JP2016172216A - Cleaning method of separation membrane of membrane separation device, cleaning chemical, and separation membrane cleaning system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning method of a separation membrane which can sufficiently clean a separation membrane in a short time.SOLUTION: A separation membrane of a membrane separation device 6 used in membrane separation activated sludge treatment is cleaned by using a chemical 36 containing sodium hypochlorite 20 and acid 23. A mixed amount of the acid 23 of the chemical 36 is adjusted so that pH is in a range of 7-9.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separation membrane cleaning method, a cleaning chemical solution, and a separation membrane cleaning system for a membrane separation apparatus used in membrane separation activated sludge treatment.

  Conventionally, as shown in FIG. 4, a membrane separator 81 is immersed in an activated sludge treatment tank 80, and a header pipe 84 communicates with each membrane cartridge 82 of the membrane separator 81 via a tube 83. When the separation membrane (filtration membrane) of each membrane cartridge 82 is washed, the filtration operation of the membrane separation device 81 is stopped, the sodium hypochlorite solution 86 is injected into the header pipe 84, and the hypochlorous acid in the header pipe 84 is injected. Hypochlorite is produced by natural head 88 due to the difference between the level of sodium acid solution 86 and the level of liquid 87 to be treated in activated sludge treatment tank 80 (for example, a mixture of raw water such as human waste and activated sludge). A sodium acid solution 86 is injected into each membrane cartridge 82. As a result, the sodium hypochlorite solution 86 permeates the separation membrane 85 from the permeate side to the liquid to be treated with a minute flux, and the separation membrane (not shown) is washed.

  Incidentally, as described above, the washing of the separation membrane of the membrane cartridge using the sodium hypochlorite solution is described in, for example, Patent Document 1 below.

Japanese Patent No. 3290555

  In the above conventional format, a commercially available sodium hypochlorite stock solution (generally having an effective chlorine concentration of 12 wt%) is diluted with water, and this diluted sodium hypochlorite solution is used for cleaning the separation membrane. Since the pH of the commercially available sodium hypochlorite stock solution is approximately 12 to 13, there is a problem that the oxidizing power is low, the separation membrane is not sufficiently cleaned, and the cleaning requires a long time.

  An object of the present invention is to provide a separation membrane cleaning method, a cleaning chemical solution, and a separation membrane cleaning system of a membrane separation apparatus that can sufficiently clean the separation membrane in a short time.

  In order to achieve the above object, a method for cleaning a separation membrane of a membrane separation device according to the first aspect of the present invention includes a separation membrane of a membrane separation device used in membrane separation activated sludge treatment, containing sodium hypochlorite and an acid. Cleaning is performed using a chemical solution.

  Conventionally, in general, when sodium hypochlorite solution is mixed with an acid, chlorine gas may be generated. Therefore, the idea of washing a separation membrane using a sodium hypochlorite solution and a chemical solution containing an acid can be obtained. There wasn't. This time, the inventors of the present invention have found that by using a chemical solution obtained by adding an acid to a sodium hypochlorite solution, the pH of the chemical solution is lowered, the oxidizing power of the chemical solution is increased, and the detergency is improved. . Thereby, the separation membrane can be sufficiently washed in a short time using a small amount of chemical solution.

In the separation membrane cleaning method of the membrane separation apparatus according to the second aspect of the present invention, the amount of acid mixed is adjusted so that the chemical solution has a pH in the range of 7 to 9.
According to this, by mixing the sodium hypochlorite solution and the acid and adjusting the pH of the chemical solution to 9 or less, the oxidizing power of the chemical solution is increased and the cleaning power is improved. Moreover, generation | occurrence | production of chlorine gas can be suppressed (reduced) by adjusting pH of a chemical | medical solution to 7 or more.

  In the method for cleaning a separation membrane of the membrane separation apparatus according to the third aspect of the invention, the chemical solution is adjusted in pH by adding an acid during the feeding of sodium hypochlorite in contact with the separation membrane. is there.

According to this, since the pH of sodium hypochlorite is adjusted immediately before the chemical solution comes into contact with the separation membrane, generation of chlorine gas can be suppressed (reduced).
The separation membrane cleaning method of the membrane separation apparatus according to the fourth aspect of the present invention determines the acid mixing amount from the relationship between the acid mixing amount with respect to sodium hypochlorite and the pH determined in advance.

