KR102766275B1 - Desalination Device and Desalination Method Using a Net Flow in a Constant Direction - Google Patents

Abstract

The present invention relates to a desalination device for removing contaminants in water to be treated, comprising: an electrolysis unit including a cathode, an anode, and an anion exchange membrane; a water supply channel located on the cathode side and supplying water to be treated from the outside of the desalination device in the direction of the anion exchange membrane; a water discharge channel located on the cathode side and discharging water to the outside of the desalination device, from which the contaminants have passed through the anion exchange membrane and been removed and transferred to the anode side; a wash water supply channel located on the anode side and supplying wash water from the outside of the desalination device in the direction of the anion exchange membrane; and a wash water discharge channel located on the anode side and discharging wash water including the contaminants transferred from the cathode side through the anion exchange membrane to the outside of the desalination device, wherein a net flow of the wash water has a linear flow along the longitudinal direction of the wash water supply channel.

Description

{Desalination Device and Desalination Method Using a Net Flow in a Constant Direction}

The present invention relates to a desalination technology using wash water, and more specifically, to a technology for preventing damage to ion exchange membranes and electrodes and efficiently separating salt in waste water by supplying treated water discharged from a waste water facility as wash water having a constant directional flow.

Conventional desalination devices using electrochemical reactions are mainly configured as batch types or continuous flow types, but they have the disadvantage that the surface of the ion exchange membrane in the desalination device becomes contaminated during the ion exchange process, and as a result, the concentration gradient in the ion exchange membrane drops significantly, resulting in a rapid decrease in ion exchange efficiency. This is because organic substances generated on the surface of the ion exchange membrane during the desalination reaction process are deposited on the surface of the ion exchange membrane and cover the functional groups that play a role in ion exchange, resulting in a significant decrease in ion exchange performance.

Therefore, in order to maintain ion exchange performance, cleaning of the ion exchange membrane surface is necessary. However, ion exchange membranes are generally very vulnerable to acids and bases, so acid and base cleaning of ion exchange membranes is not possible, and ion exchange membranes are periodically replaced without separate scale removal.

Due to the shortcomings of these desalination devices, most continuous-flow industrial processes are not able to utilize electrochemical desalination devices equipped with ion exchange membranes, and even in some facilities that are being used, continuous electrochemical desalination operation is not possible, and ion exchange membranes are replaced after intermittent interruptions. This leads to problems such as reduced performance and increased maintenance costs of electrochemical ion exchange facilities, and makes it difficult to commercialize electrochemical desalination technology using ion exchange membranes.

For this reason, in most electrochemical desalination systems for the purpose of separating chloride ions, ion exchange membranes cannot be used, and high-performance, selective separation of chloride ions using ion exchange membranes is virtually impossible. In the case of electrochemical desalination of seawater, chlorine ions are oxidized to chlorine gas and converted to hypochlorous acid without using an ion exchange membrane, but since no ion exchange membrane is used, all cations and anions move, so selective separation of chloride ions from raw water through electrochemistry is impossible. In addition, high-concentration chlorine gas, hypochlorous acid, and hypochlorous acid generated during the desalination of chloride ions oxidize the electrode, making continuous operation of the desalination process impossible, and there is a disadvantage in that the electrodes must be replaced periodically.

Therefore, in order to remove high concentrations of salt from wastewater, the use of ion exchange membranes is essential, and an electrochemical desalination device must be used to configure a high-performance salt separation system through ion exchange membranes. However, despite this necessity, there is no technology to safely separate chlorine ions from raw water, and even if chlorine ions are separated, there is no desalination device that can maintain high efficiency in the long term without damaging the ion exchange membrane and electrodes, which is showing limitations in the treatment technology of high concentration salt wastewater.

The present invention is intended to solve the above-described problem, and provides a desalination device and a desalination method in which electrochemically separated chlorine ions and contaminants diffused through an ion exchange membrane are sequentially passed from a wash water supply conduit through an anion exchange membrane to a wash water discharge conduit without mixing in the flow direction within the wash water by wash water having a linear forward flow, so that the ion exchange membrane is washed.

According to one embodiment of the present invention, a desalination device for removing contaminants in water to be treated is provided, comprising: an electrolysis unit including a cathode, an anode, and an anion exchange membrane; a water supply channel located on the cathode side and supplying water to be treated from the outside of the desalination device in the direction of the anion exchange membrane; a water discharge channel located on the cathode side and discharging water to the outside of the desalination device, from which the contaminants have passed through the anion exchange membrane and been removed and transferred to the anode side; a wash water supply channel located on the anode side and supplying wash water from the outside of the desalination device in the direction of the anion exchange membrane; and a wash water discharge channel located on the anode side and discharging wash water including the contaminants transferred from the cathode side through the anion exchange membrane to the outside of the desalination device, wherein a net flow of the wash water has a linear flow along the longitudinal direction of the wash water supply channel.

In addition, according to another embodiment of the present invention, a desalination method for removing contaminants in water to be treated is provided, comprising: a water supply step of supplying the water to be treated through a water supply conduit through a cathode of an electrolysis unit toward an anion exchange membrane; a contaminant transfer step of removing the contaminants in the water to be treated by passing them through the anion exchange membrane toward the anode; a water discharge step of discharging the water to be treated from which the contaminants have been removed from the anion exchange membrane through the cathode to the outside through a water discharge conduit; a washing water supply step of supplying washing water through the washing water supply conduit toward the anion exchange membrane; and a washing water discharge step of discharging washing water including the contaminants transferred through the anion exchange membrane to the outside through the anode to the outside through a washing water discharge conduit; wherein the net flow of the washing water has a linear flow along the longitudinal direction of the washing water supply conduit.

By using the desalination device and desalination method of the present invention, the surface of the ion exchange membrane is continuously washed by continuously injecting the wash water in one direction along the wash water supply path and simultaneously continuously discharging it along the wash water discharge path, so that the salt, organic pollutants or ammonia contained in the influent water or the wash water can be moved toward the anode without reverse flow. Accordingly, wastewater containing a high concentration of salt can be treated with high efficiency in a simpler process.

