Method for removal of contaminants from water and resource recovery through use of colloidal gas aphrons

Abstract

A method for creating colloidal gas aphrons (CGAs) and using the CGAs to remove contaminants from a contaminated water comprises feeding the contaminated water into a reactor; optionally adding at least one surface active substances to the reactor; fluidly connecting the reactor to a microbubble generation device that generates microbubbles therein; circulating the water from the reactor to the microbubble generation device and back to the reactor; creating the CGAs in the microbubble generation device and forwarding the CGA containing water to the reactor, wherein the CGAs adsorb the contaminates in the water and carries the contaminates to the surface of the water forming a layer of microfoam thereon; removing the layer of the microfoam; and extracting a treated water.

Description

METHOD FOR REMOVAL OF CONTAMINANTS FROM WATER AND RESOURCE RECOVERY THROUGH USE OF COLLOIDAL GAS APHRONSCross Reference to Related Applications

[0001] The present application claims the benefit of U.S. Provisional Patent Application No. 63 / 545,391 filed October 24, 2023, being incorporated herein by reference in its entirety for all purposes.Field of the Invention

[0002] The present invention relates to a method for generating colloidal gas aphrons (CGAs) and applications for removal of contaminants from water and resource recovery using the CGAs, in particular, for the removal of per- and polyfluoroalkyl substances (PFAS) from water using the CGAs.Background

[0003] PFAS are found in many drinking water supply sources throughout the world. Due to their numerous and widespread uses, mobility and persistence, PFAS have been found both in the environment and in human blood samples. Once released into the environment, PFAS may easily travel long distances and can contaminate the soil and drinking water sources, which may be surface or groundwater. Two most known species of this class of compounds are perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonic acid (PFOS).

[0004] High water solubility of these compounds make it difficult to treat the PFAS- impacted water. Conventional water treatment processes for their removal such as ion exchange and activated carbon both result in the generation of large quantities of solid waste containing PFAS.

[0005] CGAs are gas microbubbles in water encapsulated in a surfactant multilayer. The outer surface chemistry of these microbubbles is the same as that of the surfactant used to produce the CGA. This allows tailoring the surface chemistry of the microbubbles to remove or recover target components from water.

[0006] CGA bubbles retain the same charge as the surfactant solution from which they are generated. The layer of surfactant encapsulating gas bubbles creates repulsion among likely charged surfaces preventing microbubbles from coalescing giving CGAs some colloidal properties and making then more stable in water compared to regular foam.

[0007] CGAs have found numerous applications in fields where large interfacial surfacecontact areas and adsorption at interfaces are beneficial. These include biological separation, soil remediation, remediation of contaminated water, fermentation and bioreactors, material synthesis and oil recovery (Jauregi and Varley 2000).

[0008] CGAs, however, were generated by using mixing water at 8000-15000 rpm. Such high mixing rates are very difficult to achieve in industrial scale systems. Therefore, CGAs did not find much footprint in large-scale water treatment systems. A significant boost in efficiency of the CGA process achieved if a microbubble generation device is used to generate microbubbles instead. The advantages of CGAs generated through the combination of microbubbles and surface-active substances are simplicity and versatility for the applications in water and wastewater purification. By choosing an appropriate combination of the gas and gas bubble coating surfactant it is possible to tune the process to maximize the removal of individual compounds from water.

[0009] In addition, microbubble generation devices are commonly used in a variety of water treatment systems and, therefore, significantly simplify the process of generation of CGAs in large-scale installations.

[0010] US10752521 B2 discloses a system and method for treatment of soil and groundwater contaminated with PFAS discloses a method for PFAS removal from groundwater by injecting a gas through a diffuser into the water so that to form bubbles in the water. As a result it is claimed that one or more PFAS contaminants accumulate on bubbles that then rise to the surface of the water. The resulting foam is then collected and transported away where it condenses into a liquid and can be treated and / or disposed of. The gas that is injected is 95% nitrogen.

