Combined electrochemical pretreatment and sorption of pollutants

Abstract

The present invention relates to a system and method for removing contaminants or pollutants from a fluid using a combination of electrochemical processing and sorption. Contaminants can be removed from water or other fluids using the systems and methods described herein. The systems and methods described herein apply an electric current to a dirty fluid, such as water. As a result, the target contaminants are ionized and forced through a reactive sorption media through the use of an electrical gradient or polarization. The sorbent chemically binds to the contaminants.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 302,899, filed January 25, 2023, and entitled "COMBINED ELECTROCHEMICAL PRE-TREATMENT AND SORPTION OF POLLUTANTS," the contents of which are incorporated herein in their entirety. [Background technology]

[0002] Environmental pollution can be caused by industrial processes, fossil fuels, waste disposal, plastics, and other processes and materials. Many pollutants have the potential to cause significant harm to people, and once released into the environment, they are extremely difficult to remove. Pollution of waterways is of particular concern because we depend on clean drinking water to survive, and even very low levels of contamination can cause damage. People are increasingly aware of the need to prevent the release of pollutants into the environment. However, the environment is already polluted by pollutants released in the past, and harmful pollutants continue to be released or leak into the environment.

[0003] Contamination, especially heavy metal contamination and organic contaminant contamination, presents a significant challenge in water purification. Inorganic heavy metal contamination from components such as mercury (Hg) poses a major threat to aquatic life and human health by entering the food chain. Mercury contamination of surface waters has led to mercury accumulation in fish, leading health agencies around the world to establish fish consumption guidelines (Lamborg et al., 2014). Removal of mercury and other toxic metals from water is a significant challenge for many sites, including mining operations, power plants, waste treatment facilities, and dental clinics. In dentistry, for example, mercury is used as a component of amalgam fillings, along with metals including silver, indium, and tin (George et al., 2009). As amalgam fillings are introduced or scraped, mercury-containing particles are captured by dentists and sent down the drain. According to the US-EPA, there are over 100,000 dental practices in the United States that discharge approximately 5.1 metric tons of Hg to publicly owned water treatment plants annually, and despite the use of filter systems, the cost of Hg removal is $82 million per year (Goodis, 2017).

[0004] Organic contamination from components such as per- and polyfluoroalkyl substances (PFAS) and other persistent organic pollutants also present challenges to water quality. PFAS are a broad category of synthetic organofluorine compounds in which all (per-) or some (poly-) of the hydrogen atoms in an alkyl chain are replaced by fluorine. PFAS are widely used in the manufacture of waterproof coatings, firefighting foams, and chemicals. These compounds have been shown to be highly mobile and bioaccumulative in both animals and humans, resulting in associated health effects including cancer and renal failure (Grandjean & Clapp, 2015; Rahman et al., 2014).

[0005] A major obstacle to removing inorganic and organic contaminants from water is their ability to change solubility and surface charge as a function of water quality metrics including pH, ionic strength, and redox potential. For metals, chemical forms can vary within these systems from dissolved ionic forms to solid phase elemental (zero charge) forms or solid phase oxides / hydroxides (Atwood & Zaman, 2006). Similarly, the overall charge and solubility of organic compounds can change dramatically with the protonation and deprotonation of functional groups within the compound (Nguyen et al., 2020). The presence of these mixed phases complicates removal using traditional filter systems. One significant limitation of traditional filter systems such as amalgam separators is the removal of very fine solid phase or uncharged particles from air or water streams. These particles, ranging in size from 10 nanometers (nm) to 3 micrometers (μm), can pass through traditional size exclusion filter systems that typically remove particles larger than 3 to 0.5 μm (Stone et al., 2008). Additionally, these small particles are uncharged and do not typically interact with adsorption media such as activated carbon (Gai et al., 2019; Kah et al., 2021). Other selective adsorption materials, such as ion exchange resins, are highly dependent on the overall charge of the components being removed (Kah et al., 2021; Kucharzyk et al., 2017).

[0006] Current approaches to treating mixed-phase contamination streams include the addition of coagulants to precipitate ionic components, the addition of acids and bases to stabilize the pH, and the addition of oxidizing or reducing chemicals to produce the desired chemical form. These methods require constant controlled input of chemicals, incurring higher recurring costs for the treatment system.

