JPH09141068A - Cleaning method of hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an enough cleaning effect without requiring a high flow rate or pressure of water. SOLUTION: A hollow fiber membrane 1 is dipped in a mixture soln. of water to which 0.01-1wt.% surfactant and >=0.1wt.% alkali material are added. An org. matter 3 in a contaminant layer on the surface of the hollow fiber membrane 1 can be hydrolyzed by the effect of the alkali material, and the hydrolysis of the org. matter can be promoted by the permeation effect due to addition of the surfactant. As a result, contamination on the surface of the hollow fiber membrane 1 can be cleaned by washing with water in the ranges of flow rate and pressure of city water available for ordinary home.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used alone or in combination with activated carbon as a filter medium in household water purifiers to remove iron rust in water, suspended substances such as organic substances, and water-soluble pollutants. The present invention relates to a method for cleaning a hollow fiber membrane.

[0002]

2. Description of the Related Art Hollow fiber membranes are used as filter media in household water purifiers, etc., and suspended substances such as iron rust and organic substances in water are filtered and removed with this hollow fiber membrane. There is. Therefore, these are deposited on the surface of the hollow fiber membrane, and the filtration flow rate decreases with time due to clogging of the hollow fiber membrane. The degree of this decrease in flow rate depends largely on how dirty the water to be treated is, but the degree of contamination of water such as tap water has a large regional difference, and depending on the area, filtration cannot be performed within a few days to a few weeks. It may be necessary to replace the cartridge filled with the hollow fiber membrane.

This dirty hollow fiber membrane cannot be used again, and if the dirt deposited on the surface of the hollow fiber membrane is removed, the filtration flow rate is recovered and it can be reused. As a method for cleaning the hollow fiber membranes to remove dirt, the dirt layer on the surface of the hollow fiber membranes is washed away with running water, and the dirt is thrown by flowing water in the direction opposite to the flowing direction during normal use of filtration. Conventionally, two methods, that is, a method of washing off (commonly called backwashing) have been industrially adopted.

[0004]

However, in this method,
In order to completely wash off the dirt on the surface of the hollow fiber membrane, a flow velocity of 4 to 6 m / s or more is required, and even a hollow fiber membrane of a household water purifier has a flow rate of several tens to one hundred and several liters / min. A large amount of water is required, and it is practically impossible to obtain such amount of running water from the water supply of ordinary households. In the other method, when backwashing, a water pressure (about 3 to 5 kg / cm ² ) that is 3 to 5 times or more the water pressure during normal use (about 1 kg / cm ² ) is required, and such a water pressure can be obtained. Only a few households can do it, and the tap water pressure of a normal household cannot obtain a sufficient cleaning effect.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for cleaning a hollow fiber membrane, which can obtain a sufficient cleaning effect without requiring a large amount of flowing water or water pressure. It is what

[0006]

In the method for cleaning a hollow fiber membrane according to claim 1 of the present invention, 0.01 to 1% by weight of a surfactant and 0.1% by weight or more of an alkaline substance are added. The hollow fiber membrane is immersed in the mixed aqueous solution. As this alkaline substance, sodium hydrogen carbonate can be used.

The method for cleaning a hollow fiber membrane according to a third aspect of the present invention is the hollow fiber membrane in an aqueous solution in which an organic substance-degrading enzyme is added and the pH is adjusted so that the enzymatic reaction of the organic substance-degrading enzyme remains active. It is characterized by immersing. 0.01 to 1% by weight of a surfactant can be added to this aqueous solution. A method for cleaning a hollow fiber membrane according to a fifth aspect of the present invention is characterized by immersing the hollow fiber membrane in an aqueous solution containing 0.1 to 10% by weight of an oxidizing agent.

0.01 to 1% by weight of a surfactant can be added to this aqueous solution.

