Ballasted anaerobic method for treating wastewater

Abstract

A ballasted anaerobic system for treating wastewater including at least one anaerobic treatment reactor. A weighting agent impregnation subsystem is configured to mix weighting agent with the biological flocs to form weighted biological flocs to create a weighted anaerobic sludge blanket in the at least one anaerobic treatment reactor. A weighting agent recovery subsystem is configured to recover the weighting agent from excess sludge and reintroduce the weighting agent to the weighting agent impregnation subsystem.

Description

FIELD OF THE INVENTION

This invention relates to a ballasted anaerobic system and method for treating wastewater.

BACKGROUND OF THE INVENTION

One method of treating wastewater, such as wastewater from ethanol plants, breweries, pharmaceutical plants, food processing plants, pulp and paper facilities, and the like, is to use an anaerobic treatment reactor. The anaerobic treatment reactor is typically seeded with a population of microorganisms that ingest contaminants in the influent wastewater to form biological flocs or granules (hereinafter “biological flocs”). Wastewater is typically fed into the bottom of the anaerobic treatment reactor and microorganisms consume the waste therein and from biological flocs. After a sufficient startup period, the biological flocs form an anaerobic sludge blanket near the bottom of the anaerobic treatment reactor.

In operation, wastewater is fed into the bottom of the anaerobic treatment reactor and flows upward through the anaerobic sludge blanket bringing the wastewater in contact with the microorganisms that consume the waste therein. The treated wastewater then flows over the weir of the anaerobic treatment reactor as clean effluent.

Conventional anaerobic treatment reactor systems have a limited difference in the specific gravity between the anaerobic sludge blanket and the influent wastewater. Therefore, if the flow rate of the influent wastewater is too high, the limited specific gravity difference can cause the sludge blanket to become diffuse. The result may be an elevated loss of microorganisms over the weir which can result in compromised treatment efficiency and system capacity.

BRIEF SUMMARY OF THE INVENTION

This invention features a ballasted anaerobic system for treating wastewater including at least one anaerobic treatment reactor. A weighting agent impregnation subsystem is configured to mix weighting agent with the biological flocs to form weighted biological flocs to create a weighted anaerobic sludge blanket in the at least one anaerobic treatment reactor. A weighting agent recovery subsystem is configured to recover the weighting agent from excess sludge and reintroduce the weighting agent to the weighting agent impregnation subsystem.

In one embodiment, the weighted anaerobic sludge blanket may be configured to treat wastewater and provide a treated effluent. The weighting agent impregnation subsystem may include an impregnation tank and at least one mixer. The weighting agent impregnation subsystem may include a storage subsystem for storing virgin weighting agent and dispensing the virgin weighting agent into the impregnation tank. The weighting agent impregnation subsystem may include a venturi mixer/eductor. The weighting agent recovery subsystem may include a separator subsystem for separating the weighting agent from the biological flocs. The separator subsystem may include a shear mill. The separator subsystem may include a centrifugal separator. The separator subsystem may include an ultrasonic separator. The separator subsystem may include a shear mill and a wet drum magnetic separator. The separator subsystem may include a shear mill and a centrifugal separator. The separator subsystem may include an ultrasonic separator and a wet drum magnetic separator. The separator subsystem may include an ultrasonic separator and a centrifugal separator. The shear mill may include a rotor and a stator, wherein the rotor and/or the stator includes slots sized as to optimize separation of weighting agent from the weighted biological flocs. A majority of the weighting agent may have a particle size less than about 100 μm. A majority of the weighting agent may have a particle size less than about 40 μm. A majority of the weighting agent may have a particle size less than about 20 μm. The weighting agent may include magnetite. The system may include a wasting subsystem for wasting excess sludge to control the population of microorganisms. The capacity of the system may be increased by increasing the concentration of microorganisms solids in the anaerobic treatment reactor by reducing the amount of the sludge wasted by the wasting subsystem. The weighted biological flocs may enhance the quality of the treated effluent by reducing suspended solids and associated contaminants therein.

This invention also features a ballasted anaerobic method for treating wastewater, the method including the steps of: a) receiving influent wastewater in at least one biological reactor, b) forming biological flocs in the at least one anaerobic treatment reactor, c) impregnating weighting agent into the biological flocs to form weighted biological flocs to create a weighted anaerobic sludge blanket, and d) recovering weighting agent from the weighted biological flocs to reintroduce the weighting agent to step c).

