JP2016150283A - Membrane treatment apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane treatment apparatus and method which can simplify the apparatus and enable long-term stable treatment by suppressing adhesion of contaminants to a separation membrane.SOLUTION: A membrane treatment apparatus comprises: a treatment tank 1 that adsorbs contaminants in water to be treated on bubbles and separates the contaminants to obtain treated water from which the bubbles have been separated; a membrane filtration device 2 that accommodates therein separation membranes 20 for filtering the treated water to obtain a permeate; a bubble generator 6a that generates bubbles supplied to the membrane filtration device 2 to wash the separation membranes 20; and a return pipe 8 that pulls out a part of the treated water containing the bubbles from the membrane filtration device 2 to return it into a lower region of the treatment tank 1. A part of the treated water containing the contaminants-adsorbed bubbles generated by the washing of the separation membranes 20 is returned into the treatment tank 1 through the return pipe 8, and the bubbles returned into the treatment tank 1 are brought into contact with the water to be treated, whereby the contaminants in the water to be treated are adsorbed on the bubbles and separated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a membrane treatment apparatus and a membrane treatment method, and more particularly to a membrane treatment apparatus and a membrane treatment method that can be used for purification of water to be treated such as river water, seawater, brackish water, sewage, industrial wastewater, and oil-containing wastewater.

  Conventionally, membrane treatment technology has been used as a technology for purifying treated water such as river water, seawater, brackish water, sewage, industrial wastewater, and oil-containing wastewater. For example, seawater desalination pretreatment using a reverse osmosis (RO) membrane and sewage treatment using a precision (MF) membrane method or an ultra (UF) membrane method are known.

  In such membrane treatment technology, turbidity and soluble organic matter in the water to be treated adhere and accumulate on the membrane surface and pores, causing clogging or blockage, etc., thereby reducing the permeation flux of the separation membrane. There is a known problem that a phenomenon (fouling) occurs. When fouling occurs, filtration efficiency decreases and membrane treatment cannot be performed efficiently. Therefore, as pretreatment, precipitation treatment, agglomeration treatment, sand filtration treatment, pressurized flotation treatment, etc. are performed alone or in combination. It has been known.

  For example, the apparatus shown in FIG. 7 is a typical apparatus using a non-powder gravity type two-layer sand filtration process in the preceding stage of the membrane filtration apparatus. Gravity type double layer sand filtration device 16 receives supply of treated water from treated water introduction pipe 30, and filters treated water with a sand filtration layer inside the device, and obtains filtered water. The filtered water is sent out from the raw water feed pipe 40 by the raw water feed pump 50 and supplied to the membrane filtration device 20. In the membrane filtration device 20, permeated water is obtained by membrane filtration using a separation membrane disposed inside the device, and the permeated water is discharged through the discharge pipe 70. A circulation pipe 150 is connected to the upper part of the membrane filtration device 20, and one permeated water is passed through the raw water feed pipe 40 connected to the output side of the gravity double-layer sand filtration device 16 through the circulation pipe 150. Part is returned.

  Alternatively, as another method for suppressing the occurrence of fouling, generally, the separation membrane is washed by backwashing or chemical washing. However, there is a problem that the film life is reduced due to an increase in the frequency of backwashing and chemical cleaning, or there is a problem that processing cost is increased due to an increase in chemical cost necessary for cleaning.

  In order to extend the life of the separation membrane by reducing the frequency of backwashing and chemical cleaning of the separation membrane and to reduce the processing cost, for example, Japanese Patent No. 5068727 (Patent Document 1) discloses that raw water is limited or precise. There is described a method for suppressing dirt and clogging of a membrane module by mixing ultrafine particle bubbles in raw water and filtering the membrane before flowing into the filtration membrane module.

  Japanese Patent No. 5108226 (Patent Document 2) discloses a technique in which a liquid phase obtained by solid-liquid separation by a membrane filtration device is supplied to a microbubble generator, and the microbubble mixed solvent generated thereby is returned to a solvent tank. Have been described.

  In Japanese Patent No. 3273665 (Patent Document 3), when the differential pressure in the filter containing the hollow fiber membrane module reaches a specified value, bubbles are ejected from the bubble distribution pipe arranged at the lower part of the filter. An example of a cleaning technique for removing the iron oxide adhesion layer formed on the surface of the hollow fiber membrane is described.