[0009]

Embodiments of the present invention will be described below. As shown in FIG. 1, when the hollow fiber membrane is used for filtering water in a household water purifier, the surface of the hollow fiber membrane is clogged with iron rust, sand, clay, etc. It is considered that the fine particles 2 of the inorganic substance are closely deposited by using the organic substance 3 such as humin, polysaccharide, protein, and lipid as a binder to close the pores 4 of the hollow fiber membrane 1. Therefore, it is considered that the reason why a high flow velocity is required in the washing method using running water or the like is that the tackiness of the organic substance plays a role of a binder and the dirt layer firmly adheres to the surface of the hollow fiber membrane. Therefore, in the present invention, the adhesion of the soil layer to the surface of the hollow fiber membrane is reduced by chemically decomposing the organic matter in the soil layer, and a low flow rate (low flow rate) equivalent to tap water in general households is obtained.
The hollow fiber membrane can be sufficiently washed even under low water pressure.

First, an embodiment of the invention of claim 1 will be described. According to the invention of claim 1, a mixed aqueous solution containing 0.01 to 1% by weight of a surfactant and 0.1% by weight or more of an alkaline substance is prepared as a cleaning liquid, and the hollow fiber membrane is immersed in the cleaning liquid. After that, the hollow fiber membrane is washed by washing with running water. Generally, organic substances such as humin, polysaccharides, proteins and lipids are hydrolyzed in the presence of water, but the hydrolysis reaction by water alone is slow and the decomposition is incomplete. Therefore, the invention of claim 1 is to add an alkaline substance to water to accelerate hydrolysis by using an alkali as a catalyst to completely decompose organic substances. Then, by further adding a surfactant, the surface tension of this alkaline mixed aqueous solution is lowered, the alkaline mixed aqueous solution swells and permeates quickly into the dirt layer to further accelerate the hydrolysis of organic matter, and in a shorter time. It can decompose organic substances.

The amount of the alkaline substance added to water is 0.1% by weight in order to sufficiently obtain the effect of hydrolysis of the organic substance.
It is necessary to set it so that it is higher than the density. The higher the amount of alkaline substance added, the higher the hydrolysis reaction of organic substances, and the more organic substances can be decomposed.Therefore, the upper limit of the amount of alkaline substances added is not set, but safety to the human body is ensured. For this purpose, the upper limit is an amount such that the pH of the mixed solution after addition of the alkaline substance does not exceed 11. As the alkaline substance, sodium carbonate, sodium hydrogen carbonate, potassium pyrophosphate, sodium pyrophosphate, or the like can be used, but in addition to these,
The mixed aqueous solution has a pH of about 8 to 11 and can be used without particular limitation as long as it is less harmful to the human body.

The amount of the surfactant added to water is 0.01 to 1 in order to lower the surface tension and enhance the cleaning effect.
It is necessary to set the concentration within the range of the weight% concentration. As the surfactant, any of an anionic surfactant, a cationic surfactant, a nonionic surfactant and a zwitterionic surfactant can be used. Examples thereof include oxyalkyl ether, polyoxylauryl ether, sodium alkylbenzene sulfonate, propylene glycol and the like.

As described above, by immersing the hollow fiber membrane in the mixed aqueous solution containing 0.01 to 1% by weight of the surfactant and 0.1% by weight or more of the alkaline substance, the hollow fiber membrane is removed. Since the organic substance is decomposed, the adhesion between the soil layer and the soil layer on the hollow fiber membrane is reduced. The time for immersing the hollow fiber membrane in the mixed aqueous solution may be appropriately set according to the degree of contamination, and several hours is sufficient. Then, after soaking, the hollow fiber membrane can be washed by exposing the hollow fiber membrane to running water or back-washing with running water to peel off and remove the dirt layer on the surface of the hollow fiber membrane.
Since the adhesion of the dirt layer to the surface of the hollow fiber membrane is lowered as described above, it is within the range of 1 that can be obtained with tap water of ordinary households.
It can be sufficiently washed with running water of about 0 liter / min or running water with a water pressure of about 1 kg / cm ² .

