JP2007167713A - Method for operating separation membrane and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a separation membrane which makes a performance stable and enables a continuous operation while preventing a degradation of the separation membrane, and an apparatus. <P>SOLUTION: The method for operating the separation membrane and the apparatus comprises a continuous or intermittent load of a raw water supply system to the separation membrane with water including an organic substance containing polyphenol during the operation of passing raw water to the separation membrane to separate it into permeated water and concentrated water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for operating a separation membrane, particularly a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane), which can be operated with stable performance.

Conventionally, as a method for obtaining seawater desalination, ultrapure water, and water for various production processes, for example, a method of separating ionic components and low molecular components from raw water using a module having an RO membrane or NF membrane as a separation membrane is known. It has been. Compared to before, the performance of RO membranes and NF membranes has been greatly improved, and membranes capable of high blocking performance and low pressure operation are also used.
JP 2003-117360 A JP 58-109182 A

  However, RO membranes and NF membranes with polyamide material as the skin layer are prone to oxidative degradation, especially when raw materials contain oxidizing substances such as sodium hypochlorite, and ORP ( When the oxidation-reduction potential is high, the deterioration rate of the film is accelerated, which is a cause of shortening the lifetime. Some piperazine amide films are relatively resistant to oxidative degradation, but their performance is not sufficient.

  In view of such circumstances, an object of the present invention is to provide a separation membrane operating method and apparatus that can stabilize the performance and continue the operation while preventing the degradation of the separation membrane.

  As a result of intensive studies on the actual situation as described above, the present inventors have continually or intermittently supplied certain organic substances to the separation membrane, and in particular, the blocking performance of RO membranes and NF membranes. Has been found to be able to be operated stably, and the present invention has been completed.

  That is, in the operation method of the separation membrane according to the present invention, the raw water is passed through the separation membrane and separated into permeated water and concentrated water, and continuously or intermittently into the raw water supply system to the separation membrane. And adding water containing an organic substance containing polyphenol. By this method, it becomes possible to continue a stable operation with respect to a system in which the blocking performance of the conventional separation membrane deteriorates with time. The raw water supply system referred to here refers to all preceding stages leading to the separation membrane, and is a concept including piping, tanks and the like.

  In this operation method of the separation membrane, when water containing the organic substance containing the polyphenol is intermittently added, the interval between the additions can be set at regular intervals. In this way, since it is only necessary to add at regular intervals, a stable operation can be realized by a simple method. It can be added by automatic control, or when automatic control is difficult, it may be added manually at regular intervals. The interval is preferably added once a day to once a month. If it is less than one day, the addition frequency is too high, the chemical cost is increased, and the effect of further stabilizing the operation by increasing the frequency cannot be expected. If it exceeds 1 month, the frequency will be too low and stable operation will not be possible.

  Or when adding intermittently, it can also be added when the permeated water quality of a separation membrane becomes below a set standard value. According to this method, since it can be added at an appropriate timing, there is no wasteful consumption of chemicals, and more stable operation is possible. Although it does not specifically limit as a reference value set, It is good to set according to the permeated water quality required by the system. As an example, when the reference value is set according to the rejection rate, it is preferable that the value be deteriorated at a rate of 5% to 30% with respect to the initial rejection rate. If it is less than 5%, the effect of addition is low, and if it exceeds 30%, it cannot be said that the operation is stable. In addition, “the value deteriorated at a rate of about 5% to 30%” referred to here is, for example, “a state in which a film having a 90% rejection rate initially deteriorates at a rate of 10%” % X 0.90 = 81%, not 90%-10% = 80%.

  Moreover, when adding intermittently, the time which adds the water containing the organic substance containing polyphenol can also be made into the fixed fixed time. The addition time is set to 5 minutes to 7 days, preferably 5 minutes to 1 day, and more preferably 5 minutes to 3 hours. If it is less than 5 minutes, the effect is low, and if it exceeds 7 days, it can no longer be said to be intermittent addition.

