JP4415592B2 - Membrane separation method and apparatus - Google Patents

Description

  The present invention relates to a membrane separation method and apparatus for carrying out membrane separation using a separation membrane such as a reverse osmosis membrane, a UF membrane, etc., and recovering the performance by washing the separation membrane with a reduced permeation flow rate with an alkaline washing liquid. The present invention relates to a membrane separation method and apparatus for efficiently washing a separation membrane using an exchanger.

  In the fields of boiler water, industrial water, washing water, drinking water treatment, etc., membrane separation is performed using separation membranes such as reverse osmosis membranes and UF membranes to obtain boiler water, industrial water, washing water, drinking water, etc. Yes. In a membrane separation apparatus that performs such a membrane separation treatment, the separation membrane is contaminated with fine particles, dissolved organic substances, microorganisms, etc. in the feed water, and the permeation flux (water amount) decreases with time. Things are generally done. As this cleaning agent, alkaline agents, detergents, enzymes, dilute oxidizing agents and the like have been used.

  Non-Patent Document 1 describes an example in which a reverse osmosis membrane is washed using a dilute aqueous sodium hydroxide solution having a pH of 11. At this pH, Mg precipitates as hydroxide and Ca also precipitates as calcium carbonate. Therefore, it is assumed that the diluted sodium hydroxide used softened water, pure water, reverse osmosis membrane treated water, etc. Since there is no description about the liquid, it is estimated that the cleaning wastewater was processed at the general wastewater treatment facility, but these are processed separately, which is inefficient.

  Patent Document 1 describes that a permeation membrane having a reduced permeation flux by treating a protein-containing liquid is washed by immersing it in a static or fluid alkaline solution prior to washing with fresh water. . However, when immersed in an alkaline liquid, if the degree of contamination is severe, it is difficult to recover the permeation flux in a short time, and the permeation flux recovery rate does not reach 100%.

  Patent Document 2 discloses a method of softening a washing water containing silicic acid and a hardness component and separating the membrane with a reverse osmosis membrane at a pH of 8 or higher, and desalting the reverse osmosis membrane with a washing solution having a pH higher than that in the desalting step. In order to clean the surface, a method is described in which an alkali is added to the cleaning solution for cleaning, and the silicic acid adhering to the film surface is dissolved in the alkali and washed away. However, in this method, it is necessary to add an alkali to the cleaning liquid, and the cleaning waste liquid needs to be separately treated such as neutralization.

As described above, in the conventional cleaning method, the cleaning chemical contains a relatively high concentration of alkali, detergent and the like, and water treatment such as neutralization and activated carbon adsorption treatment is necessary to discharge this. It was. Further, since the alkaline cleaning agent precipitates calcium, magnesium, etc., it is necessary to use pure water or soft water from which these have been removed. In these cases, the decalcification of the cleaning liquid, the addition of alkali, and the neutralization of the cleaning waste liquid are performed separately, and there are problems such as waste of chemicals and many processing steps.
Chemical Engineering August 2000 issue p34-39 Japanese Patent Laid-Open No. 54-99783 JP-A-60-125208

  The object of the present invention is to efficiently perform decalcification and pH adjustment of the cleaning liquid, neutralization of the cleaning waste liquid, etc., reduce the amount of chemicals used and processing steps, and clean the separation membrane safely and economically. An object of the present invention is to provide a membrane separation method and apparatus that can efficiently recover membrane separation performance.

