Wastewater aerator/digesters

Abstract

A mixing aerator is disclosed that includes a housing defining a chamber having a bottom end and a top end, the housing having at least one inlet and at least one outlet; and a longitudinally extending diffuser disposed within the chamber and configured to deliver air bubbles into the chamber when the chamber is filled with liquid. The diffuser includes (a) a tubular elastomeric membrane having a plurality of perforations and, within the tubular elastomeric membrane, (b) an air pipe having a plurality of openings, the openings being larger and fewer than the perforations, and the tubular membrane having upper and lower ends that are sealed against an outer surface of the air pipe.

Claims

1. A mixing aerator comprising: a housing defining a chamber having a bottom end and a top end, the housing having at least one inlet and at least one outlet; and a longitudinally extending diffuser disposed within the chamber and configured to deliver air bubbles into the chamber when the chamber is filled with liquid, the diffuser comprising (a) a tubular elastomeric membrane having a plurality of perforations and, within the tubular elastomeric membrane, (b) an air pipe having a plurality of openings, the openings being larger and fewer than the perforations, and the tubular membrane having upper and lower ends that are sealed against an outer surface of the air pipe, wherein a gap is provided between an inner surface of the membrane and an outer surface of the air pipe to allow air to flow therebetween and wherein the membrane includes a central region having a first wall thickness and end portions having a second wall thickness greater than the first wall thickness, and the difference in wall thickness is configured to provide the gap that extends around the circumference and along the length of the air pipe.

2. The mixing aerator of claim 1 wherein the size of the gap is from about 0.1 to 0.2 inch.

3. The mixing aerator of claim 1 wherein the perforations are self-closing.

4. The mixing aerator of claim 2 wherein the perforations are in the form of slits.

5. The mixing aerator of claim 1 wherein the first wall thickness is from about 0.03 to 0.08 inch.

6. The mixing aerator of claim 1 wherein the membrane is formed of an elastomer having a durometer of from about 25 A to 50 A.

7. The mixing aerator of claim 1 wherein the membrane is formed of an elastomer that is ozone resistant.

8. The mixing aerator of claim 1 wherein the openings in the air pipe comprise elongated slots.

9. A diffuser for a mixing aerator comprising: a tubular elastomeric membrane having a plurality of perforations and, within the tubular elastomeric membrane, an air pipe having a plurality of openings, the openings being larger and fewer than the perforations, and the tubular membrane having upper and lower ends that are sealed against an outer surface of the air pipe, wherein a gap is provided between an inner surface of the membrane and an outer surface of the air pipe to allow air to flow therebetween and wherein the membrane includes a central region having a first wall thickness and end portions having a second wall thickness greater than the first wall thickness, and the difference in wall thickness is configured to provide the gap that extends around the circumference and along the length of the air pipe.

10. The diffuser of claim 9, wherein the size of the gap is from about 0.1 to 0.2 inch.

11. The diffuser of claim 9 wherein the perforations are self-closing.

12. The diffuser of claim 10 wherein the perforations are in the form of slits.

13. The diffuser of claim 9 wherein the first wall thickness is from about 0.03 to 0.08 inch.

14. The diffuser of claim 9 wherein the membrane is formed of an elastomer having a durometer of from about 25 A to 50 A.

15. The diffuser of claim 9 wherein the membrane is formed of an elastomer that is ozone resistant.

16. The diffuser of claim 9 wherein the openings in the air pipe comprise elongated slots.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a prior art aerator/digester.

(2) FIG. 2 is a perspective view of a diffuser according to one implementation.

(3) FIG. 2A is a longitudinal cross-sectional view of the diffuser taken along line A-A in FIG. 2.

(4) FIG. 3 is a perspective view of the air tube used in the diffuser shown in FIG. 2.

(5) FIG. 4 is a perspective view of the membrane used in the diffuser shown in FIG. 2.

(6) FIG. 4A is a highly enlarged detail view of region A in FIG. 4, showing the perforations in the membrane.

(7) FIG. 5 is a cross-sectional view of the diffuser shown in FIG. 2.

(8) FIG. 6 is an enlarged view of one of the clamps used in the implementation shown in FIG. 2.

DETAILED DESCRIPTION

(9) FIGS. 2 and 5 show a diffuser 100 suitable for use in a mixing aerator such as the one shown in FIG. 1. In the case of the system shown in FIG. 1, the diffuser 100 would replace the air tube 38. The diffuser 100 can be used in other types of mixing aerators that include an air delivery tube having apertures and would replace the air delivery tube in such systems. The diffuser 100 may also be used in mixing aerators for delivery of gaseous ozone, e.g., for chemical-free odor control. It is noted that the term air is used herein for the sake of simplicity to refer to the gas being delivered by the diffuser; air can be replaced with gaseous ozone in the description below, which would be delivered through the diffuser in the same manner as air.