According to this, a chemical | medical solution can be adjusted to predetermined | prescribed pH easily and correctly.
In the fifth aspect of the present invention, the separation membrane cleaning method of the membrane separation apparatus is such that the effective chlorine concentration of the chemical solution is 0.01 to 0.2 wt%.

In the sixth aspect of the present invention, at least one of the number of times of cleaning and the effective chlorine concentration of the chemical solution is changed according to the transmembrane pressure difference before cleaning.
According to this, by measuring the transmembrane pressure difference before washing, it is possible to determine the degree of contamination of the separation membrane, and by changing the number of washings and the effective chlorine concentration of the chemical solution accordingly, the separation membrane Cleaning according to the degree of contamination can be performed. For example, when the transmembrane pressure difference is high, it is determined that the degree of contamination of the separation membrane is large, and the number of washings is increased or the effective chlorine concentration of the chemical solution is increased. Further, when the transmembrane pressure difference is low, it is determined that the degree of contamination of the separation membrane is small, and the number of washings is reduced or the effective chlorine concentration of the chemical solution is reduced. Thereby, effective cleaning without waste becomes possible.

  The seventh invention is a chemical solution for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment, which is a mixture of sodium hypochlorite and an acid so as to have a predetermined pH. is there.

The eighth invention is a separation membrane cleaning system for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
A first chemical reservoir for storing sodium hypochlorite;
A second chemical storage section for storing acid;
A dilution water reservoir for storing dilution water;
A chemical solution supply path for supplying dilution water from the dilution water reservoir to the membrane separation device;
A first chemical supply means connected to the chemical supply path for supplying sodium hypochlorite into the diluted water;
A second chemical supply means connected to the chemical supply path for supplying acid into the diluted water;
And a chemical liquid mixing means arranged in a chemical liquid supply path downstream of the first and second chemical liquid supply means.

  According to this, while supplying dilution water from a dilution water storage part to a chemical solution supply path, it supplies sodium hypochlorite from the first chemical solution storage part to dilution water of a chemical solution supply path by the first chemical solution supply means, The second chemical solution supply means supplies acid from the second chemical solution reservoir to the dilution water in the chemical solution supply path, and the chemical solution mixing means mixes the dilution water, sodium hypochlorite, and acid, thereby generating a chemical solution. The chemical solution is supplied to the separation membrane of the membrane separation device through the chemical solution supply path. As dilution water, clean water, MBR treated water, river water, etc. can be used.

  As described above, according to the present invention, by using a chemical solution obtained by adding an acid to a sodium hypochlorite solution, the pH of the chemical solution is lowered, the oxidizing power of the chemical solution is increased, and the detergency is improved. Can be sufficiently washed with a small amount of chemical solution or in a short time. Further, by adjusting the pH of the chemical solution to a range of 7 or more and 9 or less, the oxidizing power of the chemical solution is increased, the cleaning power is improved, and generation of chlorine gas can be suppressed.

It is a figure which shows the structure of the activated sludge processing tank in embodiment of this invention. It is a graph which shows the relationship between pH of a chemical | medical solution, and ORP. It is a graph which shows the neutralization curve when hydrochloric acid is added to sodium hypochlorite. It is a figure which shows the structure of the conventional activated sludge processing tank.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
In the first embodiment, as shown in FIG. 1, reference numeral 1 denotes an activated sludge treatment tank for supplying organic waste water (for example, sewage, human waste, factory waste water, etc.) to the upper part of the tank body 2. The supply system 4 communicates, and a discharge system 5 for discharging excess sludge communicates with the lower portion of the tank body 2. Inside the tank body 2, a liquid to be treated 3 (mixed liquid of organic waste water and activated sludge) is stored, and a submerged membrane separation device 6 is disposed so as to be immersed therein.

  The membrane separation device 6 includes a box-shaped casing 7 that is open at the top and bottom, and a plurality of flat-plate-shaped immersion membrane cartridges 8 arranged in the casing 7. Each membrane cartridge 8 is arranged in parallel in the vertical direction, and on the back side of the separation membrane 9, a membrane support plate, a separation membrane 9 (filtration membrane) provided to cover the surface of the membrane support plate, and And a permeate passage formed on the surface or inside of the membrane support plate.

  Each membrane cartridge 8 is connected to a suction pipe 12 via a tube 10, and a suction pump 13 is provided in the suction pipe 12. An air diffuser 14 is installed below the arrangement group of the membrane cartridges 8, and the air diffuser 14 is provided with a blower 16 via an air supply pipe 15.

