Device for filtering charged particles using electrokinetics

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 a filtration device, and more specifically, to a filtration device utilizing electrokinetics. Non-limitingly, more specifically, it relates to electrokinetic-assisted filtration technology for rapidly and efficiently removing charged particles such as fine plastics with water.

Background Art

[0002] Water treatment, including water and sewage treatment and industrial wastewater or sewage treatment, is considered very important in a wide range of areas. The filtration target substances contained in the fluid to be treated have various properties, and among them, filtration of charged particles may be required. Plastics can be exemplified as typical charged particles to be filtered.

[0003] Recently, in recent years, plastic pollution has become one of the major environmental problems, and related concerns have been increasing. As the use of plastics steadily increases, the annual global plastic production volume currently reaches about 400 million tons and is expected to reach about 800 million tons in 2050. The problem is that plastics do not rot. Since it takes a minimum of several decades to several hundred years to be completely decomposed, the plastics used are continuously accumulating in the ecosystem. On the other hand, discarded plastic waste is decomposed into various forms of small pieces through mechanical or chemical processes, and among them, pieces smaller than 5 mm are called micro plastics (MP). Micro plastics flow into the entire aquatic environment including rivers and seas due to their chemical stability and float in water for a long time. As a result, not only aquatic organisms but also humans and animals are inevitably exposed to MP, increasing the ecological and environmental risks.

[0004] In addition, due to its high specific surface area and hydrophobicity, MP can easily adsorb organic chemical pollutants such as bacteria, heavy metals, and compounds. If humans ingest contaminated MP through the food chain, it will also have harmful effects on human health. In particular, extremely small plastic fragments less than 1 μm in size, called nanoplastics (NP), can enter cells and tissues, cause inflammation, and potentially have an adverse impact on cell activities.

[0005] Among various engineering separation and decomposition technologies, membrane filtration (MF) is currently regarded as a promising strategy for successfully removing MP in the aquatic environment. By simply adjusting the pore size of the membrane filter based on the size exclusion mechanism, MP of various sizes can be effectively removed through MF. According to recent research, MF shows effective MP removal performance compared to existing water treatment processes (such as 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 polymer membranes.

[0006] However, despite its excellent MP removal performance, due to the inherent trade-off between removal efficiency and flow rate, MF has the problem of not being suitable for reliable industrial application fields. Generally, a pressure of several bar is applied to a membrane filter with an average pore size of about 1 μm, and a flow rate of several hundred Lm -2 h -1 is achieved. However, if a membrane filter with a finer pore size is used to separate even finer particles, the drop in membrane passing pressure further increases, and a considerably high energy consumption is required to ensure the same level of flow rate.

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

[0008] Therefore, in order to completely remove MPs in the aquatic environment, a practical approach that can solve such problems is required.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] One object of the present invention for solving the above problems is to filter substances to be filtered, which are conventionally difficult to remove by a membrane filtration method, such as having a fine size or having a fiber form, by filtering charged particles using electrokinetics, and to provide an electrokinetic charged particle filtration device that can solve the membrane fouling problem.

[0011] Another object of the present invention for solving the above problems is to provide an electrokinetic charged particle filtration device that can prevent excessive energy consumption for reducing or maintaining the flow rate while achieving high removal efficiency for substances to be filtered by using electrokinetics for filtration.

[0012] However, the problems to be solved by the present invention are not limited thereto, and can be variously extended within the scope not deviating from the idea and scope of the present invention.

Means for Solving the Problems

[0013] A charged particle filtration device according to an embodiment of the present invention for achieving the above object is a device that filters charged particles using electrokinetics, and includes a main channel into which a fluid containing charged particles is introduced and flows, a first electrode disposed inside the main channel to allow fluid flow, 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 is approved to have a polarity different from that of the charged particles to be filtered, the ion exchange membrane is an ion exchange membrane for ions having a polarity different from that of the charged particles to be filtered, and a second electrode having 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 may be formed upstream of the ion exchange membrane to block the charged particles from moving into the voids of the ion exchange membrane.

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

[0018] According to one aspect, the first electrode may include an additional ion exchange membrane having a plurality of voids that allow fluid flow.

[0019] According to one aspect, the ion depletion region may be configured such that an electrophoretic force acts 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 by a drag force along the fluid flow and the electrophoretic force.

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

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

[0023] According to one aspect, the porous layer may limit the electroconvection induced in the ion depletion region to a size equal to or smaller than a predetermined size, and the ion depletion region may have a cross-sectional area in the fluid flow direction of a fluid that is equal to or greater than a predetermined second 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 microfibers.

[0027] According to one aspect, it may further include a dome-shaped cap configured to fix the porous layer while allowing fluid flow.

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

[0029] According to one aspect, the filtration efficiency of the charged particle filtration device may be varied by at least one of the flow rate of the fluid passing through the filtration device, the voltage approved for the first electrode and the ion exchange membrane, the zeta potential of the charged particles, or the type of the charged particles.

[0030] According to one aspect, the charged particle filtration device may be used to filter again the fluid that has passed through the reverse osmosis pressure-based filtration device.

[0031] According to one aspect, it 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 transferred to the branch channel by the resultant force of the electrophoretic force of the ion depletion region formed in the upstream direction of the ion exchange membrane and the resistance force along the fluid flow.

Advantages of the Invention

[0033] The disclosed technology can have the following effects. However, it should not be understood that the scope of the rights of the disclosed technology is limited thereby, in the sense that a specific embodiment must include all of the following effects or only the following effects.

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

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

Brief Description of the Drawings

[0036]

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Best Mode for Carrying Out the Invention

[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, this is not intended to limit the present invention to specific embodiments, and it must be understood to include all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention.

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

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

[0041] The terms used in this application are merely for the purpose of describing specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that they do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof in advance.

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

[0043] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. In describing the present invention, for the sake of easy overall understanding, the same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

[0044] Summary

[0045] Hereinafter, in this description, for the sake of convenience of explanation, fine plastic may be used as an example of charged particles for description, but it should be easily understood by those of ordinary skill in the technical field to which the invention according to this description pertains that the filtration target according to the technical idea of the present invention is not limited to plastic, and any charged particle can be the filtration target.

