JPH084728B2 - Membrane module cleaning method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used, for example, when an aggregating agent is added for the purpose of removing COD, color and phosphorus of an organic wastewater such as a secondary treatment liquid of human waste, and separation treatment is carried out. The present invention relates to a cleaning method for Iruru membrane module.

[0002]

2. Description of the Related Art As a conventional method for cleaning a membrane module, as described in Japanese Patent Laid-Open No. 1-307407, a membrane module used in a pure water production line or the like and having rust on the membrane surface is treated with an acid. 1 kg of phosphoric acid aqueous solution as
circulating washing at a pressure of cm ^2, washed with water, sterilizing and washing process of membrane modules then circulated wash aqueous sodium hypochlorite solution at a pressure of 1 kg / cm ² have been known. Further, as described in this publication, it is known that cleaning can be performed by immersing in an aqueous solution of these acids or oxidizing agents, and that oxalic acid, citric acid, etc. are also used as the acid. Has been. In addition, JP-A-2-63529
As described in Japanese Patent Publication No. JP-A-2004-242242, an ultrafiltration membrane module used in the treatment of organic wastewater is circulated and washed with an aqueous solution of oxalic acid, washed with water, and then washed with an aqueous solution of sodium hypochlorite. Is known. Further, as described in JP-A-2-253832, a membrane module in which tap water is filtered is subjected to acid cleaning and alkali cleaning, and then an ion exchange resin is introduced to remove residual acid or alkali. Is known.

[0003]

However, the above-mentioned Japanese Patent Laid-Open Nos. 1-307407 and 2-6352.
In any of the cleaning methods for membrane modules as described in Japanese Patent Publication No. 9, only the first chemical solution is circulated and cleaned, the second chemical solution is circulated and cleaned, or the membrane module is only immersed in these chemical solutions. The circulation cleaning alone cannot remove the substance strongly adhered to the film, and the immersion cleaning alone causes the chemical solution to act on the substance strongly adhered to the film and the substance that is easily separated. Excess chemicals and soaking time are required, and the reaction between the inner and outer surfaces of the membrane and the inner surface of the membrane module and the chemical solution is insufficient with only one of the circulation cleaning and the immersion cleaning. However, since it is a toxic substance, there is a problem in safety. Furthermore, JP-A-2-
The method described in Japanese Patent No. 253832 has a problem that an expensive ion exchange resin is required. Furthermore, conventionally,
Although the citric acid cleaning is performed at about pH2, the aggregated organic matter is denatured at pH2, and it is difficult to remove the aggregated organic deposits in the alkaline cleaning performed after the citric acid cleaning.

The present invention has been made in view of the above-mentioned problems. By removing the substance that easily adheres to the film by circulating cleaning, and dipping cleaning only the strongly adhered residual substance, Adhesives on the inner and outer surfaces of the membrane and the inner and outer surfaces of the membrane module react sufficiently with chemicals to remove membrane contaminants and prevent redeposition, reducing drug consumption and shortening dipping time The present invention provides a method for cleaning a membrane module, which is capable of enhancing the cleaning effect, is safe, and can be operated at low cost.

[0005]

According to a first aspect of the present invention, there is provided a method for cleaning a membrane module according to the first aspect of the present invention, in which a coagulant is added to organic wastewater to cause coagulation and solid-liquid separation into coagulation flocs and treated water. In the method of cleaning the membrane module, the wastewater in the membrane is extruded and washed with water, and then the citric acid aqueous solution having a pH of 3.5 to 4.5 is circulated to wash the membrane, and then the membrane is immersed in the same aqueous solution to further wash the inside of the membrane. After the remaining citric acid aqueous solution is extruded and washed with water, an effective chlorine-containing alkaline aqueous solution is circulated for washing, then the membrane is immersed in the same aqueous solution, and then washed with water.

The method for cleaning a membrane module according to a second aspect of the present invention is the same as the method for cleaning a membrane module according to the first aspect, in which extrusion with water, an aqueous solution of citric acid and an aqueous solution of sodium hypochlorite and circulation are performed. The membrane inlet operation pressure during cleaning is 1 kg / cm ^{2 to 2} kg / cm ² , and the membrane surface velocity is 1 m / s.
Is what is.

