JPH119973A - Method for filtration back-washing of membrane module for turbidity removal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for filtration back washing of a membrane module for turbidity removal by which high fluxes are obtained and by which the membrane module can stably and continuously be driven for a long duration. SOLUTION: At the time when filtered water is obtained from raw water by employing a membrane module 5 for turbidity removal and comprising hollow-yarn membranes, this method for filtration back-washing of the module 5 for turbidity removal is carried out by properly combining a back washing process of back-washing the membrane module 5 by back-washing water mixed with a disinfectant 8 and a back-washing process of back washing the module 5 by back-washing water mixed with an acid 9 with a filtration process of filtering raw water 1 by the membrane module 5 to provide filtered water. In this case, the acid 9 may be citric acid, ammonium dihydrogen citrate, or a mixed acid of citric acid and glycolic acid and the acid is so added as to control the concentration of the acid (in the case of conversion of the acid into citric acid) in the membrane module to be 50-1500 mg/l or an inorganic acid is used and the inorganic acid is so added as to control the pH in the membrane module 5 to be 1.0-3.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for backwashing a clarifying membrane module by filtration, and more particularly to a clarifying membrane module comprising a hollow fiber membrane using river water, industrial water or the like as raw water. The present invention relates to a method for backwashing a membrane module for turbidity in a method of performing a filtration operation to obtain filtered water.

[0002]

2. Description of the Related Art Conventional water quality of general river water and industrial water is described as follows. Raw water contains mineral fine particles, microorganisms, algae, etc. as turbid components. In addition, humic substances, microbial organisms, and high molecular organic substances generated by decomposition of algae may be included. In order to remove these components, a coagulation filtration method or a coagulation sedimentation filtration method in which a flocculant is injected to form a floc and then filtered is conventionally applied depending on the application. In addition to these conventional general treatment methods, a membrane filtration method has recently been developed. In this method, raw water that is difficult to treat by the conventional method, that is, since there is little turbidity, the purpose is to inject kaolin or the like as a turbidity and to promote floc formation by a flocculant,
Furthermore, in order to minimize the leakage concentration of aluminum from the coagulant such as polyaluminum chloride (PAC) into the filtered water, even in the case of raw water that requires pH adjustment (injection of acid or alkali), the coagulant may be used. Without using
By membrane filtration, filtered water with very good water quality can be obtained, the amount of generated sludge can be reduced, the operation method, maintenance and management are easy, the installation area is small, compact Because of various advantages, a method for removing turbidity using a membrane module using a UF membrane and an MF membrane has been studied and put into practical use.

[0003] When the chromaticity of raw water is due to organic matter, for example, PAC or the like as a coagulant is injected into the raw water in the filtration step of several mg / liter as aluminum in order to remove it.
In this case, the injection amount of PAC tends to be smaller than that of the conventional method, but the countermeasure against leakage of aluminum into the filtered water is the same as that of the conventional method, and the merit thereof is slightly reduced. Usually, in a filtration backwashing method using a hollow fiber membrane, the filtration step is usually performed for 15 to 90 minutes, and enters the backwashing step. During the filtration step, raw water is passed from the inside to the outside of the membrane in the case of the internal pressure type, and from the outside to the inside of the membrane in the case of the external pressure type. Therefore, the flow direction of the backwash water during the backwash process is completely opposite between the internal pressure type and the external pressure type. Regardless of the internal pressure type or the external pressure type, in general, cross-flow filtration is often used to increase the flow velocity on the membrane surface and prevent the adhesion of turbid matter to the membrane surface as much as possible. About 5 to 50% of the water is filtered water. And the remaining 5
0 to 95% always circulates in the system as raw water.

[0004] The total filtration system is sometimes employed because the power cost for the circulation pump can be reduced as compared with the cross flow system. However, since the flow of the cross flow disappears, the adhesion of the turbidity to the membrane surface is inevitably increased and strong, so it differs depending on the membrane material and the backwashing method,
Chemical cleaning is required periodically, for example, about every 1 to 10 days. Which one to use depends on the total comparison of initial cost, running cost, installation area, ease of maintenance, operation stability, and the like. Taking the conventional internal pressure type, cross-flow type hollow fiber membrane module filtration apparatus as an example, after the filtration step of 15 to 60 minutes is completed, usually a short backwash of about 40 seconds to 2 minutes is performed as described below. This is generally done. Backwash water from the upper part of the module (filtration water outlet, circulating water outlet side) to the lower part of the module (raw water inlet, backwash drainage outlet side) from the outside to the inside of the membrane is about 1.5 to 4 times as high as when filtering. By passing the water at a flow rate for about 20 to 30 seconds, the turbid component that has adhered to the inner surface of the membrane and that has been captured during filtration is discharged out of the system. The same operation may be performed from the lower part of the module to the upper part.

After that, the flashing step is called
Raw water and backwash water are simultaneously passed from the lower part of the module to the upper part, and the turbid component may be discharged out of the system at a higher flow rate. Normally, sodium hypochlorite is used as a disinfectant in the backwash water, and 0.2 to 3.0 mg / liter is injected as residual chlorine in the backwash wastewater. External pressure type, in the example of a cross-flow type hollow fiber membrane module filtration device, generally, after the filtration step, backwash water into which sodium hypochlorite is injected from the inside to the outside of the membrane in the same manner as the internal pressure type, is used. Water is passed at a high flow rate. Furthermore, air is introduced from the lower part of the membrane module periodically (every several hours to several days), air bubbling is performed for several minutes, and the hollow fiber membrane is physically shaken to remove turbidity on the outer surface of the hollow fiber membrane. A backwash method of peeling and discharging is performed. The flat membrane module filtration device is an external pressure type, and a method of obtaining filtered water by suction rather than pressurization is often adopted. In order to simultaneously perform the filtration step and the backwashing step, the air bubbling operation is performed continuously or intermittently in many cases.

[0006] In addition to the above, there have been proposed several backwashing methods as follows. A study of backwash pressure and backwash flow. Air is blown into the hollow fiber so that it becomes turbulent.
Investigating backwashing by changing the pressure, the amount of air, and the amount of water retained in the module (Japanese Patent Laid-Open No. Hei 7-236818). For internal pressure type, especially external pressure type, physical cleaning with a mixture of water and air, that is, an air bubbling operation was studied (JP-A-60-19002, JP-A-61-153104, JP-A-2-164423, JP-A-4-110023, JP-A-6-23246). In the external pressure type and cross-flow type filtration, a physical cleaning method in which water and air are mixed after the process where free chlorine is detected in the backwash waste liquid each time was examined (Japanese Patent Laid-Open No. 7-27).
5672).

