JP2002210337A - Method for cleaning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively cleaning a semipermeable membrane and a membrane separator having a semipermeable membrane without accelerating the deterioration of the membrane. SOLUTION: In cleaning with a cleaning fluid a semipermeable membrane and/or a semipermeable apparatus that separate a raw liquid into a permeate and a concentrate, the cleaning fluid has a pH value different from that of the raw liquid by at least 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semipermeable membrane and a method for cleaning an apparatus therefor. For more information,
Production of ultrapure water used for desalination of seawater and irrigation water, semiconductor cleaning, etc., purification of tap water, production of boiler water, treatment for recycling wastewater and sewage, electrodeposition used for undercoat painting of automobiles, etc. The present invention relates to a semipermeable membrane suitable for use in the processing of food industries such as collecting paints, concentrating fruit juice, producing wine, producing dairy products, and the like, and a method for cleaning the apparatus.

[0002]

2. Description of the Related Art Separation techniques using semipermeable membranes are used in a wide range of fields such as desalination of seawater and irrigation water, medical treatment, production of industrial pure water and ultrapure water, and industrial wastewater treatment. In these membrane separations, contamination of the separation device by microorganisms causes deterioration of water quality of the obtained permeated water, propagation of microorganisms on the membrane surface or adhesion of the microorganisms and their metabolites to the membrane surface, etc. Causes a decrease. In order to avoid such an important problem, various methods for cleaning a membrane separation device have been proposed. As a countermeasure against the adhesion of microorganisms and their metabolites, generally, a method of constantly or intermittently adding a bactericide to a supply liquid has been adopted. As a disinfectant, 0.1 to 50 p
Most commonly, it is added to a concentration of about pm. However, a chlorine-based disinfectant causes chemical degradation of the reverse osmosis membrane. Therefore, when the disinfectant is used, it is necessary to reduce free chlorine using a reducing agent before supplying the reverse osmosis membrane. In addition, sodium bisulfite is intermittently fed, usually 50 times.
A method of disinfection by adding it at a concentration of 0 ppm has been developed and has been generally used. However, this method is not effective in some cases, and it is gradually revealed that microorganisms accumulate on the membrane. ing. In addition, JP 20
A washing method using an acid as described in JP-A-00-237555 can be mentioned. However, since the washing is carried out with a strong acid, there is a possibility that the membrane may be deteriorated. On the other hand, the cleaning effect was not sufficient.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to suppress the acceleration of deterioration of a semipermeable membrane, and to provide a method for effectively cleaning a semipermeable membrane and its apparatus. It is in.

[0004]

In order to achieve the above object, the present invention provides a method for cleaning a semipermeable membrane and / or a semipermeable membrane apparatus for separating a stock solution into a permeate and a concentrate using a cleaning solution. The present invention also provides a cleaning method using a cleaning solution having a pH value at least 4 different from the pH value of the stock solution as the cleaning solution.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a semipermeable membrane refers to a membrane through which some components in a solution or a dispersion system can pass but other components cannot. Specific examples include a reverse osmosis membrane, an ultrafiltration membrane, and a microfiltration membrane. A nanofiltration membrane is a membrane having a fractionation performance between a reverse osmosis membrane and an ultrafiltration membrane. In the present invention, this is also included in the reverse osmosis membrane.
The cleaning method according to the present invention includes, among the above-mentioned films,
Suitable for reverse osmosis membranes and devices that are difficult to physically clean.