[0007] Electrochemistry, the use of electricity to drive chemical reactions, has been utilized in environmental remediation. In a typical setup for water, an anode and a cathode are added to a water sample and a current is applied. Target constituents are ionized and removal is achieved by two mechanisms: 1) precipitation and settling in solution, or 2) collection on the surface of an electrode (Drogui et al., 2008; Pulkka et al., 2014). These methods have the disadvantage of requiring frequent removal and disposal of precipitates, which may themselves be harmful substances. Furthermore, precipitation of material on the surface of the electrode causes fouling and performance degradation.

[0008] Improved methods for capturing contaminants and managing the end products of contaminant capture are needed. Summary of the Invention

[0009] The present invention relates to a system and method for removing contaminants or pollutants from a fluid using a combination of electrochemical processing and sorption. Contaminants can be removed from water or other fluids using the systems and methods described herein. The systems and methods described herein apply an electric current to a dirty fluid, such as water. As a result, the target contaminants are ionized and forced through a reactive sorption media through the use of an electric gradient or polarization. To achieve polarization, power is applied to both electrodes (an anode located on one side of the vessel, a cathode located on the opposite vessel connected by a sorbent that forms a bridge). The sorbent acts to chemically bind the dissolved ionized components to the sorption media.

[0010] In one embodiment, a system for removing targeted contaminants includes an electrochemical cell. The electrochemical cell includes a first fluid chamber including a cathode and a second fluid chamber including an anode. A sorbent is disposed in a fluid bridge between the first and second chambers. The sorbent allows for the passage of an electric current between the first and second fluid chambers. The targeted contaminants are forced through the sorbent and chemically bond to the sorbent.

[0011] While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming various embodiments of the disclosure, it is believed the disclosure may be better understood from the following description taken in conjunction with the accompanying figures. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an electrochemical processing system in accordance with various embodiments.

[0013] [Diagram 2] FIG. 2 is a schematic diagram of an alternative embodiment of an electrochemical processing system.

[0014] [Diagram 3] FIG. 2 is a schematic diagram of another alternative embodiment of an electrochemical processing system.

[0015] [Figure 4] Photographs of the electrochemical system containing wastewater a. before treatment and b. after treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention relates to a process for removing contaminants or pollutants from a fluid using a combination of electrochemical processing and sorption. The systems and methods described herein can be used to remove contaminants from water or other fluids. The systems and methods described herein apply an electric current to a dirty fluid, such as water. As a result, the target contaminants are ionized and forced through a reactive sorption media by the use of an electrical gradient.

[0017] Contaminants that may be removed include, but are not limited to, inorganic contaminant metals such as cadmium, lead, mercury, gold and silver, and organic contaminants such as PFAS, polycyclic aromatic hydrocarbons, dioxane, hormones, antibiotic compounds, and volatile organic compounds (VOCs). Some embodiments may be capable of absorbing two or more contaminants simultaneously. Examples of PFAS that may be removed include synthetic organofluorine compounds such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). Various embodiments are particularly useful for contaminants that have mixed phases, such as a combination of dissolved ionic forms, solid phase elemental forms (zero charge), and / or solid phase oxides and hydroxides, as well as contaminants that have two or more charges or solubilities depending on the conditions. In some cases, the components removed from the water are valuable materials that can be captured and recovered. Examples include inorganic materials such as lithium, cobalt, cadmium, nickel, silver, gold, and platinum, and organic materials such as pharmaceutical compounds and amino acid molecules.

[0018] The electrochemical processes utilized in various embodiments may involve one or more of two primary mechanisms for the electrochemical treatment of contaminants, electrochemical oxidation and reduction, as illustrated in the representative examples below.

[0019] Electrochemical oxidation: Hg 0 (s) ←→ Hg 2+ (aq)+2e - (aq)

[0020] Electrochemical reduction: Ag 2+ (aq)+2e - (aq) ← → Ag 0 (s)

[0021] Although the above examples show the processes of mercury oxidation and silver reduction, respectively, these are merely examples and other oxidation or reduction processes may be used with any of the other contaminants that may be removed using the systems and methods described herein.