The present invention is the following membrane separation method and apparatus.
(1) A membrane separation step of supplying a liquid to be treated to a separation membrane and performing membrane separation,
A cleaning liquid preparation step of bringing the cleaning water into contact with the alkali metal type first cation exchanger and performing an ion exchange treatment, and adjusting the pH to be alkaline.
A cleaning step of supplying the prepared cleaning liquid to the separation membrane for cleaning, and a neutralizing step of neutralizing the discharged cleaning drainage by contacting with the second cation exchanger in the acid form,
A method for cleaning a separation membrane, wherein a second cation exchanger that has become an alkali metal form by neutralization is used as the first cation exchanger.
(2) The method according to (1) above, wherein the first or second cation exchanger is a weakly acidic cation exchanger.
(3) A membrane module that includes a separation membrane and performs membrane separation,
A treatment liquid supply path for supplying a treatment liquid to the concentrate side of the membrane module,
A treatment liquid take-out path for removing the treatment liquid from the permeate side of the membrane module,
A cleaning liquid supply path for supplying a cleaning liquid to the concentrate side of the membrane module;
A cleaning drainage passage for removing the cleaning drainage from the permeate side of the membrane module;
An alkali metal type first cation exchanger tank provided in the cleaning liquid supply path; and an acid type second cation exchanger tank provided in the cleaning drainage path,
The cleaning liquid supply path is also connected to the second cation exchanger tank, and the cleaning drainage discharge path is also connected to the first cation exchanger tank, and the first cation exchanger tank and the second cation exchanger tank are connected to each other. Ri drop-in replacement Ri switch and a cation exchanger tank, configured membrane separation device to use a second cation exchanger became alkali metal form by neutralization as the first cation exchanger.
(4) The apparatus according to (3) above, wherein the first or second cation exchanger is a weakly acidic ion exchanger.

  The separation membrane used for membrane separation in the present invention is a separation membrane widely used for membrane separation in boiler water, industrial water, washing water, drinking water treatment and other fields, such as reverse osmosis membrane, UF membrane, MF membrane, etc. A general separation membrane is included. The liquid to be treated for membrane separation includes food and drink, raw materials, intermediate products, products, etc. in addition to water such as irrigation water and waste water. Such a separation membrane is often used in the form of a membrane module configured to separate the concentrate side and the permeate side, but the separation membrane may be used independently.

  A membrane separation apparatus using the above separation membrane includes a membrane module partitioned by a separation membrane on the concentrated liquid side and the permeate side, and the liquid to be treated is applied to the concentrated liquid side of the membrane module under pressure from the liquid supply path to be treated. Supply, partially permeate through the separation membrane, discard the non-permeated concentrate or circulate it, and remove the permeate from the permeate side of the membrane module as the treatment liquid through the treatment liquid take-out path to perform the membrane separation process Configured. Since the membrane separation performance such as the permeation flux decreases with time by continuing the membrane separation, the separation membrane is washed to recover the membrane separation performance.

  In the membrane separation method of the present invention, the liquid to be treated is supplied to the separation membrane in the membrane separation step to perform membrane separation, and in the cleaning liquid preparation step, the cleaning water is brought into contact with the first alkali metal cation exchanger to perform ion exchange. In addition to the treatment, the pH is adjusted to alkaline to prepare a cleaning liquid, the prepared cleaning liquid is supplied to the separation membrane in the cleaning process to clean the separation membrane, and the cleaning waste liquid discharged from the cleaning process is converted to the acid form in the neutralization process. In contact with the second cation exchanger. The liquid to be treated and the cleaning water may be the same, but if they are different, the liquid to be treated and the cleaning liquid are exchanged as necessary.

In order to perform the above-described cleaning, the membrane separation apparatus of the present invention communicates a cleaning liquid supply path for supplying a cleaning liquid to the concentrated liquid side of the membrane module and takes out a cleaning waste liquid to the permeate side of the membrane module. The liquid take-out path is connected, the alkali metal type first cation exchanger is provided in the cleaning liquid supply path, and the acid type second cation exchanger is provided in the cleaning drain liquid take-out path. The first cation exchanger and the second cation exchanger are switched to the merry-go-round system, and the second cation exchanger that has become an alkali metal form by neutralization is used as the first cation exchanger. Configured.

  The first or second cation exchanger may be a strong acid ion exchanger, but if a weak acid cation exchanger is used, the water for washing is ion-exchanged to remove hardness components with high selectivity, An alkaline cleaning solution can be prepared by adjusting the pH to be alkaline, and it is preferable because it can be easily regenerated. Examples of the ion exchanger include an ion exchange resin, an ion exchange fiber, an ion exchange membrane, zeolite, IXE (inorganic ion exchanger manufactured by Toa Gosei Co., Ltd.), and the ion exchange resin is preferable. The first cation exchanger is used in alkali metal form such as sodium form, and the second cation exchanger is used in acid form, that is, H form.