[0011] US10865128B2 discloses a method, apparatus, and system for the remediation of contaminated soils, groundwater, water, and / or waste using a combination of reagents, particularly treating various recalcitrant halogenated substances, such as perfluoroalkyls and polyfluoroalkyls. Particular combinations of reagents that may be used include but are not limited to: (1) persulfate, oxygen and ozone; (2) persulfate, salt, oxygen and ozone; (3) persulfate, phosphate, and / or oxygen; (4) persulfate, phosphate, oxygen and ozone; (5) persulfate, phosphate, salt and oxygen (6) persulfate, phosphate, salt, oxygen and ozone; (7) oxygen and salt; and (8) air and salt. The oligosaccharide is also disclosed that is cyclodextrin, hydrogen, iron, zero valent iron, ferrous sulfate, sulfur dioxide, hydrogen sulfide, dithionate, thiosulfate, iodinites, hydrogen peroxide, oxalic acid formic acid, ascorbic acid, vitamin B12, reducing sugars, sulfites, phosphites and hypophosphites.

[0012] US20230110561 A1 discloses a method for generating CGAs and using them for PFAS removal from water. CGAs are generated by mixing a gas, water, and one or moresurfactants together with high shear forces followed by introducing the CGAs and a PFAS- containing water. It is stated that the CGAs may be generated by using anionic or cationic surfactant by mixing at high speeds or surfactant concentration. The treatment may be with gas bubbles to remove PFAS from water gas bubbles or destruction of PFAS by plasma reactor or deployed in situ through wells into geologic ground formations.

[0013] Ebersbach et al. (Ebersbach, I., Ludwig, S. M., Constapel, M., & Kling, H. W., “An alternative treatment method for fluorosurfactant-containing wastewater by aerosol- mediated separation”’ Water Research, 101 , 333-340, 2016) discloses proposes alternative method for PFAS removal from electroplating wastewater using foam by sparging water with gas via a diffuser. The method required 60 to 120 min of treatment time to achieve over 99% removal rate.

[0014] Lee et al. (Lee, Y. C., Wang, P. Y., Lo, S. L., & Huang, C. P., “Recovery of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) from dilute water solution by foam flotation”, Separation and Purification Technology, 173, 280-285, 2017) descloses a method for PFOA and PFAS removal from water by foam flotation using metal activators such as Al(lll), Fe(lll), La(lll), Ca(ll), Fe(ll), and K(l). PFOS and FPOA had a removal efficiency of >99% in the presence of 11 .5 mM of Fe(lll) in 5 min.

[0015] Li et al. (Li, Y. F., Chien, W. Y., Liu, Y. J., Lee, Y. C., Lo, S. L., & Hu, C. Y. (2021)). Perfluorooctanoic acid (PFOA) removal by flotation with cationic surfactants. Chemosphere, 266, 128949) used a number of cationic surfactants to PFOA from water - cetyl-trimethyl-ammonium bromide (CTAB), tetra-n-butyl-ammonium bromide (TBAB), decyl-trimethyl-ammonium bromide (DTAB), n-octyl-trimethyl-ammonium bromide (OTAB) and sodium dodecylsulfate (SDS). Air bubbles were introduced into water by passing compressed air through a gas diffuser with a pore size of 25-50 pm. The dose of surfactants ranged from 0.5 to 1 .25 mM, which corresponds to 185 - 455 mg / L dose for CTAB.

[0016] Pal et al (Pal, P., Corpuz, A. G., Hasan, S. W., Sillanpaa, M., & Banat, F., “Simultaneous removal of single and mixed cationic / anionic dyes from aqueous solutions using flotation by colloidal gas aphrons”, Separation and Purification Technology, 255, 117684, 2021) discloses CGAs generated by the addition of sodium dodecyl benzenesulfonate (SDBS) methylene blue (MB) and Congo red (CR). Sodium alginate used to stabilize the CGAs. The SDBS concentration was 500 mg / L. CGAs were produced by stirring the solution at 3000 rpm.

[0017] Kulkarni et al. (Kulkarni, P. R., Aranzales, D., Javed, H., Holsen, T. M., Johnson, N. W., Richardson, S. D., Thagard, S.M. & Newell, C. J., “Process to separate per-and polyfluoroalkyl substances from water using colloidal gas aphrons”, Remediation Journal,32(3), 167-176, 2022) descloses a method for the removal of PFAS from water using two types of surfactants - cetyltrymethylammonium bromide (CTAB) also known as hexadecyltrimethylammonium bromide (HDTMAB) and sodium dodecylbenzene-sulfonate (NaDBS) at concentrations of 380 and 540 mg / L. CGAs were generated by mixing impacted water with a rotary tool capable of 5000-35,000 rpm. No perfluorooctanesulfonic acid (PFOS) removal was achieved in this study.Summary