[0046] In an aqueous environment, for example, among engineering decomposition and separation methods for removing charged particles such as micro plastics (MP), membrane filtration (MF) based on the size exclusion mechanism can effectively process charged particles of various sizes ranging from submicrons to several millimeters. However, due to the trade-off between the essential efficiency and flow rate and the problems associated with membrane fouling in MF, doubts have been raised about its actual applicability.

[0047] Although not limited, more specifically, in this description, an electrokinetic-assisted filtration method that integrates electrokinetic assistance into physical filtration to overcome the fundamental trade-off between filtration efficiency and flow rate in MF and be free from membrane fouling-related problems is presented. The filtration method according to one aspect of this description is based on the electrokinetic control of ion concentration polarization (ICP)-based charged particles and can effectively block the downstream movement of charged particles by inducing an electric force barrier in a fluid channel system.

[0048] In an electrokinetic-assisted filtration system, since charged particles with a small size passing through the physical filter lattice are electrically screened, the trade-off between efficiency and flow rate is very much alleviated, and a high removal efficiency of over 99.9% and a flow rate of 10,000 Lm -2 h -1 can be achieved simultaneously without using a fine filter. Since the filtration mechanism according to one aspect depends entirely on the electrophoretic mobility of charged particles, consistent filtration performance can be realized for charged particles of the same type regardless of their size, shape, and chemical composition. Also, due to the characteristics of the force-based charged particle filtration mechanism, it is not affected by the concentration of charged particles.

[0049] In the following, the theoretical background of the filtration method using an expandable electrokinetic system according to one aspect of the present description will be specifically described. Through the study of parameters regarding predetermined control variables (voltage and flow rate), the basic operating principle of the system according to one aspect of the present description will be explained. As an example of charged particles, polyethylene microspheres of various sizes ranging from several hundred nanometers to several hundred micrometers are used in the study of parameters to closely verify the filtration mechanism according to the examples of the present description. Thereafter, the influence of the electrophoretic mobility of charged particles on the system performance will be explained. Also, the filtration performance of the system according to one aspect of the present description regarding various types and forms of MPs most frequently found in the aquatic environment will be systematically evaluated. Three types of MPs (polyethylene, PE; polystyrene, PS; polypropylene, PP) and three types of fibrous MPs (polyester, PEST; acrylic, nylon) are adopted as exemplary model MPs.

[0050] Electrokinetic-assisted filtration system

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

[0052] The inventors of the present description, for example, focused on the fact that charged particles such as fine plastics actually have a surface charge when floating in an electrolyte and devised a filtration system based on electrokinetics. The system may be embodied as a hybrid filter system that assists electrokinetics in physical filtration. As shown in Figure 1, the system according to one embodiment may be composed of a main channel 100 and buffer channels 110, 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 between the first electrode and the ion exchange membrane to generate an electric field.

[0053] Non-limitingly, and more specifically, as exemplarily shown in FIG. 1, a filtration device 1000 utilizing electrokinetics may be provided according to an embodiment of the present invention. For example, a fluid 10 containing charged particles such as fine plastics may be introduced into the inlet of the buffer channel 110, and the fluid 90 from which the charged particles have been filtered may be discharged to the outlet of the buffer channel 120 through the main channel 100. According to one aspect, the main channel 100 may mean the main filtration path through which the fluid containing charged particles is introduced and the fluid 90 from which the charged particles have been filtered is discharged. That is, the main channel 100 may provide a path through which the fluid containing charged particles is introduced and flows.

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

[0055] As described above, the first electrode 210 may be arranged to allow the flow of the 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 the fluid by including a plurality of voids 211 into which the fluid containing charged particles is introduced. Also, according to one aspect, such a first electrode may be an ion exchange membrane having a plurality of voids 211 that allow the flow of the 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" to be distinguished from the ion exchange membrane 220. However, the first electrode 210 according to this description is not limited to such a flat plate electrode or ion exchange membrane, and for example, any form that can form an electric field facing the ion exchange membrane 220 while allowing the flow of the fluid inside the main channel, regardless of its shape such as a rod form or a mesh form, may be adopted.

[0056] Referring to FIG. 1, the ion exchange membrane 220 is disposed downstream of the first electrode 210, and the ion exchange membrane 220 may be provided with a plurality of voids 221 through which a fluid with charged particles filtered out is discharged. For example, in order to smooth the flow of the fluid inside the main channel, micro-holes 211 may also be formed in the first electrode 210, and micro-holes 221 may also be formed in the ion exchange membrane 220. The first electrode 210 and the ion exchange membrane 220 may be configured to physically allow the flow of the fluid inside the main channel 100 while 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 ejected from the electric force barrier and minimizing the accumulation of charged particles in the physical filter 400. The charged particles filtered through the outlets 30-1 and 30-2 of the branch channel 900 may be discharged. 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 so that charged particles are discharged. According to one aspect, the charged particles can be transferred 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 mean a path through which the charged particles branched from the main channel 100 and filtered are discharged.

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

[0059] FIG. 1 shows, as a non-limiting example, the polar connection relationship for negatively charged fine plastics. As shown in FIG. 1, for example, according to one embodiment for the filtration of charged particles having a negative charge such as fine plastics, a positive electrode may be approved for the first electrode 210, and a negative electrode may be connected to the ion exchange membrane 220. That is, the first electrode 210 may itself be an electrode for which a positive electrode is approved or may be formed of an electrode material connected to the positive electrode, the negative electrode may be connected to the downstream ion exchange membrane 220, and the ion exchange membrane 220 may be a cation exchange membrane (CEM). According to one aspect, it should be noted that the first electrode 210 may also be a cation exchange membrane (CEM) having a plurality of microholes 211, but is not limited thereto. The inlets and outlets of the main channel 100 and the branch channel 900 may be electrically floated. 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 nanochannel. Thereby, an ion depletion region 300 may be formed 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 ion concentration polarization.