Figure 1 is a schematic diagram showing a desalination device using laminar flow according to Example 1.
Figure 2 is a schematic diagram showing a desalination device using turbulent flow according to Comparative Example 1.
Figure 3 is a graph comparing the pH of the final effluent from the desalination device according to Example 1 and the final effluent from the desalination device according to Comparative Example 1 according to current density.
Figure 4 is a graph comparing the concentration of chloride ions (Cl ^- ) in the treated water flowing into the desalination device according to Example 1 and the final discharged washing water according to the current density.
Figure 5 is a graph comparing the COD of the final effluent from the desalination device according to Example 1 and the final effluent from the desalination device according to Comparative Example 1 according to current density.
Figure 6 is a graph comparing the concentration of ammonium ions (NH ₄₊ ⁾ in the final effluent from the desalination device according to Example 1 and the final effluent from the desalination device according to Comparative Example 1 according to current density.
Figure 7 is a graph comparing theoretical and measured values of the flux of COD, ammonium ions, and chloride ions on the surface of an anion exchange membrane of a desalination device according to Example 1 and a desalination device according to Comparative Example 1.

Hereinafter, with reference to the attached drawings, the present invention will be described in detail regarding the method for treating decontamination waste liquid so that a person having ordinary skill in the art to which the present invention pertains can easily perform the method.

According to one embodiment of the present invention, a desalination device is provided as a desalination device for removing contaminants in water to be treated, comprising: an electrolysis unit including a cathode, an anode, and an anion exchange membrane; a water supply channel located on the cathode side and supplying water to be treated from the outside of the desalination device in the direction of the anion exchange membrane; a water discharge channel located on the cathode side and discharging water to the outside of the desalination device from which the contaminants have passed through the anion exchange membrane and have been removed and transferred to the anode side; a wash water supply channel located on the anode side and supplying wash water from the outside of the desalination device in the direction of the anion exchange membrane; and a wash water discharge channel located on the anode side and discharging wash water including the contaminants transferred from the cathode side through the anion exchange membrane to the outside of the desalination device, wherein a net flow of the wash water has a linear flow along the longitudinal direction of the wash water supply channel.

Desalination technology is a technology to desalinate polluted water such as seawater or wastewater by removing various suspended substances or ionic components. It includes an evaporation method that evaporates moisture using a heat source such as fossil fuels or electricity, a filtration method that filters out foreign substances using a membrane, and an electrodialysis method that removes ions using the electrolytic action of electrode cells.

The evaporation method uses fossil fuels or electricity as a heat source to evaporate moisture. However, the desalination device used when applying the evaporation method is large in volume, which is inefficient, increases energy consumption, increases manufacturing costs, and causes air pollution due to the use of fossil fuels. The filtration method requires high pressure to the separation membrane to remove foreign substances, which increases energy costs, and the electrodialysis method requires continuous replacement of electrode cells, which not only generates waste factors due to replacement of electrode cells, but also increases human and material costs, which is a disadvantage.

The desalination device according to the present invention supplies wash water having a linear flow along the longitudinal direction of the wash water supply channel, and specifically, the net flow of the wash water may have a linear flow from the outside of the desalination device toward the anion exchange membrane along the wash water supply channel, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane toward the outside of the desalination device along the wash water discharge channel.

Accordingly, the ion-exchanged pollutants move toward the anode without reverse flow by the wash water having a constant forward flow, and as a result, the oxidative decomposition of the cationic functional group contained in the ion exchange membrane can be prevented. Specifically, among the pollutants, particularly the chlorine ion is converted into a chlorine-based oxidizer at the anode of the desalination device, and then oxidizes and decomposes other pollutants contained in the wash water or separated from the treated water, and is then converted back into a chlorine ion, thereby preventing the oxidative decomposition of the cationic functional group contained in the ion exchange membrane due to the reverse flow of the chlorine-based oxidizer, and there is an effect of enabling high-efficiency desalination without a separate ion exchange membrane replacement or cleaning.

The above-mentioned untreated water may be wastewater to be treated in a separate wastewater treatment facility. Specifically, the above-mentioned untreated water may be food wastewater, livestock wastewater, landfill leachate, etc. containing a high concentration of difficult-to-decompose organic matter or a high concentration of salt.

The above-mentioned net flow of the treated water may have a linear flow from the outside of the desalination device along the treated water supply path toward the anion exchange membrane, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane along the treated water discharge path toward the outside of the desalination device. Since the treated water has a net flow in a certain direction, the separation efficiency of contaminants, including chlorine ions, in the treated water can be further increased.

The above pollutants may include ionic pollutants and dissolved organic pollutants including at least one selected from the group consisting of chloride ion (Cl ^- ), ammonium ion (NH ₄ ⁺ ), sulfate (SO ₄ ^2- ), nitrate (NO ₃ ^- ), nitrite (NO ₂ ^- ), and phosphate (PO ₄ ^3- ). In particular, cations such as ammonium ion and dissolved organic pollutants in the treatment water may be dispersed or diffused through the anion exchange membrane by the Donnan effect.

The above chlorine ions may be classified into a high concentration and discharged by the desalination device, and the chlorine ions that have passed through the ion exchange membrane may be converted into a chlorine-based oxidizer at the anode of the electrolysis unit, and then the chlorine-based oxidizer may oxidize and decompose other pollutants except for the chlorine ions to remove them. The chlorine-based oxidizer may be converted back into chlorine ions after the oxidative decomposition reaction and discharged from the desalination device.

The anion exchange membrane included in the above electrolysis unit may be porous and serves to separate ions and selectively adsorb them to the electrode. The ionic substance dissolved in wastewater can be separated by using an electric field formed in the anion exchange membrane by a direct current power source. The anion exchange membrane may include a cationic functional group on the surface of the skin layer, and accordingly, an anionic substance capable of ionically bonding with the fixed cationic functional group can exhibit selective permeability.

The above anion exchange membrane can be manufactured by coating an ion exchange solution prepared by dissolving a polymer resin having a cationic functional group in an organic solvent on a woven or nonwoven fabric as a support, and then drying the solution to manufacture a skin layer, or by grafting a polymer resin having a cationic functional group onto the woven or nonwoven fabric.

The above woven or nonwoven fabric is a support for coating or impregnating an ion exchange solution, and may be formed of at least one polymer selected from the group consisting of polyamide series, polyethylene series, polypropylene series, cellulose series, polyacryl series, polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyester series, and natural fibers.

The above organic solvent may be at least one selected from dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone acetone, chloroform, dichloromethane, trichloroethylene, ethanol, methanol, normal hexane, and the like.

