Method and kit for cleaning up environments contaminated with halogenated organic compounds

Abstract

1. A method for remediation of an environment contaminated with halogenated organic compounds, particularly perfluoroalkyl and polyfluoroalkyl substances, comprising the steps of: disposing a plurality of electrodes in the contaminated environment; applying a direct current between the electrodes; providing at least one conductive reducing agent for the halogenated organic compounds; obtaining information indicative of the electrical resistance between the electrodes; analyzing the information to detect whether at least one of the electrodes introduces a lower current into the contaminated environment compared to the remaining electrodes; and, in response to the detection, introducing the reducing agent into or into proximity with the contaminated environment such that the electrical resistance of at least one of the electrodes identified to introduce a lower current into the contaminated environment decreases.

Description

[Technical Field]

[0001] The present invention relates to a method for remediating an environment contaminated with halogenated organic compounds, a kit for carrying out the remediation of an environment contaminated with halogenated organic compounds, and the use of the kit for the remediation of an environment contaminated with halogenated organic compounds. [Background technology]

[0002] Halogenated organic compounds, also known as halocarbons, are chemical compounds in which one or more carbon atoms are covalently bonded to one or more halogen atoms (fluorine, chlorine, bromine, or iodine), forming organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds, respectively. Their use and misuse in industry and agriculture result in large amounts of these chemicals entering the environment, resulting in widespread diffusion and often causing undesirable conditions, i.e., environmental pollution. In particular, contamination by perfluoroalkyl and polyfluoroalkyl substances (PFAS, perfluoroalkylated substances) has become a serious problem for human health in recent years.

[0003] PFAS are a diverse class of man-made organofluorine compounds that contain multiple fluorine atoms attached to an alkyl chain. Therefore, they contain at least one perfluoroalkyl moiety (C n F 2n There are many different PFAS, some of which are widely used in industrial, military, and consumer products, including non-stick surfaces, electronics, high-performance plastics, carpets, fabric and paper coatings, and aqueous film-forming foams (AFFF).

[0004] The high stability of carbon-fluorine bonds and relatively high solubility and mobility of PFAS make them resistant to chemical and biological reactions and, as a result, prone to persistence in the environment. Numerous studies have demonstrated that PFAS are reproductive and developmental toxins, endocrine disruptors, potential carcinogens, bioaccumulative, and ubiquitous.

[0005] Similar to PFAS, organobromine compounds (organobromides) are also of great concern as environmental contaminants due to their persistence, bioaccumulation, and toxicity. As an important group of synthetic organobromine compounds, brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs), are released into the environment during the manufacture, use, and disposal of flame retardant-containing products.

[0006] Therefore, the efficient removal of halogenated organic compounds, especially PFASs, from affected environments is an important challenge from both biological and environmental perspectives.

[0007] Several techniques for removing halogenated organic compounds are known in the state of the art. For example, carbon adsorption, ion exchange, reverse osmosis, or nanofiltration are traditionally used in wastewater and drinking water treatment plants, but these methods require frequent renewal or modification to effectively remove the aforementioned substances. Other removal methods use extreme conditions, such as high temperature and pressure, which are costly.

[0008] Recently, the adsorption process of halocarbons onto carbonaceous materials such as carbon nanotubes (CNTs), graphene, and powdered activated carbon (AC) has been investigated, where adsorption occurs through electrostatic and hydrophobic interactions. However, the need for further destruction of adsorbed PFASs and the need for regeneration of the adsorbent limit the applicability of this approach.

[0009] Advanced reduction treatment (ARP) is a new treatment method that has been successful in decomposing various halogenated organic compounds.

[0010] Similar to oxidation processes, reduction processes involve direct electron transfer to treat pollutants or the generation of hydrogen radicals (H⋅) or hydrated electrons (e aq - This involves the generation of reactive free species such as .

[0011] Granular zero-valent iron (ZVI) or nanoscale zero-valent iron (nZVI) is a non-toxic, abundant, and relatively inexpensive material that can function as an adsorbent and / or a reducing agent.

[0012] In general, removal of contaminants by ZVI in the reduction process involves mass transfer of the contaminants to the ZVI surface, adsorption and / or reaction of the contaminants at or near the ZVI surface, and mass transfer of benign end products from the ZVI to solution.

[0013] ZVI corrodes in the presence of water (Equation 1), and corrosion accelerates further under acidic conditions (Equation 2). Fe(0) + 2H2O → Fe(+II) + H2 + 2OH - (1) Fe(0)+2H + →Fe(+II)+H2(2) Over time, ZVI can transform into iron hydroxides and oxides according to the so-called Schikorr equation. 3Fe(+II)+2H2O→Fe(+II)+2Fe(+III)+H2+2OH - (3) Fe(+II)+2OH - →Fe(OH)2(4) Fe(+III)+3OH - →Fe(OH)3(5) 3Fe(OH)2→FeO+Fe2O3+2H2O+H2(6) 3Fe(OH)2 → Fe3O4 + 2H2O + H2(7) As a result, ZVI particles have an inner oxide shell of Fe3O4 and an outer shell of Fe2O3 surrounding a reduced iron core. The iron oxide shell acts as an adsorption site for contaminants, while the reduced iron core acts as an anode and undergoes dissolution (Equation 8). Fe(0) → Fe(+II) + 2e - (8) Because there is little electron transfer at the Fe2O3 interface, further corrosion of the Fe2O3 shell must occur, resulting in an increasingly porous iron oxide shell surrounding the reduced iron core, before electron transfer from the reduced iron core to the PFAS is possible. Iron oxide corrosion occurs to reach equilibrium with the anodic reaction (Equation (8)) via the following reaction: Fe2O3+6H + +2e - →2Fe(+II)+3H2O (9) Fe3O4+8H + +2e - →3Fe(+II)+4H2O (10) For example, US 8,048,317 B2 discloses the use of zerovalent iron and other metals in combination with oxygen gas to decompose chlorinated and non-chlorinated organic compounds in aqueous solutions. However, because fluorinated organic compounds are unreactive to hydroxyl free radicals, this method cannot be successfully applied to the remediation of PFAS-contaminated environments.

