Apparatus that uses electrokinetic to filter electrically charged particles

Abstract

To provide a charged particle filtration apparatus capable of quickly and efficiently removing charged particles such as fine plastics in water.SOLUTION: An apparatus for filtering charged particles using electrokinetic technology includes a main channel (100) into which fluid containing charged particles is supplied and flows, a first electrode (210) arranged inside the main channel to allow flow of the fluid, and an ion exchange membrane (220) arranged downstream of the first electrode and provided with a plurality of voids through which the fluid from which the charged particles are filtered is discharged.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to filtration devices, and more particularly to filtration devices that utilize electrokinetics, and more particularly, but not exclusively, to electrokinetic assisted filtration techniques for the rapid and efficient removal of charged particles, such as fine plastics, from water. [Background technology]

[0002] Water treatment, including water supply and sewerage treatment and industrial wastewater or sewage treatment, is considered to be very important in a wide range of fields. The substances to be filtered contained in the fluid to be treated have various properties, and one of them is the filtration of electrically charged particles. A typical example of electrically charged particles to be filtered is plastic.

[0003] In recent years, plastic pollution has become one of the major environmental issues, and related concerns are growing. As the use of plastic steadily increases, the annual global plastic production currently stands at about 400 million tons, and is expected to reach about 800 million tons by 2050. The problem is that plastic does not decay. It takes at least several decades to several hundred years to completely decompose, so used plastics continue to accumulate in the ecosystem. Meanwhile, discarded plastic waste is decomposed into small pieces of various shapes through mechanical or chemical processes, and among these, pieces smaller than 5 mm are called microplastics (MP). Due to their chemical stability, microplastics flow into the entire aquatic environment, including rivers and oceans, and drift in the water for a long time. As a result, humans and animals as well as aquatic organisms are inevitably exposed to MP, which increases the ecological and environmental dangers.

[0004] In addition, MPs can easily adsorb organic chemical pollutants such as bacteria, heavy metals, and compounds due to their high specific surface area and hydrophobicity, and if humans ingest contaminated MPs through the food chain, they can have a harmful effect on human health. In particular, extremely small plastic fragments less than 1 μm in size, called nanoplastics (NP), can enter cells and tissues, causing inflammation and adversely affecting cellular activity.

[0005] Among various engineered separation and decomposition technologies, membrane filtration (MF) is currently considered to be a promising strategy to successfully remove MPs in aquatic environments. Based on the size exclusion mechanism, MPs of various sizes can be effectively removed through MF simply by adjusting the pore size of the membrane filter. Recent studies have shown that MF exhibits more effective MP removal performance than existing water treatment processes (e.g., rapid sand filtration, dissolved air filtration, oxidation ditch method, etc.). Various types of membranes have been developed for MP removal as effective alternatives to existing polymeric membranes.

[0006] However, despite its excellent MP removal performance, MF is not suitable for reliable industrial applications due to the inherent trade-off between removal efficiency and flow rate. Generally, membrane filters with an average pore size of about 1 μm are subjected to pressures of several bar and can withstand hundreds of Lm -2 h -1 However, using membrane filters with finer pore sizes to separate finer particles results in a greater transmembrane pressure drop and requires a significantly higher energy expenditure to achieve the same level of flow rate.

[0007] Along with the trade-off between removal efficiency and flow rate, membrane fouling is an inevitable challenge in MF. Membrane fouling induces serious flow rate reduction, affects the quality of produced water, and ultimately induces a variety of economic and operational problems. In addition, fibrous MPs, which are the most dominant form of MPs present in aquatic environments, penetrate vertically into the small gaps and pores of membrane filters, making it difficult to remove fibrous MPs based on MF.

[0008] Therefore, in order to completely remove MP from an aquatic environment, a practical approach that can solve these problems is required. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2023-0037519 Summary of the Invention [Problem to be solved by the invention]

[0010] In order to solve the above problems, one object of the present invention is to provide a charged particle filtering device using electrokinetics, which can filter out even target substances that are difficult to remove using conventional membrane filtration methods, such as those having a fine size or a fibrous form, by filtering charged particles using electrokinetics, thereby solving the problem of membrane fouling.

[0011] Another object of the present invention to solve the above problems is to provide a charged particle filtration device using electrokinetics, which can achieve high removal efficiency of the target material by using electrokinetics for filtration, while preventing a decrease in flow rate or excessive energy consumption for maintaining the flow rate.

[0012] However, the problem to be solved by the present invention is not limited to this, and can be expanded in various ways without departing from the spirit and scope of the present invention. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, a charged particle filtering device according to one embodiment of the present invention is a device for filtering charged particles using electrokinetics, and may include a main channel through which a fluid containing charged particles is introduced and flows, a first electrode disposed inside the main channel to allow the flow of fluid, and an ion exchange membrane disposed downstream of the first electrode and having a plurality of voids through which the fluid from which the charged particles have been filtered is discharged.

[0014] According to one aspect, the first electrode and the ion exchange membrane may be configured to generate an electric field between the first electrode and the ion exchange membrane.

[0015] According to one aspect, the first electrode may have a polarity different from that of the charged particles to be filtered, the ion exchange membrane may be an ion exchange membrane for ions of a polarity different from that of the charged particles to be filtered, and a second electrode of the same polarity as the charged particles to be filtered may be connected to the ion exchange membrane.

[0016] According to one aspect, an ion depletion region that blocks the charged particles from moving into the pores of the ion exchange membrane may be formed in the upstream direction of the ion exchange membrane.

[0017] According to one aspect, the ion depletion region may be formed based on Ion Concentration Polarization (ICP).

[0018] In one aspect, the first electrode may include an additional ion exchange membrane with a plurality of voids that permit fluid flow therethrough.

[0019] According to one aspect, the ion depletion region may cause an electrophoretic force to act on the charged particles.

[0020] According to one aspect, the charged particles may be configured to move in a direction different from the fluid flow due to a drag force along the fluid flow and the electrophoretic force.

[0021] According to one aspect, the ion depletion region may include sub-ion depletion regions corresponding to each of a plurality of voids provided in the ion exchange membrane, and may be configured to have a cross-sectional area in a fluid flow direction that is equal to or greater than a predetermined first area by providing a plurality of sub-ion depletion regions.

[0022] According to one aspect, the charged particle filtration device may further include a porous layer disposed within the main channel upstream of the ion exchange membrane and configured to filter particles contained in the fluid that are equal to or larger than a first predetermined size.

[0023] In one aspect, the porous layer may restrict electrical convection induced in the ion depletion region to less than a predetermined magnitude, such that the ion depletion region has a cross-sectional area in the direction of fluid flow that is greater than or equal to a second predetermined area.

[0024] According to one aspect, the electroconvection may be induced by electroosmotic instability.

[0025] According to one aspect, the electroconvection may include three-dimensional helical vortex pairs.

[0026] According to one aspect, the porous layer may be formed of polyester microfiber.

[0027] According to one aspect, the device may further include a dome-shaped cap configured to secure the porous layer but permit fluid flow.

[0028] In one aspect, the dome-shaped cap may be configured to curve an upper boundary of the porous layer such that the ion depletion region has a convex shape.

[0029] According to one aspect, the filtration efficiency of the charged particle filtration device may vary depending on at least one of the flow rate of a fluid passing through the filtration device, the voltage applied to the first electrode and the ion exchange membrane, the zeta potential of the charged particles, or the type of the charged particles.

[0030] In one aspect, the charged particle filter may be used to re-filter a fluid that has passed through a reverse osmosis based filter.

[0031] According to one aspect, the fuel cell may further include a branch channel branched from the main channel upstream of the ion exchange membrane and configured to discharge the charged particles.

[0032] According to one aspect, the charged particles may be transported to the branch channel by a resultant force of an electrophoretic force of an ion depletion region formed in the upstream direction of the ion exchange membrane and a drag force along the flow of the fluid. Effect of the Invention

[0033] The disclosed technology may have the following effects. However, this does not mean that a particular embodiment must include all of the following effects or only the following effects, and therefore the scope of the disclosed technology should not be understood to be limited thereby.

