Plasma-assisted water treatment system for elimination of persistent organic and inorganic water contaminants

Abstract

A method and system for treating water. A method includes providing a discharge cell having a first group of electrodes and a second group of electrodes arranged to provide a discharge zone therebetween; filling the discharge cell with a reducing gas that includes a least one reductive gas selected from a group consisting of hydrogen, a gaseous organic compound, a vapour of a volatile organic compound, carbon monoxide, ammonia, hydrazine and hydrogen sulfide; applying high voltage to the electrodes in the discharge cell to generate a plasma environment within the discharge zone that includes one of a pulsed corona or a barrier discharge; and introducing water containing persistent organic compounds or reducible inorganic compounds into the discharge zone and subjecting the water to the plasma environment to reduce the organic or inorganic compounds.

Description

PLASMA-ASSISTED WATER TREATMENT SYSTEM FOR ELIMINATION OFPERSISTENT ORGANIC AND INORGANIC WATER CONTAMINANTSTECHNICAL FIELD

[0001] The present invention relates to a plasma-assisted water treatment system for elimination of persistent organic water contaminants, especially halogenated organic water contaminants, and reducible inorganic water contaminants, such as heavy metal ions, arsenate-arsenite ions and others.BACKGROUNDWater contamination due to the presence of persistent organic and inorganic contaminants, such as perfluorinated compounds, chlorinated and brominated phenols, halogenated furanes and dioxines, chromium (VI) ions, arsenate, etc., pose significant challenges to both human health and the environment. These compounds are known for their resistance to conventional water treatment methods, making their removal a complex and pressing concern. Existing water treatment technologies often struggle to effectively remove these contaminants, leading to their persistence in water supplies. Although most of these contaminants can be removed by ion exchange or adsorption approaches, these methods often lack selectivity’, resulting in a huge consumption of regenerants and a regeneration process generating vast amounts of liquid waste, relatively diluted in target compounds while containing high amounts of salt. Thus, using ion exchange or adsorption often apparently solves the problem at the point of use, simultaneously aggravating it by generation of difficult-to-handle waste streams.SUMMARY

[0002] The present invention addresses the challenge of eliminating persistent organic compounds, especially fluorinated, chlorinated, and brominated organic compounds, as well as reducible inorganic compounds, from contaminated water by utilizing a novel plasma-assisted water treatment system. In one aspect, a method for treating contaminated water is provided that includes: providing a discharge cell having a first group of electrodes and a second group of electrodes arranged to provide a discharge zone therebetween, filling the discharge cell with a reducing gas that includes at least one reductive gas selected from a group consisting of hydrogen, a gaseous organic compound, a vapour of a volatile organic compound, carbon monoxide, ammonia, hydrazine and hydrogen sulfide; applying high voltage to the electrodes in the discharge cell to generate a plasma environment within the discharge zone that includes one of a pulsed corona or a barrier discharge; and introducing contaminated water into the dischargezone and subjecting the contaminated water to the plasma environment to reduce at least one of persistent organic compounds or reducible inorganic compounds.

[0003] In a further aspect, a system for treating contaminated water is provided that includes: a discharge cell having a first group of electrodes and a second group of electrodes arranged to provide a discharge zone therebetween; a reducing gas configured for introduction into the discharge cell, wherein the reducing gas includes at least one reductive gas selected from a group consisting of hydrogen, a gaseous organic compound, a vapour of a volatile organic compound, carbon monoxide, ammonia, hydrazine and hydrogen sulfide; a high voltage generator configured to apply high voltage to the electrodes in the discharge cell to generate a plasma environment within the discharge zone that includes one of a pulsed corona or a barrier discharge; and an inlet for introducing contaminated water into the discharge zone and subjecting the water to the plasma environment to reduce at least one of persistent organic compounds or reducible inorganic compounds.

[0004] Further aspects may include the above aspects: wherein the reductive gas mixture further includes a non-reductive gas selected from a group consisting of nitrogen, carbon dioxide, oxygen (contained in very low amount), argon, helium or another noble gas; wherein the water further contains reducible inorganic compounds which are reduced by the plasma environment; wherein the persistent organic compounds include at least one of fluorinated, chlorinated, and brominated compounds; wherein the water is introduced using at least one of showering, pulverizing, or a free-flowing film; wherein the discharge cell includes a dielectric barrier between the first group of electrodes and second group of electrodes; wherein the water is passed through the discharge cell in a continuous flow process; wherein the contaminated water is passed through the discharge cell in a batch processing mode; wherein the plasma environment is configurable to reduce oxygen or nitrogen-containing compounds; wherein, in addition to primary’ reduction (halogen abstraction) processes secondary oxidation with water or traces of oxygen can take place, resulting in the formation of, for instance, ketones from polyfluorinated aliphatic compounds; wherein the electrodes are comprised of two groups, both represented by wires running horizontally and / or vertically, wherein the first group of electrodes comprise parallel plates and the second group of electrodes comprise wires running horizontally and / or vertically between the plates; and / or wherein the first group of electrodes comprise concentric tubes and the second group of electrodes comprise wires running horizontally and / or vertically between the tubes, wherein the treatment cell is comprised by at least one dielectric barrier with two groups of electrodes located at different sides of the barrier.