[0060] The ion depletion region with almost no ions is regarded as an electrical resistance and acts as an electrical force barrier that prevents the movement of ions. Therefore, the ion depletion region 300 can block the movement of charged particles such as fine plastics into the voids 221 of the ion exchange membrane 220. More specifically, the ion depletion region 300 can be made to act on an electrophoretic force on charged particles such as fine plastics. Therefore, the charged particles can move in a direction different from the fluid flow by the drag force and the electrophoretic force along the fluid flow.

[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 anionic spherical charged particles, the drag force and the electrophoretic force mainly act on the charged particles, and among them, the velocity component is given by the following mathematical formula.

[0062]

Equation

[0063]

Equation

[0064] Here, ρ is the density of the particle, ρ0 is the density of the fluid, V is the volume of the particle, g is the acceleration due to gravity, 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, ε0 is the permittivity of free space, ε r is the relative permittivity, ζ is the zeta potential, and E is the electric field. Here, it can be assumed that the drag velocity is the same as the velocity of the fluid.

[0065]

Equation

[0066] Here, Q is the flow rate and A is the cross-sectional area of the channel. Since the relaxation time (τ p ~ 10 -4 -10 -2 seconds) of micrometer-sized particles in the fluid is very short, it can be assumed that the drag velocity is the same as the velocity of the fluid. As a result, charged particles approaching the ion depletion region have a forward drag velocity component, a drag velocity component in the direction of the branch channel, and a reverse electrophoretic velocity component (the direction of which is perpendicular to the tangent of the ion depletion region boundary).

[0067] According to one aspect of this description, as shown in FIG. 1, a slightly convex ion depletion region 300 is induced so that the direction of the electrophoretic velocity is formed obliquely with respect to the direction of the drag velocity, and as a result, the direction of the resultant velocity can be set to the direction in contact with the ion depletion region. As a result, charged particles moving to the center of the main channel 100 are continuously deflected toward the branch channel 900 side before entering the physical filter 400, alleviating the accumulation of charged particles in the filter, and enabling stable and long-term system operation. FIG. 2 shows the kinetic relationship between the charged particle 1a located at the edge of the main channel and the charged particle 1b located at the center.

[0068] For example, charged particles such as fine plastics actually have an arbitrary shape such as a plate, rod, disk, etc., and may exhibit rotational motion and lateral movement in addition to inertial movement. However, this type of particle motion is mainly observed at high particle Reynolds numbers of ~10 1 -10 2 and may be ignored in the system according to the embodiments of this description that exhibit low particle Reynolds numbers.

[0069] An electrokinetic system having the advantage of being able to easily and accurately manipulate fine particles may be used in various microfluidic point-of-care diagnostic applications. However, unfortunately, due to two fundamental upscaling problems, the channel size of the electrokinetic system has been limited to the microscale and has not been applied to environmental applications that require large volumes.

[0070] The first problem is to generate an electric field (ion depletion region) with a uniform direction and intensity across the entire width of the channel. In a typical microfluidic H-type electrokinetic system, the ion depletion region cannot expand uniformly over the width of the channel by more than a millimeter scale, so the channel size is limited to several hundred micrometers. For this reason, although the directions of the drag velocity and the electrophoretic velocity are completely opposite in a microchannel, there is a problem that they are oblique or perpendicular in a wide channel, resulting in a decrease in filtration efficiency.

[0071] According to one aspect of this description, an ion exchange membrane with microholes can 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 a 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 predetermined first area. More specifically, the ion exchange membrane with microholes can serve as parallelized microchannels connected by nanoscale channels, and the local ion depletion regions generated in each microchannel can be combined to form an ion depletion region that is uniformly extended in a uniform direction across the entire width of the channel. Therefore, unlike conventional microfluidic electrokinetic systems in which the channel size is limited to several hundred micrometers, the ion exchange membrane with microholes according to one aspect of this description may be configured to have a cross-sectional area in the fluid flow direction that is equal to or greater than a predetermined first area, for example, a cross-sectional area in the fluid flow direction of millimeter scale or greater.

[0072] A second problem is to suppress electroconvection (e.g., three-dimensional helical vortex pairs) induced by electroosmotic instability (EOI) that interferes with the formation of an appropriately distributed electrokinetic barrier in a wide channel. FIG. 3 is a schematic diagram showing the formation of ion depletion regions for each of an ion exchange membrane alone and a combination of an ion exchange membrane - porous layer. As the channel size mainly increases, an excessive current is transmitted by EOI, and active 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, considering 300a, charged particles that enter the three-dimensional helical vortex pair generated near the ion exchange membrane with microholes may move along the streamline and leak through the membrane due to electroconvection drag as shown in FIG. 3. According to one aspect of the present description, for example, by introducing a porous layer that serves as a physical filter for separating a filtration target substance having a relatively large size such as a large plastic piece, the above problems can be solved. According to one aspect of the present description, in addition to the configuration for filtration using electrokinetics, a porous layer 400 that can serve as a physical filter may be further provided. The porous layer 400 can filter not only charged particles but also particles having no charge if they are larger than the voids of the porous layer 400. Moreover, it can also serve to suppress the electroconvection of the ion depletion region 300 for electrokinetic-based filtration as described below.

[0073] Although not limited, more specifically, for example, the filtration device according to an embodiment described herein may further include a porous layer 400 disposed upstream of the ion exchange membrane 220 and configured to filter particles having a size equal to or larger than a predetermined first size among the particles contained in the fluid. In the present description, the porous layer may be referred to as a "microstructure". The porous layer or microstructure 400 that may be disposed upstream of the ion exchange membrane 220 can limit the electroconvection to a microscale shape and enable the overcurrent mechanism to be converted into an electroosmotic flow at the EOI (see 300b in FIG. 3). In such a manner, a uniform and stable ion depletion region can be realized even in a wide channel of centimeter scale or more. That is, the porous layer 400 according to one aspect of the present description may limit the electroconvection induced in the ion depletion region to a size equal to or smaller than a predetermined size, and the ion depletion region may have a cross-sectional area in the flow direction of the fluid equal to or larger than a predetermined second 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 mean an area of centimeter scale or more. According to one aspect, the porous layer 400 may be formed of polyester microfibers, but is not limited thereto.

