JPH1066972A - Cleaning and regenerating method of separation membrane for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restore water permeating quantity by executing a 1st step for cleaning a separation membrane for water treatment with an acidic solution and a 2nd step for cleaning it with an alkaline solution containing formalin and an alkali assistant in this order to effectively remove a mixed soil stuck to the membrane without damaging the membrane. SOLUTION: At the time of cleaning a module 7, a cleaning solution is prepared in a cleaning tank 5 and fed to the module 7 with a cleaning pump 6. The 1st cleaning step for cleaning with the acidic solution and the 2nd step for cleaning with the alkaline solution containing formalin and the alkali assistant are successively executed. As a result, salts contained in the raw water, calcium salts and iron matter in a scale and an aluminum complex leaking from the pretreating device or the like are removed in the 1st step top facilitate the infiltration of the 2nd step cleaning solution in the coil. Next, in the 2nd step cleaning, the soil not removed with the acid cleaning is almost removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reverse osmosis membrane (RO), an ultrafiltration membrane (UF), and a microfiltration membrane (RO) used for producing treated water such as pure water or ultrapure water. The present invention relates to a method for cleaning and regenerating a separation membrane for water treatment such as MF), and particularly to a method suitable for cleaning and regenerating a reverse osmosis membrane.

[0002]

2. Description of the Related Art In the electronics industry for manufacturing liquid crystal panels and ultra LSIs, pharmaceutical manufacturing plants, and the like, so-called ultrapure water in which the amounts of colloidal substances and ions are reduced to the order of ppb is required. Pure water production plants that produce such ultrapure water include atmospheric degassing equipment, reverse osmosis membrane equipment, filter equipment, vacuum deaeration equipment, ultraviolet irradiation organic matter decomposition equipment, ion exchange equipment, ultrafiltration membrane equipment, etc. From which the dissolved component and the fine particle component of the water to be treated are removed, and the specific resistance value is 18 MΩ.
The purity has been increased to not less than cm, not more than 1 ppb of TOC, and several particles / ml having a particle size of 0.05 μm.

[0003] Among the apparatuses used in such a pure water production plant, a reverse osmosis membrane apparatus supplies raw water to a reverse osmosis membrane under a pressure higher than the osmotic pressure of a dissolved salt osmosis membrane and reverse osmosis of most of the salts. The permeated water, which is reduced by salts by blocking with a membrane, is obtained as treated water, and the permeated water, which is concentrated with salts, is discharged.The colloidal substances contained in the raw water during this treatment are also reverse osmosis. This is advantageous for the production of the ultrapure water because it can be stopped by a membrane.

Since the reverse osmosis membrane treats raw water by the above-described operation, the larger the concentration ratio of raw water, in other words, the higher the recovery rate of permeated water, the larger the amount of raw water supplied from a certain amount. Permeated water can be obtained, which is advantageous in terms of cost.

However, when a raw water containing a large amount of hardness components such as calcium and magnesium, sulfate ions, silica and the like is treated by a reverse osmosis membrane apparatus, if the recovery rate of permeated water is increased, the solubility is relatively small. Precipitates such as calcium sulfate and silica precipitate on the membrane, causing problems such as an increase in pressure loss and a decrease in the amount of permeated water.

[0006] Contamination of a membrane separation device by microorganisms in raw water deteriorates the quality of ultrapure water as fine particles in treated water, or organic substances consisting of microorganisms and metabolites of microorganisms due to the propagation of bacteria on the membrane. Is attached, and problems such as a decrease in water permeability of the membrane occur.

[0007] For this reason, efficient removal of such membrane contaminants has become a major problem in practical use of membrane separators.

[0008] As a membrane cleaning method for removing membrane contaminants,
There are physical and chemical methods. As a physical method, there are hot water, pulsation, and a mixture method of steam and water. However, the apparatus and operation are complicated, and sufficient cleaning is often not performed. For this reason, chemical cleaning methods using various cleaning agents are generally performed. Detergents include surfactants, acids, alkalis, oxidizing / reducing agents, chelating agents,
Enzymes and the like are used, and these are used alone or in combination.

However, in the conventional cleaning method, there is no method suitable for removing mixed contaminants composed of scale substances such as calcium sulfate and silica and organic substances such as microorganisms and metabolites thereof. Was not enough.

