JP6576062B2 - Separation membrane cleaning method for membrane separation apparatus - Google Patents

Description

  The present invention relates to a method for cleaning a separation membrane of a membrane separation apparatus used in membrane separation activated sludge treatment.

  Conventionally, as shown in FIG. 7, 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, the oxidizing power is low, the separation membrane is not sufficiently cleaned, and one cleaning requires a long time (about 2 hours). There was a problem.

  An object of the present invention is to provide a separation membrane cleaning method of a membrane separation apparatus that can sufficiently clean the separation membrane.

In order to achieve the above object, the first invention is a method of cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
As a chemical for cleaning, a chemical containing sodium hypochlorite and acid is used.
Compare the transmembrane pressure difference after washing the separation membrane with chemicals and the predetermined threshold,
If the transmembrane pressure difference after the first cleaning is greater than or equal to the threshold, the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning are compared,
If the difference between the transmembrane differential pressure before cleaning and the transmembrane differential pressure after the initial cleaning is equal to or greater than the preset reference value, it is judged that the cleaning power of the chemical at the first cleaning is strong, and the effective chlorine concentration of the chemical Wash the separation membrane lower than the first time washing,
If the difference between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning is less than the preset reference value, it is judged that the cleaning power of the chemical at the first cleaning is weak, and the effective chlorine concentration of the chemical Is higher than that at the time of the first cleaning, and the separation membrane is cleaned .

  According to this, in general, when sodium hypochlorite solution is mixed with an acid, chlorine gas may be generated, so the idea of cleaning the separation membrane using a sodium hypochlorite solution and a chemical solution containing an acid is It was not obtained. 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 using the chemical solution.

  When the separation membrane is washed using a chemical solution containing sodium hypochlorite and an acid as described above, the higher the effective chlorine concentration of the chemical solution, the better the cleaning power against the separation membrane. There is a concern that residual chlorine oozes from the surface of the separation membrane and adversely affects activated sludge.

  In the present invention, the effective chlorine concentration of the chemical solution is set to a predetermined concentration in advance, and the transmembrane differential pressure before cleaning and the transmembrane differential pressure after the initial cleaning are compared, and if the difference between these two transmembrane differential pressures is large Then, it is determined that the effective chlorine concentration of the chemical solution is high and the cleaning power of the chemical solution is strong, and then the separation membrane is cleaned using a chemical solution having an effective chlorine concentration lower than a predetermined concentration. As a result, excessive supply of chlorine to the separation membrane can be prevented, the amount of residual chlorine can be reduced, and residual chlorine can be prevented from seeping out from the surface of the separation membrane and adversely affecting the activated sludge. Can do.

  In addition, if the difference between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the first cleaning is small, it is determined that the effective chlorine concentration of the chemical solution is insufficient and the cleaning power of the chemical solution is weak. Clean the separation membrane using a chemical solution with high effective chlorine concentration. Thereby, the detergency of the chemical solution is improved and the separation membrane can be sufficiently washed.

  Alternatively, a predetermined threshold value is set in advance for the transmembrane pressure difference, and the transmembrane pressure difference before the cleaning and the transmembrane pressure difference after the first cleaning are compared, and the transmembrane pressure difference after the first cleaning is less than the threshold value. If there is, it is determined that the separation membrane has been sufficiently washed by the first (first) washing, and the washing is terminated. If the transmembrane pressure difference after the first cleaning is equal to or greater than the threshold value, it is determined that the initial cleaning alone is insufficient, and the cleaning is performed again until the transmembrane pressure difference after the cleaning becomes less than the threshold value. repeat.

This second invention is a method for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
As a chemical for cleaning, a chemical containing sodium hypochlorite and acid is used.
Compare the transmembrane pressure difference after washing the separation membrane with chemicals and the predetermined threshold,
If the transmembrane pressure difference after the first cleaning is greater than or equal to the threshold, determine the difference between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning,
When the difference between the transmembrane pressure difference before washing and the transmembrane pressure difference after the first washing is less than the preset reference value, the number of washings after the first washing The difference is greater than the number of cleanings after the initial cleaning when the difference from the transmembrane pressure difference is greater than or equal to a preset reference value .
The separation membrane cleaning method of the membrane separation apparatus according to the third aspect of the present invention reduces the effective chlorine concentration of the chemical solution as the number of times increases when cleaning with the chemical solution is performed a plurality of times.
According to this, it is possible to prevent excessive supply of chlorine to the separation membrane, reducing the amount of residual chlorine, and suppressing the residual chlorine from seeping out from the surface of the separation membrane and adversely affecting the activated sludge. be able to.
In the method for cleaning a separation membrane of a membrane separation apparatus according to the fourth aspect of the present invention, the amount of acid mixed is adjusted so that the chemical solution has a pH of 7 or more and 9 or less.
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 fifth aspect of the invention, the separation membrane cleaning method of the membrane separation apparatus is such that the effective chlorine concentration of the chemical solution is in the range of 0.01 wt% or more and 0.1 wt% or less.
In the sixth aspect of the invention, the separation membrane cleaning method of the membrane separation apparatus is such that the contact time between the chemical solution and the separation membrane is 60 minutes or less per cleaning.

