Patent Application
20190344221
The present invention relates generally to remediation of fluids, and more particularly, a system and method for utilizing hydrodynamic cavitation to prevent or obviate membrane fouling and/or scaling as it pertains to fluid treatment systems, generally, and to reverse osmosis (RO) systems, more specifically.
The many diverse activities of humans produce innumerable waste materials and by-products. As the environmental, health and industrial impact of pollutants increase, it has become increasingly important to develop new methods for the rapid and efficient removal of a wide range of contaminants from polluted waters and other liquids. Remediation, as it is often referred to, aims to reduce or eliminate pollutants and other unsafe materials from fluid.
Many methods of remediation exist. Some biological treatment techniques include bioaugmentation, bioventing, biosparging, bioslurping, and phytoremediation. Some chemical treatment techniques include ozone and oxygen gas injection, chemical precipitation, membrane separation, ion exchange, carbon absorption, aqueous chemical oxidation, and surfactant enhanced recovery. Some chemical techniques may be implemented using nanomaterials. Physical treatment techniques include, but are not limited to, pump and treat, air sparging, and dual phase extraction.
One example of a remediation technique that incorporates the use of membrane technology is reverse osmosis (RO), which is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from contaminated water by pushing water under pressure through a semi-permeable membrane, which is a membrane that will allow the passage of water molecules but not the majority of dissolved salts, organics, bacteria, and pyrogens.
RO works by using a high-pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable membrane, leaving almost all of dissolved salts behind in the reject stream. The desalinated water that is demineralized or deionized is called permeate water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream. As the feed water enters the RO membrane under pressure, the water molecules pass through the semi-permeable membrane and the salts and other contaminants are not allowed to pass and are discharged through the concentrate stream. In some RO systems, the concentrate stream can be fed back into the RO system through the feed water supply and recycled through the RO system. The water that makes it through the RO membrane is called permeate or product water and usually has around 95%-99% of the dissolved salts removed from it.
Reverse osmosis can remove many types of dissolved and suspended species from water, including bacteria, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective”, this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as solvent molecules) to pass freely. The solute, many times, include silica, barium and other solids. An example of a RO membrane is disclosed in U.S. Pat. No. 4,277,344, which describes an aromatic polyamide film which is the interfacial reaction product of an aromatic polyamine having at least two primary amines substituents with an aromatic acyl halide having at least three acyl halide substituents.
While RO is itself efficient, problems exists due to what is referred to as “membrane fouling,” which occurs when contaminants accumulate on the membrane surface effectively plugging the membrane and drastically reducing its remediation effectiveness. Fouling typically occurs in the front end of a RO system and results in a higher pressure drop across the RO system and therefore a lower permeate flow. Fouling mainly stems from three sources, namely: (i) particles in the feed water (e.g. solute or concentrate); (ii) buildup of sparsely soluble minerals; and (iii) byproducts of microorganism growth. Because of fouling, membranes must be cleaned frequently, which is costly and overall reduces the efficiency of the system by requiring more maintenance. In addition, cleaning the membranes is often expensive and leads to shorter service life of the membrane elements. This is especially true when more than one fouling condition prevails, which can leave the membrane irreversibly fouled with the only suitable solution is the complete replacement of the membrane elements.
Several pre-treatment methods using both mechanical and chemical treatments have been suggested to diminish membrane fouling. For example, antiscalant may be injected into the supply prior to reaching the RO membrane. However, this only delays the scale formation process. This delay is sufficient to avoid precipitation of calcium carbonate and calcium sulfate on the membrane surface. As this delay is for a finite period, scaling can take place in systems on shut down. Another example is that dispersant can be injected in the feed water. Dispersants keep fine suspended solids from coagulating and coming down on the membrane surface. Proper use of dispersants can minimize fouling due to problem particulates that are difficult to pre-filter. However, dispersants have the same problems as anti-scalents. For example, U.S. Pat. No. 6,365,101 discloses a method for inhibiting scale deposits in an aqueous system comprising a comprises at least one of polyvalent metal silicate and polyvalent metal carbonate, wherein the aqueous system has a pH of at least about 9, and wherein a mean particle size of the anti-scalant is less than about 3 microns.