[0022] The method and system includes two chambers in fluid communication with each other through a sorption medium, the placement of the sorption medium acting as a bridge between the two chambers and thus may be considered a third chamber. Alternatively, rather than including separate chambers, the system may be formed from a single large chamber having a first and second portion separated by a sorption medium between them. Thus, while the application generally discusses a first, second, third, and fourth chamber, it should be understood that each such chamber may alternatively be a separate vessel where one or more chambers may be portions of a chamber rather than separate chambers. The first and second chambers each comprise an electrode, either a cathode or an anode, with the cathode and anode each being disposed in one or the other chamber. The third chamber or bridge chamber includes a sorbent that occupies the entire cross section of the fluid connection in the bridge chamber. Thus, the only fluid connection between the first and second chambers is through the bridge chamber and through the sorbent in the bridge chamber. The cathode and anode are connected to a power source such that an electric current may be applied to the system. When an electric current is applied, the target pollutant(s) are converted to a chemical form that can be captured by the sorbent as described later in this disclosure.

[0023] The first and / or second chambers may optionally include additives, such as additives to facilitate electrolysis. For example, the first and / or second chambers may include one or more additives, such as electrolyte salts, such as magnesium chloride, sodium chloride, or zinc chloride, among others, and other additives, such as hydrochloric acid, sulfuric acid, or acetic acid. One of the first or second chambers may contain an uncontaminated fluid, such as water, while the other of the first or second chambers may contain a contaminated fluid, such as wastewater, that contains contaminants targeted for removal using the system.

[0024] The sorbent included in the bridge chamber may be a targeted sorbent selected to remove one or more target contaminants from the dirty fluid. Examples of sorbents that may be used include ionic resins, activated carbon, and nanocomposite sorbents, such as Clarosafe Hg (Clarosafe Hg is a trademark of Claros Technologies Inc and is the subject of U.S. Patent Application Publication No. 2021 / 0331137, the relevant portions of which are incorporated herein by reference), for example, where wastewater treatment of mercury or other suitable target contaminants is desired. Sorbents that may be used include materials with large surface areas that allow for binding or sorption of target contaminants from water. These binding interactions include, but are not limited to, electrostatic interactions, hydrogen bonding, covalent bonding, and ion exchange. For application in electrochemical devices as described herein, these sorbents may preferably be porous in nature and may not impede the flow of electricity between the chambers of the system.

[0025] Nanocomposite sorbents, such as Clarosafe Hg, may be used in various embodiments to absorb one or more contaminants from a fluid such that the contaminants are bound to the sorbent. Thereafter, in some embodiments, the contaminants may be released from the sorbent, the sorbent may be recycled, and the contaminants may be rendered harmless. Various types of sorption systems may be used. In some embodiments, the sorbent comprises a foam, such as polyurethane. In some embodiments, the sorption system comprises nanoparticles. In some such embodiments, the sorption system comprises a support matrix, such as a foam, with nanoparticles on and within the foam matrix as a nanocomposite. In some embodiments, the nanocomposite is a two-phase material that includes metal or non-metallic nanoparticles on and within the support matrix. The nanoparticles may have sizes in the nanoscale range, such as between about 1 nm and 1000 nm, or between about 100 nm and 700 nm. The matrix may be porous and have a sponge-like structure, with the nanoparticles bound to the porous interior and exterior surfaces of the matrix throughout the pores. The matrix may act as a support structure for the metal or non-metallic nanoparticles bound to its surface. In some embodiments, the particles may be one or more metals or metal oxides, such as copper, iodine, silver, tin, zinc, titanium, selenium, nickel, iron, cerium, zirconium, magnesium, manganese, copper oxide, titanium dioxide, iron oxide, and zinc oxide, nonmetals, such as selenium and carbon (including graphene, graphite and their oxides), or combinations of two or more of these or other nanoparticles or alloys thereof. Sorption systems including nanoparticles useful in various embodiments may be made using a thermal reduction process to create nanocomposites of metal or nonmetal nanoparticles bound within a matrix. The particular nanoparticles and matrices used may be selectively tailored to improve the adsorption of one or more particular target pollutants. Sorbents including nanocomposites used in various embodiments may be produced using thermal synthesis methods, such as those disclosed in U.S. Patent Application Publication No. 2021 / 0331137, the relevant portions of which are incorporated herein by reference.