In the seventh aspect of the present invention, the separation membrane cleaning method determines the mixing amount of the acid from the relationship between the mixing amount of the acid 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 suitable for washing | cleaning easily and correctly.

  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 thoroughly washed. Moreover, it is possible to prevent excessive supply of chlorine to the separation membrane, reducing the amount of residual chlorine, and suppressing the residual chlorine from seeping out from the surface of the separation membrane and adversely affecting the activated sludge. it can.

It is a figure which shows the structure of the activated sludge processing tank in the 1st 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 flowchart which shows the washing | cleaning method of the separation membrane in 1st Embodiment. 3 is a flowchart showing a separation membrane cleaning method. It is a flowchart which shows the washing | cleaning method of the separation membrane in 2nd Embodiment. 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 passes through the suction pipe 12 from the chemical solution supply path 29 to the inside of each membrane cartridge 8. To the separation membrane 9, and 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 0.1 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 the pH is in the range of 8 or more and 9 or less, improvement of the detergency and suppression of generation of chlorine gas can be realized in a balanced manner.

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, a pH range of 8 or more and 9 or less is more preferable.

  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.

  As described above, the separation membrane cleaning system 19 uses the chemical solution 36 in which the pH is in the range of 7 to 9 and the effective chlorine concentration is adjusted to the range of 0.01 wt% to 0.1 wt%. When the separation membrane 9 of the membrane cartridge 8 is washed, the higher the effective chlorine concentration of the chemical solution 36, the better the cleaning power for the separation membrane 9. On the other hand, the amount of residual chlorine increases and the residual chlorine is separated from the separation membrane 9. There is a concern that it may ooze out from the surface and adversely affect activated sludge.

As a countermeasure against the above-mentioned concerns, the separation membrane 9 is cleaned by the following cleaning method.
In advance, the effective chlorine concentration of the chemical solution 36 is set to a predetermined concentration A within a range of 0.01 wt% or more and 0.1 wt% or less, and further, a predetermined threshold B is set to the transmembrane pressure difference of the membrane cartridge 8. deep.

  As shown in FIG. 4, the separation membrane 9 is washed using the chemical solution 36 having the effective chlorine concentration of the predetermined concentration A (step-1). At this time, the transmembrane differential pressure of the membrane cartridge 8 before cleaning and the transmembrane differential pressure of the membrane cartridge 8 after the first (first) cleaning are measured, and the transmembrane differential pressure after the first cleaning is less than the threshold value B. If so (step-2), it is determined that the separation membrane 9 has been sufficiently washed by the first washing, and the washing is terminated.

  In Step-2, if the transmembrane pressure difference after the first cleaning is equal to or greater than the threshold value B, it is determined that the first cleaning alone is insufficient, and the transmembrane pressure difference before the cleaning and the first cleaning time When the difference C is equal to or greater than a preset reference value D (step -4), the detergency of the chemical liquid 36 at the first cleaning is strong. And the waste liquid of the chemical liquid 36 remaining in the membrane cartridge 8 at the time of the first cleaning is discharged from the suction pipe 12 to the outside of the system (Step-5), and thereafter 0.01 wt% or more and 0.1 wt% or less In this range, the chemical solution 36 having an effective chlorine concentration AL lower than the predetermined concentration A is supplied to each membrane cartridge 8 to perform the second cleaning (step-6).

  The transmembrane pressure difference of the membrane cartridge 8 after the second washing is measured, and if the transmembrane pressure difference after the second washing is less than the threshold B (Step-7), the separation membrane 9 is removed by the second washing. Judge that it has been sufficiently washed, and finish washing. As a result, excessive supply of chlorine to the separation membrane 9 can be prevented, the amount of residual chlorine is reduced, and the residual chlorine oozes from the surface of the separation membrane 9 and suppresses adverse effects on the activated sludge. can do.