(10) Diffuser 100 includes an elongated tubular membrane 102 and an air tube 104. The membrane 102 is formed of an elastomeric material. The membrane 102 is secured to the air tube in a sealing manner by clamps 106 as will be discussed further below. The membrane 102 includes a plurality of perforations in the form of slits 108 (FIG. 4A) which preferably cover substantially the entire surface of the membrane, as shown in FIGS. 2 and 4, and extend generally parallel to the long axis of the air tube as shown in detail in FIGS. 4 and 4A. It is noted that in the actual diffuser the slits when closed are not readily visible; they are shown diagrammatically in FIGS. 2, 4 and 4A for the sake of explanation.)

(11) Because the membrane is formed of elastomeric material the slits will be normally closed and will only open in response to air pressure. As a result, the slits are self-closing and act as check valves, making both the membrane and the diffuser as a whole resistant to fouling by grease and other contaminants. The structure and characteristics of the membrane 102 will be discussed in further detail below.

(12) The air tube 104 is disposed within the tubular membrane 102, as shown in FIG. 5. Air tube 104, shown without the membrane 102 in FIG. 3, includes a plurality of elongated slots 110 that extend generally parallel to the long axis of the air tube and are spaced at intervals around its circumference. Preferably the slots are uniformly distributed around the circumference. The slots may be any size as long as the area of the slots is sufficient to allow air to flow out of the air tube at a desired volumetric flow rate with the available air delivery equipment. The appropriate flow rate can be determined empirically by operating the mixing aerator in the intended environment and observing whether adequate breakdown of grease, oil, fats, or other contaminants is obtained. In some implementations the slots are at least 1.5 inches long, but this dimension will depend on the size of the mixing aerator as it will be scalable based on the length and diameter of the air tube. The slots simply need to be big enough to allow sufficient airflow to pressurize the gap 116 (discussed below) between the air tube and the membrane. There is no maximum size for the slots, as long as the structural integrity of the air tube is not compromised.

(13) As can be seen in FIG. 2A, the membrane 102 has a greater wall thickness at its two ends (portions 112A, 112B) than along the remainder of its length (central region 114). For example, in some implementations the portions 112A, 112B may be about 3 to 6 times as thick as the central portion 114 of the membrane. The additional thickness of portions 112A, 112B faces inward, thus providing a gap 116 between the inner surface of the central region 114 and the outer surface of the air tube 104 that extends around the circumference and along the length of the air tube 104. (The size of this gap, which may be, for example, from about 0.1 to 0.2 inches, is not shown to scale in FIG. 2A but rather is exaggerated so that it can be seen.) It is noted that a portion of each of the end portions 112A, 112B is inboard of the clamps 108; otherwise, the gap would not be provided because the clamps 108 would press central portion 114 against the outer surface of the air pipe.

(14) During use, air flows from the slots 110 into the gap 116 creating air pressure that causes the membrane to expand and balloon outwardly. If the gap is too small, the membrane may not expand sufficiently in response to air pressure. This expansion of the membrane 102 causes the slits 108 to expand and open, emitting a flow of small air bubbles into the oxygen transfer chamber that surrounds the diffuser 100 (chamber 44 defined by tubular housing 12 in FIG. 1). The slits act like check valves, closing behind each bubble and thus preventing debris from back-flowing into the diffuser through the membrane.

(15) The membrane 102 may be formed, for example, of a thermoplastic elastomer such as EPDM (ethylene propylene diene monomer). Other suitable materials include other synthetic rubbers such as fluoroelastomer polymers including those sold under the tradename VITON, chlorosulfonated polyethylenes such as those sold under the tradename HYPALON, or silicone rubbers. The material should be resistant to the chemicals to which it will be exposed, for example if the diffuser will be used for ozone delivery the material should be ozone resistant. The material used for the membrane should have sufficient flexibility to allow the slits to open enough to release a bubble under the air pressure that will be present in the gap 116, and close after releasing the bubble. It is also important that the membrane be soft and flexible enough so that the membrane does not create excessive back pressure. In some implementations the material has a durometer of from about 25 A to 50 A, for example from about 30 A to 40 A.

(16) The central region 114 of the membrane may have a thickness, in some implementations, of from about 0.03 to 0.08 inch, e.g., 0.035 to 0.065 inch. Generally, the thickness should be sufficient to provide the membrane 102 with sufficient durability and resistance to tearing, while being thin enough to provide the necessary degree of flexibility to allow the slits to open under the supplied air pressure without creating back pressure.

(17) The slits 108 may be formed, for example, by running a tube of membrane material through a perforating machine. In some implementations, the slits have a length of from about 0.06 to 0.3 inch, preferably from about 0.15 to 0.25 inch. The membrane may have, for example, from 15 to 30 slits per square inch.

(18) Referring now to FIG. 6, it is preferred that the clamps 108 be band clamps, and that the free end (not shown) of the band 120 be cut off and the lock 122 be crimped. This configuration prevents the clamps from catching rags and other debris that could foul the diffuser.

Other Embodiments

(19) A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.

(20) For example, the dimensions given above are merely by way of example and can be scaled or changed to suit various applications.

(21) Moreover, while the implementation above utilizes elongated slots in the air tube for simplicity of manufacture of the air tube, other types of openings may be used, for example round holes.

(22) Accordingly, other embodiments are within the scope of the following claims.