JP2011056395A - Water treatment method for producing purified water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency of filtration with a reverse osmosis membrane by beforehand reducing endotoxin in raw material water before reverse osmosis treatment for obtaining purified water used for an artificial dialysis solution. <P>SOLUTION: In water treatment method for producing purified water by passing water to be treated through a reverse osmosis treatment apparatus 4 comprising reverse osmosis membranes, an electrolyzer 2 is installed which has a working electrode 11 where a diamond thin film is formed on a substrate, and a counter electrode 13 facing the working electrode 11 so as to leave a space of 0.05 or 1.0 mm between them, and uses the space as a passage of the water to be treated, a voltage less than a voltage causing water electrolysis is applied between the working electrode 11 and the counter electrode 13 to electrolyze the water to be treated, and the water to be treated whose endotoxin content is reduced to 1,000 unit/L or less is supplied to the reverse osmosis treatment apparatus 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water treatment method for producing purified water, for example, purified water used in an artificial dialyzer, from raw water such as tap water, and particularly provides a method that can favorably remove endotoxin.

  Endotoxin is a ribopolysaccharide that forms the outer wall of the cell membrane of Gram-negative bacilli, and is eluted by lysis or destruction of bacterial cells to act as a bacterial toxin. In the case of Gram-negative bacilli, common bacteria such as Escherichia coli can cause the above-mentioned toxic effects. There is. Inflammatory cytokines are also produced by endotoxin in an amount that does not cause fever. In long-term artificial dialysis patients, the accumulation of proteins generated thereby causes dialysis amyloidosis.

  The dialysate for artificial dialysis is prepared by diluting the stock solution with purified water, and the purified water for this dilution is obtained by treating raw water such as tap water. Since general tap water is sterilized, the number of fungi is less than 100 per liter, which is suitable for beverages. However, endotoxin is usually contained at about 10,000 units / L and is unsuitable for medical use. The water for dialysis is required to be 10 units / L or less, preferably to 0. For this reason, dialysis water is generally produced by purification by reverse osmosis, and the reverse osmosis membrane allows only water molecules to pass through, so that endotoxin and the like are removed. Before reverse osmosis treatment, remove microorganisms and fine particles in the raw water with a filter, pass through an ion exchange resin layer to soften water, remove chlorine with activated carbon, etc. Often combined processing.

  However, even if various means other than reverse osmosis membranes are used in combination, it is actually difficult to produce purified water completely free of endotoxins. For this reason, it has been proposed to further use special means. ing. For example, Japanese Patent Application Laid-Open No. 2007-237062 (Patent Document 1) states that endotoxin can be completely removed by further treating purified water after reverse osmosis treatment with an electric regeneration type pure water apparatus. This electric regenerative water purifier fills a filling chamber separated by an anion exchange membrane and a cation exchange membrane with a mixture of an anion exchange resin and a cation exchange resin, and energizes between electrodes provided in parallel therewith. Is. Thus, the treated purified water can be taken out from the ion exchange resin filling chamber.

Japanese Patent Application Laid-Open No. 2007-252396 (Patent Document 2) also discloses a method for removing microorganisms and endotoxin in purified water by passing reverse osmosis membrane treated water through an electric deionized water production apparatus. According to the cited document 2, the electric deionized water production apparatus is filled with an ion exchanger in a demineralization chamber divided by a cation exchange membrane and an anion exchange membrane, and a concentration chamber is provided on both sides of the demineralization chamber. A desalting chamber and a concentrating chamber are arranged between an anode chamber having an anode and a cathode chamber having a cathode, and purified water can be obtained while applying a voltage.

JP 2007-237062 A JP 2007-252396 A

  In the method described in JP 2007-237062 A and JP 2007-252396 A, since bacteria are prevented from breeding in the system due to deionization action and bactericidal action by electrolysis, purification without endotoxin is performed. You can get water. However, the purified water filtered through the reverse osmosis membrane is only water molecules, but in many cases endotoxin is contained.

  The efficiency of filtration using reverse osmosis membranes is affected by the quality of the raw water. If the amount of endotoxin in the raw water is large, the endotoxin of the filtered water also increases, and the efficiency of filtration decreases when trying to improve the endotoxin blocking rate To do. For this reason, when trying to obtain purified water having an endotoxin content of 10 units / L or less, it is common to obtain purified water of only about 10% of the treated raw water. In view of the above, an object of the present invention is to obtain purified water with little endotoxin by improving the efficiency of filtration by a reverse osmosis membrane by performing treatment on raw water before performing reverse osmosis treatment.