Therefore, the frequency of washing must be increased in order to maintain the amount of water permeated through the membrane, resulting in a shortened life of the membrane.

On the other hand, when looking at the membrane itself, instead of the conventional asymmetric cellulose acetate membrane, a high-performance composite reverse osmosis membrane in which a polysulfone porous support membrane or the like is coated with an active layer that controls membrane performance, or a polyamide asymmetric cellulose acetate membrane is used. Membranes have emerged and have been used industrially in recent years.

However, such a newly developed reverse osmosis membrane is inferior in chlorine resistance as compared with an asymmetric cellulose acetate membrane, and thus cannot be constantly sterilized and washed with chlorine as before. was there.

As described above, in a separation membrane for water treatment used in a water treatment step such as a step of producing ultrapure water, scale substances such as calcium sulfate and silica and organic substances such as microorganisms and metabolites thereof are used. There is no suitable method for removing mixed contaminants consisting of, and there is a problem that the frequency of cleaning is increased in order to maintain the amount of water permeated through the membrane, thereby shortening the life of the membrane. In addition, high-performance separation membranes for water treatment, such as composite reverse osmosis membranes and asymmetric membrane reverse osmosis membranes, have poor chlorine resistance and cannot be constantly sterilized and washed with chlorine. There was a problem that was not done.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and effectively removes mixed contaminants adhering to a membrane without damaging the membrane, thereby reducing the amount of permeated water. It is an object of the present invention to provide a method for regenerating and washing and regenerating a separation membrane for water treatment such as a reverse osmosis membrane. Also,
The second objective is to clean reverse osmosis membranes that effectively remove mixed contaminants without using chlorine in order to maximize the performance of water treatment separation membranes that have high performance but lack salt resistance. It is to provide a regeneration method.

[0015]

Means for Solving the Problems The present inventors have made intensive studies to solve the disadvantages of the prior art, and as a result, it has been found that formalin and an alkali auxiliary are used for removing the mixed contaminants deposited on the reverse osmosis membrane. Alternatively, it was found that washing with an alkaline solution containing formalin, an alkaline auxiliary agent and a surfactant is effective. However, simply contacting an alkaline solution containing formalin and an alkaline auxiliary or a formalin and an alkaline auxiliary and a surfactant with the mixed contaminant is not always sufficient, but in practice, it is still difficult Improvement is desired.

As a result of repeated experiments, the present inventors found that the membrane was washed with an acidic solution prior to washing the membrane with an alkaline solution containing formalin and an alkali assistant or formalin, an alkali assistant and a surfactant. The present inventors have found that the mixed contaminants can be effectively removed by performing the method, and have reached the present invention.

The present invention is suitable for washing and regenerating a spiral type module or a hollow fiber type module using an asymmetric membrane or a composite membrane reverse osmosis membrane. It is also effective for a method for washing and regenerating a microfiltration membrane or the like.

Therefore, the present invention provides a method for washing and regenerating a separation membrane for water treatment comprising at least two washing steps, wherein a first washing step of washing the membrane of the separation membrane for water treatment with an acidic solution, It is characterized in that a second washing step of washing with an alkaline solution containing formalin and an alkali auxiliary is performed in order.

A surfactant may be added to the alkaline solution used in the second washing step.

After washing with an alkaline solution, washing is carried out using, for example, treated water of a reverse osmosis membrane stored in advance until dissolved components are no longer extracted.

The first washing step is a step of lowering the pH and removing the acidicly soluble deposits.

The acids that can be used in the first washing step include:
Any inorganic acid or organic acid can be used as long as it lowers the pH of the washing solution.

The inorganic acids usable in the present invention include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrogen fluoride, chromium trioxide and the like, and the organic acids include formic acid, acetic acid, propionic acid and lactic acid. Monocarboxylic acids, oxalic acid, tartaric acid, succinic acid, dicarboxylic acids such as malic acid, and tricarboxylic acids such as citric acid. In the present invention, for example, oxalic acid and citric acid are preferably used. The concentration of the acid solution to be used is appropriately determined experimentally depending on the type of the acid, the components of the contaminants, and the like.
Those having a pH of 10 to 10% by weight and a pH of 1 to 5 are used. The most preferred acid solution uses oxalic acid, citric acid, or tartaric acid as the acid.
In the range of 1 to 10% by weight, and at pH 2 to 4
Of the range.

