Patent Application
20130088190
The present invention relates generally to energy recovery during wastewater treatment, and, more particularly, to energy recovery from aerated wastewater treatment tanks
Diffusers are conventionally used to support aerobic biological processes in wastewater treatment tanks A diffuser typically comprises a disc-, tube-, or strip-shaped membrane, which is constructed of rubber or other similar materials and is punctured to provide a number of perforations in the form of holes or slits. In operation, pressurized air is sent through these perforations to create a plume of small bubbles. The bubbles rise through the wastewater and, in so doing, provide the surrounding wastewater with the oxygen needed to sustain the desired biological processes occurring therein. The rising bubbles also create motion in the wastewater, which aids in suspending solids (e.g., sludge) and mixing.
The pressurized air required to drive the diffusers in a wastewater treatment tank is usually produced by one or more air blowers. In many wastewater treatment plants, these air blowers may need to supply from about 1-500,000 cubic feet per minute of air at pressures sufficient to overcome dynamic heads of about 5-40 feet. Accordingly, these air blowers are typically large and consume large amounts of power. An air blower may, for example, consume about 0.085 kilowatt-hours (kwh) of energy for each cubic meter of tank volume to supply about 0.6 cubic meters of air per cubic meter of tank volume. The aeration aspects of a water treatment process may consume about 70% of the energy used by a wastewater treatment plant. For this reason, it would be highly advantageous to be able to recover some of this energy while, at the same time, not adversely affecting the treatment of the wastewater.
Embodiments of the present invention address the above-identified needs by providing apparatus and methods for recovering energy during wastewater treatment. Advantageously, these apparatus and methods are operative to function without adversely affecting the treatment of the wastewater itself.
In accordance with aspects of the invention, a system for recovering energy while treating a body of wastewater comprises a tank, a plurality of diffusers, a propeller, and a generator. The tank contains the body of wastewater. The plurality of diffusers is immersed in the body of wastewater and is operative to create motion therein by the discharge of bubbles. The propeller is immersed in the body of wastewater and is operative to spin in response to the motion in the body of wastewater. The generator is linked to the propeller and is operative to generate electrical energy in response to the spinning of the propeller.
In accordance with additional aspects of the invention, a method of recovering energy while treating a body of wastewater comprises placing the body of wastewater in a tank. A plurality of diffusers is immersed in the body of wastewater and caused to create motion in the body of wastewater by the discharge of bubbles. In addition, a propeller is immersed in the body of wastewater and caused to spin in response to the motion in the body of wastewater. A generator is linked to the propeller and caused to generate electrical energy in response to the spinning of the propeller.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings where:
The present invention will be described with reference to illustrative embodiments. For this reason, numerous modifications can be made to these embodiments and the results will still come within the scope of the invention. No limitations with respect to the specific embodiments described herein are intended or should be inferred.
The wastewater treatment system 100 comprises a tank 110 which contains a body of wastewater 120 being treated. An array of conduits 130 is positioned near the bottom of the tank 110 and is fed pressurized air from a plurality of air blowers 140. The conduits 130 themselves support a series of diffusers 150 that are mounted on the conduits 130 and are in fluidic communication thereto. Moving upward, a matrix of cylindrical shrouds 160 is positioned near the top of the tank 110. Each of the cylindrical shrouds 160 has substantially vertical sidewalls and encircles a respective propeller 170, which is suspended near the top of its cylindrical shroud 160 by a respective linkage rod 180. The linkage rods 180, in turn, link each of the propellers 170 to a respective electrical generator 190 that is supported above the tank 110 by a suitable support structure (not explicitly shown). Each of the propellers 170 has a respective axis of rotation that is substantially perpendicular to the plane formed by the upper surface of the body of wastewater 120.
Conduits and diffusers suitable for use in implementing aspects of the invention are largely conventional and may be sourced from, for example, Stamford Scientific International Inc. (Poughkeepsie, N.Y., USA). The conduits 130 may comprise, for example, polyvinylchloride. The diffusers 150, in turn, may comprise diffuser bodies formed from, as another example, polypropylene or polyethylene on which are mounted flexible, perforated diffuser membranes. The diffuser membranes may comprise, for example, perforated ethylene-propylene-diene-monomer rubber, and may, in preferred embodiments, further comprise fluoroelastomer- or polytetrafluoroethylene-containing coatings or, alternatively, fluorine-modified upper surfaces, to inhibit contamination by the body of wastewater 120. When pressurized gas generated by the air blowers 140 is applied to such diffusers 150 via the conduits 130, the gas pressure expands the flexible diffuser membranes away from the diffuser bodies and causes their perforations to open so that the gas discharges through them in the form of fine bubbles. The bubbles subsequently rise through the body of wastewater 120 and, in so doing, provide the surrounding body of wastewater 120 with the oxygen needed to sustain the desired biological processes occurring therein. The rising bubbles also create motion in the body of wastewater 120, which aids in mixing. When the gas pressure is relieved, the flexible diffuser membranes collapse on the diffuser bodies to close the perforations and prevent the body of wastewater 120 from entering the diffuser bodies in the opposite direction. Generally, a flexible diffuser membrane configured in this way produces bubbles smaller than five millimeters in diameter. The resultant large ratio of surface area to volume in these bubbles promotes efficient oxygen mass transfer between the bubbles and the surrounding body of wastewater 120.