  The present invention solves the above-mentioned problems, and in a water treatment method for producing purified water by passing water to be treated through a reverse osmosis treatment apparatus comprising a reverse osmosis membrane, a diamond thin film is formed on a substrate. An electrolysis apparatus having a working electrode and a counter electrode facing the working electrode with a gap of 0.05 to 1.0 mm and using the gap as a flow path for the water to be treated is generated to electrolyze water. A voltage lower than the working voltage is applied between the working electrode and the counter electrode to electrolyze the water to be treated, and the water to be treated whose contained endotoxin is 1000 units / L or less is fed to the reverse osmosis treatment device. Is a water treatment method for producing purified water.

Here, the water to be treated that has been electrolyzed by the electrolyzer is stored in a water tank, and the water to be treated is fed from the water tank to the reverse osmosis treatment device.
Furthermore, the electrolytic voltage applied to the working electrode is characterized by being 1.2 to 2.5 V with respect to the Ag / AgCl reference electrode.

  Tap water usually contains about 10000 units / L of endotoxin, but according to the present invention, it is possible to reduce the treated water before reverse osmosis treatment to 1000 units / L or less. Purified water with little endotoxin can be obtained by improving the efficiency of filtration.

It is a layout of the apparatus used for the water treatment method of the present invention. It is a layout of the apparatus used for the water treatment method of the present invention. It is sectional drawing parallel to an axial direction which shows the electrolysis apparatus used for this invention. It is AA 'arrow sectional drawing in FIG.

  In the water treatment method of the present invention, purified water is basically produced by passing the water to be treated through a reverse osmosis treatment apparatus comprising a reverse osmosis membrane. It is characterized by feeding water to a reverse osmosis treatment device. It does not specifically limit about a reverse osmosis processing apparatus, It consists of a reverse osmosis module and the pump which supplies treated water to this at high pressure. The reverse osmosis module may be any of a planar membrane module, a spiral module, and a tubular module.

  The layout of the apparatus used for the water treatment method of the present invention is shown in FIG. Reference numeral 1 denotes a raw water tank, from which the raw water fed by the pump 7 is sent to the electrolyzer 2. The water to be treated that has come out of the electrolysis device 2 is sent to the reverse osmosis treatment device 4 through the ion exchange treatment device 3, and the purified water obtained is stored in the purified water tank 5. The ion exchange treatment device 3 is generally added for pretreatment even in a conventional reverse osmosis treatment device, and is preferably provided also in the method of the present invention. The ion exchange treatment device removes cations and anions such as calcium ions and chlorine ions. Such a device to be added is not limited to the one shown in FIG. 1 or FIG. 2 shown later. For example, it is added for sterilization of tap water or a filter for removing microorganisms and fine particles in raw water. An activated carbon treatment apparatus that adsorbs and removes chlorine by activated carbon can be further added.

  In the water treatment apparatus of FIG. 1, the electrolysis apparatus 2 is provided upstream of the reverse osmosis treatment apparatus 4 so that water to be treated flows from the electrolysis apparatus to the reverse osmosis treatment apparatus. That is, there is an ion exchange treatment device 3 between the electrolysis device 2 and the reverse osmosis treatment device 4, but in any case, the electrolysis device 2 and the reverse osmosis treatment device 4 are coupled by a flow path. However, as shown in the layout diagram in FIG. 2, the water to be treated that has been electrolyzed by the electrolyzer 2 is temporarily stored in the water tank 6, and the treated water is supplied from the water tank 6 to the reverse osmosis treatment device 4. It may be. In addition, although 8 is a pump, a pump can be suitably provided also in the position which is not described in FIG.1 and FIG.2. There may be a plurality of water storage tanks 6. In this case, when the water to be treated flows into one water tank, the water to be treated can be sent out from the other water tank. By arranging as shown in FIG. 2, smooth processing is possible even if the processing speeds of the electrolysis apparatus and the reverse osmosis processing apparatus do not match.