The preferred range of concentration and pH can be adjusted by adding sodium hydroxide. The concentration of formalin used in the second washing step is usually 0.1 to 10% by weight.
The degree is suitable, preferably 0.5 to 3% by weight. If the concentration of formalin is too low, the effect of the present invention is small. If the concentration is too high, not only may the membrane be damaged, but also the washing time required for drug removal becomes long.

The alkaline auxiliaries used in the second washing step include ammonia, hydrazine, sodium thiosulfate, sodium hydroxide, sodium carbonate, sodium metasilicate, sodium sesquisilicate, sodium orthosilicate, sodium orthophosphate, pyrroline Sodium acid, sodium bicarbonate, sodium sesquicarbonate, sodium tripolyphosphate, sodium tetraphosphate, sodium hexametaphosphate and the like are exemplified. In the present invention, ammonia, hydrazine, and sodium hydroxide are preferable, and sodium hydroxide is more preferable in that the pH can be easily adjusted. Some of the alkaline auxiliaries used in the present invention by themselves have little or no detergency, but the alkaline solution of the present invention shows a remarkable detergency-enhancing action.

The pH of the alkaline solution can be from 9 to 11, and the pH is more preferably from 10 to 11. pH
If the pH is less than 9, the cleaning effect is reduced, and if the pH exceeds 11, the membrane may be damaged.

As the surfactant that can be added to the alkaline solution, a synthetic detergent system, a soap system, and a complex soap system can be used, and any of anionic and surfactant materials can be used. . Specifically, sodium alkylbenzene sulfonate, sodium higher alcohol sulfate, sodium alkyl sulfate, sodium alkyl sulfonate, sodium alkyl sulfosuccinate, sodium fatty acid soap, sodium alkyl sulfate, sodium polyoxyetherene alkyl ether sulfate, alkyl phosphorus sodium Examples thereof include sodium acid.

The concentration of the surfactant is preferably adjusted appropriately in the range of 0.001 to 10% by weight, and more preferably in the range of 0.2 to 0.5% by weight, depending on the type of the reverse osmosis membrane. .

The optimum condition is that the surfactant is at least one of sodium alkylbenzene sulfonate, sodium alkyl sulfonate and sodium polyoxyethylene alkyl ether sulfate, and the concentration is in the range of 0.2 to 0.3% by weight.

There is no problem in using the above-mentioned anionic surfactants alone or in combination of two or more. Further, as long as the surfactant concentration can be adjusted within a specified range, a commercially available surfactant containing an additive may be used.

Examples of such additives include (1) detergency enhancers, specifically, aluminosilicates, carbonates, and silicates. (2) builders (dispersants), specifically, polymerized phosphates. , Natural zeolite, carboxymethylcellulose (3) sequestering agents, specifically ethylenediaminetetraacetic acid (EDTA), citric acid, gluconic acid, hydroxyacetic acid, and salts thereof.

In the present invention, the first-stage washing removes salts contained in raw water, calcium salts and iron in the scale, aluminum complexes leaking from the pretreatment device, and the like. It becomes easy to penetrate into contaminants on the membrane.

Next, the second-stage washing is performed using an alkaline solution containing formalin and an alkaline auxiliary, or an alkaline solution further containing a surfactant. The second stage of cleaning removes most of the contaminants that could not be removed by acid cleaning.

The first stage of washing is carried out by passing an acidic solution, which has been adjusted to the required final concentration, for 30 minutes to 48 hours, preferably 60 minutes to 24 hours.

In the second washing step, an alkaline solution previously adjusted to the required final concentration is washed with 30% of the alkaline solution.
It is carried out by passing the solution for minutes to 48 hours, preferably 60 minutes to 24 hours.

Thereafter, when the water to be treated is passed and extraction from the membrane is no longer recognized, the washing regeneration is completed.

The water temperature is suitably from 5 to 40 ° C, preferably from 15 to 30 ° C.

According to the present invention, a mixed contaminant consisting of scale substances such as calcium sulfate and silica and organic substances such as microorganisms and metabolites thereof, which is difficult to remove by the conventional cleaning method, causes deterioration of the film. It can be removed efficiently without the need.

[0039]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram for explaining a module cleaning test apparatus used for carrying out the present invention.