[0005] In still other aspects, a reagent selected from a group consisting of hydrogen peroxide, sodium persulphate, or sodium peracetate is added to the contaminated water. Further, a reagentselected from a group consisting of sulfite ions, iodide ions, or other agent capable of generating solvated electrons when exposed to ultraviolet radiation is added to the contaminated water. Additionally, the contaminated water may be introduced using a nozzle of about 0. 5mm at about 6 bars of pressure. In still other aspects, water can be pulverized using ultrasonic, electrostatic, impeller or other fine pulverization means. In still other aspects, the discharge cell may be filled with an inert non-conducting media allowing the downward or upward flow of the treated liquid simultaneously with allowing the reductive gas to fill in between the media particles. In still other aspects, the porous media may possess non-inert surface properties, including adsorption, catalytic or acid / base properties.

[0006] Two or more aspects described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects and advantages will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:

[0008] Figure 1 depicts a water decontamination system, in accordance with an illustrative embodiment.

[0009] Figure 2 depicts a flow chart showing a method for treating contaminated water, in accordance with an illustrative embodiment.

[0010] Figure 3 depicts a discharge cell with a first electrode arrangement, in accordance with an illustrative embodiment.

[0011] Figure 4 depicts a discharge cell with a second electrode arrangement, in accordance with an illustrative embodiment.

[0012] Figure 5 depicts a discharge cell with a third electrode arrangement, in accordance with an illustrative embodiment

[0013] Figure 6 depicts a discharge cell with a third electrode arrangement, in accordance with an illustrative embodiment.

[0014] Figure 7 depicts a further embodiment of the water decontamination system of Figure 1, in accordance with an illustrative embodiment.

[0001] Figure 8 depicts another further embodiment of the water decontamination system of Figure 1, in accordance with an illustrative embodiment.

[0016] Figure 9 depicts a still further embodiment of the water decontamination system of Figure 1, in accordance with an illustrative embodiment.

[0017] The drawings are intended to depict only t pical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure.DETAILED DESCRIPTION

[0018] The present invention pertains to the field of water treatment and, more specifically, to a system for the elimination of persistent organic and inorganic contaminants, including fluorinated, chlorinated, and brominated compounds, oxygen-containing organic compounds and inorganic ions, from water sources. The invention utilizes plasma-assisted technology to achieve efficient removal of these contaminants, contributing to the improvement of water quality and environmental sustainability.

[0019] Halogenated organic compounds are widespread in the environment, and they pose serious threats to human health and ecosystems due to their toxicity, bioaccumulation, and persistence. Some examples of halogenated organic water contaminants are per- and polyfluoroalkyl substances (PFAS / PFOS), dioxins, halogenated furans, dioxin-like halogenated biphenyls, chlorinated solvents, pesticides, and disinfection by-products. Heavy metals and toxic non-metals represent a significant problem for water treatment and typically require the utilization of expensive selective adsorbents, with metals and non-metals in high oxidation states (chromates, arsenates, etc.) being the most problematic due to poor adsorption on common adsorbents.

[0020] Conventional water treatment methods have limitations in efficiently removing stubborn organic compounds. For instance, most of the compounds listed above show moderate to low adsorption capacity on activated carbon and other high-surface absorbents. Although advanced oxidation (processes based on generation of active oxy gen-containing oxidative species) demonstrates decent efficiency for degradation of some halogenated compounds, they fail to reach deep degradation for polyhalogenated, especially polyfluorinated compounds. Adsorption and ion exchange work well in many cases for the elimination of polyhalogenated compounds as well as many toxic inorganic compounds. However, in case of a non-regenerable adsorption and / or ion exchange material, the need for correct disposal of the contaminated material arises. If the material is regenerated, the generated toxic liquid wastes with often high salt content should be subsequently treated. Thus, the use of regenerable adsorption / ion exchange material presents the need for a technology for concentrated streams decontamination, with the present approach being a viable candidate for this technology.

[0021] The removal of heavy metals and toxic non-metal elements is generally a less complex process when compared with recalcitrant organic contaminants, though it is typically characterized by the recuperation of these elements in their original, soluble states. In contrast, plasma-assisted reduction has the capacity to yield elemental powders, enabling the direct recovery' of raw metallic and non-metallic forms. This aspect is particularly pertinent in the context of galvanic wastewater treatment, where metal concentrations may reach substantial levels, often in the order of hundreds of milligrams per litre.