[0014] Another technology that has attracted a lot of attention is electrokinetic purification. In situ electrokinetic remediation (electroremediation) typically involves applying a voltage difference across a pair of electrodes distributed over a significant area (usually tens to hundreds of meters) of the contaminated environment, over a significant period of time (usually months to years). To make such processes economically viable, it is desirable to use as few simple electrodes as possible and to effectively pass as large an electrical current as possible through these electrodes. Also, a significant amount of electrical energy is used; it is desirable to utilize this energy as efficiently as possible.

[0015] The term "electrokinetic" includes all electrically induced mass transport processes, including fluid flow and the movement of charged particles and ions toward electrodes. The basic transport mechanisms induced by electric fields are electroosmosis, i.e., the movement of a liquid against a charged stationary surface; electromigration, i.e., the movement of charged ions or ion complexes in solution; and electrophoresis, i.e., the movement of charged particles / colloids against a stationary liquid.

[0016] In electroremediation, not only mass transport processes but also electrode reactions occur: water is electrolyzed to form oxygen and protons at the anode and hydrogen and hydroxyl ions at the cathode. Anode: H2O → 2H + +1 / 2O2+2e - (11) Cathode: 2H2O+2e - →2OH - +H2(12) Ion migration proceeds along the current lines perpendicular to the electrodes and the resulting equipotential surfaces, with positive ions moving toward the negatively charged cathode and negative ions being attracted to the positively charged anode.

[0017] The electric dipole field generated by the electrodes in the system can be visualized by computer mapping the equipotential lines between the electrodes. The single electric fields generated by each electrode pair overlap each other, resulting in no or very little electric gradient in the region between the cathode and anode. In this low electric gradient region, electromigration rates are low and water convection may dominate. The electric gradient is linear and is steepest in the zone between the oppositely charged electrodes. Therefore, electromigration rates are highest in this zone.

[0018] In existing commercial electrokinetic systems, contaminants are typically extracted by a secondary recovery system or deposited on electrodes. For example, WO 2019 / 046743 discloses an apparatus, system, and method for removing contaminant ions from water in an aquifer. Electroremediation is employed to induce the migration of ionic contaminants to electrodes, where they can be concentrated and removed from the aquifer. However, such techniques only concentrate contaminants in the medium, without breaking them down into harmless or at least less harmful substances.

[0019] Other techniques are technically complex and require the use of expensive catalysts. For example, US Pat. No. 6,255,551 B1 discloses an electrokinetic purification method and system for treating media contaminated with halogenated hydrocarbons, particularly chlorinated solvents. The method involves detecting uneven conductivity or electroosmotic permeability in the contaminated media and selectively applying an electric field to the contaminated media by placing one or more segmented electrodes in close proximity to the contaminated media. Each segmented electrode includes multiple conductive segments, each separated by an insulating segment and connected to a power source that can individually apply a respective current to each conductive segment, making such segmented electrodes technically complex and quite expensive.

[0020] U.S. Patent No. 6,214,202 describes a method for groundwater remediation by catalytic reductive dehalogenation facilitated by water electrolysis using an electrode pair or electrode array. The contaminated groundwater and dissolved hydrogen generated by water electrolysis are pumped through a catalyst bed containing palladium, making the process expensive. After passing through the catalyst bed, the groundwater is extracted from the environment and reinjected into the ground via a dedicated well, which complicates the process.

[0021] US 6,265,205 B1 discloses a method for increasing the biodegradation rate of chlorinated organic compounds by supplying hydrogen to the environment. In one embodiment, an electric field is used to induce horizontal transport of pore fluids to move hydrogen gas and other electron donors between electrodes. In an alternative embodiment, metal particles are used to generate hydrogen through an in situ corrosion reaction. The metal particles are introduced into groundwater at any point in the soil.

[0022] However, the state-of-the-art methods do not address the role of the distance between the electrode and any added reducing agent. Furthermore, most of the currently known methods are not aimed at removing PFAS from contaminated environments or do not completely mineralize PFAS, producing short-chain degradation products with unknown toxicity. Summary of the Invention [Problem to be solved by the invention]

[0023] It is an object of the present invention to overcome these and other shortcomings of the prior art and to provide an improved electrokinetic method that is cost-effective, reliable, and easy to implement, particularly for remediating environments contaminated with halogenated organic compounds, particularly PFAS. [Means for solving the problem]

[0024] This object is achieved by a method for remediating environments contaminated with halogenated organic compounds, in particular PFAS, a kit for carrying out the remediation of environments contaminated with halogenated organic compounds and the use of the kit for the remediation of environments contaminated with halogenated organic compounds according to the independent claims.

[0025] In accordance with the present invention, a method for remediating an environment contaminated with halogenated organic compounds includes the steps of placing a plurality of electrodes in the contaminated environment, applying a direct current through the electrodes, obtaining information indicative of the electrical resistance between the electrodes, analyzing the information to detect whether at least one of the electrodes introduces a lower current into the contaminated environment compared to the remaining electrodes, and providing at least one conductive reducing agent for halogenated organic compounds, wherein in response to the detection, the at least one reducing agent is introduced into or brought into proximity with the contaminated environment such that the electrical resistance of at least one of the electrodes identified as introducing a lower current into the contaminated environment decreases. DETAILED DESCRIPTION OF THE INVENTION

[0026] Surprisingly, in contrast to previous disclosures that focused solely on electrokinetics or reducing species, efficient and effective mineralization of halocarbons is achieved by the method according to the present invention, which specifically involves spatially defined placement of a conductive reducing agent in combination with controlled electrokinetics. The introduction of the conductive reducing agent also allows for an increase in the distance between the placed electrodes, thereby reducing the overall number of electrodes required to cover any given area. Furthermore, the method disclosed herein allows for the specific placement of the reducing agent in the amount needed depending on the local conditions and the progress of the purification process.