  Further, the activated sludge treatment tank 1 is provided with a separation membrane cleaning system 19 (separation membrane cleaning device) for cleaning the separation membrane 9 of each membrane cartridge 8. The separation membrane cleaning system 19 includes a first chemical solution storage tank 21 (an example of a first chemical solution storage unit) that stores a sodium hypochlorite solution 20 and a second chemical solution that stores hydrochloric acid 23 (an example of an acid). A storage tank 24 (an example of a second chemical solution storage unit), a dilution water storage tank 27 (an example of a dilution water storage unit) that stores dilution water 26, and each membrane cartridge of the membrane separation device 6 from the dilution water storage tank 27 8, a chemical supply path 29 for supplying the dilution water 26, a first chemical supply means 30 connected to the chemical supply path 29 for supplying the sodium hypochlorite solution 20 into the dilution water 26, and a chemical supply Second chemical liquid supply means 31 connected to the path 29 for supplying the hydrochloric acid 23 into the dilution water 26, dilution water supply means 32 for supplying the dilution water 26 to the chemical liquid supply path 29, and first and second chemical liquids From supply means 30, 31 And a static mixer 33 (an example of a chemical-liquid mixing means) disposed in the chemical supply path 29 on the downstream side.

  The chemical solution supply path 29 is composed of a pipe, the upstream side is connected to the dilution water storage tank 27, and the downstream side is connected to the suction pipe 12. A chemical solution supply valve 35 is provided in the chemical solution supply path 29 between the static mixer 33 and the suction pipe 12. The first and second chemical liquid supply means 30, 31 and the dilution water supply means 32 are each constituted by a valve, a supply pump, and the like.

Hereinafter, the operation of the above configuration will be described.
During the filtration operation, the chemical solution supply valve 35 is closed and the suction pump 13 is driven to apply a suction negative pressure to the inside of each membrane cartridge 8, and the liquid to be treated 3 is filtered by this suction negative pressure. The liquid 3 to be treated is filtered by passing through the separation membrane 9 of each membrane cartridge 8, flows into the permeate flow path as a permeate, and is taken out of the system through the suction pipe 12. Further, the blower 16 is driven to diffuse air from the air diffuser 14.

  When the filtration operation as described above is performed for a predetermined period or when a cake layer adheres to the membrane surface of the separation membrane 9 of each membrane cartridge 8 due to the continuation of the filtration operation, the separation membrane 9 is washed as follows. .

First, the suction pump 13 and the blower 16 are stopped to stop the filtration operation.
Thereafter, the chemical solution supply valve 35 is opened, the dilution water 26 in the dilution water storage tank 27 is supplied to the chemical solution supply path 29 by the dilution water supply means 32, and the sodium hypochlorite in the first chemical solution storage tank 21 is supplied. The solution 20 is supplied to the dilution water 26 of the chemical solution supply path 29 by the first chemical solution supply means 30, and the hydrochloric acid 23 in the second chemical solution storage tank 24 is diluted with the dilution water of the chemical solution supply path 29 by the second chemical solution supply means 31. 26, the diluted water 26, the sodium hypochlorite solution 20, and the hydrochloric acid 23 are mixed by the static mixer 33. As a result, a chemical solution 36 containing the sodium hypochlorite solution 20 and hydrochloric acid 23 and diluted with the dilution water 26 is generated, and this chemical solution 36 is supplied from the chemical solution supply path 29 to the membrane cartridges 8 through the suction pipe 12. In contact with the separation membrane 9, the separation membrane 9 is washed with the chemical liquid 36.

  The sodium hypochlorite solution 20 uses a commercial product, and its pH is approximately 12-13. In contrast, the chemical solution 36 is adjusted to have a pH of 7 or more and 9 or less by mixing hydrochloric acid 23 and dilution water 26 with a commercially available sodium hypochlorite solution 20. The effective chlorine concentration is adjusted within the range of 0.01 wt% or more and 0.2 wt% or less.

  As described above, by setting the pH of the chemical liquid 36 to 9 or less, the oxidizing power of the chemical liquid 36 is increased and the cleaning power is improved. Further, by setting the pH of the chemical liquid 36 to 7 or more, generation of chlorine gas can be suppressed (reduced). In addition, when the pH is in the range of 7 or more and 9 or less, preferably by making the pH in the range of 8 or more and 9 or less, the improvement of the cleaning power and the suppression of the generation of chlorine gas can be realized in a balanced manner. It is possible to keep the ratio of hydrochloric acid 23 to be low.