[0022] Furthermore, conventional remediation strategies that rely on adsorption and ion exchange processes are often ineffectual against metal and non-metal ions that exist within chelate complexes with organic or inorganic ligands — a scenario that is commonplace in galvanic wastewater streams. Plasma reduction addresses this challenge by effectuating the reduction of the complexing agents, thereby releasing the bound metals or non-metals, which are then subject to reduction to their elemental states.

[0023] The application of plasma technologies in environmental remediation is a rapidly emerging field. Plasma, often referred to as the fourth state of matter, consists of a mixture of electrons, ions, and neutral particles, and has the unique ability to produce a variety’ of highly reactive species. These reactive species can break down even the most recalcitrant organic pollutants, thereby offering a potential solution for the degradation of persistent organic and inorganic contaminants in water.

[0024] Advanced reduction processes, analogous to their oxidation counterparts but focusing on the transfer of electrons to contaminants, have been explored as a treatment method for various pollutants. While advanced oxidation processes can be effective against a broad spectrum of contaminants, advanced reduction methods prove to be more potent for the removal of halogenated compounds. This is primarily because these halogenated (especially polyhalogenated) compounds are already highly oxidized, making reduction-based treatments inherently more efficacious for their degradation.

[0025] However, while the promise of advanced reduction is evident, the application of plasmabased advanced reduction heretofore remains notably underexplored. Research and implementations integrating plasma into advanced reduction processes are relatively scarce, highlighting a gap in the literature and potentially untapped potential for more effective water purification strategies. In investigations pertaining to advanced reduction via non-thermal plasmas, the plasma carrier gas employed is typically an inert medium, such as argon, or nitrogen, rather than an inherently reductive gas like hydrogen.

[0026] The present approach seeks to address the aforementioned challenges by introducing a novel plasma-assisted system and method based on excitation of non-thermal plasmas,preferably pulsed corona discharge (PCD) and barrier discharge (BD) plasmas in a reducing atmosphere, e.g., a hydrogen-rich atmosphere, providing direct contact of treated liquid with cold plasma. The species generated in plasmas include free electrons, that can be directly transferred to aqueous solutions via gas-liquid interface and act as powerful reducing agents. However, the presence of a significant amount of oxygen in the plasma carrier gas drastically reduces the generation of electrons due to their scavenging by oxygen-containing species. In contrast, the presence of a reducing gas in the plasma media can increase the generation of free electrons. Moreover, electric discharges in hydrogen-rich atmosphere are known to generate short-lived atomic hydrogen, which is also transformed to solvated electrons upon contact with water. The dissolved electrons realize the reductive activity and eliminate halogens from polyfluorinated compounds, resulting in the formation of aliphatic and aromatic hydrocarbons and inorganic fluoride. It should be noted that reductive plasma conditions can frequently be established within non-oxidizing carrier gases, even in the absence of an intrinsic reductive gas component. For example, the processing of aqueous solutions containing organic compounds with argon plasma frequently culminates in the in-situ generation of hydrogen. Consequently, the imperative is to ensure an environment with the prevalence of reductive species to facilitate effective plasma- induced reduction, rather than the obligatory introduction of reductive gases per se. However, for most practical uses, the introduction of a reductive gas to the plasma gas mixture may be preferred. It should also be noted that, in the presence of a reductive gas like hydrogen, small amounts of oxygen can counterintuitively increase the efficiency of reductive plasmas by facilitating a two-step reduction-oxidation mechanism, starting from contaminant reduction with atomic hydrogen or dissolved electrons (for instance, halogen abstraction in the case of halogenated pollutants), followed by an oxidation step, resulting in the formation of less halogenated or non-halogenated aldehydes and ketones.

[0027] In cases where oxygen is utilized, care must be taken as oxygen and hydrogen and other reductive gases become explosive when they coexist in high concentrations. Accordingly, in cases involving a binary mixture, e.g., hydrogen with oxygen, the system remains operative (i.e.. safe) so long as the oxygen is below half of the hydrogen’s content by volume and the overall volume concentration of oxygen does not exceed about 4%. The same applies to other reductive gases with the corresponding application of their stoichiometry coefficients for the reaction with oxygen. Thus, for example, the content of hydrogen in volume percentage (e.g., 2%) should be at least double of the oxygen's content (e.g., 1%), while the oxygen's content should not exceed 2% to ensure explosion safety.

[0028] The utilization of a reducing gas like hydrogen in plasma-based treatment has been limited to the context of gas phase reactions or surface treatments, rather than liquid phase watertreatment. The present approach capitalizes on this gap by enabling efficient electron transfer to the aqueous phase, which significantly enhances the reductive dehalogenation process.