The cationic functional group may include at least one positively charged functional group selected ^from the group consisting of -NH ₃₊ ^{, -NRH 2+} _, -NR ₂ H ⁺ , ^{-NR 3+} _, -PR ₃₊ ^and -SR ₂₊ .

The anode may comprise at least one metal or alloy or oxide thereof selected from the group consisting of iridium (Ir), ruthenium (Ru), tin (Sn), titanium (Ti), molybdenum (Mo), tantalum (Ta), zirconium (Zr), and boron (B) doped diamond (BDD).

The cathode may have a high reaction potential, and the anode may have a low reaction potential. The cathode may be characterized by having a high reaction potential, relatively low reactivity, and being difficult to oxidize, and the anode may be characterized by having a low reaction potential, relatively high reactivity, and being easy to oxidize. Accordingly, when voltage is applied to the electrolysis unit, a reduction reaction may occur at the cathode, and an oxidation reaction may occur at the anode.

Chloride ions present in the space between the anode and the anion exchange membrane can be converted into a chlorine-based oxidizing agent on the surface of the anode due to an electrochemical reaction with the anode. At this time, the electrical neutrality of the space between the cathode and the anion exchange membrane and the space between the anode and the anion exchange membrane is temporarily broken, and the anions present in the space between the cathode and the anion exchange membrane can diffuse and move to the space between the anode and the anion exchange membrane through the anion exchange membrane. By placing an anion exchange membrane between the anode and the cathode to allow contaminants including chloride ions to move, desalination and production of a chlorine-based oxidizing agent can be performed simultaneously.

Meanwhile, after the chloride ion is converted into a chlorine-based oxidizer at the anode, the chlorine-based oxidizer ^can oxidize and ^decompose pollutants that have moved through the anion exchange membrane, such as ammonium ion ( _NH4 ⁺ ), sulfate _{( SO42-} ), nitrate ( _NO3- ), nitrite ( _NO2- ), phosphate ( ^PO43- ) ^, etc., and then be converted back into chloride ion. Accordingly, not only can contamination of the anion exchange membrane due to the reverse flow of the pollutants and oxidative decomposition of the cationic functional group included in the anion exchange membrane due to the reverse flow of the chlorine-based oxidizer be prevented, but also chloride ions in wastewater can be separated with high efficiency.

The desalination device according to the present invention may include an electrolysis unit for separating salt contained in wastewater, as well as a treatment water supply path, a treatment water discharge path, a wash water supply path, and a wash water discharge path so that the function of the electrolysis unit can be more effectively performed.

The above-mentioned treatment water supply path may be located on the cathode side to supply treatment water from the outside of the desalination device toward the anion exchange membrane. In addition, the above-mentioned treatment water discharge path may be located on the cathode side to discharge treatment water in which the pollutants are removed by passing through the anion exchange membrane to the anode side to the outside of the desalination device.

Specifically, the treatment water supply path and the treatment water discharge path are in contact with each other with a diaphragm therebetween, and the opposite sides of the treatment water supply path's inlet and the treatment water discharge path's outlet are both blocked by an anion exchange membrane. Accordingly, the treatment water introduced along the treatment water supply path passes through the cathode and moves to the anion exchange membrane, and then the contaminants in the treatment water are separated through the anion exchange membrane, and the treatment water from which the contaminants have been separated can be discharged again through the treatment water discharge path.

As shown in Fig. 1, the treated water has a constant directional net flow between the cathode and the anion exchange membrane by the treated water supply channel and the treated water discharge channel located on the cathode side, that is, the treated water introduced into the treated water supply channel flows to the anion exchange membrane, and when the treated water reaches the anion exchange membrane, it can bend and flow in the direction of the treated water discharge channel. At this time, contaminants in the treated water, such as chloride ions, ammonium ions, and nitrate ions, can selectively move to the anode side on the surface of the anion exchange membrane.

Meanwhile, the washing water supply path may be located on the anode side to supply washing water from the outside of the desalination device toward the anion exchange membrane. In addition, the washing water discharge path may be located on the anode side to discharge washing water containing the contaminants transmitted through the anion exchange membrane from the cathode side to the outside of the desalination device.

Specifically, the washing water supply path and the washing water discharge path are in contact with each other with a diaphragm in between, and the opposite sides of the inlet of the washing water supply path and the outlet of the washing water discharge path are both blocked by an anion exchange membrane. Accordingly, the washing water introduced along the washing water supply path can pass through the anode and move to the anion exchange membrane, and then flow in a folded manner in the direction of the washing water discharge path.

In this process, chlorine ions in the wash water are oxidized as they pass through the anode and converted into a chlorine-based oxidizer. The converted chlorine-based oxidizer moves along the direction of the forward flow of the wash water, oxidizes and decomposes contaminants derived from the treated water that have moved through the anion exchange membrane, and is then reconverted into chlorine ions. The wash water including the reconverted chlorine ions can be discharged through the wash water discharge channel.

The above wash water may be supplied by treating the treated water from a wastewater treatment facility. Alternatively, the wash water may be supplied from external groundwater. That is, treated water or groundwater from which a significant portion of contaminants in the treated water have been removed may be supplied to the anode as wash water. As the supplied wash water passes through the wash water supply conduit and the wash water discharge conduit, it has a constant directional positive flow between the anode and the anion exchange membrane, and through an electrochemical reaction at the anode, residual contaminants in the wash water are removed, and contaminants remaining in the anion exchange membrane can be washed. Accordingly, the concentration gradient of ionic contaminants on the surface of the anion exchange membrane can be maintained to the maximum, thereby enabling stable and efficient separation of chloride ions.

Chlorine ions contained in ionic pollutants derived from the treatment water and chlorine ions contained in ionic pollutants derived from the wash water, which have moved to the anode side through the anion exchange membrane, are converted into at least one chlorine-based oxidizing substance selected from the group consisting of chlorine (Cl ₂ ), chlorous acid (HClO ₂ ), hypochlorous acid (HClO), and hypochlorite ion (OCl ^- ) at the anode side, and the converted chlorine-based oxidizing substance can oxidize and decompose the pollutants derived from the treatment water or the wash water.

The chlorine-based oxidizing agent converted on the anode side can be reconverted into chlorine ions after oxidizing and decomposing the ionic pollutants, and the converted chlorine-based oxidizing agent moves along the direction of the forward flow of the washing water, thereby preventing oxidation of the anode electrode by the chlorine-based oxidizing agent and oxidative decomposition of the cationic functional group included in the anion exchange membrane.