  If the transmembrane pressure difference after the second cleaning is equal to or greater than the threshold value B in the above step-7, it is determined that the second cleaning alone is insufficient, and the two remaining in the membrane cartridge 8 are present. The waste liquid of the chemical liquid 36 at the time of the second cleaning is discharged from the suction pipe 12 to the outside of the system (step -8), and then the chemical liquid 36 having an effective chlorine concentration AL lower than the predetermined concentration A is supplied to each membrane cartridge 8 for cleaning. Washing is repeated until the subsequent transmembrane pressure difference falls below the threshold value B (step-9).

  Further, as shown in FIG. 4, the transmembrane pressure difference after the first cleaning in Step-2 is equal to or greater than the threshold value B, and the transmembrane pressure difference before the cleaning and the transmembrane difference after the first cleaning in Step-4. When the difference C from the pressure is less than the reference value D, it is determined that the cleaning power of the chemical liquid 36 at the first cleaning is weak, and the chemical liquid 36 at the first cleaning remaining in the membrane cartridge 8 as shown in FIG. The waste liquid is discharged from the suction pipe 12 to the outside of the system (step -10), and thereafter each chemical solution 36 having an effective chlorine concentration AH higher than a predetermined concentration A is within a range of 0.01 wt% or more and 0.1 wt% or less. The film is supplied to the membrane cartridge 8 and the second cleaning is performed (step-11). Thereby, the cleaning power of the chemical liquid 36 is improved, and the separation membrane 9 can be sufficiently cleaned.

  The transmembrane pressure difference of the membrane cartridge 8 after the second washing is measured, and if the transmembrane pressure difference after the second washing is less than the threshold value B (step -12), the separation membrane 9 is removed by the second washing. Judge that it has been sufficiently washed, and finish washing. As a result, excessive supply of chlorine to the separation membrane 9 can be prevented, the amount of residual chlorine is reduced, and the residual chlorine oozes from the surface of the separation membrane 9 and suppresses adverse effects on the activated sludge. can do.

  Further, if the transmembrane pressure difference after the second cleaning is equal to or higher than the threshold value B in the above step-12, it is determined that the second cleaning alone is insufficient, and the second time remaining in the membrane cartridge 8. The waste liquid of the chemical liquid 36 at the time of cleaning is discharged from the suction pipe 12 to the outside of the system (step -13), and then the chemical liquid 36 having an effective chlorine concentration AH higher than the predetermined concentration A is supplied to each membrane cartridge 8 and after cleaning The cleaning is repeated until the transmembrane pressure difference of the pressure drops below the threshold value B (step -14).

  For example, as an example, the effective chlorine concentration of the chemical solution 36 is set to a predetermined concentration A of 0.05 wt%, the transmembrane differential pressure threshold B of the membrane cartridge 8 is set to 5 kPa, the reference value D is set to 3 kPa, and the initial water flow The transmembrane differential pressure at the time is 3 kPa, and the transmembrane differential pressure before cleaning is 12 kPa.

  Then, the membrane cartridge 8 is cleaned using the chemical solution 36, and the transmembrane pressure difference of the membrane cartridge 8 after the initial cleaning is measured. For example, when the measured transmembrane differential pressure after the initial cleaning is 4 kPa, the threshold value Since it is less than B (5 kPa), it is determined that the separation membrane 9 has been sufficiently washed by the first washing, and the washing is terminated.

  In addition, when the measured transmembrane pressure difference after the first cleaning is 7 kPa, it is determined that the initial cleaning alone is insufficient because the pressure is equal to or higher than the threshold value B (5 kPa). 12 kPa) and the difference C (12−7 = 5 kPa) between the transmembrane pressure difference (7 kPa) after the first cleaning. Since the difference C (5 kPa) is equal to or greater than the reference value D (3 kPa), it is determined that the cleaning power of the chemical liquid 36 at the time of the initial cleaning is strong, and the waste liquid of the chemical liquid 36 at the time of the initial cleaning remaining in the membrane cartridge 8 Is discharged out of the system from the suction pipe 12, and then a chemical solution 36 having an effective chlorine concentration AL (for example, 0.03 wt%) lower than a predetermined concentration A is supplied to each membrane cartridge 8 to perform the second cleaning.