  In the cleaning liquid preparation step, the cleaning water is brought into contact with the alkali metal type first cation exchanger, thereby performing ion exchange treatment to remove hardness components such as calcium and magnesium and softening, and to adjust the pH to alkaline. Prepare an alkaline cleaning solution. The cleaning water is not limited as long as it is suitable for the preparation of the cleaning liquid, and may be the same as the liquid to be processed, may be different water, or may be a processing liquid. The washing water may contain hardness components such as calcium and magnesium, which are removed by ion exchange treatment, but preferably do not contain particles or organic substances that cause clogging. Is preferred.

  In the pH adjustment, when the first cation exchanger is a weakly acidic cation exchanger of the alkali metal type, the alkali metal is eluted by hydrolysis simultaneously with the ion exchange treatment, and the pH is adjusted to alkalinity so that an alkaline cleaning solution is prepared. Although it can be obtained, the pH may be adjusted by adding an alkaline solution separately in the case of a strongly acidic cation exchanger. The pH of the cleaning liquid after pH adjustment is preferably 9 to 12, and more preferably 9 to 11.

  In the washing step, the washing liquid prepared as described above is supplied to the separation membrane under pressure to wash the separation membrane and restore the membrane separation performance. In this case, the cleaning liquid is caused to flow along the separation membrane to wash away the adhering matter adhering to the membrane surface, and at the same time, a part of the cleaning liquid is permeated through the separation membrane, and the adhering matter that has entered the inside of the separation membrane is also washed away. By washing with an alkaline washing liquid, the attached deposits are peeled off or dissolved and removed in the washing liquid, and the membrane separation performance such as permeation flux is recovered.

  When cleaning the membrane separation device, supply the cleaning liquid under pressure from the cleaning liquid supply path to the concentrated liquid side of the membrane module, and flush the adhering matter adhering to the membrane surface by flowing the cleaning liquid along the separation membrane. Then, a part of the cleaning liquid is permeated through the separation membrane, and the adhering matter that has entered the inside of the separation membrane is also washed away, and the non-permeated cleaning liquid is discarded as it is or circulated to the concentrated liquid side to wash the separation membrane.

  The ratio of the cleaning liquid that flows along the separation membrane during cleaning and the ratio of the cleaning liquid that permeates through the separation membrane is arbitrary, but the cleaning liquid 0.1 to 0 that permeates through the separation membrane with respect to the cleaning liquid 1 that flows along the separation membrane. .9, preferably with a volume ratio of 0.6 to 0.8. The cleaning liquid flowing along the separation membrane and the cleaning liquid that has permeated the separation membrane may be taken out as they are as the cleaning waste liquid, but can also be circulated to the concentrate side for cleaning. The cleaning time varies depending on the degree of contamination, the properties of the cleaning liquid, and the like, but is generally 10 to 120 minutes, preferably 20 to 60 minutes.

  The washing waste liquid is neutralized by separately taking out the washing liquid flowing along the separation membrane and the washing liquid permeating the separation membrane, or bringing them into a mixed state and bringing them into contact with the second cation exchanger in the acid form. Discharge. Since the washing effluent is alkaline, ion exchange is easily performed even in the case of a weakly acidic cation exchanger, and alkali metal ions such as sodium in the washing effluent are exchanged and adsorbed on the cation exchanger, and washing is repeated. Thus, the second cation exchanger becomes an alkali metal form. It is preferable that the neutralized washing drainage has a pH of 6-8.

  The second cation exchanger in the alkali metal form can be used as a first cation exchanger in a merry-go-round manner, thereby reducing the amount of alkali used as a regenerant and efficiently treating it. It can be performed. The first cation exchanger having exchanged and adsorbed hardness components such as calcium and magnesium can be regenerated into an acid form with an acid such as hydrochloric acid and used as the second cation exchanger. If the amount of the second cation exchanger in the alkali metal form is reduced by repeated washing, the cation exchanger can be regenerated with alkali to form the alkali metal form.