[0034] According to the above-mentioned charged particle filtering device using electrokinetics according to one embodiment of the present invention, by filtering charged particles using electrokinetics, it is possible to filter even target substances that are difficult to remove using conventional membrane filtration methods, such as those having a fine size or a fiber shape, and this has the advantage of solving the problem of membrane fouling.

[0035] In addition, by using electrokinetics for filtration, it is possible to achieve high removal efficiency for the substances to be filtered, while preventing a decrease in flow rate or excessive consumption of energy for maintaining the flow rate. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a schematic diagram of an electrokinetically assisted filtration system for removing charged particles from a fluid. [Diagram 2] The dynamics of charged particles located at the edge and center of the main channel, respectively, are shown. [Diagram 3] FIG. 2 is a schematic diagram showing the formation of an ion depletion region for an ion exchange membrane alone and for an ion exchange membrane-porous layer combination. [Figure 4] 1 shows a model experimental setup for a filtration device according to one embodiment of the present invention. [Diagram 5] FIG. 2 is an exploded view of the configuration showing the arrangement of the major device components. [Figure 6] FIG. 5 is a side view of the experimental setup of FIG. [Figure 7] Shown is an ion exchange membrane with a microhole array and a porous layer covered with a dome-shaped cap. [Figure 8] The assembled experimental setup is shown. [Figure 9] A comparison of the microplastic removal performance between mathematical analysis and experimental results is shown. [Figure 10] Three different filtration conditions are shown, classified according to the voltage-flow rate relationship. [Figure 11]Photographs and microscope images of sampled PE microsphere feed and filtrate with varying voltage are shown, along with the removal efficiency of PE microspheres with voltage. [Figure 12] Photographs and microscope images of sampled PE microsphere feed and filtrate with varying flow rates and removal efficiency of PE microspheres with flow rate are shown. [Figure 13] 1 shows the particle size distribution of PE microspheres feed and filtrate with voltage changes. [Figure 14] 1 shows particle size distribution of PE microspheres feed and filtrate with varying flow rate. [Figure 15] Photographs and microscope images of the feed and filtrate at various pH conditions with varying voltage and the removal efficiency of PS microspheres at various pH conditions with varying voltage are shown. [Figure 16] Photographs and microscope images of the feed and filtrate at various pH conditions with varying flow rates and the removal efficiency of PS microspheres at various pH conditions with varying flow rates are shown. [Figure 17] Photographs and microscope images of the feed and filtrate for sampled PE, PS and PP microspheres with varying voltage and removal efficiency of PE, PS and PP microspheres with voltage are shown. [Figure 18] Photographs and microscope images of feed and filtrate for sampled PE, PS and PP microspheres with varying flow rates and removal efficiency of PE, PS and PP microspheres with different flow rates are shown. [Figure 19] Photographs and microscope images of the feed and filtrate for sampled PEST, acrylic and nylon bundles with varying voltage and removal efficiency of PEST, acrylic and nylon bundles with varying voltage are shown. [Figure 20] Photographs and microscope images of the feed and filtrate for sampled PEST, acrylic and nylon bundles at different flow rates and removal efficiency of PEST, acrylic and nylon bundles at different flow rates are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] While the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail.

[0038] However, it should be understood that this is not intended to limit the invention to the particular embodiment, but rather to include all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0039] Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only to distinguish one component from another. For example, a first component may be named a second component, and similarly, a second component may be named a first component, without departing from the scope of the invention. The term "and / or" includes any combination of multiple related listed items or any of multiple related listed items.

[0040] When a component is referred to as being "coupled" or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but that there may be other components in between. On the other hand, when a component is referred to as being "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0041] The terms used in this application are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0042] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms, such as those defined in commonly used dictionaries, should be interpreted to have a meaning consistent with the meaning they have in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless expressly defined in this application.

[0043] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the following description of the present invention, the same reference numerals are used for the same components in the drawings to facilitate an overall understanding, and duplicated descriptions of the same components are omitted.

[0044] overview

[0045] In the following description, for the sake of convenience, fine plastics may be used as an example of charged particles; however, it should be easily understood by anyone with ordinary knowledge in the technical field of the invention described herein that the subject of filtration according to the technical idea of ​​the present invention is not limited to plastics, and any particle that carries an electric charge can be the subject of filtration.

[0046] Membrane filtration (MF), which is based on the size exclusion mechanism among the engineering decomposition and separation methods for removing charged particles such as microplastics (MP) in aquatic environments, has shown potential to effectively treat charged particles of various sizes ranging from submicrons to several millimeters. However, the trade-off between intrinsic efficiency and flow rate and problems with MF related to membrane fouling have raised doubts about its practical applicability.

[0047] More specifically, but not exclusively, the present description presents a method for removing charged particles that can overcome the trade-off between the fundamental filtration efficiency and flow rate of MF by integrating electrokinetic assistance with physical filtration, and is free from membrane fouling-related problems. The filtration method according to one aspect of the present description is based on electrokinetic control of charged particles based on ion concentration polarization (ICP), and can effectively block downstream movement of charged particles by inducing an electric force barrier in a fluid channel system.

[0048] Because small charged particles that pass through the physical filter grid are electrically screened, the trade-off between efficiency and flow rate is greatly mitigated in electrokinetic assisted filtration systems, achieving a high removal efficiency of over 99.9% and a flow rate of 10,000 Lm3 without the use of fine filters. -2 h -1 In one aspect, the filtration mechanism is entirely dependent on the electrophoretic mobility of charged particles, and therefore can achieve consistent filtration performance for the same type of charged particles regardless of their size, shape, and chemical composition. In addition, due to the nature of the force-based charged particle filtration mechanism, it is not affected by the concentration of charged particles.

[0049] The theoretical background of the filtration method using the scalable electrokinetic system according to an aspect of the present disclosure is specifically described below. The basic working principle of the system according to an aspect of the present disclosure is described through a parametric study of predetermined control variables (voltage and flow rate). As an example of charged particles, polyethylene microspheres with various sizes ranging from hundreds of nanometers to hundreds of micrometers are used in the parametric study to thoroughly verify the filtration mechanism according to the embodiment of the present disclosure. Then, the influence of electrophoretic mobility of charged particles on the system performance is described. In addition, the filtration performance of the system according to an aspect of the present disclosure for various types and forms of MPs most frequently found in aquatic environments is systematically evaluated. Three types of MPs (polyethylene, PE; polystyrene, PS; polypropylene, PP) and three types of fiber MPs (polyester, PEST; acrylic, nylon) were selected as exemplary model MPs.

[0050] Electrokinetic Assisted Filtration System

[0051] FIG 1 is a schematic diagram of an electrokinetically assisted filtration system for removing charged particles from a fluid. Hereinafter, the filtration system in this description may also be referred to as a "filter". Hereinafter, the working principle of the electrokinetically assisted filtration system according to one aspect of the present description will be described in more detail with reference to FIG 1.

[0052] The inventors of the present disclosure have devised an electrokinetic-based filtration system by focusing on the fact that charged particles, such as fine plastic particles, actually have a surface charge when suspended in an electrolyte. The system may be embodied as a hybrid filter system that supplements physical filtration with electrokinetics. As shown in FIG. 1, the system according to one embodiment may be composed of a main channel 100 and buffer channels 110 and 120, and a first electrode 210 and an ion exchange membrane 220 may be disposed in the main channel 100. The first electrode 210 and the ion exchange membrane 220 may allow a current to flow between the first electrode and the ion exchange membrane to generate an electric field.

[0053] More specifically, and without limitation, as illustrated in FIG 1, an embodiment of the present invention may provide a filtration device 1000 using electrokinetics. A fluid 10 containing charged particles, such as fine plastics, may be input to an inlet of a buffer channel 110, and a fluid 90 from which the charged particles have been filtered may be discharged to an outlet of a buffer channel 120 via a main channel 100. According to one aspect, the main channel 100 may refer to a main filtration path through which a fluid containing charged particles is input and through which a fluid 90 from which the charged particles have been filtered is discharged. That is, the main channel 100 may provide a path through which a fluid containing charged particles is input and flows.