Another pre-treatment solution includes the use of a multi-media filter to help prevent fouling. A multi-media filter typically contains three levels of media consisting of anthracite coal, sand and garnet, with a supporting layer of gravel at the bottom. The filter media arrangement allows the largest dirt particles to be removed near the top of the media bed with the smaller dirt particles being retained deeper in the media. This allows the entire bed to act as a filter allowing much longer filter run times and more efficient particulate removal. Further methods also include the use of microfiltration membranes, water softeners that help exchange scale forming ions with non-scale forming ions, insertion of sodium bisulfit, and granular activate carbon.
However, these current pretreatment methods can be costly and fouling still occurs at a rate at which it may be deemed inefficient. Furthermore, regardless of the level of care taken, fouling will take place eventually to some extent given the extremely fine pore size of a RO membrane no matter how effective your pretreatment and cleaning schedule is.
As such, post-treatment methods have also been suggested as well. For example, methods to change the electrical charge of the membrane surface to repel certain solutes have been proposed, as has certain coating for membrane surfaces been disclosed. For example, U.S. Pat. No. 6,913,694 describes aa selective membrane is a composite polyamide reverse osmosis membrane in which a hydrophilic coating has been applied to the polyamide layer of the membrane, the hydrophilic coating being made by (i) applying to the membrane a quantity of a polyfunctional epoxy compound, the polyfunctional epoxy compound comprising at least two epoxy groups, and (ii) then, cross-linking the polyfunctional epoxy compound in such a manner as to yield a water-insoluble polymer.
Further, U.S. Pat. No. 9,089,820 describes a selective membrane that is a composite polyamide reverse osmosis membrane having a hydrophilic coating made by covalently bonding a hydrophilic compound to the polyamide membrane, the hydrophilic compound including (i) a reactive group that is adapted to covalently bond directly to the polyamide membrane, the reactive group being at least one of a primary amine and a secondary amine; (ii) a non-terminal hydroxyl group; and (iii) an amide group. In another embodiment, the hydrophilic compound includes (i) a reactive group adapted to covalently bond directly to the polyamide membrane, the reactive group being at least one of a primary amine and a secondary amine; (ii) a hydroxyl group; and (iii) an amide group, the amide group being linked directly to the hydroxyl group by one of an alkyl group and an alkenyl group.
However, these methods have achieved only moderate success, can be expensive, and also make cleaning the membranes more difficult. Accordingly, there is a need for an improved system and method to prevent membrane fouling. One potential solution would be the use of hydrodynamic cavitation prior to the contaminated water being fed through the RO membrane.
Cavitation, generally, is the formation of vapor cavities in a liquid that creates small liquid-free zones. In engineering terminology, the term cavitation is used in a narrower sense, namely, to describe the formation of vapor-filled cavities in the interior or on the solid boundaries created by a localized pressure reduction produced by the dynamic action of a liquid system.
In hydrodynamic cavitation, decontamination may be achieved through the use of submerged jets which trigger hydrodynamic cavitation events in the liquid. These cavitation events drive chemical reactions by generating strong oxidants and reductants, and efficiently decomposing and destroying contaminating organic compounds, as well as some inorganics. These same cavitation events both physically disrupt or rupture the cell walls or outer membranes of microorganisms (such as E. coli and Salmonella) and larvae (such as Zebra mussel larvae), and also generate bactericidal compounds, such as peroxides, hydroxyl radicals, etc., which assist in the destruction of these organisms. Following disruption of the cell wall or outer membrane, the inner cellular components are susceptible to oxidation.
Cavitation technology has uses in a wide variety of industrial and ecological remediation settings, including but not limited to farming, mining, pharmaceuticals, food and beverage manufacture and processing, fisheries, petroleum and gas production and processing, water treatment and alternative fuels. With such a wide field of use, companies have been increasingly eager to further develop cavitation technologies.
Some examples include the use of rotating jet nozzles for cleaning and maintenance purposes disclosed in U.S. Pat. No. 5,749,384 (Hayasi, et al.) and U.S. Pat. No. 4,508,577 (Conn et al.). The apparatus of Hayashi employs a driving mechanism capable of causing the jet nozzle itself to travel upward-and-downward, to rotate and swing. Conn et al. describe the rotation of a cleaning head including at least two jet forming means, for cleaning the inside wall of a conduit.
These current hydrodynamic cavitation technologies, in many cases, aim to reduce particle distribution size of suspended solids, such as the kind often found in RO to be the cause of membrane fouling. Despite the advances in utilizing cavitation, there has remarkably been little to no use of cavitation in combination with RO that can take advantage of the benefits of cavitation to assist in preventing membrane fouling. Accordingly, there is a need for a new system and method incorporation hydrodynamic cavitation into RO to create a more efficient and effective RO process that also reduces the likelihood of membrane fouling.