Next, an embodiment of the invention of claim 2 will be described. The invention of claim 2 is characterized in that, in the invention of claim 1, the alkaline substance is sodium hydrogen carbonate. Sodium hydrogen carbonate (baking soda) is a substance that is also recognized as a food additive, has very little harm to the human body, and is a hollow fiber membrane that filters water used for beverages like a household water purifier in the kitchen. Ideal for cleaning.

Next, an embodiment of the invention of claim 3 will be described. According to the invention of claim 3, an organic matter degrading enzyme is added and dissolved in an aqueous solution whose pH is adjusted so that the enzymatic reaction of the organic matter degrading enzyme maintains its activity to prepare a washing solution, and the hollow fiber membrane is dipped in this washing solution, followed by running water. The hollow fiber membrane is washed by washing with. Rivers and lakes are generally used as tap water sources, but at present, there are many cases in which the water of the tap water sources, rivers and lakes, is contaminated with general domestic wastewater and sewage. When tap water derived from such a water source is subjected to purification treatment with a hollow fiber membrane, the main components of stains that cause a reduction in the filtration treatment capacity of the hollow fiber membrane are often organic substances such as humin, polysaccharides, proteins and lipids. By decomposing and removing these organic substances, the filtration treatment capacity of the hollow fiber membrane can be restored. Generally, organic substances such as humin, polysaccharides, proteins and lipids are hydrolyzed in the presence of water, but the hydrolysis reaction by water alone is slow and the decomposition is incomplete. Therefore, in the invention of claim 2, by adding an organic substance decomposing enzyme to water, the hydrolysis is accelerated by the catalytic action of these enzymes, and the dirt deposited on the surface of the hollow fiber membrane is decomposed in a short time. It is a thing.

As the organic substance decomposing enzyme, lipase, protease, amylase, cellulase and the like can be used, and these can be used alone or in combination of two or more kinds. It is preferable to select the organic matter degrading enzyme according to the type of organic matter in the water to be filtered. When the amount of humic acid is large, cellulase is used. When the amount of polysaccharide is large, amylase is used. When the amount of protein is large, protease is used. In this case, it is preferable to use lipase. Organic matter-degrading enzymes are generally non-toxic and easily decomposed and do not pollute the environment, so the amount added is not particularly limited, and can be appropriately set according to the degree of fouling of the hollow fiber membrane. Good.

The activity (catalytic activity) of the enzymatic reaction of the organic substance degrading enzyme depends on the pH of the solvent (water), and generally exhibits activity in the range of pH 5-8. For this reason, an organic substance degrading enzyme is added to water, and at the same time, the pH is adjusted so that the pH becomes 5-8. Thus the pH
By performing the adjustment, the dirt on the hollow fiber membrane can be decomposed in a shorter time. The pH can be adjusted by adding an acid or an alkali. For example, when adjusting in the range of pH 3.2 to pH 6.2, it can be adjusted by mixing acetic acid and sodium acetate and changing the mixing ratio thereof.
When adjusting in the range of 6 to pH 9.2, it can be adjusted by mixing potassium dihydrogen citrate and sodium tetraborate and changing the mixing ratio thereof.
When adjusting in the range of 2 to 11.0, it can be adjusted by mixing sodium tetraborate and sodium carbonate and changing the mixing ratio thereof.

As described above, by immersing the hollow fiber membrane in an aqueous solution in which the organic substance-degrading enzyme is added and the pH of the enzyme reaction of the organic substance-degrading enzyme is kept active, the organic matter in the stain layer is immersed. As a result of being decomposed, the adhesion between the dirt layer and the dirt layer on the hollow fiber membrane is reduced. The time for immersing the hollow fiber membrane in the aqueous solution may be appropriately set according to the degree of fouling, and several hours is sufficient. Then, after soaking, the hollow fiber membrane can be washed by exposing the hollow fiber membrane to running water or back-washing with running water to peel off and remove the dirt layer on the surface of the hollow fiber membrane. Since the adhesion of the dirt layer to the surface of the hollow fiber membrane is lowered as described above, a running water flow rate of about 10 liters / min or 1 kg / cm, which is a range that can be obtained with tap water of general households.
It can be sufficiently washed with running water at a water pressure of about ² .

