KR20230099621A - Microplastic Separation Method using Concentration Apparatus - Google Patents

Abstract

The present invention includes a first step of supplying water (w1) in the first state containing microplastics accommodated in the thickening tank (10) to the assisted electric separator (20); a second step of separating microplastics from the inside of the electric auxiliary separator using a filter 30 disposed horizontally in the electric auxiliary separator; a third step of discharging the water (w2) in the second state located below the filter through the filter in the electric auxiliary separator to the outside of the electric auxiliary separator; a fourth step of discharging the water (w3) of the third state, which does not pass through the filter in the electric auxiliary separator and is located above the filter, to the outside of the electric auxiliary separator and resupplies it to the thickening tank; And a fifth step of applying a positive electric field to the upper surface of the auxiliary electric separator and applying a negative electric field to the lower surface of the auxiliary electric separator, wherein the electric field applied in step 5 is the height of the electric auxiliary separator 20 ( H), and the magnitude of the electric field is 10V to 60V per unit cm of height (H).

Description

Microplastic Separation Method using Concentration Apparatus

The present invention relates to a method for separating microplastics (1 μm < d < 10 μm, d is the diameter) in water in a force field where gravity and electrostatic force act, and can be used as a pretreatment device for microplastic analysis. . Specifically, the present invention concentrates and separates microplastics by discharging water through repeated filtration using a device for separating microplastics. It is about technology to overcome the phenomenon.

Plastics that flow into the sea from land include materials such as polyethylene, polyvinyl chloride, polypropylene, and polystyrene. In the process of entering the sea, they are decomposed by weathering and erosion and broken into small particles. They are classified into macro, meso, micro, and nano plastics according to their size. These microplastics are mistaken for food by animals and phytoplankton and marine organisms and ingested, causing digestive disorders, disease, and death.

In consideration of the fact that microplastics adversely affect the ecosystem, efforts to remove microplastics present in water such as sea water or river water are being made worldwide.

However, it is necessary to separate microplastics in order to identify the types and characteristics of microplastics contained in sea water, river water, or other various types of water, or to carry out experimental research.

The problems of conventional filtration devices for separating plastic particles are as follows. When the particle size of the microplastic is smaller than 10 μm, the microplastic exhibits a colloidal behavior, and at this time, based on sieving and density separation, the submicron filtration time may be prolonged due to the formation of a cake on the filter surface. In the process of filtering, microplastics are accumulated on the surface of the filter, resulting in deterioration of filter performance or durability of the filter. And, the small mass and volume of microplastics makes diffusion comparable to separation, resulting in inefficiency of density separation using high-density solutions.

The present invention is to provide a pretreatment device for separating microplastics in order to analyze microplastics present in water, and specifically, to provide a technology capable of concentrating and separating microplastics present in water using static electricity. It is purpose.

The present invention includes a first step of supplying water (w1) in the first state containing microplastics accommodated in the thickening tank (10) to the assisted electric separator (20); a second step of separating microplastics from the inside of the electric auxiliary separator using a filter 30 disposed horizontally in the electric auxiliary separator; a third step of discharging the water (w2) in the second state located below the filter through the filter in the electric auxiliary separator to the outside of the electric auxiliary separator; a fourth step of discharging the water (w3) of the third state, which does not pass through the filter in the electric auxiliary separator and is located above the filter, to the outside of the electric auxiliary separator and resupplies it to the thickening tank; And a fifth step of applying a positive electric field to the upper surface of the auxiliary electric separator and applying a negative electric field to the lower surface of the auxiliary electric separator, wherein the electric field applied in step 5 is the height of the electric auxiliary separator 20 ( H), and the magnitude of the electric field is 10V to 60V per unit cm of height (H).

In the first step, the water in the first state is supplied to one side of the auxiliary electric separator, and in the fourth step, the water in the third state that is supplied back to the thickening tank is supplied to the other side facing the one side of the auxiliary electric separator. It is discharged through and re-supplied to the concentration tank.

Water in the first state and water in the third state may be circulated by a pump.

Since pores of a size that do not allow microplastics to pass through are formed in the filter, the water in the third state has a higher content ratio of microplastics than the water in the first state, and the water in the second state contains microplastics. Do not do this.