[0007] Further, it is known to carry out backwashing using sodium hypochlorite (NaOCl) as a disinfectant, that is, backwashing water into which free chlorine is injected, and a flux (unit membrane area and unit time) is used. Normal unit m with different filtered water flow rate
³ / m ² · day) is known to have a stabilizing effect. For example, in order to reduce membrane contamination of the UF membrane, 3.5 m of free chlorine is used by using sodium hypochlorite as backwash water.
The method of injecting g / liter is known to be effective. The free chlorine in the backwash wastewater at this time is 0.1 to 1 mg.
Per liter. In the method of operating the hollow fiber membrane, as described above, continuous operation is repeatedly performed with a short operation of filtration for 15 to 90 minutes and backwashing for 40 seconds to 2 minutes. When the flux decreases, or when the membrane inlet pressure (pressure loss of the membrane) rises and exceeds the set value, the design value of the flux is maintained constant, so that the hollow fiber membrane in the module is damaged. Chemical cleaning is performed to prevent the occurrence. Chemicals for chemical cleaning are roughly divided into two. One is a disinfectant, an oxidizing agent, etc., which disinfects and dissolves microorganisms, organic substances, etc., and improves the removability of turbidity from the film, for example, sodium hypochlorite, hydrogen peroxide,
Caustic soda, ozone and the like. The other is citric acid, oxalic acid, and other organic acids having a chelating action. Further, an inorganic acid such as hydrochloric acid is also used.

In consideration of the chemical resistance of the membrane and the state of contamination of the membrane, one or more effective ones are selected, and their concentration, contact time, contact liquid temperature, etc. are determined, and circulating cleaning or An immersion treatment is performed. The frequency varies widely from one day to several months. In general, the concentration of a chemical used for chemical cleaning is high, the concentration of sodium hypochlorite is about 50 to 500 mg / liter, and in the case of a film material to which sodium hypochlorite cannot be applied, caustic soda is used.
The concentration is determined by the pH resistance of the film material. The concentration of hydrochloric acid is also determined by a pH-resistant rack made of a membrane material, and the pH is often about 1.0 to 3.0.
The concentration of citric acid is usually about 0.5 to 2.0%. And in order to maintain high flux,
In many cases, chemical cleaning is carried out as frequently as every 0 days and using a highly concentrated solution having a concentration of several percent.

As described above, various improvements have been proposed and implemented. However, during a chemical cleaning operation due to frequent chemical cleaning, the apparatus is stopped for a considerably long time, during which filtered water is obtained. The problem of disappearance, when the turbid components of the raw water tend to adhere to the membrane surface, or when the concentration of the turbid is high, and further, as the water temperature of the raw water becomes as low as 10 ° C. or lower, 1/2 to 1/4 of normal flux
Low flux, and the flux decreases quickly. As a result, the time during which continuous operation can be performed is shortened, and it is necessary to allow the apparatus to have a margin to maintain the design flow rate stably, and it is necessary to increase the apparatus capacity or increase the number of series at the time of design. There are disadvantages. Therefore, there is a problem that the merit of the membrane application itself is reduced in terms of initial cost, running cost, maintenance and the like as compared with the conventional general processing method. Originally, there is a demand for a filtration backwashing method that can stably maintain a high flux of a membrane for a long period of time and that is easy to maintain.

[0010]

SUMMARY OF THE INVENTION In view of the above prior art, the present invention uses an internal pressure type as an operation method using a hollow fiber membrane,
It can be applied to the external pressure type cross-flow system, total filtration system, UF membrane and MF membrane as membrane materials, and can obtain high flux and stable continuous long-term flux. It is an object of the present invention to provide a method for backwashing a membrane module for turbidity by filtration, which can suppress the tendency of decrease in water content and perform an appropriate (filtration-backwashing) operation.

[0011]

In order to solve the above problems, in the present invention, when obtaining filtered water from raw water using a membrane module for turbidity comprising a hollow fiber membrane, the raw water is passed through the membrane module. In the filtration step of obtaining filtered water, a backwash step of backwashing the membrane module with backwash water injected with a bactericide and a backwash step of backwashing with an acid-injected backwash water are performed in an appropriate combination. A method for backwashing a membrane module for turbidity, characterized by the above feature. In the method, citric acid, ammonium dihydrogen citrate, or a mixed acid of citric acid and glycolic acid is used as the acid, and the concentration in the membrane module is 50 to 1500 mg as citric acid.
/ Liter or using an inorganic acid so that the pH in the membrane module becomes 1.0 to 3.0. In addition, the back washing step of injecting the acid is performed in 15
The backwashing step is preferably performed using backwash water heated to ４０40 ° C., and before or after backwashing of the membrane module, a raw water circulation piping system or a chemical for chemical washing is used via the membrane module. The washing is preferably performed by passing the above-mentioned washing water into which the acid or the germicide is injected into a piping system including a storage tank.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied the raw water state, the filtration and backwashing method, and the state of flux decrease in order to suppress the tendency of flux decrease and to carry out appropriate filtration-backwash operation. As a result, they found that the problems to be solved are summarized in the following two points. Prevention of membrane contamination, measures for lowering raw water temperature And, the basic problems mainly related to raw water quality and backwashing method, module structure, membrane material, filtration time (the amount of suspended solids per filtration process) ), Etc., have a considerable effect, but it is highly expected that they will be improved by future development and study, and it is considered to be a problem that can be solved. The present invention also contributes to this problem. It has also been found that when the raw water quality is a property containing a turbid substance that easily adheres to the hollow fiber membrane, the progress of membrane contamination cannot be slowed (prevented) unless the backwashing method is appropriate.