Next, an embodiment of the invention of claim 4 will be described. The invention of claim 4 is characterized in that, in the invention of claim 3, 0.01 to 1% by weight of a surfactant is added to the aqueous solution. By adding the surfactant in this manner, the surface tension of the aqueous solution in which the organic substance-degrading enzyme is dissolved is lowered, and the aqueous solution quickly swells and permeates into the dirt layer. Therefore, the organic substance-degrading enzyme quickly spreads inside the dirt layer, and not only the decomposition of the organic matter progresses from the surface of the stain layer, but also from the inside to decompose the organic matter in a shorter time. It is possible to shorten the immersion cleaning time of the hollow fiber membrane.

Next, an embodiment of the invention of claim 5 will be described.
I do. The invention of claim 5 is 0.1 to 10% by weight of an oxidizing agent.
Prepare a cleaning solution with an aqueous solution containing
After soaking the thread film, rinse it with running water
The hollow fiber membrane is washed. As oxidizing agent
Is persulfate, percarbonate, superphosphate, perborate
The addition of an oxidizer to water
The oxidizer reacts with water and decomposes, at which time the oxidizer
Occur. And this oxidizing substance oxidizes organic matter and
To remove the dirt accumulated on the surface of the hollow fiber membrane in a short time.
It can be done. This as an oxidant
Potassium peroxocarbonate (K _TwoC
_TwoO₆), The hollow fiber membrane is immersed
Add this potassium peroxocarbonate to the running water
Then, the following reaction occurs in water and oxygen is generated.

K ₂ C ₂ O ₆ + H ₂ O → 2KHCO ₃ + (O) A part of the generated oxygen can oxidize the organic substance and decompose the organic substance. The amount of the oxidizing agent added to water is 0.1 to 0.1% in order to effectively exhibit the oxidizing effect.
The concentration is set to be 10% by weight. By immersing the hollow fiber membrane in an aqueous solution containing 0.1 to 10% by weight of an oxidizing agent as described above, the generated oxidizing substance serves as a binder for the dirt layer on the surface of the hollow fiber membrane. Since the organic substances present therein are decomposed, the adhesion between the soil layer and the soil layer on the hollow fiber membrane is reduced. The time for immersing the hollow fiber membrane in the aqueous solution may be appropriately set according to the degree of fouling, and several hours is sufficient. Then, after soaking, the hollow fiber membrane can be washed by exposing the hollow fiber membrane to running water or backwashing with running water to peel off and remove the dirt layer on the surface of the hollow fiber membrane. Since the adhesion of the dirt layer to the surface of the hollow fiber membrane is lowered as described above, it is in the range of 10 that can be obtained with tap water of ordinary households.
It can be sufficiently washed with a running water amount of about 1 liter / min or a running water pressure of about 1 kg / cm ² .

Next, an embodiment of the invention of claim 6 will be described. The invention of claim 6 is characterized in that, in the invention of claim 5, 0.01 to 1% by weight of a surfactant is added to the aqueous solution. When the hollow fiber membrane is immersed in an aqueous solution containing an oxidant, if the adhesion of the soil layer to the hollow fiber membrane is high, it is difficult for the oxidant to penetrate into the soil layer, and the decomposition reaction It will gradually progress from the surface of the dirt layer toward the back, and it will take some time. Therefore, when a surfactant is added, the surface tension of the aqueous solution containing the oxidant is lowered, and the aqueous solution quickly swells and permeates into the dirt layer. For this reason, the oxidant quickly spreads inside the dirt layer, and not only the decomposition of the organic matter progresses from the surface of the dirt layer, but also from the inside to decompose the organic matter in a shorter time. The hollow fiber membrane can be immersed and washed in a shorter time.