  In the present invention, by passing or permeating an alkaline cleaning liquid, contaminants adsorbed on or in the membrane surface of the separation membrane are peeled off and eluted to restore the performance of the separation membrane. Generally, the hardness component is precipitated due to alkalinity and causes clogging. However, in the present invention, the ion exchange treatment with the alkali metal type first cation exchanger causes precipitation and clogging. The hardness component that becomes can be removed. As a result, precipitation of hardness components under alkalinity can be prevented, and the separation membrane can be washed to efficiently recover the membrane separation performance.

  At this time, when an alkali metal weakly acidic cation exchanger is used as the first cation exchanger, the selectivity to the hardness component is high, and alkali metal ions are eluted by hydrolysis, so an alkali such as NaOH is not added. However, it is preferable because the cleaning liquid can be made alkaline. Moreover, since a weakly acidic cation exchanger can be easily regenerated, it can be converted into an acid form with a small amount of a regenerant and used as a second cation exchanger. In the second cation exchanger, it is preferable that the hardness component is removed, but alkali metal ions may remain and may be partially in an acid form.

  When a strongly acidic ion exchanger is used as the alkali metal ion exchanger, the hardness component is removed by the softening treatment, but there is almost no effect of raising the pH because hydrolysis does not occur. On the other hand, when an alkali metal weakly acidic ion exchanger is used, the alkali metal attached to the exchange group is easily eluted, so that the alkali metal ion is eluted by hydrolysis and becomes alkaline. On the other hand, since the weakly acidic resin has higher selectivity for Ca and Mg, treated water having a lower hardness component can be obtained.

As described above, in the present invention, a trace amount of CaCO ₃ , Ca (OH) is prepared by preparing a cleaning liquid through an alkali metal ion exchanger, as compared with the case of preparing a cleaning liquid by replacing with treated water and adding an alkali. ₂ , Mg (OH) _{2 and the} like are not clogged, so that the cleaning effect is enhanced. Further, by neutralizing and discharging the cleaning effluent with the acid-type second cation exchanger, there is no need for another neutralizing treatment step for the cleaning effluent, and the apparatus can be simplified.

    As described above, in the present invention, by using the first and second cation exchangers, the preparation of the alkaline cleaning liquid and the treatment of the alkaline cleaning waste liquid can be performed systematically and efficiently. In the above-described treatment, the alkaline washing effluent can be pretreated with activated carbon or the like before being brought into contact with the acid-form second cation exchanger. Further, as the washing water, it is more preferable to employ a membrane separation treated water such as a reverse osmosis membrane because the fouling substance of the membrane that cannot be removed by the ion exchanger is removed.

    According to the present invention, the decalcification and pH adjustment of the cleaning liquid and the neutralization of the cleaning waste liquid can be performed efficiently, the amount of chemicals used and the processing steps can be reduced, and the separation membrane can be cleaned safely and economically. Thus, a membrane separation method and apparatus capable of efficiently recovering the membrane separation performance can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing a membrane separation method and apparatus according to an embodiment applied to a reverse osmosis membrane separation apparatus, wherein (a) shows a membrane separation step, and (b) and (c) show a washing step.

  In FIG. 1, the membrane separation apparatus includes a membrane module 1 partitioned into a concentrate side 1a and a permeate side 1b by a separation membrane 2 and performs membrane separation. To the concentrated liquid side 1a of the membrane module 1, there are communicated a liquid supply path 11 for supplying a liquid to be processed and a liquid extraction path 12 for extracting the concentrated liquid. A processing liquid extraction path 13 for extracting the processing liquid communicates with the permeate side 1b of the membrane module 1. A cleaning liquid supply path 14 for supplying a cleaning liquid to the concentrated liquid side 1 a of the membrane module 1 communicates with the liquid supply path 11 to be processed. The concentrated liquid extraction path 12 and the processing liquid extraction path 13 communicate with a cleaning drainage extraction path 15 that extracts the cleaning drainage from the concentrated liquid side 1a and the permeate side 1b of the membrane module 1 in a switchable manner. The cleaning liquid supply path 14 is provided with a first cation exchange tank 22 containing a first weakly acidic cation exchanger 21 of an alkali metal type. The washing drainage discharge passage 15 is provided with a second cation exchange tank 24 containing an acid-form second weakly acidic cation exchanger 23. P is a pump and 25 is a cleaning liquid storage tank.