[0018] There is disclosed a method for creating colloidal gas aphrons (CGAs) and using the CGAs to remove contaminants from a contaminated water, the method comprising the steps of: feeding the contaminated water into a reactor; optionally adding at least one surface active substance to the reactor; fluidly connecting the reactor to a microbubble generation device that generates microbubbles therein; circulating the water from the reactor to the microbubble generation device and back to the reactor; creating the CGAs with the microbubbles in the microbubble generation device and flowing the CGA containing water to the reactor, wherein the CGAs adsorb the contaminates and carries the contaminates to the surface of the water in the reactor forming a layer of microfoam thereon; removing the layer of the microfoam; and extracting a treated water from the reactor.

[0019] In some embodiments, the at least one surface active substance is a cationic surfactant selected from quaternary ammonium salts having the carbon chain length from 8 to 18.

[0020] In some embodiments, the cationic surfactant is selected from octyltrimethylammonium bormide (OTMAB) hexadecyltrimethylammonium bromide (HDTMAB), tetrabutylammonium bromide (TBAB), decyltrimethylammonium bromide (DTAB), octyltrimethylammonium bromide (OTAB), lauric arginate (LAE), benzethonium chloride, or alkylbenzyldimethylammonium chloride compounds.

[0021] In some embodiments, the at least one surface active substance is an anion surfactant.

[0022] In some embodiments, the anionic surfactant is sulfate, sulfonate, phosphate, carboxylate head groups, ammonium dodecyl sulfate, sodium dodecyl sulfate, sodiumdodecylbenzenesulfonate, other alkyl-ether sulfates selected from sodium laureth sulfate or sodium myreth sulfate.

[0023] In some embodiments, the contaminant is per- and polyfluoroalkyl substances (PFAS).

[0024] In some embodiments, the contaminant is organic or inorganic impurities in water.

[0025] In some embodiments, the size of the microbubble is 50-200 micrometers.

[0026] In some embodiments, the method further comprising the step of giving a sufficient residence time to have the CGAs rise to the surface of the water in the reactor.

[0027] In some embodiments, the sufficient residence time ranges from 2-20 min.

[0028] In some embodiments, the method further comprising the step of pumping the water from the microbubble generation device to the reactor, so that a water circulation loop is formed between the reactor and the microbubble generation device.

[0029] In some embodiments, the method further comprising the step of injecting a gas into the microbubble generation device to generate the microbubbles therein.

[0030] In some embodiments, the gas is nitrogen, hydrogen, carbon dioxide, ozone, oxygen, air or compressed air.

[0031] In some embodiments, the method further comprising the step of adding an additive to the reactor, so that the created CGAs are stable in the water.

[0032] In some embodiments, the additive is selected from beta-cyclodextrin, polyacrylamide, polyamine, chitosan, poly(diallyldimethylammoniumchloride), emulsifiers selected from xanthan gum or carboxymethylcellulose.

[0033] In some embodiments, the method further comprising the step of forwarding the treated water containing first residual CGAs to a second reactor forming a second layer of microfoam thereon; and removing the second layer of the microfoam and extracting a second treated water from the second reactor.

[0034] In some embodiments, the method further comprising the step of forwarding the treated water containing first residual CGAs to a second reactor forming a second layer of microfoam thereon; removing the second layer of the microfoam and extracting a second treated water from the second reactor that contains second residual CGAs; forwarding the second treated water to a third reactor forming a third layer of microfoam thereon; andremoving the third layer of the microfoam and extracting a third treated water from the third reactor, wherein a second water circulation loop is formed between the third reactor and a second microbubble generation device to generate second CGAs.

[0035] There is disclosed a method for creating colloidal gas aphrons (CGAs) and using the CGAs to remove contaminants from a contaminated water, the method comprising: feeding the contaminated water, a surface active substance and an additive to a first reactor; fluidly connecting the first reactor to a microbubble generation device that generates microbubbles therein by injecting a gas into the microbubble generation device; circulating the water from the first reactor to the microbubble generation device and back to the first reactor by pumping the water therein; creating the CGAs with the microbubbles in the microbubble generation device and flowing CGA containing water to the first reactor, wherein the CGAs adsorb the contaminants and carries the contaminates to the surface of the water forming a first layer of microfoam in the first reactor; removing the first layer of the microfoam; extracting a first treated water that contains first residual CGAs from the first reactor; forwarding the first treated water to a second reactor forming a second layer of microfoam thereon; removing the second layer of the microfoam; and extracting a second treated water from the second reactor.