[0026] The first chamber may contain a counter electrode (cathode) including, but not limited to, rhodium, platinum, or graphite. The second chamber may contain a working electrode (anode) including, but not limited to, gold, glassy carbon, zinc, stainless steel, or nickel alloy, and a reference electrode including, but not limited to, silver / silver chloride, mercury / mercury oxide, or saturated calomel. The only fluid connection between the first and second chambers is through a bridge chamber containing a sorbent for one or more target pollutants.

[0027] Examples of treatment systems that may be used in various embodiments are shown in Figures 1-3. The treatment system shown in Figure 1 includes a first chamber, labeled Chamber A, that may be used to receive wastewater. The first chamber includes a cathode, a wastewater inlet, and a wastewater outlet. The treatment system further includes a second chamber, labeled Chamber B, that includes an anode. The first and second chambers are connected via a third chamber, which is a bridge chamber, labeled Chamber C, that contains a sorbent.

[0028] An alternative embodiment of a treatment system is shown in Figure 2. Similar to the system shown in Figure 1, the system of Figure 2 includes first and second chambers, labeled Chamber A and B, with electrodes for applying an electric current, and a bridge chamber, labeled Chamber C, containing a sorbent. At the bottom of the first chamber, the system also includes a valve for controlled release of the reaction products. Downstream of the release valve is an optional fourth chamber, labeled Chamber D, which may contain a sorbent and / or one or more selective membranes for redundant or additional capture of contaminants remaining in the purified wastewater stream after electrochemical treatment and release from the first chamber.

[0029] In another alternative embodiment shown in FIG. 3, the first and second chambers are first and second parts of a single large vessel, separated from each other by a sorption barrier rather than a bridge. In the example shown, the first and second chambers are vertically oriented with the wastewater solution in the lower chamber and the wastewater treatment product discharge at the bottom, optionally passing through an additional sorption column for redundant capture, such as chamber D in FIG. 2. The system may further include an optional discharge valve (not shown) between the wastewater portion and the outflow, as in the embodiment shown in FIG. 2. In alternative embodiments, the wastewater solution may alternatively be directed to the top by repositioning the wastewater inlet and discharge, if desired, or the system may be vertically oriented with the first and second chambers side-by-side. In some embodiments, the system may use one or more membranes as a barrier, instead of a sorption barrier. Alternatively, the system may include one or more membranes and a sorption barrier.

[0030] Although not shown, the system may include additional inlets or outlets that may be regulated by valves in various arrangements to the first, second, third or fourth chambers, etc. Additionally, the arrangement of the cathodes and anodes may be as shown or may be reversed in any embodiment.

[0031] Using the systems described herein, contaminants can be removed from the contaminated fluid using a process that involves applying a voltage in the first and second chambers by an external power source, such as an electrochemical workstation. This voltage can range from 1 mV to 50 V (1 to 10 V is ideal) and can be applied for a period ranging from 10 minutes to 100 hours, with 4 to 48 hours being ideal in some embodiments. The application of the voltage induces a change in the chemical state of the organic and inorganic contaminants, either through oxidation or reduction. These chemical constituents, referred to herein as "ionizable contaminants," can be understood as chemicals that undergo a change, such as a change in charge (ionization) or a change in physical state (such as a transformation from solid to liquid). Ionizable inorganic contaminants that may be removed using these processes include, but are not limited to, mercury, lead, cadmium, arsenic, or manganese or iron, including associated oxide or hydroxide species. Ionizable organic contaminants that may be removed using these processes include, but are not limited to, PFAS, polycyclic aromatic hydrocarbons, organophosphate pesticides, neonicotinoid insecticides, and dioxane. Ionizable high-value constituents that may be removed and recovered from water include, but are not limited to, inorganic materials such as lithium, cobalt, cadmium, nickel, silver, gold, and platinum, and organic materials such as pharmaceutical compounds and amino acid molecules. In some embodiments, contaminants that may be removed include nanometer-sized solids, e.g., solids from about 10 nm to about 1000 nm. In other embodiments, contaminants may be micrometer-sized solids, e.g., 0.5 to 1000 μm. These contaminants may be solid particles or amalgams or alloys of solid particles. Examples include dental amalgams and electronic components that contain macroscale solid mercury (>1 mm).