[0027] Determining the resistance increase at or near the surface of the electrodes can be achieved in various ways. For example, each of the anodes is connected to a controlled current I A When supplying the cathode resistance R C The resistance R of the environment between the anode and the cathode Environment The sum of these indices is the voltage difference U between the cathode and the anode according to equation (13). AC can be obtained from

[0028]

number

[0029] If either the current or voltage is held constant, it is not even necessary to explicitly determine the resistance, since in this case the other variable, current or voltage, represents the resistance if either voltage or current, respectively, is held constant.

[0030] Information indicative of the electrical resistance between each anode-cathode pair is used to effect placement of a conductive reducing agent.

[0031] In particular, a method for remediating an environment contaminated with per- and polyfluoroalkyl substances (PFAS) includes disposing a plurality of electrodes in the contaminated environment, applying a direct current through the electrodes, obtaining information indicative of electrical resistance between the electrodes, analyzing the information to detect whether at least one of the electrodes introduces a lower current into the contaminated environment compared to the remaining electrodes, providing at least one conductive reducing agent for per- and polyfluoroalkyl substances, and, in response to the detection, introducing the at least one reducing agent into or proximate to the contaminated environment such that the electrical resistance to the contaminated environment of at least one of the electrodes identified as introducing a lower current into the contaminated environment is reduced.

[0032] Surprisingly, we found that while electrokinetics or reducing agents alone do not lead to PFAS reduction, combining direct current with conductive reducing agents effectively and efficiently reduces PFAS. In the method described herein, reducing agents are deployed in a targeted manner based on information about electrical resistance, i.e., to enhance electrokinetics and optimize reducing agent use and consumption, thus increasing the effectiveness and efficiency of the remediation process.

[0033] As used herein, the term "halogenated organic compound reducing agent" refers to a chemical, mixture of substances, or material capable of either direct electron transfer to treat contaminants or the generation of reactive free radicals, which then decompose the contaminants. The reducing agent, in combination with its electrical conductivity, increases the effective surface of the electrode and its radius of action.

[0034] Optionally, the reducing agent is capable of migrating under the influence of an electric field between oppositely charged electrodes, thereby concentrating halogenated organic compounds from the liquid mixture at its interface and transporting said materials to an electrode, preferably the cathode, for electrochemical decomposition.

[0035] Reducing agents that can migrate under the influence of a hydraulic gradient and / or an electric field between oppositely charged electrodes extend the effective range of the purification technique while simultaneously inhibiting further diffusion of contaminants by adsorption.

[0036] Target values ​​for common drinking water are typically in the parts per trillion (ppt) or nanograms per liter (ng / L) range.

[0037] As used herein, the term "contaminated environment" means an environment in which the sum of halogenated organic compounds exceeds the maximum concentration prescribed by an authority for a given location. If not regulated by a relevant authority, the term "contaminated environment" means an environment in which the sum of halogenated organic compounds exceeds a concentration of 500 ppt and / or in which the concentrations of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) each exceed 100 ppt.

[0038] For example, the European Union's 1998 Drinking Water Directive establishes legally binding drinking water limits of 100 ppt for 20 compounds in the vast PFAS family of chemicals, including PFOA and PFOS, and a maximum of 500 ppt for PFASs combined. The U.S. Environmental Protection Agency recently established non-mandatory health advisory levels of 70 parts per trillion (ppt) for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) combined, and 300-7000 ng / L for C4-C7 PFASs.

[0039] The methods described herein can be performed in situ or ex situ.

[0040] In situ cleanup has the advantage of avoiding potentially costly excavation, removal, or disposal costs.

[0041] Ex situ remediation of contaminated environments can be an especially viable option when contaminant concentration levels are very high, when the contaminants themselves are particularly persistent, or when the time frame for cleanup is short. Ex situ remediation of contaminated environments can be carried out on-site to avoid costly transportation.

[0042] Preferably, the contaminated environment is selected from the group consisting of wastewater, groundwater, industrial effluent, sediment, soil, hazardous liquid waste, environmental effluent and process by-products or combinations thereof.

[0043] As used herein, the term "proximal" refers to a location where the reducing agent can immediately interact with the contaminant, or at least where no further action is required for interaction between the contaminant and the agent at a later time. Depending on the environment, this typically means a distance of 1 m or less, preferably 0.1 m or less, from the contaminated environment.

[0044] Electrodes used in connection with the present invention may be placed directly in the contaminated environment or inserted into a well or trench in fluid communication with the contaminated environment.

[0045] Depending on the local conditions of the contaminated environment, in particular the conductivity of the environment to be purified, the electrodes can be positioned at a distance of 30 cm to 5 m, preferably 30 cm to 3 m, from each other.

[0046] The electrodes that can be used in the present invention can have a variety of shapes, such as rods or flat sheets. The electrode wells can also have a variety of shapes.

[0047] In any particular case, multiple anodes and cathodes can be used, and dozens of electrodes can be used simultaneously in a single location. The current and voltage are selected to match the conductivity of the contaminated environment. Typically, voltages between 10 V and 60 V are used, depending on electrical properties such as resistivity, and the power introduced into a 10 m x 10 m field is approximately 3 kilowatts.

[0048] Electrodes inert to anodic dissolution are preferably used for electroremediation. Electrode materials include graphite, platinum, gold, silver, IrO2, RuO2, boron-doped diamond (BDD), Ti / SnO2, Ce / PbO2, Ti / RuO2, substoichiometric and doped TiO2, although inexpensive electrodes made from titanium and stainless steel can also be used.

[0049] In contrast to negatively charged hydroxyl ions, which tend to deposit at the cathode, protons formed at the anode efficiently migrate toward the cathode in the electric field. The resulting acid front (excess H + Ionic oxidation (see Equation 11) can aid in contaminant removal by solubilizing certain types of contaminants and forming ionic species that are easily transported by electromigration. Because the zeta (ζ) potential of a particle, i.e., its apparent surface charge, has been shown to be strongly dependent on the pH of the solution, an acidic front also serves to make the zeta potential of the reducing agent more positive, thereby enhancing its electromigration toward the cathode.

[0050] Preferably, the at least one reducing agent is placed in or in close proximity to the contaminated environment less than 50 centimeters from at least one of the electrodes identified as introducing a lower current into the contaminated environment compared to the remaining electrodes, more preferably less than 30 centimeters.