[0036] In some embodiments, the method further comprising the step of giving a sufficient residence time to have the CGAs rise to the surface of the water in the first and second reactors, respectively.

[0037] In some embodiments, the sufficient residence time ranges from 2-20 min.Brief Description of the Drawings

[0038] For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:FIG. 1 shows the schematic representation of colloidal gas aphrons as described in prior art;FIG. 2 shows a block flow diagram of an exemplary embodiment of a one-stagesystem for CGA generation and PFAS removal;FIG. 3 shows a two-state system for CGA generation and PFAS removal in continuous mode;FIG. 4 shows a multi-state system for CGA generation and PFAS removal in continuous mode;FIG. 5 shows total PFAS removed 14.2 mg / L, 7.1 mg / L, 3.0 mg / L, and 1 mg / L surfactant (hexadecyltrimethylammonium bromide), referring to FIG. 3 The residence time for stage 1 and stage 2 were 5 min each.FIG. 6 shows the removal of individual PFAS compounds from impacted water, referring to FIG. 3; andFIG. 7 shows the removal of perfluourooctanoic acid (PFOA) and perfluorohexanoic acis (PFHxA) in a multistage CGA treatment process, referring to FIG. 4. The treatment residence time in each stage was 5 min.Description of Preferred Embodiments

[0039] Disclosed are systems and methods for generating colloidal gas aphrons (CGAs) and applications for removal of contaminants from water and resource recovery using CGAs. More specifically, the CGAs are generated by passing a contaminated water, to which surface-active substances or surfactants and other modifying additives are added, through a microbubble generation device that generates microbubbles with injecting a gas such as nitrogen, hydrogen, carbon dioxide, ozone, oxygen, or compressed air. The choice of the surfactant and the gas depends on the type and amount of the contaminants to be extracted or removed from the contaminated water. In the disclosed embodiments, the CGAs are produced by microbubbles through gas injection into impacted or contaminated water using a commercially available microbubble generation device. A surfactant is added to the contaminated water either alone or in combination of appropriate additives. The size of microbubbles generated may be in a range from 50 to 200 micrometers. The disclosed is a process of generation of a large number of microbubbles in the contaminated water, and outer layer of which contains surface active substance, i.e. surfactant, which adsorbs the contaminants, such as per- and polyfluoroalkyl substances (PFAS). The surfactant may be a cationic surfactant and an anionic surfactant.

[0040] The cationic surfactant may be quaternary ammonium salts having a structure including but not limited to the following molecules.R2 CH3§ ! i j: + ! +R1 - N .. R3 CH3- N .. R i A' i A’ t iR4 CH3wherein R1 , R2, R3, R4 and R each are independently a Cs to C alkyl, aryl, or organyl group, or any combinations thereof, A’ is an anion.

[0041] Examples of such cationic surfactants include, but are not limited to, octyltrimethylammonium bromide (OTMAB) hexadecyltrimethylammonium bromide (HDTMAB), tetrabutylammonium bromide (TBAB), decyltrimethylammonium bromide (DTAB), octyltrimethylammonium bromide (OTAB), lauric arginate (LAE), benzethonium chloride, alkylbenzyldimethylammonium chloride compounds, and the like.

[0042] Examples of the anionic surfactants include, but are not limited to, sulfate, sulfonate, phosphate, carboxylate head groups, ammonium dodecyl sulfate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, other alkyl-ether sulfates such as sodium laureth sulfate and sodium myreth sulfate, or the like.

[0043] The contaminant may be organic or inorganic impurities in water, PFAS, heavy metals, and other positively charged contaminants. With a proper selection of the surfactant, different contaminants may be adsorbed by the surfactant and removed.