[0032] In some embodiments, the system and method may be used to remove metal solids, including but not limited to mercury, silver, lead and their respective oxides, reduced and organically bound forms. In such embodiments, the method of ionization is oxidation, and thus occurs in the second chamber with the anode. Upon ionization and subsequent dissolution of the metal solids, the applied voltage induces the migration of positively charged metal ions to the first chamber with the cathode. Inevitably, these metal ions must pass through the bridge chamber, thereby resulting in capture by the sorbent therein. In other embodiments, reduction may be an electrochemical method for the target contaminants, occurring in the first chamber with the cathode. After reduction of the contaminants, the applied voltage again induces migration through the bridge chamber towards the first chamber. In brief, the systems and methods described herein allow for the conversion of contaminants and high-value recoverable materials, such as solid metals including, but not limited to, mercury, lead, cadmium, arsenic, manganese, iron, or gold or platinum with associated oxide or hydroxide species, as well as metal-containing mineral particles including, but not limited to, lithium-containing titanium, aluminum, or manganese particles and their associated oxides and hydroxides, which are ionized and then dissolved in solution, followed by electrically induced migration of said dissolved components to a sorbent. In this way, the systems and methods provide an integrated procedure for the capture of targeted contaminants without the need for pretreatment such as filtration or chemical oxidation or reduction. Furthermore, the systems and methods provide a more complete means of treatment for contaminants, including solid contaminants, in contrast to other methods of filtration or chemical absorption, which cannot reliably treat nanometer-scale solids.

[0033] The systems and methods described herein can generate lower or higher redox potentials within the reaction chambers (first or second chambers, respectively) through the respective electrochemical reduction and oxidation inherent in the application of voltage / current.

[0034] After completion of the process, the solution in the chamber (either the chamber that originally contained the contaminated fluid, such as the second chamber, and / or the chamber to which the ionized contaminants have been transferred) may be released to the environment or subjected to further processing. For example, one or both of the final solutions, such as the fluid in the second chamber, may be treated with a reducing agent, including but not limited to ascorbic acid or activated carbon, prior to its disposal to avoid the traditional problem of waste release as the effluent flows through piping.

[0035] The compounds captured by the systems and methods described herein may be present, for example, in the water of the environment. Sorption systems can be used to remove compounds from water, for example, in water treatment plants, or on the surface or underground of water, such as lakes, rivers, groundwater and wells. However, in some embodiments, the removal of these compounds can be performed before they are discharged into the environment, for example, in industrial situations, such as wastewater before or during discharge from industrial plants, or during manufacturing processes, such as chemical manufacturing processes, so that pollutants are never released or are minimized. Thus, although the compounds captured are referred to as pollutants, the disclosure also extends to other compounds that never become pollutants or are not normally pollutants, but need to be captured and removed from the liquids or gases in which they are present.

[0036] The systems and methods described herein provide for the treatment of dirty fluids, such as water, via electrochemical means to convert constituents to a form that can be captured via a sorbent. The invention overcomes the significant limitations of conventional filters with respect to the removal of very fine solid phase particles and uncharged organic contaminants from air or water streams. The described process is carried out in a system that includes three chambers, consisting of an oxidation chamber, a reduction chamber, and a sorption chamber, such as a sorption cartridge. The system overcomes the limitations of current technology, particularly the ability to treat multiphase, complex matrices with one sorption technology, and the elimination of harmful precipitates. The system can further extend the usable life of the electrochemical system by reducing or preventing fouling of the cathode and / or anode as ionized contaminants migrate to the sorbent where they are captured. After completion of the process, the sorption material utilized in the removal of the contaminants may be subjected to an extraction process, whereby valuable constituents are recovered from the sorbent. This may be accomplished by methods including, but not limited to, the addition of solutions to the chambers at high or low pH, applying an electric current to replace the captured targets with protons or hydroxides. Competing ions may also be utilized in the process. For example, a sorbent containing lithium may be subjected to a solution containing sodium. Upon application of an electric current, sodium is driven into the sorbent via an electrochemical gradient, displacing the lithium bound in the sorbent and releasing lithium ions into solution, thereby making these ions available for value-added products.