[0074] Examples

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

[0076] The device may be mainly composed of an upper frame 510 including an electrode buffer channel and a lower frame 540, and an intermediate frame 530 including a branch channel. A single hole with a diameter of, for example, 1 cm may be formed in the center of each frame, and these holes can be assembled to form the 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 are provided with a plurality of voids 211, 221. The first electrode 210 and the ion exchange membrane 220 prevent potential damage to the main channel by by-products of the electrode reaction by allowing the flow of fluid and at the same time allowing the flow of current. Elastic silicon gaskets 521, 523, 525 may be laminated together with the first electrode 210 to prevent fluid leakage between the contact surfaces during the operation of the device. For example, a plurality of silicon gaskets 521, 523, 525 may be provided between the upper frame 510 and the intermediate frame 530. For example, the first electrode 210 may be disposed in the intermediate silicon gasket 523, but is not limited thereto.

[0077] Figure 7 shows an ion exchange membrane with a microhole array and a porous layer covered with a dome-shaped cap. For the movement of charged particles and the uniform flow distribution of the main channel, microholes 211, 221 with a diameter of, for example, 400 μm may be densely formed in the first electrode 210 and / or the ion exchange membrane 220. A porous layer 400 or a micro-structure composed of, for example, PEST ultra-fine filaments may be installed in the central hole of the intermediate frame 530, which is configured to screen out relatively large particles and at the same time suppress the electroconvection below a predetermined level.

[0078] According to one aspect, a dome-shaped cap 410 configured to fix the porous layer 400 while allowing fluid flow may be disposed upstream of the porous layer 400. For example, the dome-shaped cap 410 may include a plurality of openings to allow fluid flow. According to one aspect, the upper boundary of the porous layer 400 can be slightly rounded using the dome-shaped cap 410 to induce a convex ion depletion region. More specifically, the dome-shaped cap 410 can cause the ion depletion region 300 to have a convex shape by bending the upper boundary of the porous layer 400. FIG. 8 shows the assembled experimental apparatus. The components of the element may be assembled, for example, by simple screwing as shown in FIG. 8.

[0079] Experimental Example 1 - Investigation of the filtration behavior of MPs based on the relationship between voltage and flow rate

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

[0081] The equilibrium point at which the drag velocity and the electrophoretic velocity cancel each other out is shown in FIG. 9. As described above, plastic fragments entering the ion depletion region induced in a simple linear channel system have a forward drag velocity and a reverse electrophoretic velocity. The fragment stops near the boundary of the ion depletion region where the two velocity components cancel each other out, and this is called the equilibrium point. Based on the equilibrium point, if the drag velocity is dominant, the fragment moves downward, and if the electrophoretic velocity is dominant, the fragment moves upward. Therefore, the equilibrium point serves as a reference point for theoretically predicting the filtration behavior of MP (Micro Plastic). If Mathematical Formula 2 and Mathematical Formula 3 are set in the same way as each other, a simple linear relationship between the voltage and the flow velocity indicated by the equilibrium point line in the plot shown in FIG. 9 is confirmed. Theoretically, looking at this line as a reference, the upper region of the line is the non-filtration region where MP passes through the electric force barrier (u drag >u ep) and the lower region is a filtering region (at the boundary of the depletion region where u drag = u ep ) that achieves a removal efficiency of 99.9% or more. MP filtration experiment results were obtained under various voltage-current conditions and plotted and displayed superimposed. The experimental conditions that showed a removal efficiency of 99.9% or more were indicated by circular symbols, and other conditions were indicated by cross symbols. The superimposed experimental results show a significant correlation with mathematical analysis, indicating that the hybrid filtration mechanism according to the described embodiments operated properly.

[0082] FIG. 10 shows three different filtration conditions classified by the voltage-flow rate relationship. Referring to FIG. 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 MPs are repelled from the outer boundary of the porous layer and electrokinetically filtered, while some MPs remain in the porous layer.

[0083] When the flow rate is slightly increased, an equilibrium point appears in the center of the porous layer (condition 2, 1020). Under such conditions, large plastic fragments are physically sieved by the porous layer lattice, and small plastic fragments that pass through the lattice are electrokinetically confined to the equilibrium point. Since MPs cannot pass through the electric force barrier, near-100% complete removal efficiency is achieved in conditions 1 and 2. When the flow rate further increases and the drag velocity overwhelms the electrophoretic velocity (condition 3, 1030), the equilibrium point no longer appears in the porous layer, and the depletion region is suppressed near the interface of the cation exchange membrane (CEM)-electrolyte. Large plastic fragments are still physically filtered, but small plastic fragments penetrate the electric force barrier and flow into the filtrate, resulting in a lower removal efficiency.

[0084] Figure 11 shows the feed and filtrate photographs and microscope images of the sampled PE microspheres due to voltage changes, and the removal efficiency of the PE microspheres by voltage. Also, Figure 12 shows the feed and filtrate photographs and microscope images of the sampled PE microspheres due to flow rate changes, and the removal efficiency of the PE microspheres by 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 6,000 Lm -2 h -1 (Condition 1), 8,000 Lm -2 h -1 (Condition 2), 12,000 Lm -2 h -1 (Condition 3) show various patterns in which PE microspheres accumulate in the microstructure at the indicated flow rates, and the scale bar indicates 4 mm

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

[0086] In Figure 11, it can be confirmed that a removal efficiency of 27.6% is achieved even without applying voltage, which is due to physical filtration of mainly large particles and some small particles. The effect of physical filtration remains the same under voltage - applied conditions, as evidenced by the microscope image of the filtrate showing no large particles. At a constant flow rate of 8,000 Lm -2 h -1 as the voltage increases, the electrokinetic assistance gradually intensifies and the removal efficiency increases, reaching over 99.9% under voltage conditions of 150 V and above