As a material for the reverse osmosis membrane, a polymer material such as a cellulose acetate polymer, polyamide, polyester, polyimide, and vinyl polymer is often used. The membrane structure has a dense layer on at least one surface of the film, and an asymmetric film having fine pores having a large pore diameter gradually from the dense layer toward the inside of the film or the other surface. There are composite membranes with a very thin active layer formed of a material. The membrane form includes a hollow fiber membrane and a flat membrane. The thickness of the hollow fiber membrane and the flat membrane is 10 μm to 1 mm, and the outer diameter of the hollow fiber membrane is 50 μm to 4 mm. In the flat membrane, the asymmetric membrane or the composite membrane is preferably supported by a substrate such as a woven fabric, a knitted fabric, or a nonwoven fabric. However, the method of the present invention
It can be used irrespective of the material, membrane structure or membrane form of the reverse osmosis membrane, and all are effective. Typical reverse osmosis membranes include cellulose acetate-based and polyamide-based asymmetric membranes and composite membranes having a polyamide-based or polyurea-based active layer. Among these, the method of the present invention is more effective for polyamide-based composite reverse osmosis membranes having high chemical stability against acids and alkalis. Reverse osmosis membranes can also be used in module form. The flat membrane can be used in a spiral, tubular, plate and frame module, and the hollow fiber membrane can be bundled and used in a module. It does not depend on. Further, the reverse osmosis membrane module incorporates members such as a supply liquid flow path material and a permeated water flow path material in a spiral shape, and these members may have any configuration.

The semipermeable membrane device according to the present invention uses a semipermeable membrane, and supplies a stock solution to the semipermeable membrane under pressure for the purpose of producing water, concentrating, separating, etc., and converting the permeated liquid and / or concentrated liquid. Means to obtain. For example, a reverse osmosis membrane device usually includes a reverse osmosis membrane element, a pressure vessel, a pressure pump, and the like. The stock solution supplied to the reverse osmosis membrane device is added with a chemical solution such as a bactericide, a flocculant, a reducing agent, a pH adjuster, etc., flocculation, sedimentation, sand filtration, polishing filtration, activated carbon filtration, microfiltration, ultrafiltration, It is possible to combine with pre-processing by security filters. When pretreatment by microfiltration or ultrafiltration is performed, the amount of scale and fouling generated during operation is lower than that without pretreatment. Pretreatment with a bactericidal effect reduces the amount of scale and fouling generated. Here, the pretreatment having a bactericidal effect is generally known to have a bactericidal effect such as an inorganic reducing agent such as sodium bisulfite, an organic acid, an inorganic acid, an alkali, a chlorinated bactericide, hydrogen peroxide, and ammonia. Treatment methods generally known to have a bactericidal effect, such as treatment with a compound or a chemical solution, or ultraviolet treatment.

In the present invention, the semipermeable membrane and / or the semipermeable membrane device is washed with a washing solution having a pH value at least 4 different from the pH value of the stock solution. Such a washing solution is alkaline, neutral or acidic. Either may be used. By using a washing solution whose pH value is changed by 4 or more during washing, fouled microorganisms can be effectively sterilized. Just by making the cleaning solution alkaline or acidic as in the past, a chemical solution was used more than necessary, the cleaning effect was small, and in severe cases, the cleaning sometimes caused deterioration of the semipermeable membrane. Microorganisms that adhere to the semipermeable membrane and / or the semipermeable membrane device vary in type depending on the pH value of the operating conditions, but are generated in any pH range. In disinfecting or washing such microorganisms, the pH value of the washing solution is simply increased or decreased.
The effect is not sufficient just by setting the H value. Microorganisms have a pH range in which they can inhabit, and most microorganisms die in an environment deviated by 4 or more from the pH at which they normally inhabit. The present invention utilizes this concept, and the present invention enables effective cleaning of a semipermeable membrane and a membrane separation device having the same. Further, washing with a washing solution having a pH value at least 5 different from the pH value of the undiluted solution is preferable because the kill ratio of microorganisms is improved and the washing property is enhanced. However, since the semipermeable membrane may be deteriorated at the same time, it is necessary to appropriately set the pH of the cleaning liquid in consideration of the semipermeable membrane and the degree of contamination.
In addition to the microorganisms, there is a scale due to inorganic components other than microorganisms, which also occurs in the pH range under any operating conditions. The cleaning method of the present invention is also effective for this stain. For example, calcium carbonate and calcium sulfate are likely to be generated in an alkaline stock solution, and silica scale is likely to be generated in an acidic stock solution. On the other hand, if the pH value is changed by 4 or more, the solubility of the scale component changes greatly, and washing becomes possible. However, in this case, since the pH region in which the solubility is improved by the scale component is determined, it is necessary to set the direction of the pH value to be changed by 4 or more in the direction in which the solubility of the scale component is improved. That is, when it is desired to also remove inorganic components, it is preferable to change the pH value by 4 or more so that the solution has a property opposite to that of the stock solution in which the scale is generated. For example, when the pH value of the stock solution is 8 (alkaline), the pH value of the washing solution is preferably 4 (acidic) or less if scale removal is required.

