Solution processing method and solution processing apparatus

Abstract

The purpose of the present invention is to provide a solution processing method by which an electrolyte and water are recovered from a solution that contains at least 1,000 mg / L or more of the electrolyte and a non-electrolyte low-molecular-weight material having a molecular weight of 70 or less, while removing the non-electrolyte low-molecular-weight material by means of a combination of membranes of a plurality of kinds. This solution processing method processes a starting material solution with a separation membrane 1 and a separation membrane 2, which separate a supplied liquid into a permeated liquid and a concentrated liquid, so as to separate the starting material solution into a purified liquid that contains water and the electrolyte and a waste liquid that contains the non-electrolyte low-molecular-weight material.

Description

[Technical Field]

[0001] The present invention relates to a solution treatment method using membrane separation to recover electrolytes and water from a solution containing at least 1000 mg / L or more of an electrolyte and small non-electrolyte molecules having a molecular weight of 70 or less, while separating the small non-electrolyte molecules. [Background technology]

[0002] In recent years, there has been an increasing need for selective separation technologies that can extract useful substances from solutions containing multiple dissolved components or separate impurities. Examples include extracting valuable materials from salt lake water containing various dissolved elements, or removing impurities from solutions containing impurities. More specifically, Patent Document 1 describes a method for removing boron dissolved in freshwater obtained by seawater desalination or raw water used for tap water using a reverse osmosis membrane and a loose RO membrane. Patent Document 2 describes a method for removing salt from seawater or deep ocean water while leaving mineral components intact using a reverse osmosis membrane and a nanofiltration (NF) membrane.

[0003] Among the needs for various selective separation technologies, in recent years, the number of patients undergoing dialysis treatment has increased worldwide as living standards have improved, and technology that removes impurities from dialysis wastewater discharged during treatment and recycles it as dialysis fluid has been attracting attention. A typical dialysis treatment requires the use of large amounts of dialysis fluid, ranging from 90 to 150 liters per treatment. Because the dialysis fluid used in dialysis treatment contains waste products such as urea that have migrated from the blood, the dialysis fluid is generally discarded after one use. This has led to the problem of large amounts of dialysis wastewater being generated.

[0004] The most common method for producing dialysis fluid is to add necessary electrolytes, glucose, etc. to purified water obtained by treating tap water with a reverse osmosis (RO) membrane or other device. However, in water-scarce regions where tap water supply is intermittent, it can be difficult to secure the necessary amount of tap water, necessitating a reduction in water consumption. Furthermore, even in regions with sufficient water supply, a prolonged water outage during a disaster can make it impossible to produce dialysis fluid from tap water. Therefore, there is an increasing demand for the reuse of dialysis waste fluid, which involves removing waste products such as urea from the dialysis waste fluid and reusing it as dialysis fluid. Several dialysis waste fluid reuse technologies have been proposed.

[0005] For example, it has been proposed to use adsorbents to remove impurities, waste products, and electrolytes from used dialysis wastewater. However, depending on the dialysis treatment performed, several kilograms of adsorbent material is required to regenerate the dialysis wastewater, and a system that minimizes weight and cost is desired.

[0006] As a method for reducing the amount of adsorbent, Patent Document 3 proposes a system that uses adsorbent cartridges in two stages.

[0007] Patent Document 4 proposes a urea removal system using urease and an ion exchange resin or an inorganic adsorbent.

[0008] Patent Document 5 proposes a system in which electrolytes are removed to a certain extent using an adsorbent or electrodialysis, and then impurities are removed using a reverse osmosis membrane. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 9-290275 [Patent Document 2] Japanese Patent Application Publication No. 2003-88863 [Patent Document 3] Japanese Patent Application Publication No. 2014-204958 [Patent Document 4] Japan Special Publication No. 2014-530643 [Patent Document 5] International Publication No. 2020-218571 Summary of the Invention [Problem to be solved by the invention]

[0010] The technologies described in Patent Documents 3 and 4 involve using urease to decompose urea into ammonia, which is then further captured, thereby separating urea from used dialysis fluid. Therefore, multiple adsorbents are required to completely capture urea and the ammonia, which is the decomposition product. Since a small amount of adsorbent may result in residual ammonia that has not been captured, a large amount of adsorbent is required, which poses problems such as increased costs and increased weight of the dialysis waste fluid recycling device.

[0011] The technology described in Patent Document 5 uses a reverse osmosis membrane with a pore size of 7.0 Å or less to separate waste products such as urea and regenerate dialysis wastewater. This technology requires pretreatment to remove electrolytes from the dialysis wastewater, particularly when treating water with high water recovery rates, in order to reduce the osmotic pressure difference across the reverse osmosis membrane. This pretreatment requires the use of ion exchange resins or electrodialysis equipment. However, the use of ion exchange resins poses a problem: waste ion exchange resins are discharged after each dialysis treatment. Furthermore, the use of electrodialysis equipment requires high voltage for desalination and is undesirable from a safety standpoint due to the risk of chlorine gas generation.

[0012] Therefore, an object of the present invention is to provide a solution treatment method that combines multiple types of membranes to treat a solution containing substances to be separated, such as neutral molecules, and separates unnecessary substances to be separated while recovering components to be retained as a purified solution and water. More specifically, an object of the present invention is to provide a solution treatment method that combines multiple membranes to treat a solution containing at least 1000 mg / L of electrolytes and small non-electrolyte molecules with a molecular weight of 70 or less, and recovers electrolytes and water while removing the small non-electrolyte molecules. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention mainly employs one of the following configurations. (1) A solution treatment method in which a raw solution is treated with a separation membrane 1 and a separation membrane 2 that separate a feed solution into a permeate and a concentrate, and the raw solution is separated into a purified solution containing water and electrolytes and a waste liquid containing non-electrolyte small molecules, The stock solution is a solution containing at least 1000 mg / L or more of an electrolyte and a non-electrolyte low-molecular-weight substance having a molecular weight of 70 or less, The permeate of the separation membrane 1 is supplied to the separation membrane 2 for separation treatment, The separation membrane 1 was subjected to the following reaction when a solution 1 containing 10,000 mg / L of sodium chloride (NaCl) and 250 mg / L of urea at a pH of 7 was supplied at 36°C and a pressure of 1.2 MPa: The removal rate is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, and the NaCl removal rate is 90% or more. the separation membrane 2 has a urea rejection rate of 85% or more, which is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, when a solution 2 having a pH of 7 and containing 1000 mg / L of sodium chloride (NaCl) and 700 mg / L of urea is supplied at 36°C and a pressure of 1.8 MPa; the difference between the urea rejection rate of the separation membrane 2 under the evaluation conditions of the separation membrane 2 and the urea rejection rate of the separation membrane 1 under the evaluation conditions of the separation membrane 1 is 40% or more; Furthermore, the solution processing method is characterized by satisfying either of the following requirements (i) and (ii): (i) A portion of the permeate of the separation membrane 2 is mixed with the raw liquid and then supplied to the separation membrane 1, and all or a portion of the remaining permeate of the separation membrane 2 is mixed with the concentrated liquid of the separation membrane 1 to obtain the purified liquid. (ii) The entire amount of the permeate through the separation membrane 2 is mixed with the raw liquid, and then supplied to the separation membrane 1, and the concentrate through the separation membrane 1 is obtained as the purified liquid. (2) A solution treatment apparatus comprising a separation membrane 1 and a separation membrane 2 that separate a feed liquid into a permeate and a concentrate, and that separates a raw liquid into a purified liquid containing water and electrolytes and a waste liquid containing non-electrolyte small molecules, The stock solution is a solution containing at least 1000 mg / L or more of an electrolyte and a non-electrolyte low-molecular-weight substance having a molecular weight of 70 or less, The permeate line of the separation membrane 1 is connected to the feed line of the separation membrane 2, The separation membrane 1 was subjected to the following reaction when a solution 1 containing 10,000 mg / L of sodium chloride (NaCl) and 250 mg / L of urea at a pH of 7 was supplied at 36°C and a pressure of 1.2 MPa: The removal rate is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, and the NaCl removal rate is 90% or more. The separation membrane 2 has a urea rejection rate of 85% or more, which is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, when a solution 2 having a pH of 7 and containing 1000 mg / L of sodium chloride (NaCl) and 700 mg / L of urea is supplied at 36°C and a pressure of 1.8 MPa, the difference between the urea rejection rate of the separation membrane 2 under the evaluation conditions of the separation membrane 2 and the urea rejection rate of the separation membrane 1 under the evaluation conditions of the separation membrane 1 is 40% or more; Furthermore, the solution treatment device satisfies either of the following requirements (i) and (ii): (i) The permeate line of the separation membrane 2 is branched into at least two lines, at least one of which is connected to the raw liquid line, a line for a mixture of the raw liquid and the permeate of the separation membrane 2 is connected to the supply line of the separation membrane 1, and at least one of the remaining lines is connected to the concentrated liquid line of the separation membrane 1 to form a purified liquid line. (ii) The permeate line of the separation membrane 2 is connected to the raw liquid line, the line for the mixed liquid of the raw liquid and the permeate of the separation membrane 2 is connected to the supply line of the separation membrane 1, and the concentrate line of the separation membrane 1 is used as the purified liquid line.