[0007]

In the method for cleaning a membrane module according to the first aspect of the present invention, the inorganic deposit on the membrane is a metal of an aqueous solution of citric acid while the organic matter is kept in an agglomerated state by circulating cleaning with an aqueous solution of citric acid. It is dissolved and removed by the blocking force. Next, the aggregating organic matter remaining on the membrane is decomposed and removed by the oxidizing power of effective chlorine by circulating cleaning with a chlorine-containing alkaline aqueous solution. Further, after circulating cleaning with each chemical, the membrane is immersed in the same chemical to cause the chemical to act from the inner and outer surfaces of the membrane, thereby effectively promoting the decomposition, peeling, and dissolution reaction of the substance attached to the membrane. Moreover, by adjusting the pH of the citric acid solution to 4, the denaturation of the aggregated organic substance can be prevented, and it becomes easy to remove the inorganic adhering substance by acid washing and the organic adhering substance by alkaline washing.

In the method for cleaning a membrane module according to the second aspect of the present invention, a flow velocity is applied to the membrane surface to remove substances that easily adhere to the membrane and are easily peeled off, and at the same time, the membrane module is filled with a chemical solution. Then, when the circulation cleaning is performed under high pressure, the adhered substance once peeled from the membrane adheres again, and when the pressure of the circulation cleaning is low, it takes a long time to fill the membrane module with the chemical solution. By extruding with an aqueous solution and an aqueous solution of sodium hypochlorite, and operating pressure at the membrane inlet at the time of circulating cleaning to 1 kg / cm ^{2 to 2} kg / cm ² and a membrane surface flow rate of 1 m / s, contaminants in the cleaning waste liquid are Does not reattach to the film surface.

[0009]

EXAMPLES An apparatus for carrying out the method for cleaning a membrane module of the present invention will be described with reference to FIG.

1 is a water tank, 2 is an acid liquid tank, 3 is an alkaline liquid tank, and each of these tanks 1, 2 and 3 is a valve 1a,
It is connected via 2a, 3a to a feed line 5 to which a pump 4 is connected, which feed line 5 is connected via a membrane inlet valve 6 to a tubular membrane 8 of a membrane module 7. Also,
The tubular membrane 8 is connected to a discharge line 10 via a membrane outlet valve 9. This discharge line 10 has a valve 1b,
It is connected to the tanks 1, 2 and 3 via 2b and 3b, and the discharge pipeline 10 is connected to the external drainage path via a valve 11b.

Further, the drainage pipe 10 connected to the outlet on the lower side of the permeate side of the membrane module 7 through the valve 12 has valves 1c, 2c,
It is connected to each of the tanks 1, 2 and 3 via 3c, and this discharge line 10 is connected to the outside drainage line via a valve 11c.

A drainage pipe 13 connected to the upper outlet of the permeate side of the membrane module 7 is connected to each of the tanks 1, 2 and 3 via valves 1d, 2d and 3d, and further, this discharge pipe 13
Is connected to the outside drainage system via valve 11d.

Next, a method of cleaning the membrane module with this apparatus will be described.

In the extrusion process, the valves 6 and 9 connected to both ends of the tubular membrane 8 and the valve 12 connected to the lower outlet of the permeate side of the membrane module 7 are opened to make the water tank 1
Open the valve 1a connected to the other tanks 2 and 3 and close the valves 2a and 3a connected to the other tanks 2 and 3 to open the valve 2a connected to the acid solution tank 2 and the other tank 1 , 3 connected to valves 1a and 3a are closed, the valve 3a connected to the acid solution tank 2 or the alkaline solution tank 3 is opened, and valves 1a and 2a connected to the other tanks 1 and 2 are closed and alkali Water, an acid solution, or an alkaline solution is passed from the liquid tank 3 by the pump 4 to the membrane module 7, and the residual liquid in the tubular membrane 8 is removed by the valves 1b, 2b,
By closing 3b and opening 11b, the water is pushed out of the system and drained, while the valve 12 connected to the lower outlet of the permeate side is opened.
The cleaning wastewater that has permeated the membrane 8 is discharged to the outside of the system by opening the valve 11c.

In the full water full circulation process, the valve 12 connected to the lower outlet of the permeate side of the membrane module 7 is closed, the valve 11b for discharging the drainage pipe 10 out of the system is closed, and the valve 6 connected to both ends of the membrane 8 is closed. , 9 are opened, valves 1a and 1b connected to the water tank 1 are opened, and valves 2a, 2b, 3a and 3b connected to the other tanks 2 and 3 are closed from the water tank 1 and the acid solution tank. Valves 2a and 2b connected to No. 2 are opened, valves 1a, 1b, 3a and 3b connected to other tanks 1 and 3 are closed, and valves 3a and 3b are connected from the acid solution tank 2 or the alkaline solution tank 3 And the valves 1a, 1b, 2a and 2b connected to the other tanks 1 and 2 are closed, and water or acid solution or alkali solution is supplied from the alkaline solution tank 3 by the pump 4 to the membrane 8 of the membrane module 7 by the chemical solution pump 4, respectively. To each tank 1, 2, 3 To circulate.