When the transmembrane pressure difference after the second cleaning is 4 kPa, for example, it is less than the threshold value B (5 kPa), so it is determined that the separation membrane 9 has been sufficiently cleaned by the second cleaning, and the cleaning ends.
Further, when the transmembrane pressure difference after the second cleaning is 6 kPa, for example, it is equal to or higher than the threshold B (5 kPa), so it is determined that the second cleaning alone is insufficient, and remains in the membrane cartridge 8. The waste liquid of the chemical liquid 36 at the time of the second cleaning is discharged out of the system from the suction pipe 12, and then the chemical liquid 36 having the effective chlorine concentration AL is supplied to each membrane cartridge 8, and the transmembrane pressure difference after the cleaning is increased. Washing is repeated until it drops below the threshold B (5 kPa).

  Further, when the transmembrane pressure difference after the first cleaning is, for example, 10 kPa (that is, the threshold value B or more), the difference C between the transmembrane pressure difference before the cleaning and the transmembrane pressure difference after the first cleaning is 2 kPa (12− 10 = 2 kPa), which is less than the reference value D (3 kPa). In this case, it is determined that the cleaning power of the chemical liquid 36 at the time of the initial cleaning is weak, and the waste liquid of the chemical liquid 36 at the time of the initial cleaning remaining in the membrane cartridge 8 is discharged out of the system from the suction pipe 12 and then has a predetermined concentration A chemical solution 36 having an effective chlorine concentration AH (for example, 0.09 wt%) higher than A is supplied to each membrane cartridge 8 to perform the second cleaning.

  When the transmembrane pressure difference of the membrane cartridge 8 after the second washing is measured and the transmembrane pressure difference after the second washing is 4 kPa, for example, it is less than the threshold value B (5 kPa). It is determined that the separation membrane 9 has been sufficiently washed, and the washing is finished.

  If the transmembrane pressure difference after the second cleaning is 6 kPa (that is, the threshold value B or more), for example, it is determined that the second cleaning alone is insufficient, and the two remaining in the membrane cartridge 8 The waste liquid of the chemical liquid 36 at the time of the second cleaning is discharged from the suction pipe 12 to the outside of the system, and then the chemical liquid 36 having the effective chlorine concentration AH (for example, 0.09 wt%) is supplied to each membrane cartridge 8. Washing is repeated until the differential pressure drops below threshold B (5 kPa).

(Second Embodiment)
In the second embodiment, the effective chlorine concentration of the chemical liquid 36 is set to a predetermined concentration A in the range of 0.01 wt% or more and 0.1 wt% or less in advance, and the transmembrane pressure difference of the membrane cartridge 8 is set. A predetermined threshold B is set.
As shown in FIG. 6, the separation membrane 9 is washed using the chemical solution 36 having the effective chlorine concentration of the predetermined concentration A (step-1). At this time, the transmembrane differential pressure of the membrane cartridge 8 before cleaning and the transmembrane differential pressure of the membrane cartridge 8 after the first (first) cleaning are measured, and the transmembrane differential pressure after the first cleaning is less than the threshold value B. If so (step-2), it is determined that the separation membrane 9 has been sufficiently washed by the first washing, and the washing is terminated.

  Further, if the transmembrane pressure difference after the first cleaning in the step-2 is equal to or higher than the threshold value B, it is determined that the first cleaning alone is insufficient, and the transmembrane differential pressure before the cleaning and the first cleaning after the first cleaning are determined. When the difference C from the transmembrane pressure difference is obtained (step -3) and the difference C is equal to or larger than a preset reference value D (step -4), the cleaning power of the chemical liquid 36 at the first cleaning is strong. Judgment is made, and the number of times of cleaning after the first cleaning is set to one time (that is, a total of two times including the first cleaning) (Step-5), and the first cleaning remaining in the membrane cartridge 8 after the first cleaning. The chemical liquid 36 is discharged from the suction pipe 12 to the outside of the system (step-6), the second cleaning is performed using the chemical liquid 36 having a predetermined concentration A (step-7), and then the cleaning is terminated.

  Further, the transmembrane pressure difference after the first cleaning is equal to or higher than the threshold value B in Step-2, and the difference C between the transmembrane pressure difference before the cleaning and the transmembrane pressure difference after the first cleaning is the reference in Step-4. If it is less than the value D, it is judged that the cleaning power of the chemical liquid 36 at the time of the first cleaning is weak, and the number of cleanings after the first cleaning is set to two times (that is, a total of three times including the first cleaning) (Step-8) ) After the first cleaning, the second and third cleanings are performed (Step-9 to Step-12), and the cleaning is completed.