  Moreover, when adding intermittently, the time which adds the water containing the organic substance containing polyphenol can also be made into the time until the permeated water quality of a separation membrane becomes more than a certain standard. Although it does not specifically limit as a reference value set, It is good to set according to the permeated water quality required by the system. As an example, when the reference value is set according to the rejection rate, it is preferable that the value be increased in a range of 5% to 50% with respect to the rejection rate before addition and not exceeding the initial rejection rate. If it is less than 5%, it cannot be said that there is an effect of addition, and it is difficult to achieve an increase rate exceeding 50%. Note that the ratio calculation here is based on the same concept as described above.

  Moreover, when adding continuously, the addition amount of the water containing the organic substance containing a polyphenol can be controlled according to the permeated water quality of a separation membrane. By using this method, it becomes possible to minimize the amount of organic substance used and efficiently perform stable operation of the separation membrane.

  The raw water supplied to the separation membrane preferably has an oxidation-reduction potential (ORP) at pH = 7 of +200 mV or more. ORP serves as an index of whether or not water has an oxidizing atmosphere, and water having a large value is water having an oxidation tendency. When the raw water contains an oxidizing agent such as sodium hypochlorite, it naturally has a tendency to oxidize, but even if it does not contain an obvious oxidizing agent, it may show a high ORP value. This method can be applied to such a case and can be an effective measure. Specifically, it is desirable that the raw water has an ORP of +200 mV or more, more preferably +300 mV or more, and still more preferably +400 mV or more. ORP is often used for relative evaluation, but is considered to be oxidative at +200 mV or more based on our experience.

  It is preferable to use a reverse osmosis membrane or a nanofiltration membrane as the separation membrane. By using this method, it becomes possible to stabilize the membrane salt blocking performance, non-dissociation component blocking performance such as silica and boron, and organic component blocking performance.

  Moreover, it is preferable to use a spiral membrane element as the separation membrane. Spiral membrane elements are inexpensive and have high versatility, so there are significant advantages to using membranes with this structure.

  Moreover, it is preferable to use a membrane containing at least an aromatic polyamide material as the separation membrane. More preferred materials are wholly aromatic polyamides, more preferably crosslinked wholly aromatic polyamides. By including a polyamide-based material in the membrane, the effect of stable operation becomes high.

  Further, as the separation membrane, it is preferable to use a separation membrane having a performance of 99% or less in blocking rate of a 500 mg / L sodium chloride aqueous solution. A more preferable range of the blocking rate is 10% or more and 99% or less, more preferably 20% or more and 98.5% or less, still more preferably 98% or less, and further preferably 30% or more and 98% or less. By using this method, stable operation of the separation membrane can be realized more efficiently. The effect of stable operation is low for membranes with a rejection rate exceeding 99%. The rejection rate depends on the temperature and permeation flux at the time of measurement, so the manufacturer applies standard conditions for measuring the performance of the membrane, or in the case of a spiral membrane element, 25 ° C, 1.0 m / day It is better to measure with the permeation flux of. In the present application, the blocking rate refers to that measured by this method unless otherwise specified.

  The average molecular weight of the organic substance is preferably 200 to 5000. A more preferable average molecular weight is 200 to 3000, and more preferably 200 to 2000. If the average molecular weight is less than 200, the organic substance may permeate the membrane, so the effect is weak. When the average molecular weight exceeds 5000, membrane fouling is caused, and only the permeation flux is lowered, and it does not contribute to stable operation.

  Moreover, it is preferable to use tannic acid as the organic substance. Among polyphenols, the effect of tannic acid is particularly high, and it is preferable to use this substance.

  As the tannic acid, hydrolyzable tannin can be used. Tannic acid has a hydrolysis type and a condensation type, and the former is particularly effective.