In one embodiment, the method may include the step of directing the wastewater through the weighted anaerobic sludge blanket to provide a treated effluent. The method may include the step of separating the weighting agent from the weighted biological flocs. The method may include the step of collecting the weighting agent and recycling the weighting agent to step c). The method may further include the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 100 μm. The method may further include the step of providing weighting agent in which the majority of the weighting agent has having a particle size less than about 40 μm. The method may further include the step of providing weighting agent in which the majority of the weighting agent has having a particle size less than about 20 μm. The method may further include the step of enhancing the quality of the treated effluent by reducing suspended solids and associated contaminants therein.

The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic side-view of one embodiment of the ballasted anaerobic system for treating wastewater of this invention;

FIG. 2A is a schematic side-view showing in one example of a weighted sludge blanket formed at the bottom of the anaerobic treatment reactor shown in FIG. 1;

FIG. 2B is a schematic side-view of the system for treating wastewater shown in FIGS. 1 and 2A depicting one example of an effluent recycling line and gas collectors;

FIG. 3 is a microscopic photograph showing one example of weighting agent impregnated into biological flocs to form weighted biological flocs in accordance with this invention;

FIG. 4 is a schematic side-view showing another embodiment of the weighting agent impregnation subsystem shown in FIG. 1;

FIG. 5A is a schematic side-view of one embodiment of the separator shown in FIG. 1;

FIG. 5B is a schematic top view showing one example of slots in the rotor and stator of the shear mill shown in FIG. 5A;

FIG. 5C is a three-dimensional view of one embodiment of the shear mill in FIG. 5A;

FIG. 6 is a three-dimensional front-view of another embodiment of the separator shown in FIG. 1; and

FIG. 7 is a three-dimensional front-view of yet another embodiment of the separator shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

There is shown in FIG. 1 one embodiment of ballasted anaerobic system 10 for treating wastewater of this invention. System 10 includes at least one anaerobic treatment reactor 12, e.g., a bulk volume fermenter (BVF) treatment reactor, an up-flow anaerobic sludge blanket (UASB) treatment reactor, an internal circulation (IC) treatment reactor, an anaerobic contactor, a continuous stirred reactor, or similar type reactor. Anaerobic treatment reactor 12 receives flow of influent wastewater 14 by line 16. Anaerobic treatment reactor 12 is preferably covered as shown at 13 to create an anaerobic environment therein. Influent wastewater 14 is typically high strength wastewater from ethanol plants, breweries, pharmaceutical plants, pulp and paper facilities, or any similar type facilities or plants. Influent wastewater 14 is typically fed into bottom 15 of anaerobic treatment reactor 12 by line 16 and flows in an upward direction, as shown by arrows 17. Anaerobic treatment reactor 12 is preferably seeded with population of microorganisms which promotes growth of biological flocs 23. After a sufficient startup period, sludge blanket 18 forms near bottom 15 of anaerobic treatment reactor 12.

To overcome the problems discussed in the Background section above, system 10 includes weighting agent impregnation subsystem 26 which impregnates biological flocs 23 to form weighted biological flocs 25, FIG. 2A, to create weighted anaerobic sludge blanket 19. Weighting agent impregnation subsystem 26, FIGS. 1 and 2A, in one embodiment, includes impregnation tank 28 and mixer 30 which receives biological flocs from anaerobic sludge blanket 18, FIG. 1, and/or from weighted anaerobic sludge blanket 19, FIG. 2A, by line 32. Impregnation tank 28 also preferably receives virgin weighting agent 33, e.g., from feed hopper 34 by line 36, and/or recycled weighting agent 38 from weighting agent recovery subsystem 74 (discussed below). Mixer 30 mixes the biological flocs with virgin weighting agent 33 and/or with recycled weighting agent 38 in impregnation tank 28 to impregnate the weighting agent into the biological flocs to form weighted biological flocs 25. In one example, mixer 30 utilizes a mixing energy which is sufficient to impregnate the weighting agent into biological flocs to form weighted biological flocs. FIG. 3 shows a microscopic view of one example of weighting agent 33, 38 impregnated into biological flocs 23 to form weighted biological floc 25. The weighted biological flocs are then sent back to anaerobic treatment reactor 12 by line 37 and/or line 37′ connected to line 16 to form weighted anaerobic sludge blanket 19, FIG. 2A.