The microplastic particles receive an upward electrostatic force by the electric field applied to the upper and lower surfaces of the electrically assisted separator, thereby preventing microplastics from accumulating on the upper side of the filtration membrane of the filter to be clogged.

When the initial amount of water in the thickening tank 10 is Q ₀ , the amount of water supplied to the thickening tank in the third state is 10% or less of the initial amount of Q ₀ Re-supply of the thickening tank it is better to stop

The present invention provides an apparatus capable of concentrating and separating microplastics present in water, thereby providing an advantageous effect of providing equipment necessary for a pretreatment process in the field of researching microplastics present in water.

1 is a conceptual schematic diagram of an apparatus for concentrating and separating microplastic particles according to the present invention;
2 shows a flow chart of the mass balance according to the control volume in the microplastic particle concentration and separation device according to the present invention.
Figure 3 shows the force received by the negatively charged microparticles in water,
4 is a schematic diagram of an electro-assisted filtration (EAS) device for separating microplastics according to the present invention;
5 shows the critical electric field (Ec) of microplastics having various zeta potentials required at various QP/Q0 ratios with ionic strengths of 0.01 to 0.5 M (ionic strengths of fresh water and seawater) as an example according to the present invention. .

Objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments taken in conjunction with the accompanying drawings. In addition, the terms used are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of the user operator. Therefore, definitions of these terms should be made based on the content throughout the present specification.

The present invention is a technology for concentrating and separating micro-sized plastics by applying an electrostatic field. In this process, it is characterized by adding electrostatic force to prevent microplastics from accumulating on the filter membrane. Hereinafter, the present invention will be described with reference to the drawings.

In general, most of the particulates in water are negatively charged, so in the electrostatic field, these particulates are collected on the anode surface of the electrode. Using this principle, it can be applied to a technology for separating microplastics. The three forces that control the motion of particulates in water are gravity, static electricity, and concentration. In the case of microplastic particles, the diffusional movement is not important because the distribution concentration is small, and for the movement of charged colloidal particles, gravity and static electricity become the main movement-causing forces. Using this principle, a device for separating microplastic particles was designed.

The apparatus for concentrating and separating microplastic particles according to the present invention uses electrical power and uses an electrically assisted separator (20 in FIG. 1), which is hereinafter also referred to as an 'EAS cell' or 'EAS' , electrically-assisted separator).

In order to analyze and study microplastic particles present in water, it is necessary to efficiently separate microplastics. The present invention is a device for collecting particulate matter by selectively concentrating and separating microplastics as a pre-stage technology for microplastic analysis. The resulting concentrate is suitable for pretreatment to remove inorganic particles and biosolids, and has the advantage of overcoming the disadvantages of the prior art filtration methods mentioned above.

The present invention is an electric auxiliary separator to separate plastic particles from a solution with the help of an electric field, and an EAS stream separator for separation of microplastics to perform filtration without clogging of the filtration membrane of plastic particles. The use of an electric field prevents microplastics from accumulating on the permeable membrane of the filter, causing pressure buildup and loss, thus retaining microplastics in the concentrate stream. In addition, the critical electric field, the concentration coefficient of the EAS device, and the concentration change of the reservoir can be calculated and modeled.

[Development of mathematical model]

Referring to Figures 1 and 2, a conceptual diagram of the present invention shows the design of an EAS cell device integrated with a reaction vessel. EAS cell devices use a mesh screen to separate the flow in the presence of an electric field against gravity. With the help of electricity the microplastic particles can be retained in the concentrate which is returned to the reservoir 10. A mesh screen (30, filter) serves as a stream separator. In the drawing, the electrically assisted separator 20 (EAS) is where the concentration of microplastics occurs. The thickener 10 is considered a continuous stirred tank reactor (CSTR) with the same concentration of microplastics. In EAS, the mathematical model that explains the movement of microplastics and the concentration change in the thickening tank is derived here.