[0029] Previous techniques have introduced methods and systems for the generation of high voltage, pulsed, periodic corona discharges in the presence of conductive liquid droplets as well as stable barrier discharge in the presence of a free-flowing liquid film on the barrier material, paving the way for advancements in the purification of gaseous and liquid media. While such systems have effectively harnessed the oxidizing power of corona and barrier discharges, they have not capitalized on the profound potential of reductive gas atmospheres within the discharge zone. The present approach distinguishes itself with the innovative integration of reductive gases, such as hydrogen, as the discharge medium, which has not been conventionally employed. This novel approach exploits the inherent reductive properties of these gases to enhance the generation of solvated electrons, thereby significantly improving the efficiency of reduction and dehalogenation processes. The synergy between the pulsed corona or barrier discharge and the intrinsically reductive atmosphere provides a previously untapped mechanism for the breakdown of resistant organic and inorganic compounds, offering a new paradigm in advanced reduction processes for water treatment.

[0030] In the context of existing technologies, ultrasonic methods have shown promise due to their capability to induce cavitation effects in aqueous solutions, leading to the generation of solvated electrons. These electrons can play a pivotal role in the reduction and degradation of persistent per- and poly fluoroalkyl substances. However, the production of solvated electrons through cavitation mechanisms is often limited and requires significant energy7inputs due to the need to maintain high ultrasound intensities.

[0031] Contrastingly, the plasma technology7proposed in the present approach ensures a more efficient and targeted production of solvated electrons using non-thermal plasma in a reductive atmosphere. This approach not only reduces the energy expenditure compared to ultrasonic processing but also achieves a higher level of electron generation, which potentially increases the efficacy7of the reduction of recalcitrant compounds. Thus, the current approach provides new opportunities for purifying water sources of persistent halogenated and some non-halogenated organic contaminants, as well as free and coordinated ions of metals and non-metals, expanding the capabilities of existing methods and offering a more advanced solution to this environmental challenge.

[0032] The present approach extends prior efforts involving the plasma treatment of water. For example, US Patent Publication US2022 / 0212959, filed January76, 2022, entitled Plasma Aerosol Hybrid Method for Fluoro Compound Abatement, which is hereby incorporated by reference, utilizes the afterglow region of a non-thermal plasma discharge for contaminanttreatment. However, the efficiency of this method may not be optimal, as the recombination and energy loss of active particles and transient compounds in the afterglow are significantly higher compared to the active plasma zone.

[0033] PCT application W02008008958A1, filed July 13, 2007, entitled Device for Generation of Pulsed Corona Discharge, which is hereby incorporated by reference, attempts to address the direct introduction of water — as droplets, a continuous stream, or aerosols — into the active plasma discharge zone, which poses a substantial technical challenge due to the high electrical conductivity7of water, which complicates the stability of the gas discharge.

[0034] The current approach enhances the pulsed corona discharge or barrier discharge concepts in a gaseous discharge zone laden with liquid, namely the use of reductive gases, providing a highly effective method for liquid treatment with exceptionally high reductive potential, employing free electrons, atomic hydrogen, and other potent reductive (and, in the secondary7steps, sometimes oxidative) species.

[0035] An additional significant advantage of the present approach lies in its tolerance to liquid input with a high load of mechanical impurities. Commonly, wastewater streams, such as landfill leachate, heavily laden with polyhalogenated impurities, also carry substantial amounts of clay and other mechanical contaminants. Conventional plasma treatment systems that depend on fine aerosolization of the liquid require stringent pre-filtration to prevent clogging and maintain efficiency, which adds to the complexity and cost of the treatment process. In stark contrast, the present system’s robust design permits the direct introduction of such contaminated streams, using large droplets or films, w ithout the need or with minimal need for pre-filtration. This not only simplifies the overall treatment process but also significantly reduces the cost and time associated with pre-treatment steps. The capability7to handle unfiltered and highly contaminated liquids directly translates to a broader applicability in real-world environmental clean-up scenarios, where the complexity and variability7of waste streams can otherwise be a limiting factor.

[0036] A feature of the present approach is the application of high voltage, e.g., in the form of pulses, to the discharge cell, typically at voltages in the range of several tens of kilovolts (e.g., 10-100 kilovolts at 1 kilow att), with pulse durations ranging from nanoseconds to hundreds of nanoseconds and a typical pulse repetition rate in the kilohertz range for corona discharge and DC, AC or pulsed nature of the current for barrier discharge. The discharge chamber (or cell) is filled with reductive gases, including but not limited to hydrogen, gaseous organic compounds or vapours of volatile organic compounds, carbon monoxide, ammonia, hydrazine, and hydrogen sulfide, sometimes combined with other gases such as nitrogen or inert gases.

[0037] A feature of this approach involves the use of plasma to efficiently reduce fluorinated, chlorinated, or brominated compounds, as well as some other classes of highly oxidized organic compounds (e.g. carboxylic acids, aldehydes, ketones) and inorganic compounds (heavy metals and nonmetals in ionic form) leading to their degradation and removal from the water source. This innovative approach accordingly offers a promising solution for the remediation of water contaminated with persistent organic and inorganic compounds, thereby contributing to improved water quality and environmental sustainability. The approach allows for contaminated water to be treated to levels compliant with established water quality' standards.