Is a serious problem in practice. At a water temperature of 15 ° C. or lower, particularly at a temperature of 10 ° C. or lower in winter, the flux increases from 15 ° C. to 25 ° C. due to an increase in the viscosity of water.
At present, it has to be reduced to ２〜 to １ ／.
There is a limit to obtaining the design flow rate by increasing the inlet pressure of the membrane without lowering the flux. Excessive increase may cause damage to the membrane or increase pump power cost (running cost). Various proposals have been made as a countermeasure for the above. At present, a) increasing the inlet pressure of the membrane, b) by the frequent chemical cleaning described above,
Recover the water permeability of the membrane, reduce its resistance as much as possible, and maintain the flux. C) Measure the flux at the time of low water temperature in winter as the value at the time of design and make the capacity of the equipment with a sufficient margin. Has been done. However, none of these methods can be said to be a method for fully utilizing the merits of the film. Therefore, development of a membrane material that can reduce the water permeability resistance of the membrane during filtration has been performed.

Further, the influence of the raw water state was examined in detail. (1) When the raw water is river water or industrial water The quality of river water varies considerably depending on the geology of the river water basin, domestic drainage, industrial drainage, and other inflow conditions. When treating river water directly by using a membrane, the following components are problematic. Aluminum, iron, silica and the like as turbid substances are not soft and fine floc-like substances generated when a coagulant is used, but may be generally described as hard. It is considered that these are often present alone or in combination or mixed. Therefore, it is considered that it does not easily adhere to the film surface, and even if it adheres, it is easily peeled off by backwashing. Suspended substances further include organisms such as microorganisms and algae. These contaminate the membrane and are often difficult to process. Therefore, in order to easily peel off at the time of backwashing, for sterilization of microorganisms and algicidal treatment, the raw water itself contains a disinfectant, for example, sodium hypochlorite as free chlorine for free sterilization, although it differs depending on the membrane material. 2 to 1.5 mg / liter,
Or it is said that it is effective to inject an appropriate amount of other disinfectant and keep it present, or to inject 2 to 5 mg / l as free chlorine into the backwash water at the time of backwash in terms of flux stability. It is the same as described as a known fact.

The chromaticity component has a chromaticity of
The removal performance of the film varies depending on whether it occurs. In the case of iron, it is filtered because it changes from soluble (ionic) to a turbid substance showing chromaticity by oxidation treatment with free chlorine and the like. In the case of manganese, the oxidation is not sufficiently advanced, so that it can be said that most of the manganese passes through the membrane without being filtered. Therefore, a separate measure for manganese removal is required. Conversely, when manganese is present, oxidation by chlorine at the time of backwashing may gradually attach as a turbid substance to the membrane surface on the filtered water side of the membrane, resulting in a decrease in flux. In the case of organic substances such as humic substances,
It is necessary to inject an appropriate amount of a coagulant such as PAC into raw water, perform coagulation treatment, and perform membrane filtration or the like. River water fluctuates depending on the season, and often falls to 10 ° C. or less, and sometimes to 5 ° C. or less in winter, which causes a decrease in flux. Therefore, in order to supply the filtered water stably, the design flux of the apparatus is often based on the flux at the time of low water temperature in winter.

On the other hand, industrial water is subjected to flocculation treatment using river water or the like and a sulfuric acid band as a flocculant, and the supernatant water is supplied to each factory. Therefore, it can be said that the quality of the raw water is unlikely to cause the problem of the chromaticity due to the organic matter. However, although the turbidity is as low as 2 to 6 degrees, the residual aluminum after the coagulation treatment shows a considerably high value of 0.2 to 0.4 mg / l, and sometimes 1.0 mg / l, and a fine, soft floc. And easily adhere to the film surface. Also, since the piping to each factory is long,
Iron from elution from piping is also added to raw water iron,
It shows a high value of up to 1.0 mg / liter, has the same properties as residual aluminum, and easily adheres to the film surface. Industrial water is mostly agglomerated from river water or lake water and supplied to each factory. Like river water, the water temperature varies considerably depending on the season.
Sometimes the water temperature is as low as 5 ° C or less. At such low water temperatures, the same measures as for river water are required. Filtration by membrane was considered to be more difficult in the case of industrial water than in the case of directly targeting river water.

(2) In the case where the raw water is lake water, groundwater, etc. The water quality components of the lake water that cause the flux are different from river water and industrial water,
Depending on the pollution status and sampling depth, it is often a combined effect of microorganisms, algae, and organic matter generated by their decomposition. The effects of mineral turbidity are not expected to be significant. In addition, the raw water temperature often drops to 10 ° C. or less in winter. In many cases, the target of filtration by the membrane is raw water used in a backwashing method or a chemical cleaning method that requires further measures in consideration of the microorganisms, algae, and organic substances. In the case of groundwater, the water quality varies depending on the depth of the pumping well and the geology around it. However, the water temperature is 10
The water temperature is almost constant between -20 ° C and the problem of lowering of flux due to low water temperature is small. Even if iron is present, it is often sufficient to take measures similar to those for industrial water.

However, when manganese is present, as described in (1) above, a separate manganese removal facility is required. Based on the results of the detailed examination of raw water and the results of experiments as described above, the hollow fiber membrane module filtration device itself is applied in the current backwash method of injecting a disinfectant such as sodium hypochlorite during backwash. There is a limit to the raw water that can be produced, and in the case of raw water that exceeds the applicable limit, it is necessary to provide a conventional general pretreatment device as pretreatment or a manganese removal device as posttreatment. In order to overcome this limitation, the inventors of the present invention solve the above-mentioned measures for preventing the progress of membrane contamination and for lowering the raw water temperature by the following means.

Hereinafter, the present invention will be described in detail. The present invention, as raw water, river water, lake water, groundwater, and when using industrial water that has been subjected to a primary treatment of these, further, as a turbid component, when filtering raw water containing iron, aluminum, etc., when collecting and reusing, Alternatively, it can be suitably applied to a case where seawater is used as raw water. The following is a description of an example of industrial water as raw water that is more difficult to filter by a membrane.
As described above, industrial water is subjected to coagulation treatment using sulfuric acid bands using river water or the like as a coagulant, and the supernatant water is supplied to each factory or the like. Therefore, although the turbidity is as low as 2 to 6 degrees, the residual aluminum at the time of aggregation is 0.2 to 0.4 mg / liter,
Sometimes it is 1.0 mg / liter. Usually, it is several times as large as 0.05 to 0.15 mg / liter, which is aluminum remaining in drinking water treated by the coagulation sedimentation filtration method. In addition, iron which is eluted from the long pipe of industrial water is added to iron of raw water, and shows a high value of about 0.2 to 1.0 mg / liter. These show a fine and soft floc shape and easily adhere to the film surface. Organic substances are generally not so high because they have been treated once with a sulfuric acid band, and have a chromaticity of about 10 to 20 degrees. However, organic substances are few and most of them are mainly iron.