In operation, influent wastewater 14 is fed into bottom 15 of anaerobic treatment reactor 12 by line 16 and flows upward through weighted anaerobic sludge blanket 19 bringing the wastewater in contact with the microorganisms that consume the waste therein to provide treated effluent 50 which flows over weir 27. In one design, anaerobic treatment reactor 12, FIG. 2B, may include weirs 60 and 62 which treated effluent 50 flows over. Anaerobic treatment reactor 12 may also include one or more gas collectors 64, 66, and 68 coupled to line 70 which remove methane, carbon dioxide, and other gases generated by the anaerobic process of system 10 discussed herein. Treated effluent 50 may be recycled by line 41 to line 16 to maintain a constant upflow velocity in anaerobic treatment reactor 12, e.g., as shown by arrows 17. Recycling treated effluent 50 may also be used to adjust the flow rate of the influent in line 16.

Increasing the density of weighted anaerobic sludge blanket 18, FIG. 1, to form weighted anaerobic sludge blanket 19, FIG. 2A, creates a significant difference between the specific gravities of the influent wastewater 14 and weighted anaerobic sludge blanket 19. The result is system 10 can accommodate higher loading rates (flow rate/reactor size) of influent wastewater while preventing weighted sludge blanket 19 from becoming diffuse. Therefore, system 10 is more efficient and effective than conventional anaerobic treatment reactor systems. The weighted biological flocs in weighted anaerobic sludge blanket 19 also improve the quality of the treated effluent by reducing suspended solids and associated contaminants therein.

In one embodiment, the weighting agent may be magnetite, or any similar type weighting agent or magnetically separable inorganic material known to those skilled in the art which increases the density of the biological flocs. In one example, the majority of the weighting agent particles have a size less than about 100 μm. In other examples, the majority of weighting agent particles has a size less than about 40 μm, or the majority of particle size of the weighting agent may be less than about 20 μm.

Weighting agent recovery subsystem 74 preferably includes separator 78 which recovers the weighting agent from the excess weighted biological flocs in line 76 and reintroduces (recycles) the weighting agent to weighting agent impregnation subsystem 26. Weighting agent recovery subsystem 74 may include recovery subsystem 83, e.g., a wet drum magnetic separator or similar type device, which recovers the excess weighted biological flocs processed by separator 78. Recovery subsystem 83 reintroduces recovered weighting agent 38 to weighting agent impregnation subsystem 26.

System 10 also preferably includes wasting subsystem 85 which wastes the excess sludge in line 76 generated by weighting agent recovery subsystem 74 by line 87 to control the population of microorganisms in anaerobic treatment reactor 12. In one example, the capacity of system 10 may be increased by increasing the concentration of microorganisms in weighted anaerobic sludge blanket 19 by reducing the amount of sludge wasted by wasting subsystem 85.

System 10, FIG. 1, may also utilize weighting agent impregnation subsystem 26′, FIG. 4, where like parts have been given like numbers. In this example, weighting agent impregnation subsystem 26′ includes venturi mixer/eductor 27 with nozzle 31 and funnel 45 which receives virgin weighting agent 33, e.g., from tank 34 by line 36, and/or recycled weighting agent 38 from separator 78. Venturi mixer/eductor 27 preferably receives sludge from anaerobic sludge blanket 18, FIG. 1, and/or from anaerobic sludge blanket 19, FIG. 2A, by line 32.

In operation, the velocity of sludge in line 32 is increased through nozzle 31. Virgin weighting agent 33 and/or recycled weighting agent 38 is dispensed into funnel 45 and then enters nozzle 31 by line 39 and travels downstream to line 37 and/or line 37′ as shown in FIGS. 1 and 2A. The widening of line 37, 37′, FIG. 4, shown at 41 induces intimate mixing and entrainment, as shown at 43. This impregnates the virgin and/or recycled weighting agent into the biological flocs to form weighted biological flocs. The weighted biological flocs are then returned to anaerobic treatment reactor 12 by line 37, and/or line 37′, FIGS. 1 and 2A, to form weighted anaerobic sludge blanket 19, FIG. 2A.

In one design, separator subsystem 78 discussed above may be configured as shear mill 112, FIG. 5A, which shears the sludge in line 76 to separate the weighting agent from the weighted biological flocs. Shear mill 112 ideally includes rotor 80 and stator 82. In operation, the excess sludge in line 76 enters shear mill 112 and flows in the direction of arrows 180 and enters rotor 80 and then stator 82. Shear mill 112 is designed such that there is a close tolerance between rotor 80, FIG. 5B and stator 82, as shown at 93. Rotor 80 is preferably driven at high rotational speeds, e.g., greater than about 1,000 r.p.m. to form a mixture of weighting agent and obliterated flocs in area 181, FIG. 5A, of shear mill 112. The mixture of weighting agent and obliterated flocs exits shear mill 112 by line 79, as shown by arrows 184. FIG. 5C shows in further detail the structure of one embodiment of shear mill 112. Preferably, rotor 80, FIGS. 5A-5C, and/or stator 82 includes slots which function as a centrifugal pump to draw the excess sludge from above and below rotor 80 and stator 82, as shown by paths 182, FIG. 5A, and then hurl the materials off the slot tips at a very high speed to break the weighted biological flocs into the mixture of weighting agent and obliterated flocs. For example, rotor 80, FIG. 5B, may include slots 186, and stator 82 may include slots 188. Slots 186 in rotor 80 and/or slots 188 in stator 82 are preferably optimized to increase shear energy to efficiently separate the weighting agent from the weighted biological flocs. The shear developed by rotor 80 and stator 82 depends on the width of slots 186 and 188, the tolerance between rotor 80 and stator 82, and the rotor tip speed. The result is shear mill 112 provides a shearing effect which effectively and efficiently separates the weighting agent from the weighted biological flocs to facilitate recovery of the weighting agent.