  In Japanese Patent No. 55604021 (Patent Document 4), a separation tank for floating and separating oil is arranged in a supply path of raw water consisting of oil-containing waste water, a membrane separation module is arranged downstream of the separation tank, and the membrane separation module An example of a technique for performing membrane cleaning by generating coarse bubbles and fine bubbles from below is described.

Japanese Patent No. 5068727 Japanese Patent No. 5108226 Japanese Patent No. 3273665 Japanese Patent No. 5564221

  However, any of the conventional apparatuses and methods still has room for improvement in view of processing efficiency and apparatus simplification. For example, in the method described in Patent Document 1, the introduced fine bubbles become coarse as they circulate on the primary side of the membrane module, and the phenomenon that the gas enters the water pump and is called “air biting” occurs. Since the contaminants attached to the bubbles are not discharged out of the system, the cleaning performance of the film surface may gradually deteriorate.

  In Patent Document 2, there is a description about a technique for supplying activated bubbles to a reaction process by supplying microbubbles. However, water necessary for generating bubbles is secured from membrane-treated water, and water necessary for generating bubbles is generated in the system. Techniques for effective use are merely described or suggested, and no knowledge or suggestion about using the generated microbubbles for membrane cleaning is described. In Patent Document 3, the apparatus configuration for removing the amorphous iron oxide and the like attached to the membrane surface of the hollow fiber membrane module is very complicated, and the versatility is low because a special membrane module is used. .

  In Patent Document 4, an efficient treatment may not always be obtained depending on the treatment conditions and the properties of the water to be treated. The number of instruments arranged in the separation tank is also large, and it may not always be efficient from the viewpoint of simplifying the apparatus.

  In view of the above-described problems, the present invention provides a membrane treatment apparatus and a membrane treatment method that can simplify the apparatus and can stably perform treatment for a long period of time by suppressing the adhesion of contaminants to a separation membrane.

  As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, a part of the treated water containing bubbles supplied into the membrane filtration device for removing contaminants is disposed at the front stage of the membrane filtration device. By adopting a configuration in which the bubbles returned to the tank are returned through a return pipe, and the bubbles returned to the processing tank are brought into contact with the water to be treated to adsorb and remove the contaminants in the processing tank. The present inventors have found that a membrane treatment apparatus and a membrane treatment method that can be simplified and can stably perform membrane separation treatment for a long period of time while suppressing the adhesion of contaminants to the separation membrane are obtained.

  In one aspect, the present invention completed on the basis of the above knowledge is a treatment tank for separating the contaminants in the water to be treated by adsorbing them to the bubbles, and obtaining the treated water from which the bubbles are separated, and the filtered water for permeation. A membrane filtration device that contains a separation membrane for obtaining water, a bubble generation device that generates bubbles for cleaning the separation membrane supplied to the membrane filtration device, and membrane filtration of part of the treated water containing bubbles A return pipe that is extracted from the apparatus and returned to the lower region of the treatment tank, and a part of the treated water containing bubbles adsorbing contaminants generated by cleaning of the separation membrane is introduced into the treatment tank through the return pipe. There is provided a membrane treatment apparatus characterized in that bubbles returned to the treatment tank are brought into contact with the water to be treated so that contaminants in the water to be treated are also adsorbed and separated by the bubbles.

  In another aspect of the present invention, a treatment tank that obtains treated water from which bubbles are separated by adsorbing contaminants in the water to be treated and separation for obtaining treated water by filtering the treated water. A membrane filtration device that contains the membrane inside, a bubble generation device that is arranged outside the membrane filtration device and generates bubbles for cleaning the separation membrane supplied to the membrane filtration device, and a part of the treated water containing bubbles A part of the treated water containing bubbles adsorbing the contaminants generated by washing the separation membrane into the treatment tank through the return pipe. A membrane treatment apparatus is provided, which is returned and brought into contact with water to be treated in the treatment tank, so that contaminants in the water to be treated are also adsorbed and separated by the bubbles.

  In one embodiment, the membrane treatment apparatus according to the present invention includes a foam separation unit that collects bubbles in the treatment tank at the upper part of the tank and separates the bubbles from the water to be treated.