In the present invention, the chemical used for adjusting the pH of the cleaning solution is not particularly limited. As an acidic substance,
Examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid and citric acid. Sodium hydroxide, potassium hydroxide, sodium bicarbonate,
Examples include inorganic compounds such as ammonia and organic compounds. A plurality of these acidic substances and alkaline substances may be mixed. Further, a surfactant may be mixed in order to remove a stain component attached by electrostatic interaction or hydrophobic interaction. The surfactant is preferably added by dissolving in water or the like when adjusting the pH of the washing solution. The concentration at that time is appropriately set according to the required pH value.

The method for cleaning the semipermeable membrane and / or the semipermeable membrane apparatus using the cleaning liquid of the present invention is not particularly limited. For example, it is possible to circulate the inside of the semipermeable membrane and / or the semipermeable membrane apparatus with a cleaning liquid, or to perform cleaning with one pass. Further, it is also possible to stop the flow of the liquid after immersing the semipermeable membrane in the cleaning liquid or filling the inside of the membrane separation device with the cleaning liquid. In order to efficiently remove dirt components, it is preferable to create a flow of the cleaning liquid in the semipermeable membrane and / or the semipermeable membrane device. Since most of the dirt components adhere to the undiluted solution supply side of the semipermeable membrane, it is efficient to supply the cleaning liquid to the semipermeable membrane from the supply side in the same manner as the undiluted solution. Of the permeate is 1/5
Washing is preferably performed under the following conditions.
More preferably, it is 10 or less. Further, when cleaning is performed by circulation or one-pass, the film surface flux of the cleaning liquid to the semipermeable membrane surface also affects the cleaning efficiency, and a large film surface flux increases the cleaning effect, which is preferable. Since it is difficult to measure the membrane surface flux of the semipermeable membrane in the form of a module, it is common practice to substitute the concentrated solution flux in practice. That is, in order to increase the washing efficiency, it is preferable to increase the flux of the concentrated liquid.

The cleaning method according to the present invention is also effective for cleaning a semipermeable membrane and / or a semipermeable membrane apparatus in which the membrane separation operation has been stopped for a long time. In this case, the semipermeable membrane and / or
Alternatively, the pH value of the solution remaining in the semipermeable membrane device may be checked, and the solution may be washed with a washing solution having a pH value different from the pH value by at least 4 or more.

The pressure of the supply liquid when the cleaning liquid is circulated or supplied in one pass is not particularly limited. However, in order to enhance the cleaning efficiency, the amount of the permeate is reduced to 1/5 or less of the amount of the concentrated liquid. Such pressure is preferred. The pressure that satisfies such conditions is a pressure close to or lower than the osmotic pressure of the cleaning liquid, and more preferably a pressure lower than the osmotic pressure.

The temperature of the cleaning liquid for the semipermeable membrane and / or the semipermeable membrane device is not particularly limited. If the temperature is high, the cleaning effect is enhanced, but the semipermeable membrane performance may be changed, so it is preferably 2 to 99 ° C, more preferably 5 to 50 ° C.
Temperature range.