The above washing water may have a laminar flow having a Reynolds number of 2000 or less. The Reynolds number may be defined as in Equation 1 below.

[Formula 1]

(Re: Reynolds number, u: flow velocity, d: pipe diameter, μ: dynamic viscosity of the fluid)

If the Reynolds number of the above-mentioned washing water exceeds 2000, i.e., if it is a turbulent flow, the washing water cannot have a constant flow direction and is irregularly mixed, so that the chlorine-based oxidizing agent converted on the anode side is distributed throughout the entire fluid by dispersion or diffusion, which may further aggravate the contamination of the anion exchange membrane, and the cationic functional group included in the anion exchange membrane may be oxidized and decomposed, thereby causing the anion exchange membrane to lose its selective separation function for chlorine ions.

In addition, the treatment water may be a laminar flow having a Reynolds number of 2000 or less. As with the wash water, the treatment water also has a laminar flow, which allows the treatment water to be continuously and uniformly brought into contact with the anion exchange membrane, thereby further increasing the separation efficiency of contaminants, including chlorine ions, contained in the treatment water through the anion exchange membrane.

In the case of the desalination device according to the present invention, since a pH increase on the cathode side and a pH decrease on the anode side continuously occur, a process of adjusting the pH of the treated water and the wash water to near neutral may be absolutely necessary.

Specifically, on the cathode side where the treated water is supplied, a water reduction reaction occurs as shown in Equation 2 below, and as hydroxide ions (OH ^- ) are continuously generated, the pH can increase to 12 or more.

[Formula 2]

2H ₂ O + 2e ^- → H ₂ + 2OH ^-

Meanwhile, the anode side, where ionic contaminants including chloride ions are separated and moved, can have the pH reduced to 2 or more as hydrogen ions (H ⁺ ) are continuously generated by the continuous electrolytic reaction of water as shown in Equation 3 below.

[Formula 3]

2H ₂ O → O ₂ + 4H ⁺ + 4e ^-

Accordingly, the pH of the treatment water and the wash water may each be independently 5 to 10, preferably pH 6 to 9, and more preferably pH 7 to 8. If the pH of the treatment water and the wash water exceeds the upper limit of the numerical range, there may be a problem that the cationic functional group included in the anion exchange membrane forms an excessive ionic bond with hydroxide ions or the functional group is substituted by hydroxide ions, thereby losing the ion exchange function, and if it is below the lower limit of the numerical range, the functional group distributed in the anion exchange membrane may be oxidized and decomposed by hydrogen ions and separated from the polymer support, which may seriously deteriorate the ion exchange performance of the ion exchange membrane.

The desalination device according to the present invention may be configured such that a plurality of repeating units including the treatment water supply conduit and the treatment water discharge conduit and the repeating units including the wash water supply conduit and the wash water discharge conduit are arranged facing each other with the anion exchange membrane interposed therebetween. By arranging a plurality of repeating units including the treatment water supply and discharge conduit and the wash water supply and discharge conduit, the efficiency of separation of chlorine ions and removal of contaminants in wastewater can be further increased.

In addition, the desalination device according to the present invention may have a plurality of repeating units including a cathode and an anode arranged at the rear end of the electrolysis unit in order to perform additional electrolysis on the wash water discharged from the wash water discharge conduit. Accordingly, separated chlorine ions can be continuously used to continuously form a chlorine-based oxidizing agent and thereby oxidatively decompose pollutants, thereby maximizing the desalination and pollutant decomposition performance.

The concentration of chloride ions in the discharged treated water may be reduced by 80% or more, preferably 85% or more, and more preferably 90% or more, compared to the concentration of chloride ions in the supplied treated water. In addition, the chemical oxygen demand (COD) in the wash water discharged from the wash water discharge unit may be reduced by 75% or more, preferably 80% or more, and more preferably 82% or more, compared to the chemical oxygen demand in the supplied wash water.

The concentration of ammonium ions ( _NH4 ⁺ ) in the wash water discharged from the wash water discharge port through the electrolysis unit may be reduced by 94% or more, preferably 95% or more, compared to the concentration of ammonium ions in the supplied wash water.

In order to achieve the reduction rates of the chloride ion concentration in the treatment water, the chemical oxygen demand in the wash water, and the ammonium ion concentration as described above, the desalination device according to the present invention may be applied with a current density of 10 to 30 mA/cm2, preferably 15 to 30 mA/cm2, and more preferably 20 to 25 mA/cm2 or more.

According to another embodiment of the present invention, a desalination method for removing contaminants in water to be treated is provided, comprising: a water supply step of supplying the water to be treated through a water supply conduit through a cathode of an electrolysis unit toward an anion exchange membrane; a contaminant transfer step of removing the contaminants in the water to be treated by passing them through the anion exchange membrane toward the anode; a water discharge step of discharging the water to be treated from which the contaminants have been removed from the anion exchange membrane through the cathode to the outside through a water discharge conduit; a washing water supply step of supplying washing water through the washing water supply conduit toward the anion exchange membrane; and a washing water discharge step of discharging washing water including the contaminants transferred through the anion exchange membrane to the outside through the anode to the outside through a washing water discharge conduit; wherein the net flow of the washing water has a linear flow along the longitudinal direction of the washing water supply conduit.

Among the contents described for the desalination device of the present invention, any contents that overlap with the desalination method of the present invention may be applied equally even if the detailed description is omitted.

The above-mentioned net flow of the washing water may have a linear flow from the outside of the desalination device along the washing water supply path toward the anion exchange membrane, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane along the washing water discharge path toward the outside of the desalination device.

In addition, the net flow of the treated water may have a linear flow from the outside of the desalination device along the treated water supply path toward the anion exchange membrane, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane along the treated water discharge path toward the outside of the desalination device.

The above washing water may be a laminar flow having a Reynolds number of 2000 or less. If the Reynolds number of the washing water exceeds 2000, i.e., if it is a turbulent flow, the washing water cannot have a constant flow direction and is irregularly mixed, so that the chlorine-based oxidizing agent converted on the anode side is distributed throughout the entire fluid by dispersion or diffusion, which may further aggravate the contamination of the anion exchange membrane, and the cationic functional group included in the anion exchange membrane may be oxidized and decomposed, thereby causing the anion exchange membrane to lose its selective separation function of chlorine ions.