[0014] The term "raw solution" refers to the solution supplied to the most upstream side in the present invention, and the solution supplied to each separation membrane based on the separation membrane is referred to as the "feed solution." [Effects of the Invention]

[0015] According to the solution treatment method of the present invention, by performing a specific membrane separation process on a solution containing a substance to be separated, it is possible to recover a desired component while separating the substance to be separated. Furthermore, when such membrane separation process is performed on dialysis wastewater after artificial dialysis treatment, for example, it is possible to recover electrolytes such as salt and water while separating urea. Therefore, the dialysis wastewater can be reused, which makes it possible to stabilize the supply of dialysis fluid and reduce dialysis medical costs. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating a solution processing method according to an embodiment of the present invention. [Figure 2] 1A to 1C are schematic diagrams illustrating a solution processing method according to another embodiment of the present invention. [Figure 3] FIG. 1 is a partially exploded perspective view of an I-type separation membrane element that can be used in the present invention. [Figure 4] FIG. 2 is a schematic diagram showing an example of an I-type separation membrane body. [Figure 5] FIG. 2 is a schematic diagram showing an example of an inverted L-shaped separation membrane body. [Figure 6] FIG. 2 is a schematic diagram showing an example of an L-shaped separation membrane body. [Figure 7] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of an inverted L-shaped separation membrane element. [Figure 8] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of an L-shaped separation membrane element. [Figure 9] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of a U-turn type (I-type-inverted L-type) separation membrane element. [Figure 10] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of the structure of a separation membrane module equipped with an I-type separation membrane element. [Figure 11]FIG. 1 is a schematic diagram (cross-sectional view) showing an example of a separation membrane module equipped with an I-type separation membrane element and an inverted L-type separation membrane element. [Figure 12] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of a separation membrane module equipped with an I-type separation membrane element and an L-type separation membrane element. [Figure 13] FIG. 1 is a schematic diagram (cross-sectional view) showing an example of a separation membrane module equipped with an I-type separation membrane element and a U-turn type separation membrane element. [Figure 14] 1 is a schematic diagram of a dialysis system including a solution treatment device and a dialysis device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these in any way.

[0018] (1) Undiluted solution In the present invention, the stock solution is a solution containing at least 1000 mg / L or more of electrolytes and containing non-electrolyte small molecules with a molecular weight of 70 or less (hereinafter, may be simply referred to as "non-electrolyte small molecules"). Examples of such solutions include dialysis wastewater containing urea as a non-electrolyte small molecule, and seawater or brine containing boron as a non-electrolyte small molecule.

[0019] Examples of electrolytes include sodium ions, potassium ions, calcium ions, magnesium ions, chloride ions, sulfate ions, and nitrate ions. Examples of low-molecular-weight non-electrolytes with a molecular weight of 70 or less include urea, boron, methanol, and ethanol. These can be confirmed by analyzing the components using methods such as ion chromatography and liquid chromatography. As will be described later, in order for separation membrane 1 to exhibit sufficient selective separation performance, the molecular weight of the low-molecular-weight non-electrolytes contained in the stock solution must be 70 or less. Furthermore, in order to fully exhibit the selective separation performance of the present invention, the concentration of the low-molecular-weight non-electrolytes in the stock solution is preferably 10 mg / L or more, more preferably 100 mg / L or more, and even more preferably 500 mg / L or more.

[0020] Here, dialysis and dialysis waste will be described in detail.

[0021] Dialysis is performed using known methods. The dialysis device has a dialysis membrane that is permeable to toxins such as urea but not to plasma components. Dialysis fluid is supplied to one side of the dialysis membrane, while blood is supplied to the other side. The composition of the dialysis fluid is known and includes sodium ions, potassium ions, calcium ions, magnesium ions, glucose, etc. Urea in the blood is removed from the blood by diffusing into the dialysis fluid through the dialysis membrane. In addition to urea, potassium ions are another substance that must be removed by dialysis. Because approximately 90% of potassium ions are excreted by the kidneys, they tend to accumulate in the body of dialysis patients. Hyperkalemia can lead to cardiac arrest, so controlling blood potassium ion concentrations is also an important role in dialysis. The dialysis system must remove 26% to 35% of blood potassium ions with each dialysis session and control blood potassium ion concentrations.

[0022] The dialysis wastewater that has passed through the dialysis device is expected to contain, for example, 10,000 mg / L of electrolytes, including 100 mg / L of potassium ions and approximately 600 mg / L of urea, a low-molecular-weight non-electrolyte. In the present invention, such dialysis wastewater is preferably treated as a raw liquid. A solution containing a small amount of electrolytes is then added to the purified liquid obtained by the present invention to produce a regenerated dialysis liquid. The regenerated dialysis liquid preferably has a urea concentration reduced by 65% ​​or more and a potassium ion concentration reduced by 2% or more compared to the dialysis wastewater. To reduce the amount of electrolytes to be added, the purified liquid preferably recovers 80% or more of the electrolytes from the dialysis wastewater.

[0023] (2) Separation membrane <Summary> In the present invention, the raw solution is treated using at least two types of separation membranes. Each of these two types of separation membranes may be a single layer or a composite membrane comprising a separation functional layer and a substrate. In addition, the composite membrane may further include a porous support layer between the separation functional layer and the substrate.

[0024] The two membranes, separation membrane 1 and separation membrane 2, are arranged so that the permeate through separation membrane 1 is supplied to separation membrane 2. Separation membrane 1 preferably has a pore size of 7 Å or more as measured by positron annihilation lifetime spectroscopy to ensure a required electrolyte removal rate (described below). On the other hand, separation membrane 2 preferably has a pore size of 7 Å or less as measured by positron annihilation lifetime spectroscopy to ensure a required electrolyte removal rate (described below). By having a pore size of 7 Å or less, separation membrane 2 can highly effectively remove components such as urea and electrolytes.

[0025] The pore size is measured using positron annihilation lifetime spectroscopy. Positron annihilation lifetime spectroscopy measures the time (on the order of hundreds of picoseconds to tens of nanoseconds) between the time a positron is incident on a sample and the time it is annihilated. Based on the annihilation lifetime, information such as the size, number density, and size distribution of pores of 0.1 to 10 nm can be nondestructively evaluated. This measurement method is described in "Experimental Chemistry Lectures, 4th Edition," Vol. 14, p. 485, edited by the Chemical Society of Japan, Maruzen Co., Ltd. (1992).

[0026] When the separation membrane is a composite membrane, the average pore radius R in the separation functional layer is calculated from the following formula (1) based on the above-mentioned positron annihilation lifetime τ. Formula (1) shows the relationship when it is assumed that o-Ps (ortho-positronium) exists in a pore of radius R in an electron layer of thickness ΔR, and ΔR has been empirically determined to be 0.166 nm (Nakanishi et al., Journal of Polymer Science, Part B: Polymer Phys ics,Vol.27,p.1419,John Wiley & Sons,Inc.( The details are given in (1989).

[0027]

number

[0028] In the present invention, it is necessary that the separation membranes 1 and 2 have the following salt rejection rate and urea rejection rate, respectively.

[0029] First, the salt rejection rate and urea rejection rate of separation membrane 1 are defined as the rate of decrease in the concentration of components in the permeated solution relative to the concentration of the components in the supplied solution when solution 1, a mixture of 10,000 mg / L of sodium chloride (NaCl) and 250 mg / L of urea with a pH of 7, is supplied at a temperature of 36°C and a pressure of 1.2 MPa.

[0030] The salt rejection rate and urea rejection rate of the separation membrane 2 are defined as the rate of decrease in the concentration of components in the permeated solution relative to the concentration of the components in the supplied solution when a solution 2 containing a pH of 7, 1000 mg / L of sodium chloride (NaCl) and 700 mg / L of urea is supplied at a temperature of 36°C and a pressure of 1.8 MPa.

[0031] Under the above evaluation conditions, the recovery rate, which is the ratio of the amount of permeated liquid to the amount of supplied liquid, can be approximated to 0, that is, a sufficient membrane surface flow rate is required.

[0032] The urea concentration is measured using the urease GLDH method, which involves carrying out the following first and second reactions and measuring the change in coenzyme (NADPH) to measure urea nitrogen (BUN).

[0033] (First reaction) In the following reaction formula (II), the endogenous ammonia produced in the following reaction formula (I) is eliminated by the action of α-ketoglutaric acid, reduced nicotinamide adenine dinucleotide phosphate (NADPH), and glutamate dehydrogenase (GLDH). The oxidized nicotinamide adenine dinucleotide phosphate (NADP) produced in this process is reduced to NADPH by the action of L-isocitrate dehydrogenase (ICDH) in reaction formula (III).

[0034] (Second reaction) After the endogenous ammonia is eliminated by the first reaction, urea is broken down into ammonia and carbon dioxide by the action of urease. This ammonia and α-ketoglutaric acid (α-KG) are converted to glutamic acid by the action of GLDH, and at the same time, NADPH is converted to NADP. NADPH has an absorption maximum at 340 nm, and the rate of decrease in this absorbance is measured to determine the urea nitrogen value. At this point, the first reaction, reaction formula (III), is stopped by the action of the chelating agent added to the second reagent. Urea + H2O (+ urease) → 2NH3 + CO2 (I) α-Ketoglutarate + NH3 + NADPH + H+ (+GLDH) → glutamate + NAD P++H2O···(II) NADP++L-isocitrate (+ICDH) → NADPH++α-ketoglutarate + CO 2 (III)

[0035] In the present invention, the sodium chloride rejection rate of separation membrane 1 measured under the evaluation conditions for separation membrane 1 is 90% or higher. Furthermore, in order to preferentially remove 65% or more of urea throughout the entire system, the urea rejection rate of separation membrane 2 measured under the evaluation conditions for separation membrane 2 is 85% or higher, and the difference between the urea rejection rate of separation membrane 2 measured under the evaluation conditions for separation membrane 2 and the urea rejection rate of separation membrane 1 measured under the evaluation conditions for separation membrane 1 is 40% or higher (preferably 60% or higher). By satisfying these rejection rates, the entire process can exhibit sufficient performance.