  In yet another embodiment, the membrane treatment apparatus according to the present invention includes supplying bubbles having a diameter of 50 μm or less to the membrane filtration apparatus.

  In yet another embodiment, the membrane treatment apparatus according to the present invention further includes a bubble addition device for adding bubbles to a part of the treated water returned from the membrane filtration device.

  In another aspect of the present invention, the water to be treated is supplied to the treatment tank, the contaminants in the water to be treated are adsorbed and separated by the bubbles, the treated water from which the bubbles are separated is extracted, and the separation membrane is disposed inside. In the membrane filtration device housed in, supply bubbles and treated water for cleaning the separation membrane, filter the treated water to obtain permeated water, extract a part of the treated water containing bubbles, and process Returning to the lower region of the tank, and bringing the bubbles returned into the treatment tank into contact with the water to be treated so that contaminants in the water to be treated are also adsorbed and separated by the bubbles. Is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the apparatus can be simplified and the membrane processing apparatus and the membrane processing method which can suppress the adhesion of the contaminant to a separation membrane and can process stably for a long period of time are provided.

It is the schematic showing an example of the film | membrane processing apparatus which concerns on embodiment of this invention. It is the schematic showing the specific example of the processing tank of FIG. It is the schematic showing the specific example of the membrane filtration apparatus of FIG. It is the schematic showing an example of the film processing apparatus which concerns on a 1st modification. It is the schematic showing an example of the film | membrane processing apparatus which concerns on a 2nd modification. It is the schematic showing an example of the film processing apparatus which concerns on a 3rd modification. It is the schematic showing the structure of the film processing apparatus as a prior art example (comparative example 1).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention specifies the structure, arrangement, etc. of components as follows. Not what you want.

  As shown in FIG. 1, a membrane treatment apparatus according to an embodiment of the present invention includes a treatment tank 1 that obtains treated water from which bubbles are separated by adsorbing and separating contaminants in water to be treated by the bubbles. A membrane filtration device 2 that houses a separation membrane 20 (see FIG. 3) for filtering the water to obtain permeate, and a bubble that generates bubbles for washing the separation membrane 20 supplied to the membrane filtration device 2 A generator 6a and a return pipe 8 for extracting a part of the treated water containing bubbles from the membrane filtration device 2 and returning them to the treatment tank 1 are provided.

  The treatment tank 1 is a tank for performing floating separation in which contaminants in the water to be treated introduced into the treatment tank 1 are separated and removed by bubbles using the property that the contaminants are adsorbed and concentrated on the gas-liquid interface of the bubbles. is there. As the processing tank 1, for example, a tank having a longitudinal direction in the vertical direction (vertical direction in FIG. 1) is preferably used. The bubbles introduced into the treatment tank 1 are bubbles contained in the return water returned from the membrane filtration device 2 via the return pipe 8. As a result, the power for supplying bubbles to the treatment tank 1 can be omitted, and the entire apparatus can be simplified, and contaminants remaining in the membrane filtration apparatus 2 can be removed. Can be performed.

  As shown in FIG. 2, at the upper part of the treatment tank 1, there is a foam separation unit 9 that collects the bubbles in the treatment tank 1 rising from the lower part of the treatment tank 1 to the upper part and separates them from the water to be treated. Is provided. The specific apparatus aspect of the foam separation part 9 is not specifically limited. For example, it may be one or a plurality of partition walls arranged substantially perpendicular to the water surface of the water to be treated supplied into the treatment tank 1, or an inclined partition inclined obliquely with respect to the water surface. It may be a partition having a reverse funnel shape (a shape having a mountain shape and an opening for discharging bubbles at the top) with respect to the water surface. As the foam separation unit 9, a pipe skimmer, a scum pump, a foam scraping device or the like can be used, or these can be used in combination with the partition.

  As water to be treated, water containing pollutants such as river water, seawater, brackish water, sewage, industrial wastewater, oil-containing wastewater is used. As shown in FIG. 1, the return pipe 8 is connected to the lower region of the processing tank 1. “Lower region” means a height of 1/2 or less of the height of the treatment tank 1 (vertical tank length), typically 1/3 or less, and more typically 1/4 or less. .