  Further, as the tannic acid, it is preferable to use a pentonic acid made as a raw material. Tannic acid extracted from pentaploids generally has an average molecular weight of about 1700, and is estimated to be suitable for stable operation.

  The operation device of the separation membrane according to the present invention includes a polyphenol continuously or intermittently supplied to the raw water supply system to the separation membrane during operation of passing raw water through the separation membrane and separating into permeated water and concentrated water. It has the means to add the water containing the organic substance containing this.

  In the means for adding water containing an organic substance containing polyphenol, when the water is added intermittently, the interval between the additions can be set at regular intervals.

  In addition, in the means for adding water containing an organic substance containing polyphenol, when water is added intermittently, it can be added when the permeated water quality of the separation membrane is below a set reference value.

  Moreover, in the means for adding water containing an organic substance containing polyphenol, when the water is added intermittently, the time for adding water containing an organic substance containing polyphenol can be set to a predetermined fixed time.

  Moreover, in the means for adding water containing an organic substance containing polyphenol, when the water containing an organic substance containing polyphenol is added intermittently, the permeated water quality of the separation membrane exceeds a certain standard. It can also be between.

  In the means for adding water containing an organic substance containing polyphenol, when it is continuously added, the amount of water containing an organic substance containing polyphenol can be controlled according to the permeated water quality of the separation membrane.

  The raw water supplied to the separation membrane preferably has an oxidation-reduction potential (ORP) at pH = 7 of +200 mV or more.

  The separation membrane is preferably composed of a reverse osmosis membrane or a nanofiltration membrane.

  Furthermore, a spiral membrane element is preferably used as the separation membrane.

  Moreover, it is preferable that a membrane containing at least an aromatic polyamide material is used as the separation membrane.

  Further, as the separation membrane, it is preferable to use a separation membrane having a performance of a rejection rate of 500 mg / L sodium chloride aqueous solution of 99% or less.

  The average molecular weight of the organic substance is preferably 200 to 5000.

  Further, tannic acid is preferably used as the organic substance.

  As tannic acid, hydrolyzable tannin is preferably used.

  Moreover, as tannic acid, it is preferable to use what was made from a pentaploid as a raw material.

  According to the present invention, by continuously or intermittently supplying water containing an organic substance containing polyphenol to a separation membrane, operation is continued with stable performance even in raw water where the separation membrane is susceptible to oxidative degradation. The industrial utility value can be very high.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below shows an example of the present invention and does not limit the contents of the present invention.

  A separation membrane operating method and apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic system diagram of a separation membrane operating device for carrying out the separation membrane operating method according to the present embodiment (pressure gauge, flow meter, valve and the like are omitted as appropriate). 1 is a raw water tank (feed water tank) supplied to the separation membrane, 2 is a pressurizing pump, 3 is a separation membrane module, 4 is a pressure control valve, 4 to 9 are ball valve valves, and 10 is a chemical solution. A tank (organic substance aqueous solution storage tank), 11 is a chemical injection pump, and 12 is a water quality meter. The separation membrane module 3 includes a membrane element 31 that is the separation membrane itself and a vessel 32 that is a pressure-resistant container for storing the membrane element.

  During normal operation, the feed water tank 1 receives water from the previous stage, for example, raw water subjected to turbidity treatment. The valves 5 and 7 are opened, the valve 4 is opened to a predetermined pressure, the valves 6, 8 and 9 are closed, and the raw water pressurized by the pressure pump 2 is converted into concentrated water by the separation membrane module 3. The water is separated into permeated water, the concentrated water is blown, and the permeated water is sent to the subsequent apparatus. In some cases, the ball valves 6 and 7 are appropriately adjusted to partially circulate the concentrated water.

  In the chemical tank 10, an organic substance aqueous solution having a predetermined concentration is stored in advance. When the water quality meter 12 falls below a certain reference value, an electric signal is sent to the chemical injection pump 11 and the pump 11 is activated. The medicinal pump 11 is set in advance to have a predetermined injection amount.