[0087] In contrast, as shown in Figure 12, when the flow rate increases at a constant voltage of 200 V, the removal efficiency decreases. A removal efficiency of over 99.9% is confirmed at a maximum flow rate of 10,000 Lm -2 h -1 and the flow rate conditions, and when the flow rate is 12,000 Lm -2 h -1 and 14,000 Lm -2 h -1They decrease to 88.7% and 76.0% respectively as it increases. The aforementioned Conditions 1 to 3 can be distinguished by the particle accumulation distribution of the porous layer formed during system operation. As can be seen from the inserted image in Fig. 12, the particles are mainly accumulated on the upper surface of the porous layer at a flow velocity of 6,000 µm -2 h -1 while the accumulation region expands to a deeper position at a flow velocity of 8,000 µm -2 h -1 This such distribution behavior corresponds to Conditions 1 and 2 in Fig. 10. As a result, the point where the conversion from Condition 1 to Condition 2 occurs is expected to exist at a specific flow velocity between 6,000 µm -2 h -1 and 8,000 µm -2 h -1 It can be easily inferred at 10,000 µm -2 h -1 where the removal efficiency of the critical flow velocity at which the condition conversion from Condition 2 to Condition 3 begins to decrease as MP starts to pass through the electric force barrier.

[0088] On the one hand, Fig. 12 shows photographs and microscope images of the filtrate under various flow rate conditions. Similar to the filtrate under various voltage conditions, no large particles have been observed by physical filtration. The particle size distributions of the PE microspheres in the filtrate under various voltage and flow rate conditions are shown in Figs. 13 and 14, respectively. That is, Fig. 13 shows the particle size distributions of the feed and filtrate of the PE microspheres due to the change in voltage, and Fig. 14 shows the particle size distributions of the feed and filtrate of the PE microspheres due to the change in flow rate. Here, it was confirmed that particles with various size distributions were uniformly dispersed in the feed solution. On the other hand, particles having a size distribution of 250 - 300 μm could not be observed in the plot, presumably because their number (or concentration) was lower than the analytical detection limit. All particles of 50 μm or more have been removed only by physical filtration (0 V), and the proportion of particles larger than several tens of micrometers has also decreased significantly. Under the voltage condition of 25 V, the proportion of particles having a size distribution of 20 to 45 μm decreased, while the proportion of particles of 10 μm or less increased, which is presumably due to the assistance of electrokinetics. As the voltage increased, the proportion of relatively large particles decreased and the proportion of small particles increased. Such a change pattern may be due to the fact that the zeta potential is proportional to the particle size for the same type of particles. In particular, for the distribution under the voltage condition of 150 V or more where a removal efficiency of 99.9% or more was confirmed, since both of the two filtrates contained the number of particles less than the analytical detection limit, the reference line was expressed as 0. For the same reason, the distribution under the flow rate condition of 4,000 - 10,000 Lm -2 h -1 was expressed as the zero reference line. As the flow rate increased, the proportion of small particles decreased and the proportion of relatively large particles increased, showing a pattern opposite to the distribution change due to the increase in voltage.

[0089] Experimental Example 2 - Influence 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. To maintain the electrolyte concentration of the buffer at a constant level between 0.1 mM and 1 mM in such experiments, three specific pH conditions of pH 4, 7, and 10 were selected. Also, PS microspheres with a diameter of 6 μm that are negatively charged in the corresponding pH range were used, and 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 concentration of each sample was set to 0.2 g / L for all.

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

[0092] First, FIGS. 15 to 16 show photographs and microscopic images of the filtrate for various pH conditions due to changes in voltage and flow rate. The fact that the concentration of MPs in the filtrate decreases or increases as the voltage and flow rate increase proves that the system experienced an electroosmotic repulsive force regardless of the pH conditions, based on the fact that all MPs are negatively charged when suspended in the buffer. As theoretically predicted, the degree of electrokinetic assistance varies overall depending on the magnitude of the electrophoretic mobility of the MPs, so different filtration behaviors are observed for MPs with different zeta potentials. The removal efficiency distribution clearly distinguished by the zeta potential of the MPs can be confirmed in FIGS. 15 to 16, and as can be seen from Equation 2, the electrophoretic velocity is proportional to the electric field and zeta potential of the MPs, so the same degree of voltage change causes a greater velocity change for MPs with a larger zeta potential. Therefore, considering the characteristics of the electrokinetic-assisted filtration mechanism, it can be thought that the zeta potential has a correlation with the removal efficiency and quantity. In the case of MPs in the pH 4 buffer with the lowest zeta potential, the removal efficiency gradually increases as the voltage increases and reaches 97.8% at 200 V. The MP removal efficiency in the pH 7 buffer is similar to that of MPs in the pH 4 buffer at 25 V, but increases more rapidly as the voltage increases and reaches a peak (>99.9%) at 150 V. The steepest slope is observed in the removal efficiency curve of MPs in the pH 10 buffer with the highest zeta potential. As a result, it reaches the peak first at 100 V. On the other hand, as a result of testing the same MPs, there is almost no difference in the effect of physical filtration under the overall pH conditions, and the MP removal efficiencies in the pH 4, 7, and 10 buffers were shown to be 13.5%, 12.7%, and 13.8%, respectively. The aspect of the change in the removal efficiency due to the change in the flow rate was mainly affected by the magnitude of the electrophoretic mobility of the MPs. The magnitude of the electrophoretic velocity changes in proportion to the zeta potential of the MPs. As the flow rate increases, the MPs with the lowest zeta potential enter Condition 3 first and begin to leak downstream. However, unlike the case of voltage change, the flow rate is an independent variable from the electrophoretic velocity and does not have a significant impact on the rate of change of the removal efficiency, so it only determines the start of MP leakage. The removal efficiency of MPs in the pH 4 buffer is 4,000 Lm -2 h-1 exceeds 99.9% only at a flow rate of, and decreases by 46.3% as the flow rate increases to 16,000 Lm -2 h -1 while the removal efficiency of MPs in buffers at pH 7 and 10 remains stagnant up to a flow rate of 14,000 Lm -2 h -1 It can be confirmed that there is no close relationship between the reduction rate of the removal efficiency and the zeta potential of MPs according to the previously mentioned assumptions. The same critical flow rate was confirmed for MPs in other pH 7 and 10 buffers at 2,000 Lm -2 h -1 in this study, which is presumably due to a large change in the flow rate. Therefore, in reality, for MPs in pH 7 and 10 buffers, a distinct critical flow rate is presumed to exist between 14,000 Lm -2 h -1 and 16,000 Lm -2 h -1 and is expected to be slightly lower for MPs in the pH 7 buffer with a lower zeta potential than for MPs in the pH 10 buffer. In this experiment, the effect of the electrophoretic mobility of MPs on the filtration performance in a hybrid filtration system was verified through experimental evidence. As a result of the experiment, it was revealed that the operating conditions showing the optimal removal efficiency vary according to the zeta potential of MPs. Appropriate adjustment of the zeta potential of MPs in this regard can help achieve faster and more effective MP removal in the filtration system according to one aspect of this description.