[0037] experiment:

[0038] Example 1

[0039] The systems and methods described herein have been used successfully to treat wastewater containing solid mercury. As described above, an electric current was applied to the waste stream to liberate and ionize the mercury. These mercury ions then migrated through the sorbent Clarosafe Hg via an electrochemical gradient. A photograph of the electrochemical treatment system is shown in Figure 4. In image a, prior to treatment, chamber A is filled with mercury-containing wastewater, while chamber B is filled with clean water. Image b shows the system after treatment with application of an electric current through chambers A and B.

[0040] The results are shown in Table 1 below, which shows the mercury concentration (parts per billion, ppb, μg / L) in the reactor system before and after the treatment reaction. As can be seen, using this system, over 98% of the mercury was removed from the water by solid dissolution / ionization with subsequent sorption. Chamber C had a sorption capture efficiency of over 98.9%.

[0041] [Table 1]

[0042] Example 2

[0043] The system and method described herein was used to successfully dissolve solid mercury in dental wastewater. As described above, an electric current was applied to the waste stream contained in a 1 liter waste vessel to liberate and ionize the mercury. After electrochemical treatment, the resulting dissolved mercury remaining after electrochemical treatment was then captured in a secondary vessel containing Clarosafe Hg. The results are shown in Table 2 below, which shows the mercury concentration (parts per billion, ppb, μg / L) in the reactor system before and after the treatment reaction. As can be seen, with this system, dissolution of more than 93% of the initial solid mercury was achieved. The dissolved mercury was then completely removed from the solution using Clarosafe Hg.

[0044] [Table 2]

[0045] As used herein, the term "substantially" or "generally" refers to a complete or nearly complete degree or extent of an action, feature, characteristic, state, structure, item, or result. For example, an object that is "substantially" or "generally" means that the object is either completely included or nearly completely included. The exact acceptable deviation from absolute completeness may depend on the specific situation, as the case may be. However, the closeness to completeness will generally have the same overall result as if absolute and complete completion had been obtained. The use of "substantially" or "generally" is equally applicable when used in a negative sense, referring to a complete or nearly complete lack of an action, feature, characteristic, state, structure, item, or result. For example, an element, combination, embodiment, or composition that is "substantially free" or "generally free" of an element may still actually include such element, so long as there is no significant effect of it.

[0046] In the foregoing description, various embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments have been chosen and described to provide illustration of the principles of the present invention and its practical application, and to enable those skilled in the art to utilize the invention in various embodiments, and with various modifications as suited to the particular use contemplated. All such modifications and variations are within the scope of the present invention, as determined by the appended claims, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. 1. A system for removing targeted contaminants comprising an electrochemical cell, the electrochemical cell comprising: a. a first fluid chamber containing a cathode; b. A second fluid chamber containing an anode c. a sorbent disposed in a fluid bridge between the first and second chambers, the sorbent enabling the passage of electrical current between the first and second fluid chambers. A system comprising:

2. The system of claim 1 , wherein the electrochemical cell is configured to simultaneously dissolve, ionize, and sorb the target contaminant.

3. The system of claim 2 , wherein the target contaminant is in water.

4. The system of claim 3 , wherein the target contaminants comprise nanometer-scale solids.

5. The system of claim 3 , wherein the contaminants comprise micrometer-scale solids.

6. The system of claim 3 , wherein the target contaminant comprises solid mercury.

7. The system of claim 3 , wherein the target contaminants comprise a mixture of nanometer or micrometer scale solids.

8. 13. A method of removing targeted contaminants from a fluid using the system of claim 1, comprising: a. adding the fluid containing the contaminant to either the first or second chamber; b. adding a fluid to the other of the first or second chamber; c) applying an external voltage to the electrochemical cell; A method comprising:

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