  After the start of injection, when the water quality meter 12 exceeds a certain reference value, an electric signal is sent to the chemical injection pump 11 and the pump 11 is stopped.

  In addition, in the case of adding intermittently and when adding at regular time intervals, the electrical signal from the water quality meter 12 is not necessary, and the chemical injection pump 11 is started automatically or manually at regular time intervals. That's fine. Moreover, when adding continuously, the chemical injection pump 11 is always started.

  During the addition of organic substances, normal operation does not need to be stopped if there is no hindrance to the subsequent stage. If leakage of organic substances into the permeated water is observed and there is a possibility that the latter stage may be hindered, the permeated water can be blown by closing the valve 5 and opening the valve 9 during the addition, or The permeated water can be circulated by closing the valve 5 and opening the valve 8. In the case of circulation, the concentrated water may be circulated by closing the valve 7 and opening the valve 6. In this case, the chemical injection pump 11 is stopped when the chemical concentration reaches a certain concentration.

  In the above-described embodiment, the form of one module is exemplified, but the present invention can also be applied to a separation membrane device constituted by a plurality of modules including a plurality of elements such as a Christmas tree-like arrangement and a two-stage RO.

  The concentration of the organic substance as a chemical to be added is not particularly limited, but is preferably 0.1 to 200 mg / L, preferably 0.5 to 100 mg / L at the separation membrane module inlet for efficient treatment. Less than 0.1 mg / L is less effective, and more than 200 mg / L may cause fouling, which is not preferable.

  The polyphenol as used in the field of this invention refers to the general polyphenol which named generically the aromatic compound which the some hydroxyl group couple | bonded. Examples of the polyphenol include anthocyanins, catechins, tannins, rutin, quercetin, isoflavones, flavonoids, humins, and fulvic acids, but are not particularly limited.

  Tannins are also called tannic acid and tannins, and are used confusedly, but are all used synonymously in the present application. In addition, pentaploid tannin is sometimes called gallotannin. In addition, a quintuplet is an insect cob of the genus Nurde.

  Tannic acid has a hydrolysis type and a condensation type. Examples of the former ingredients include pentaploid, gallic, chestnut, oak wood, eucalyptus, divi-divi, tara, sumac, myrabolam , Algarobilla, Valonea, walnuts, chestnuts, mallet, gummy, pomegranate, red-crowned whale, urchinaceae, sanshuyu, genokosho. Examples of the latter raw materials include Keebracho, Burma Cutch, Wattle, Mimosa, Spruse, Hemlock, Mangrove, Oak bark , Abalam, Gambier, tea, persimmon astringent, cypress, grape, apple, lotus root, coffee, perilla, bokeh, persimmon, rosemary, parsley, salvia flower, sunflower, and the like. The hydrolysis type is also called pyrogallol type (Hydrolyzable Tannin), and the condensation type is also called catechol type (Condensel Tannin).

  EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.

Example 1
Using pentaploid tannin as an organic substance, continuous operation was performed by the above method using the apparatus shown in FIG. The raw water received in tank 1 was groundwater that was turbidized by the membrane turbidizer in the previous stage, and the conductivity during the operation period was stable at an average of around 20 mS / m. The ORP averaged +600 mV, and it was water with an oxidation tendency. As the membrane, ES-15-D8 manufactured by Nitto Denko Corporation was used. The chemical concentration was adjusted to 20 mg / L at the inlet of the separation membrane module. The conductivity of permeated water was monitored with a water quality meter, and an organic substance was set to be intermittently added under the following conditions.
・ 1mS / m or more: Start of addition ・ 0.7mS / m or less: Stop of addition