[0051] We found that introducing a conductive reducing agent within a given distance of the electrode can increase the effective electrode coverage, allowing the electrodes to be spaced further apart and reducing the total number of electrodes required for any given application. This reduces capital expenditures and improves the cost-effectiveness of the overall process. The reducing agent increases the conductivity of the contaminated environment, promoting electrokinetic processes in the contaminated environment and increasing the reduction rate and mobility of contaminants. By introducing the reducing agent into the contaminated environment where it has the most beneficial effect—i.e., areas of the environment with high resistivity that prevent effective coverage by a DC electric field—the overall efficiency of the process is improved and the use of expensive reducing agents can be limited.

[0052] As used herein, the term "active area of ​​an electrode" refers to the sphere around the electrode within which electrochemical reactions originating from the electrode can occur.

[0053] Preferably, the method described herein further comprises the steps of placing a plurality of measurement electrodes in the contaminated environment, measuring the voltage drop between said measurement electrodes and / or from each of the measurement electrodes to its respective nearest neighbor electrode, and obtaining information indicative of the electrical resistance value from the measured voltage drops.

[0054] By using a measurement electrode in addition to the electrode, the electrical resistance of the contaminated environment between the measurement electrodes or between the measurement electrodes can be determined, thereby enabling the electrical resistance of the contaminated environment to be determined with higher spatial resolution.

[0055] The electric field can be measured using a means for measuring the DC electric field, such as a grid of probes, capable of recording the introduced current and measured voltage, and / or by electrodes used in the methods described herein, i.e., the electrodes can be appropriately functioning anodes or cathodes used in the purification. Alternatively, the probes can be, for example, dedicated electrodes for measuring current and voltage data. Ideally, the probes and / or electrodes should be positioned as close together as possible to improve measurement resolution and cover the entire environment to be purified in at least one extended plane.

[0056] The method according to the invention disclosed herein preferably further comprises the following steps: - placing means for measuring a DC electric field, in particular at least one reference electrode and at least one measuring electrode, in the contaminated environment; and - measuring the electric field generated by the direct current applied between the electrodes, in particular measuring the potential difference between the reference electrode and the at least one measuring electrode.

[0057] By placing at least one reference electrode and at least one measuring electrode in the polluted environment and measuring the voltage and / or current between said electrodes in a region where a constant current flows through the polluted environment, an indication of the resistance of the polluted environment can be obtained from which the attribution of the polluted environment to the resistance from cathode to anode can be calculated.

[0058] In many cases, it may be assumed that the contaminated environment will react similarly at different locations within the treatment area, in which case the at least one reference electrode and the at least one measurement electrode need not be located near the anode and / or cathode whose resistance is being determined. Thus, a single pair of measurement electrodes can be used to obtain information indicative of the electrical resistance between a number of different cathodes and / or anodes.

[0059] By placing at least one measurement electrode and / or electrodes in a location where the potential applied between the electrodes used in the methods described herein is near zero, with the respective electrode being a reference electrode, and by placing at least one remaining probe and / or electrode in the region of the electric field being investigated, it is possible to obtain the potential difference between the probes and / or electrodes, as well as the shape of the equipotential and current lines across the region of investigation. When the means for measuring a DC electric field includes electrodes used in the methods described herein, it is clear that the electrodes placed in a location where the potential is near zero are used to measure only the DC electric field and are not actively creating the electric field.

[0060] Measuring the potential difference over the investigation area provides the basis for interpreting the shape of the DC electric field.

[0061] In one embodiment, the aforementioned method further comprises the steps of determining electric field lines and / or equipotential lines between electrodes, preferably between electrodes and / or measurement electrodes, and switching the polarity of at least one of said electrodes and / or placing at least one additional electrode in the contaminated environment based on said determined electric field lines and / or equipotential lines, in particular to increase the area of ​​the contaminated environment covered by the electric field and / or to increase the electric intensity in a given area of ​​the contaminated environment.

[0062] Switching selective electrode polarity and / or introducing additional electrodes into the contaminated environment has the advantage that the largest possible area of ​​the contaminated environment is under the influence of the electric field, increasing the effectiveness of the purification process.

[0063] For example, during the interpretation of the measurement results, it may be desirable to switch the polarity of one or more electrodes if a high potential gradient is detected around said one or more electrodes, such as due to an increased presence of deposits.

[0064] By altering the distribution of the electric field, the position of the voltage gradient, the velocity rate, and the direction of contaminant movement can be controlled, thereby improving the overall effectiveness and efficiency of the purification methods disclosed herein.

[0065] From the shape of the equipotential and current lines it is also possible to draw conclusions about the distribution of pollutants in the polluted environment during the remediation period.

[0066] For example, fine-grained soils with high ion concentrations and high conductivity will have a low potential gradient, while coarse-grained soils with low ion concentrations and low conductivity will have a high potential gradient. The development of a higher voltage gradient, i.e., an increase in electrical resistance, can be explained by the depletion of ions due to electromigration to the respective electrodes, precipitation reactions, and the development of a waterfront due to reactions of water electrolysis products (see Equations 11 and 12). It will be apparent to those skilled in the art that the methods described herein are not limited to PFAS but are broadly applicable and particularly suited for controlling and optimizing the distribution of electric fields throughout contaminated environments and tracking the progress of remediation of PFAS and other contaminants.

[0067] The DC field mapping described herein can be performed repeatedly, whereby the frequency of measurements depends on the degradation rate of the contaminant of interest.

[0068] In the case of PFAS, the inventors have found in laboratory experiments that 75-90% removal of PFAS occurs within approximately two weeks of remediation. After this time, it may be appropriate to switch the polarity of the electrodes or change the arrangement of the cathode and anode used in the methods described herein.

[0069] In a preferred embodiment, the measurement electrodes are arranged in such a way that one measurement electrode is placed at a position where the potential is approximately zero, i.e. the reference electrode, and the remaining measurement electrodes are distributed over the area to be cleaned, so that the number and positions of the electrodes do not change during the course of the cleaning.