The cause of the membrane contamination is that in the case of the internal pressure type hollow fiber membrane module, from the long-term operation results, the turbidity, which is a fine, soft floc-like composite of aluminum and iron, is usually found. Is not sufficiently discharged by backwashing, adheres to the film surface and in the film little by little and remains,
It accumulates and covers the inner surface of the hollow fiber membrane, eventually causing a phenomenon that the inner surface is clogged. Then, it was determined that the number of hollow fiber membranes at which water no longer flows gradually increased, that is, the process of decreasing the flux by decreasing the effective membrane area followed the process of decreasing the flux. Since the above-mentioned phenomenon is more likely to occur than when river water is directly filtered, it can be called troublesome or raw water. In the case of the external pressure type hollow fiber membrane module, it is determined that the turbid substance having high adhesion to the membrane surface causes the hollow fiber membranes to adhere to each other and similarly reduces the effective membrane area that can be filtered as a whole. In particular, turbidity adhered to the upper and lower membrane fixing portions of the hollow fiber membrane module is difficult to remove by ordinary backwashing.

As a result of various experiments, in normal backwashing, sodium hypochlorite was typically added to the backwash water as a bactericide to prevent the flux from decreasing due to accumulation of microorganisms in the raw water. About 5 to about 5 mg / liter, so that about 0.5 to about 3.0 mg / liter of free chlorine remains in the backwash wastewater. It is better to do this every backwash. However, when the amount of microorganisms is extremely small, it may be appropriately performed once every several times of (filtration-backwashing). The disinfectant may be hydrogen peroxide, ozone, or the like, as long as the material of the membrane can withstand, other than sodium hypochlorite, and a concentration effective for disinfecting microorganisms or removing turbid matter may be injected. Then, after performing [backwashing by sterilizing agent injection and filtration for 15 to 90 minutes] several times to several tens of times, the phenomenon that the hollow fiber membrane inner surface due to the turbidity is clogged is suppressed and eliminated. , Backwash by acid injection. The frequency depends on the condition of raw water, operating conditions,
It depends on the film material, but it is performed as follows.

In the case of ordinary backwashing, the film adheres and remains on the inner surface of the membrane, and excessive turbidity causing a reduction in flux accumulates excessively.
Before the conventional chemical cleaning is required, that is, while the turbidity accumulation in the hollow fiber membrane is at a low level, the concentrated turbidity is periodically removed by performing a low concentration acid injection backwash. Dissolution,
Or, the basic idea of the present invention is to promote solubility and releasability from the inner and outer surfaces of the hollow fiber membrane and the inside of the membrane. Dissolves suspended matter and removes acid at a low concentration to a certain extent
At regular intervals of (filtration-backwashing), it is injected at the time of backwashing periodically to prevent and reduce accumulation of turbid matter. Here, the conventional chemical cleaning means, for example,
Circulating solution treatment with 0.5-2.5% citric acid is performed for several hours to one day. Similarly, 50 to 300 mg / liter of sodium hypochlorite (as Cl ₂ ) is circulated and washed, and the immersion time is several hours to 1 day longer than that of citric acid. Washing performed by appropriately combining the above.

In the present invention, in the case of a general film material, it is not preferable to simultaneously inject a bactericide and an acid. This is because a disinfectant, particularly free chlorine, promotes deterioration of the hollow fiber membrane itself under acidic conditions. For example, any material such as polyvinylidene fluoride that can withstand free chlorine and ozone can be used. The acid used in the present invention is suitably citric acid alone, a mixed acid of citric acid and glycolic acid, ammonium dihydrogen citrate, or an inorganic acid, hydrochloric acid. Other organic acids, inorganic acids, and complexing agents can be used, but in consideration of safety in handling, safety in the event of leakage into filtered water, use concentration and its effect (running cost), etc. The above-mentioned acids are suitable. For example, citric acid is neither a deleterious substance nor a poisonous substance, is easy to handle, is permitted as a food additive, and is also added for soft drinks. In addition, the injection amount during acid cleaning is also 50 to 1500 m.
g / liter, preferably about 200 to 600 mg / liter. For example, if the amount of water held in the system per module with a membrane area of 50 m ² is about 50 liters,
The total amount used is as small as about 10 to 30 g per backwash.

The mixed acid of citric acid and glycolic acid is, for example, a mixed acid of citric acid (-hydrate) and glycolic acid (70%) at a ratio of 1: 1. Ammonium dihydrogen citrate is a solution in which ammonia (NH ₃ , molecular weight 17) is injected into citric acid (molecular weight 192) at a ratio of 1: 1 and mixed to adjust the pH to about 3.5 to 4.0. is there. These are chemicals often used for chemical cleaning of piping and the like. Ammonium dihydrogen citrate has a much higher ability to dissolve iron oxide than citric acid. However, it is necessary to treat nitrogen (N) in the backwash waste liquid, and glycolic acid is not a deleterious substance or poisonous substance, but its unit price is considerably high.
Therefore, as described above, it is preferable to use citric acid alone, which is simple in handling, the unit price is not so high, and the wastewater is easily biotreated. Care must be taken when handling hydrochloric acid, but even if it slightly leaks into the filtered water, it reacts with the bicarbonate of the raw water to produce salts such as NaCl and carbon dioxide, and the filtered water becomes acidic. Not
No problem. Taking the case where the membrane material is a cellulose acetate type as an example, it can withstand up to about pH 2.0, so the total amount of use depends on the quality of the raw water, if it is determined in the same manner as citric acid per acid backwashing. 50m film area
² to 60 g of 35% hydrochloric acid per module
It is about.