[0038] Note that the present approach can be successfully combined with ion exchange or adsorptive approaches by implementing the process for treating the liquid waste generated by the latter. The insensitivity of the proposed plasma-assisted method to high salt contents in the treated solution makes it ideal for such a concerted use. On the other hand, ion exchange and adsorptive approaches are capable of removing contaminants, especially PFAS / PFOS, from extremely diluted streams (down to ppt levels in some cases), which makes it beneficial to combine them with plasma-assisted approaches for these low concentration applications.Illustrative Embodiments

[0039] Figure 1 depicts an illustrative water decontamination system 10 configured to receive a source of contaminated water 14 and output decontaminated or treated w ater 16. System 10 generally includes a discharge cell 12, a high-voltage (HV) generator 18, and a source of reducing gas 28. Reducing gas 28 is introduced into discharge cell 12, and for example includes one or more reductive gases or a mixture of one or more reductive gases and non-reductive gases. Reductive gases may for example include hydrogen, gaseous organic compounds or vapours of volatile organic compounds, carbon monoxide, ammonia, hydrazine, and hydrogen sulfide, and non-reductive gases may for example include nitrogen, carbon dioxide, oxygen, carbon dioxide, argon, helium, or another noble gas.

[0040] Selective mixtures of the gases allow for a tailored plasma environment suitable for the degradation or modification of a wide range of organic compounds.

[0041] Once the discharge cell 12 if filled with the reducing gas 28, HV generator 18 is configured to apply high voltage to a first group of electrodes 20 and a second group of electrodes 22, e.g., to generate a pulsed corona or barrier discharge within a discharge zone in the discharge cell 12. In an illustrative embodiment, HV generator 18 outputs voltages in the range of several tens of kilovolts, with pulse durations ranging from nanoseconds to hundreds ofnanoseconds and a typical pulse repetition rate in the kilohertz range for pulsed corona discharge and high voltage DC, AC or pulsed feed for barrier discharge. It is understood that the parameters of the high voltage generated by HV generator 18 can vary to, e.g., be optimized for efficient plasma generation.

[0042] In certain aspects, the first group of electrodes 20 can comprise a series of flat or low curvature electrodes with suitable spacing between them. These electrodes can be arrays of rectangular plates, concentric tubes or any other geometry' providing fixed distance to the second group of electrodes 22. The second group of electrodes 22 can comprise an array of high curvature electrodes with active emitting surface located at a fixed distance from one or more of the first group of electrodes 20. In such arrangements, the second group of electrodes 22 have a curvature that is substantially greater than the curvature of the first group of electrodes (e.g., the second group has a curvature radius at least twice that of the first group). The spacing between the first group of electrodes 20 and the curvature diameter of the second group of electrodes 22 can be adjusted to optimize the treatment process for specific applications. In an illustrative configuration, the spacing between the first group of electrodes and corresponding second group of electrodes 20 can range from millimeters to centimeters, depending on the desired treatment efficiency. In yet another configuration, the second group of electrodes 22 can be realized as metal wires strung in parallel between metal plates or between concentrically aligned metal tubes (i.e., the first group of electrodes 20). The first group of electrodes 20 can be solid or comprise a mesh. The described configurations allow for a type of discharge referred to as pulsed corona discharge. In other cases, the second group of electrodes may comprise a mesh, e.g., woven from metal wires. In certain cases, the mesh wires arranged between plate-like electrodes can effectively form a grid with a large distance between the constituting wires (e.g., larger than the distance to the plates).

[0043] The discharge cell 12 can optionally include an electrically insulating material 26 between the first and second groups of electrodes 20, 22. Insulating material 26 can for example comprise a dielectric material such as glass, quartz, ceramics, and polymers. When such a material is used, the type of discharge comprises a barrier discharge.

[0044] It is understood that the size, arrangement, and number of electrodes 20, 22, as well as any insulating material 26, can vary' depending on the particular implementation.

[0045] Once the plasma discharge is created, contaminated water 14 is introduced into the discharge cell 12. Introduction may for example be at a low pressure and comprise droplets 24 by showering, pulverizing or as a free-flowing film on electrodes 20, 22 or the insulating barrier material 26.

[0046] In various aspects, reducing the droplet size by spraying the solution using nozzles or ultrasonic atomization can enhance process efficiency. The increase in the rate of contaminant degradation is almost directly proportional to the increase in the surface area of the droplets. Illustrative implementation may for example include nozzles ranging from about 0.4-0.6 mm, with a bar pressure of about 5-7 bars. For example, using 0.5 mm nozzles and spraying at 6 bar pressure gives droplets with an average size of 25 micrometers, the efficiency is improved by 245%. Water accordingly may be introduced using ultrasonic dispergation (i.e., dispersion), mechanical dispergation (e.g., with an impeller or the like), or electrostatic dispergation (e.g., electrospraying). Using ultrasonic dispergation, droplets under 10 micrometers can be achieved. Ultrasonic dispergation is a technique that uses sound waves to break up particles in a suspension. For example, a system may be utilized to generate droplets that average 5 micrometers, which gives 1100% rise in efficiency.