[0044] In some embodiments, a cationic surfactant is added to the contaminated water to produce the microbubbles with surface chemistry specific for removal of per- and polyfluoroalkyl substances (PFAS). In addition to the cationic surfactant, an additive, such as xanthan gum, carboxymethylcellulose, may be added. The purpose of adding the additive is to produce stable CGAs in the contaminated water and / or improve the removal of the contaminants. After modifying chemical compositions of the contaminated water, a gas is injected into a microbubble generation device to generate microbubbles to the contaminated water, and a water circulation loop is formed with the microbubble generation device and a tank that contains the contaminated water. Here, the gas used may be nitrogen, hydrogen, carbon dioxide, ozone, oxygen, or compressed air. Here the microbubbles may be ultra-fine bubbles.

[0045] In some embodiments, an anionic surfactant may be used to extract heavy metals, cationic PFAS, and organic matter or other positively charged contaminants from water. In this case the additive may be anionic polyacrylamides, or other commercially availableanionic polymers.

[0046] In some embodiments, an additive, such as, beta-cyclodextrin, cationic polymers may be added either alone or in combination with the cationic surfactant to the contaminated water to improve the removal of PFAS. The additives may include polyacrylamide, polyamine, chitosan, poly(diallyldimethylammoniumchloride), emulsifiers such as xanthan gum, carboxymethylcellulose, or the like.

[0047] In some embodiments, the disclosed system for CGA generation includes a reactor with a water residence time of 2 - 20 min to which the surfactant is added and water is recirculated through a microbubble generation device through which a gas is injected into the recirculating water in the microbubble generation device. The water residence time may include two portions, one is for generating and adsorbing the contaminants onto the CGAs, the other is for letting the CGAs carrying the contaminants to rise up to the surface of the water. The water and gas flow rates are adjusted so that the average size of the microbubbles is in the range 50-200 micrometers. This size range allows a sufficient residence time in the reactor to maximize the removal of contaminants or PFAS and also allows the microbubbles to float to the water surface quickly enough to allow short residence times.

[0048] FIG. 1 is a schematic figure demonstrates the CGA formation and PFAS removal in contaminated water according to the present invention. CGA is described as a microbubble consisting of a multilayered shell. CGA consist of gas core 11 , water shell 12 surrounding gas core 11. Surfactants 16 are adsorbed onto inner surface 13 of water shell 12 and outer surface 14 of water shell 12. The surfactants on outer surface 14 form electrical double layer 15. The charge of electrical double layer 15 depends on the type of the surfactant being used, i.e. cationic or anionic. These microbubbles have diameter above 25 pm and have been shown to have some colloidal-like properties. The repulsion of microbubbles with likely charged surfaces prevents their coalescence. CGAs adsorb contaminants 17 on electrical double layer 15 from water predominantly by electrostatic forces, forming a contaminant-CGA complex. However, in some cases CGAs can adsorb contaminants 17 by the combination of hydrophobic and electrostatic forces. Since CGAs have lower density than the surrounding liquid or water, the resulting contaminant-CGA complex floats to the surface of the water. It is known that CGAs are called microfoams in the art. Due to the buoyancy in a reactor containing the contaminated water, a network of connected microfoam is formed on the surface of water, which may be extracted, so that the contaminants in the contaminated water is removed.

[0049] In one exemplary embodiment, the processes of the CGA generation and PFASremoval are accomplished in continuous mode in a one-stage system as shown in FIG. 2. With this embodiment, a treatment of a contaminated water with surfactants and additives as well as the removal of foam floated on the surface of the contaminated water is accomplished in one reactor. Reactor 1 may be a column tank or a plug flow reactor (PFR). All reagents, such as the surfactants and additives, are added to reactor 1 in which a contaminated water is added as well. In some embodiments, the contaminated water may contain surfactants capable of producing CGAs. In this case the surfactant addition is optional. Water is recirculated using pump 2 through microbubble generation device 3 and then back to reactor 1. The doses of the surfactant may range from 1 to 100 mg / L, preferably, the surfactant dose is in the range 1 to 15 mg / L. The doses of the additive may range from 1 to 100 mg / L. The treatment of the contaminated water may be accomplished in batches where the water is recirculated from reactor 1 to microbubble generation device 3 and then back to reactor 1 by pump 2. The size of reactor 1 is chosen so that a residence time of 2-20 min is allowed. Water is continuously recirculated to achieve a lower final PFAS concentrations. Gas is injected into microbubble-generating device 3 for generating microbubbles in reactor 1 while the water is recirculated. The water may be recirculated for a certain time, for example 5 min, through pump 2, and the microbubbles are generated in reactor 1. The gas injected into microbubble generation device 3 may be nitrogen, hydrogen, carbon dioxide, ozone, oxygen, air or compressed air, or the like. The microbubbles generated in reactor 1 may be in the range 50-200 micrometers in size. The microbubbles generated in reactor 1 then carry the contaminants, such as PFAS, to the surface of water from where they are easily extracted and removed. Here, a sufficient residence time, such as 2-20 mins, is given for microbubbles to rise to the surface of the water in reactor 1 forming a layer of microfoam 4 thereon that contains a concentrated contaminanats such as PFAS. By removing the layer of microfoam 4 in reactor 1, the contaminant PFAS is removed and the purified water is extracted from reactor 1 by way of vacuum suction, blade scheming or the like. A baffle (not shown) may be added to reactor 1 to prevent CGAs enter the purified water line.