Further, as a result of experiments, the present invention shows that low-temperature filtered water used as backwashing water is used at 15 ° C. to 40 ° C., preferably at 18 ° C. to 2
By heating to about 5 ° C., it was found that the backwashing at the time of the acid injection was effective. That is, as described above, dissolution of the suspended matter adhered and accumulated on the inner and outer surfaces of the hollow fiber and in the membrane, and the releasability thereof can be more easily performed. Therefore, heated backwash water is not required at every backwash, and it is sufficient to apply only at the time of injecting a low-concentration acid. Citric acid at 15 ° C
In the following, the effect is small, the heat resistance of the film material is high, and the running cost is as high as 25 ° C. to 40 ° C. as long as it is within an allowable range. This is because the action mechanism of citric acid is a chelating action (complex ion forming action), so that the low concentration used in the present invention can be used without applying the concentration of several% used in pipe washing or general chemical washing. 50 to 1500 mg / l, preferably 200 to 600 mg / l has the same action mechanism, and sufficiently acts as a chelating agent on iron, aluminum, manganese, calcium and the like constituting the turbid substance, and turbidity as a whole. It seems to facilitate dissolution and exfoliation of the quality.

On the other hand, since hydrochloric acid does not have the effect of a chelating agent, it is considered that the dissolution of a part of the turbidity causes the turbidity to be easily separated by backwashing. In order to promote this, the pH in the membrane module is generally set to the range of 1.5 to 3.0, which is allowed by the material of the membrane, and the temperature is also set to 1
The temperature is preferably set to 8 ° C to 40 ° C, preferably 25 ° C to 40 ° C, which is as high as possible than that of citric acid and lower than the heat resistance of the membrane. The above-mentioned acids may be set at a temperature of 40 ° C. or higher if the heat resistance of the film material and the running cost do not matter. In the present invention, in the case of river water, lake water and the like, if the raw water contains a considerable amount of suspended matter derived from organic matter, before backwashing by low-concentration acid injection of the present invention,
Alternatively, the germicide used in the present invention is used as an oxidizing agent for decomposing organic substances, that is, decomposing turbidity adhering to the membrane, or promoting releasability. It is effective to inject into a piping system including a chemical storage tank for use and to perform a circulation operation through the membrane module to wash the hollow fiber membrane surface.

The concentration of the bactericide (oxidizing agent) in the circulation piping system at this time depends on the chlorine resistance of the membrane. For example, sodium hypochlorite is 20 to 300 mg / liter, preferably 20 to 60 mg / liter. Inject so that liters are maintained. If there is an organic substance on the film surface, etc., free chlorine will be consumed.
/ Circulation and wash with circulation. The process at this time is roughly divided as follows, and is determined according to the quality of raw water. Example) a: circulating washing with an oxidizing agent such as sodium hypochlorite b: back washing with an acid such as low-concentration citric acid Combination example: ab, aba, ba, ba
-B

Next, an example of a specific process of the present invention of the internal pressure type cross flow system will be described below. (1) Filtration step; 30 minutes, flux: 1.0 to
2.5 m ³ / m ² · day, (2) Backwashing step of injecting a bactericide; Downflow backwash: 20 to 30 seconds, Free chlorine: 2 to 5 m
g / liter injection Upflow backwash: 20-30 seconds, free chlorine: 2-5m
g / liter injection Flushing: 20-40 seconds, Free chlorine: 2-5m
The g / liter injection flushing is performed once every several to ten to several times (filtration-backwashing). For example, upflow backwashing is performed with [backwashing water + raw water]. The flushing may be omitted when the flux is sufficiently recovered by the backwashing operation or the backwashing step of injecting an acid described below. Similarly, when flushing is performed, the downflow backwash or the upflow backwash may be omitted. Further, free chlorine at the time of flushing may not be injected when the presence of free chlorine becomes a problem in a later step.

(3) Backwashing step of injecting acid; Circulation-1: 30 seconds to 10 minutes, Injection of acid:
Yes, backwash water: heating downflow backwash: 20-30 seconds, acid injection:
Yes, backwash water: heating Upflow backwash: 20-30 seconds, acid injection:
Yes, backwash water: heating Circulation-2: 30 seconds to 10 minutes, injection of acid:
Yes, backwash water: heating Blow (water replacement): 30 seconds to 3 minutes, acid injection: no,
Raw water flushing: 20-40 seconds, acid injection:
The operation of none, raw water + backwash water is exactly the same, and if it is judged that the contamination of the hollow fiber membrane is large, perform the operation. Usually incorporating [----], [----],
What is necessary is to perform a series of operations such as [----], that is, without injecting the acid, discharging the dissolved and exfoliated turbidity in the module and piping, and the injected acid, and remaining in the system You need to do that to avoid it. Flushing may not be performed as long as blowing (water replacement) is sufficient.

In the present invention, the above-described backwashing step and filtration step are combined, for example, as follows, and continuous operation is performed without performing conventional chemical cleaning. The above-mentioned backwashing method is defined as the following A to D, and the whole filtration (→),
An example of the combination of backwashing is as follows. A: Backwashing step of injecting germicide (+): flushing step, no B: Backwashing step of injecting germicide (+): Flashing step, C: Backwashing step of injecting acid: injecting of germicide No flushing, blow process, yes D: Circulation washing with C + disinfectant (oxidizing agent) →: Filtration process Operation example 1), [A → A → A → B → A → A → C →] repetition Operation example 2 ), Repetition of [A → A → A → A → A → A → C →] Operation example 3), [A → A → A → A → A → A → B → A → A →
Repeating A → A → A → A → C →] Operation example 4), [A → A → A → A → A → A → B → A → A →
A → A → A → A → B →], etc., and C is performed about 1 to 3 times a day. In operation examples 5) and 4), C performs semi-automatically, once every several days to several weeks, as necessary, while observing the driving situation. Driving Examples 6) and D are performed semi-automatically as necessary when the raw water quality deteriorates in Examples 1) to 5).