[0036] When the process of the present invention is combined with a dialysis device as shown in Figure 14, potassium ions are recovered along with other electrolytes and accumulate in the regenerated dialysate. However, the inventors of the present invention carefully examined the relationship between the salt rejection rate of separation membrane 1 and the blood potassium ion rejection rate after 4 hours of dialysis and found that if the salt rejection rate of separation membrane 1 is in the range of 99% or less, potassium ions are removed by 2% or more in the entire system shown in Figure 14, and the blood potassium ion rejection rate can be controlled to 26% or more. If too much potassium ions are removed by using a membrane with a low salt rejection rate as separation membrane 1, potassium ions can be added to the electrolyte-containing adjustment solution that is added when the purified liquid is converted into regenerated dialysate.

[0037] In the present invention, the type of separation membrane 1 is not particularly limited as long as it satisfies the above conditions, but generally, a nanofiltration membrane or a low-pressure RO membrane is preferably used.

[0038] The type of separation membrane 2 is not particularly limited as long as it satisfies the above conditions, but a dense RO membrane used for desalination of seawater and the like is preferably used.

[0039] <Separation functional layer> The separation functional layer may be a layer having both a separation function and a support function, or may have only a separation function. Note that the term "separation functional layer" refers to a layer having at least a separation function.

[0040] When the separation functional layer has both a separation function and a support function, a layer containing, as a main component, a polymer selected from the group consisting of cellulose, polyvinylidene fluoride, polyethersulfone, and polysulfone is preferably used as the separation functional layer.

[0041] On the other hand, if the only purpose is to achieve separation functionality, crosslinked polymers are preferred because of their ease of pore size control and excellent durability. In particular, polyamide separation layers obtained by polycondensation of polyfunctional amines and polyfunctional acid halides, as well as organic-inorganic hybrid functional layers, are preferred because of their excellent separation performance of components in the feed solution. These separation layers can be formed by polycondensing monomers on a separately prepared porous support layer. For example, a polyamide separation layer can be obtained by applying an aqueous solution of a polyfunctional amine to a porous support layer, removing the excess aqueous solution of the polyfunctional amine with an air knife, and then applying an organic solvent solution containing a polyfunctional acid halide to cause interfacial polycondensation.

[0042] <Porous support layer> The porous support layer is a layer that supports the separation function layer, and when made of resin, it can also be called a porous resin layer.

[0043] The material and shape of the porous support layer are not particularly limited. For example, it may be formed on a substrate using a porous resin. The composition of the porous support layer is not particularly limited. However, it is preferably formed using a thermoplastic resin. Here, a thermoplastic resin is a resin made of a chain polymer that exhibits the property of deforming or flowing when heated under external forces. Examples of thermoplastic resins include homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose-based polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide, which can be used alone or in blends. Examples of cellulose-based polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, and acrylonitrile-styrene copolymers. Among these, polysulfone is preferred due to its high chemical, mechanical, and thermal stability and ease of pore size control.

[0044] The porous support layer can be produced, for example, by casting a solution of the above-mentioned polysulfone in N,N-dimethylformamide onto a substrate (e.g., a tightly woven polyester nonwoven fabric) described below to a certain thickness, and then wet-coagulating the resulting mixture in water.

[0045] <Base material> From the viewpoint of the strength, dimensional stability, etc. of the separation membrane, the separation membrane may have a substrate. As the substrate, a fibrous substrate is preferably used in terms of strength and fluid permeability. In particular, a long-fiber nonwoven fabric and a short-fiber nonwoven fabric are preferred.

[0046] (3) Separation membrane module <Summary> In the present invention, the separation membrane 1 and the separation membrane 2 can be configured as a spiral type element in which a flat membrane is wound around a perforated central tube, a plate-and-frame type element in which flat membranes are stretched on both sides of a plate-type support plate and laminated at a constant interval via spacers, a tubular type element using a tubular membrane, or a hollow fiber membrane element in which a bundle of hollow fiber membranes is housed in a case. Further, these elements are connected in series, singly or in plurality, and housed in a pressure-resistant container to form a separation membrane module. As the form of the element, any form may be used, but from the viewpoints of operability and compatibility, it is preferable to use a spiral type separation membrane element as shown in FIG. 3. The spiral type separation membrane element is a laminate of a separation membrane, a permeate side flow path material, and a supply side flow path material wound around a perforated central tube for collecting the permeate fluid.

[0047] <Separation membrane body of spiral type separation membrane element> The flat membrane-shaped separation membrane has a permeate side surface and a supply side surface. A separation membrane leaf arranged such that the permeate side surfaces face each other with the permeate side flow path material interposed therebetween and a supply side flow path material arranged on one side of the supply side surface of the separation membrane leaf are combined and referred to as a separation membrane body. The permeate side flow path is formed such that the permeate fluid flows into the perforated central tube, and the space between the permeate side surfaces of the separation membrane is opened only at one side on the inner side in the winding direction and sealed at the other three sides. The supply side flow path is formed between the supply side surfaces of the separation membrane, and depending on the sealing method of the supply side flow path material, various types of separation membrane elements such as type I, L type, reverse L type, U-turn type, etc. are formed as described later.

[0048] <Type I separation membrane element> As shown in FIG. 3, a feed liquid (206) flows into one end of a so-called I-type separation membrane element (201), and a concentrate (207) is discharged from the other end. The I-type separation membrane element (201) includes a separation membrane (203), a feed-side channel material (204), a permeate-side channel material (205), and a perforated central tube (202). In the I-type separation membrane element (201), the separation membrane (203), together with the feed-side channel material (204) and the permeate-side channel material (205), form a separation membrane assembly (213) as shown in FIG. 4. The separation membranes (203) are arranged such that their permeate-side surfaces face each other, with the permeate-side channel material (205) sandwiched between them. In addition, a feed-side channel material (204) is arranged on the feed-side surface (211) of the separation membrane (i.e., between the feed-side surface of the separation membrane constituting the adjacent separation membrane assembly). The permeate-side flow path is formed by opening only one inner side in the winding direction between the permeate-side surfaces of the separation membranes constituting two adjacent separation membrane bodies and sealing (closing) the other three sides so that the permeate (208) flows into the perforated central tube (202). The feed-side flow path material is disposed so as to be sandwiched between the feed-side surfaces of the separation membranes, and forms a flow path for supplying the feed liquid to the separation membranes (i.e., the feed-side flow path).

[0049] Furthermore, the feed-side channel material is preferably shaped to disturb the flow of the feed liquid in order to suppress concentration polarization of the feed liquid. Specifically, the feed-side channel material may be a continuous member such as a net or a perforated film with convex portions, or may be a plurality of discontinuous members disposed directly on the separation membrane. The discontinuous members are disposed so that the projected area ratio to the separation membrane is greater than 0 and less than 1. Furthermore, the feed-side channel material may be separable from the separation membrane, or may be fixed to the separation membrane.

[0050] The material of the feed-side channel material is not particularly limited, and may be the same material as the separation membrane or a different material.

[0051] If the thickness of the feed-side channel material is large, the pressure loss will be small, but when it is made into an element, the membrane area that can be packed into a pressure vessel will be small. If the thickness is small, the pressure loss in the channel will be large, and the separation performance and permeation performance will be reduced. Considering the balance of each performance and operating costs, the thickness of the feed-side channel material is preferably 200 to 1000 μm, and more preferably 300 to 900 μm. The thickness of the feed-side channel material can be measured directly using a commercially available thickness measuring device, or can be measured by analyzing images taken using a microscope.

[0052] When the supply-side channel material is a net, the net is composed of a plurality of threads. The plurality of threads intersect with each other at intersections, and the intersections are the thickest. The diameter of the threads constituting the net may be constant in the length direction of the threads, may increase or decrease uniformly in the length direction, or may be in a form in which the diameter increases and decreases repeatedly. When the diameter of the threads increases and decreases repeatedly in the length direction, it is preferable that the plurality of threads intersect at the point where the thread diameter is largest. By having the plurality of threads intersect at the point where the thread diameter is largest, the pressure loss in the supply-side channel can be reduced.

[0053] Furthermore, the diameters of the intersecting yarns may be the same or different. When the diameters of the intersecting yarns are different, if the thickness is constant, yarns with smaller diameters have a greater effect of reducing pressure loss, while yarns with larger diameters have a greater turbulent effect that disturbs the flow.

[0054] In order to balance the above-mentioned pressure loss and turbulence effect, the diameter of the cross section of the yarn constituting the net is preferably such that (diameter at the smallest part) / (diameter at the largest part) is 0.1 or more and 0.7 or less, more preferably 0.3 or more and 0.6 or less.

[0055] If the inclination angle of the threads constituting the net is parallel to the flow direction of the supply liquid, the pressure loss can be reduced, but the concentration polarization reduction effect will be smaller. On the other hand, if the inclination angle is closer to the perpendicular direction, the pressure loss will be higher, but the concentration polarization reduction effect can be increased. In order to balance the pressure loss and the concentration polarization reduction effect, the inclination angle of the threads is preferably between -60° and 60° with respect to the average flow angle of the supply liquid. Here, the average flow angle is the average value of the flow angle within one separation membrane body.

[0056] The larger the interval between the intersections of multiple yarns, the smaller the pressure loss, and the smaller the interval, the larger the pressure loss. In order to balance these factors, the interval between the intersections is preferably 1.0 mm or more and 10 mm or less, more preferably 1.1 mm or more and 8 mm or less, and even more preferably 1.2 mm or more and 5 mm or less.