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

[0094] The filtration performance of the filtration system according to this description was evaluated for the three most frequently found types of MPs (PE, PS, PP) in the aquatic environment. Each feed contained PE microspheres with a diameter of 10 - 45 μm, PS microspheres with a diameter of 20 μm, and PP fragments 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 microscopic images of the feed and filtrate for sampled PE, PS, and PP microspheres due to voltage changes, and the removal efficiency of PE, PS, and PP microspheres by voltage. Figure 18 shows the photographs and microscopic images of the feed and filtrate for sampled PE, PS, and PP microspheres due to flow rate changes, and the removal efficiency of PE, PS, and PP microspheres by flow rate. The scale bars in the photographs and images are 6 mm and 500 μm, respectively. Hereinafter, the filtration performance regarding various types of MPs will be described with reference to FIGS. 17 to 18.

[0096] The filtration behavior for each type of MP due to changes in voltage and flow rate is classified by the magnitude of the zeta potential of the MP as shown in FIGS. 17 to 18. The PS microspheres with the largest zeta potential were not observed with the naked eye in the filtrate under voltage conditions of 100 V or more, and began to leak into the filtrate at a flow rate of 16,000 Lm -2 h -1 . On the other hand, the PP fragments with the smallest zeta potential were observed in the filtrate even at a voltage of up to 150 V, and flowed into the filtrate under flow rate conditions of 10,000 Lm -2 h -1 or more. The removal efficiency distributions corresponding to microscopic observations are explained in FIGS. 17 to 18, and the highest and lowest increase rates of removal efficiency are confirmed for PS microspheres and PP fragments, respectively, as the voltage increases. 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 the largest for PP fragments (58.4%), followed by PE microspheres (35.7%) and PS microspheres (17.6%) in that order, which is presumably due to the difference in average size distribution. The critical flow rates of PP fragments, PE microspheres, and PS microspheres are 8,000, 10,000, and 14,000 Lm -2 h -1 respectively, showing a proportional relationship with the zeta potential. The removal efficiencies of PE microspheres, PS microspheres, and PP fragments are such that the flow rate is 16,000 Lm-2 h -1 As it increases to h, they decrease to 55.0%, 79.6%, and 74.6% respectively. In particular, it can be seen that the reduction rate of the removal efficiency of PP fragments is lower than that of other MPs, which is presumably due to the high physical filtration effect. The results of this experiment show that the MP removal performance has no significant relation with the type of MP and depends on the zeta potential of the MP. In the hybrid filtration method, when the voltage and the flow rate are properly balanced, it is possible to effectively remove all of PE, PS, and PP, which are the most dominant types of MPs present in the aquatic environment, with a removal efficiency of over 99.9%. Considering the inherent electrokinetic-assisted filtration mechanism, it must be understood that the filtration device according to the described embodiments can be applied not only to the MPs investigated in this experiment but also to any other type of charged MPs.

[0097] Experimental Example 4 - Removal of microfibers

[0098] Microfibers, which are mainly scattered during the washing of synthetic fibers, are the most dominant form of MPs existing in the aquatic environment and are very important for the successful treatment of MPs. Since microfibers penetrate vertically through narrow grids or small pores, membrane and filter-based methods such as membrane bioreactors, disk filters, and reverse osmotic pressure have been somewhat difficult to completely remove fiber MPs. Fundamentally, the hybrid filtration method according to the embodiments described herein, regardless of the form of MPs, the electric force barrier operates consistently depending only on the electrophoretic mobility, so that leakage of such types of fiber MPs does not occur. Therefore, according to one aspect, the hybrid filtration device according to one aspect described herein may be used to filter the fluid that has passed through the reverse osmotic pressure-based filtration device again. To verify this, the filtration performance of the filtration system according to one aspect described herein for the most common fiber MPs (PEST, acrylic, nylon) in the aquatic environment was evaluated. PEST, acrylic, and nylon flocks with a diameter of 10 - 30 μm and a length of 250 μm were used as model fiber MPs and uniformly dispersed in a 1 mM NaCl electrolyte with a concentration of 0.2 g / L. The zeta potentials of the PEST, acrylic, and nylon flocks were -9.94 ± 0.18, -3.24 ± 0.61, and -7.60 ± 0.26 mV, respectively.

[0099] Figure 19 shows the photographs and microscopic images of the feed and filtrate for the sampled PEST, acrylic, and nylon flocks with the change in voltage, and the removal efficiency of the PEST, acrylic, and nylon flocks by the voltage. Figure 20 shows the photographs and microscopic images of the feed and filtrate for the sampled PEST, acrylic, and nylon flocks with the change in flow rate, and the removal efficiency of the PEST, acrylic, and nylon flocks by the flow rate. Hereinafter, with reference to FIGS. 19 to 20, the removal of microfibers of the filtration system according to one aspect described herein will be described in more detail. The scale bars of the photographs and images indicate 6 mm and 1 mm, respectively.