[0054] The main channel 100 may include a first electrode 210 and an ion exchange membrane 220 arranged to permit fluid flow therethrough. The ion exchange membrane 220 may be arranged downstream of the first electrode 210 and configured to include a number of voids 221 through which the fluid from which the charged particles have been filtered may be discharged.

[0055] As described above, the first electrode 210 may be disposed to allow the flow of a fluid. For example, as exemplarily shown in FIG. 1 or FIG. 5, the first electrode 210 has a flat plate shape and can allow the flow of a fluid by having a plurality of gaps 211 into which a fluid containing charged particles is introduced. In addition, according to one aspect, such a first electrode may be an ion exchange membrane having a plurality of gaps 211 that allow the flow of a fluid. For example, in this description, the first electrode 210 formed of an ion exchange membrane may be referred to as an "additional ion exchange membrane 210" in distinction from the ion exchange membrane 220. However, it should be understood that the first electrode 210 according to this description is not limited to such a flat plate electrode or ion exchange membrane, and may have any shape, such as a rod shape or a mesh shape, that can allow the flow of a fluid inside the main channel and can be opposed to the ion exchange membrane 220 to form an electric field, regardless of its shape.

[0056] 1, the ion exchange membrane 220 may be disposed downstream of the first electrode 210, and may have a plurality of voids 221 through which the fluid from which the charged particles have been filtered is discharged. For example, in order to facilitate the flow of fluid inside the main channel, the first electrode 210 may also have microholes 211 formed therein, and the ion exchange membrane 220 may also have microholes 221 formed therein. The first electrode 210 and the ion exchange membrane 220 may be configured to physically allow the flow of fluid inside the main channel 100 while simultaneously generating a flow of current between the first electrode 210 and the ion exchange membrane 220.

[0057] A branch channel 900 may be introduced in the middle of the main channel 100 for the purpose of continuously discharging the charged particles repelled from the electric force barrier and minimizing the accumulation of the charged particles in the physical filter 400. The filtered charged particles may be discharged through the outlets 30-1 and 30-2 of the branch channel 900. According to one aspect, the branch channel 900 may be configured to branch from the main channel 100 between the first electrode 210 and the ion exchange membrane 220 to discharge the charged particles. According to one aspect, the charged particles may be transported to the branch channel 900 by an ion depletion region 300 formed in the upstream direction of the ion exchange membrane 220, which will be described in detail later in this description. According to one aspect, the branch channel 900 may refer to a path through which the filtered charged particles are discharged by branching from the main channel 100.

[0058] According to one embodiment of the present disclosure, the first electrode 210 may be configured to have a polarity different from that of the charged particles to be filtered, the ion exchange membrane 220 may be an ion exchange membrane for ions of a polarity different from that of the charged particles to be filtered, and a second electrode of the same polarity as that of the charged particles to be filtered may be connected to the ion exchange membrane 220. That is, the polarity of the voltages respectively applied to the first electrode 210 and the ion exchange membrane 220 and / or the type of the ion exchange membrane 220, such as a cation exchange membrane or an anion exchange membrane, may be determined according to the polarity of the charged particles to be filtered.

[0059] FIG. 1 shows a polarity connection relationship for negatively charged microplastics as a non-limiting example. As shown in FIG. 1, according to an embodiment for filtering charged particles having a negative charge, such as microplastics, the first electrode 210 may be connected to a positive electrode and the ion exchange membrane 220 may be connected to a negative electrode. That is, the first electrode 210 may be an electrode that is connected to a positive electrode or may be formed of an electrode material connected to a positive electrode, and the negative electrode may be connected to the downstream ion exchange membrane 220, which may be a cation exchange membrane (CEM). In one aspect, the first electrode 210 may also be a cation exchange membrane (CEM) having a plurality of microholes 211, but it should be noted that this is not limiting. The inlet and outlet of the main channel 100 and the branch channel 900 may be electrically floating. In this configuration, ion concentration polarization (ICP) occurs in both ion exchange membranes due to the difference in ion mobility between the bulk solution and the nanochannels. This may result in the formation of an ion depletion region 300 in the upstream direction of the ion exchange membrane 220, in other words, in the direction toward the positive electrode of the ion exchange membrane 220. That is, the ion depletion region may be formed based on the ion concentration polarization.

[0060] The ion depletion region, which is substantially free of ions, is regarded as an electrical resistance and acts as an electrical barrier that prevents the movement of ions. Thus, the ion depletion region 300 can block the movement of charged particles, such as fine plastic particles, into the gap 221 of the ion exchange membrane 220. More specifically, the ion depletion region 300 can cause an electrophoretic force to act on the charged particles, such as fine plastic particles. Thus, the charged particles can move in a direction different from the flow of the fluid due to a drag force along the flow of the fluid and an electrophoretic force.

[0061] The movement behavior of charged particles in a fluid is governed by Stokes' law because the particle Reynolds number is very low (Re p ≪1). For example, considering a negative ion spherical charged particle, drag force and electrophoretic force mainly act on the charged particle, and the velocity components of these are given by the following mathematical formula:

[0062]

number

[0063]

number

[0064] where ρ is the particle density, ρ 0 is the density of the fluid, V is the volume of the particle, g is the gravitational acceleration, m is the mass of the particle, η is the dynamic viscosity of the fluid, and r is the Stokes radius of the particle. Also, ε 0 is the permittivity of free space, ε r is the relative permittivity, ζ is the zeta potential, and E is the electric field. Here, the drag velocity can be assumed to be the same as the fluid velocity.

[0065]

number

[0066] where Q is the flow velocity and A is the cross-sectional area of ​​the channel. The relaxation time (τ p ~10 -4 -10 -2 seconds) is so short that the drag velocity can be assumed to be the same as the fluid velocity. As a result, a charged particle approaching the ion depletion region has a forward drag velocity component, a drag velocity component towards the branching channel, and a reverse electrophoretic velocity component (whose direction is perpendicular to the tangent to the ion depletion region boundary).

[0067] According to one aspect of the present disclosure, as shown in FIG. 1, a slightly convex ion depletion region 300 is induced so that the direction of electrophoretic velocity is formed diagonally to the direction of drag velocity, and as a result, the direction of velocity can be set to a direction tangent to the ion depletion region. As a result, charged particles moving to the center of the main channel 100 continuously slide toward the branch channel 900 before entering the physical filter 400, reducing the accumulation of charged particles in the filter and enabling stable and long-term system operation. FIG. 2 shows the dynamic relationship between a charged particle 1a located at the edge of the main channel and a charged particle 1b located at the center.

[0068] For example, charged particles such as microplastics can have any shape, such as a plate, rod, or disk, and can therefore exhibit not only inertial motion but also rotational and lateral motion. However, this type of particle motion is estimated to occur within ~10 1 -10 2 This is primarily observed at high particle Reynolds numbers and may be ignored in systems according to embodiments of the present disclosure that exhibit low particle Reynolds numbers.

[0069] Electrokinetic systems, which have the advantage of being able to easily and precisely manipulate microparticles, may be used in a variety of microfluidic field diagnostic applications. Unfortunately, however, two fundamental upscaling problems have limited the channel size of electrokinetic systems to the microscale, preventing their application in environmental applications requiring large volumes.

[0070] The first problem is to generate an electric field (ion depletion region) of uniform direction and strength across the width of the channel. In typical microfluidic H-type electrokinetic systems, the ion depletion region cannot extend uniformly across the width of the channel beyond the millimeter scale, limiting the channel size to a few hundred micrometers. This causes problems such as the drag velocity and electrophoretic velocity being completely opposite in microchannels, but being oblique or perpendicular in wider channels, resulting in poor filtration efficiency.