Next, a specific implementation method will be described with reference to the internal pressure type cross flow process diagram shown in FIG. The raw water 1 in the raw water tank 2 is automatically filtered by the raw water pump P1 into the automatic filter 3 (8
0-100 mesh), and furthermore, circulation pump P2
The filter water is introduced into the hollow fiber membrane inner surface from the lower part of the module 5, 40 to 45% of the filtrate is filtered, the filtered water outlet valve V 2 a is opened from the filtered water line 12, the filtered water tank 6 is received, and the filtered water 14 is obtained. Further, a certain amount of filtered water required for backwashing is received in the backwashing water tank 7 by opening the backwashed filtered water outlet valve V2b. V2b may be eliminated, and filtered water required for backwashing may be stored in the backwashing water tank 7 by a water pump (not shown) provided in the filtered water tank 6. On the other hand, the remaining 55 to 60% of the raw water repeats circulation through the cross flow line 11 and the circulation valve V1. The flow rate of the filtered raw water is supplied by the raw water pump P1. The turbid matter having a large particle diameter captured by the automatic filter 3 opens the valve of the drain line 4 and periodically discharges 1.5 to 2.0 times the amount of water retained in the automatic filter 3. Then, after filtering for 15 to 60 minutes, the aforementioned A, B,
Backwashing of C is performed as follows.

In A, basically, the backwash water discharge valve V
7a is opened, and backwash water inlet valve V3 and backwash drain outlet valve V3 are used by backwash pump P3 using unheated backwash water.
5 open and sodium hypochlorite injection pump P
4 and start from storage tank 8 to backwash line as free chlorine
A downward flow backwash (backwash step) is performed for 20 to 30 seconds while pouring the inside of the module to 5 mg / liter.
Next, similarly, the backwash water inlet valve V4 and the backwash drain outlet valve V6 are opened to perform an upward flow backwash (backwash step). In B, after the step of A, the blowing step is performed as follows. The raw water pump P1 and the circulation pump P2 are started, the backwash drainage outlet valve V6 is opened, and the suspended matter in the hollow fiber membrane is discharged. At this time, it is preferable that the circulation pump is controlled by an inverter to increase the flow velocity on the hollow fiber membrane surface. Also, at this time, the backwash pump P3 may be started to introduce backwash water, also serving as a flushing step. At the time of acid backwashing of C, the backwashing water in the backwashing water tank 7 used at the time of acid injection is heated to 15 to 40 by the heating device 10.
℃, preferably 18-25 ℃ considering running cost
About. The heating means uses an electric heater or a heat exchanger using steam, etc., is stirred by a pump or the like so that the water temperature is averaged, and is controlled by a temperature switch TS. At the time of acid backwashing, V7b is opened, the backwash pump P3 is started, and the backwash water inlet valve V3 and the backwash drain outlet valve V5.
Is opened, and a downflow backwash (backwash step) is performed for 20 to 30 seconds.

At this time, the backwashing acid pump P5 is started from the acid storage tank 9 at the common backwashing line, and the acid is injected so as to have a low concentration according to the present invention. Similarly, the backwash water inlet valve V4 and the backwash drain outlet valve V6 are opened, and the upward backflow (backwash step) is performed for 20 to 30 seconds. Either or both of the upflow backwash and the downflow backwash may be performed as necessary. Next, the above-mentioned circulation pump P2 is started, the module 5, the cross flow line 11, and the circulation valve V1 are opened, and the circulation acid pump P6 is started from the acid storage tank 9, and any position in the circulation line system may be used. For example, circulation is performed for 30 seconds to 10 minutes while injecting an acid at * 3. The injection of the acid is performed when the concentration in the circulation system is 50 to 15 as citric acid.
200 mg / liter, preferably 200 to 6 with citric acid
Stop when 00 mg / l is reached. This is the same in the case of mixed acid of citric acid and glycolic acid and ammonium dihydrogen citrate. When the pressure in the system increases due to the injection of the acid, for example, the backwash drain valve V6 is sometimes opened by a pressure switch (not shown) or a timer, and the pressure in the system is reduced below the pressure of the hollow fiber membrane, preferably 0. 0.5 to 2 kg
Circulation (backwash step, circulation-2) is performed at f / cm ² or less. The circulation flow rate at this time is preferably as large as the flow rate of the hollow fiber membrane surface, and may be, for example, about 8 to 15 m ³ / h in the above-described 50 m ² membrane module, but a pressure loss between the module inlet and the outlet is allowed. Make it as large as possible in the range. Therefore, the opening of the circulation valve V1 is adjusted and the circulation pump P
2. Inverter control and the like are performed.

Next, a blowing step (water replacement) is performed as follows. The raw water pump P1 and the circulating pump P2 are started, and the circulating valve V1 and the backwash drain valve V6 are opened to circulate, and water is replaced in the circulating line. At this time, the backwash pump P3 also starts up,
If the backwash water inlet valve V4 or V3 is opened to introduce backwash water, the membrane surface flow rate on the inner surface of the hollow fiber membrane can be further increased. In this case, the necessity of performing the above-described flushing step is reduced. When D is performed, A is performed and then performed as follows. While the circulation valve V1 is opened and the circulation pump P2 is activated and circulated, the circulation cleaning sodium hypochlorite injection pump P
7 is started and the free chlorine concentration in the circulating system is maintained at 20 to 60 mg / liter while being injected into the injection point of * 4, for example, and circulatingly washed for 3 to 15 minutes, for example. At this time, the pressure of the circulating system is detected by a pressure switch or the like, and the pressure of the backwash drain valve V6 is adjusted to 0.4 to ² kgf / cm ^2.
Etc. are regularly opened for a certain period of time. Also, it is preferable to make the circulation flow rate as large as possible as in C. In general, the necessity of the operation of D is often considered to be semi-automatic instead of being incorporated in the automatic, since the nature of the raw water often differs depending on the sampling point and the season.

In the case of the external pressure type, usually, backwashing corresponding to the internal pressure type backwash A is performed, and air bubbling corresponding to the internal pressure type flushing step is periodically performed in addition to the flow of FIG. Although not provided, a compressor as an air source, air injection piping and an automatic valve at the lower part of the module, and air and water discharge piping and an automatic valve (equivalent to 11, V6 in FIG. 1) at the upper part of the module are provided. The bubbling operation is periodically performed to shake the hollow fiber membrane, to remove the turbidity mainly attached to the outer surface of the membrane, and then to wash the water in the module with a backwash drain valve at the bottom of the module (equivalent to V5 in FIG. 1) Discharged from When the operation is performed by the total filtration method, the circulation pump P2, the circulation valve V1, and the piping connected thereto are provided in FIG. 1, but they are not normally used. However, at the time of backwashing with a low concentration of acid according to the present invention, the operation is performed as described for the internal pressure type to wash the module.