  The electrolysis apparatus used in the water treatment method of the present invention has a working electrode in which a diamond thin film is formed on a substrate, and a counter electrode facing the working electrode with a gap therebetween. It is what. 3 and 4 show such an electrolysis apparatus, where FIG. 3 is a cross-sectional view parallel to the axial direction, and FIG. 4 is a cross-sectional view taken along line AA ′ in FIG. In these figures, reference numeral 11 denotes a working electrode (in FIG. 4, the positional relationship is indicated by a two-dot chain line), which is at least on the front surface of the thin plate-like conductive substrate, that is, on at least the left surface in FIG. A conductive diamond film is formed. Reference numeral 12 denotes a spacer made of a chemical-resistant electrical insulator such as fluorine resin, and has one elongated hole 121 as shown in FIG. Reference numeral 13 denotes a counter electrode made of a corrosion-resistant conductor block such as titanium, which faces the surface of the working electrode 11 on which the diamond is formed with the spacer 12 interposed therebetween. Therefore, the distance between the working electrode and the counter electrode is determined by the thickness of the spacer.

  The working electrode 11 is a conductive thin plate, for example, a conductive silicon single crystal plate having a thickness of about 0.7 mm, and has a thickness of about 30 μm made of fine diamond crystals of several μm in size. Created by forming a coating. The diamond film can be formed by plasma CVD in hydrogen gas containing a carbon source such as acetone. In order to impart conductivity to diamond, boron oxide or the like is doped in boron by dissolving it in the carbon source.

  Each of the spaces 14 formed by the holes 121 of the spacer 12 is opened to have an inlet 15 and an outlet 16 for the liquid to be processed, both of which are provided in the block of the counter electrode 13. That is, the inlet 15 and the outlet 16 of the liquid to be processed are formed by making holes in the block of the counter electrode 13, and fluid couplings 17 and 18 for introducing and discharging the liquid to be processed are screwed into the block of the counter electrode. . Reference numeral 19 denotes an energization terminal for the counter electrode 13.

  Reference numeral 30 denotes a reference electrode, which is screwed into a counter electrode block so that its tip is flush with the counter electrode. Here, an example of an Ag-AgCl system is shown, but a chemical resistant container 301 such as a fluororesin in which a saturated KCl solution is gelatinized with gelatin is filled as an electrolytic solution 302. Further, an Ag wire having a surface made of AgCl is inserted as an electrode material 303 therein. Reference numeral 304 denotes a filter made of porous ceramic or the like that separates the electrolyte solution 302 of the reference electrode from the liquid to be treated. Although the reference electrode is not essential for the electrolytic treatment apparatus of the present invention, it is preferable to provide the reference electrode in order to measure an accurate voltage between the working electrode and the counter electrode.

  Further, a current-carrying plate 20 for the working electrode is provided on the back surface of the electrode plate of the working electrode 11, that is, on the opposite side of the surface facing the counter electrode 13, and is in contact with the working electrode 11. Reference numeral 21 denotes an energization terminal for the working electrode 11. Reference numeral 22 denotes a seal cover made of a chemical-resistant electrical insulator, which is connected to the block of the counter electrode 13 by a plurality of set screws (not shown). Seal the inside. In addition, an O-ring 26 is provided in a part of the energizing plate 20 so that the liquid to be treated does not enter inside thereof, and the energizing plate is directly brought into electrical contact with the back surface of the electrode plate without passing through the liquid. A plastic insulating cover 27 covers the entire metal block of the counter electrode 13.

  As will be described later, in the present invention, utilizing the fact that the diamond electrode does not cause electrolysis of water even in a relatively high voltage range, endotoxin is decomposed without causing electrolysis of water. However, the back surface and the end surface of the working electrode 11 are not necessarily formed with a diamond coating, and the current-carrying plate 20 naturally has no diamond coating. Accordingly, when the liquid to be treated wraps around a portion of the electrode plate or the like where there is no diamond coating, water electrolysis may occur. The structure allows contact with liquid. Even in this way, even if bubbles are generated in a place where there is no flow of the liquid, it stops at that portion, and since the metal surface is covered with bubbles and is not energized, electrolysis of water does not proceed any further. If the liquid to be treated is to be sealed so as to remain within the range facing the spacer hole 121 of the working electrode, it is difficult to press the gap between the working electrode and the counter electrode with a large force, which is difficult due to the problem of damage to the electrode plate. It is. Therefore, as described above, it is practically important to have a structure that allows contact with the liquid to be treated except for a portion of the surface of the working electrode opposite to the surface facing the counter electrode, that is, the energized portion.