[EAS device]

Flow rate and particle count are balanced in the concentration chamber of EAS. As can be seen in FIG. 2, when the control volume at position x has a width of W, a height of H, and a length of Δx, the inflow water (Qx) is equal to the sum of the outflow water (Qx+Δx) and Water (QP,x), water flow (Qx and Qx+Δx) is expressed as the horizontal velocity (ux) multiplied by the cross-sectional area perpendicular to the transverse flow (W×H). Permeation flow is equal to the vertical velocity of water (vw) multiplied by the cross-sectional area parallel to the transverse flow (W×Δx). When Δx approaches zero infinitely, Equation 38 can be rewritten in differential form as Equation 39. The integral form is Eq. The integral form expressing the function u _x of x is shown in Equation 40.

Cx+Δx)에서 수평 흐름으로 또는 분리기를 가로질러 투과하는 수직 흐름으로 제어 볼륨을 나갈 수 있다. 수직 입자 플럭스는 위치 x에서의 입자 투과 플럭스(Nz,x)에 분리기의 단면적(WΔx)을 곱하여 표시된다. 따라서 입자의 number balance는 다음과 같이 표현된다(식 41). Qx를 WDux로 대체하고 Δx를 무한히 작게 접근함으로써 식41의 미분 형태는 식 42와 같이 얻어진다.The control volume concept also applies to the balance of particle numbers. It is assumed that the particle concentration in the EAS concentration chamber changes only in the x direction. As can be seen in FIG. 2, the number of particles entering the control volume per unit time (#/sec) is equal to the product of Qx (cm3/sec) and Cx (#/cm3). The particle is at position x+Δx(Qx+Δx

It can exit the control volume either as a horizontal flow at Cx+Δx) or as a vertical flow permeating across the separator. The vertical particle flux is expressed as the particle permeation flux at position x (Nz,x) multiplied by the cross-sectional area of the separator (WΔx). Therefore, the number balance of the particles is expressed as (Equation 41). By replacing Qx with WDux and Δx approaching infinity, the differential form of Eq. 41 is obtained as Eq. 42.

Here, application of the product rule to the term d(C _x u _x ) converts Eq. 42 to Eq. 43, which becomes the governing equation in the number balance of the particles. The vertical particle flux depends on the terminal velocity (v _t ) and the vertical water velocity (v _w ) achieved by the electric field. Considering that an electric field allows a particle to move with respect to the vertical penetration velocity, we can define a critical electric field (Ec) when vt and vw are equal. Since we are dealing with MP, we need to consider the effect of net gravity on the final velocity (Equation 25). Ec can be expressed as Equation 44. At E ≥ Ec, v _t > v _w , no particles leave the control volume with permeate, and N _z,x = 0. However, if E < E _c and v _w > v _{t ,} then the particle leaves the control volume with vertical permeate (Fig. 2(d)). Considering that the particles are uniformly dispersed at the concentration C _x (#/cm3), N _z,x (#/sec-cm2) is denoted by C _x (vw-vt). If E ≥ Ec and Nz,x = 0, then the solution of Cx/C0 is solved as in Equation 45a. If E < E _c and N _z,x = C _x (vw-vt), the solution is given by Equation 45b. When x = L, the concentration factor (CF) of the EAS device is calculated as the ratio of the outlet concentration to the inlet concentration (C _L /C ₀ ) as shown in Equation 34.

이다.here,

am.

[Increase in the concentration of the thickening tank 10]

The EAS is continuously operated to return the concentrate stream to the thickener (10, CSTR) to concentrate the microplastics to the desired level. As a result, the particle concentration of the SCSTR will continuously increase and the focus of this section is to describe the change in the particle concentration of the CSTR as a function of time.

To simplify model development, we make the following assumptions:

(1) The concentrations of CSTR are well mixed. The concentration entering the EAS unit at time t is equal to the concentration of CSTR, Ct.

(2) The flow rates of EAS, namely Q0, QC and QP, are constant. The concentration factors (CF, Ct,out/Ct) of EAS are the same during operation.

(3) The holding time (τ) of the EAS device is very short (~3 min) compared to the total operation time (~3 h). Therefore, since the variation of Ct within 1 τ is negligible, Ct,C can be expressed as Ct×CF.