[0050] In another exemplary embodiment, the CGA generation and PFAS removal is accomplished in continuous mode in a two-stage system as shown in FIG. 3. In the first stage, similar to the one-stage continuous system stated above, all reagents, such as surfactant and additives, are added into first reactor 10. In some embodiments, the contaminated water may contain surfactants capable of producing CGA. In this case the surfactant addition is optional. The doses of the surfactant may range from 1 to 100 mg / L, preferably, the surfactant dose is in the range 1 to 15 mg / L. The doses of the additive mayrange from 1 to 100 mg / L. When pump 20 is turned on, the water is recirculated. Simultaneously, gas is injected into microbubble generation device 30. The size of reactor 10 is chosen so that a residence time of 2-20 mins is allowed. Water is continuously recirculated to achieve a lower final PFAS concentrations. Similarly, with the water circulation, the microbubbles are generated in reactor 10. The gas injected into microbubble generation device 30 may be nitrogen, hydrogen, carbon dioxide, ozone, oxygen, air or compressed air, or the like. The microbubbles generated in reactor 10 may be in the range 50-200 micrometers in size. The microbubbles generated in reactor 10 then carry the contaminants as shown in FIG. 1. A sufficient residence time, such as 2-20 mins, is given for the microbubbles to rise to the surface of the water in reactor 10 forming a layer of microfoam 40 thereon that contains a concentrated contaminants such as PFAS. By removing the layer of microfoam 40 in reactor 10, the contaminants are removed. In this embodiment, after the treatment in reactor 10 the water is transferred to reactor 50 where microbubbles are allowed to float to the top of the water in reactor 50 forming a layer of microfoam 60 that is extracted by way of vacuum suction, blade scheming or the like. Then purified water is discharged from the bottom of reactor 50. Here reactor 10 and reactor 50 may be a column tank, a plug flow reactor (PFR), or combinations thereof. A baffle (not shown) may be added to reactors 10 and 50, respectively, to prevent CGAs enter the purified water line.

[0051] In another exemplary embodiment, the CGA generation and PFAS removal is accomplished in continuous mode in a multi-stage system as shown in FIG. 4. Here the multi-stage system includes two sets of the two-stage system as shown in FIG. 3. Here reactor 10’, pump 20’, microbubble generation device 30’ foam 40’, reactor 50’ and foam 60’ may be the same as reactor 10, pump 20, microbubble generation device 30 foam 40, reactor 50 and foam 60, or may be different, depending on requirements to the final effluent quality and / or the implementation. Reactor 10, pump 20, microbubble generation device 30 foam 40, reactor 50 and foam 60 in FIG. 4 may be the same as those in FIG. 3. Instead of extracting the purified water from reactor 50 as shown in FIG. 3, the purified water from reactor 50 is fed to reactor 10’ and further treated therein with reactor 10’ and reactor 50’. In this way, the treatment of the contaminated water may be purified even more efficiently. The multi-stage system in continuous mode may include more than two sets of the two- stage systems, or various combination sets of the one-stage system and / or two-stage systems. For example, three sets of the two-stages systems, or even more. The treatment process of the multi-stage in FIG. 4 is the same as that described in FIG. 3, except for the feed water for reactor 10’ is the treated water from reactor 50, instead of the contaminatedwater. A baffle (not shown) may be added to reactors 10, 50, 10’ and 50’, respectively, to prevent CGAs enter the purified water line. In this embodiment, all reactors each may be a column tank, a plug flow reactor (PFR), or combination thereof. In this embodiment, combinations of the types of the reactors and the number of the reactors may vary and the microbubble generation devices fluidly connected to which reactors along with the pump may also vary.