In the illustrated apparatus, raw water is stored in a raw water tank 1 and then transferred by a transfer pump 2 to a membrane pretreatment device (Co., Ltd.).
Kuraray ML-7101 (0602)) 3
After the turbid components in the raw water are removed, the raw water is stored in the permeated water tank 4. When cleaning the module, the cleaning liquid is adjusted in the cleaning tank 5 and supplied to the module 7 by the cleaning pump 6. When removing the cleaning liquid, the permeated water is supplied from a permeated water tank 4 to an RO (reverse osmosis) pump 8.
And supplied to the module 7 by the high pressure pump 9.

[0042]

EXAMPLE A comparative test of the cleaning effect of the method of the present invention and the conventional method was conducted using the above-described module cleaning test apparatus.
The removal rate of the mixed contaminants showing the effect of the film cleaning in the examples was obtained by the following equation.

Removal rate (%) = (1−conductivity in membrane permeate / conductivity in membrane feed solution) × 100 Example 1 Industrial water was used as raw water, and this water was used to remove turbid components in the raw water. Water was passed through a coagulation filtration device for removal, and supplied to a reverse osmosis membrane device (Toray Industries, Ltd., SU-720, spiral type reverse osmosis membrane). The coagulation filtration device is a device in which a stirring tank is provided on a filter, and raw water to which PAC (polyaluminum chloride) or the like is added as a coagulant is stirred in the stirring tank to form micro flocs. The raw water that has produced the microfloc flows into the lower anthracite-sand filter having a two-layer structure, where the filtration operation is performed, and the water becomes clear without turbidity.

SU-720 used for the reverse osmosis membrane is a spiral type reverse osmosis membrane module. The reverse osmosis membrane is formed into a flat membrane, processed into a bag shape with a woven fabric flow path agent interposed therebetween, and mesh spacers are formed. The parts are overlapped and wrapped around a tube with a number of holes on the outer periphery in a nori roll. Only water that has passed through the column-wound reverse osmosis membrane collects in the central tube, and the concentrated water is discharged from one end of the column.

The average supply water temperature to the reverse osmosis membrane device is 20
° C, operating pressure 15 kg / cm ² , water recovery rate 60%
And the continuous operation was performed for 24 hours. The water quality of the raw water and the membrane permeated water one week after the start of the operation was as shown in Table 1.

[0046]

[Table 1] The amount of membrane permeated water began to decrease from about 2200 hours after the start of operation, and the amount of membrane permeated water was reduced by 32% compared to the initial membrane permeated water amount by about 5000 hours of operation. The module was pulled out and subjected to a washing test of the module under the following conditions.

First stage cleaning 100 l of a 0.2% by weight aqueous solution of oxalic acid adjusted to pH 2 using sodium hydroxide was placed in a cleaning tank 5
And supplied to the module 7 pulled out from the reverse osmosis membrane device. At this time, the cleaning liquid flowing out from the permeation side and the concentration side of the module is returned to the tank 5,
The circulation operation was performed for a minute. After the circulation operation, the pump 6 was stopped and allowed to stand for 60 minutes. During this time the cleaning tank 5
The washing liquid in the inside was discharged. A sample in which the first-stage cleaning was omitted was designated as Comparative Example 1, and the effects were compared.

Second stage cleaning 100 l of a 1.0% by weight aqueous formalin solution adjusted to pH 12 using sodium hydroxide was adjusted in the cleaning tank 5 and supplied to the module 7. On this occasion,
The cleaning liquid flowing out from the permeating side and the concentrating side of the module is returned to the tank 5 and supplied for 30 minutes. Further, permeated water is supplied by the pumps 8 and 9 so that the formalin concentration in the washing water becomes 0 ppm and the pH is medium. Washing was carried out until it became sexual. In order to confirm the effect of the washing method, before and after the washing, the water temperature was adjusted to 25 ° C. and 1500 pp.
The module was evaluated using an aqueous sodium chloride solution. Table 2 (Example 1) and Table 3 (Comparative Example 1) show the results of comparison with the module performance when new (when shipped from the manufacturer).

[0049]

[Table 2]

[Table 3] As is clear from Tables 2 and 3, the membrane permeated water amount in the case of performing the first-stage cleaning is regenerating more than when new, but the first-stage washing with the acidic solution is omitted. Although there is no great difference in the removal rate in the cleaning method of Comparative Example 1, the amount of permeated water is regenerated only up to about 80% of that of a new product. Thus, it can be said that the first-stage cleaning with the acidic solution is necessary to further enhance the cleaning effect in the second stage.