The mass balance for the particles of CSTR is Equation 48, and is expressed by Equation 49 using QC = Q0 - QP and Ct,C = Ct × CF. Applying the product rule to d(VtCt) based on the relationship of Vt as in Equation 47, the governing equation becomes Equation 50.

The solution to Equation 50 is expressed as Equation 51. The equation suggests that the change in Ct/C0 depends on the ratio of the permeate flow to the initial sample volume (QP/V0), the ratio of the input flow to the permeate flow (Q0/QP), and the concentration coefficient in units of EAS. (CF).

[Simulation of concentration factor and critical electric field]

The concentration factor (CF) of the EAS device is a key parameter determining the efficiency of MP separation. According to Equation 46, CF is greatly affected by the vertical transmission velocity (v _w ) and the terminal velocity driven by the electric field. Therefore, it is very important to know the critical electric field (Ec) under various conditions. This section assumes the dimensions of the EAS cell are 2.5 cm wide, 20 cm long, and 1 cm high. The inlet flow rate (Q0) is fixed at 25 mL/min, corresponding to τ of 1 min. The electric field is applied against gravity. As presented in the [EAS State Table] below, the QP/Q0 ratio determines the permeate flow rate (QP) and vertical permeation rate (vw).

5 shows the critical electric field (Ec) of microplastics with various zeta potentials required at various QP/Q0 ratios with ionic strengths of 0.01 to 0.5 M (ionic strengths of fresh water and seawater). Simulations show that Ec increases with the value of QP/Q0 due to an increase in the vertical permeation rate (vw). That is, a larger E is needed to obtain a vt that can prevent particles from migrating with permeation. The electrostatic force is proportional to the zeta potential, so EC decreases as the plastic becomes more negatively charged. The zeta potential range of PMMA (a type of plastic) and PS (a type of plastic) is -40 to -60 mV. In this case, Ec is 20 to 60 V/cm, which is a practical range. The larger E values at smaller particle sizes result from Henry's factor correcting the distortion of the electric field due to the particle, especially when the radius of the particle is comparable to the double layer thickness.

PS, PMMA with density of 　　ρs = 1.2 g/cm3 with zeta potential ζ = -40 mV Confirmed that microplastic particles can be applied at 60 V/cm or less with 90% concentration efficiency up to <10 um size did In other words, 90% removal efficiency can be obtained at a power intensity of 60 V/cm up to 10 μm particles under the above conditions. Here, the V/cm unit means the potential value per unit height of the electrically assisted separator (EAS).

When the width, length, and height of the electric auxiliary separator 20 are W, L, and H, respectively, the magnitude of static electricity added by the electrostatic field adding device is preferably 10V to 60V per height (cm). That is, if the height is 1 cm, a voltage of 10 to 60 V is applied.

Figure 5 summarizes the E of MPs with zeta potentials of -40 mV at ionic strengths of 0.01 M, 0.05 M, 0.1 M and 0.5 M and the double layer thicknesses (κ -1) are 3.0 nm, 1.4 nm, 1.0 nm and 0.4 . nm, respectively. Henry's correction factor f(α) approaches 1.0 for r < 0.1κ −1 and 1.5 for r > 100κ −1, so the electrophoretic mobility is small when the magnitude of the MP is comparable to κ −1. Therefore, the effect of ionic strength on E is only small in magnitude at low ionic strength.

The table below is an example of a simulation according to the present invention, Q _O is the hourly amount of water input to the EAS, and Q _P is the respective hourly discharge amount at the outlet exiting the EAS. In this embodiment, the EAS unit has a width (W), a length (L), and a height (H) as follows.

W × L × H = 2.5 cm × 20 cm × 1 cm, Q0 = 50 mL/min

[EAS Status Table]

Referring to FIG. 3 , the three fields that control the movement of particles in water can be referred to as gravity, static electricity, and concentration. In the case of microplastic particles, the movement due to diffusion is not important because the concentration is small, and for the movement of charged colloidal particles, gravity and static electricity are the main driving forces. Referring to FIG. 3 , the microparticles receive an upward force due to electrostatic force and a downward force due to gravity.