  Depending on the properties of the water to be treated, there are some contaminants that are easily adsorbed and separated into the bubbles in a short time by contacting with the bubbles, such as oil-containing wastewater. However, in this embodiment, the return pipe 8 is connected to the lower region of the treatment tank 1, so that a sufficient contact time between the water to be treated and the bubbles can be secured. For this reason, for example, contaminants that are difficult to adhere to bubbles, such as soluble organic substances, can be effectively adsorbed and separated. The “contaminant” to be separated and removed in the present embodiment refers to soluble organic substances such as exogenous polymer particles (TEP) biopolymers and humic substances contained in seawater in addition to oil contained in oil-containing wastewater. including.

  Furthermore, the treatment water introduction port 1a of the treatment tank 1 connected to the treatment water introduction pipe 3 is provided above the connection portion 1b with the return pipe 8 of the treatment tank 1, and the treatment water is extracted. A drain outlet 1c is provided below the connecting portion 1b with the return pipe 8 of the processing tank 1. Thereby, in the treatment tank 1, the water to be treated flows from the upper side to the lower side of the treatment tank 1, and the treated water containing bubbles supplied from the return pipe 8 flows from the lower side to the upper side of the treatment tank 1. . That is, in the treatment tank 1, the water to be treated and the bubbles are brought into contact with each other in a countercurrent manner, so that the water to be treated and the bubbles can be efficiently brought into contact without providing a stirring means or the like.

  In order to lengthen the floating path of the bubbles in the treatment tank 1 and to allow more contaminants of the water to be treated to adhere to the bubbles, the distance between the inlet 1a and the connecting portion 1b is preferably as far as possible. Furthermore, in order to prevent bubbles from being caught in the treated water outlet 1c, it is preferable to install the treated water outlet 1c below the connecting portion 1b.

  By using such a treatment tank 1, a membrane treatment device using a non-poured gravity gravity double-layer sand filtration device as a pretreatment for removing contaminants from the treated water as in the prior art (see FIG. 7). Compared to the above, the processing time required for removing contaminants can be greatly shortened. Specifically, the water retention time (HRT) of the water to be treated in the treatment tank 1 is 10 minutes or less, more specifically 5 minutes or less. The effect of suppressing the adhesion of contaminants to the separation membrane 20 in the apparatus 2 is obtained.

  The water to be treated in the treatment tank 1 is supplied to the lower part of the membrane filtration device 2 through a pump 5 connected to the water pipe 4. A bubble generating device 6 a is connected further downstream of the pump 5 connected to the water supply pipe 4. As the bubble generating device 6a, for example, a membrane-type air diffuser or a ceramic air diffuser or ejector having a hole diameter for ejecting air bubbles of 1 mm or less is preferably used.

In particular, the bubble generating device 6a is preferably a device for supplying bubbles having a diameter of 50 μm or less to the membrane filtration device 2. For example, a sufficient amount of gas is dissolved in water at high pressure, and then the pressure-dissolving generator that releases pressure and generates bubbles, or an ejector or special nozzle, is used to disrupt the vortex containing bubbles. Thus, a gas-liquid two-phase flow swirling generator that generates bubbles is preferably used. An ejector may be provided in the middle of the water supply pipe 4 to provide a simpler configuration. Since OH ⁻ , Cl ⁻ , COO ^{−, and the} like are concentrated on the surface of the bubble and have a negative charge, there is an advantage that contaminants attached to the membrane surface of the separation membrane 20 can be more easily removed. Further, by causing turbulent flow due to the fine bubbles supplied from the bubble generating device 6a on the side of the separation membrane 20 in contact with the treated water, it is possible to promote the separation of the contaminants on the surface of the separation membrane 20 and to effectively attach the contaminants. Can be suppressed.

  The bubble generating device 6a is arranged outside the membrane filtration device 2 to facilitate maintenance work of the bubble generating device 6a, and the bubble generating device 6a is arranged in the membrane filtration device 2 so that the membrane filtration device 2 Since there is no need to remodel the membrane module arranged in 2, there is an advantage that various types of commercially available membrane modules can be applied in the membrane filtration device 2. However, it goes without saying that the bubble generating device 6a may be arranged in the membrane filtration device 2. Although there is no particular limitation on the size distribution of the bubbles actually generated by the bubble generating device 6a, fine bubbles having a diameter of 50 μm or less are present in the membrane filtration device 2 at a volume-based gas-liquid ratio (gas / liquid). It is preferable that 0.1 or more exist.