  The membrane separation method in the membrane separation apparatus of FIG. 1 adds the liquid to be processed to the concentrated liquid side 1a of the membrane module 1 by the pump P from the liquid supply path 11 as shown in FIG. The pressure is supplied, membrane separation is performed by the separation membrane 2, and the processing liquid is taken out from the permeate side 1 b through the processing liquid outlet 13. The concentrated liquid is taken out from the concentrated liquid side 1 a of the membrane module 1 through the concentrated liquid extraction path 12.

  First, as shown in FIG. 1B, the cleaning process supplies the liquid to be treated as cleaning water from the cleaning liquid supply path 14 to the first cation exchange tank 22 to form the first weakly acidic cation exchanger in the alkali metal form. 21, the hardness component is removed and softened by ion exchange, and the alkali is eluted to prepare an alkaline cleaning solution. The prepared cleaning liquid is pressurized and supplied to the concentrated liquid side 1 a of the membrane module 1 through the liquid supply path 11 to be processed by the pump P, partly permeates the separation membrane 2, and partly flows along the separation membrane 2. Then, contaminants attached to the separation membrane 2 are removed. When using the processing liquid as the cleaning water, the processing liquid taken out through the processing liquid extraction path 13 is stored in the cleaning liquid storage tank 25 from the line 31 and supplied to the first cation exchange tank 22 from the line 32 to prepare an alkaline cleaning liquid. To do.

  The concentrated liquid taken out from the concentrated liquid side 1a of the membrane module 1 and the permeated liquid taken out from the permeated liquid side 1b are taken out from the concentrated liquid take-out path 12 and the treatment liquid take-out path 13 to the wash waste liquid take-out path 15 as a wash drain and circulate. In the case of washing, circulation is performed from line 31 through line 32 or line 33, and washing is repeated. When the cleaning process is completed or when the cleaning liquid is discharged, the cleaning waste liquid is supplied from the cleaning drain liquid discharge path 15 to the second cation exchange tank 24 to be in the acid form of the second weakly acidic cation exchanger 23. And then neutralized by ion exchange and discharged out of the system.

  By repeating the washing, the first weakly acidic cation exchanger 21 of the first cation exchange tank 22 becomes a hardness component form, and the second weakly acidic cation exchanger 23 of the second cation exchange tank 24 becomes an alkali metal. When it becomes a shape, as shown in FIG.1 (c), it wash | cleans by switching the 1st cation exchange tank 22 and the 2nd cation exchange tank 24. FIG. In this case, the second weakly acidic cation exchanger 23 of the second cation exchange tank 24 is used as the first weakly acidic cation exchanger 21 of the alkali metal type, and the first cation exchanger 22 of the first cation exchange tank 22 is used. The weakly acidic cation exchanger 21 is regenerated with acid and used as the second weakly acidic cation exchanger 23 in the acid form, and the cleaning liquid supply path 14, the cleaning drainage path 15 and the lines 31, 32, 33 are switched. Wash.

Example 1:
Nitto Denko's 12-inch reverse osmosis membrane module (NTR759HR) equipped with 12 reverse osmosis membrane devices, treated wastewater treated with MF and filtered after biological treatment of industrial wastewater with electrical conductivity of 200mS / m and pH7.2 Is supplied at an operating pressure of 1.2 Mpa and a flow rate of 15 m ³ / h to conduct membrane separation, with an electric conductivity of 1.8 mS / m, pH 6.9 permeated water (treated water) of 12 m ³ / h, and an electric conductivity of 960 mS. 3 m ³ / h of concentrated water having a pH of 7.3 was obtained.

As a washing step, a washing liquid obtained by biologically treating the factory wastewater once a day and then aggregating and MF-filtering washing water through a first cation exchange resin to adjust the pH to 10 is used as an operating pressure of 1.2 Mpa and a flow rate of 15 m ^3. Permeated at / h for 30 minutes to wash with alkali, and the washing effluent was neutralized with a second cation exchange resin. As the first and second cation exchange resins, weak acid cation exchange resin BAYER Levacit CNP80 was used and regenerated to Na form and H form with 25% sodium hydroxide and 5% hydrochloric acid, respectively. In addition, when not performing the said washing | cleaning process, the treated water flow rate is 8.5 m < ³ > / h (reduction rate 29%) after 1 day, and 5.2 m < ³ > / h (reduction rate 56%) after 2 days. there were.