Example 2
Using pentaploid tannin as an organic substance, continuous operation was performed by the above method using the apparatus shown in FIG. The raw water received in tank 1 was groundwater that was turbidized by the membrane turbidizer in the previous stage, and the conductivity during the operation period was stable at an average of around 20 mS / m. The ORP averaged +600 mV, and it was water with an oxidation tendency. As the membrane, ES-15-D8 manufactured by Nitto Denko Corporation was used. The conductivity of the permeated water was monitored with a water quality meter, and the organic substance was set (proportional control) to be added intermittently under the following conditions. (y: Concentration of organic substance at separation membrane module inlet [mg / L], x: Permeate conductivity [mS / m])
・ When x <0.7: y = 0 (addition stopped)
・ When 0.7 ≦ x <1.4: y = (200/7) x−20
・ When 1.4 ≦ x: y = 20

Example 3
Using pentaploid tannin as an organic substance, continuous operation was performed by the above method using the apparatus shown in FIG. The raw water received in tank 1 was groundwater that was turbidized by the membrane turbidizer in the previous stage, and the conductivity during the operation period was stable at an average of around 20 mS / m. The ORP averaged +600 mV, and it was water with an oxidation tendency. As the membrane, ES-15-D8 manufactured by Nitto Denko Corporation was used. The conductivity of the permeated water was monitored with a water quality meter, and setting (proportional control) was performed so that organic substances were continuously added under the following conditions. (y: Concentration of organic substance at separation membrane module inlet [mg / L], x: Permeate conductivity [mS / m])
・ When x <0.7: y = 5
・ When 0.7 ≦ x <1.4: y = (100/7) x-5
・ When 1.4 ≦ x: y = 15

Comparative Example 1
In Example 1, the treatment was performed in the same manner as in Example 1 except that no organic substance was added.

  Continuous operation was carried out under the above conditions, and the performance was evaluated in the initial operation, after 1 month, 2 months, and 3 months. The permeated water amount is shown as a relative value with the initial operation being 100. The results are shown in Table 1.

  In Comparative Example 1 in which no organic substance was added, the permeated water quality deteriorated and the permeated water amount increased over time, indicating a tendency of oxidative degradation. On the other hand, in Examples 1 and 2 where intermittent addition of the organic substance was performed and Example 3 where continuous addition was performed, stable performance could be maintained in continuous operation.

  The method and apparatus for operating a separation membrane according to the present invention can be applied to any application that requires continuous operation of a separation membrane, and is particularly suitable for a system using a reverse osmosis membrane or a nanofiltration membrane.

It is an equipment distribution diagram of a separation membrane operation device concerning one embodiment of the present invention.

Explanation of symbols

1 Raw water tank (supply water tank)
2 Pressurizing pump 3 Separation membrane module 4, 5, 6, 7, 8, 9 Valve 10 Chemical tank (organic substance aqueous solution storage tank)
11 Chemical injection pump 12 Water quality meter 31 Membrane element 32 Vessel as pressure vessel

Claims (30)

