface action is created generating significant cavitation and a concentrated water-air-mixture. The diffuser operating under these conditions produces a greater rate of gas dissolution than when the diffuser is places within 12 inches (30.5 cm) of the surface with air being introduced into the bottom opening at rates from 200-2000 milliliters per minute. The lower rates produce high percentage oxygen solution, while the higher rates produce poorer percentage oxygen solution, but achieve a greater total rate of solution.

v1 PATENT
The slower rates might be ideal for dissolving gases like ozone, where the high percentage oxygen solution would be desirable, but large quantities are not required. For oxygenating a fish pond or sewage plant effluent, rotating a diffuser near the surface without introducing additional gases is a more efficient means of oxygenating, primarily, because the energy required to pump the gases is not required.
FIG. 4 shows an alternate embodiment of the present invention. Diffuser 200 is constructed of PVC plastic water pipe fittings, including a top cap and a reducing adapter glued together with PVC cement. The top cap is approximately 66 millimeters (mm) in diameter. The bottom opening is approximately 34 mm in diameter and approximately 94 mm in height. The internal cone angle of the reducing adapter is approximately 143° and the overall height diffuser 200 is approximately 94 mm, creating an internal volume of approximately 22G ml.
Diffuser 200 is connected to hollow shaft 222, which is constructed of 1 inch (2.54 cm) PVC hollow water pipe and is approximately a 16.5 inches (43 cm) in length, with pvc cement. A metal fitting is attached to the top of hollow shaft 222 to allow for connection to motor 34. Four 3/16 inch (5 mm) holes were drilled two inches below the top of hollow shaft 222 as air holes. Forty 3/8 inch (9.5 mm) holes were drilled into the top cap of diffuser 200.
Tests have shown that submerging diffuser 200 into reservoir 28 to a depth of 12 3/8 inches (30.5 cm) below the surface of the water and turning the diffuser at approximately 3500 rpm pulls air down into the hollow shaft and expels it at high velocities into diffuser 200, producing violent gas-water mixing. When diffuser 200 is rotated at high speed, it acts like a centrifuge-pump and pumps water through the side holes creating a vacuum inside the cone that pulls air down through the hollow shaft. The air-water mixture inside the spinning cone is thrown out ., PATENT
through the side holes. Thus, this embodiment of the invention pumps its own air into the cone without requiring an external air or gas source.
Tests have Shawn that relatively large internal volumes are required for good results using this embodiment of the invention, primarily because the water in the hollow shaft must be displaced by air, before the air can mix with the water inside the diffuser. The greater the height of water in the hollow shaft, the greater the vacuum must be to displace the water. For example, for the shaft length described above, a diffuser of approximate volume of 182 ml with twenty 5/16 inch (8 mm) holes in the top cap is not capable of pumping air down the shaft. A larger volume inside the cone appears to produce a greater vacuum for displacing the water in the cone in the shaft. It also appears that if the total number and/or size of holes on the parallel portion of the cone is decreased, the solution efficiency is reduced.
Variations of the parameters of the embodiments described above produce very similar results without departing from the heart of the invention. For example, FIG. 3 shows an alternate embodiment of the diffuser, a single hollow frustum 100 with bottom opening 114 and closed top 119 to which rotating shaft 22 is attached.
Plurality of openings 120 are positioned near the top of frustum 100. Thus, cylindrical member 18 of FIG. 1 is not necessary.
Preliminary test results have shown that the only essential parameter of the diffuser is that it must be conical in nature and have a closed top. The smoothness of the frustum wall is not critical. For example, the frustum can be pyramidal. Also, it is not critical that the diffuser be hollow. For example, deflecting flanges may be included, but they reduce the efficiency of the diffuser.
Other parameters, such as the size, shape, number, and location of openings are not critical.

PATENT
The area of the plurality of openings relative to the area of the bottom opening is an influential factor, but not a critical factor. A diffuser having opening area of at least 20% or less than the area of the bottom opening, produces better results than other commercial devices, but the results are much poorer than when the area of the plurality of the openings is more than 20% or greater than that of the bottom opening. Good results are achieved when the area of the plurality of openings is 100 - 450% larger than the area of the bottom opening.
Since the ratio of plurality of opening area to bottom opening area appear to be the influential parameter, the number and size of the holes can vary. Good results have been achieved with both small and large openings, with the number of openings depending on the size. For a diffuser of the dimensions described above the maximum whole size that will produce good results is in the range from 9/32 inch (7 mm) to 1/2 inch (12.5 mmj. The maximum whole size dimension varies with the size of the diffuser.
In the preferred embodiment of the invention, round openings were used. However, there is no indication that the opening must be limited to a round shape.
The location of the holes on the vertical dimension of the diffuser is not critical. However, better results are obtained when the openings are concentrated at the closed top. Also the direction that the holes are drilled into the diffuser influences the results, but only slightly.
The selection of diffuser material is not critical.
The diffuser of the preferred embodiment is aluminum;
however, any substantially rigid material can be used, including hard plastic. Diffusers made of only tough plastic are good for dissolving relatively unreactive oxygen in water. For dissolving the more reactive gases, such as ozone, the diffuser should be made of certain stainless steel alloys, unreactive plastics, or possibly PATENT
aluminum. The diffuser can also be made of two materials including plastic and aluminum.