[0070] This has the advantage that the positions of all working and measuring electrodes used in the cleaning method described herein are determined from the start and no additional work is required during the cleaning process for repositioning said electrodes, e.g. remote control of the procedure is also possible.

[0071] By reversing or switching the direct current flow path, i.e., the polarity of at least one of the electrodes, the contaminants can be encouraged to pass multiple times through the treatment zone containing the reducing agent, activating the electrodes. For example, in the case of the cathode, switching the polarity can cause the acid to remove deposited mineral deposits that cause increased resistance. Furthermore, the electromigration pathway of the contaminants can be altered, retaining residual PFAS in areas of the contaminated environment that were not previously covered by the electric field.

[0072] Preferably, the measurements are interpreted by a computing system by graphing the measured and / or simulated data and optionally interpolating and / or extrapolating.

[0073] For example, measured current and voltage (volt) data can be plotted in a diagram against the position or distance of the electrode introduced into the contaminated environment, or against the width and length of the environment being cleaned.

[0074] In this way, the distribution and development of the electric field, i.e., equipotential and current lines, and in particular the interactions and differences between the electric fields emanating from the electrodes, can be visualized in two dimensions. In particular, it is possible to identify areas of the environment to be purified that are covered by the DC electric field and those that are not covered by the DC electric field, respectively.

[0075] If indicated by the information thus obtained, the DC electric field is optimized by switching the polarity of the at least one anode and / or at least one cathode and / or by placing at least one additional anode and / or at least one additional cathode in the contaminated environment to change the distribution of the electric field in the contaminated environment.

[0076] Preferably, the aforementioned method further comprises the step of measuring the pH of the environment within the effective range of the anode and / or cathode.

[0077] During electrolysis, water close to the electrode is electrolyzed to produce H + ions, OH at the cathode - Ions can be produced, changing the pH of the water according to Equations 11 and 12. If the produced ions are not neutralized or removed, these reactions will decrease the pH at the anode and increase the pH at the cathode. This increase in pH can lead to the precipitation and deposition of insoluble minerals at or near the cathode, creating a region of high electrical resistance and low electroosmotic flow.

[0078] By measuring the pH, redox potential, conductivity and temperature of the environment within the electrode's effective range, it is possible to monitor the electrode's operation and accelerate the purification process as much as possible by identifying the maximum sustained current that can be supplied without endangering the proper operation of the electrode system.

[0079] Optionally, a pH adjuster can be added within the effective range of the anode and / or cathode.

[0080] Adjusting the pH value within the effective range of the electrode can extend the electrode's service life and ensure optimal pH conditions for PFAS decomposition.

[0081] Preferably, the pH adjusting solution is added within the effective range of the anode and / or cathode.

[0082] This has the advantage that pH adjustment can be easily and accurately achieved, for example, by using a conventional dosing pump.

[0083] Preferably, the aforementioned method further comprises the step of providing at least one monitoring well in the contaminated environment and at least one sensor per monitoring well capable of measuring at least one chemical property and / or at least one physical property.

[0084] As used herein, the term "monitoring well" refers to an access to a contaminated environment where at least one sensor can be in fluid communication with the medium to be purified. Additionally, samples can be taken from these monitoring wells.

[0085] By providing at least one monitoring well, each with at least one sensor, to survey the contaminated environment, it becomes possible to continuously monitor the functioning of the system and determine the progress and endpoint of the cleanup process.

[0086] Preferably, the physical and / or chemical property to be monitored in the aforementioned method is selected from the group consisting of fluoride, hydrogen fluoride, bromide, hydrogen bromide, chloride, hydrogen chloride, redox potential, temperature, pH, conductivity or electrical resistance.

[0087] Fluoride concentration can be used as an indicator of the progress of PFAS degradation and mineralization, i.e., remediation. Similarly, bromide and chloride concentrations can be used as indicators of the degradation and mineralization of organobromine and organochloride compounds, respectively. Monitoring hydrogen fluoride and / or hydrogen bromide and / or hydrogen chloride concentrations is beneficial from an operational safety perspective. Temperature measurements can be used to correlate with the resistance or conductivity of the contaminated environment. pH / ORP readings can be used to adjust the pH / ORP to optimal reducing conditions. Conductivity or electrical resistance measurements can be used as indicators of electrode condition.

[0088] Preferably, the reducing agent in the above method comprises a zero-valent metal, which has the advantage of being readily commercially available.

[0089] Preferably, the zero-valent metals used in the methods described herein are coated with an inorganic sulfur-based structure.

[0090] Sulfidation (or sulfurization), i.e., the modification or transformation of metal-based materials by exposure to sulfur compounds in various oxidation states, can play an important role in the overall reactivity of ZVI with contaminants because it mitigates the problem of surface passivation by oxide and hydroxide species resulting from the competitive reaction of ZVI with water. While numerous metals have a strong affinity for sulfides, iron is the most prominent, with iron sulfide minerals such as mackinawite (FeS), greigite (FeS), pyrite (FeS), and pyrrhotite (FeS) being common forms.

[0091] Sulfided ZVI particles are more stable in water than uncoated ZVI because electrostatic repulsion inhibits ZVI aggregation. This increases the zero-valent metal lifetime and the effectiveness of the resulting species in remediating PFAS-contaminated environments. At the same time, the positively charged surface enhances the attraction of negatively charged PFASs, making them more susceptible to reductive degradation by sulfided ZVI and / or the cathode upon arrival.

[0092] Preferably, the zero-valent metal used in the methods described herein is coated with a carbonaceous structure.

[0093] Alternatively, a bimetallic compound or a mixture of one or more zerovalent metals and / or one or more bimetallic compounds can be used in the methods described herein.

[0094] The use of bimetallic compounds or mixtures has the advantage that the reactivity of the reducing agent can be tailored to the PFAS contaminants present in the contaminated environment, optimizing the effectiveness of the remediation process.

[0095] Preferably, the anodes and cathodes used in the methods described above are made of zero-valent metals, and such electrodes are readily available.