[0047] Depending on the type of reducing gas 28 being used, discharge cell 12 may or may not include a gas output 30. For example, if the gas consists solely of hydrogen, gas output 30 may not be required since the hydrogen will be consumed as part of the process.

[0048] Depending on the implementation, the water may be recirculated 27 to enhance the decontamination process. In other cases, decontamination may be achieved with a single pass. Accordingly, the contaminated water 14 can be passed through the discharge cell 12 in a continuous, recirculated, or batch mode process.

[0049] System 10 accordingly provides a plasma-assisted reduction process that can result in the complete elimination of fluorinated, chlorinated, and brominated organic compounds from the contaminated water 14, as well as the elimination of reducible inorganic compounds from the contaminated water 14. In other cases, the plasma-assisted reduction process can reduce the concentration of fluorinated, chlorinated, and brominated organic compounds, as well as some oxygen and nitrogen-containing compounds and reducible inorganic compounds in the contaminated w ater 14 to levels compliant with established water quality standards.

[0050] Figure 2 depicts a flow diagram of an overview of the process. At SI. a discharge cell is provided having a first group of electrodes and a second group of electrodes. In some embodiments, the first group of electrodes have substantially less curvature than the second group of electrodes. For example, the first group of electrodes may comprise parallel plates or concentric tubes, and the second group of electrodes may comprise thin wires having substantially round cross sections arranged between the first group of electrodes. In other cases, the second group of electrodes may for example comprise a wire mesh configuration. Next, at S2, the discharge cell is filled with a reducing gas, e.g., a reductive gas or a mixture of reductive / non-reductive gases. Reductive gases may for example include hydrogen, gaseousorganic compounds or vapours of volatile organic compounds, carbon monoxide, ammonia, hydrazine and hydrogen sulfide, and non-reductive gases may for example include nitrogen, carbon dioxide, noble gases, and small amounts of oxygen. At S3, a plasma environment within the discharge cell is generated by applying high voltage to the electrodes, and at S4 contaminated water is introduced into the cell for purification. At S5, the treated water is discharged.

[0051] Figure 3 depicts an illustrative embodiment of a discharge cell 40 having an electrode arrangement that includes a first group of electrodes 42 that comprise parallel plates and a second group of electrodes 44 that have rounded cross-sections and run horizontally in between the electrodes 42 (i.e., in and out of the page). When the water droplets 46 strike one of the second group of electrodes 44, a reaction 48 occurs that decontaminates the droplet.

[0052] Figure 4 depicts a similar electrode arrangement as that of Figure 3, except the second group of electrodes 60 comprise a wire mesh (that runs vertically and horizontally in an out of the page).

[0053] Figure 5 depicts a further illustrative embodiment of a discharge cell 50 having an electrode arrangement that includes a first group of electrodes 52, 54 that comprise concentric tubes and a second group of electrodes 56 that include vertically oriented wires (e.g., having rounded cross-sections) with a substantially greater curvature than the concentric tubes. As the water droplets fall downward and strike the second group of electrodes 56, a reaction 58 occurs that decontaminates the water.

[0054] It is understood that other electrode arrangements could be utilized. For instance, both groups of electrodes (positive and negative) can run substantially parallel to each other, e.g., either in the vertical or horizontal direction. Further, the electrodes may comprise curved wires wherein the curvature of the electrodes in both groups are the same, i.e., parallel to each other. An example of this is shown in Figure 6 in which a first group of electrodes 72 runs parallel to a second group of electrodes.

[0055] Figure 7 depicts the water decontamination system 10 of Figure 1 with an additional enhancement. In this case, process enhancers 15, such as hydrogen peroxide, sodium persulphate, sodium peracetate, etc., are added to the contaminated water 14 prior to being introduced to the discharge cell 12. Introduction of these reagents increase process efficiency, e.g., by reacting with atomic hydrogen and solvated electrons to produce hydroxyl (OH) radicals. An OH radical is a highly reactive molecule consisting of one oxygen atom and one hydrogen atom with a single unpaired electron. Consequently, powerful reducing and oxidizing agents simultaneously emerge in the contaminated water 14, which improves the degradation efficiency of halogenated contaminants through a combined degradation mechanism. Illustrative concentration ranges tested for these reagents were from 0.1mmol / l to 5mmol / liter, which maybe utilized in the described system and method. For all these chemicals, a pronounced effect was achieved by addition of 0.5 mmol / 1 of the reagent, as further addition did not significantly improve the effect during initial experimentation. The improvement was related to the standard experiment, where 251 of 2mg / l perfluorooctanoic acid (PFOA) was treated in pure hydrogen atmosphere at 20kV and 2kHz and a 90% reduction was achieved within six hours of treatment. Addition of 0.5 mmol / 1 of hydrogen peroxide reduced this time to 4 hour and 10 minutes, corresponding to a 44% improvement (i.e. reduction of required time by 44% to achieve 90% degradation of PFOA). 0.5mmol of sodium persulphate provided a 36% improvement, and sodium peracetate provided a 62% improvement.