[0052] Here, with the disclosed one-stage system in continuous mode, 50-80% of the contaminants may be removed in the treated water. With the disclosed two-stage system in continuous mode, approximately 70 to 98% of the contaminants may be removed in the treated water. With the disclosed multi-stage system in continuous mode, over 98% of the contaminants may be removed in the treated water.

[0053] The process for PFAS removal may be combined with other treatment methods that are generally used for water treatment, such as coagulation and flocculation. The presence of cationic flocculants will not affect the efficiency of PFAS removal.

[0054] In some embodiments, the contaminated water after the treatment steps shown in FIG. 2 to FIG. 4 may undergo a polishing treatment using activated carbon or ion exchange to produce high purity potable water.

[0055] After extracting the microfoam containing concentrated PFAS from the water surface, the microfoam is dried and disposed of as solid waste. The solid waste composition contains PFAS along with the surfactants and additives added to the contaminated water for extraction of PFAS. Here, the PFAS contaminated water may refer to contaminated groundwater, surface water, landfill leachate, municipal or industrial wastewater.Examples

[0056] The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the inventions described herein.Example 1

[0057] Cationic surfactant (Hexadecyltrimethylammonium - Bromide) dose at 7.1 mg / L was applied. Analysis of PFAS compounds was carried on by Method EPA 1633. The PFAS compounds include perfluorobutanoic acid (PFBA), perfluoropentanoic (PFPeA) acid, perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoicacid (PFUnA), perfluorobutanesulfonic acid (PFBS),perfluorohexanesulfonic acid (PFHxS), perfluoroheptanesulfonic acid (PFHpS), perfluorooctanesulfonic acid (PFOS), perfluoro-3-methoxypropanoic acid (PFMPA), and perfluoro-4-methoxybutanoic acid (PFMBA). Table 1 lists initial and final concentration of PFAS in impacted water before and after treatment, referring to FIG. 3 of the two-step process.Table 1Example 2

[0058] Cationic surfactant (Hexadecyltrimethylammonium - Br) dose at 3.0 mg / L was applied. Analysis of PFAS compounds was carried on by Method EPA 1633. Table 2 lists initial and final concentration of PFAS in impacted water before and after treatment, referring to FIG. 3 of the two-step process.Table 2eestimate number, value is below reporting limit. ND - not detected

[0059] FIG. 5 shows total PFAS removed 14.2 mg / L, 7.1 mg / L, 3.0 mg / L, and 1 mg / L surfactant (hexadecyltrimethylammonium bromide), referring to FIG. 3 of the two-step process (14.2 mg / L and 1 mg / L data not shown in Tables). FIG. 6 shows the percent removal of the PFAS compounds from the contaminated water in a two-stage process, referring to FIG. 3. FIG. 7 shows the removal of two exemplary PFAS compounds, PFOA and PFHxA in a multistage treatment process with the surfactant dose of 14 mg / L, referring to FIG. 4.

[0060] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily allreferring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

[0061] As used in this application, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion.

[0062] Additionally, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0063] The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

[0064] “About” or “around” or “approximately” in the text or in a claim means ±10% of the value stated.

[0065] "Comprising" in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms "consisting essentially of" and “consisting of”; “comprising” may therefore be replaced by "consisting essentially of" or “consisting of’ and remain within the expressly defined scope of “comprising”.

[0066] Ranges may be expressed herein as from about one particular value, and / or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and / or to the other particular value, along with all combinations within said range. Any and all ranges recited herein are inclusive of their endpoints (i.e., x=1 to 4 or x ranges from 1 to 4 includes x=1 , x=4, and x=any number in between), irrespective of whether the term “inclusively” is used.

[0067] It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, thepresent invention is not intended to be limited to the specific embodiments in the examples given above and / or the attached drawings.

[0068] While embodiments of this invention have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and not limiting. Many variations and modifications of the composition and method are possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.