[0100] Figures 19 to 20 show the filtration liquid photographs and microscope images of PEST, acrylic, and nylon bundles due to changes in voltage and flow rate. Fibers and fragments smaller than several tens of micrometers derived from the fiber MP bundles were distributed in significant numbers in the feed and the filtrate. When no voltage was applied, since the effective pore size of the porous layer (82.6 ± 0.21 μm) was much smaller than the average size of the bundles (length 250 μm), most of the bundles were removed through physical filtration, but most of the microfibers flowed into the filtrate after passing through the filter lattice. As the voltage increased, the electric force barrier blocked these movements, and the number of leaking fine fibers gradually decreased. On the contrary, as the flow rate increased, the fine fibers could pass through the electric force barrier, and the removal efficiency decreased.

[0101] Figures 19 to 20 show the removal efficiency distribution varying according to voltage and flow rate. High removal efficiencies of 97.3 - 98.0% were achieved with all types of fiber MPs without applying voltage by the bundles that occupied most of the sample mass floating in the feed. Since the average sizes of each type of fiber MP were similar, the physical filtration effects were almost the same. The change in removal efficiency due to the increase in voltage mainly varies according to the zeta potential of the MP. At a voltage of 200 V, the removal efficiencies of PEST and nylon bundles with relatively large zeta potentials exceeded 99.9%, while the removal efficiency of the acrylic bundle with a low zeta potential was only 99.0%. Similarly, the change pattern of the removal efficiency due to the increase in flow rate also differs according to the zeta potential of the MP. In the case of PEST and nylon bundles, the removal efficiencies were shown to be over 99.9% up to a flow rate of 8,000 Lm -2 h -1 and were confirmed to slightly decrease to 99.0% and 98.3% respectively at a flow rate of 16,000 Lm -2 h -1 In the case of the acrylic bundle, condition 3 was already dominant at a flow rate of 4,000 Lm -2 h -1 and at a flow rate of 16,000 Lm -2 h -1As it increases to [[ID=]], the removal efficiency decreases to 97.3%. As described above, the low removal efficiency due to the low zeta potential can be solved by increasing the zeta potential of MPs through adjusting the pH conditions of the sample. As a conclusion, electrokinetic assistance was able to effectively prevent the leakage of small plastic fibers and successfully remove fiber MPs. Also, in this experiment, the unique property of the hybrid filtration mechanism that the filtration system according to one embodiment described herein shows consistent filtration performance regardless of the form of MPs was verified again.

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

[0103] In connection with this, a highly efficient, high-speed, scalable filtration system for removing charged particles such as microplastics in wastewater by integrating electrokinetic assistance into physical filtration is disclosed herein. By inducing an electric force barrier in the physical filtration system, the downstream movement of charged particles passing through the filter lattice can be prevented, and the trade-off between the essential efficiency and the flow rate can be greatly alleviated. Through electrokinetic assistance, even though a filter with an average pore size of several tens of micrometers is used, a high removal efficiency of over 99.9% for charged particles can be achieved without applying high pressure, and a flow rate of 10,000 Lm -2 h -1 can be achieved. As a result of the experiment, it was verified that the filtration performance of the filtration mechanism according to one embodiment described herein can be successfully processed regardless of the type, size, shape, and chemical composition of charged particles, depending only on the electrophoretic mobility of the charged particles.

[0104] Due to the characteristics of the filtration mechanism of the electrophoresis substrate, the method according to one aspect of the present description exhibits the same filtration behavior even at various concentrations of charged particles, and the phenomenon of filter pores clogging during the operation of the device did not occur. Such unique characteristics differentiate the method according to the examples described herein from general MF techniques that 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). For the study of the core operating parameters of the hybrid filtration system, feeds containing PE microspheres (Cospheric LLC, USA) with four size ranges of 0.2 - 10 μm, 10 - 45 μm, 95 - 115 μm, and 250 - 300 μm in diameter were used. The MP concentration in each size range was the same at 0.1 g / L (total MP concentration: 0.4 g / L). In other studies, samples containing MP in a single size range were used, and the MP concentration in each sample was the same at 0.2 g / L. To determine the effect of the zeta potential of MP on the filtration behavior of the proposed system, the feeds used in the study were prepared by dispersing PS microspheres (Polysciences, USA) with a diameter of 6 μm in buffers under various pH conditions (pH 4, 7, 10). In the study of evaluating the filtration performance of the proposed system for various types of MP, PE microspheres (diameter: 10 - 45 μm), PS microspheres (diameter: 20 μm), and PP fragments (diameter: 25 - 85 μm) (Polysciences, USA) were selected as model types of MP. To demonstrate the efficacy of the proposed system for fibrous MP, PEST (diameter: 10 - 30 μm), acrylic (diameter: 19 - 25 μm), and nylon bundles (diameter: 10 - 20 μm) (Goonvean Fibres ltd, UK) were tested. These lengths were the same at 250 μm. For a stable aqueous suspension of MP, the non-ionic surfactant Tween20 (Cospheric LLC, USA) was added to the artificial MP solution at a concentration of 0.1% w / v. Together with this, to induce electrokinetic phenomena in the system, the electrolyte concentration of the artificial MP solution was adjusted to 1 mM using sodium chloride (NaCl, Sigma-Aldrich, USA). The pH of the buffer used in the study to determine the effect of the zeta potential of MP on the filtration behavior of the proposed system was adjusted with hydrochloric acid (HCl, Sigma-Aldrich, USA) and sodium hydroxide (NaOH, Sigma-Aldrich, USA).