[0057] The cross-sectional shape of the threads constituting the net is not particularly limited, and oval, circular, triangular, rectangular, irregular, etc. can be used, but a small area where the net comes into contact with the separation membrane surface is preferable because it can prevent a decrease in separation membrane performance due to friction between the separation membrane surface and the net, reduce flow dead zones, and suppress concentration polarization. The projected area ratio of the area where the net comes into contact with the separation membrane surface to the separation membrane is preferably 0.01 to 0.25, more preferably 0.02 to 0.2.

[0058] The material of the threads constituting the net is not particularly limited as long as it can maintain the rigidity required as a feed-side flow path material and does not damage the surface of the separation membrane, and may be the same material as the separation membrane or a different material. Preferred materials include polyethylene, polypropylene, polylactic acid, ethylene-vinyl acetate copolymer, polyester, polyurethane, and thermosetting elastomers.

[0059] The permeate-side channel material is placed between the permeate surfaces of two opposing separation membranes, and serves to form a permeate-side channel that guides the permeate that has permeated the separation membranes to the holes in the perforated central tube.

[0060] The permeate-side channel material preferably has a cross-sectional area ratio of 0.30 to 0.75, more preferably 0.40 to 0.60, in order to reduce the flow resistance of the permeate-side channel, suppress the separation membrane from falling into the permeate channel even under pressure filtration, and form a stable channel. The type of permeate-side channel material is not limited, and can be a weft-knitted fabric such as tricot, a porous sheet such as a nonwoven fabric with protrusions arranged thereon, or a textured sheet obtained by texture-processing a film or nonwoven fabric.

[0061] The cross-sectional area ratio is the ratio of the cross-sectional area of ​​the permeate-side channel material between the center of a convex portion and the center of an adjacent convex portion to the product of the distance between the center of a convex portion and the center of an adjacent convex portion and the height (thickness) of the permeate-side channel material in a cross section obtained by cutting the permeate-side channel material along a direction parallel to the longitudinal direction of the perforated central tube of the separation membrane element so as to pass through the convex portions of the permeate-side channel material. The cross-sectional area ratio can be calculated, for example, using a high-precision shape measurement system KS-1100 manufactured by Keyence Corporation, and can be calculated as the average value of 30 arbitrary points.

[0062] If the thickness of the permeate-side channel material is large, the pressure loss can be reduced, but the membrane area that can be packed into the container of the separation membrane element decreases. If the thickness is small, the membrane area that can be packed into the separation membrane element increases, but the pressure loss increases. In order to balance these factors, the thickness of the permeate-side channel material is preferably 0.1 mm to 0.5 mm, and more preferably 0.2 mm to 0.4 mm.

[0063] The thickness of the permeate-side channel material can be directly measured using a commercially available thickness measuring device.

[0064] The material of the permeate-side channel material may be any material that can be easily wound around the perforated central tube, and the compressive modulus of the permeate-side channel material is preferably 0.1 to 5 GPa. If the compressive modulus is within this range, the permeate-side channel material can be easily wound around the perforated central tube. Specifically, polyester, polyethylene, polypropylene, etc. are preferably used.

[0065] The compression elastic modulus of the side flow path material can be measured by performing a compression test using a precision universal testing machine and creating a stress-strain diagram.

[0066] The perforated central tube only needs to be configured such that the permeate flows through it, and the material and shape are not particularly limited. If the diameter of the perforated central tube is large, the fillable membrane area of the separation membrane element decreases, and if it is small, the flow resistance when the permeate flows through the inside of the perforated central tube increases. The diameter of the perforated central tube is appropriately designed according to the flow rate of the permeate, but is preferably 10 to 50 mm, more preferably 15 to 40 mm. As the perforated central tube, for example, a cylindrical member having a side surface provided with a plurality of holes is used.

[0067] As shown in FIG. 10, the type I separation membrane element is equipped with a brine seal (221), which is a seal member for preventing the feed liquid (206) and the concentrate (207) from mixing, and is enclosed in a pressure vessel (220) to form a separation membrane module.

[0068] <L-shaped, reverse L-shaped, U-turn type separation membrane elements> As shown in FIG. 8, the separation membrane element (223) called L-shaped has the feed liquid (206) flowing in from the outer peripheral portion of the element and the concentrate (207) being discharged from one end face. The L-shaped separation membrane element (223) has a structure in which the L-shaped separation membrane body (215) shown in FIG. 6 is wound around the perforated central tube (202).

[0069] As shown in FIG. 7, the separation membrane element (222) called reverse L-shaped is a separation membrane element with a structure in which the flow of liquid is reversed from the L-shaped one. The feed liquid (206) flows in from one end face of the element, and the concentrate (207) is discharged from the outer peripheral surface. The reverse L-shaped separation membrane element (222) has a structure in which the reverse L-shaped separation membrane body (214) shown in FIG. 5 is wound around the perforated central tube (202).

[0070] L-type and inverted-L-type separation membrane elements, which are operated at a constant recovery rate (i.e., the ratio of permeate to feed), have the following advantages. Specifically, in separation membrane elements in which the ratio L / W (W, the length of the separation membrane in the longitudinal direction of the perforated central tube, to L, the length perpendicular to the longitudinal direction of the perforated central tube) is 2.5 or greater, the flow rate of the feed liquid passing through the feed-side flow path within the separation membrane element is higher than that of an I-type separation membrane element with the same L / W ratio. Therefore, in the present invention, L-type and inverted-L-type separation membrane elements with an L / W of 2.5 or greater can suppress concentration polarization on the membrane surface even during high-recovery operation, enabling more stable operation. The flow path material used in L-type and inverted-L-type separation membrane elements may be the same as the flow path material used in I-type separation membrane elements.

[0071] To further increase the flow rate of the feed liquid, a U-turn type separation membrane element, which is a separation membrane element having two types of separation membrane bodies within a single separation membrane element, may be used. An example of a U-turn type separation membrane element is an I-type-inverted-L type separation membrane element (224) that combines an I-type separation membrane body and an inverted-L type separation membrane body, as shown in FIG. 9. The I-type-inverted-L type separation membrane element (224) is a separation membrane element having a structure in which an I-type separation membrane body (213) as shown in FIG. 4, into which the feed liquid (206) flows from one longitudinal end face of the perforated central tube (202) and is discharged from the other end face, and an inverted-L type separation membrane body (214) as shown in FIG. 5, into which the feed liquid (206) flows from one longitudinal end face of the perforated central tube (202) and is discharged from the outer peripheral surface, are simultaneously wound and enclosed. A U-turn cap (209) that makes a U-turn is attached to the end face of the inverted-L-shaped separation membrane (214) in the I-type-inverted-L separation membrane element (224) where the opening is located, as shown in FIG. 9 . This allows the feed liquid to pass through the I-type separation membrane (213) before being supplied to the inverted-L-shaped separation membrane (214). This allows the feed liquid (206) to flow at a high velocity, simulating a so-called tree-type arrangement with a single separation membrane element. By appropriately designing the ratio of the I-type separation membrane (213) to the inverted-L-shaped separation membrane (214) and the above-mentioned L / W ratio, the I-type-inverted-L separation membrane element (224) can increase the feed liquid flow velocity by approximately 5 to 20 times compared to the conventional I-type separation membrane element (201), enabling more stable operation even at high recovery rates. The flow path material used in the I-type-inverted-L separation membrane element (224) may be the same as the flow path material used in the I-type separation membrane element (201).

[0072] The L-type, reverse L-type, and U-turn type separation membrane elements are sometimes collectively called high flow rate separation membrane elements.

[0073] Next, FIG. 11 shows a separation membrane module (216) in which an I-type separation membrane element (201) and an inverted L-type separation membrane element (222) are arranged in series in a pressure vessel (220), FIG. 12 shows a separation membrane module (216) in which an I-type separation membrane element (201) and an L-type separation membrane element (223) are arranged in series in a pressure vessel (220), and FIG. 13 shows a separation membrane module (216) in which an I-type separation membrane element (201) and an I-type-inverted L-type separation membrane element (224) are arranged in series in a pressure vessel (220). Since L-type, inverted L-type, and I-type-inverted L-type separation membrane elements generally have a short length in the longitudinal direction of the perforated central tube, in the embodiments shown in Figures 11 to 13, the membrane area of ​​the separation membrane module is secured by connecting the perforated central tubes of the I-type separation membrane element, which has a short length in the longitudinal direction of the perforated central tube, and the L-type, inverted L-type, and I-type-inverted L-type separation membrane elements in series.

[0074] (4) Configuration of the solution processing method of the present invention First, the recovery rate of electrolytes such as salts, the urea removal rate, and the potassium ion removal rate for the entire process are calculated using the following formulas. Electrolyte recovery rate=[(electrolyte concentration of purified solution (102))×(flow rate of purified solution (102))] / [(electrolyte concentration of raw solution (101))×(flow rate of raw solution (101)]×100[%] Urea removal rate = [(Urea concentration of raw solution (101)) x (Flow rate of raw solution (101)) - (Urea concentration of purified solution (102)) x (Flow rate of purified solution (102))] / [(Urea concentration of raw solution (101)) x (Flow rate of raw solution (101)] x 100 [%]] Potassium ion removal rate = [(potassium ion concentration of raw solution (101)) x (flow rate of raw solution (101)) - (potassium ion concentration of purified solution (102)) x (flow rate of purified solution (102))] / [(potassium ion concentration of raw solution (101)) x (flow rate of raw solution (101)] x 100 [%]]

[0075] The numbers in parentheses in the above formulas refer to the symbols in FIGS.