  The first cation exchange resin is regenerated into H form with hydrochloric acid and used as the second cation exchange resin in the acid form at a rate of once every 5 washes. The exchange resin was used as it was as the first alkali metal type cation exchange resin, and the washing was repeated by switching to the merry-go-round type. Further, the second cation exchange resin was regenerated to Na form with sodium hydroxide at a rate of once per 5 times of regeneration of the first cation exchange resin to the H form.

At this time, Na-type resin tower inlet water has an electric conductivity of 200 mS / m, pH 7.2, total hardness 50 mg as CaCO ₃ / L, Na-type resin tower outlet water has an electric conductivity of 320 mS / m, pH 11.2, total hardness. 0.5 mg as CaCO ₃ / L or less, reverse osmosis membrane outlet water and H-shaped resin tower inlet water are conductivity 320 mS / m, pH 11.0, total hardness 0.5 mg asCaCO ₃ / L or less, H-shaped resin tower outlet water is The electric conductivity was 230 mS / m, pH 6.8, and the total hardness was 0.5 mg asCaCO ₃ / L or less.
Comparative Example 1:
As Comparative Example 1, washing was performed in the same manner with a washing solution prepared by adding sodium hydroxide to the treated water of the reverse osmosis membrane to pH 10.

  Table 1 shows the reduction rate (%) of the permeation flux of the reverse osmosis membrane after each washing in Example 1 and Comparative Example 1. As apparent from Table 1, in Example 1, the effect of reducing clogging of the reverse osmosis membrane was confirmed.

It is a flowchart which shows the membrane separation method and apparatus of embodiment. (A) shows a membrane separation step, and (b) and (c) show a washing step.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane module 1a Concentrated liquid side 1b Permeated liquid side 2 Separation membrane 11 To-be-processed liquid supply path 12 Concentrated liquid extraction path 13 Processing liquid extraction path 14 Cleaning liquid supply path 15 Cleaning waste liquid extraction path 21 1st weakly acidic cation exchanger 22 1st cation exchange tank 23 2nd weak acid cation exchanger 24 2nd cation exchange tank 25 Cleaning liquid storage tank 31, 32, 33 line

Claims (4)

A membrane separation step of supplying a liquid to be treated to the separation membrane and separating the membrane;
A cleaning liquid preparation step of bringing the cleaning water into contact with the alkali metal type first cation exchanger and performing an ion exchange treatment, and adjusting the pH to be alkaline.
A cleaning step of supplying the prepared cleaning liquid to the separation membrane for cleaning, and a neutralization step of neutralizing the discharged cleaning drainage by contacting with the second cation exchanger in the acid form,
A method for cleaning a separation membrane, wherein a second cation exchanger that has become an alkali metal form by neutralization is used as the first cation exchanger.   The method of claim 1, wherein the first or second cation exchanger is a weakly acidic cation exchanger. A membrane module having a separation membrane for membrane separation,
A treatment liquid supply path for supplying a treatment liquid to the concentrate side of the membrane module,
A treatment liquid take-out path for removing the treatment liquid from the permeate side of the membrane module,
A cleaning liquid supply path for supplying a cleaning liquid to the concentrate side of the membrane module;
A cleaning drainage passage for removing the cleaning drainage from the permeate side of the membrane module;
An alkali metal type first cation exchanger tank provided in the cleaning liquid supply path; and an acid type second cation exchanger tank provided in the cleaning drainage path,
The cleaning liquid supply path is also connected to the second cation exchanger tank, and the cleaning drainage discharge path is also connected to the first cation exchanger tank, and the first cation exchanger tank and the second cation exchanger tank are connected to each other. Ri drop-in replacement Ri switch and a cation exchanger tank, configured membrane separation device to use a second cation exchanger became alkali metal form by neutralization as the first cation exchanger.   4. An apparatus according to claim 3, wherein the first or second cation exchanger is a weakly acidic ion exchanger.

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