BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fine bubble diffuser systems of the variety used to disperse fine bubbles of air or oxygen into a liquid for purposes of aeration, such as into a body of wastewater, such as a tank or pool in a wastewater treatment plant. More specifically, the present invention is a tube diffuser, which includes a porous pipe, for use in aeration.

2. Description of the Prior Art Porous pipe is known in the prior art for use in irrigation and aeration. It is also known in the prior art to use porous pipe in aerating wastewater.

Diffuser systems have been developed to disperse fine bubbles of air or oxygen into a body of wastewater (e. g., reservoir or lagoon; tank; pond). With these fine bubble diffuser systems, oxygen transfer efficiency (OTE) of up to two percent per foot of fluid depth has been achieved.

This OTE is a great improvement over coarse bubble diffusion systems having an OTE of 0.75 percent per foot of fluid depth. Irrespective of the ability of the prior- art fine bubble systems to relatively efficiently transfer air and oxygen to wastewater, relatively high head loss is

present, thus requiring high energy requirements to compensate for such losses.

SUMMARY OF THE INVENTION Accordingly, the present invention is submitted to overcome this shortcoming of the prior art by showing a head loss which is lower than that of the diffusers of the prior art across a range of flow rates.

The present invention, a tube diffuser designed for use in a fine bubble diffuser system to disperse fine bubbles of air or oxygen into a liquid for purposes of aeration, such as into a body of wastewater, comprises an outer porous pipe. The outer porous pipe has an inner dimension, an outer dimension, a wall thickness and a length.

An inner nonporous pipe is disposed within the outer porous pipe. The inner nonporous pipe has a first end, a second end, a length substantially equal to that of said outer porous pipe, an interior and at least one hole passing outwardly through a wall thereof from said interior. The at least one hole is closer to the first end of the inner nonporous pipe than to the second end.

The interior of the pipe is plugged between the at least one hole and the second end.

The inner nonporous pipe has an outer diameter which is smaller than the inner dimension of the outer porous pipe to provide a space between the two pipes.

The tube diffuser includes means for clamping the outer porous pipe around the inner nonporous pipe at the first and second ends thereof to close off the space between them.

The tube diffuser also includes means at the first end of the inner nonporous pipe for connecting the tube diffuser to a source of air or oxygen.

In operation, the air or oxygen is pumped to the tube diffuser, which is submerged in the liquid to be aerated. Air or oxygen first enters the interior of the inner nonporous pipe and passes through the at least one hole into the space between the inner nonporous pipe and the outer porous pipe. Finally, it passes through the pores in the outer porous pipe as fine bubbles to aerate the liquid.

The present invention will now be described in more complete detail with frequent reference being made to the figures briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view, partially in cross section, of the tube diffuser of the present invention; and Figure 2 is a graphical representation of the data set forth in Table 1 below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to Figure 1, a view of the tube diffuser 10 of the present invention, a porous pipe 12 is provided herein having an inner dimension of approximately 1.32 inches (3.35 cm) and an outer dimension of approximately 1.72 inches (4.37 cm), thus having a 0.2- inch (0.51-cm) wall thickness, it being understood that these specific dimensions are but examples to which the present invention should not be construed to be limited.

Commonly, wastewater applications utilize pipes of two-

foot (0.6-meter) length, and, thus, porous pipe 12 is specified as having a two-foot length. It should be noted that any size may be utilized. The porous pipe 12 is preferably formed in accordance with the methods disclosed in U. S. Patents Nos. 5,811, 038 and 5,811, 164 to the present inventor, William S. Mitchell. The teachings of these patents are incorporated herein by reference.

To be used in a wastewater aeration diffuser, the porous pipe 12 requires support. With reference to Figure 1, an exemplary construction for applying stiffening support to the porous pipe 12 is depicted.

Advantageously, the shown construction may be utilized with conventional diffuser systems. A nonporous pipe 14, such as one made of polyvinyl chloride (PVC), is disposed within the porous pipe 12 and has a length slightly less than that of the porous pipe 12, that is, 23.75 inches (60.3 cm) when the porous pipe 12 is two feet (61.0 cm) long. The outer diameter, for example 1.05 inches (2.67 cm), of the nonporous pipe 14 is less than the inner dimension of the porous pipe 12 so that an annular space 16 is defined between them.