  As shown in FIG. 3, a separation membrane 20 is accommodated in the membrane filtration device 2. As the separation membrane 20, a UF membrane or MF membrane having a pore diameter of about 0.001 to 0.1 μm is preferably used. Although the shape and material of the separation membrane 20 accommodated in the membrane filtration device 2 are not particularly limited, generally available hollow fiber membranes (internal pressure type, external pressure type) are preferably used.

  In the membrane filtration apparatus 2, the supply of the treated water containing air bubbles from the water supply pipe 4 causes the air bubbles to rise upward from below so as to cover the separation membrane. Thereby, contaminants in the treated water are prevented from adhering to the separation membrane, and contaminants adhere to the bubbles. Even if contaminants have already adhered to the separation membrane 20, the contaminants are peeled off by coming into contact with the air bubbles floating in the membrane filtration device 2. Contaminants adhering to the bubbles are sent to the treatment tank 1 through the return pipe 8 connected to the upper part of the membrane filtration device 2, and separated and discharged by the foam separation unit 9 in the treatment tank 1 shown in FIG. The As shown in FIG. 3, the permeated water separated by the separation membrane 20 is discharged to the outside of the membrane filtration device 2 through the discharge pipe 7 at the upper part of the device.

  Thus, according to the membrane treatment apparatus according to the embodiment of the present invention, fine bubbles generated by the bubble generation device 6a are supplied into the membrane filtration device 2 and are supplied to the separation membrane 20 in the membrane filtration device 2. By attaching adhering contaminants and contaminants in the treated water to the bubbles, the occurrence of fouling of the separation membrane 20 can be reduced, so that the frequency of cleaning the separation membrane 20 with the chemical can be reduced and stable for a long period of time. A membrane separation process can be performed. Furthermore, by returning the treated water containing bubbles supplied into the membrane filtration device 2 to the treatment tank 1, contaminants to be treated can be removed using bubbles in the treated water. Can perform more efficient processing.

  The bubbles supplied into the membrane filtration device 2 are coarsened by coming into contact with each other while floating in the membrane filtration device 2 or by contact with the device wall of the membrane filtration device 2. The bubbles may become coarse due to contact with the tube wall of the return tube 8. As a result, the diameter of the bubbles returned to the processing tank 1 via the return pipe 8 is 50 μm or more, more typically 100 μm or more, more typically 300 μm or more, and about 500 μm at maximum.

  In the case of bubbles having a diameter of 50 μm or less as supplied into the membrane filtration device 2, the ascending speed may be slow and the contaminant removal speed may be slow, but according to the present invention, the return pipe 8 to the treatment tank 1 may be used. Since the diameter of the supplied bubbles is 50 μm or more, it is possible to efficiently perform foam separation of contaminants in the water to be treated in the treatment tank 1.

(First modification)
As shown in FIG. 4, the membrane treatment apparatus according to the first modified example of the present invention supplies chemicals for supplying chemicals for aggregating contaminants in the treated water to the treated water supplied to the treatment tank 1. The film processing apparatus shown in FIG. 1 is different from the film processing apparatus shown in FIG.

  The drug supplied to the drug supply unit 11 is not particularly limited as long as it has an effect of aggregating and coarsening contaminants in the water to be treated. As the chemical, for example, an aggregating agent such as ferric chloride, polyiron, or polyaluminum chloride, an acid agent such as hydrochloric acid or sulfuric acid, or an alkali agent such as caustic soda can be used. By adding the chemical into the water to be treated via the chemical supply unit 11, the contaminants in the water to be treated are aggregated and coarsened to further improve the effect of separating the contaminants in the treatment tank 1 by the bubbles. be able to.

(Second modification)
As shown in FIG. 5, the membrane treatment apparatus according to the second modification of the present invention further includes a bubble addition device 6 b for adding bubbles to a part of the treated water returned from the membrane filtration device 2. When water to be treated having a low salt concentration is used as the water to be treated, the retention time of bubbles generated by the bubble generating device 6a may be shortened, or the amount of bubbles generated may be reduced. In some cases, the bubbles disappear in the return pipe 8 and the amount of bubbles returned to the treatment tank 1 is not sufficient. According to the second modification, by providing the bubble adding device 6b, it is possible to add bubbles when the amount of bubbles to be returned to the processing tank 1 is not sufficient, so that the foam separation of contaminants in the processing tank 1 is achieved. Processing can proceed stably.