In the semipermeable membrane device according to the present invention, it is preferable that the device piping has a structure having as few stagnation portions as possible.

[0015] The cleaning frequency of the present invention varies greatly depending on the place of use and the conditions of use of the semipermeable membrane and its apparatus. For example,
0.5 to 2.5 hours of washing every day, every week, 1
It can be performed at intervals such as every month. These can be determined by a decrease in the amount of permeated water through the membrane, an increase in the number of viable bacteria in the concentrate, an increase in the content of organic carbon, and an increase in the membrane pressure.

Further, the cleaning method of the present application can use a cleaning liquid containing a general cleaning agent such as a surfactant. When a cleaning solution containing a surfactant is used, it is possible to add a surfactant to the cleaning solution for washing, or to wash with a washing solution containing a surfactant before or after washing by the method according to the present invention. . The combined use of the cleaning method of the present invention and the cleaning with a surfactant can reduce the pH.
It is more preferable to remove contaminants adsorbed by electrostatic action that cannot be completely washed out only by changing the value. Here, the surfactant is not particularly limited, and commonly used nonionic surfactants, anionic surfactants, and cationic surfactants can be used.
In this case, it is more preferable to use a surfactant having the same charge as the semipermeable membrane.

The method of using the semipermeable membrane and / or the semipermeable membrane device of the present invention is not particularly limited, but is particularly effective for separating an aqueous solution. Separation and concentration of liquids and solids using microfiltration membranes, separation and concentration of suspended matter using ultrafiltration membranes, and separation and concentration of dissolved components using reverse osmosis membranes effective. Particularly effective in seawater desalination, irrigation desalination, industrial water production, ultrapure water, pure water production, medicinal water production, food concentration, turbidity of tap water, and advanced treatment in tap water. .

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Reference Example In a membrane separation device having a polyamide-based composite reverse osmosis membrane, microfiltration and ultrafiltration were used as pretreatment of a stock solution,
After sodium hypochlorite was added so that the residual chlorine concentration was 1 ppm, 5 ppm of sodium bisulfite was added. The pH of the undiluted solution at the time of supply to the semipermeable membrane was adjusted to 7 with the above apparatus, and the membrane was separated. The operating pressure was 0.5 MPa, and the initial permeated water amount of the membrane separation device was 1.25.
m ³ / h (30 m ³ / d).

When the membrane separator was operated under the above conditions for three months, the amount of permeated water was 0.875 m ³ / h, and decreased to 70% of the initial permeated water due to contamination. Example 1 The semipermeable membrane contaminated in Reference Example 1 and the membrane separator having the same were washed by the following method.

The pH of the cleaning solution was adjusted to 11 with an aqueous sodium hydroxide solution, and circulating cleaning was performed for 3 hours. The ratio of the amount of permeated water to the amount of concentrated water during circulation was set to be 1/5. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 2 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 1 except that the cleaning solution was adjusted with sulfuric acid to pH 3. Table 1 shows the results of measuring the amount of permeated water after washing.
Put together. Example 3 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 1 except that the cleaning solution was adjusted with sulfuric acid to pH 2. Table 1 shows the results of measuring the amount of permeated water after washing.
Put together. Example 4 Membrane separation was performed for 3 months in the same manner as in Reference Example 1, except that the stock solution at the time of supply to the semipermeable membrane was adjusted to pH 8.5.
As a result, the amount of permeated water was 0.938 m ³ / h. The contaminated semipermeable membrane and the membrane separator having the semipermeable membrane were washed by the following method.