[0096] Preferably, the anode and cathode are made of zero-valent iron, as such electrodes are readily available and relatively inexpensive.

[0097] Preferably, the reducing agent used in the aforementioned method is zero-valent iron characterized by a particle size of 50-200 nm and / or a particle size of 10-350 μm and / or granular iron with a particle size of more than 500 μm and / or an aqueous dispersion with a concentration in solution of 0.5-100 g / L.

[0098] The term "particle size" as used herein refers to the particle size distribution D50, i.e., the particle size value at 50% of the cumulative distribution, which is also known as the median size or middle value of the particle size distribution. Measurement of particle size and shape distributions can be performed by transmission electron microscopy according to ISO / DIS 21363.

[0099] As used herein, the term "concentration in solution" refers to the dry weight of zero-valent iron particles on a metal basis before dispersion in a liquid.

[0100] Aqueous dispersions of zero-valent iron are commercially available, relatively inexpensive, and can be easily applied onto the contaminated environment, for example, by using a suitable dosing pump.

[0101] Particle sizes between 50 and 200 nm offer the advantage that these smaller particles offer a larger surface area for adsorption, exhibit improved mobility in contaminated environments, and result in faster reaction rates. Particle sizes between 10 and 350 μm offer the advantage that these larger particles last longer. Particle sizes greater than 500 μm offer the advantage that such particles are typically less expensive than their smaller analogues, are easier to remove from remediation environments in ex situ applications by sedimentation or filtration, and are safer to use, i.e., not subject to bans or restrictions in certain countries like nanoparticles. Using a mixture of both small and large particles allows the benefits of both particle size ranges to be utilized in the same process.

[0102] When the zero-valent iron particle concentration in the solution is between 0.5 and 100 g / L, each aqueous solution offers optimal cost-effectiveness for the remediation of PFAS-contaminated environments, with the advantage that it can be processed using standard dispersion equipment.

[0103] Preferably, the number of cathodes used in the above method is different from the number of anodes. The use of an unequal number of anodes and cathodes, for example one anode surrounded by four cathodes, has the advantage of controlling the electromigration pathways of materials mobilized under the influence of an electric field, allowing for the decontamination of larger areas without the need to reposition the electrodes in the environment to be cleaned.

[0104] Preferably, the number of electrodes operating as cathodes in the methods described herein is greater than the number of electrodes operating as anodes, which has the advantage of increasing the number of sites for the reduction of halogenated organic compounds, particularly PFASs.

[0105] Preferably, the method described herein further comprises the step of placing at least one membrane in the contaminated environment between at least one pair of said electrodes. Preferably, said at least one membrane is an ion exchange membrane.

[0106] Surprisingly, it has been found that the combination of the conductive reducing agent used in the method as disclosed herein and a membrane through which the contaminants to be removed flow, particularly electrokinetically, contributes to a particularly high effectiveness and efficiency of the purification process.

[0107] Preferably, each of the membranes is arranged substantially transversely to the main flow direction of the contaminated environment passing through the respective membrane. In one embodiment, such an arrangement prevents the compounds to be removed from simply flowing along the membrane and passing through it, thus increasing the retention of the compounds to be removed. In another embodiment, such an arrangement of membranes is particularly advantageous when several membranes are connected in series in the form of a membrane cartridge. In this case, the parallel arrangement of membranes within such a membrane cartridge allows for a particularly space-saving and compact design of the membrane cartridge. In yet another embodiment, as described above, an arrangement of at least one membrane substantially transversely to the flow direction of the compounds to be removed is particularly useful for installation in enclosed spaces such as pipelines, piping, and / or pipes.

[0108] The object is further achieved by a kit for carrying out the remediation of environments contaminated with halogenated organic compounds, particularly perfluoroalkyl and polyfluoroalkyl substances, and in particular a kit for carrying out the methods described herein.

[0109] The kit includes a plurality of electrodes, a means for supplying DC power to the electrodes, at least one conductive reducing agent, a means for obtaining information indicative of electrical resistance between the electrodes, a means for bringing the reducing agent into proximity with the contaminated environment, and a means for controlling the assembled kit.

[0110] As used herein, the term "kit" means a distinct arrangement of components for joint use that must be assembled by the user and / or at the site of use to obtain a final product.

[0111] Preferably, the plurality of electrodes are made of zero-valent iron, the at least one conductive reducing agent is an aqueous dispersion of zero-valent iron, the means for bringing the reducing agent into proximity of the contaminated environment is a dosing unit including an injection well and a distributor, and the means for controlling the assembled kit is a control unit including a computing system capable of storing and transmitting data and a user interface.

[0112] The advantages of such a kit are that it is cost-effective, reliable, safe and easy to use.

[0113] Preferably, in the kits described herein, the means for supplying DC power comprises a battery, a generator, a fuel cell, or a power converter for a renewable energy source.

[0114] This allows the kit to be powered and operated without a remote, permanently installed power connection.

[0115] Preferably, the battery is a rechargeable battery, which is a variant of a resource-saving energy supply.

[0116] The use of generators or fuel cells allows the kit to operate for extended periods without the need to interrupt the process for battery switching, improving the overall efficiency of the process. The use of power converters for renewable energy sources, especially solar or wind energy, makes the entire process more environmentally friendly.

[0117] Preferably, the reducing agent in the kits described herein is zero-valent iron, in particular particles of zero-valent iron with a particle size of 50-200 nm and / or a particle size of 10-350 μm and / or granular iron with a particle size of more than 500 μm.

[0118] This has the advantage that such zero-valent iron is relatively cheap and commercially available. Particles in the smaller size range have faster kinetics, increasing mobility in contaminated environments, while particles in the larger size range have longer acting properties. A mixture of small and large particles can be used to take advantage of the benefits of both particle size ranges.

[0119] Preferably, the number of cathodes in the kits described herein is different from the number of anodes.

[0120] This has the advantage that the electromigration of reducing agents and / or other substances mobilized under the influence of an electric field can be controlled within the area covered by the electrode used, allowing larger areas to be decontaminated without having to remove and reinstall the electrode in the environment to be cleaned.