  In the method of the present invention, electrolysis is performed by applying a voltage of 1.2 to 2.5 V to the working electrode with respect to the Ag / AgCl reference electrode using the above-described electrolysis apparatus. The electrolytic treatment in the present invention is performed at a voltage at which electrolysis of water does not occur, but as described above, by using a diamond electrode as the working electrode of the electrolysis apparatus, the interatomic atoms of molecules that can be decomposed only at a high voltage The endotoxin targeted by the present invention can be decomposed and inactivated. That is, in the case of a platinum electrode or the like which is a working electrode in a conventional electrolysis apparatus, water electrolysis occurs when the electrolysis voltage exceeds 1.2 V. However, the electrolysis apparatus used in the present invention is about 2.5 V (Ag / AgCl reference electrode). Electrolysis of water does not occur until Endotoxin is decomposed in parallel even under conditions where water is electrolyzed. However, when water is electrolyzed, energy is consumed for this, and the endotoxin decomposition state becomes unstable. A higher electrolysis voltage promotes endotoxin decomposition and is preferably 1.3 V or more. However, when it exceeds 1.9 V, the effect is saturated. Therefore, the electrolytic voltage is more preferably 1.3 to 1.9V.

  In the present invention, in order to decompose endotoxin in a voltage range in which water is not electrolyzed, the gap between the surface of the working electrode 11 having the diamond coating and the counter electrode 13 needs to be a narrow gap of 1.0 mm or less. . In addition, since there exists a possibility that a working electrode and a counter electrode may contact if the space | interval of a working electrode and a counter electrode is smaller than 0.05 mm, 0.05 mm or more is suitable. It is unclear why such endotoxin molecule decomposition by electrolysis occurs only when the working electrode and the counter electrode face each other with a narrow gap of 0.05 to 1.0 mm.

  Naturally, the tap water, which is the water to be treated in the present invention, contains almost no electrolyte, but there are calcium ions corresponding to the hardness of the water and chlorine ions derived from chlorine added for sterilization. In the present invention, electrolysis is performed under conditions that do not cause electrolysis of water, so that a very small amount of ions contained in tap water as described above is used as the electrolyte. Although it is preferable to provide an ion exchange treatment apparatus generally provided as a treatment before the reverse osmosis treatment also in the water treatment apparatus of the present invention, it is provided at the latter stage of the electrolysis apparatus as shown in FIGS. If it is provided at the front stage of the electrolysis apparatus, the amount of electrolyte becomes very small and the electrolysis process becomes difficult.

In the water treatment method of the present invention, when the tap water is electrolyzed, the effective value of the working electrode, that is, the area of the portion facing the hole 121 of the spacer in FIGS. 3 and 4 is about 2.8 cm ² . Is about several tens of μA to several hundred μA. Impurities of tap water not only vary greatly from region to region, but also vary over time even with water from the same faucet. Furthermore, there is a change over time in the water pumped in the container. In addition to endotoxin, tap water naturally contains various impurities that are subject to electrolysis, and the above electrolysis current is not only due to decomposition of endotoxin. Since the fluctuation of the electrolysis current itself is large, it is impossible to know the degree of endotoxin degradation by measuring the course of the electrolysis current value.

  Even when the distance between the working electrode and the counter electrode is larger than 1.0 mm, an electrolysis current is observed in a voltage range in which electrolysis of water does not occur, but this is not due to decomposition of components but due to detachment of electrons from molecules. Is. In this case, the detected current is on the order of 1 μA or less, which is much smaller than in the present invention.

  The water to be treated in which the endotoxin is decomposed and inactivated by the electrolytic device as described above is sent to the reverse osmosis treatment device through the ion exchange treatment device as shown in FIGS. 1 and 2, and remains there. Endotoxin is removed. The amount of endotoxin contained in normal tap water is about 10,000 units / L. In the water treatment method of the present invention, the amount is made 1000 units / L or less, preferably 500 units / L or less by an electrolysis apparatus. As a property of the reverse osmosis membrane, the higher the initial concentration of the substance to be removed, the lower the removal efficiency. Therefore, when reverse osmosis treatment is performed using normal tap water as raw water, about 10% of the treated water is obtained as dialyzed water. On the other hand, in the present invention, the efficiency of filtration can be improved by reducing the endotoxin content of water to be treated for reverse osmosis treatment to 1000 units / L or less, and 30% or more of the treated water is dialyzed. It can be used as irrigation water.