Claims

What we claim is:1 . A method for creating colloidal gas aphrons (CGAs) and using the CGAs to remove contaminants from a contaminated water, the method comprising the steps of: feeding the contaminated water into a reactor; optionally adding at least one surface active substance to the reactor; fluidly connecting the reactor to a microbubble generation device that generates microbubbles therein; circulating the water from the reactor to the microbubble generation device and back to the reactor; creating the CGAs with the microbubbles in the microbubble generation device and flowing the CGA containing water to the reactor, wherein the CGAs adsorb the contaminates and carries the contaminates to the surface of the water in the reactor forming a layer of microfoam thereon; removing the layer of the microfoam; and extracting a treated water from the reactor.

2. The method of claim 1 , wherein the at least one surface active substance is a cationic surfactant selected from quaternary ammonium salts having the carbon chain length from 8 to 18.

3. The method of claim 2, wherein the cationic surfactant is selected from octyltrimethylammonium bormide (OTMAB) hexadecyltrimethylammonium bromide (HDTMAB), tetrabutylammonium bromide (TBAB), decyltrimethylammonium bromide (DTAB), octyltrimethylammonium bromide (OTAB), lauric arginate (LAE), benzethonium chloride, or alkylbenzyldimethylammonium chloride compounds.

4. The method of claim 1 , wherein the at least one surface active substance is an anion surfactant.

5. The method of claim 4, wherein the anionic surfactant is sulfate, sulfonate, phosphate, carboxylate head groups, ammonium dodecyl sulfate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, other alkyl-ether sulfates selected from sodium laureth sulfate or sodium myreth sulfate.

6. The method of claim 1 , wherein the contaminant is per- and polyfluoroalkyl substances (PFAS).

7. The method of claim 1 , wherein the contaminant is organic or inorganic impurities in water.

8. The method of any one of claims 1 to 7, further comprising the step of giving a sufficient residence time to have the CGAs rise to the surface of the water in the reactor, wherein the sufficient residence time ranges from 2-20 min.

9. The method of any one of claims 1 to 7, further comprising the step of pumping the water from the microbubble generation device to the reactor, so that a water circulation loop is formed between the reactor and the microbubble generation device.

10. The method of any one of claims 1 to 7, further comprising the step of injecting a gas into the microbubble generation device to generate the microbubbles therein, wherein the gas is nitrogen, hydrogen, carbon dioxide, ozone, oxygen, air or compressed air.

11. The method of any one of claims 1 to 7, further comprising adding an additive to the reactor, so that the created CGAs are stable in the water, wherein the additive is selected from beta-cyclodextrin, polyacrylamide, polyamine, chitosan, poly(diallyldimethylammoniumchloride), emulsifiers selected from xanthan gum or carboxymethylcellulose.

12. The method of any one of claims 1 to 7, further comprising the steps of: forwarding the treated water containing first residual CGAs to a second reactor forming a second layer of microfoam thereon; and removing the second layer of the microfoam and extracting a second treated water from the second reactor.

13. The method of any one of claims 1 to 7, further comprising the steps of: forwarding the treated water containing first residual CGAs to a second reactor forming a second layer of microfoam thereon;removing the second layer of the microfoam and extracting a second treated water from the second reactor that contains second residual CGAs; forwarding the second treated water to a third reactor forming a third layer of microfoam thereon; and removing the third layer of the microfoam and extracting a third treated water from the third reactor, wherein a second water circulation loop is formed between the third reactor and a second microbubble generation device to generate second CGAs.

14. A method for creating colloidal gas aphrons (CGAs) and using the CGAs to remove contaminants from a contaminated water, the method comprising: feeding the contaminated water, a surface active substance and an additive to a first reactor; fluidly connecting the first reactor to a microbubble generation device that generates microbubbles therein by injecting a gas into the microbubble generation device; circulating the water from the first reactor to the microbubble generation device and back to the first reactor by pumping the water therein; creating the CGAs with the microbubbles in the microbubble generation device and flowing CGA containing water to the first reactor, wherein the CGAs adsorb the contaminants and carries the contaminates to the surface of the water forming a first layer of microfoam in the first reactor; removing the first layer of the microfoam; extracting a first treated water that contains first residual CGAs from the first reactor; forwarding the first treated water to a second reactor forming a second layer of microfoam thereon; removing the second layer of the microfoam; and extracting a second treated water from the second reactor.

15. The method of claim 14, further comprising the step of giving a sufficient residence time to have the CGAs rise to the surface of the water in the first and second reactors, respectively, wherein the sufficient residence time ranges from 2-20 min.

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