[0121] Preferably, the kit includes an equal number of cathodes and anodes, or more cathodes than anodes, thereby increasing the number of sites for reductive dehalogenation of organic compounds, especially PFAS, and accelerating the cleaning process.

[0122] In one embodiment, the kit according to the invention described herein further comprises a plurality of measurement electrodes.

[0123] A kit including a plurality of measurement electrodes can provide information indicative of the electrical resistance between an electrode and a measurement electrode placed in the vicinity of said electrode, or between measurement electrodes.

[0124] Preferably, the kits described herein further comprise at least one membrane, preferably at least one ion exchange membrane.

[0125] The object is further achieved by the use of a kit for remediating an environment contaminated with halogenated organic compounds, in particular perfluoroalkyl and polyfluoroalkyl substances, as described above, and in particular according to the method described above.

[0126] The present invention is explained in further detail by the figures, in which: Unless otherwise stated, like reference numerals are used to designate the same or similar elements. [Brief explanation of the drawings]

[0127] [Figure 1a] FIG. 1 is a schematic diagram of a PFAS-contaminated environment at the start of a remediation method. [Figure 1b] FIG. 1 is a schematic diagram of a PFAS-contaminated environment after a period of time of remediation. [Figure 1c] FIG. 1 shows a schematic of a PFAS-contaminated environment after switching the polarity of the electrodes. [Figure 1d] FIG. 10 shows a schematic of the PFAS-contaminated environment after switching the electrode polarity again. [Figure 2a] FIG. 1 is a schematic diagram of a PFAS-contaminated environment at the start of a remediation method using an electromigration reducing agent. [Figure 2b] FIG. 1 is a schematic diagram of a PFAS-contaminated environment after a period of time of remediation using an electromigration reducing agent. [Figure 3] FIG. 1 shows a schematic diagram of a kit assembled and set up for carrying out the method according to the invention.

[0128] Figure 1a shows a cross-sectional view of an environment (2) contaminated with PFAS (3). It is understood that the method described here, by way of non-limiting example, applies equally to environments contaminated with other halogenated organic compounds. Two electrodes, one cathode (4) and one anode (5), are placed in the contaminated environment, such that the cathode (4) is positioned in the cathode well (41) and the anode (5) is positioned in the anode well (51). Alternatively, the electrodes can be introduced directly into the contaminated environment. Applying a direct current between the electrodes (4, 5) induces electromigration of charged species along the electric field lines toward the oppositely charged electrode. In this example, negatively charged PFAS (3) and other negatively charged halogenated organic compounds (not shown) migrate toward the anode (5). The direction of migration is illustratively indicated by a single arrow. The applied current and the resulting potential between the electrodes (4, 5) are used to calculate the electrical resistance of the cell. The resulting data was analyzed to reveal an area of ​​increased electrical resistance in the region between the two electrodes (4, 5). In this example, the amount of reducing agent (6) added around the cathode was equal to the amount of reducing agent (6) added around the anode, i.e., the reducing agent (6) was equally distributed between the treatment zones around the anode and cathode. The reducing agent was introduced into the contaminated environment at a distance less than d1 around each electrode, where d1 represents a distance of 50 cm in this particular example. It is understood that once the reducing agent is introduced into the contaminated environment, its location in the contaminated environment may change due to current, electric field effects, water flow, sediment movement, diffusion of the reducing agent, etc., and as a result, the reducing agent may be found further away from each electrode than where it was introduced into the contaminated environment.

[0129] Figure 1b shows the cross section referenced in Figure 1a after a period of time for the purification method. The substantially immobile reducing agent (6) used in this example remained largely at the respective injection point, while the negatively charged mobile PFAS (3) and other negatively charged halogenated organics (not shown) migrated toward the anode (5). Passing through the reducing agent (6) in the treatment zone resulted in a reduction in the contaminants, as indicated by the lighter shading corresponding to PFAS (3) in the figure.

[0130] Figure 1c shows the cross section referenced in Figure 1b after switching the polarity of the electrodes. The new direction of migration of PFAS (3) and other negatively charged halogenated organics (not shown) toward the newly formed anode is again indicated by a single arrow. Passing through the reducing agent (6) in the treatment zone results in the continuous degradation of the contaminants, as shown by the hatching corresponding to the further reduced PFAS (3) in this figure.

[0131] Figure 1d shows the cross section referenced in Figure 1c after the electrode polarity has been reversed. The direction of migration of PFAS (3) and other negatively charged halogenated organic pollutants (not shown) is again indicated by a single arrow. Repeated passage of PFAS (3) and other negatively charged halogenated organic pollutants (not shown) through the treatment zone formed by the combination of electrodes (4, 5) and reducing agent (6) continuously reduced the amount of PFAS (3) and other negatively charged halogenated organic pollutants (not shown) present in the environment (2), as indicated by the lower number of PFAS (3) and other negatively charged halogenated organic pollutants (not shown) compared to the initial situation shown in Figure 1a.

[0132] FIG. 2a shows a cross-sectional view of a PFAS-contaminated environment (2) at the beginning of a remediation method using an electromigration reducing agent (6). It is understood that the method described here, by way of non-limiting example, applies equally to environments contaminated with other halogenated organic compounds. One cathode (4) and one anode (5) are placed in the contaminated environment, such that the cathode (4) is placed in the cathode well (41) and the anode (5) is placed in the anode well (51). Alternatively, the electrodes can be introduced directly into the contaminated environment. The reducing agent (6) is brought into close proximity to the contaminated environment at a distance less than d2 around each of the one cathode and one anode, which in this example corresponds to a distance of 30 cm. In this example, information indicating the electrical resistance between the cathode (4) and the anode (5) was obtained from a known voltage difference applied between the cathode (4) and the anode (5) and measurements of the average current flowing through the anode (5) and the cathode (4), respectively. Applying a direct current between the electrodes (4, 5) to reduce the overall resistance between the anode (5) and cathode (4) induces electromigration of charged species along the electric field lines toward the oppositely charged electrode. In this example, the negatively charged PFAS (3) migrates toward the anode (5) and the reducing agent (6) migrates toward the cathode (4), as indicated by the single arrows in each.