In addition, the treatment water may be a laminar flow having a Reynolds number of 2000 or less. As with the wash water, the treatment water also has a laminar flow, which allows the treatment water to be continuously and uniformly brought into contact with the anion exchange membrane, thereby further increasing the separation efficiency of contaminants, including chlorine ions, contained in the treatment water through the anion exchange membrane.

The above pollutants may include ionic pollutants and dissolved organic pollutants including at least one selected from the group consisting of chloride ion (Cl ^- ), ammonium ion (NH ₄ ⁺ ), sulfate (SO ₄ ^2- ), nitrate (NO ₃ ^- ), nitrite (NO ₂ ^- ), and phosphate (PO ₄ ^3- ). In particular, cations such as ammonium ion and dissolved organic pollutants in the treatment water may be dispersed or diffused through the anion exchange membrane by the Donnan effect.

The above pollutants may be included in both the untreated water and the wash water, and may be included in a relatively higher concentration in the untreated water than in the wash water.

In addition, the desalination method may further include a step of converting chlorine ions contained in pollutants derived from the treatment water or wash water into at least one substance selected from the group consisting of chlorine (Cl ₂ ), chlorous acid (HClO ₂ ), hypochlorous acid (HClO), and hypochlorite ion (OCl ^- ) at the anode side; and a step of causing the converted substance to oxidize and decompose the pollutants derived from the treatment water or wash water.

In the above oxidation decomposition step, the converted substance may be reconverted back into chloride ions after oxidizing and decomposing the pollutant.

Since the above-described treatment water and wash water maintain a constant directional flow, contaminants contained in the treatment water and wash water move constantly toward the anode, as a result, chlorine ions in the treatment water and chlorine ions in the wash water passing through the anion exchange membrane are converted into chlorine-based oxidizing agents such as chlorine, chlorous acid, hypochlorous acid, and hypochlorite ions at the anode, and then contaminants except for chlorine ions contained in the treatment water and wash water are oxidized and decomposed, and then converted back to chlorine ions and discharged, thereby preventing contamination of the anion exchange membrane and oxidation of the electrode due to the counterflow of the chlorine-based oxidizing agent, and preventing oxidative decomposition of cationic functional groups contained in the anion exchange membrane. In addition, since the surface of the anion exchange membrane is continuously washed, the concentration gradient of contaminants on the surface of the anion exchange membrane can be maintained to the maximum, thereby enabling stable and efficient separation of chlorine ions.

Hereinafter, the present invention will be described more specifically through examples. However, these examples are only intended to help understanding of the present invention, and the scope of the present invention is not limited to these examples in any way.

<Example 1> Confirmation of desalination effect using a desalination device using laminar flow

As shown in Fig. 1, the electrolysis unit of the desalination device consisted of a Ti mesh cathode, an anion exchange membrane, and an IrO ₂ /Ti mesh anode. An anion exchange nonwoven fabric with 1 μm micropores was used as the anion exchange membrane. The cathode was positioned 10 cm away from the anion exchange membrane, and the anode was positioned 15 cm away. The size of the cathode and anode was 7 cm x 7 cm.

A treatment water supply channel and a treatment water discharge channel were installed on the cathode side, a wash water supply channel and a wash water discharge channel were installed on the anode side, and a repeating unit consisting of a treatment water supply channel and a treatment water discharge channel made of a cylindrical tube with a diameter of 10 cm and a repeating unit consisting of a wash water supply channel and a wash water discharge channel were installed five at a time, facing each other along the anion exchange membrane.

To supply the treated water and wash water in the direction of the anion exchange membrane while maintaining a laminar flow, pumps were installed in each of the treated water supply path and the wash water supply path.

In addition, in order to perform continuous generation of chlorine-based oxidizers and oxidative decomposition of ionic organic pollutants including ammonium ions and to continuously use the separated chlorine ions, five pairs of cathodes and anodes were installed at 10 cm intervals so that the wash water passes through the cathode and then the electrolysis unit multiple times to undergo an electrochemical reaction. Additionally, the distance between the installed anode and cathode pairs was 1 cm. The anion exchange membranes were installed to match the diameters of the five influent and wash water pipes.

The overall dimensions of the cathode side of the desalination device were 150 cm in width, 10 cm in height, and the overall dimensions of the anode side were 150 cm in width, 10 cm in width, and 100 cm in height.

The wastewater used as treatment water had pH 8.0, COD 8,310 ppm, ammonia 2,450 ppm, and salinity 51,200 ppm (5.12%), and the effluent discharged from the treatment water treatment facility had pH 8.3, COD 840 ppm, ammonia 880 ppm, and salinity 5,300 ppm as wash water.

The Reynolds number was maintained at 2000 or less by supplying the treated water and wash water at a flow rate of 50 L/h to the treated water supply path and wash water supply path through the above pump.

Meanwhile, the pH was adjusted by pHI/C using 0.1 N sulfuric acid and 0.1 N sodium hydroxide so that the pH could be operated between 5 and 10.

The desalination reaction was performed by applying current densities of 10, 15, 20, 25, and 30 mA/cm2 to the above desalination device, respectively. In order to confirm the cleaning effect of the anion exchange membrane surface and the optimization of the concentration gradient, the desalination device was operated continuously for 24 hours, and the concentrations of pH, COD, ammonia, and chloride ions before and after passing through the anion exchange membrane were measured and compared. In addition, the flux passing through the anion exchange membrane surface was calculated to observe the degree of cleaning of the anion exchange membrane surface immediately after ion exchange, which are shown in Tables 1 to 4 below. Specifically, Table 1 shows a comparison of concentrations before and after passing through the anion exchange membrane, Table 2 shows the difference between the treatment water effluent concentration and the treatment water inflow and effluent concentrations (the concentration ion-exchanged through the anion exchange membrane), Table 3 shows the wash water inflow and final effluent concentrations, and Table 4 shows a comparison of flux according to the ion exchange membrane cleaning effect by wash water at 25 mA/cm2 after 24 hours.