  In the second modification, supply of treated water containing bubbles supplied to the treatment tank 1 through the drive of the bubble generating device 6a or the return pipe 8 based on the quality of the treated water supplied into the treatment tank 1 You may provide the control means 12 which can control.

  For example, when there are few contaminants in the for-treatment water supplied to the treatment tank 1 and the water quality is relatively good, the introduction of bubbles into the membrane filtration device 2 may be intermittent. In such a case, the control means 12 can also control the generation of bubbles by the bubble generation device 6a, for example, so as to be performed only for 5 minutes within 1 hour. At this time, the continuous supply of bubbles to the processing tank 1 can be performed by the bubble adding device 6b.

  Alternatively, a detection means (not shown) for detecting the amount of bubbles (number of bubbles and bubble diameter) in the return water flowing through the return pipe 8 is disposed in the pipe line of the return pipe 8, and the control means 12 is provided with the detection means. When the amount of bubbles is insufficient based on the amount of bubbles generated in the return water, the drive to the treatment tank 1 via the return pipe 8 is controlled by controlling the drive of at least one of the bubble generating device 6a and the bubble adding device 6b. You may control supply of the treated water containing the bubble to supply. As an example of the detection means for detecting the amount of bubbles, a commercially available particle counter (fine particle meter) or the like can be used.

  Furthermore, the control means 12 may control the size and amount of bubbles to be added by the bubble adding device 6b based on the quality of the water to be treated supplied to the treatment tank 1. For example, it is known that seawater contains exocrine polymer particles (TEP), which are transparent and highly sticky jelly-like organic substances, as causative substances that cause clogging of the separation membrane of the membrane filtration device 2. Yes. Therefore, when the water to be treated in this treatment is seawater and it is desired to remove TEP as a contaminant, the control means 12 controls the bubble adding device 6b to generate bubbles having a diameter effective for removing TEP.

  Specifically, when removing TEP, it is easier to float and separate by attaching a plurality of TEPs around one relatively large bubble than by attaching a plurality of small bubbles around TEP. Therefore, the control means 12 can control the bubble adding device 6b to generate bubbles having a diameter of 0.5 to 1 mm, which is a size suitable for the TEP process. In addition, substantially the same bubble diameter can be adjusted for various contaminants contained in the water to be treated.

  Furthermore, in order to perform the process in the processing tank 1 more satisfactorily, a gas-liquid ratio adjusting means 13 for adjusting the gas-liquid ratio in the processing tank 1 may be provided. When foam separation is effectively performed in the processing tank 1, the gas-liquid ratio (gas / liquid) in the processing tank 1 is 0.1 to 1.0, more preferably 0.4 to 0.6 in volume ratio. Is desirable. Therefore, the gas-liquid ratio adjusting means 13 controls the gas / liquid ratio in the processing tank 1 to a suitable range by controlling the supply amount of the processing water containing bubbles supplied through the return pipe 8 (return water). Control. Thereby, the process more suitable for the quality of the to-be-processed water and the fluctuation | variation of water quality can be performed.

(Third Modification)
As shown in FIG. 6, you may further provide the desalination means 15 which desalinates the permeated water extracted from the membrane filtration apparatus 2 using the pump 14 using a reverse osmosis membrane. A reverse osmosis membrane is used for the desalting means 15. By providing the desalting means 15, it is possible to efficiently treat the water to be treated containing salts such as seawater. Further, by applying the membrane treatment apparatus shown in FIG. 6 to a pretreatment facility for seawater and brackish water desalination, the desalination treatment can be made more efficient.

(Other embodiments)
Although the present invention has been described according to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments and operational techniques will be apparent to those skilled in the art.

  Although not shown, the membrane filtration device 2 can be provided with a mechanism for washing the separation membrane 20 using washing water, and the washing water is returned from the membrane filtration device 2 to the treatment tank 1. It is also possible to discharge via a branch pipe provided in It is of course possible to appropriately combine the devices shown in FIGS. The upper part of the treatment tank 1 is open to the atmosphere, and the foam containing the contaminants floating near the water surface via the foam separator 9 may be overflowed and discharged. As described above, the present invention is expressed by the invention specifying matters in the scope of claims reasonable from the above disclosure, and can be modified and embodied without departing from the spirit of the invention in the implementation stage.