Example 1
The endotoxin contained was decomposed and inactivated by electrolyzing tap water with the electrolysis apparatus shown in FIGS. Electrolysis was carried out under conditions where the distance between the working electrode and the counter electrode was 0.5 mm, and the voltage was changed while flowing tap water at a flow rate of 1.5 ml / min, and the endotoxin content was measured. Samples of each condition were obtained by allowing the water to be treated to pass through the electrolysis apparatus for 5 minutes or more and then collecting the water from the electrolysis apparatus in a container free from endotoxin contamination. The endotoxin concentration was measured using a Limulus reagent manufactured by Wako Pure Chemical Industries, Ltd.

  Table 1 shows the relationship between the electrolysis voltage (relative to the Ag / AgCl reference electrode) and the endotoxin remaining after the electrolytic treatment. The endotoxin content of raw water, which is tap water, was 12400 units / L. In addition, electrolysis of water did not occur within the voltage range shown in Table 1. As seen in Table 1, there is almost no decrease in endotoxin at an electrolysis voltage of 1.0 V or less, but it suddenly decreases at 1.3 V or more. As described above, when the endotoxin content is 1000 units / L or less, the filtration efficiency can be improved in the reverse osmosis treatment. In addition, it turns out that the fall of endotoxin reaches a peak even if it raises electrolysis voltage exceeding 1.9V.

(Example 2)
In the electrolysis apparatus used in Example 1, an experiment was performed in which the distance between the working electrode 11 and the counter electrode 13 was changed by using spacers 11 having different thicknesses. Since the tip position of the reference electrode 30 is the same as the counter electrode surface in any case, the distance between the reference electrode and the counter electrode is also the same as the distance between the working electrode and the counter electrode. Electrolysis was carried out under various conditions while flowing tap water at a flow rate of 1.5 ml / min, and the endotoxin content was measured. The raw water used, the sample collection method and the measurement method are the same as in Example 1. The working electrode applied voltage of the electrolyzer was 1.9 V with respect to the Ag / AgCl reference electrode, but water electrolysis did not occur.

  Table 2 shows the relationship between the distance between the working electrode and the counter electrode and the endotoxin remaining after the electrolytic treatment. As can be seen from Table 2, the endotoxin decreases when the electrode spacing is 1.0 mm or less. The narrower the electrode spacing, the greater the degree of decrease, but when 2.0 mm, the endotoxin decreases. I couldn't. The endotoxin content of raw water as tap water was 12400 units / L as in Example 1. An electrolytic current of around 100 μA was observed under the condition where the distance between the electrodes was 1.0 mm or less, but in the case of 2.0 mm, the electrolytic current was detected only at the margin of measurement sensitivity.

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Electrolysis apparatus 3 Ion exchange processing apparatus 4 Reverse osmosis processing apparatus 5 Purified water tank 6 Water storage tank 7, 8 Pump 11 Working electrode 12 Spacer 121 Hole 13 Counter electrode 14 Space 15, 16 Eluate inlet and outlet 17, 18 Fluid coupling 19 Current-carrying terminal 20 Current-carrying plate 21 Current-carrying terminal 22 Seal cover 23, 24, 26 O-ring 27 Insulating cover 30 Reference electrode 301 Container 302 Electrolyte 303 Electrode material 304 Filter

Claims (3)

In a water treatment method for producing purified water by passing water to be treated through a reverse osmosis treatment apparatus comprising a reverse osmosis membrane, a working electrode having a diamond thin film formed on a substrate, a working electrode, and 0.05 to 1. An electrolyzer having a counter electrode facing with a gap of 0 mm and using the gap as a flow path for the water to be treated is provided, and a voltage lower than a voltage at which water electrolysis is generated is provided between the working electrode and the counter electrode. Water treatment for producing purified water, characterized in that the water to be treated is electrolyzed and the treated water whose endotoxin content is 1000 units / L or less is fed to the reverse osmosis treatment device Method. 2. The purified water according to claim 1, wherein the treated water electrolyzed by the electrolyzer is stored in a water storage tank, and the treated water is fed from the water storage tank to the reverse osmosis treatment apparatus. Water treatment method to do. The water treatment method for producing purified water according to claim 1 or 2, wherein the electrolytic voltage applied to the working electrode is 1.2 to 2.5 V with respect to the Ag / AgCl reference electrode.

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