Claims

WHAT IS CLAIMED:

1. An apparatus for dissolving soluble gases located above the surface of a liquid 30 in the liquid, comprising:
a hollow device (10, 100, 200) having an inner conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of said device; and means (22, 222) connected to said device for rotating said device sufficiently below the surface of the liquid (30) at sufficient speed to create a centrifugal pumping action to draw the liquid up through said bottom opening (14, 114) and out through said plurality of side openings to interact with gases above the surface of the liquid to create cavitation.

2. Apparatus for dissolving soluble gases located above the surface of a liquid in the liquid, comprising:
a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of said device; and a rotating shaft (22, 222) connected to said device to rotate the top of said device below the surface of the liquid at sufficient speed to create a centrifugal pumping action to draw the liquid up through said bottom opening and out through said plurality of side openings to interact with gases above the surface of the liquid.

3. Apparatus for dissolving soluble gases in a liquid, comprising:
a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of said device;
a gas injector (38) positioned to inject gas through the bottom opening (14, 114); and means (22, 222) connected to said device for rotating the top of said device below the surface of the liquid (30) at sufficient speed to create a centrifugal pumping action to draw the liquid and gas from said gas injector up through said bottom opening and out through said plurality of side openings.

4. The apparatus in accordance with Claim 3, wherein said injected gas is oxygen.

5. The apparatus in accordance with Claim 3, wherein said injected gas is ozone.

6. The apparatus in accordance with Claims 1, 2, or 3, wherein the conical structure is a bottom member (12) having a top opening and said bottom opening (14) and vertical sides extending up from the top opening to the closed top (19).

7. The apparatus in accordance with Claim 6, wherein said bottom member is a hollow frustum.

8. The apparatus in accordance with Claim 7, wherein said hollow frustum has smooth sides.

9. The apparatus in accordance with Claim 7, wherein said hollow frustum is pyramidal.

10. The apparatus in accordance with Claims 1, 2, or 3, wherein total surface area of the plurality of openings is greater than 20g of surface area of said bottom opening.

11. The apparatus in accordance with Claims 1, 2, or 3, wherein said plurality of side openings are located nearer to said closed top than said bottom opening.

12. The apparatus in accordance with Claims 1, 2, or 3, wherein said rotating means (222) is a hollow shaft with openings (240) therein, said shaft being connected to a motor (34) for rotating the shaft so that air is drawn down through the shaft and into the hollow device as the hollow shaft is rotated.

13. The apparatus in accordance with Claims 1 or 2, additionally comprising:
a gas injector (38) positioned to inject gas through the bottom opening.

14. The apparatus in accordance with Claim 13, wherein said injected gas is oxygen.

15. The apparatus in accordance with Claim 13, wherein said injected gas is ozone.

16. A method of oxygenating treated sewage water comprising the steps of:
submerging a diffuser to a depth sightly below the surface of the treated sewage water, wherein said diffuser is an oxygen dispersement device that includes a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20,120) around the perimeter of said device; and rotating the diffuser at sufficient speed to create a centrifugal pumping action to draw water up through the bottom opening and out through the plurality of side openings to create cavitation.

17. A method in accordance with Claim 16, additionally comprising the steps of:
submerging the diffuser further below the surface of the treated sewage water; and introducing a stream of gas including oxygen into the bottom opening while said structure is rotating.

18. A method of oxygenating water in a horticultural pond comprising the steps of:

submerging a diffuser to a depth sightly below the surface of the water, wherein the diffuser includes a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of the device; and rotating the diffuser at sufficient speed to create a centrifugal pumping action to draw water up through the bottom opening and out through the plurality of side openings to create cavitation.

19. A method in accordance with Claim 18, additionally comprising the steps of:
submerging the diffuser further below the surface of the pond water; and introducing a stream of gas, including oxygen, into the bottom opening while said structure is rotating.

20. A method of removing impurities from a liquid, comprising the steps of:
submerging a diffuser to a depth slightly below the surface of the liquid, wherein the diffuser includes a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of the device; and rotating the diffuser at sufficient speed to create a centrifugal pumping action to draw in a liquid up through the bottom opening and out through the plurality of side openings.

21. A method in accordance with Claim 20, additionally comprising submerging the diffuser further below the surface of the liquid; and introducing a stream of ozone into the bottom opening, while the diffuser is rotating.

22. A method in accordance with Claim 20, additionally comprising submerging the diffuser further below the surface of the liquid; and introducing a stream of gas, including oxygen, into the bottom opening, while the diffuser is rotating.

23. A method of dissolving a gas in a liquid (30);
comprising the steps of:
submerging a diffuser to a depth sightly below the surface of the liquid, wherein said diffuser includes a hollow device (10, 100, 200) having a conical surface, a closed top (19, 119), and a bottom opening (14, 114) with the closed top being larger than the bottom opening, said hollow device having a plurality of side openings (20, 120) around the perimeter of said device; and rotating the diffuser at sufficient speed to create a centrifugal pumping action to draw a water up through the bottom opening and out through the plurality of side openings to create cavitation.

24. A method in accordance with Claim 23, additionally comprising submerging the diffuser further below the surface of the liquid; and introducing a stream of ozone into the bottom opening, while the diffuser is rotating.

25. A method in accordance with Claim 23, additionally comprising submerging the diffuser further below the surface of the liquid; and introducing a stream of gas, including oxygen, into the bottom opening, while the diffuser is rotating.