[0071] According to one aspect of the present disclosure, an ion exchange membrane with microholes may be introduced to overcome such problems. For example, the ion depletion region 300 according to one aspect may include sub-ion depletion regions corresponding to each of the plurality of voids 221 provided in the ion exchange membrane 220, and may be configured to have a cross-sectional area in the fluid flow direction that is equal to or greater than a first predetermined area. More specifically, the ion exchange membrane with microholes may act as parallel microchannels connected by nanochannels, and local ion depletion regions generated in each microchannel may be combined to form an ion depletion region that is uniformly expanded in a uniform direction across the entire width of the channel. Thus, unlike conventional microfluidic electrokinetic systems in which the size of the channel is limited to several hundred micrometers, the ion exchange membrane with microholes according to one aspect of the present disclosure may be configured such that the ion depletion region 300 has a cross-sectional area in the fluid flow direction that is equal to or greater than a first predetermined area, for example, a cross-sectional area in the fluid flow direction that is equal to or greater than a millimeter scale.

[0072] The second problem is to suppress electroconvection (e.g., three-dimensional helical vortex pairs) induced by electro-osmotic instability (EOI), which prevents the formation of a properly distributed electric force barrier in a wide channel. FIG. 3 is a schematic diagram showing the formation of an ion depletion region in an ion exchange membrane alone and in an ion exchange membrane-porous layer combination. Excessive current is transmitted by EOI, mainly as the size of the channel increases, and vigorous electroconvection can be generated near the ion exchange membrane. In the filtration device according to one aspect of the present description, when the porous layer 400 is not provided, 300a is considered, and charged particles that enter the three-dimensional helical vortex pairs generated near the ion exchange membrane with microholes move along the flow lines and may leak through the membrane due to electroconvection resistance as shown in FIG. 3. According to one aspect of the present description, the above problem can be solved by introducing a porous layer that acts as a physical filter to screen out relatively large objects to be filtered, such as large plastic pieces. According to one aspect of the present description, in addition to the configuration for filtering using electrokinetics, a porous layer 400 that can act as a physical filter may be further provided. The porous layer 400 can filter not only charged particles but also uncharged particles if the porous layer 400 is larger than the pores of the porous layer 400. In addition, the porous layer 400 can also suppress electrical convection in the ion depletion region 300 for filtering based on electrokinetics, as described below.

[0073] More specifically, but not limited to, for example, the filtration device according to an embodiment of the present disclosure may further include a porous layer 400 arranged upstream of the ion exchange membrane 220 and configured to filter particles contained in a fluid that are equal to or larger than a first predetermined size. In the present disclosure, the porous layer may be referred to as a "microstructure." The porous layer or microstructure 400, which may be arranged upstream of the ion exchange membrane 220, may confine electroconvection to a microscale shape, and may allow the eddy current mechanism to be converted to electroosmotic flow at EOI (see 300b in FIG. 3). In this manner, a uniform and stable ion depletion region may be realized even in a wide channel of centimeter scale or larger. That is, the porous layer 400 according to an aspect of the present disclosure may confine electroconvection induced in the ion depletion region to a predetermined size or smaller, and may allow the ion depletion region to have a cross-sectional area in the direction of fluid flow that is equal to or larger than a second predetermined area. Here, the second area may have any value and may be the same as or different from the first area. For example, the second area may refer to a large area, such as a centimeter scale or larger. According to one aspect, the porous layer 400 may be formed of, but is not limited to, polyester microfiber.

[0074] Working Example

[0075] Figure 4 shows a model experimental apparatus for a filtration device according to one embodiment of the present invention, Figure 5 is an exploded view showing the arrangement of the main components of the apparatus, and Figure 6 is a side view of the experimental apparatus of Figure 4. The configuration of the experimental apparatus for the filtration device according to one aspect of the present disclosure will be described in detail with reference to Figures 4 to 6.

[0076] The device may be largely composed of an upper frame 510 and a lower frame 540 containing an electrode buffer channel, and an intermediate frame 530 containing a branch channel. Each frame may have a single hole, for example, 1 cm in diameter, in the center, which may be assembled to form a main channel. The first electrode 210 and the ion exchange membrane 220 are located between the intermediate frame 530 and the upper frame 510 / lower frame 540, and have multiple voids 211, 221. The first electrode 210 and the ion exchange membrane 220 allow fluid flow while allowing current to flow, thereby preventing potential damage to the main channel by by-products of the electrode reaction. Elastic silicone gaskets 521, 523, 525 may be laminated with the first electrode 210 to prevent leakage of fluid between the contact surfaces during operation of the device. For example, multiple silicone gaskets 521, 523, 525 may be provided between the upper frame 510 and the intermediate frame 530. For example, but not limited to, the first electrode 210 may be disposed in the middle silicon gasket 523 .

[0077] 7 shows an ion exchange membrane with a micro-hole array and a porous layer covered with a dome-shaped cap. The first electrode 210 and / or the ion exchange membrane 220 may be densely formed with micro-holes 211, 221, for example, with a diameter of 400 μm, for the movement of charged particles and uniform flow distribution in the main channel. The central hole of the intermediate frame 530 may be provided with a porous layer 400 or microstructure, which may be made of, for example, PEST microfiber, and may be configured to sieve out relatively large particles while suppressing electrical convection below a predetermined level.

[0078] According to one aspect, a dome-shaped cap 410 may be disposed upstream of the porous layer 400, configured to fix the porous layer 400 but allow fluid flow. For example, the dome-shaped cap 410 may include a number of openings to allow fluid flow. According to one aspect, the dome-shaped cap 410 may be used to slightly round the upper boundary of the porous layer 400 to induce a convex ion depletion region. More specifically, the dome-shaped cap 410 may curve the upper boundary of the porous layer 400, thereby causing the ion depletion region 300 to have a convex shape. FIG. 8 shows an assembled experimental setup. The components of the device may be assembled, for example, by simple screwing, as shown in FIG. 8.

[0079] Experimental Example 1 - Investigation of MP filtration behavior depending on voltage and flow rate

[0080] Figure 9 shows a comparison of the removal performance of fine plastics between mathematical analysis and experimental results. In the following, the removal performance of fine plastics will be described as an example of charged particles. However, it should be noted that the filtering target according to this description is not limited to fine plastics.

[0081] The equilibrium point where the drag velocity and electrophoretic velocity cancel each other out is shown in Figure 9. As mentioned above, a plastic piece entering an ion depletion region induced by a simple straight channel system has a drag velocity in the forward direction and an electrophoretic velocity in the reverse direction. The piece stops near the boundary of the ion depletion region where the two velocity components cancel each other out, which is called the equilibrium point. Based on the equilibrium point, if the drag velocity is dominant, the piece moves downward, and if the electrophoretic velocity is dominant, the piece moves upward. Therefore, the equilibrium point serves as a reference point that can theoretically predict the filtration behavior of MP (Micro Plastic). If Equation 2 and Equation 3 are set in the same way, a simple linear relationship between the voltage and flow velocity shown by the equilibrium line in the plot shown in Figure 9 is confirmed. Theoretically, based on this line, the area above the line is the non-filtration area (u drag >u ep), and the lower region is the filtering region (at the boundary of the ion depletion region, u) which achieves a removal efficiency of 99.9% or more. drag =u ep ) MP filtration experimental results were obtained under various voltage-current conditions and overlaid on the plot. Experimental conditions that showed removal efficiency of 99.9% or more are indicated by circle symbols, and other conditions are indicated by cross symbols. The overlaid experimental results show considerable correlation with the mathematical analysis, indicating that the hybrid filtration mechanism according to the described embodiment worked successfully.

[0082] Figure 10 shows three different filtration conditions classified by the voltage-flow rate relationship. Referring to Figure 10, three filtration conditions (conditions 1 to 3) classified by the voltage-flow rate relationship are shown. When the electrophoretic velocity is relatively dominant compared to the drag velocity (condition 1, 1010), most of the MPs are repelled from the outer boundary of the porous layer and electrokinetically filtered, while some of the MPs remain in the porous layer.