  In the second embodiment, the transmembrane pressure difference after the first cleaning is greater than or equal to the threshold value B, and the difference C between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the first cleaning is greater than or equal to the reference value D. In this case, cleaning is performed twice in total, and when the transmembrane pressure difference after the first cleaning is not less than the threshold value B and the difference C is less than the reference value D, cleaning is performed three times in total. Washing may be performed multiple times other than twice and multiple times other than three times. In this case, the number of cleanings when the difference C is less than the reference value D is set to be larger than the number of cleanings when the difference C is greater than or equal to the reference value D.

  In the second embodiment, the cleaning is performed a plurality of times using the chemical liquid 36 having the predetermined concentration A, but the effective chlorine concentration of the chemical liquid 36 is decreased below the predetermined concentration A each time the number of cleanings is increased. Also good. For example, when the predetermined concentration A is 0.05 wt%, the chemical solution 36 having an effective chlorine concentration of 0.05 wt% is used at the first cleaning, and the chemical solution 36 having an effective chlorine concentration of 0.04 wt% is used at the second cleaning. In addition, a chemical solution 36 having an effective chlorine concentration of 0.03 wt% may be used during the third cleaning.

  According to this, it is possible to prevent the excessive supply of chlorine to the separation membrane 9, the amount of residual chlorine is reduced, and the residual chlorine oozes from the surface of the separation membrane 9 and adversely affects the activated sludge. Can be suppressed.

In the first and second embodiments, hydrochloric acid 23 is used as an example of the acid, but a mineral acid other than hydrochloric acid 23 may be used.
Further, the cleaning method shown in the flowchart of FIGS. 4 and 5 of the first embodiment and the cleaning method shown in the flowchart of FIG. 6 of the second embodiment are respectively provided with control means (not shown). It may be configured to be used automatically.

  In the first and second embodiments described above, when considering that the residual chlorine adversely affects the activated sludge, the contact time between the chemical liquid 36 required for one cleaning and the separation membrane 9 is set to the conventional two hours. It is important that the contact time is shorter than the degree, and the contact time is preferably 60 minutes or less per washing.

6 Membrane separator 9 Separation membrane 20 Sodium hypochlorite solution 23 Hydrochloric acid (acid)
36 chemicals

Claims (7)

A method for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
As a chemical for cleaning, a chemical containing sodium hypochlorite and acid is used.
Compare the transmembrane pressure difference after washing the separation membrane with chemicals and the predetermined threshold,
If the transmembrane pressure difference after the first cleaning is greater than or equal to the threshold, the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning are compared,
If the difference between the transmembrane differential pressure before cleaning and the transmembrane differential pressure after the initial cleaning is equal to or greater than the preset reference value, it is judged that the cleaning power of the chemical at the first cleaning is strong, and the effective chlorine concentration of the chemical Wash the separation membrane lower than the first time washing,
If the difference between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning is less than the preset reference value, it is judged that the cleaning power of the chemical at the first cleaning is weak, and the effective chlorine concentration of the chemical The separation membrane cleaning method of the membrane separation apparatus is characterized in that the separation membrane is cleaned with a higher value than at the first cleaning . A method for cleaning a separation membrane of a membrane separation device used in membrane separation activated sludge treatment,
As a chemical for cleaning, a chemical containing sodium hypochlorite and acid is used.
Compare the transmembrane pressure difference after washing the separation membrane with chemicals and the predetermined threshold,
If the transmembrane pressure difference after the first cleaning is greater than or equal to the threshold, determine the difference between the transmembrane pressure difference before cleaning and the transmembrane pressure difference after the initial cleaning,
When the difference between the transmembrane pressure difference before washing and the transmembrane pressure difference after the first washing is less than the preset reference value, the number of washings after the first washing A method for cleaning a separation membrane of a membrane separation apparatus, characterized in that the number of cleanings after the initial cleaning is greater when the difference from the transmembrane pressure is greater than or equal to a preset reference value . 3. The method for cleaning a separation membrane of a membrane separation apparatus according to claim 2, wherein when the cleaning using the chemical solution is performed a plurality of times, the effective chlorine concentration of the chemical solution is lowered as the number of times increases . 4. The separation membrane of the membrane separation device 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 . 5. Cleaning method. 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 0.1 wt% or less. . The method for cleaning a separation membrane of a membrane separation device according to any one of claims 1 to 5, wherein the contact time between the chemical solution and the separation membrane is 60 minutes or less per cleaning. 7. The membrane separation apparatus according to claim 1, wherein the acid mixing amount is determined from a relationship between the acid mixing amount with respect to sodium hypochlorite and the pH determined in advance. Separation membrane cleaning method.

Images