[0076] As shown in the above formulas, the electrolyte recovery rate, urea removal rate, and potassium ion removal rate for the entire process are defined not by the removal rate defined by concentration but by the amount of substance including the flow rate ratio. This is because, for example, when this membrane process is used to regenerate dialysis wastewater, the water volume and electrolyte concentration are adjusted by adding an adjustment solution in the latter stage to produce regenerated dialysis fluid, and the concentration of the final regenerated dialysis fluid differs from that of the purified fluid.

[0077] In the solution treatment method of the present invention, a raw solution is separated into a purified solution containing water and electrolytes and a waste solution containing small non-electrolyte molecules using separation membranes 1 and 2 having the above-mentioned properties. In this process, the permeate of separation membrane 1 is supplied to separation membrane 2 for separation treatment, and further, (i) a portion of the permeate of separation membrane 2 is mixed with the raw solution and then supplied to separation membrane 1, and the remaining entire amount or a portion of the permeate of separation membrane 2 is mixed with the concentrate of separation membrane 1 to obtain a purified solution, or (ii) the entire amount of the permeate of separation membrane 2 is mixed with the raw solution and then supplied to separation membrane 1, and the concentrate of separation membrane 1 is obtained as a purified solution.

[0078] That is, a solution obtained by mixing the permeate of separation membrane 2 with the raw solution is pressurized and treated with separation membrane 1, which has a sodium chloride rejection rate of 90% or more and a urea rejection rate at least 40 percentage points lower than that of separation membrane 2, to obtain the permeate of separation membrane 1 and a concentrate of separation membrane 1. At this time, the recovery rate, which is the ratio of the amount of solution supplied to separation membrane 1 to the amount of solution that permeates separation membrane 1, is preferably 75% or more. By achieving such a recovery rate, the selective separation performance of separation membrane 1 can be better exhibited. Because separation membrane 1 has the above-mentioned rejection rate, the permeate of separation membrane 1 contains a large amount of small non-electrolyte molecules such as urea and little electrolytes. On the other hand, the concentrate of separation membrane 1 contains both electrolytes and small non-electrolyte molecules, but because separation membrane 1 has a higher electrolyte rejection rate than urea rejection rate, the concentrate contains more electrolytes than small non-electrolyte molecules.

[0079] Furthermore, the permeate from separation membrane 1 is treated with separation membrane 2, which has a urea rejection rate 40% or more higher than that of separation membrane 1, to obtain a concentrate from separation membrane 2 and a permeate from separation membrane 2. At this time, the recovery rate, which is the ratio of the amount of solution supplied to separation membrane 2 to the amount of solution that has permeated separation membrane 1, is set according to the water recovery rate of the entire process, but because the permeate from separation membrane 2 is used to circulate back to the feed liquid for separation membrane 1, the recovery rate of separation membrane 2 is preferably 50% or higher. Because separation membrane 2 exhibits the above-mentioned rejection rate, the permeate from separation membrane 2 contains only trace amounts of electrolytes and small non-electrolyte molecules such as urea, while the concentrate from separation membrane 2 contains large amounts of small non-electrolyte molecules such as urea.

[0080] Finally, the concentrated liquid from separation membrane 1 is taken out while optionally being mixed with the permeate from separation membrane 2, thereby obtaining a purified liquid in which only non-electrolyte low molecular weight compounds such as urea have been selectively separated.

[0081] 1 and 2 show an embodiment of the solution treatment method of the present invention. Herein, a module having the above-described separation membrane 1 is referred to as separation membrane module (1), and a module having the above-described separation membrane 2 is referred to as separation membrane module (2). For convenience, the following description will be given of a case where dialysis wastewater after dialysis treatment is treated as a raw solution, but "urea" can be read as "non-electrolyte small molecule."

[0082] 1 , as described above, urea that has permeated the separation membrane module (1) is treated in the separation membrane module (2) and extracted as a concentrate (108) from the separation membrane module (2) for removal. Therefore, the amount of permeate (106) from the separation membrane module (1) must be increased to increase the overall urea removal rate. That is, to increase the urea removal rate in the process, it is necessary to increase the recovery rate in the separation membrane module (1). However, because the total component concentration in the dialysis wastewater, i.e., the raw solution (101), is generally as high as 10,000 mg / L or more, the pressure applied to the separation membrane module (1) must also be increased to increase the recovery rate. For example, when the NaCl concentration in the feed solution (104) to the separation membrane module (1) is 10,000 mg / L and the separation membrane module (1) is operated at a recovery rate of 90%, the NaCl concentration in the concentrate (105) from the separation membrane module (1) will be approximately 10 times higher, resulting in an osmotic pressure difference of approximately 8.8 MPa. On the other hand, in the solution treatment method shown in FIG. 1, a portion of the permeate (109) from the separation membrane module (2) is mixed with the raw solution (101) supplied to the separation membrane module (1) and circulated. In solution treatment methods that do not circulate the permeate (109) from the separation membrane module (2), there is a problem in that the NaCl concentration in the concentrate (105) from the separation membrane module (1) becomes high. However, by using the solution treatment method of the present invention as shown in Figure 1, the NaCl concentration in the feed solution (104) to the separation membrane module (1) can be reduced, so that the NaCl concentration in the concentrate (105) from the separation membrane module (1) can be kept low even if the separation membrane module (1) has a high recovery rate. For example, when treating a raw solution (101) with an NaCl concentration of 10,000 mg / L, if the NaCl concentration in the feed solution (104) to the separation membrane module (1) can be reduced to 2,000 mg / L by circulating the permeate (109) from the separation membrane module (2), even if the recovery rate of the separation membrane module (1) is 90%, the osmotic pressure difference between the concentrate (105) from the separation membrane module (1) and the permeate (106) will be approximately 1.7 MPa. As described above, according to the present invention, treatment can be performed at a lower pressure than in a solution treatment method that does not involve circulation of the permeate (109) of the separation membrane module (2).If treatment can be performed at low pressure, there is no need to use a high-pressure pump, a high-pressure-compatible flow path, or a pressure vessel, which is expected to reduce equipment costs and noise. Taking into consideration the operating pressure in dialysis wastewater treatment in particular, the ratio of the circulation (110) volume to the volume of the permeate (109) from the separation membrane module (2) is preferably 0.6 or more. Furthermore, to adjust the concentration of the purified liquid (102), a portion of the permeate (109) from the separation membrane module (2) may be withdrawn, or pure water or a solution may be added to the purified liquid (102).

[0083] The solution treatment method shown in FIG. 2 is basically the same as the embodiment shown in FIG. 1, but all of the permeate (109) from the separation membrane module (2) is mixed with the raw solution (101) and circulated. In this way, all of the permeate (109) from the separation membrane module (2) can be supplied to the separation membrane module (1) and circulated. This has the advantage of significantly reducing the osmotic pressure difference in the separation membrane module (1). In addition, the valve operation at the branch point of the permeate (109), which was necessary in the embodiment shown in FIG. 1, is no longer necessary, and both the device configuration and process can be simplified.

[0084] (5) Dialysis System with Dialysis Waste Treatment Device To treat dialysis waste fluid according to the present invention, a solution treatment device with lines configured as described in (4) above and valves and pumps appropriately positioned can be incorporated into the dialysis system as a dialysis waste fluid treatment device. That is, as shown in FIG. 14, a dialysis waste fluid treatment device (301) can be combined with a dialysis device (302). In this way, dialysis waste fluid (307) can be treated online while being used for dialysis treatment. Since the dialysis waste fluid treatment device (301) discharges trace amounts of water and electrolytes as the effluent (103), an adjustment solution (305) is added to the purified solution (102) from the dialysis waste fluid treatment device (301) to produce regenerated dialysis fluid (304), as shown in FIG. 14.

[0085] In addition, the dialysis wastewater treatment device of the present application can be combined with a tank to treat the dialysis wastewater offline, adjust the electrolyte concentration, and then provide it for dialysis treatment. [Example]

[0086] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0087] (Measurement of separation membrane performance) For the polyamide membranes PA Membrane A, PA Membrane B, PA Membrane C, and PA Membrane F, and the cellulose acetate membrane CA Membrane, the NaCl rejection rate and urea rejection rate were measured at a temperature of 36°C and a pressure of 1.2 MPa using Solution 1, which was a mixture of 10,000 mg / L sodium chloride (NaCl) and 250 mg / L urea at pH 7.

[0088] For the polyamide membranes PA Membrane D, PA Membrane E, and PA Membrane G, the NaCl rejection rate and urea rejection rate were measured at a temperature of 36°C and a pressure of 1.8 MPa using Solution 2, which was a mixture of 1000 mg / L sodium chloride (NaCl) and 700 mg / L urea at pH 7.

[0089] The removal rate here is defined as the rate of decrease in the concentration of a component in the solution that has permeated each membrane relative to the concentration of that component in the solution that is fed to each membrane.

[0090] (Positron annihilation lifetime measurement using a positron beam) The positron annihilation lifetime measurement of the separation functional layer in each example was carried out using a positron beam method as follows. That is, the separation functional layer was dried at room temperature under reduced pressure and cut into a 1.5 cm x 1.5 cm square to prepare a test sample. A thin film compatible positron annihilation lifetime measurement device equipped with a positron beam generator (this device is, for example, the one described in Radiation Physics and Chemistry, The test samples were measured using a barium difluoride scintillation counter with a photomultiplier tube at a beam intensity of 1 keV, room temperature, and vacuum, with a total count of 5 million, and the POSITIVE T The analysis was performed using RONFIT. The average pore diameter was calculated from the average positron annihilation lifetime τ of the fourth component obtained by the analysis.