Summarizing the device in which the enrichment process in the present invention is performed, the first state water (w1) including microplastics is accommodated in the thickening tank 10 and the first pipe connected to the thickening tank ( w2), an electric auxiliary separator (20, EAS) for concentrating and filtering microplastics, a filter 30 provided at a predetermined distance from the bottom of the electric auxiliary separator, and provided on the bottom of the electric auxiliary separator, A second pipe for discharging water (w2) in a second state that has passed through the filter in the auxiliary electric separator, and provided on a side surface of the auxiliary electric separator facing the first pipe, and in the auxiliary electric separator A third pipe for discharging water (w3) in a third state located above the filter, and a positive electric field applied to the upper surface of the auxiliary electric separator and a negative electric field applied to the lower surface of the auxiliary electric separator Adding an electrostatic field It consists of a device (E).

One end of the third pipe is connected to the side of the electric auxiliary separator, and the other end is connected to the thickening tank, so that the water in the third state is re-supplied to the thickening tank, and the first pipe or the third pipe A pump is provided to circulate the water.

The permeable membrane provided in the filter is formed with pores of a size that the microplastics cannot pass through, so that the water in the third state has a higher content ratio of microplastics than the water in the first state, and the water in the second state does not contain microplastics.

The microplastic particles receive an upward electrostatic force by the electric field applied to the upper and lower surfaces of the electric assist separator by the electrostatic field adding device, thereby preventing microplastics from accumulating on the upper side of the filtration membrane of the filter to be clogged.

When the width, length, and height of the electrically assisted separator 20 are W, L, and H, respectively, the magnitude of static electricity added by the electrostatic field adding device is 10V to 60V per unit cm of the height (H). When added (V/cm), it was confirmed that the particle size of microplastics was effectively concentrated to 10 μm particles.

When the initial amount of water in the thickening tank 10 is Q ₀ , the amount of water supplied to the thickening tank in the third state is 10% or less of the initial amount of Q ₀ Re-supply of the thickening tank it is better to stop That is, the concentration process is performed until more than 90% of the initial amount of water is excluded.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also made according to the present invention. falls within the scope of the rights of

Claims (6)

A first step of supplying water (w1) in a first state containing microplastics accommodated in the thickening tank (10) to the assisted electric separator (20);
a second step of separating microplastics from the inside of the electric auxiliary separator using a filter 30 disposed horizontally in the electric auxiliary separator;
a third step of discharging the water (w2) in the second state located below the filter through the filter in the electric auxiliary separator to the outside of the electric auxiliary separator;
a fourth step of discharging the water (w3) of the third state, which does not pass through the filter in the electric auxiliary separator and is located above the filter, to the outside of the electric auxiliary separator and resupplies it to the thickening tank; and
Step 5 of applying a positive electric field to the upper surface of the electrically assisted separator and applying a negative electric field to the lower surface of the electrically assisted separator,
The electric field applied in step 5 is proportional to the height (H) of the electric assist separator 20, and the magnitude of the electric field is 10V to 60V per unit cm of height (H) Microplastic particle concentration separation, characterized in that method. According to claim 1,
In the first step, the water in the first state is supplied to one side of the electric auxiliary separator,
The microplastic particle concentration and separation method, characterized in that the water in the third state, which is supplied back to the thickening tank in step 4, is discharged through the other side facing the one side of the electric auxiliary separator and re-supplied to the thickening tank. According to claim 2,
The method for concentrating and separating microplastic particles, characterized in that the water in the first state and the water in the third state are circulated by a pump. According to claim 2,
The filter is formed with pores of a size that does not allow microplastics to pass through.
Wherein the water in the third state has a higher content ratio of microplastics than the water in the first state, and the water in the second state does not contain microplastics. According to claim 2,
Microplastic particles are concentrated and separated, characterized in that by the electric field applied to the upper and lower surfaces of the electrically assisted separator, the microplastic particles receive an upward electrostatic force to prevent the accumulation of microplastics on the upper side of the filtration membrane of the filter and clogging. According to claim 2,
When the initial amount of water in the thickening tank 10 is Q ₀ , the amount of water supplied to the thickening tank in the third state is 10% or less of the initial amount of Q ₀ Re-supply of the thickening tank A microplastic particle concentration separation method, characterized in that to stop.

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