[0023]

As described above, according to the present invention of claim 1,
Since the hollow fiber membrane was soaked in a mixed aqueous solution to which 01 to 1% by weight of a surfactant and 0.1% by weight or more of an alkaline substance were added, the organic matter of the dirt layer on the surface of the hollow fiber membrane was Can be hydrolyzed by the action of an alkaline substance, and the hydrolysis of organic substances can be promoted by the osmotic action of the addition of a surfactant. With this, it is possible to wash away the dirt on the surface of the hollow fiber membrane and wash it, and it is possible to sufficiently wash the hollow fiber membrane and restore the filtering ability without requiring a large amount of flowing water or water pressure. is there.

According to the second aspect of the present invention, sodium hydrogencarbonate is used as the alkaline substance, and sodium hydrogencarbonate is safe for the human body.
The hollow fiber membrane can be safely washed. According to the invention of claim 3, the hollow fiber membrane is soaked in an aqueous solution in which the organic matter degrading enzyme is added and the pH of the enzyme reaction of the organic matter degrading enzyme is kept active. The organic matter in the dirt layer can be decomposed by the action of the organic matter decomposing enzyme, and the pH of the organic matter decomposing enzyme can be increased to accelerate the decomposition of the organic matter. It is possible to wash away the dirt on the surface of the hollow fiber membrane with running water due to the flowing water amount or water pressure, and to sufficiently wash the hollow fiber membrane without requiring a large amount of running water or water pressure to restore the filtration capacity. It can be done.

According to the invention of claim 4, 0.01 to 1% by weight of a surfactant is added to the above-mentioned aqueous solution, and the decomposition of organic substances is promoted by the permeation action by the addition of the surfactant. Therefore, the immersion cleaning can be performed in a short time. According to the invention of claim 5, the hollow fiber membrane is soaked in an aqueous solution containing 0.1 to 10% by weight of the oxidizing agent, so that the organic matter in the dirt layer on the surface of the hollow fiber membrane is oxidized by the oxidizing agent. It can be decomposed by decomposing action, and it is possible to wash away the dirt on the surface of the hollow fiber membrane with running water in the range that can be obtained with general household tap water or running water pressure. It is possible to sufficiently wash the hollow fiber membrane and restore the filtering ability without the need for.

According to the invention of claim 6, 0.01 to 1% by weight of a surfactant is added to the above-mentioned aqueous solution, and the decomposition of organic substances is promoted by the permeation action by the addition of the surfactant. Therefore, the immersion cleaning can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a state of dirt on the surface of a hollow fiber membrane.

[Explanation of symbols]

 1 hollow fiber membrane 2 fine particles 3 organic matter 4 pores

Claims (6)

[Claims] 1. 0.01 to 1% by weight of surfactant and 0.
A method for cleaning a hollow fiber membrane, comprising immersing the hollow fiber membrane in a mixed aqueous solution containing 1% by weight or more of an alkaline substance. 2. The method for cleaning a hollow fiber membrane according to claim 1, wherein the alkaline substance is sodium hydrogen carbonate. 3. A method for cleaning a hollow fiber membrane, which comprises immersing the hollow fiber membrane in an aqueous solution in which an organic substance-degrading enzyme is added and the pH of the enzyme reaction of the organic substance-degrading enzyme is kept active. 4. The method for cleaning a hollow fiber membrane according to claim 3, wherein 0.01 to 1% by weight of a surfactant is added to the aqueous solution. 5. A method for cleaning a hollow fiber membrane, which comprises immersing the hollow fiber membrane in an aqueous solution containing 0.1 to 10% by weight of an oxidizing agent. 6. The method for cleaning a hollow fiber membrane according to claim 5, wherein 0.01 to 1% by weight of a surfactant is added to the aqueous solution.