Washing was carried out in the same manner as in Example 1 except that the pH of the washing solution was adjusted to 12.5 with an aqueous sodium hydroxide solution. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 5 Membrane separation was performed for 3 months in the same manner as in Reference Example 1 except that microfiltration and ultrafiltration were not used as pretreatment of a stock solution. As a result, the amount of permeated water was 0.25 m ³ / h. The contaminated semipermeable membrane and the membrane separator having the semipermeable membrane were washed in the same manner as in Example 1. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 6 As a pretreatment of a stock solution, membrane separation was performed for 3 months in the same manner as in Reference Example 1 except that sodium hypochlorite and sodium bisulfite were not used. As a result, the amount of permeated water is 0.5
0 m ³ / h. The contaminated semipermeable membrane and the membrane separator having the semipermeable membrane were washed in the same manner as in Example 1. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 7 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 4, except that the pH of the washing solution was adjusted to 4.5 with oxalic acid. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 8 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 1 except that the ratio of the amount of permeated water to the amount of concentrated water was adjusted to be 1/2. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 9 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 1, and then further washed under the following conditions.

Washing was carried out in the same manner as in Example 1 except that the washing solution was adjusted to pH 3 with hydrochloric acid. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Example 10 After washing under the following conditions, the semipermeable membrane and the membrane separator having the semipermeable membrane were further washed in the same manner as in Example 1.

To the washing solution, 100 ppm of TC-100 (anionic surfactant) manufactured by Toray Industries, Inc. was added, and circulating washing was performed for 3 hours. The ratio of the amount of permeated water to the amount of concentrated water during circulation is 1
/ 5.

After washing, the results of measuring the amount of permeated water are summarized in Table 1. Comparative Example 1 Membrane separation was performed for 3 months in the same manner as in Reference Example 1 except that the stock solution at the time of supply to the semipermeable membrane was adjusted to pH 4. As a result, the amount of permeated water was 0.93 m ³ / h. The contaminated semipermeable membrane and the membrane separator having the semipermeable membrane were washed by the following method.

Washing was carried out in the same manner as in Example 1 except that the washing solution was adjusted to pH 2 with sulfuric acid. After washing, the results of measuring the amount of permeated water are summarized in Table 1. Comparative Example 2 A semipermeable membrane and a membrane separator having a semipermeable membrane were washed in the same manner as in Example 1, except that the cleaning solution was adjusted with sulfuric acid so as to have a pH of 4. After washing, the results of measuring the amount of permeated water are summarized in Table 1.

[0026]

[Table 1]

[0027]

According to the present invention, when a semipermeable membrane and / or a semipermeable membrane device for separating a stock solution into a permeated solution and a concentrated solution is washed with a washing solution, the pH value of the stock solution as a washing solution is pH Since the cleaning liquids having at least four different values are used, the semipermeable membrane and / or the semipermeable membrane device contaminated by the membrane separation operation can be effectively sterilized and scale removed without using an excessive chemical solution. In addition, it is possible to suppress the promotion of deterioration of the semipermeable membrane and / or the semipermeable membrane device due to the cleaning.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C02F 1/44 C02F 1/44 HKZ F term (Reference) 4D006 GA03 GA06 GA07 HA01 HA41 HA61 KA01 KB11 KB14 KC02 KC16 KD04 KD11 KD12 KD15 KD16 KD30 KE03R KE15R MA01 MA03 MA33 MC18 MC21 MC48 MC54X MC58 PA01 PB03 PB06 PB08 PC02 PC14 PC17 PC21 PC31

Claims (5)

[Claims] When washing a semipermeable membrane and / or a semipermeable membrane device for separating a stock solution into a permeate and a concentrate using a washing solution, the washing solution has a pH value at least 4 different from the pH value of the stock solution. A cleaning method using a cleaning solution. 2. The cleaning method according to claim 1, wherein a cleaning solution having a pH value at least 5 different from that of the stock solution is used. 3. The method according to claim 1, wherein the amount of the permeate is 1/5 or less of the amount of the concentrate. 4. The cleaning method according to claim 1, wherein a cleaning liquid containing a surfactant is used. 5. The cleaning method according to claim 1, wherein the cleaning is performed at least once using two types of acidic and alkaline cleaning liquids.