For example, hydrochloric acid 23 having a concentration of 4 wt% is used.
Table 1 below shows measured values of pH and ORP (redox potential) when diluting a commercially available sodium hypochlorite stock solution having an effective chlorine concentration of 12 wt% with water, and sodium hypochlorite diluted with water. The measured value of ORP when the pH is adjusted to approximately 8 by mixing hydrochloric acid into the solution is shown. The ORP value is a value obtained by converting a platinum electrode value into a hydrogen electrode equivalent value.

  According to this, for example, as described in the bottom column, when a sodium hypochlorite stock solution having an effective chlorine concentration of 12 wt% is diluted five times with water, the effective chlorine concentration of the sodium hypochlorite solution is 2.4 wt%. The pH at that time is 12.1 and the ORP is 740 mV. The ORP when the pH is adjusted to 8.0 by mixing hydrochloric acid with this diluted sodium hypochlorite solution is 1089 mV. Thus, it can be seen that by reducing the pH from 12.1 to 8.0 by mixing hydrochloric acid, the ORP increases from 740 mV to 1089 mV, so that the oxidizing power is improved. Similarly, in the 10 to 80-fold dilution, the ORP increases by lowering the pH to 8.0 or 8.1, so that the oxidizing power is improved.

また、下記表２は、有効塩素濃度０．６ｗｔ％の次亜塩素酸ナトリウム溶液１００ｍＬに濃度４ｗｔ％の塩酸を混合したときのｐＨとＯＲＰ（水素電極換算値）との測定値を示し、例えば次亜塩素酸ナトリウム溶液に塩酸を１５ｍＬ添加した場合、このときの塩酸の添加量は１６．４ミリ当量となり、混合液のｐＨが８．１４、ＯＲＰが１０６９ｍＶとなる。

Table 2 below shows measured values of pH and ORP (hydrogen electrode equivalent) when 100 mL of sodium hypochlorite solution having an effective chlorine concentration of 0.6 wt% was mixed with hydrochloric acid having a concentration of 4 wt%. When 15 mL of hydrochloric acid is added to the sodium hypochlorite solution, the amount of hydrochloric acid added at this time is 16.4 milliequivalent, the pH of the mixture is 8.14, and the ORP is 1069 mV.

図２に、上記表２のｐＨとＯＲＰの関係を示すグラフを記載している。これによると、次亜塩素酸ナトリウム溶液に塩酸を混合してｐＨを１２から下げていくことにより、ＯＲＰが上昇するため、酸化力が向上することが分かる。

FIG. 2 is a graph showing the relationship between pH and ORP in Table 2 above. According to this, it can be understood that ORP increases by mixing hydrochloric acid with sodium hypochlorite solution and lowering the pH from 12, so that the oxidizing power is improved.

  Therefore, by diluting the commercially available sodium hypochlorite solution 20 with the dilution water 26 and mixing hydrochloric acid 23 to adjust the pH of the chemical solution 36 within the range of 7 or more and 9 or less, the chemical solution Since the oxidizing power of 36 is increased and the cleaning power is improved, the separation membrane 9 can be sufficiently cleaned in a short time.

  FIG. 3 shows a neutralization curve in which the relationship between the addition amount of hydrochloric acid and the pH of the mixed solution shown in Table 2 is graphed, and the pH of the mixed solution decreases as the added amount of hydrochloric acid (mg / liter) increases. However, from the vicinity of pH 8, the pH tends to gradually decrease with an increase in the amount of hydrochloric acid added. In addition, when the pH is in the range of 7 or more and 9 or less, the pH gradually decreases as the amount of hydrochloric acid added increases as described above. Therefore, based on the viewpoint of sufficiently suppressing the generation of chlorine gas and the viewpoint of suppressing the addition amount of hydrochloric acid 23, the pH is more preferably in the range of 8 or more and 9 or less.

  By preparing a neutralization curve as shown in FIG. 3 for sodium hypochlorite solutions with various effective chlorine concentrations in advance, the amount of hydrochloric acid mixed with the sodium hypochlorite solution with various effective chlorine concentrations and The relationship with pH can be grasped in advance. Based on this relationship, the first chemical solution supply means 30, the second chemical solution supply means 31, and the dilution water supply means 32 of the separation membrane cleaning system 19 are controlled by the control means (not shown), and the dilution water 26 and the next By adjusting the mixing amount of the sodium chlorite solution 20 and the hydrochloric acid 23, the pH of the chemical solution 36 can be easily and accurately adjusted within the range of 7 or more and 9 or less.