[0083] By slightly increasing the flow rate, an equilibrium point appears in the center of the porous layer (condition 2, 1020). Under these conditions, the larger plastic fragments are physically screened by the porous layer lattice, and the smaller plastic fragments that pass through the lattice become electrokinetically trapped at the equilibrium point. Because the MPs cannot pass through the electric force barrier, a perfect removal efficiency of nearly 100% is achieved in conditions 1 and 2. By further increasing the flow rate, the drag velocity dominates the electrophoretic velocity (condition 3, 1030), and the equilibrium point no longer appears in the porous layer, and the ion depletion region is suppressed near the CEM-electrolyte interface. The larger plastic fragments are still physically filtered, but the smaller plastic fragments pass through the electric force barrier and flow into the filtrate, resulting in a lower removal efficiency.

[0084] Figure 11 shows the photographs and microscope images of the sampled PE microsphere feed and filtrate with varying voltage, and the removal efficiency of PE microspheres with varying voltage. Also, Figure 12 shows the photographs and microscope images of the sampled PE microsphere feed and filtrate with varying flow rate, and the removal efficiency of PE microspheres with varying flow rate. The scale bars in the photographs and microscope images indicate 6 mm and 500 μm, respectively, and the photograph inserted in the graph of Figure 12 is for 6,000 Lm -2 h -1 (Condition 1), 8,000Lm -2 h -1 (Condition 2), 12,000Lm -2 h -1 At a flow rate of (Condition 3), various patterns of PE microsphere accumulation on the microstructures are shown, with the scale bar indicating 4 mm.

[0085] In FIG. 11 the filtration performance of the MP is shown as a function of voltage, and in FIG. 12 the filtration performance of the MP is shown as a function of flow rate.

[0086] In Figure 11, it can be seen that even without applying voltage, a removal efficiency of 27.6% is achieved, which is entirely due to physical filtration of larger particles and some smaller particles. The effect of physical filtration is the same even under voltage-approved conditions, and this is supported by the microscopic images of the filtrate, which show the absence of larger particles. -2 h -1 As the voltage increases at a constant flow rate, the electrokinetic assistance gradually strengthens and the removal efficiency increases, reaching 99.9% or more at a voltage of 150V or more.

[0087] In contrast, as shown in Figure 12, the removal efficiency decreases as the flow rate increases at a constant voltage of 200 V. Removal efficiency of over 99.9% is achieved up to 10,000 Lm -2 h -1 The flow rate was confirmed to be 12,000Lm -2 h -1 and 14,000Lm -2 h -1As the temperature increases, the particle accumulation distribution in the porous layer formed during the operation of the system decreases to 88.7% and 76.0%, respectively. As can be seen from the inset image in Figure 12, the particles are mainly accumulated in the 6,000 Lm -2 h -1 At a flow rate of 1000 Lm, the water accumulates on the upper surface of the porous layer, whereas the accumulation area is 8,000 Lm -2 h -1 This distribution behavior corresponds to conditions 1 and 2 in Figure 10. As a result, the point where condition 1 is converted to condition 2 is 6,000 Lm -2 h -1 From 8,000Lm -2 h -1 It can be expected that there exists a specific flow velocity between 10,000 Lm and 10,000 Lm. The critical flow velocity at which the removal efficiency of MPs begins to decrease from condition 2 to condition 3 begins to decrease. -2 h -1 This can be easily inferred from the above.

[0088] Meanwhile, Figure 12 shows photographs and microscope images of the filtrate for various flow rate conditions. As with the filtrate for various voltage conditions, no large particles were observed by physical filtration. The particle size distribution of PE microspheres in the filtrate for various voltage and flow rate conditions is shown in Figures 13 and 14, respectively. That is, Figure 13 shows the particle size distribution of the PE microsphere feed and filtrate with a change in voltage, and Figure 14 shows the particle size distribution of the PE microsphere feed and filtrate with a change in flow rate. Here, it was confirmed that particles with various size distributions were uniformly dispersed in the feed solution. Meanwhile, particles with a size distribution of 250 to 300 μm could not be observed in the plot, which is probably because their number (or concentration) was lower than the analytical detection limit. All particles larger than 50 μm were removed by physical filtration (0 V) alone, and the proportion of particles larger than tens of micrometers was also significantly reduced. Under the voltage condition of 25V, the proportion of particles with a size distribution of 20 to 45μm decreased, while the proportion of particles below 10μm increased, which is presumably due to the aid of electrokinetics. As the voltage increased, the proportion of relatively large particles decreased, while the proportion of small particles increased. This pattern of change may be due to the fact that the zeta potential is proportional to the particle size for the same type of particle. In particular, the distribution for the voltage condition of 150V or more, where a removal efficiency of 99.9% or more was confirmed, was expressed as a baseline of 0, since both filtrates contained particle numbers below the analytical detection limit. For the same reason, the distribution for the voltage condition of 4,000-10,000Lm -2 h -1 The distribution for the flow rate condition was expressed as the zero baseline. As the flow rate increased, the proportion of small particles decreased and the proportion of relatively large particles increased, which was the opposite of the distribution change caused by increasing voltage.

[0089] Experimental Example 2 - Effect of Zeta Potential on MP Removal Performance

[0090] To clarify the electrokinetic assisted filtration mechanism based on the electrophoretic mobility of MPs, the filtration performance of the filtration system described herein was investigated for the same type of MPs with different zeta potentials under various pH conditions. In these experiments, three specific pH conditions, pH 4, 7, and 10, were selected to maintain the electrolyte concentration of the buffer at a constant level between 0.1 mM and 1 mM. In addition, using PS microspheres with a diameter of 6 μm that are negatively charged in the corresponding pH range, the zeta potentials of the buffers at pH 4, 7, and 10 were -5.95 ± 0.47, -28.5 ± 0.50, and -31.7 ± 0.58 mV, respectively. The MP concentrations of each sample were all set to 0.2 g / L.

[0091] FIG. 15 shows the photographs and microscopic images of the feed and filtrate at various pH conditions with voltage change, and the removal efficiency of PS microspheres at various pH conditions with voltage change, and FIG. 16 shows the photographs and microscopic images of the feed and filtrate at various pH conditions with flow rate change, and the removal efficiency of PS microspheres at various pH conditions with flow rate change. That is, the photographs and microscopic images of PS microsphere feed and filtrate at various pH conditions (pH 4, 7, 10) sampled in the voltage control and flow rate control studies are shown. The scale bars of the photographs and images indicate 6 mm and 250 μm, respectively. The effect of zeta potential on MP removal performance will be described below with reference to FIG. 15 to FIG. 16.