The following summary of the invention is provided in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.
To achieve the foregoing and other aspects and in accordance with the purpose of the invention, a system and method for preventing membrane fouling in a fluid treatment system.
In an embodiment of the present invention, a system is provided to prevent membrane fouling, the system for preventing membrane fouling in a fluid treatment system having at least one membrane, the system comprising a hydrodynamic cavitating reactor for cavitating a fluid flow prior to injecting it into the fluid treatment system and through the at least one membrane; wherein after undergoing hydrodynamic cavitation in the cavitation reactor, solid components in the fluid change their (i) molecular structure, (ii) a charge, or both, such that the components repulse each other and disperse around an edge of the membrane to prevent fouling.
In an embodiment of the present invention, a method for preventing membrane fouling in a fluid treatment system having at least one membrane is provided. The method comprises hydrodynamically cavitating a fluid flow prior to injecting it into the fluid treatment system and through the at least one membrane; wherein after undergoing hydrodynamic cavitation in the cavitation reactor, solid components in the fluid change their (i) molecular structure, (ii) a charge, or both, such that the components repulse each other and disperse around an edge of the membrane to prevent fouling.
This method is useful in areas such as industrial and ecological remediation settings, including, for example, municipal drinking water, de-salination, farming, mining, pharmaceuticals, food and beverage manufacture and processing, fisheries, petroleum and gas production and processing, water treatment and alternative fuels. Particularly, the system and method is useful in settings that utilize filters having membranes that are prone to fouling, such as in reverse osmosis systems and water desalinization.
Another object of the present invention is to provide a new and improved system and method that is easy and inexpensive to construct.
Other features, advantages, and aspects of the present invention will become more apparent and be more readily understood from the following detailed description, which should be read in conjunction with the accompanying drawings.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale.
The present invention is best understood by reference to the detailed figures and description set forth herein.
Embodiments of the invention are discussed below with reference to the Figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. For example, it should be appreciated that those skilled in the art will, in light of the teachings of the present invention, recognize a multiplicity of alternate and suitable approaches, depending upon the needs of the particular application, to implement the functionality of any given detail described herein, beyond the particular implementation choices in the following embodiments described and shown. That is, there are numerous modifications and variations of the invention that are too numerous to be listed but that all fit within the scope of the invention.
It is to be further understood that the present invention is not limited to the particular methodology, compounds, materials, manufacturing techniques, uses, and applications, described herein, as these may vary. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “an element” is a reference to one or more elements and includes equivalents thereof known to those skilled in the art. Similarly, for another example, a reference to “a step” or “a means” is a reference to one or more steps or means and may include sub-steps and subservient means. All conjunctions used are to be understood in the most inclusive sense possible. Thus, the word “or” should be understood as having the definition of a logical “or” rather than that of a logical “exclusive or” unless the context clearly necessitates otherwise. Structures described herein are to be understood also to refer to functional equivalents of such structures. Language that may be construed to express approximation should be so understood unless the context clearly dictates otherwise.
As used herein, the term “concentrate stream” shall mean the stream of water that carries the concentrated contaminants that did not pass through the RO membrane. Reject water may also be referred to herein as the “reject stream.”
As used herein, the term “contaminated water” shall mean water molecules in combination with dissolved salts, organics, bacteria and pyrogens.
As used herein, the term “permeate water” shall mean the desalinated water that is demineralized or deionized after passing through an RO membrane. Permeate water may also be referred to herein as “product water.”
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Preferred methods, techniques, devices, and materials are described, although any methods, techniques, devices, or materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. Structures described herein are to be understood also to refer to functional equivalents of such structures. The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings.
Those skilled in the art will readily recognize, in accordance with the teachings of the present invention, that any of the foregoing steps and/or system modules may be suitably replaced, reordered, removed and additional steps and/or system modules may be inserted depending upon the needs of the particular application, and that the systems of the foregoing embodiments may be implemented using any of a wide variety of suitable processes and system modules, and is not limited to any particular computer hardware, software, middleware, firmware, microcode and the like. For any method steps described in the present application that can be carried out on a computing machine, a typical computer system can, when appropriately configured or designed, serve as a computer system in which those aspects of the invention may be embodied.
While exemplary embodiments of the present invention will be described with reference to certain industries in which cavitation finds use, a skilled artisan will realize that embodiments of the invention are applicable to any type application in which cavitation is beneficial.