[0091] (Preparation of microporous support membrane (porous support layer)) Polyester nonwoven fabric (air permeability 2.0cc / cm 2 A 16.0 wt% DMF (dimethylformamide) solution of polysulfone (PSf) was cast onto the substrate at room temperature (25°C) to a thickness of 200 μm, and the substrate was immediately immersed in pure water and left for 5 minutes to prepare a support membrane.

[0092] (Preparation of PA membrane A) A 1.5 wt% aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, then slowly lifted vertically. Nitrogen was sprayed from an air nozzle to remove excess aqueous solution from the support membrane surface. A 25°C decane solution containing 0.065 wt% trimesoyl chloride (TMC) was then applied to the surface in a booth maintained at 25°C until the surface was completely wet. The membrane was then left to stand for 60 seconds to obtain a reverse osmosis membrane. The performance of the resulting reverse osmosis membrane was 97% NaCl rejection and 18% urea rejection. The pore diameter measured using positron annihilation lifetime spectroscopy was 7.2 Å.

[0093] (Preparation of PA film B) A 1.8 wt% aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, then slowly lifted vertically. Nitrogen was sprayed from an air nozzle to remove excess aqueous solution from the support membrane surface. A 25°C decane solution containing 0.06 wt% trimesoyl chloride (TMC) was then applied to the surface in a booth maintained at 25°C until the surface was completely wet. The membrane was then left to stand for 60 seconds to obtain a reverse osmosis membrane. The performance of the resulting reverse osmosis membrane was 98% NaCl rejection and 25% urea rejection. The pore diameter measured using positron annihilation lifetime spectroscopy was 7.0 Å.

[0094] (Preparation of PA membrane C) A 0.2 wt% aqueous solution of piperazine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, slowly lifted vertically, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the support membrane surface. After that, a 45°C decane solution containing 0.17 wt% trimesoyl chloride (TMC) was applied to the surface in a booth maintained at 45°C until the surface was completely wet, and the membrane was left to stand for 1 minute. Next, to remove excess solution from the membrane, the membrane was held vertically for 1 minute to drain, and then dried by blowing air at 25°C using a fan. After drying, the membrane was immediately washed with water and stored at room temperature to obtain a nanofiltration membrane. The performance of the resulting nanofiltration membrane was a NaCl rejection rate of 93.7% and a urea rejection rate of 16%. The pore diameter measured using positron annihilation lifetime spectroscopy was 9.0 Å.

[0095] (Preparation of PA film D) A 6.0% by weight aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, then slowly lifted vertically. Nitrogen was sprayed from an air nozzle to remove excess aqueous solution from the support membrane surface. After that, a 45°C decane solution containing 0.17 wt% trimesoyl chloride (TMC) was applied to the surface in a booth maintained at 45°C until the surface was completely wet, and the membrane was left to stand for 10 seconds. The membrane was placed in a 140°C oven and heated for 30 seconds while supplying 100°C steam from a nozzle on the backside of the membrane to obtain a reverse osmosis membrane. The performance of the resulting reverse osmosis membrane was 99.6% NaCl rejection and 90% urea rejection. The pore diameter measured using positron annihilation lifetime spectroscopy was 5.1 Å.

[0096] (Preparation of PA film E) A 5.5 wt% aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, then slowly lifted vertically. Nitrogen was sprayed from an air nozzle to remove excess aqueous solution from the support membrane surface. After that, a 45°C decane solution containing 0.15 wt% trimesoyl chloride (TMC) was applied to the surface in a booth maintained at 45°C until the surface was completely wet, and the membrane was left standing for 10 seconds. The membrane was placed in a 140°C oven and heated for 30 seconds while supplying 100°C steam from a nozzle on the backside of the membrane to obtain a reverse osmosis membrane. The performance of the resulting reverse osmosis membrane was 99.1% NaCl rejection and 85% urea rejection. The pore diameter measured using positron annihilation lifetime spectroscopy was 6.0 Å.

[0097] (Preparation of PA membrane F) A 2.0 wt% aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above procedure was immersed in the above aqueous solution for 2 minutes, then slowly lifted vertically. Nitrogen was sprayed from an air nozzle to remove excess aqueous solution from the support membrane surface. After that, a 25°C decane solution containing 0.12 wt% trimesoyl chloride (TMC) was applied to the surface in a booth maintained at 25°C until the surface was completely wet, and the membrane was left standing for 40 seconds. The membrane was placed in a 140°C oven and heated for 30 seconds while supplying 100°C steam from a nozzle on the backside of the membrane to obtain a reverse osmosis membrane. The performance of the resulting reverse osmosis membrane was 99.0% NaCl rejection and 58% urea rejection. The pore diameter measured using positron annihilation lifetime spectroscopy was 6.8 Å.

[0098] (Preparation of PA membrane G) An aqueous solution containing 1.8 wt% m-phenylenediamine and 4.5 wt% ε-caprolactam was prepared. This solution was applied to the support membrane obtained by the above procedure. After removing excess solution from the support membrane surface with nitrogen from an air nozzle, a 25°C n-decane solution containing 0.06 wt% trimesoyl chloride was applied to completely wet the surface. The excess solution was then removed from the membrane with air, washed with hot water at 80°C, and drained with air to obtain a reverse osmosis membrane. The resulting reverse osmosis membrane demonstrated a NaCl rejection rate of 98.5% and a urea rejection rate of 75%. The pore size measured using positron annihilation lifetime spectroscopy was 7.2 Å.

[0099] (Preparation of cellulose acetate (CA) membrane) A casting solution consisting of 25% cellulose acetate, 45% acetone, and 30% formamide by weight was cast onto the support membrane obtained by the above procedure. The casting solution was allowed to evaporate for 2 minutes, and then the membrane was immersed in ice water. The membrane was then immersed in warm water at 90°C to obtain a nanofiltration membrane. The resulting nanofiltration membrane exhibited a NaCl rejection rate of 93.0% and a urea rejection rate of 15%. The pore size measured using positron annihilation lifetime spectroscopy was 10 Å.

[0100] (Preparation of Type I Separation Membrane Element) Six separation membranes were cut and folded with the feed side facing inward so that the inner peripheral edge formed a crease. A net (thickness: 0.8 mm, pitch of the fibers constituting the net (hereinafter referred to as pitch): 5 mm × 5 mm, fiber diameter: 380 μm, projected area ratio of the contact area between the net and the separation membrane surface to the separation membrane (hereinafter referred to as projected area ratio): 0.15) was used as the feed-side channel material, and the net-constituting yarns were arranged so that the inclination angle was 45° with respect to the winding direction. A uniformly thick tricot (thickness: 280 μm) was prepared as the permeation-side channel material and cut into six pieces. Six separation membrane bodies measuring 850 mm in length and 930 mm, 465 mm, or 230 mm in width were produced from these. The permeate-side channel material was placed on the permeate side of the separation membrane, and an adhesive was applied to the permeate-side channel material so that the inner peripheral end was open. The permeate-side channel material was then spirally wound around a perforated central tube made of ABS (acrylonitrile-butadiene-styrene) (length: 1020 mm, 510 mm, or 280 mm, diameter: 30 mm, number of holes: 40 or 20 x 1 linear row). After winding, a film was wrapped around the outer circumference and secured with tape. After that, the edges were cut, end plates were attached, and filament winding was performed to obtain an effective membrane area of ​​8 m. 2 , 4m 2 , or 2m 2 A type I separation membrane element was fabricated.

[0101] (Fabrication of L-type and inverted L-type separation membrane elements) Six separation membranes were cut and folded with the feed side facing inward so that the inner peripheral edge formed the crease. A net (thickness: 0.8 mm, pitch: 5 mm x 5 mm, fiber diameter: 380 μm, projected area ratio: 0.15) was used as the feed-side channel material, and the netting yarns were arranged so that the inclination angle of the netting yarns was 45° relative to the winding direction. Six uniformly thick tricot (thickness: 280 μm) was prepared as the permeation-side channel material and cut into six pieces. Six separation membranes measuring 850 mm in length and 230 mm in width were fabricated from these. The ratio L / W of the length W of the separation membrane in the longitudinal direction of the perforated central tube to the length L perpendicular to the longitudinal direction of the perforated central tube was 3.7. The permeate-side flow path material was placed on the permeate-side surface of the separation membrane, and an adhesive was applied to the permeate-side flow path material so that the inner peripheral edge was open. The material was then spirally wound around a perforated central tube (length: 280 mm, diameter: 30 mm, 12 holes in one linear row) made of ABS (acrylonitrile-butadiene-styrene). After winding, a perforated film was wrapped around the outer periphery and secured with tape, and the edges were then cut. Then, an adhesive was applied to one longitudinal end face of the perforated central tube to seal it. Furthermore, an adhesive was applied to the end face opposite the sealed side so that 20% of the inner peripheral portion was open, and the effective membrane area was 2 m 2 The L-type and inverted L-type separation membrane elements were fabricated. Since the ratio L / W of these L-type and inverted L-type separation membrane elements was 3.7, the length L was 8 m and the effective membrane area was 8 m. 2 This is one-fourth of the I-type separation membrane element, and the effective membrane area is also 8m 2 This separation membrane element is an L-type separation membrane element when the feed liquid is supplied from the outer periphery, and an inverted L-type separation membrane element when the feed liquid is supplied from one end face of the separation membrane element.