[0108] Fabrication of an Expandable Electrokinetic-Assisted Filtration Device

[0109] For the experiments on the filtration device described herein, an expandable electrokinetic assisted filtration device with a simple assembly base was devised. The upper, lower, and intermediate frames of the device, including the main channel, buffer channel, and branch channels, were fabricated by 3D printing (Object3500 using the Veroclear material from Stratasys, USA). The 1-mm-thick carbon paper electrodes were cut into a circular shape using a paper punch, inserted into the slots of the upper and lower frames, and then fixed using a silver conductive epoxy adhesive (MG Chemicals 8330, MG Chemicals, Canada). Titanium wires were firmly attached to the carbon paper electrodes for DC electrical application. The microholes of the CEM were prepared through a simple drilling process. A microhole array with a spacing between holes of 400 μm in diameter and 500 μm was formed in a commercial CEM (Fumasep, FTCM-E, Germany) using a desktop engraver (DE-3 desktop engraver, Roland DF, Japan). After forming the microhole array, the CEM was cut into a circular shape using a paper punch. A silicon gasket for preventing 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 mid-frame was densely filled with a porous layer material (PEST ultra-fine fiber, Hubis, 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 and screwed together as shown in Figure 5 for assembly. 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] Before the experiment, the CEM was immersed in DI water for 5 minutes for smooth current flow between the main channel and the buffer channel. The supply reservoir and the buffer reservoir were each connected to the inlets of the main channel and the buffer channel with silicon tubes (Cole-Parmer, USA), and 0.3 M sodium sulfate (Na2SO4, Samchun, Korea) in the electrode buffer was used. A Luer-lock syringe (BD Luer-Lok, BD, USA) was connected to a tube connector attached to the outlets of the main channel and the branch channel with a silicon tube, and a specific withdrawal flow rate was applied to the outlet using a syringe pump (PHD2000, Harvard Apparatus, USA). A constant DC electric field was applied to the working electrode using a source measurement unit (B2902A, Keysight, USA). Prior to the formation of the ion depletion region, the introduction of the feed solution was preceded to obtain a reliable filtrate that was not affected by the MP leakage occurring before the generation of the electric potential barrier. First, the main channel was filled with 1 mM NaCl without MP. Then, to prevent the downstream movement of MP, the outlets of the main channel and the branch channel were blocked, and the feed reservoir was connected to the inlet of the main channel while maintaining a negative pressure. After authorizing electricity to the system in this state to induce an ion depletion region near the negative electrode side CEM, the fluid flow was allowed. The filtrate collected in the Luer-lock syringe connected to the outlets of the main channel and the branch channel was smoothly extracted from the conical tube.

[0113] Determination and Characterization of MP

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

[0115]

Equation

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

[0117] As described above with reference to the drawings and embodiments, it does not mean that the protection scope of the present invention is limited by the said drawings or embodiments. Those skilled in the relevant technical field should understand that the present invention may be variously modified and changed within the scope not deviating from the idea and scope of the present invention 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 by the foregoing embodiments and the attached drawings. It should be apparent to those 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 deviating from the technical idea of the present invention.

[0119] The combination of the foregoing embodiments is not limited to the foregoing embodiments, and not only the foregoing embodiments but also various forms of combinations may be provided depending on implementation and / or necessity.

[0120] In the foregoing embodiments, the method has been described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and a certain step may occur in an order different from or simultaneously with another step described above. Also, those having ordinary knowledge in the relevant technical field should be able to understand that the steps shown in the flowchart are not exclusive, and that other steps may be included or one or more of the steps in the flowchart may be deleted without affecting the scope of the present invention.

[0121] The foregoing embodiments include illustrations of various aspects. Although it is not possible to describe all possible combinations for showing the various aspects, those having ordinary knowledge in the relevant technical field should be able to 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 Reference Numerals

[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, comprising: a main channel into which a fluid containing charged particles is introduced and flows; a first electrode disposed inside the main channel to allow fluid flow; 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; and a porous layer disposed inside the main channel upstream of the ion exchange membrane and configured to filter particles in the fluid having a size equal to or greater than a predetermined first size, wherein the first electrode and the ion exchange membrane generate an electric field therebetween; a polarity different from that of the charged particles to be filtered is approved for the first electrode; the ion exchange membrane is an ion exchange membrane for ions having a polarity different from that of the charged particles to be filtered; a second electrode having the same polarity as the charged particles to be filtered is connected to the ion exchange membrane; an ion depletion region that blocks the charged particles from moving into the voids of the ion exchange membrane is formed upstream of the ion exchange membrane; the porous layer limits the electroosmotic flow induced in the ion depletion region to a size equal to or smaller than a predetermined size, so that the ion depletion region has a cross-sectional area in the fluid flow direction equal to or greater than a predetermined second area; a charged particle filtering device.

2. The ion depletion region is formed based on ion concentration polarization (ICP), the charged particle filtering device according to claim 1.

3. The first electrode includes an additional ion exchange membrane having a plurality of voids that allow fluid flow, the charged particle filtering device according to claim 1.

4. The ion depletion region is configured such that an electrophoretic force acts on the charged particles, the charged particle filtering device according to claim 1.

5. The charged particles move in a direction different from the fluid flow direction by a drag force along the fluid flow and the electrophoretic force, the charged particle filtering device according to claim 4.

6. The ion depletion region Including sub-ion depletion regions corresponding to each of a plurality of voids provided in the ion exchange membrane, and configured to have a cross-sectional area in the fluid flow direction of not less than a predetermined first area by providing the plurality of sub-ion depletion regions, the charged particle filtration device according to claim 1.

7. The electroconvection is induced by electroosmotic instability, the charged particle filtration device according to claim 1.

8. The electroconvection includes helical vortex pairs, the charged particle filtration device according to claim 1.

9. The porous layer is formed of polyester microfibers, the charged particle filtration device according to claim 1.

10. A dome-shaped cap configured to fix the porous layer while allowing fluid flow; further included, the charged particle filtration device according to claim 1.

11. The dome-shaped cap is configured to make the ion depletion region convex by bending an upper boundary of the porous layer, the charged particle filtration device according to claim 10.

12. The filtration efficiency of the charged particle filtration device is varied by at least one of a flow velocity of fluid passing through the filtration device, a voltage approved for the first electrode and the ion exchange membrane, a zeta potential of the charged particles, or a type of the charged particles, the charged particle filtration device according to claim 1.

13. The charged particle filtration device is used to re-filter fluid that has passed through a reverse osmosis pressure-based filtration device, the charged particle filtration device according to claim 1.

14. A branch channel configured to branch from the main channel upstream of the ion exchange membrane and configured to discharge the charged particles; further included, the charged particle filtration device according to claim 1.

15. The charged particles are transferred to the branch channel by a resultant force of an electrophoretic force of an ion depletion region formed in an upstream direction of the ion exchange membrane and a drag force along a flow of the fluid, the charged particle filtration device according to claim 14.

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