The system and method of the present invention prevent membrane fouling and remediate fluids. The system is configured to change the molecular and/or structural characteristic of the organic and inorganic species of concentrate that in normal circumstances clogs or fouls membranes in filtration systems. The detailed elements and specific embodiments of the present decontamination system can be best appreciated by further understanding the cavitation phenomenon employed to drive the physical and chemical decontamination reactions. Due to large pressure drop in flow, microscopic bubbles grow in the regions of pressure drop and collapse in the regions of pressure rise. When subjected to cavitation, various molecules in the liquid undergo dissociation and form free radicals, which are powerful oxidizing or reducing agents. For example, in aqueous liquids, the dissociation of water to form hydroxyl radicals occurs under intense cavitation due to the growth and collapse of microscopic bubbles. Analogous dissociation of other molecules may occur as a result of cavitation in aqueous solutions as well as in non-aqueous liquids and solutions, producing radicals which similarly aid in the decontamination reactions described herein. Moreover, cavitation generated in any liquid environment will result in the physical disruption of contaminants, without regard to the generation of particular radicals. The methods and systems of this invention will be applicable for all fluid environments comprising contaminants susceptible to decomposition via the physical and/or chemical effects of the cavitation employed.
The inventors have found that using the system and methods described herein, the concentrate changes form and does not foul the membranes of a RO membrane, as described herein. The inventors have also found that the system and methods are useful in other types of filtration utilizing membrane technology.
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In the current embodiment, there is only one pump 148 which is configured to operate at a high pressure. In optional embodiments, the pump 148 may be operated at a different pressure to account for the concentration of different types of contaminants found within the contaminated water (e.g., arsenic, lead, radium, cadmium, and zinc). In even other optional embodiments, more than one pump 148 may be used.
Although simple rectangular tanks are illustrated in
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It was found that once the fluid passed through the cavitation reactor of
The filters did not foul at nearly the same rate when RO ran by itself, this being s=discussed with relation to
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An example of wastewater treatment using membrane technology is RO. RO may utilize, for example, membranes that are spiral wound elements which comprise a sandwich consisting of two membrane sheets with an inserted permeate carrier is glued together and a feed spacer is inserted between the opposing membrane surfaces to complete the membrane package. The membrane package is wound around a perforated central tube through which the permeate exits the element. In a typical setting, the membranes will collect permeate which act as a “fouling layer.” The fouling layer typically consists of colonies of microbes, salts and inorganics such as Al, As, Ch, Co, Mg, BaSO4, O, S, Ni, P, Si, Fe, Ba and Sr and the like.
After undergoing cavitation in the reactor 204, the components in brackish or brown water change their molecular structure and/or charge of the molecules of the precipitate to make them “naturally” disperse and not clog or foul the membrane. In this way, cavitating the fluid, or even cavitating the concentrate after a first run through a RO membrane, as a pre-treatment method and remediation technique reduce the likelihood of the RO membrane being subject to clogging or fouling. If cavitation is used at a “first pass”, effective pre-treatment of RO feed water (for complete or partial removal of potential foulants such as particulates, colloids, and organic matter).
It was found that the buildup on the outside of the filters consisted of a fine white powder containing small amounts of larger aggregates, and strongly resembles the appearance of corn starch. The power was analyzed via ICP/OES to detect inorganic components present in the sample. Given the results of solubility tests, it was suspected the powder to be a heterogeneous mixture of insoluble salts. Any metallic components detected by elemental analysis can thus be assumed to be the cationic species in these salt crystals. By far the most abundant metal was found to be calcium, followed by magnesium and potassium. Molar ratios between these metals were determined as follows: Calcium: Magnesium (mole: mole) 18.6:1 and Calcium: Potassium (mole: mole) 114:1. Trace amounts of the following metals were also detected (less than 1 ppm each): barium, cobalt, copper, molybdenum, nickel, titanium, vanadium, zinc and silver. The following elements were detected by the instrument and produced reliable spectra, but we were unable to quantify them: carbon, sulfur and phosphorous.
In order to determine the anionic components of the powder, a small sample was analyzed via ion chromatography (IC). The anions tested for were fluoride, chloride, nitrite, sulfate, bromide, and phosphate. Since nitric acid was used to dissolve the powder, we were unable to test for nitrate.