[0102] (Fabrication of U-turn type separation membrane element) Six separation membranes were cut and folded with the feed side facing inward so that the inner peripheral edge formed the crease. A net (thickness: 0.8 mm, pitch: 5 mm × 5 mm, fiber diameter: 380 μm, projected area ratio: 0.15) was used as the feed-side channel material. The netting yarns were arranged so that the inclination angle of the netting yarns was 45° relative to the winding direction. Of the separation membranes sandwiching these feed-side channel materials, the outer peripheral edges of the feed-side channel materials of three separation membranes were bonded to form an I-shaped separation membrane body as shown in Figure 4. The other three membranes had both longitudinal end faces of the perforated central tube bonded to form an inverted L-shaped separation membrane body as shown in Figure 5. The opening ratio of the openings on one end face relative to the length of the separation membrane body was 20%. A uniformly thick tricot (thickness: 280 μm) was prepared as the permeation-side channel material and cut into six pieces. Six separation membrane bodies measuring 850 mm in length and 230 mm in width were fabricated from these. The ratio L / W of the length W of the perforated central tube in the longitudinal direction of the separation membrane to the length L in the direction perpendicular to the longitudinal direction of the perforated central tube was 3.7. The permeate-side flow path material was placed on the permeate-side surface of the separation membrane, and an adhesive was applied to the permeate-side flow path so that the inner peripheral end was open. The perforated central tube (length: 280 mm, diameter: 30 mm, 12 holes in one linear row) made of ABS (acrylonitrile-butadiene-styrene) was spirally wound around it. After wrapping, a perforated film was wrapped around the outer periphery and secured with tape, followed by edge cutting. An adhesive was applied near the outer periphery of both longitudinal end faces of the perforated central tube. A U-turn cap, which turns the feed liquid flow in a U-turn, was then attached to the end face of the inverted L-shaped separation membrane body on the side with the opening, and the effective membrane area was 2 m 2 Since the above-mentioned L / W ratio of this U-turn type separation membrane element is 3.7, the length L is 8 m and the effective membrane area is 8 m. 2 This is one-fourth of the I-type separation membrane element, and the effective membrane area is also 8m 2 This is one-fourth of the I-type separation membrane element.

[0103] (Undiluted) Artificial dialysis waste liquid was used as the raw solution in Examples 1 to 10 and Comparative Examples 1 to 3. The components in the raw solution were electrolytes: approximately 10,000 mg / L (including potassium ions: 100 mg / L), and urea (molecular weight: 60.06): 630 mg / L.

[0104] In Example 11, the raw solution was brine with a high boron concentration. The raw solution contained 1500 mg / L of electrolytes and 1.5 mg / L of boron (in the form of boric acid) (molecular weight: 61.83).

[0105] (Measurement of process performance) The electrolyte recovery rate, urea removal rate, and boron removal rate for the entire process were calculated using the following formulas. Electrolyte recovery rate=[(electrolyte concentration of purified solution (102))×(flow rate of purified solution (102))] / [(electrolyte concentration of raw solution (101))×(flow rate of raw solution (101)]×100[%] Urea removal rate = [(Urea concentration of raw solution (101)) x (Flow rate of raw solution (101)) - (Urea concentration of purified solution (102)) x (Flow rate of purified solution (102))] / [(Urea concentration of raw solution (101)) x (Flow rate of raw solution (101)] x 100 [%]] Potassium ion removal rate = [(potassium ion concentration of raw solution (101)) x (flow rate of raw solution (101)) - (potassium ion concentration of purified solution (102)) x (flow rate of purified solution (102))] / [(potassium ion concentration of raw solution (101)) x (flow rate of raw solution (101)] x 100 [%]] Boron removal rate = [(boron concentration in raw solution (101)) - (boron concentration in refined solution (102)) / [(boron concentration in raw solution (101)] × 100 [%]]

[0106] The numbers in parentheses in the above formulas refer to the symbols in FIGS.

[0107] Furthermore, the maximum operating pressure and maximum pump flow rate in each module were measured using a flow meter and a pressure meter.

[0108] Example 1 The raw solution was used as dialysis waste liquid. Separation membrane 1 was PA membrane A obtained by the method described above, and separation membrane 2 was PA membrane D obtained by the method described above. For each, one I-type separation membrane element with a width of 930 mm was produced by the method described above.

[0109] End plates and brine seals were attached to the prepared separation membrane elements and placed in a pressure vessel to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared and the piping was connected as shown in Figure 2. The valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was about 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1.

[0110] [Table 1]

[0111] Example 2 The raw solution was used as dialysis wastewater. Separation membrane modules (1) and (2) were prepared in the same manner as in Example 1, except that the width of the I-type separation membrane element was 465 mm. Using these, pumps and valves were prepared and piping was connected as shown in Figure 1. The valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was approximately 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1. The circulation ratio of the purified liquid was 0.80. By recovering a portion of the permeate from separation membrane module (2) as the purified liquid, the amount of water sent to separation membrane modules (1) and (2) was reduced compared to Example 1, and a system could be established with half the membrane area of ​​Example 1.

[0112] Example 3 The raw solution was used as dialysis waste liquid. A separation membrane module was prepared in the same manner as in Example 2, except that the separation membrane used in the separation membrane module (1) was a CA membrane. End plates and brine seals were attached to the prepared separation membrane element, and the element was placed in a pressure vessel to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared and piping was connected as shown in Figure 1. The valves were adjusted so that the overall solution recovery rate was 93% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1. The circulation ratio of the permeate in the separation membrane module (2) was 0.85.

[0113] Example 4 The raw solution was used as dialysis waste liquid. A separation membrane module was prepared in the same manner as in Example 1, except that the separation membrane used in the separation membrane module (2) was PA membrane E. End plates and brine seals were attached to the prepared separation membrane elements, and the elements were placed in pressure vessels to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared as shown in Figure 1, and piping connections were made. The valves were adjusted so that the overall solution recovery rate was 95% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1. The circulation ratio of the permeate in the separation membrane module (2) was 0.85.

[0114] Example 5 The raw solution was used as dialysis waste liquid. A separation membrane module was prepared in the same manner as in Example 1, except that the separation membrane used in the separation membrane module (1) was PA membrane B. End plates and brine seals were attached to the prepared separation membrane elements, and the elements were placed in pressure vessels to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared and piping was connected as shown in Figure 1. The valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1. The circulation ratio of the permeate in the separation membrane module (2) was 0.85.

[0115] Example 6 The raw solution was used as dialysis wastewater. A separation membrane module was prepared in the same manner as in Example 2, except that the separation membrane used in the separation membrane module (1) was PA membrane C. End plates and brine seals were attached to the prepared separation membrane elements, and the elements were placed in pressure vessels to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared and piping was connected as shown in Figure 1. The valves were adjusted so that the overall solution recovery rate was 93% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 1, with the results shown in Table 1. The circulation ratio of the permeate in the separation membrane module (2) was 0.85.

[0116] Example 7 The raw solution was used as dialysis wastewater. A separation membrane module similar to that in Example 2 was prepared. End plates and brine seals were attached to the prepared separation membrane elements, and the elements were placed in a pressure vessel to obtain one separation membrane module (1) and one separation membrane module (2). Pumps and valves were prepared as shown in Figure 1, and piping connections were made. The valves were adjusted so that the overall solution recovery rate was 75% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 2, with the results shown in Table 2. The circulation ratio of the permeate in separation membrane module (2) was 0.60.

[0117] [Table 2]

[0118] Example 8 The raw liquid was used as dialysis wastewater. Separation membranes similar to those in Example 1 were used, and one 230 mm-wide I-type separation membrane element and one inverted L-type element were prepared as separation membrane modules (1) and (2). End plates and brine seals were attached to each separation membrane element, and the elements were enclosed in a pressure vessel with the inverted L-type element positioned at the rear, as shown in Figure 11. Pumps and valves were prepared and piping was connected as shown in Figure 1. Valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 2, with the results shown in Table 2. The circulation ratio of the permeate in separation membrane module (2) was 0.80.

[0119] Example 9 The raw liquid was used as dialysis wastewater. Separation membranes similar to those in Example 1 were used, and one I-type separation membrane element and one L-type element, each 230 mm wide, were prepared as separation membrane modules (1) and (2). End plates and brine seals were attached to each separation membrane element, and they were enclosed in a pressure vessel with the L-type element in the latter stage as shown in Figure 12. Pumps and valves were prepared as shown in Figure 1, and piping connections were made. The valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 2, with the results shown in Table 2. The circulation ratio of the permeate in separation membrane module (2) was 0.80.

[0120] Example 10 The raw liquid was used as dialysis wastewater. Separation membranes similar to those in Example 1 were used, and one 230 mm-wide I-type separation membrane element and one U-turn element were prepared as separation membrane modules (1) and (2). End plates and brine seals were attached to each separation membrane element, and the elements were enclosed in a pressure vessel with the U-turn element positioned at the rear, as shown in Figure 13. Pumps and valves were prepared as shown in Figure 1, and piping connections were made. Valves were adjusted so that the overall solution recovery rate was 97% and the urea removal rate was around 70%, and evaluation was performed under the conditions shown in Table 2, with the results shown in Table 2. The circulation ratio of the permeate in separation membrane module (2) was 0.80.

[0121] Example 11 The raw solution was brine with a high boron concentration. One each of separation membrane modules (1) and (2) was prepared in the same manner as in Example 2. Using these, a pump and valve were prepared and pipe connections were made as shown in Figure 1. The valves were adjusted so that the overall solution recovery rate was 95% and the recovery rate of separation membrane 1 was about 95%, and evaluation was performed under the conditions shown in Table 2, with the results shown in Table 2. The circulation ratio of the purified liquid was 0.80. It was possible to selectively separate only boron from brine with a high boron concentration while retaining the electrolyte components.