[0036]

The present invention will be described below in more detail with reference to examples. Example 1 Processing of the internal pressure type cross flow system according to the processing flow of FIG. 1 was performed. (1) Raw water: Industrial water The water quality is as shown in Table 1 below.

(2) Operating conditions 1) Membrane module; membrane area: 50 m ² (total area inside hollow fiber membrane), module: 1, membrane material: CA membrane (UF)
Membrane) 2) Operation method: Cross flow method: filtered water, 45%, recovery rate Filtration time: symbol → 30 minutes Actual flux: 1.5 m ³ / m ² · day Backwash process: Backwash A; Downflow reverse Washing: 20 seconds, Cl ₂ 3 mg / L, Backwash water: Heating (No) Upflow backwash: 20 seconds, Cl ₂ 3 mg / L, Backwash water: Heating (None) Backwash B-1; Backwash A + flushing (starting of raw water pump and backwash pump) 30 seconds, backwash water heating (no) Backwash C; downflow backwash: 20 seconds, acid injection available, backwash water: heated to 20 ° C Upflow backwash: 20 seconds, acid injection Yes, backwash water: heated to 20 ° C Circulation-2: 3 minutes, acid injection yes, backwash water: heated to 20 ° C Blow (water replacement): 30 Second, acid injection: no, using raw water Flushing: 30 seconds, acid injection: none, raw water + backwash water Acid: citric acid injection concentration, about 600 mg / liter (In the circulatory system)

3) Combination example of operation The following combination was used. Operation example 1), repetition of [A → A → A → B → A → A → C →] Operation example 2), Repetition of [A → A → A → A → A → A → C →] Operation example 3) , [A → A → A → A → A → A → B → A → A →
Repeating A → A → A → A → C →] Operation example 4), [A → A → A → A → A → A → B → A → A →
A → A → A → A → B →], etc., and C was performed once a day. In operation examples 5) and 4), C was performed semi-automatically, once every seven days.

4) Results Table 1 shows the quality of the raw water and the filtered water.

[Table 1]

A: In each case, the treated water obtained good water quality shown in Table 1. The actual flux is 1.5 m ³ / m ² · day, and the corrected flux converted to 0.4 kgf / cm ² at 25 ° C. is an operation example) 1, 2, 3, 4, and 5, which are all 3.0 m. High flux was obtained stably at about ³ / m ² · day for a long period of 6 months or more. The injection amount of citric acid is 600 mg / liter in the operation examples 1, 2 and 3, and the operation example)
In 4, 5 it was 1200 mg / liter. b: In addition, although the actual flux was increased to 2.0 m ³ / m ² · day and the same operation was performed, all of the operation examples 1, ² , ³ , and 4 were stable and could be continuously operated for a long period of 6 months or more. Was. The corrected flux at 0.4 kgf / cm ² and 25 ° C. was about 3.0 m ³ / m ² · day, and almost no increase in the membrane inlet pressure was observed. In operation example 5), an actual flux of 2.0 m ³ / m ² · day was similarly obtained stably, but the corrected flux after 6 months was 2.0 m ³ / m ² · day.
Day fell.

Example 2 The same raw water and internal pressure type cross-flow treatment as in Example 1 was carried out using citric acid to a mixed acid of citric acid and glycolic acid, and ammonium dihydrogen citrate. / L, the temperature of the backwash water in the backwash C was set to about 20 ° C., and the operation example 3) [A → A →
A → A → A → A → B → A → A → A → A → A → A → C →]
Was repeatedly operated. All chemicals are stable 6
Months or more of a long period of time, the actual flux is 2.0m ³ / m ² ·
Days were obtained, treatment was good, and treated water quality was almost the same as the values shown in Table 1. During this time, 3.0m ³ / m ²
A correction flux on the order of days was obtained, and almost no increase in the membrane inlet pressure was observed.

Example 3 In the same manner as in Example 1, the raw water and internal pressure type cross-flow treatment was changed from citric acid to hydrochloric acid. .5
From about 2.8. Operation example 1 of Example 1)
The continuous operation time until the correction flux was reduced to 1.0 m ³ / m ² · day was 3.0 to 3.5 months, which was longer than the comparative example described later, but shorter than the case of citric acid and the like.
Conventional chemical cleaning is required.

Example 4 The same raw water as in Example 1 was subjected to an external pressure type cross flow treatment. 1) Membrane module; membrane area: 40 m ² (total area outside the hollow fiber membrane), module: 1, membrane material: PAN (UF)
Membrane) 2) Operation method; Cross flow method: filtered water, 45% recovery Filtration time: symbol → 20 minutes (flow of filtered water, from outside to inside of membrane) Actual flux: 0.5 m ³ / m ² · day

Backwashing step: The direction of backwashing water is completely opposite to that of the internal pressure type. Backwash A; downflow backwash: 15 seconds, Cl ₂ 3 mg / l, backwash water: heating (no) upflow backwash: 15 seconds, Cl ₂ 3 mg / l, backwash water: warming ( None) Backwash B-2; Backwash A + Air Bubbling This step was performed once a day for 40 seconds, and then the water in the module was immediately blown with raw water, replaced, and filled with water. Backwash C: This step was performed once a day, and was performed as follows. Downstream backwash: 15 seconds, with acid injection, backwash water: heated to 20 ° C Upstream backwash: 15 seconds, acid injected, backwash water: heated to 20 ° C Acid: citric acid, in module Concentration: about 600mg
/ Liter Air bubbling: 40 seconds, no acid injection, backwash water:
Heating blow (water replacement): 40 seconds, acid injection: no, using raw water Filling process: 20 seconds, using raw water

3) Example of operation combination Usually, backwash A is performed, and backwash B and C are each performed once a day.
Approximately every 12 hours, B and C were alternately operated. 4) Result Continuous operation for about 3.0 months was completed. After 3.0 months, the correction flux decreased to 1.0 m ³ / m ² · day or less, and the membrane inlet pressure also increased to 2.0 kgf / cm ² , necessitating conventional chemical cleaning. The treated water quality was almost the same as in Table 1 and was good.