Wastewater treatment in such a manner is largely conventional and is described in, as just one example, F. L. Burton, Wastewater Engineering (McGraw-Hill College, 2002), which is hereby incorporated by reference herein. The provisioning, arrangement, and functioning of the cylindrical shrouds 160, the propellers 170, the linkage rods 180, and the electrical generators 190 in the wastewater treatment system 100 are, in contrast, entirely novel. A purpose of the cylindrical shrouds 160, the propellers 170, the linkage rods 180, and the electrical generators 190 is to recapture at least some of the energy supplied to the body of wastewater 120 through the combination of the air blowers 140, the conduits 130, and the diffusers 150.
More particularly, the cylindrical shrouds 160 act to capture the motion created in the body of wastewater 120 by the rising plumes of bubbles and to channel that motion towards the propellers 170. The propellers 170, in turn, spin about the longitudinal axes of the cylindrical shrouds 160 in response to this channeled motion. Finally, the linkage rods 180 transmit the spinning motion (i.e., rotational motion) of the propellers 170 to the electrical generators 190, which convert that motion into electrical energy. Without this energy recovery apparatus, the supplied energy is, instead, simply lost into the atmosphere above the upper surface of the body of wastewater 120.
The cylindrical shrouds 160, the propellers 170, and the linkage rods 180 may comprise plastic or metallic components, or a combination thereof. The electrical generators 190 may be commercially sourced and may be of the type wherein permanent magnets are moved relative to conductive coils, or vice versa, to create an electromotive force in the conductive coils.
In a preferred but non-limiting embodiment of the invention, the cylindrical shrouds 160 are mounted near the top of the tank 110 but below the upper surface of the body of wastewater 120. In the illustrative wastewater treatment system 100, the cylindrical shrouds 160 may, for example, be 8-10 feet in length and may be disposed about four feet below the upper surface. In addition, the cylindrical shrouds 160 are preferably placed more than about four feet above the diffusers 150.
Aerated wastewater treatment tanks are very complex hydrodynamic and biological systems. The above-described configuration, while non-limiting, is thereby informed by several significant and unexpected experimental observations made by the inventors while studying prototypes in a laboratory environment. It was experimentally observed, for example, that configuring a cylindrical shroud to break the upper surface of the wastewater appeared to reduce the efficiency of the wastewater treatment. This suggests that it is unfavorable to the wastewater treatment process to interfere with the mixing and the gas-liquid interface at the uppermost surface of the wastewater. Moreover, it was also experimentally observed that the motion transferred from wastewater to a propeller held above a diffuser was diminished when the propeller was less than about 3-4 feet above the diffuser. Here, it is postulated that the bubbles produced at the diffusers require some vertical distance to fully transfer their upward motion to the surrounding wastewater.
The inclusion of the cylindrical shrouds 160 in the illustrative wastewater treatment system 100 is also in response to the same experiments. The experiments unexpectedly showed, for example, that the use of a propeller without an encircling cylindrical shroud captured substantially less motion from the wastewater than a configuration with the cylindrical shroud in place. This effect appears to be due to the channeling properties of the cylindrical shrouds 160, which effectively vector the motion of the wastewater into a largely upward direction.
Advantageously, a wastewater treatment system like the wastewater treatment system 100 shown in
It should again be emphasized that the above-described embodiments of the invention are intended to be illustrative only. Other embodiments can use different types and arrangements of elements for implementing the described functionality. These numerous alternative embodiments within the scope of the invention will be apparent to one skilled in the art.
In one or more other embodiments of the invention, for example, alternative diffuser designs such as, but not limited to, tube- and strip-type diffusers may be utilized in addition to or as a replacement for the disk diffusers shown in
In addition, other embodiments within the scope of the invention may utilize propeller designs different from the particular propeller design shown in
In even one or more additional alternative embodiments of the invention, electrical storage devices such as batteries may be utilized to store the energy recovered from a wastewater treatment system like the wastewater treatment system 100 described above.
While the propellers 170 in the wastewater treatment system 100 were arranged so as to predominantly capture vertical motion in the body of wastewater 120, propellers can additionally or alternatively be arranged so that they are operative to capture lateral motion in a body of wastewater. An illustrative embodiment of such an arrangement is shown in
Lastly, while the above-described embodiments have focused on actuating generators to produce electrical energy, alternative embodiments of the invention may be arranged to share kinetic energy between elements of the same wastewater treatment tank or elements of separate wastewater treatment tanks A perspective view of an illustrative embodiment of such an arrangement is shown in
In closing, it should again be emphasized that all the features disclosed herein may be replaced by alternative features serving the same, equivalent, or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
Moreover, all the features disclosed herein may be replaced by alternative features serving the same, equivalent, or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
Finally, any element in a claim that does not explicitly state “means for” performing a specified function or “step for” performing a specified function is not to be interpreted as a “means for” or “step for” clause as specified in 35 U.S.C. §112, ¶6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. §112, ¶6.
| Number | Date | Country | |
|---|---|---|---|
| 61545642 | Oct 2011 | US |