Current density
(mA/㎠) 10 15 20 25 30 Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) pH 8.0 8.1 8.0 8.1 8.0 8.1 8.0 8.1 8.1 8.1 COD
(mg/L) 8300 1320 8310 1450 8210 1360 8310 1420 8350 1330 NH ₄ ⁺
(mg/L) 2400 580 2410 675 2410 670 2450 680 2470 690 Cl ^-
(mg/L) 51200 23300 51150 24500 51200 25750 51200 27420 51200 26950

In the above Table 1, the concentration before passing through the anion exchange membrane is the concentration of the untreated water, and the concentration after passing through the anion exchange membrane is the concentration of the untreated water mixed with the wash water after passing through the anion exchange membrane.

Current density
(mA/㎠) 10 15 20 25 30 Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water pH 8.0 - 8.0 - 8.0 - 8.0 - 8.1 - COD
(mg/L) 6500 1810 6510 1980 4620 1890 6520 1790 6510 1790 NH ₄ ⁺
(mg/L) 2150 300 1980 470 2000 450 1940 510 2010 510 Cl ^-
(mg/L) 9820 41380 7430 43770 2860 45840 2500 48700 2570 48630

In the above Table 2, the treatment water effluent concentration is the concentration that flows out from the treatment water influent through the anion exchange membrane, and is the residual concentration that remains after ion exchange through the anion exchange membrane in the treatment water influent.

Current density
(mA/㎠) 10 15 20 25 30 Wash water inflow concentration Final effluent concentration of wash water Wash water inflow concentration Final effluent concentration of wash water Wash water inflow concentration Final effluent concentration of wash water Wash water inflow concentration Final effluent concentration of wash water Wash water inflow concentration Final effluent concentration of wash water pH 8.3 7.2 8.3 7.3 8.3 7.2 8.3 6.8 8.3 6.9 COD
(mg/L) 840 185 845 150 840 145 840 120 860 150 NH ₄ ⁺
(mg/L) 890 40 900 45 880 42 890 32 880 48 Cl ^-
(mg/L) 5300 22000 5100 21800 5250 26300 5150 27100 5200 27200

In Table 3 above, the effluent concentration of the wash water is the residual concentration remaining after passing through the anion exchange membrane and undergoing oxidation and decomposition through five repeating units consisting of anode and cathode pairs.

Theoretical value after passing through anion exchange membrane Actual value after passing through anion exchange membrane Difference between theoretical value and measured value (%) COD flux (kg/㎡·s) 0.16 0.12 25% NH ₄ ⁺ flux (kg/㎡·s) 0.05 0.04 20% Cl ^- flux (kg/㎡·s) 4.31 4.27 0.9%

In Table 4 above, the theoretical plus value after passing through the anion exchange membrane is the flux value of ionic contaminants on the surface of the ion exchange membrane that appear when the treated water passes through the anion exchange membrane immediately after ion exchange.

The actual value after passing through the anion exchange membrane is the flux value on the surface of the anion exchange membrane calculated by measuring the concentration of ionic contaminants that have been ion-exchanged on the surface of the anion exchange membrane when the anion exchange membrane has been washed with washing water.

If the theoretical and measured values of the anion exchange membrane flux are similar, it indicates that the anion exchange membrane surface is washed after ion exchange and the concentration of contaminants on the anion exchange membrane surface is reduced, so that the ion exchange rate of ionic contaminants due to the electric gradient and concentration gradient is not reduced and ion exchange continues close to the theoretical value.

<Comparative Example 1> Confirmation of desalination effect using a desalination device utilizing turbulent flow

In order to compare the desalination effect with that of a desalination device using laminar flow according to Example 1, a reactor having the same volume as Example 1 was manufactured as shown in Fig. 2, and a desalination experiment was performed using a completely mixed flow in the form of turbulent flow.

The electrolysis unit of the desalination device consisted of a Ti mesh cathode, an anion exchange membrane, and an IrO ₂ /Ti mesh anode. An anion exchange nonwoven fabric with 1 μm micropores was used as the anion exchange membrane. The reaction tank sizes on the cathode side and the anode side were manufactured to be the same with the anion exchange membrane at the center, and the cathode and anode were positioned 10 cm and 15 cm away from the ion exchange membrane, respectively, as in Example 1.

A treatment water supply path and a treatment water discharge path were installed on the cathode side, and an influent water supply path and an influent water discharge path were installed on the anode side. In order to supply the treatment water and influent water, pumps were installed in each of the treatment water supply path and the influent water supply path.

The overall size of the cathode side was 150 cm in width, 10 cm in height, and 100 cm in height, and the overall size of the anode side was 150 cm in width, 10 cm in width, and 100 cm in height. The size of the anion exchange membrane was 10 cm in width, 100 cm in height, as in Example 1, and the sizes of the cathode and anode were 10 electrodes each 7 cm in width and 7 cm in height, which were connected vertically in series.

For comparison with Example 1, 50 L/h of untreated water was introduced into the cathode side and 50 L/h of influent was introduced into the anode side. The untreated water used was wastewater with pH 8.1, COD 8,420 ppm, ammonia 2,150 ppm, and salinity 50,800 ppm (5.08%), and the effluent discharged from the untreated water treatment facility was used as the influent supplied to the anode side, and it had pH 8.2, COD 1020 ppm, ammonia 1250 ppm, and salinity 7,100 ppm. The cathode-side and anode-side reactors were completely mixed using a mixer.

The pH was adjusted by pHI/C using 0.1 N sulfuric acid and 0.1 N sodium hydroxide.

The current density of the above desalination device was applied as 10, 15, 20, 25, and 30 mA/cm2 as in Example 1, and in order to confirm the concentration gradient on the surface of the anion exchange membrane, the concentrations of pH, COD, ammonia, and salt before and after passing through the anion exchange membrane were measured and compared near the surface of the anion exchange membrane after continuous operation for 24 hours, and the flux passing through the surface of the anion exchange membrane was calculated to observe the degree of cleaning of the surface of the anion exchange membrane immediately after ion exchange, which are shown in Tables 5 to 8 below. Specifically, Table 5 shows a comparison of concentrations before and after passing through the anion exchange membrane, Table 6 shows the difference between the concentration of the effluent of treated water and the concentrations of the influent and effluent of treated water (the concentration ion-exchanged through the anion exchange membrane), Table 7 shows the concentrations of the influent and final effluent on the anode side, and Table 8 shows a comparison of flux according to the effect of washing the ion exchange membrane with washing water at 25 mA/cm2 after 24 hours.