[0092] First, Figures 15 to 16 show photographs and microscope images of the filtrate under various pH conditions with changes in voltage and flow rate. The decrease or increase in the concentration of MP in the filtrate as the voltage and flow rate increase proves that the system experienced a repulsive electrophoretic force regardless of the pH condition, based on the fact that MPs are all negatively charged when suspended in a buffer. As theoretically predicted, the degree of electrokinetic assistance depends entirely on the magnitude of the electrophoretic mobility of the MP, so different filtration behaviors are observed for MPs with different zeta potentials. The removal efficiency distribution, which is clearly distinguished by the zeta potential of the MP, can be seen in Figures 15 to 16. As can be seen from Equation 2, the electrophoretic velocity is proportional to the electric field and zeta potential of the MP, so the same change in voltage leads to a larger velocity change for MPs with a larger zeta potential. Therefore, considering the characteristics of the electrokinetically assisted filtration mechanism, it can be considered that the zeta potential is correlated with the removal efficiency and amount. In the case of MPs in pH 4 buffer, which has the smallest zeta potential, the removal efficiency increases gradually as the voltage increases, reaching 97.8% at 200V. The MP removal efficiency of pH 7 buffer is similar to that of pH 4 buffer at 25V, but increases more rapidly as the voltage increases, reaching a peak (>99.9%) at 150V. The steepest slope is observed in the removal efficiency curve of MPs in pH 10 buffer, which has the largest zeta potential. As a result, it reaches the peak first at a voltage of 100V. Meanwhile, when the same MPs were tested, the effect of physical filtration was almost the same under all pH conditions, and the removal efficiency of MPs in pH 4, 7, and 10 buffers was 13.5%, 12.7%, and 13.8%, respectively. The change in removal efficiency due to the change in flow rate was mainly affected by the magnitude of the electrophoretic mobility of MPs. The magnitude of the electrophoretic velocity changes in proportion to the zeta potential of MPs. As the flow rate increases, MPs with the smallest zeta potential enter condition 3 first and begin to leak downstream. However, unlike the case of voltage change, the flow rate does not have a significant effect on the rate of change in removal efficiency, but rather determines the onset of MP leakage because it is a variable independent of the electrophoretic velocity. The removal efficiency of MPs in a pH 4 buffer solution is 4,000 Lm -2 h-1 The rate exceeds 99.9% only at flow rates of 16,000Lm -2 h -1 The MP removal efficiency in the pH 7 and 10 buffers decreased by 46.3% as the concentration increased to 14,000 Lm -2 h -1 The stagnation state is maintained up to a flow rate of 2,000 Lm. According to the assumptions mentioned earlier, it can be confirmed that there is no close relationship between the rate of decrease in removal efficiency and the zeta potential of MP. The same critical flow rate was confirmed for MPs with other buffers of pH 7 and 10 with zeta potentials at 2,000 Lm in this study. -2 h -1 Therefore, in reality, the MP of the pH 7 and 10 buffers was 14,000 Lm -2 h -1 From 16,000Lm -2 h -1 It is estimated that there is a distinct critical flow rate between the MP and the zeta potential, and in the case of MP in a pH 7 buffer, which has a low zeta potential, it is expected to be slightly lower than that of MP in a pH 10 buffer. In this experiment, the effect of electrophoretic mobility of MP on filtration performance in a hybrid filtration system was verified through experimental verification. As a result of the experiment, it was revealed that the operating conditions showing optimal removal efficiency vary depending on the zeta potential of MP. In this aspect, appropriately adjusting the zeta potential of MP can help achieve faster and more effective MP removal in the filtration system according to one aspect of the present disclosure.

[0093] Experimental Example 3 - Filtration performance for various types of MP

[0094] The filtration performance of the described filtration system was evaluated against three types of MP (PE, PS, and PP) that are most frequently found in aquatic environments. Each feed contained PE microspheres with diameters of 10-45 μm, PS microspheres with diameters of 20 μm, and PP fragments with diameters of 25-85 μm, uniformly dispersed in 1 mM NaCl electrolyte at a concentration of 0.2 g / L. The zeta potentials of the PE microspheres, PS microspheres, and PP fragments were -12.5 ± 0.79, -25.7 ± 0.82, and -6.29 ± 0.98 mV, respectively.

[0095] Figure 17 shows the photographs and microscope images of the feed and filtrate for sampled PE, PS and PP microspheres with varying voltages, and the removal efficiency of PE, PS and PP microspheres with varying voltages, and Figure 18 shows the photographs and microscope images of the feed and filtrate for sampled PE, PS and PP microspheres with varying flow rates, and the removal efficiency of PE, PS and PP microspheres with varying flow rates. The scale bars in the photographs and images are 6 mm and 500 μm, respectively. The filtration performance of various types of MPs will be described below with reference to Figures 17 to 18.

[0096] The filtration behavior of each type of MP according to the change in voltage and flow rate is classified according to the magnitude of the zeta potential of the MP as shown in Figures 17 to 18. PS microspheres, which have the highest zeta potential, were not observed with the naked eye in the filtrate at voltages of 100 V or more, and were observed at 16,000 Lm -2 h -1 On the other hand, the PP fragments with the lowest zeta potential were observed in the filtrate even at a maximum voltage of 150 V, and began to leak into the filtrate at a flow rate of 10,000 Lm -2 h -1 The filtrate was fed under the above flow rate conditions. The corresponding removal efficiency distributions observed by microscope are illustrated in Figures 17 to 18, and as the voltage increases, the highest and lowest increase rates of removal efficiency are confirmed for PS microspheres and PP fragments, respectively. Therefore, the higher the zeta potential, the lower the voltage at which the removal efficiency curve reaches its peak. The effect of physical filtration was greatest for PP fragments (58.4%), followed by PE microspheres (35.7%) and PS microspheres (17.6%), which is probably due to the difference in average size distribution. The critical flow velocities for PP fragments, PE microspheres and PS microspheres are 8,000, 10,000 and 14,000 L m -2 h -1 and shows a proportional relationship with the zeta potential. The removal efficiency of PE microspheres, PS microspheres and PP fragments was-2 h -1 As the voltage increases, the removal efficiency of PP fragments decreases to 55.0%, 79.6% and 74.6%, respectively. In particular, the reduction rate of the removal efficiency of PP fragments is lower than that of other MPs, which is believed to be due to the high physical filtration effect. The results of this experiment show that the MP removal performance is not significantly related to the type of MP, but depends on the zeta potential of the MP. In the hybrid filtration method, when the voltage and flow rate are properly balanced, PE, PS, and PP, which are the most predominant types of MPs present in the aquatic environment, can all be effectively removed with a removal efficiency of 99.9% or more. Considering the inherent electrokinetic assisted filtration mechanism, it should be understood that the filtration device according to the embodiment described herein can be applied not only to the MPs investigated in this experiment, but also to any other types of charged MPs.

[0097] Experimental Example 4 - Microfiber Removal

[0098] Microfibers, which are primarily dispersed during synthetic fiber washing, are the most predominant form of MPs present in aquatic environments and are therefore very important for successful MP ​​treatment. Because microfibers permeate vertically through narrow lattices or small pores, membrane and filter-based methods such as membrane bioreactors, disk filters, and reverse osmosis have had some difficulty in completely removing fiber MPs. Fundamentally, the hybrid filtration method according to the present embodiment does not allow leakage of such types of fiber MPs, because the electric force barrier operates consistently, relying only on electrophoretic mobility, regardless of the form of the MPs. Thus, according to one aspect, the hybrid filtration device according to one aspect of the present embodiment may be used to re-filter fluids that have passed through a reverse osmosis-based filtration device. To verify this, the filtration performance of the filtration system according to one aspect of the present embodiment for the most common fiber MPs in aquatic environments (PEST, acrylic, nylon) was evaluated. PEST, acrylic, and nylon flocks with diameters of 10 to 30 μm and lengths of 250 μm were used as model fiber MPs and were uniformly dispersed in 1 mM NaCl electrolyte at a concentration of 0.2 g / L. The zeta potentials of the PEST, acrylic and nylon bundles were −9.94 ± 0.18, −3.24 ± 0.61 and −7.60 ± 0.26 mV, respectively.

[0099] FIG. 19 shows photographs and microscope images of feed and filtrate for sampled PEST, acrylic and nylon bundles with varying voltage and removal efficiency for PEST, acrylic and nylon bundles with varying voltage, and FIG. 20 shows photographs and microscope images of feed and filtrate for sampled PEST, acrylic and nylon bundles with varying flow rate and removal efficiency for PEST, acrylic and nylon bundles with varying flow rate. The removal of microfibers in a filtration system according to one aspect of the present disclosure will now be described in more detail with reference to FIG. 19-20. The scale bars in the photographs and images indicate 6 mm and 1 mm, respectively.

[0100] Figures 19 and 20 show the filtrate photographs and microscope images of PEST, acrylic, and nylon bundles as the voltage and flow rate are changed. A significant number of fibers and debris smaller than tens of micrometers derived from the fiber MP bundles were distributed in the feed and filtrate. When no voltage was applied, most of the bundles were removed through physical filtration because the effective pore size of the porous layer (82.6 ± 0.21 μm) was much smaller than the average bundle size (length 250 μm), but most of the microfibers flowed into the filtrate after passing through the filter grid. As the voltage increased, the electric force barrier blocked their movement, and the number of leaking fine fibers gradually decreased. Conversely, as the flow rate increased, the fine fibers were able to pass through the electric force barrier, and the removal efficiency decreased.