  Examples of the present invention will be described below together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

Example 1
In the seawater desalination treatment experimental facility, a test using the membrane filtration device of FIG. 1 according to the present embodiment was performed as a pretreatment for seawater desalination by the RO membrane method. The water to be treated is sea water in Tokyo Bay, and as a separation membrane, a hollow fiber UF membrane module (HFU2008) made of external pressure PVDF (polyvinylidene fluoride) with a nominal pore diameter of 0.01 μm manufactured by Toray Industries, Inc. is placed in a cylindrical casing. Used by filling. A microbubble generator (MBG20ND07ZE-1BG003) manufactured by Nikuni Co., Ltd. equipped with an air shearing pump and a pressurized dissolution tank was used as the bubble generating device. For the foam separation part, a bubble separation part of a protein skimmer (RK10AC) manufactured by RK2 Systems, USA was used.

The treatment flow rate of the separation membrane was 10 m ³ / d, and the water recovery rate was 70%. The separation membrane was set to perform constant pressure backwashing when the inlet pressure reached 55 kPa. As the backwash water, UF membrane treated water into which sodium hypochlorite was injected at 10 mg / L was used. During the operation, the separation membrane inlet pressure and the constant pressure backwash frequency were monitored.

  About the processing tank provided with the foam separation part, it drive | operated so that mass ratio of the separation water containing the separation bubble (foam) with respect to the to-be-processed water to flow might be set to 0.01-0.05. The flocculant was not added to the water to be treated. Further, the gas-liquid ratio (ratio of gas flow rate to liquid flow rate) in the treatment tank was set to be 0.4: 1 by volume ratio.

To examine the load of fouling substances on the separation membrane, measure the TEP concentration of the treated water (inflow water) supplied to the treatment tank and the treated water (outflow water) drawn from the treatment tank. The removal rate of TEP was examined. Here, the TEP removal rate was calculated by the following equation (1).
TEP removal rate = (1−TEP concentration of treated water / TEP concentration of treated water) × 100− (1)

  As a result of carrying out the above operation for about 2 weeks, the average removal rate of TEP in the treatment tank arranged in the preceding stage of the membrane filtration device was 52%, and the number of backwashing of the separation membrane in the membrane filtration device was an average of 17 per day. It was confirmed that it was operating well. Here, the TEP average removal rate is an arithmetic average value of the TEP removal rate measured by the above method n times during the operation period.

(Example 2)
Water to be treated was treated using the membrane treatment apparatus shown in FIG. A flocculant (ferric chloride) was injected from the chemical supply section at a concentration of 5 mg-FeCl ₃ / L, and an attempt was made to improve the coagulability of turbidity and soluble organic substances in the treatment tank. Other conditions were the same as in Example 1.

  As a result of carrying out the above operation for about two weeks, the average removal rate of TEP in the bubble separation water tank in the front stage of the UF membrane device is 78%, and the number of UF backwash operations is an average of 7 times per day. It was confirmed. In other words, the TEP separation and removal rate could be further improved by supplying the chemical to the water to be treated from the chemical supply unit. This is considered to be because the iron ions (positive charge) derived from the flocculant have a positive charge when the TEP which is a negative charge aggregates, and are easily attached to the bubbles which are a negative charge.

(Example 3)
Although the water to be treated was treated using the membrane treatment apparatus shown in FIG. 5 under the same conditions as in Example 1, it was confirmed that Example 3 was also operated well.

Example 4
Water to be treated was treated using the membrane treatment apparatus shown in FIG. 5 under the same conditions as in Example 3 for river water in Kanagawa Prefecture. Compared with the case of Example 3, the ratio of the bubbles generated in the bubble generating device 6a disappearing in the membrane filtration device 2 was about 50 to 70% higher. By adding more than in the case, it was confirmed that even in cases other than seawater, the vehicle can be operated well.

(Comparative Example 1)
As a comparative example 1, a test using a device for removing contaminants by a non-pour-gravity gravity double-layer sand filtration process was carried out in a seawater desalination treatment experimental facility in front of a membrane filtration device as shown in FIG. This treatment method is a typical method as a pretreatment for seawater desalination by the RO membrane method.