[0056] Figure 8 depicts the water decontamination system 10 with a further additional enhancement. In this case, ion enhancers 19 are introduced into the contaminated water 14. Namely, sulfite ions, iodide ions, and / or other agents capable of generating solvated electrons when exposed to ultraviolet (UV) radiation are added. In one embodiment, a UV radiation system 17 is deployed to generate UV radiation. The resulting effect is due. e.g., to the fact that the discharge in, for instance, a hydrogen medium, emits a significant portion of its energy as short-wave UV radiation. In the unmodified version of the process, this energy is lost, whereas adding certain reducing agents to the solution allows this radiation to be utilized for additional solvated electron generation. For both reagents, an efficiency improvement is for example achieved at lmmol / L which improvement is 72% for sodium sulphite and 44% for sodium iodide.

[0057] Figure 9 depicts the water decontamination system 10 with an additional enhancement. In this case, the discharge cell 12 is filled with an inert non-conducting media 29. The inert media 29 may comprise any suitable material, e.g.. something as simple as sand, or a more specialized inert high-surface media like Raschig rings, etc. (Raschig rings are short, hollow tubes that are used to increase the surface area within a column, which improves the interaction between liquids and gases.) In operation, the reductive gas 28 fills the space between the inert media 29. As the contaminated water 14 flows through the inert media 29. the gas and water form a thin film on the media 29. When the high voltage is applied to the electrodes 22 immersed into the media 29, a corona discharge is created in the air gaps between the media, e.g., between grains of sand, which treats the water. A benefit is that nearly the same water surface area is achieved, as in case of ultrasonic dispersion, by requiring significantly less energy. Barrier discharge could also be utilized.

[0058] The various approaches accordingly utilize a plasma environment to efficiently reduce fluorinated, chlorinated, and brominated organic compounds present in the contaminated water 14, as well as some oxygen and nitrogen-containing organic compounds and some inorganiccompounds such as heavy metal ions. When subjected to the plasma environment created within the discharge cell, the persistent organic contaminants undergo chemical reactions, leading to their degradation and eventual elimination. In the case of inorganic contaminants, they are typically reduced to form elemental powders and can be subsequently removed by filtration. It is important to note that the capability for removal of organic compounds is not limited to halogencontaining compounds only, some non-halogenated organic compounds can undergo chemical transformation as well.

[0059] The invention described herein represents a significant advancement in the field of water treatment, specifically aimed at the elimination of persistent organic and toxic inorganic contaminants, including fluonnated, chlorinated, and brominated compounds, and heavy metals and non-metals ions, although not limited to these classes of contaminants. By harnessing the power of plasma within the discharge cell and optimizing various parameters, this technology7offers an effective solution for the efficient removal of stubborn contaminants from water sources.

[0060] The innovative systems described in this detailed description demonstrate the potential to greatly improve water quality, protect the environment, and contribute to the overall well-being of communities by ensuring access to safe and clean drinking water. It is understood that two or more of the described embodiments can be combined.

[0061] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising.” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0062] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately” and “substantially.” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and / or interchanged, such ranges are identified andinclude all the sub-ranges contained therein unless context or language indicates otherwise. “Approximately” as applied to a particular value of a range applies to both values, and unless otherwise dependent on the precision of the instrument measuring the value, may indicate + / - 10% of the stated value(s).

[0063] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

[0064] The foregoing drawings show some of the processing associated according to several embodiments of this disclosure. In this regard, each drawing or block within a flow diagram of the drawings represents a process associated with embodiments of the method described. It should also be noted that in some alternative implementations, the acts noted in the drawings or blocks may occur out of the order noted in the figure or, for example, may in fact be executed substantially concurrently or in the reverse order, depending upon the act involved. Also, one of ordinary skill in the art will recognize that additional blocks that describe the processing may be added.

Claims

CLAIMS1. A method for treating contaminated water, the method comprising: providing a discharge cell having a first group of electrodes and a second group of electrodes arranged to provide a discharge zone therebetween; filling the discharge cell with a reducing gas that includes at least one reductive gas selected from a group consisting of hydrogen, a gaseous organic compound, a vapour of a volatile organic compound, carbon monoxide, ammonia, hydrazine, and hydrogen sulfide; applying high voltage to the first and second group of electrodes in the discharge cell to generate a plasma environment within the discharge zone that includes one of a pulsed corona or a barrier discharge; and introducing contaminated water into the discharge zone and subjecting the contaminated water to the plasma environment to reduce at least one of persistent organic compounds or reducible inorganic compounds.