Example 5 Using the same raw water and membrane module as in Example 1, the operation of the total filtration system was performed as follows. 1) Operation method; Filtration time: symbol → 30 minutes Actual flux: 1.5 m ³ / m ² · day In the backwashing step, backwashing A is usually performed, and backwashing B and C are each performed once a day.
The operation was performed by repeating B and C alternately, that is, about every 12 hours. The details of the backwashing steps of A, B and C were the same as in Example 1. However, in FIG. 1, during the filtration step,
The circulation valve V1 is closed, and the circulation pump P2 is not activated. At the time of backwashing C, these were started and the same operation as in Example 1 was performed. 2) Results Continuous operation was possible over a long period of about six months. The corrected flux was initially 3.0 m ³ / m ² · day, but gradually decreased to 1.2 m ³ / m ² · day after 6 months. Therefore, the actual flux 1.5m ³ / m ^2.
The pressure at the membrane inlet was also gradually increased to get the day. Then, after 6 months, conventional chemical cleaning with 2% citric acid and 50 mg / liter was performed, and the flux was returned to the initial correction flux.

Example 6 An operation example 3 of Example 1 is performed on raw water shown in Table 2 below.
In general, backwash A was performed, backwash B-1 and backwash C were performed, and then backwash D was performed twice a day. That is, the backwash D is followed by the backwash C and the sodium hypochlorite injection pump P for circulation washing.
7, the circulation valve V1 was opened, the circulation pump P2 was started, and circulation cleaning was performed for 10 minutes while injecting free chlorine into the point * 4. At this time, the pressure of the circulation system was 1.0 kgf / cm
^The backwash drain valve V6 was occasionally opened so that the value was ² or less. In addition, the circulation flow rate increases the degree of opening of the circulation valve V1, and flows within the module during filtration (6 to 8 m ³ / h) to 2 to ³ times.
The flow rate was doubled. Table 2 shows the quality of raw water and filtered water.
Raw water is river water, and no coagulant such as PAC is used at the time of filtration.

[0048]

[Table 2] <Results> Raw water is river water, which has a slight chromaticity due to organic matter, and also has a fluctuation in turbidity. The treatment was able to operate stably for a long period of six months or more. No decrease in the correction flux was observed. However, the chromaticity of the filtered water is slightly
it was high. Other water quality was good.

Comparative Example 1 The following operation examples were tested using the raw water shown in Table 1 and the same membrane module. Operation example 1), repeating [A → A → A → B → A → A → A →] Backwashing step: Backwashing A; Downflow backwashing: 20 seconds, Cl ₂ 3 mg / L, Backwashing water: heating (No) upflow backwash: 20 seconds, Cl ₂ 3 mg / l, backwash water: heating (no) backwash B-1; backwash A + flushing (the raw water pump, backwash pump start) 30 seconds , Backwash water: heated (no) <Result> The actual flux was set to the same as 1.5 m ³ / m ² · day, but the continuous operation time was as short as 2.0 to 2.5 months. Chemical cleaning was required. The corrected flux also dropped from the initial 3.0 m ³ / m ² · day to about 1.3 m ³ / m ² · day after 2.5 months.

[0050]

As described above, according to the present invention, any of river water and industrial water can be used as raw water, and the operation method can be an internal pressure type, an external pressure type cross flow method, a total filtration method, and a membrane material. UF membrane (ultrafiltration membrane), MF membrane (microfiltration membrane), hollow fiber membrane as a shape, and a hollow fiber membrane applicable to any membrane module filtration device regardless of the material of the membrane Using, performing a filtration operation, in a method of obtaining filtered water, per unit membrane area, and per unit time,
Filtration water flow rate (flux: commonly used unit, m ³ / m
² · day) was high and it was possible to provide a filtration backwash method for obtaining stable long period of time.

[Brief description of the drawings]

FIG. 1 is a flow chart for explaining a filtration backwashing method of the present invention.

[Explanation of symbols]

1: Raw water 2: Raw water tank 3: Automatic filter (open, 8
0: 100 mesh) 4: Drain line of automatic filter, 5: Membrane module, 6: Filtration tank, 7: Backwash tank, 8: Chemical storage tank (oxidizing agent, sodium hypochlorite), 9:
Chemical storage tank (acid, citric acid, etc.), 10: heating device, 11:
Cross flow line (circulation line), 12: filtered water line, downward flow backwash line, 13: upward flow backwash line, 1
4: filtered water, P1: raw water pump, P2: circulation pump, P
3: Backwash pump, P4: Sodium hypochlorite injection pump (for backwash water), P5: Backwash acid injection pump, P6: Circulation acid injection pump, P7: Circulation sodium hypochlorite injection pump , V1 to V7: automatic valve

Claims (4)

[Claims] When a filtered water is obtained from raw water using a membrane module for turbidity comprising a hollow fiber membrane, a bactericide is injected into the membrane module in a filtration step of obtaining the filtered water through the raw water through the membrane module. The backwashing step of backwashing with backwashing water and the backwashing step of backwashing with backwashing water injected with acid are performed in an appropriate combination, and citric acid, ammonium dihydrogen citrate or citric acid is used as the acid. A method of back-filtration of a membrane module for turbidity, comprising using a mixed acid of an acid and glycolic acid and injecting so that the concentration in the membrane module is 50 to 1500 mg / liter as citric acid. 2. A method for obtaining filtered water from raw water using a membrane module for turbidity comprising a hollow fiber membrane, wherein a sterilizing agent is injected into the membrane module in a filtration step of obtaining filtered water through the raw water through the membrane module. The backwashing step of backwashing with backwashing water and the backwashing step of backwashing with backwashing water injected with acid are performed in an appropriate combination, and an inorganic acid is used as the acid, and the pH in the membrane module is reduced. The method for back-filtration of a membrane module for clarification comprises injecting so as to be 1.0 to 3.0. 3. The backwashing step of injecting the acid comprises 15 to 4 steps.
3. The method for back-filtration of a membrane module for turbidity removal according to claim 1 or 2, wherein the method is carried out using back-wash water heated to 0 ° C. 4. The backwashing step of injecting the acid, before or after backwashing of the membrane module, the raw water circulation piping system or a piping system including a chemical storage tank for chemical cleaning via the membrane module. The method for back-filtration of a membrane module for turbidity removal according to any one of claims 1 to 3, wherein the washing is performed through washing water into which an acid or a bactericide has been injected.