  The sand filtration LV (linear velocity) was 120 to 150 m / d. The operating conditions of the separation membrane of the membrane filtration device were the same as those in Examples 1-3. The TEP concentration of the inflow water to be treated into the sand filtration and the outflow water from the sand filtration (inflow water to the membrane filtration device) was measured, and the removal rate of TEP in the sand filtration was examined.

  As a result of carrying out the above operation for about 2 weeks, the average removal rate of TEP by sand filtration was 30%, the number of backwashing of the UF membrane was an average of 45 times per day, and stable operation was difficult. . Compared with the conventional method, in the present invention, it is found that the TEP removal property in the treatment tank arranged in the front stage of the membrane filtration apparatus is good, the load on the separation membrane is low, and the constant pressure backwash frequency is reduced. It was. Table 1 summarizes the results of Examples 1 to 3 and Comparative Example 1.

DESCRIPTION OF SYMBOLS 1 ... Treatment tank 2 ... Membrane filtration apparatus 3 ... Processed water introduction pipe 4 ... Water supply pipe 5 ... Pump 6a ... Bubble generation apparatus 6b ... Bubble addition apparatus 7 ... Discharge pipe 8 ... Return pipe 9 ... Foam separation part 11 ... Drug supply Unit 12 ... Control means 13 ... Gas-liquid ratio adjustment means 14 ... Pump 15 ... Desalination means 16 ... Gravity-type double-layer sand filter 20 ... Separation membrane 30 ... Treated water introduction pipe 40 ... Raw water feed pipe 50 ... Raw water feed pump 70 ... discharge pipe 150 ... circulation piping

Claims (6)

A treatment tank for adsorbing and separating contaminants in the water to be treated to obtain treated water from which the bubbles have been separated;
A membrane filtration device that houses therein a separation membrane for filtering the treated water to obtain permeated water;
A bubble generating device for generating bubbles for cleaning the separation membrane to be supplied to the membrane filtration device;
A return pipe for extracting a part of the treated water containing the bubbles from the membrane filtration device and returning it to the lower region of the treatment tank,
A part of the treated water containing bubbles adsorbing contaminants generated by cleaning the separation membrane is returned to the treatment tank through the return pipe, and the bubbles returned to the treatment tank are returned to the treatment tank. The membrane treatment apparatus, wherein the contaminants in the water to be treated are also adsorbed and separated by the bubbles by contacting with the water to be treated. A treatment tank for adsorbing and separating contaminants in the water to be treated to obtain treated water from which the bubbles have been separated;
A membrane filtration device that houses therein a separation membrane for filtering the treated water to obtain permeated water;
A bubble generating device that is disposed outside the membrane filtration device and generates bubbles for cleaning the separation membrane to be supplied to the membrane filtration device;
A return pipe for extracting a part of the treated water containing the bubbles from the membrane filtration device and returning it to the treatment tank;
A part of the treated water containing bubbles adsorbing contaminants generated by cleaning the separation membrane is returned to the treatment tank through the return pipe, and the bubbles are treated in the treatment tank. A membrane treatment apparatus characterized in that contaminants in the water to be treated are also adsorbed and separated by the bubbles by contacting with water.   The membrane processing apparatus of Claim 1 or 2 provided with the foam separation part which collects the said bubble in the said processing tank on the tank upper part, and isolate | separates it from the said to-be-processed water.   The membrane treatment apparatus according to claim 1, comprising supplying bubbles having a diameter of 50 μm or less to the membrane filtration apparatus.   The membrane processing apparatus of any one of Claims 1-4 further equipped with the bubble addition apparatus for adding a bubble to some treated water returned from the said membrane filtration apparatus. Supplying treated water to the treatment tank, adsorbing and separating contaminants in the treated water into bubbles, extracting the treated water from which the bubbles were separated;
Supplying bubbles and the treated water for washing the separation membrane into a membrane filtration device containing the separation membrane therein, filtering the treated water to obtain permeated water, and treating water containing the bubbles Extracting a portion of and returning it to the lower region of the treatment tank,
A membrane treatment method comprising bringing the bubbles returned into the treatment tank into contact with the water to be treated so that contaminants in the water to be treated are also adsorbed and separated by the bubbles.