[0101] Figures 19 and 20 show the distribution of removal efficiency as a function of voltage and flow rate. With bundles accounting for the majority of the sample mass floating in the feed, high removal efficiencies of 97.3-98.0% were achieved for all types of fiber MPs without voltage applied, due to the bundles being the majority of the sample mass floating in the feed. Since the average size of each type of fiber MP was similar, the physical filtration effect was almost the same. The change in removal efficiency with increasing voltage mainly depends on the zeta potential of the MPs. At a voltage of 200V, the removal efficiency of PEST and nylon bundles, which have relatively high zeta potentials, exceeded 99.9%, whereas the removal efficiency of the acrylic bundle, which has a low zeta potential, was only 99.0%. Similarly, the change in removal efficiency with increasing flow rate also depends on the zeta potential of the MPs. In the case of PEST and nylon bundles, the removal efficiency was 8,000 Lm -2 h -1 It is shown to be 99.9% or higher up to a flow rate of 16,000Lm -2 h -1 It was confirmed that the flow rate of the acrylic bundle was slightly reduced to 99.0% and 98.3%, respectively. -2 h -1 The flow rate is predominant at 16,000Lm -2 h -1As the concentration of zeta potential increases, the removal efficiency decreases to 97.3%. As mentioned above, the low removal efficiency due to low zeta potential can be resolved by increasing the zeta potential of the MPs through adjustment of the pH conditions of the sample. In conclusion, electrokinetic assistance can effectively prevent the leakage of small plastic fibers and successfully remove fibrous MPs. This experiment also once again demonstrated the unique properties of the hybrid filtration mechanism, in that the filtration system according to one embodiment described herein exhibits consistent filtration performance regardless of the morphology of the MPs.

[0102] As discussed above, the filtration efficiency of the charged particle filtration device according to one embodiment of the present disclosure can be varied by at least one of the flow rate of the fluid passing through the filtration device, the voltage applied to the first electrode and the ion exchange membrane, the zeta potential of the charged particles, or the type of charged particles.

[0103] In this regard, the present disclosure discloses a highly efficient, high-speed, scalable filtration system for removing charged particles, such as microplastics, from wastewater by integrating electrokinetic assistance with physical filtration. By inducing an electric force barrier in the physical filtration system, the trade-off between intrinsic efficiency and flow rate can be significantly alleviated by preventing downstream migration of charged particles through the filter grid. Through electrokinetic assistance, a high removal efficiency of over 99.9% for charged particles and a flow rate of 10,000 Lm2 can be achieved without the application of high pressure, despite the use of a filter with an average pore size of several tens of micrometers. -2 h -1 The experimental results demonstrated that the filtering performance of the filtering mechanism according to one embodiment of the present invention relies solely on the electrophoretic properties of the charged particles, and can successfully process the charged particles regardless of their type, size, shape, or chemical composition.

[0104] Due to the characteristics of the electrophoresis-based filtration mechanism, the method according to one aspect of the present disclosure exhibits consistent filtration behavior even with various concentrations of charged particles, and does not experience clogging of the filter pores during operation of the device. These unique characteristics differentiate the method according to the embodiment of the present disclosure from typical MF techniques, which have inconsistent filtration performance and inevitable membrane fouling problems.

[0105] Experimental conditions

[0106] Preparation of artificial MP solution

[0107] The artificial MP solutions used in the filtration experiments were prepared by dispersing a single type of MP in deionized water (DI). To study the core operating parameters of the hybrid filtration system, a feed containing PE microspheres (Cospheric LLC, USA) with four size ranges of diameters, 0.2-10 μm, 10-45 μm, 95-115 μm, and 250-300 μm, was used. The MP concentration of each size range was the same at 0.1 g / L (total MP concentration: 0.4 g / L). In other studies, samples containing MPs of a single size range were used, and the MP concentration of each sample was the same at 0.2 g / L. The feed used in the study to determine the effect of the zeta potential of MPs on the filtration behavior of the proposed system was prepared by dispersing PS microspheres (Polysciences, USA) with a diameter of 6 μm in buffer solutions of various pH conditions (pH 4, 7, and 10). In the filtration performance evaluation study of the proposed system for various types of MPs, PE microspheres (diameter: 10-45 μm), PS microspheres (diameter: 20 μm), and PP flakes (diameter: 25-85 μm) (Polysciences, USA) were selected as model types of MPs. To verify the efficacy of the proposed system for fibrous MPs, PEST (diameter: 10-30 μm), acrylic (diameter: 19-25 μm), and nylon bundles (diameter: 10-20 μm) (Goonvean Fibres ltd, UK) were tested. Their length was identical at 250 μm. For stable aqueous suspension of MPs, Tween 20 (Cospheric LLC, USA), a non-ionic surfactant, was added to the artificial MPs solution at a concentration of 0.1% w / v. Along with this, the electrolyte concentration of the artificial MPs solution was adjusted to 1 mM using sodium chloride (NaCl, Sigma-Aldrich, USA) to induce electrokinetic phenomena in the system. The pH of the buffer solutions used in the study to determine the effect of the zeta potential of MPs on the filtration behavior of the proposed system was adjusted to hydrochloric acid (HCl, Sigma-Aldrich, USA) and sodium hydroxide (NaOH, Sigma-Aldrich, USA).

[0108] Fabrication of a scalable electrokinetically assisted filtration device

[0109] For the experiments on the described filtration device, a simple assembly-based expandable electrokinetic assisted filtration device was designed. The upper, lower and middle frames of the device, including the main channel, buffer channel and branch channel, were fabricated by 3D printing (Object 3500 using Vero transparent material, Stratasys, USA). Carbon paper electrodes with a thickness of 1 mm were cut into ring shapes using a paper punch, inserted into the slots of the upper and lower frames, and then fixed using silver conductive epoxy adhesive (MG Chemicals 8330, MG Chemicals, Canada). Titanium wires were firmly attached to the carbon paper electrodes for DC electrical application. Microholes in the CEM were prepared through a simple drilling process. A microhole array with holes of 400 μm diameter and hole spacing of 500 μm was formed in a conventional CEM (Fumasep, FTCM-E, Germany) using a desktop engraving machine (DE-3 desktop engraving machine, Roland DF, Japan). After forming the microhole array, the CEM was cut into circles using a paper punch. A silicon gasket to prevent fluid leakage was prepared by cutting a 0.5 mm thick silicon sheet (HSW, Korea) using a laser cutter (Universal Laser Systems, USA). The main channel of the midframe was densely filled with a porous layer material (PEST microfiber, Huvis, Korea) and then covered with a 3D printed dome-shaped cap to induce a convex ion depletion region. Finally, all the device components were aligned as shown in Figure 5 and assembled by screwing. Tube connectors (Harvard Apparatus, USA) were attached to the inlet and outlet of the frame to control the fluid flow of the device.

[0110] Filtration experiment

[0111] The experimental procedure for the electrokinetic assisted filtration system is as follows.

[0112] Prior to the experiment, the CEM was soaked in DI water for 5 min for smooth current flow between the main and buffer channels. The feed and buffer reservoirs were connected to the inlets of the main and buffer channels, respectively, with silicone tubing (Cole Parmer, USA), and 0.3 M sodium sulfate (Na2SO4, Samcheolri, Korea) was used as the electrode buffer. Luer-lock syringes (BD Luer-Lok, BD, USA) were connected to the tube connectors attached to the outlets of the main and branch channels with silicone tubing, and a specific withdrawal flow rate was applied to the outlets using a syringe pump (PHD2000, Harvard Apparatus, USA). A constant DC electric field was applied to the working electrode using a source-measurement device (B2902A, Keysight, USA). To obtain a reliable filtrate that is not affected by MP leakage that occurs before the generation of the electric force barrier, the introduction of the feed solution was preceded by the formation of the ion depletion region. The main channel was first filled with 1 mM NaCl that does not contain MPs. Then, to prevent downstream migration of MPs, the outlets of the main channel and the branch channel were blocked and a feed reservoir was connected to the inlet of the main channel while maintaining negative pressure. In this state, electricity was applied to the system to induce an ion depletion region near the negative CEM, and then fluid flow was allowed. The filtrate collected in the Luer-lock syringes connected to the outlets of the main channel and the branch channel was smoothly extracted from the conical tube.