A pipe female adapter 18, preferably of polyvinyl chloride (PVC), is disposed on one end 20 of the porous pipe 12 with the nonporous pipe 14 being seated therein.

A portion of the female adapter 18 preferably extends from the porous pipe 12. The female adapter 18 is solid about the nonporous pipe 14. A plug 22 is annularly disposed about the nonporous pipe 14 and within the porous pipe 12 in proximity to a second end 24 of the porous pipe 12.

The female adapter 18 and the plug 22 are fixed to rigidly maintain the porous pipe 12 and the nonporous pipe 14 in

fixed coaxial arrangement and to maintain the annular space 16. Preferably, the assembly is fixed by clamps 26, preferably of stainless steel, disposed to clamp the porous pipe 12 against the pipe adapter 18 and the plug 22. The female adapter 18 and the plug 22 form solid ends for the annular space 16 which prevent communication therethrough of the annular space 16 with the ambient atmosphere.

A plurality of holes 28, preferably eight, is formed through the nonporous pipe 14 at locations closer to the first end 20 than to the second end 24. A secondary plug 30 blocks the interior of the nonporous pipe 14 at a location intermediate the holes 28 and the second end 24, so that an unobstructed pathway is defined between the female adapter 18 and the secondary plug 30 which is in communication with all of the holes 28. To mount the entire assembly to an aeration diffuser, not shown, a pipe nipple 32, preferably of stainless steel, is provided which may be mounted threadedly into the female adapter 18. The free threads of the pipe nipple 32 may be mounted into a corresponding socket of an aeration diffuser manifold.

In use, compressed air or oxygen is injected through the female adapter 18, for example, via the pipe nipple 32, and into the nonporous pipe 14. As the compressed air or oxygen is pressurized within the nonporous pipe 14, it begins to pass through the holes 28 and into the annular space 16. As additional air or oxygen is fed into the annular space 16, pressure is built up, with the air or oxygen eventually transmitting through the porous pipe 12 to form fine bubbles in surrounding wastewater.

With reference to Figure 2, it has been found that the porous pipe 12 has a marked improvement in performance relative to head loss in comparison with conventional designs. As indicated in Table 1 and shown in the graph of Figure 2, the porous pipe 12 (Item 4) has the lowest head loss. The other products depicted therein are as follows: Item 1 2 inch x 24 inch (5.1 cm x 61.0 cm) fine bubble tube diffuser sold under the trade name "FlexAir"by EDI.

Item 2 9-inch (22.9-cm) disc diffuser sold under the trade name"FlexAir"by EDI.

Item 3 7M-inch (19.1-cm) fine bubble ceramic dome diffuser (manufacturer presently unknown).

Table 1* SCFM Item 1 Item 2 Item 3 Item 4 2 9¼ 3 13 22½ 22 im 4 14 29 39 2 5 15¼ 37 61 3 6 16½ 46 Off scale 3½ 7 171/57 Off scale 4 8 18% Off scale Off scale 51S 193/4 Off scale Off scale 6 * all head loses are provided in inches Example The following are the parameters of an example of the present invention, some of which have been previously noted above:

porous pipe 12 inner dimension-1.32 inches (3.35 cm) outer dimension-1.72 inches (4.37 cm) length-24 inches (61.0 cm) wall thickness-0. 20 inch (0.51 cm) nonporous pipe 14 inside diameter-0. 75 inch (1.91 cm) outside diameter-1.05 inches (2.67 cm) length-23.75 inches (60.3 cm) female adapter 18 inside diameter-1. 0 inch (2.54 cm) outside diameter-1. 3 inch (3.30 cm) plug 22 inside diameter-1. 0 inch (2.54 cm) outside diameter-1. 3 inch (3.30 cm) holes 28 six of 0.375-inch (0. 95-cm) diameter plug 30 diameter-0.75 inch (1.91 cm) pipe nipple 32 inside diameter-0. 75 inch (1.91 cm) outside diameter-1. 0 inch (2.54 cm) length-2.0 inches (5.1 cm) clamps 26 stainless steel-0.25 inch (0.64 cm) wide It should be understood that the present invention is not limited by the parameters given above, which characterize only an example of the present tube diffuser 10.

Modifications to the above would be obvious to those of ordinary skill in the art, but they would not bring the invention so modified beyond the scope of the appended claims.