  During operation in which raw water is passed through the separation membrane and separated into permeated water and concentrated water, water containing organic substances including polyphenols is added continuously or intermittently to the raw water supply system to the separation membrane. A method for operating a separation membrane.   2. The method for operating a separation membrane according to claim 1, wherein, when intermittently adding, the interval between additions is set at regular intervals.   The method for operating a separation membrane according to claim 1, wherein when intermittently added, the permeated water quality of the separation membrane is lower than a set reference value.   The method for operating a separation membrane according to any one of claims 1 to 3, wherein, in the case of intermittent addition, the time for adding water containing an organic substance containing polyphenol is a predetermined constant time. .   In the case of intermittent addition, the time for adding water containing an organic substance containing polyphenol is set until the permeated water quality of the separation membrane exceeds a certain standard. The operation method of the separation membrane in any one.   The method for operating a separation membrane according to claim 1, wherein, when continuously added, the amount of water containing an organic substance containing polyphenol is controlled in accordance with the permeated water quality of the separation membrane.   The method for operating a separation membrane according to any one of claims 1 to 6, wherein the raw water supplied to the separation membrane has an oxidation-reduction potential (ORP) at pH = 7 of +200 mV or more.   The method for operating a separation membrane according to any one of claims 1 to 7, wherein a reverse osmosis membrane or a nanofiltration membrane is used as the separation membrane.   The method for operating a separation membrane according to any one of claims 1 to 8, wherein a spiral membrane element is used as the separation membrane.   The method for operating a separation membrane according to any one of claims 1 to 9, wherein a membrane containing at least an aromatic polyamide-based material is used as the separation membrane.   The method for operating a separation membrane according to any one of claims 1 to 10, wherein a separation membrane having a performance of 99% or less as a rejection rate of a 500 mg / L sodium chloride aqueous solution is used as the separation membrane. .   The method for operating a separation membrane according to any one of claims 1 to 11, wherein an average molecular weight of the organic substance is 200 to 5,000.   The method for operating a separation membrane according to any one of claims 1 to 12, wherein tannic acid is used as the organic substance.   The method of operating a separation membrane according to claim 13, wherein hydrolyzed tannin is used as the tannic acid.   The method for operating a separation membrane according to claim 13 or 14, characterized in that a pentnic acid is used as a raw material.   Means for continuously or intermittently adding water containing an organic substance containing polyphenol to the raw water supply system to the separation membrane during operation in which raw water is passed through the separation membrane and separated into permeated water and concentrated water A separation membrane operating device characterized by comprising:   17. The apparatus for operating a separation membrane according to claim 16, wherein in the means for adding water containing an organic substance containing polyphenol, when the water is added intermittently, the interval of addition is set at regular intervals.   The means for adding water containing an organic substance containing polyphenol, when intermittently added, is added when the permeated water quality of the separation membrane falls below a set reference value. The separation membrane driving device according to claim 1.   In the means for adding water containing an organic substance containing polyphenol, when intermittently adding water, the time for adding water containing an organic substance containing polyphenol is set to a predetermined fixed time. Item 19. The separation membrane operating device according to any one of Items 16 to 18.   In the means for adding water containing an organic substance containing polyphenol, in the case of intermittent addition, the time for adding water containing an organic substance containing polyphenol is increased until the permeated water quality of the separation membrane exceeds a certain standard. The separation membrane operating device according to any one of claims 16 to 18, wherein the operation device is between.   In the means for adding water containing an organic substance containing polyphenol, when continuously added, the amount of water containing an organic substance containing polyphenol is controlled according to the permeated water quality of the separation membrane. The apparatus for operating a separation membrane according to claim 16.   The apparatus for operating a separation membrane according to any one of claims 16 to 21, wherein the raw water supplied to the separation membrane has an oxidation-reduction potential (ORP) at pH = 7 of +200 mV or more.   The apparatus for operating a separation membrane according to any one of claims 16 to 22, wherein the separation membrane comprises a reverse osmosis membrane or a nanofiltration membrane.   The apparatus for operating a separation membrane according to any one of claims 16 to 23, wherein a spiral membrane element is used as the separation membrane.   25. The apparatus for operating a separation membrane according to any one of claims 16 to 24, wherein a membrane containing at least an aromatic polyamide material is used as the separation membrane.   The separation membrane according to any one of claims 16 to 25, wherein a separation membrane having a performance of 99% or less as a rejection rate of a 500 mg / L sodium chloride aqueous solution is used as the separation membrane. Driving device.   27. The apparatus for operating a separation membrane according to any one of claims 16 to 26, wherein an average molecular weight of the organic substance is 200 to 5000.   The apparatus for operating a separation membrane according to any one of claims 16 to 27, wherein tannic acid is used as the organic substance.   29. The separation membrane operating device according to claim 28, wherein hydrolyzable tannin is used as the tannic acid.   30. The apparatus for operating a separation membrane according to claim 28 or 29, wherein the tannic acid is made from a pentaploid as a raw material.

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