2. The method of claim 1, wherein the second group of electrodes have a curvature that is substantially greater than the first group of electrodes.

3. The method of claim 1, wherein the second group of electrodes comprise a wire mesh.

4. The method of claim 1, wherein the reducing gas further includes a non-reductive gas selected from a group consisting of nitrogen, carbon dioxide, oxygen, argon, helium, or another noble gas.

5. The method of claim 1, wherein the persistent organic compounds include at least one of fluorinated, chlorinated, and brominated compounds.

6. The method of claim 1, wherein the contaminated water is introduced using at least one of showering, pulverizing, or a free-flowing film.

7. The method of claim 1, wherein the discharge cell includes a dielectric barrier between the first group of electrodes and second group of electrodes.

8. The method of claim 1, wherein the contaminated water is passed through the discharge cell in a continuous flow process.

9. The method of claim 1, wherein the contaminated water is passed through the discharge cell in a batch processing mode.

10. The method of claim 1, wherein the plasma environment is configurable to reduce oxygen or nitrogen-containing compounds.

11. The method of claim 1, wherein the first group of electrodes comprise parallel plates and the second group of electrodes comprise w ires running between the plates.

12. The method of claim 1, wherein the first group of electrodes comprise concentric tubes and the second group of electrodes comprise wires running between the tubes.

13. The method of claim 1, wherein both groups of electrodes comprise wires running parallel to each other either horizontally or vertically.

14. The method of claim 1. wherein the discharge cell is initially filled with an inert nonconducting media.

15. The method of claim I . wherein a reagent selected from a group consisting of hydrogen peroxide, sodium persulphate, or sodium peracetate is added to the contaminated water.

16. The method of claim 1, wherein a reagent selected from a group consisting of sulfite ions, iodide ions, or other agent capable of generating solvated electrons when exposed to ultraviolet radiation is added to the contaminated water.

17. The method of claim 1, wherein the contaminated water is introduced using a nozzle size of about 0. 5mm at a pressure of about 6 bars.

18. The method of claim 1, wherein the contaminated water is introduced using ultrasonic dispergation.

19. The method of claim 1, wherein the contaminated water is introduced using mechanical dispergation.

20. The method of claim 1, wherein the contaminated water is introduced using electrospraying.

21. A system for treating contaminated water, the comprising: a discharge cell having a first group of electrodes and a second group of electrodes arranged to provide a discharge zone therebetween; a reducing gas configured for introduction into the discharge cell, wherein the reducing gas includes at least one reductive gas selected from a group consisting of hydrogen, a gaseous organic compound, a vapour of a volatile organic compound, carbon monoxide, ammonia, hydrazine and hydrogen sulfide; a high voltage generator configured to apply high voltage to the first and second group of electrodes in the discharge cell to generate a plasma environment within the discharge zone that includes one of a pulsed corona or a barrier discharge; and an inlet for introducing contaminated water into the discharge zone and subjecting the contaminated water to the plasma environment to reduce at least one of persistent organic compounds or reducible inorganic compounds.

22. The system of claim 21, wherein the reducing gas further includes a non-reductive gas selected from a group consisting of nitrogen, oxygen, carbon dioxide, argon, helium or another noble gas.

23. The system of claim 21, wherein the persistent organic compounds include at least one of fluorinated, chlorinated, and brominated compounds.

24. The system of claim 21 , wherein the contaminated water is introduced using at least one of showering, pulverizing, or a free-flowing film.

25. The system of claim 21, wherein the discharge cell includes a dielectric barrier between the first group of electrodes and second group of electrodes.

26. The system of claim 21, wherein the contaminated water is passed through the discharge cell in one of a continuous flow process or a batch processing mode.

27. The system of claim 21, wherein the first group of electrodes comprise parallel plates and the second group of electrodes comprise wires running between the plates.

28. The system of claim 21. wherein the first group of electrodes comprise concentric tubes and the second group of electrodes comprise wires running between the tubes.

29. The system of claim 21, wherein a reagent selected from a group consisting of hydrogen peroxide, sodium persulphate, or sodium peracetate is added to the contaminated water.

30. The system of claim 21, wherein a reagent selected from a group consisting of sulfite ions, iodide ions, or other agent capable of generating solvated electrons when exposed to ultraviolet radiation is added to the contaminated water.

31. The system of claim 21, wherein the contaminated water is introduced using a nozzle size of about 0. 5mm at a pressure of about 6 bars.

32. The system of claim 21, wherein the contaminated water is introduced using ultrasonic dispergation.

33. The system of claim 21, wherein the discharge cell is initially filled with an inert nonconducting media.

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