Example 2 A module was pulled out of the reverse osmosis membrane device after the same operation as in Example 1 for about 5000 hours, and a washing test was performed under the following conditions.

First stage washing 100 l of a 0.2% by weight aqueous oxalic acid solution adjusted to pH 2 using sodium hydroxide was circulated for 30 minutes,
Allowed to stand for minutes and drained.

Second stage washing pH 10 using sodium hydroxide (Comparative Example 2
100 l of an aqueous solution containing 1.0% by weight of sodium dodecylbenzenesulfonate adjusted in 8) was circulated for 30 minutes, allowed to stand for 120 minutes, and discharged. Subsequently, washing with water was performed until the bubbling of the washing water disappeared, the formalin concentration in the washing water became 0 ppm, and the pH became neutral. In order to confirm the effect of the washing method, before and after the washing, 1500 pp adjusted to a water temperature of 25 ° C.
The module was evaluated using an aqueous sodium chloride solution. Table 4 (Example 2) and Table 5 (Comparative Example 2) show the results of comparison with the performance of the module when new (when shipped from the manufacturer).

[Table 4]

[Table 5] Here, the comparison was performed by changing the pH of the second-stage cleaning solution. As is clear from Tables 4 and 5, the pH of the washing solution
Is 8 in Comparative Example 2 (Table 5), although there is no difference in the removal rate from the example, but a large difference in the amount of water permeated through the membrane. That is, in the cleaning method of the second embodiment, regeneration is performed almost up to the amount of membrane permeated water at the time of a new article, whereas in the comparative example 2, the regeneration rate is only about 77% of that at the time of a new article. Accordingly, in order to effectively remove the contaminants attached to the film, the p of the cleaning solution in the second stage is required.
It can be said that H needs to be 9 to 10 or more.

As can be seen from the above examples, according to the present invention, it is possible to remove scale substances such as calcium sulfate and silica and organic substances such as microorganisms and metabolites thereof, which are difficult to remove by the conventional washing method. It can be said that mixed contaminants can be efficiently removed without causing deterioration of the film.

[Brief description of the drawings]

FIG. 1 is a view for explaining a flowchart of a module cleaning test apparatus for performing a cleaning test according to the present invention.

[Explanation of symbols]

1 ... raw water tank, 2 ... transfer pump, 3 ... membrane pretreatment device, 4 ... filtered water tank, 5 ... cleaning tank, 6 ... cleaning pump, 7 ... module, 8
…… RO (reverse osmosis) pump, 9 …… High pressure pump

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukihiro Nomura 2-9-8 Okada, Atsugi-shi, Kanagawa Prefecture Nomura MicroScience Co., Ltd. (72) Masahiko Kogure 2- 9-8 Okada, Atsugi-shi, Kanagawa Prefecture No. Nomura Micro Science Co., Ltd. (72) Inventor Tsutomu Abe 2-9-8 Okada, Atsugi-shi, Kanagawa Nomura Micro Science Co., Ltd.

Claims (6)

[Claims] 1. A method for washing and regenerating a separation membrane for water treatment comprising at least two washing steps, wherein a first washing step of washing the membrane of the separation membrane for water treatment with an acidic solution, A method for cleaning and regenerating a reverse osmosis membrane, comprising sequentially performing a second washing step of washing with an alkaline solution containing an agent. 2. A method for cleaning and regenerating a separation membrane for water treatment comprising at least two washing steps, wherein a first washing step of washing the membrane of the separation membrane for water treatment with an acidic solution, A method for washing and regenerating a separation membrane for water treatment, comprising sequentially performing a second washing step of washing with an alkaline solution containing an agent and a surfactant. 3. The method for cleaning and regenerating a separation membrane for water treatment according to claim 1, wherein the separation membrane for water treatment is a reverse osmosis membrane. 4. The method for cleaning and regenerating a separation membrane for water treatment according to claim 1, wherein the acid contained in the acidic solution used for the first-stage cleaning is an organic acid. 5. The pH of the acidic solution used for the first-stage washing is 6 or less.
The method for washing and regenerating a separation membrane for water treatment according to any one of the above. 6. The pH of the alkaline solution used for the second-stage cleaning is 9 or more.
6. The method for washing and regenerating a separation membrane for water treatment according to any one of items 1 to 5.