Based on the available data, it was concluded the powder in question is primarily composed of calcium sulfate (>90%) with magnesium sulfate and trace amounts of the aforementioned metals making up the remaining portion of the powder. Although this conclusion was reached largely by qualitative means, it is supported by observed empirical data and the known properties of calcium sulfate. The literature value for calcium sulfate's solubility product (KSP) is 9×10−6, which is consistent with our observation of the powder being sparingly soluble in water. Both calcium sulfate and magnesium sulfate also appear as white powders, which matches the physical appearance of the powder analyzed by the laboratory.
Finally, based on data from the input streams there appears to be a known source for calcium and magnesium to enter the hydrostatic cavitation apparatus. Water quality analysis of the concentrate input steam found both calcium and magnesium to be present at high levels. There appears to be a process by which these two cations react with sulfate to form insoluble aggregates in the hydrostatic cavitation process, which aids in avoiding filter fouling.
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During testing, not only did approximately 55-65% of the fluid get reclaimed and become useable for production water, after running the contaminated water through the cavitation reactor 304, the RO membrane 306 did not foul as they did if the contaminated water didn't undergo cavitation at all. Instead, the pressure on the membranes was maintained at an approximately stable pressure throughout daily cycles. Under “normal” circumstances in RO, pressure on the membranes builds throughout the process as precipitate builds up. An examination of the filters showed that once the contaminated water was run through the cavitation reactor 304, the fouling layer did not build up on the RO membranes 306, or at least, built up at a much lower rate. The RO membrane 306 comprises a plurality of membranes having in exemplary embodiments pore sizes range from 0.0001 μm to 0.001 μm such that is able to retain mostly all molecules except for water and due to the size of the pores, the required osmotic pressure is significantly greater than other forms of filtration. Thus, particulate build up may occur and foul the RO membrane 306, and also, cause a loss of production capacity and increase the pressure until a failure condition, at times, may occur.
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The example is for the purpose of illustrating an embodiment and is not to be construed as a limitation.
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Beginning with the existing Train A, the containment water is gathered from the feed 602. A pump 604 pushes the contaminated water towards the reactor 606 and centrifuge 608 that comprises the hydrodynamic cavitation system. Once the contaminated water is passed through the centrifuge 608, the solids are diverted to the solids storage tank 610 and the remaining water then sent to the train A RO membrane 614 through the pump 612, which is designed to provide enough pressure to cause reverse osmosis to occur as the water passes through the train A RO membrane 614. Once through the RO membrane 614, the permeate is sent to the permeate storage tank 618 via the pump 616, while the concentrate is sent to the concentrate feed 622 via the pump 620.
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The reactor plate 146 may be formed of a material that is relatively impervious to cavitation's, such as a metal alloy, or in some embodiments, a resilient elastomeric material. The reactor plate 146 may be embodied in a variety of different shapes and configurations. For example, the plate may be conically shaped, including a conically-shaped surface that induces a vortex, or may be fully cyclical as shown. It should be appreciated other shapes may be employed as well to a varying degree.
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First air injector 116 is in communication with an additional controller 906, which is in turn, in communication with PLC 902. In an optional embodiment of the present invention, the PLC 902 is configured to control air pressure based on the degree of cavitation required. The controller 906 is also in communication with the reactor plate 146 and a baffle (not shown) to rotate and tilt the reactor plate to vary the degrees of cavitation. Like the first air injector, a second air injector 120 and control valves 124 are in communication with the controller 906 for similar purposes.
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The first and second air injectors are configured to induce cavitation into the fluid to form vapor cavities in a liquid (i.e. small liquid-free zones, bubbles or voids), which occurs when the fluid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. In this way, the injectors are used to enhance chemical reactions and propagate reactions due to free radical formation in the process due to disassociation of vapors trapped in the cavitating bubbles.
A reactor plate 146 is disposed within the line 101 between the first and second air injectors and is communication with the PLC 902, and the PLC 902 is configured to tilt the reactor plate 146 in various directions (e.g., 15 degrees). The reactor plate, discussed in greater with relation to
An additional valve 124, e.g., butterfly valve, is disposed in the line to drop the head pressure when needed for egress of the fluid to outlet 104. The valve 124, like other valves in the system, is communicably coupled to the PLC such that it is fully autonomous.
While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to these herein disclosed embodiments. Rather, the present invention is intended to cover all of the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, the feature(s) of one drawing may be combined with any or all of the features in any of the other drawings. 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 herein are not to be interpreted as the only possible embodiments. Rather, modifications and other embodiments are intended to be included within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. US62/503,313, filed May 8, 2017.