Current density
(mA/㎠) 10 15 20 25 30 Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) Before passing through anion exchange membrane (treatment water) After passing through the anion exchange membrane (treated water + washing water) pH 8.1 3.0 8.1 2.8 8.1 2.1 8.1 2.2. 8.1 2.0 COD
(mg/L) 8310 1090 8340 1010 8320 1080 8420 1040 8300 1080 NH ₄ ⁺
(mg/L) 2180 1320 2240 1310 2150 1280 2150 1340 2400 1320 Cl ^-
(mg/L) 50100 7400 50100 8100 50400 7800 50800 8950 50800 8240

Current density
(mA/㎠) 10 15 20 25 30 Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water Treatment water effluent concentration Difference in concentration of inflow and outflow of treated water pH 8.1 - 8.1 - 8.1 - 8.1 - 8.1 - COD
(mg/L) 8120 190 8100 240 8240 80 8320 100 8250 50 NH ₄ ⁺
(mg/L) 2040 140 2100 140 2050 100 2040 110 2310 90 Cl ^-
(mg/L) 49900 200 48900 1200 50100 300 50700 100 50720 80

Current density
(mA/㎠) 10 15 20 25 30 Influent concentration Final influent effluent concentration Influent concentration Final influent effluent concentration Influent concentration Final influent effluent concentration Influent concentration Final influent effluent concentration Influent concentration Final influent effluent concentration pH 8.2 3.0 8.2 2.8 8.1 2.1 8.1 2.2 8.1 2.0 COD
(mg/L) 1020 1090 1030 1010 1030 1080 1020 1040 1030 1080 NH ₄ ⁺
(mg/L) 1240 1320 1210 1310 1200 1280 1320 1340 1210 1320 Cl ^-
(mg/L) 7000 7400 7200 8100 7100 7800 7150 8950 7150 8240

Theoretical value after passing through anion exchange membrane Actual value after passing through anion exchange membrane Difference between theoretical value and actual value (%) COD flux (kg/㎡·s) 0.008 0 100% NH ₄ ⁺ flux (kg/㎡·s) 0.01 0 100% Cl ^- flux (kg/㎡·s) 0.008 0 100%

<Interpretation of Results>

1. pH

Referring to FIG. 3, when using a desalination device applying a laminar flow according to Example 1, the chlorine-based oxidant generated on the surface of the anode was completely separated by the treated water and wash water flowing in a constant direction, and was introduced at a pH of 8.0 to 8.1 over the entire current density, and then was discharged at a pH of 6.8 to 7.3 in the final effluent of the wash water, thereby operating stably (e.g., at a current density of 25 mA/cm2, the treated water before passing through the anion exchange membrane in Table 1 was introduced at a pH of 8.0, and then was discharged at a pH of 6.8 in the final effluent of the wash water in Table 3).

When using the turbulent completely mixed flow desalination device according to Comparative Example 1, as the chlorine-based oxidant generated on the anode surface was mixed throughout the fluid, the pH entered at 8.1 over the entire current density and then flowed out at pH 2.2 to 3.0, and the pH continuously decreased after the 0.1 N NaOH connected to the pH I/C was completely consumed (e.g., at a current density of 25 mA/cm2, the treated water before passing through the anion exchange membrane in Table 5 entered at pH 8.1 and then flowed out at pH 2.2 in the anode-side influent and final effluent in Table 7). That is, the ion exchange functional groups of the anion exchange membrane were oxidized and decomposed, and the ion exchange function was completely lost.

2. Separation of chloride ions from treated water

When using a desalination device applying a laminar flow according to Example 1, chloride ions were separated at 80.8%, 85.5%, 94.4%, 95.1%, and 94.9% at current densities of 10, 15, 20, 25, and 30 mA/cm2, respectively (e.g., at a current density of 25 mA/cm2, 51200 ppm of chloride ions were introduced from the influent concentration of the untreated water before passing through the anion exchange membrane in Table 1, and 2500 ppm were discharged from the effluent concentration of the untreated water in Table 2, so that 95.1% chloride ion separation was possible). The results are shown in Fig. 4.

On the other hand, when using the turbulent completely mixed flow desalination device according to Comparative Example 1, chloride ions were separated at 0.4%, 2.4%, 0.6%, 0.2%, and 0.16% at current densities of 10, 15, 20, 25, and 30 mA/cm2, respectively (e.g., at a current density of 25 mA/cm2, 50,800 ppm of chloride ions were introduced from the influent concentration of the untreated water before passing through the anion exchange membrane in Table 5, and 50,700 ppm were discharged from the effluent concentration of the untreated water in Table 6, so that 0.2% chloride ion separation was possible).

3. Final discharge of organic pollutants (COD) from the anode side

Referring to FIG. 5, when using a desalination device applying a laminar flow according to Example 1, organic pollutants were removed by the chlorine-based oxidizer at current densities of 10, 15, 20, 25, and 30 mA/cm2, respectively, at rates of 78%, 82.2%, 82.7%, 85.7%, and 82.6% (e.g., at a current density of 25 mA/cm2 in Table 3, the COD of the inflowing wash water was 840 ppm, and the COD of the final effluent of the anode-side wash water was 120 ppm, indicating that 85.7% of organics were removed by the chlorine-based oxidizer).

In the case of using the turbulent type complete mixing flow desalination device according to Comparative Example 1, only 1.94% of organic pollutants were removed at a current density of 15 mA/cm2, and at current densities of 10, 20, 25, and 30 mA/cm2, the organic pollutants were not removed but rather increased (e.g., at a current density of 25 mA/cm2 in Table 7, the COD of the anode-side influent was 1020 ppm, while the COD of the anode-side final effluent was 1040 ppm, indicating that the organic pollutants (not removed). This is presumed to be a result of the absence of chlorine oxidizers.

4. Final discharge of ammonium ions from the anode side

Referring to FIG. 6, when using a desalination device applying a laminar flow according to Example 1, 95.5%, 95%, 95.2%, 96.4%, and 94.5% of ammonium ions in the wash water were removed at current densities of 10, 15, 20, 25, and 30 mA/cm2, respectively (e.g., at a current density of 25 mA/cm2 in Table 3, 890 ppm of _NH4 ⁺ was introduced and 32 ppm was discharged in the final effluent on the anode side; 96.4% of _NH4 ⁺ was removed by a chlorine-based oxidizer).