In another design, separator subsystem 78, FIG. 6, where like parts have been given like numbers, may be configured as ultrasonic separator 116. Ultrasonic separator 116 typically includes one or more ultrasonic transducers, e.g., ultrasonic transducer 262, 264, 266, 268, and/or 270, available from Hielscher Ultrasonics GmbH, Stuttgart, Germany, which generates fluctuations of pressure and cavitation in the excess sludge in line 76. This results in microturbulences that produce a shearing effect to create a mixture of weighting agent and obliterated flocs to effectively separate the weighting agent from the weighted biological flocs in the excess sludge. The resulting mixture of weighting agent and obliterated flocs exits ultrasonic separator 116 by line 79.

In yet another design, separator subsystem 78, FIG. 7, where like parts have been given like numbers, may be configured as centrifugal separator 118. Centrifugal separator 114 typically includes cylindrical section 302 located at the top of hydrocyclone 300 and conical base 304 located below section 302. The excess sludge in line 76 is fed tangentially into cylindrical section 302 via port 303. Smaller exit port 306 (underflow or reject port) is located at the bottom of conical section 304 and larger exit port 308 (overflow or accept port) is located at the top of cylindrical section 302.

In operation, the centrifugal force created by the tangential feed of the sludge by port 303 causes the denser weighting agent to be separated from the biological flocs in the excess sludge. The separated weighting agent is expelled against wall 308 of conical section 304 and exits at port 306. This effectively separates the weighting agent from the weighted biological flocs. The recovered weighting agent 38 exits via port 306 and may be deposited to weighting agent impregnation system 26, 26′, FIGS. 1 and 4. The less dense biological flocs remain in the sludge and exit via port 308 through tube 310 extending slightly into the body of the center of centrifugal separator 118.

Although as discussed above, separator subsystem 78 may be configured as a shear mill, an ultrasonic separator, or a centrifugal separator, this is not a necessary limitation of this invention. In other designs, separator subsystem 78 may be configured as a tubular bowl, a chamber bowl, an imperforate basket, a disk stack separator, and the like, as known by those skilled in the art.

In the example above where a separator 78, FIGS. 5A-5C, is configured as shear mill 112 to create the mixture of weighting agent and obliterated biological flocs, a wet drum magnetic separator or centrifugal separator 118, FIG. 7, may be used to recover the weighting agent therefrom.

In the example where separator subsystem 78, FIG. 6, is configured as an ultrasonic separator 116 to create the mixture of weighting agent and obliterated biological flocs, a wet drum magnetic separator or centrifugal separator 118, FIG. 7, may be used to recover the weighting agent therefrom.

The result of recovering and recycling the weighting agent as discussed above with reference to FIGS. 5A-7 significantly reduces the operating costs of wastewater treatment system 10.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for any claim element amended.

Claims

1. A ballasted anaerobic method for treating wastewater, the method comprising: receiving influent wastewater in at least one anaerobic treatment reactor;forming biological flocs in the at least one anaerobic treatment reactor; andimpregnating weighting agent into the biological flocs to form weighted biological flocs;allowing the weighted biological flocs to settle to create a weighted anaerobic sludge blanket; anddirecting the wastewater through the weighted anaerobic sludge blanket to provide a treated effluent.

2. The method of claim 1 further including the step of recycling the weighting agent.

3. The method of claim 1 further including the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 100 μm.

4. The method of claim 1 further including the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 40 μm.

5. The method of claim 1 further including the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 20 μm.

6. The method of claim 1 further including the step of enhancing the quality of the treated effluent by reducing suspended solids and associated contaminants therein.

7. The method of claim 1, further comprising wasting excess sludge from the at least one anaerobic treatment reactor.