(Second Embodiment)
In the second embodiment, the transmembrane differential pressure before cleaning the membrane cartridge 8 is measured, and at least one of the number of cleanings and the effective chlorine concentration of the chemical liquid 36 is changed according to the intermembrane differential pressure.

  For example, when the threshold A is set for the transmembrane pressure difference of the membrane cartridge 8 and the transmembrane pressure difference measured before washing is equal to or greater than the threshold A, it is determined that the degree of contamination of the separation membrane 9 is large, and the number of washings is set. Rinse more than two times instead of once. Further, when the transmembrane pressure difference measured before the cleaning is less than the threshold A, it is determined that the degree of contamination of the separation membrane 9 is small, and the cleaning is performed once.

As a result, cleaning according to the degree of contamination of the separation membrane 9 can be performed, and efficient cleaning without waste becomes possible.
In the second embodiment, the number of cleanings is changed according to the transmembrane pressure difference measured before cleaning, but the effective chlorine concentration of the chemical liquid 36 may be changed. For example, when the transmembrane pressure difference measured before cleaning is equal to or higher than the threshold A, it is determined that the separation membrane 9 is heavily soiled, and cleaning is performed using a chemical solution 36 having a high effective chlorine concentration (for example, a concentration of 0.2 wt%). To do. When the transmembrane pressure difference measured before washing is less than the threshold value A, it is judged that the separation membrane 9 is dirty, and washing is performed using a chemical solution 36 having a low effective chlorine concentration (for example, a concentration of 0.01 wt%). To do.

Moreover, you may change both the frequency | count of washing | cleaning and the effective chlorine concentration of the chemical | medical solution 36 according to the transmembrane differential pressure measured before washing | cleaning.
In the second embodiment, each determination and each change may be performed using a control unit (not shown).

  In each of the above embodiments, hydrochloric acid 23 is used as an example of the acid, but a mineral acid other than hydrochloric acid 23 may be used.

6 Membrane Separator 9 Separation Membrane 19 Separation Membrane Cleaning System 20 Sodium Hypochlorite Solution 21 First Chemical Solution Storage Tank (First Chemical Solution Storage Unit)
23 Hydrochloric acid (acid)
24 2nd chemical | medical solution storage tank (2nd chemical | medical solution storage part)
26 Dilution water 27 Dilution water storage tank (dilution water storage part)
29 Chemical liquid supply path 30 First chemical liquid supply means 31 Second chemical liquid supply means 33 Static mixer (chemical liquid mixing means)
36 chemicals

Claims (8)

A method for cleaning a separation membrane of a membrane separation device, comprising: cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment using a chemical solution containing sodium hypochlorite and an acid. The method for cleaning a separation membrane of a membrane separation apparatus according to claim 1, wherein the amount of the acid mixed is adjusted so that the chemical solution has a pH in the range of 7 or more and 9 or less. The membrane separation apparatus according to claim 1 or 2, wherein the chemical solution is adjusted in pH by adding an acid in the middle of feeding sodium hypochlorite in contact with the separation membrane. Method for cleaning the separation membrane. 4. The method for cleaning a separation membrane of a membrane separation apparatus according to claim 2, wherein the acid mixing amount is determined from the relationship between the acid mixing amount with respect to sodium hypochlorite and the pH determined in advance. . The method for cleaning a separation membrane of a membrane separation device according to any one of claims 1 to 4, wherein the effective chlorine concentration of the chemical solution is in the range of 0.01 wt% or more and 0.2 wt% or less. . 6. The membrane separation device according to claim 1, wherein at least one of the number of times of cleaning and the effective chlorine concentration of the chemical solution is changed according to the transmembrane pressure difference before cleaning. Method for cleaning the separation membrane. A chemical solution for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment, characterized in that sodium hypochlorite and an acid are mixed so as to have a predetermined pH. Chemical solution for cleaning. A separation membrane cleaning system for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
A first chemical reservoir for storing sodium hypochlorite;
A second chemical storage section for storing acid;
A dilution water reservoir for storing dilution water;
A chemical solution supply path for supplying dilution water from the dilution water reservoir to the membrane separation device;
A first chemical supply means connected to the chemical supply path for supplying sodium hypochlorite into the diluted water;
A second chemical supply means connected to the chemical supply path for supplying acid into the diluted water;
A separation membrane cleaning system comprising: a chemical liquid mixing unit disposed in a chemical liquid supply path downstream of the first and second chemical liquid supply units.

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