[0113] Determination and characterization of MPs

[0114] Microscopy and infrared methods have been widely used to quantify and characterize MPs in aquatic environments with high reliability, but they are tedious and time-consuming when analyzing large and complex samples. In this study, since the artificial MP solutions used in each experiment consisted of a single type of MP, instead of these methods, a weighted method was adopted to measure the removal efficiency in the electrokinetic-assisted filtration system. The detailed experimental procedure is as follows. First, the feed solution and filtrate were filtered through a 0.22 μm hydrophilic membrane filter (Millipore, USA). Then, the collected membrane filter was covered with aluminum foil to prevent the inflow of foreign matter, and then dried in a vacuum drying oven at 60 °C for 24 hours. Since there were very small amounts of MPs in each sample and filtrate, the mass of the membrane filter was measured using a 5-digit high-precision balance (MS105, METTLER TOLEDO, USA) that can read down to 0.01 mg. The mass of MPs was calculated by subtracting the mass of the pure membrane filter from the mass of the membrane filter with MPs accumulated. The removal efficiency in electrokinetic assisted filtration was calculated according to the following mathematical formula 4.

[0115]

number

[0116] where m F is the mass of MP in the sample, and m fis the mass of MPs in the filtrate. All experiments were performed twice, and the average value of the two samples was recorded. The morphology of the porous layer was observed using a multifocal light microscope (BX53M, Olympus, Japan) and an injection electron microscope (SU6600, Hitachi, Japan), and the average pore size was calculated using ImageJ software (NIH, Bethesda, MD, USA). Digital microscopic images of the samples and filtrates were acquired with an inverted fluorescent microscope (IX71, Olympus, Japan) and microscope imaging software (cellSens, Olympus, Japan). The particle size distribution of the PE microspheres was analyzed with a laser diffraction particle size analyzer (LS 13 320, Beckman Coulter, USA). The zeta potential of the MPs was measured with a zeta potential and particle size analyzer (ELSZ-2000, Otsuka Electronics, Japan).

[0117] Although the above description has been given with reference to the drawings and examples, it is not intended that the scope of protection of the present invention is limited to the drawings or examples, and a person skilled in the relevant technical field should understand that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention as described in the following claims.

[0118] The present invention described above has been described based on a series of functional blocks, but it is not limited to the above-mentioned embodiments and the accompanying drawings, and it is obvious to a person having ordinary knowledge in the technical field to which the present invention pertains that various substitutions, modifications and changes are possible within the scope not departing from the technical idea of ​​the present invention.

[0119] Combinations of the above-described embodiments are not limited to the above-described embodiments, and various combinations other than the above-described embodiments may be provided as needed and / or implemented.

[0120] In the above embodiments, the method is described based on a flow chart as a series of steps or blocks, but the present invention is not limited to the order of steps, and a step may occur in a different order or simultaneously with other steps described above. Also, a person skilled in the art will understand that the steps shown in the flow chart are not exclusive, and other steps may be included, or one or more steps in the flow chart may be deleted without affecting the scope of the present invention.

[0121] The above-described embodiments include examples of various aspects. It is not possible to describe all possible combinations for illustrating various aspects, but a person having ordinary skill in the art should recognize that other combinations are possible. Therefore, it can be said that the present invention includes all other alternatives, modifications, and variations that fall within the scope of the following claims. [Explanation of symbols]

[0122] 100: Main Channel 210: First electrode 220: Cation exchange membrane 300: Ion depletion region 400: Porous layer 410: Dome-shaped cap

Claims

1. An apparatus for filtering charged particles using electrokinetics, a main channel through which a fluid containing charged particles is introduced and flows; a first electrode disposed within the main channel to permit fluid flow therethrough; and an ion exchange membrane disposed downstream of the first electrode and having a plurality of voids through which a fluid from which the charged particles have been filtered is discharged.

2. The first electrode and the ion exchange membrane are The apparatus for filtering charged particles according to claim 1 , further comprising: an electric field generated between the first electrode and the ion exchange membrane.

3. The first electrode is provided with a polarity different from that of the charged particles to be filtered, the ion exchange membrane is an ion exchange membrane for ions of a polarity different from that of the charged particles to be filtered, 3. The charged particle filtering device according to claim 2, wherein the ion exchange membrane is connected to a second electrode having the same polarity as the charged particles to be filtered.

4. In the upstream direction of the ion exchange membrane, 4. The charged particle filtering device according to claim 3, wherein an ion depletion region is formed that blocks the charged particles from moving into the voids of the ion exchange membrane.

5. The ion depletion region is 5. The charged particle filtering device according to claim 4, which is based on Ion Concentration Polarization (ICP).

6. The first electrode is 10. The apparatus of claim 1 including an additional ion exchange membrane having a plurality of voids that permit fluid flow therethrough.

7. The ion depletion region is 5. The device for filtering charged particles according to claim 4, wherein an electrophoretic force acts on the charged particles.

8. The charged particles are 8. The device for filtering charged particles according to claim 7, wherein the charged particles move in a direction different from the flow of the fluid due to a drag force along the flow of the fluid and the electrophoretic force.

9. The ion depletion region is 5. The charged particle filtering device according to claim 4, further comprising a sub-ion depletion region corresponding to each of a plurality of voids provided in the ion exchange membrane, and configured to have a cross-sectional area in a fluid flow direction that is equal to or greater than a predetermined first area by providing a plurality of sub-ion depletion regions.

10. 5. The charged particle filtering device of claim 4, further comprising: a porous layer disposed within the main channel upstream of the ion exchange membrane and configured to filter particles having a first predetermined size or larger from particles contained in a fluid.

11. The porous layer comprises:

11. The apparatus of claim 10, wherein electrical convection induced in the ion depletion region is limited to a predetermined magnitude or less, and the ion depletion region has a cross-sectional area in a direction of fluid flow that is equal to or greater than a second predetermined area.

12. The electrical convection is 12. The device of claim 11 , induced by electroosmotic instability.

13. 12. The apparatus of claim 11, wherein the electroconvection currents include three-dimensional helical vortex pairs.

14. The porous layer comprises:

11. The device for filtering charged particles of claim 10, formed from polyester microfiber.

15. 11. The apparatus of claim 10, further comprising: a dome-shaped cap configured to secure the porous layer but permit fluid flow.

16. The dome-shaped cap is 16. The apparatus of claim 15, wherein the upper boundary of the porous layer is curved such that the ion depletion region has a convex shape.

17. The filtering efficiency of the charged particle filtering device is:

2. The charged particle filtering device of claim 1, wherein the charged particle filtering device is varied by at least one of the following: a flow rate of a fluid passing through the filtering device, a voltage applied to the first electrode and the ion exchange membrane, a zeta potential of the charged particles, or a type of the charged particles.

18. The charged particle filtering device includes:

10. The device for filtering charged particles according to claim 1, which is used to refilter a fluid that has passed through a reverse osmosis-based filtration device.

19. The charged particle filtering device according to claim 1 , further comprising: a branch channel configured to branch off from the main channel upstream of the ion exchange membrane and to discharge the charged particles.

20. The charged particles are 20. The charged particle filtering device according to claim 19, wherein the charged particles are transported to the branch channel by a resultant force of an electrophoretic force of an ion depletion region formed in the upstream direction of the ion exchange membrane and a drag force along the flow of the fluid.

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