When using the turbulent type complete mixing flow desalination device according to Comparative Example 1, the ammonium ions in the wash water were not removed but rather increased at current densities of 10, 15, 20, 25, and 30 mA/cm2 (e.g., at a current density of 25 mA/cm2 in Table 7, the COD of the anode side inflow water was 1320 ppm and 1340 ppm was discharged in the final effluent from the anode side, and _NH4 ⁺ was It is assumed that this is a result of the absence of generation of chlorine-based oxidizing agents (not removed).

5. Comparison of differences between theoretical and measured flux values

When using a desalination device applying a laminar flow according to Example 1, the differences between the theoretical values and the measured values of COD flux, NH ₄ ⁺ flux, and Cl flux at a current density of 25 mA/cm2 were 25%, 20%, and 0.9%, respectively, indicating that the flux was close to the theoretical value due to the continuous cleaning effect on the surface of the anion exchange membrane even after 24 hours of continuous operation.

On the other hand, when using a turbulent completely mixed flow desalination device according to Comparative Example 1, the differences between the theoretical values and the measured values of COD flux, NH ₄ ⁺ flux, and Cl flux at a current density of 25 mA/cm2 were 100%, 100%, and 100%, making desalination impossible during continuous operation for 24 hours.

Claims (21)

As a desalination device for removing contaminants in treated water,
An electrolysis unit comprising a cathode, an anode and an anion exchange membrane;
A treatment water supply path located on the cathode side and supplying treatment water from the outside of the desalination device toward the anion exchange membrane;
A treated water discharge path located on the cathode side to discharge the treated water, in which the pollutants are removed by passing through the anion exchange membrane to the anode side, to the outside of the desalination device;
A washing water supply path located on the anode side and supplying washing water from the outside of the desalination device toward the anion exchange membrane; and
A washing water discharge path located on the anode side for discharging washing water containing the pollutants transmitted through the anion exchange membrane from the cathode side to the outside of the desalination device;
Including,
A desalination device, wherein the net flow of the washing water has a linear flow along the length of the washing water supply path. In claim 1,
A desalination device, wherein the net flow of the washing water has a linear flow from the outside of the desalination device along the washing water supply path toward the anion exchange membrane, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane along the washing water discharge path toward the outside of the desalination device. In claim 2,
A desalination device in which the washing water has a laminar flow having a Reynolds number of 2000 or less. In claim 1,
A desalination device in which the above-mentioned washing water is supplied by treating the above-mentioned untreated water from a wastewater treatment facility. In claim 1,
A desalination device, wherein the net flow of the above-mentioned treatment water has a linear flow from the outside of the desalination device along the treatment water supply path toward the anion exchange membrane, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane along the treatment water discharge path toward the outside of the desalination device. In claim 5,
The above-mentioned desalination device has a laminar flow with a Reynolds number of 2000 or less. In claim 1,
A desalination device, wherein the anode comprises at least one metal or alloy or oxide thereof selected from the group consisting of iridium (Ir), ruthenium (Ru), tin (Sn), titanium (Ti), molybdenum (Mo), tantalum (Ta), zirconium (Zr), and boron (B) doped diamond (BDD). In claim 1,
A desalination device, wherein a plurality of repeating units including the above-described treatment water supply path and the above-described treatment water discharge path and the repeating units including the above-described wash water supply path and the above-described wash water discharge path are arranged facing each other with the above-described anion exchange membrane interposed therebetween. In claim 1,
A desalination device having a plurality of repeating units including cathodes and anodes arranged at the rear end of the electrolysis unit to perform additional electrolysis on the wash water discharged from the wash water discharge path. In claim 1,
The above anion exchange membrane is a support made of woven or non-woven fabric; and
A desalination device comprising a skin layer comprising a polymer resin having a cationic functional group. In claim 1,
A desalination device, wherein the concentration of chlorine ions in the discharged treated water is reduced by 80% or more compared to the concentration of chlorine ions in the supplied treated water. In claim 1,
A desalination device, wherein the chemical oxygen demand (COD) in the wash water discharged from the wash water discharge path is reduced by 75% or more compared to the chemical oxygen demand in the supplied wash water. In claim 1,
A desalination device, wherein the concentration of ammonium ions ( _NH4 ⁺ ) in the wash water discharged from the wash water discharge path through the electrolysis unit is reduced by 94% or more compared to the concentration of ammonium ions in the supplied wash water. In claim 1,
A desalination device, wherein the pH of the treatment water and the wash water are each independently 5 to 10. A desalination method for removing contaminants in treated water,
A step of supplying the treated water to the cathode of the electrolysis unit through the treated water supply path and toward the anion exchange membrane;
A contaminant transfer step for removing contaminants in the above-mentioned treatment water by passing them through the anion exchange membrane to the anode side;
A treatment water discharge step in which the treatment water from which the above pollutants have been removed is discharged to the outside through the treatment water discharge path via the cathode through the anion exchange membrane;
A washing water supply step for supplying washing water in the direction of the anion exchange membrane through a washing water supply path; and
A washing water discharge step of discharging washing water containing the pollutants transmitted through the anion exchange membrane to the outside through the anode and a washing water discharge path;
Including,
A desalination method, wherein the net flow of the washing water has a linear flow along the length of the washing water supply path. In claim 15,
A desalination method, wherein the net flow of the washing water has a linear flow from the outside toward the anion exchange membrane along the washing water supply path, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane toward the outside along the washing water discharge path. In claim 15,
A desalination method, wherein the washing water has a laminar flow having a Reynolds number of 2000 or less. In claim 15,
A step in which chlorine ions contained in the pollutants derived from the above-mentioned treatment water or wash water are converted into at least one substance selected from the group consisting of chlorine (Cl ₂ ), chlorous acid (HClO ₂ ), hypochlorous acid (HClO), and hypochlorite ion (OCl ^- ) at the anode side; and
A step in which the converted material oxidizes and decomposes pollutants derived from the treated water or wash water;
A desalination method further comprising: In claim 18,
A desalination method, wherein the converted substance in the oxidation decomposition step is reconverted into chloride ions after oxidizing and decomposing the pollutant. In claim 15,
A desalination method, wherein the net flow of the above-mentioned treatment water has a linear flow from the outside in the direction of the anion exchange membrane along the treatment water supply path, a flow in a direction parallel to the anion exchange membrane, and a linear flow from the anion exchange membrane in the direction of the outside along the treatment water discharge path. In claim 20,
A desalination method, wherein the above-mentioned treatment water has a laminar flow having a Reynolds number of 2000 or less.