[0133] Figure 2b shows the cross section of Figure 2a after the remediation method has been performed for a certain period of time. PFASs are adsorbed (31) by the reducing agent (6), reduced, and / or transported in the electric field toward the cathode (4), where reduction of PFASs also occurs. The negatively charged PFASs that are not captured by the reducing agent (6) are concentrated around the positively charged anode (5). By switching the polarity of the electrodes (not shown), these PFASs can be adsorbed by the reducing agent (6), which then migrates in the opposite direction—toward the newly formed cathode. This polarity switch can be repeated multiple times until the desired PFAS concentration is achieved in the remediated environment.

[0134] Figure 3 is a schematic diagram of the components of a kit for implementing the method according to the present invention. The kit (1) includes a cathode (4) and an anode (5), each in fluid communication with an aquifer (2) contaminated with halogenated organic compounds. A photovoltaic panel (94) supplies power to a control means (9), which includes a control unit (91) electrically connected to the cathode (4) and anode (5) and configured to apply an electric field between the electrodes. A series of electrodes (95) is used to measure the electric field generated by a direct current applied between the electrodes (4, 5). A treatment region is defined by the area between the cathode (4) and anode (5), and electromigration occurs along the electric field lines between the anode (5) and cathode (4). A reducing agent (6) is brought into proximity with the contaminated environment via an injection well (61) connected to a dosing unit (7), which includes a distributor (71), a water tank (72), and a reducing agent reservoir (73). The kit (1) further includes a sensor (8) in fluid communication with the aquifer, whereby the sensor (8) is electrically connected to a control means (9). It is understood that the kit may include multiple sensors (8) in fluid communication with the aquifer and electrically connected to the control means (9), depending on the chemical and / or physical properties to be measured. The system is operated by a computing system (92) having a user interface (93).

Claims

1. 1. A method for remediation of an environment contaminated with halogenated organic compounds, comprising: placing a plurality of electrodes in the contaminated environment; applying a direct current through the electrodes; obtaining information indicative of the electrical resistance between the electrodes; analyzing the information to determine whether at least one of the electrodes introduces a lower current into the contaminated environment compared to the remaining electrodes; providing at least one conductive reducing agent for the halogenated organic compound; Including, and introducing the reducing agent into or into proximity with the contaminated environment in response to the detection such that introducing a lower current into the contaminated environment decreases the electrical resistance of at least one of the identified electrodes to the contaminated environment. A method characterized by:

2. 10. The method of claim 1, wherein the reducing agent is placed in or proximate to the contaminated environment less than 50 cm from at least one of the electrodes identified as introducing a lower current into the contaminated environment compared to the remaining electrodes.

3. placing a plurality of measurement electrodes in the contaminated environment; measuring the voltage drop between said measurement electrodes and / or from each of said measurement electrodes to its respective nearest neighbor; obtaining information indicative of electrical resistance from the measured voltage drop; 3. The method of claim 1 or 2, further comprising:

4. determining electric field lines and / or equipotential lines between said electrodes; switching the polarity of at least one of the electrodes and / or placing at least one additional electrode in the contaminated environment based on the determined electric field lines and / or equipotential lines; The method of any one of claims 1 to 3, further comprising:

5. measuring the pH of the environment within the effective range of said electrode; Optionally, adding a pH adjuster within the effective range of said electrode. The method of any one of claims 1 to 4, further comprising:

6. providing at least one monitoring well in the contaminated environment; and providing at least one sensor per monitoring well capable of measuring at least one chemical property and / or at least one physical property; The method of any one of claims 1 to 5, further comprising:

7. 7. The method of any one of claims 1 to 6, wherein the reducing agent comprises a zero-valent metal, a bimetallic compound, or a mixture of one or more zero-valent metals and / or one or more bimetallic compounds.

8. The method of claim 1, wherein the anode and cathode of the electrodes are made of a zero-valent metal.

9. The reducing agent is iron in granular form with a particle size of 50 to 200 nm and / or a particle size of 10 to 350 μm and / or a particle size of more than 500 μm, and / or Concentration in solution of 0.5 to 100 g / L The method according to any one of claims 1 to 8, wherein the aqueous dispersion of zero-valent iron is

10. 10. The method of any one of claims 1 to 9, wherein the contaminated environment is selected from the group consisting of wastewater, groundwater, industrial wastewater, sediment, soil, hazardous liquid waste, environmental effluent and process by-products or combinations thereof.

11. The method of any one of claims 1 to 10, further comprising the step of placing at least one membrane in the contaminated environment between at least one pair of said electrodes.

12. 12. The method of claim 11, wherein each of the at least one membrane is positioned transverse to a primary flow direction of the contaminated environment passing through the respective membrane.

13. A kit for carrying out the method according to any one of claims 1 to 12 for remediating an environment contaminated with halogenated organic compounds, said kit comprising: A plurality of electrodes, means for supplying DC power to said plurality of electrodes; at least one conductive reducing agent for the halogenated organic compound; means for obtaining information indicative of the electrical resistance between said electrodes; an injection well as a means for bringing said reducing agent close to the contaminated environment, and a dosing unit comprising a disperser, a water tank and a reservoir for storing said reducing agent; means for monitoring information indicative of the electrical resistance between said electrodes; a control unit including a computing system capable of storing and transmitting data and a user interface for controlling the assembled kit to initiate delivery of the reducing agent from the administration unit using information indicative of the electrical resistance between the electrodes; A kit comprising:

14. 14. The kit of claim 13, wherein the means for supplying DC power comprises a battery, a generator, a fuel cell, or a power converter of a renewable energy source.

15. 15. A kit according to claim 13 or 14, characterized in that the reducing agent is particles of zero-valent iron and / or granular iron with a particle size of more than 500 μm.

16. The kit according to any one of claims 13 to 15, further comprising a plurality of measurement electrodes.

17. The kit according to any one of claims 13 to 16, further comprising at least one membrane.

18. Use of the kit according to any one of claims 13 to 17 for the remediation of an environment contaminated with halogenated organic compounds.

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