[0122] (Comparative Example 1) A separation membrane module similar to that of Example 2 was prepared. Pumps and valves were prepared and pipe connections were made as shown in Figure 1 . The permeate circulation valve was adjusted so that all of the permeate from separation membrane module (2) was mixed with the concentrated solution from separation membrane module (1) (i.e., the permeate from separation membrane module (2) was not circulated back to the feed solution in separation membrane module (1)) to produce a purified solution. Since the overall solution recovery rate was set to 97% and the maximum operating pressure of the device was 5.5 MPa, the valve was adjusted so that the maximum operating pressure was 5.5 MPa. Evaluation was performed under the conditions shown in Table 3, and the results are shown in Table 3. To increase the urea removal rate of the entire system, it is necessary to increase the recovery rate of separation membrane module (1) in order to increase the amount of urea permeated through separation membrane module (1). However, without circulation in the dialysis wastewater treatment method of Figure 1 , the osmotic pressure difference in separation membrane module (1) increases, preventing a high recovery rate and resulting in an insufficient urea removal rate.

[0123] [Table 3]

[0124] (Comparative Example 2) A separation membrane module was prepared in the same manner as in Example 1, except that the separation membrane used in the separation membrane module (1) was PA membrane F. A pump and valve were prepared and piping was connected as shown in Figure 1. Since the overall solution recovery rate was 90% and the maximum operating pressure of the device was 5.5 MPa, the valve was adjusted so that the maximum operating pressure was 5.5 MPa, and evaluation was performed under the conditions shown in Table 3, with the results shown in Table 3. The urea removal rate in the separation membrane module (1) was high, so the desired urea removal rate could not be obtained.

[0125] (Comparative Example 3) A separation membrane module was prepared in the same manner as in Example 1, except that the separation membrane used in the separation membrane module (2) was PA membrane G. A pump and valve were prepared and the piping was connected as shown in Figure 1. Since the water recovery rate of the entire system was 97% and the maximum operating pressure of the device was 5.5 MPa, the valve was adjusted so that the maximum operating pressure was 5.5 MPa, and evaluation was performed under the conditions shown in Table 3, with the results shown in Table 3. The urea removal rate in the separation membrane module (2) was low, so the desired urea removal rate could not be obtained. [Industrial Applicability]

[0126] The present invention is suitably used for the regeneration treatment of dialysis wastewater and the removal of boron from brine. [Explanation of symbols]

[0127] 1 Separation membrane module 2 Separation membrane module 3. Separation membrane module (1) supply pump 4. Concentrate valve of separation membrane module (1) 5. Separation membrane module (2) supply pump 6. Concentrate valve of separation membrane module (2) 7. Permeate flow rate distribution valve of separation membrane module (2) 8 Permeate check valve of separation membrane module (2) 101 Raw solution (dialysis waste) 102 Purified liquid 103 Effluent 104 Separation membrane module (1) feed liquid 105 Concentrated solution of separation membrane module (1) 106 Permeate from separation membrane module (1) 107 Separation membrane module (2) feed liquid 108 Concentrated solution of separation membrane module (2) 109 Permeate from separation membrane module (2) 110 Permeate circulation of separation membrane module (2) 201 I-type separation membrane element 202 Perforated central tube 203 Separation membrane 204 Supply side channel material 205 Permeate side channel material 206 Supply liquid 207 Concentrate 208 Permeate 209 U-Turn Cap 210 Sealing part 211 Feed side of separation membrane 213 I-type separation membrane body 214 Inverted L-shaped separation membrane body 215 L-type separation membrane body 216 Separation Membrane Module 217 Permeate outlet 218 Supply liquid inlet 219 Concentrate outlet 220 Pressure Vessels 221 Brine Seal 222 Inverted L-type separation membrane element 223 L-type separation membrane element 224 U-turn type (I-type - reverse L-type) separation membrane element 301 Dialysis wastewater treatment equipment 302 Dialysis equipment 303 Dialysis membrane 304 Regenerated dialysate 305 Adjustment Solution 306 Blood 307 Dialysis waste

Claims

1. A solution treatment method in which a raw solution is treated with separation membranes 1 and 2 that separate a feed solution into a permeate and a concentrate, and the raw solution is separated into a purified solution containing water and electrolytes and a waste liquid containing non-electrolyte small molecules, the stock solution is a solution containing at least 1000 mg / L or more of an electrolyte and a non-electrolyte low-molecular-weight substance having a molecular weight of 70 or less, The permeate of the separation membrane 1 is supplied to the separation membrane 2 for separation treatment, The separation membrane 1 exhibits the following characteristics when a solution 1 containing 10,000 mg / L of sodium chloride (NaCl) and 250 mg / L of urea at a pH of 7 is supplied at 36° C. and a pressure of 1.2 MPa: The removal rate is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, and the NaCl removal rate is 90% or more. the separation membrane 2 has a urea rejection rate of 85% or more, which is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, when a solution 2 having a pH of 7 and containing 1000 mg / L of sodium chloride (NaCl) and 700 mg / L of urea is supplied at 36°C and a pressure of 1.8 MPa; the difference between the urea rejection rate of the separation membrane 2 under the evaluation conditions of the separation membrane 2 and the urea rejection rate of the separation membrane 1 under the evaluation conditions of the separation membrane 1 is 40% points or more; Furthermore, the solution processing method is characterized by satisfying either of the following requirements (i) and (ii): (i) A portion of the permeate of the separation membrane 2 is mixed with the raw liquid and then supplied to the separation membrane 1, and all or a portion of the remaining permeate of the separation membrane 2 is mixed with the concentrated liquid of the separation membrane 1 to obtain the purified liquid. (ii) The entire amount of the permeate through the separation membrane 2 is mixed with the raw liquid, and then the mixture is supplied to the separation membrane 1, and a concentrate from the separation membrane 1 is obtained as the purified liquid.

2. 2. The solution processing method according to claim 1, wherein the separation membrane has an NaCl rejection rate of 99% or less under evaluation conditions for the separation membrane.

3. 3. The solution treatment method according to claim 1, wherein the raw solution is a dialysis wastewater after artificial dialysis treatment, and the non-electrolyte low-molecular-weight substance is urea.

4. 4. The solution treatment method according to claim 1, wherein, in the requirement (i), a ratio of the amount of the permeated liquid through the separation membrane 2 mixed with the raw solution to the total amount of the permeated liquid through the separation membrane 2 is 0.6 or more.

5. The method for treating dialysis wastewater according to any one of claims 1 to 4, wherein the ratio of the amount of the purified solution to the amount of the raw solution is 75% or more.

6. A solution treatment device comprising separation membranes 1 and 2 for separating a feed solution into a permeate and a concentrate, and for separating a raw solution into a purified solution containing water and an electrolyte and a waste solution containing a non-electrolyte low-molecular-weight substance, the stock solution is a solution containing at least 1000 mg / L or more of an electrolyte and a non-electrolyte low-molecular-weight substance having a molecular weight of 70 or less, The permeate line of the separation membrane 1 is connected to the feed line of the separation membrane 2, The separation membrane 1 exhibits the following characteristics when a solution 1 containing 10,000 mg / L of sodium chloride (NaCl) and 250 mg / L of urea at a pH of 7 is supplied at 36° C. and a pressure of 1.2 MPa: The removal rate is defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, and the NaCl removal rate is 90% or more. the separation membrane 2 has a urea rejection rate of 85% or more, the rejection rate being defined as the rate of decrease in the concentration of a component in the permeated solution relative to the concentration of the component in the feed solution, when a solution 2 having a pH of 7 and containing 1000 mg / L of sodium chloride (NaCl) and 700 mg / L of urea is supplied at 36°C and a pressure of 1.8 MPa; the difference between the urea rejection rate of the separation membrane 2 under the evaluation conditions of the separation membrane 2 and the urea rejection rate of the separation membrane 1 under the evaluation conditions of the separation membrane 1 is 40% points or more; The solution treatment device further satisfies either of the following requirements (i) and (ii): (i) The permeate line of the separation membrane 2 is branched into at least two lines, at least one of which is connected to the line for the raw liquid, a line for a mixture of the raw liquid and the permeate of the separation membrane 2 is connected to the supply line for the separation membrane 1, and at least one of the remaining lines is connected to the concentrate line for the separation membrane 1 to form a purified liquid line. (ii) The permeate line of the separation membrane 2 is connected to the raw liquid line, a line for a mixture of the raw liquid and the permeate of the separation membrane 2 is connected to the supply line of the separation membrane 1, and the concentrate line of the separation membrane 1 is used as a purified liquid line.

7. The solution treatment apparatus according to claim 6 , wherein the separation membrane has an NaCl removal rate of 99% or less under evaluation conditions for the separation membrane.

8. 8. The solution treatment device according to claim 6, wherein the raw solution is a dialysis waste solution after artificial dialysis treatment, and the non-electrolyte low-molecular-weight substance is urea.

9. 9. The solution treatment apparatus according to claim 6, wherein said separation membranes (1) and (2) are each wound around a perforated central tube to form a spiral separation membrane element.

10. 10. The solution treatment apparatus according to claim 9, wherein the separation membrane element has a feed liquid supply section or a concentrated liquid discharge section at an outer peripheral end portion in a direction perpendicular to the longitudinal direction of the perforated central tube.

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