The water, the acid liquid or the alkaline liquid that has passed through the membrane 8 is accumulated in the membrane module 7 by closing the valve 12, and the inside of the membrane module 7 is filled with water. By opening or closing the valves 1d, 2d, 3d connected to the permeate side upper outlet, the valves 1d, 2d, 3d are returned to the respective tanks 1, 2, 3 for circulation.

In the dipping step, the pump 4 is stopped and the valves 6 and 9 connected to both ends of the membrane 8 are closed after the water, acid solution or alkali solution is completely circulated.

As a high-level treatment after the biological reaction treatment of human waste treatment, ferric chloride was used as a flocculant, and a flocculation treatment was carried out by applying a membrane separation device to solid-liquid separation.

The specifications and operating conditions of the membrane module used for the coagulation treatment are as follows.

Membrane Module Specifications Separation Membrane; Tubular UF Membrane (Polyacrylonitrile Membrane) Fractionated Molecular Weight; 40,000 Membrane Area; 2m ² Aggregation Treatment Conditions Water Flow Period; 3 Weeks Inlet Operating Pressure; 2kg / cm ^{2 to} 3kg / cm ² Coagulant injection rate: 1000 mg / l to 1500 mg / l Polymer flocculant coagulant injection rate: 4 mg / l to 5 mg / l Coagulation treatment pH; 5 The membrane module that has been subjected to the coagulation treatment operation described above is subjected to a washing recovery treatment. It was The washing conditions are as follows.

Washing conditions Inlet operating pressure; 1.5 kg / cm ² chemical solution; Acid 2.0 wt% citric acid aqueous solution with sodium hydroxide added to pH
Aqueous solution of 4.

An alkaline aqueous solution of sodium hypochlorite having an effective chlorine concentration of 200 mg / l and sodium hydroxide added thereto to adjust the pH to 12.

In the extrusion process, the water tank 1, the acid liquid tank 2, or the alkaline liquid tank 3 to the pump 4 are used.
The water, the acid solution or the alkali solution is removed by the membrane module 7
The residual liquid in the membrane module 7 is extruded to the outside of the system and discharged, while the cleaning wastewater that has permeated the membrane 8 is also discharged to the outside of the system.

In the full water full circulation process, water or acid solution or alkaline solution is passed from the water tank 1 or the acid solution tank 2 or the alkaline solution tank 3 by the pump 4 to the membrane module 7 by the chemical solution pump 4, respectively. It is circulated back to the tanks 1, 2, and 3 of. The water, the acid solution, or the alkaline solution that has passed through the membrane module 7 is accumulated in the membrane module 7, and after the inside of the membrane module 7 is filled with water, the valves 1d, 2d, and 3d are opened or opened from the permeate-side upper outlets, respectively. By closing it, it is returned to each tank 1, 2, 3 and circulated.

In the dipping step, the pump 4 is stopped and the valves 6 and 9 connected to both ends of the membrane 8 are closed after the water, acid solution, or alkali solution is completely circulated.

In each washing, washing step 1 is carried out with water for 10 minutes before the acid solution washing, the waste water in the membrane 8 is replaced with water, and then the acid solution is extruded for 30 seconds and the full circulation is 4 times. The membrane module 7 was allowed to stand for 20 hours in the immersed state.

Cleaning Step 2 Before moving to the alkaline solution cleaning, the acid cleaning waste solution in the membrane 8 is extruded with water for 10 minutes, and then the full circulation with water is performed 30 times.
Do for a minute. Then, 30 seconds after extrusion with the alkaline solution, full water full circulation was carried out for 4 hours, and the membrane module 7 was allowed to stand in the immersed state for 20 hours.

Washing Step 3 As a washing finishing step, after the alkaline washing waste liquid in the membrane 8 is extruded with water for 10 minutes, the full circulation with water is performed 30 times.
I went for a minute.

[0029] The water permeability with the cleaning process 1, 2, 3 by a membrane 8, as was prewashed ^{15l / m 2 · h / kg} / cm 2 ^{is, 120 l / m 2 · h} / kg / rose to cm ² .

Comparative Example 1 Acid cleaning (cleaning 1) at an inlet operating pressure of 1.5 kg / cm ² and alkali cleaning were carried out in the same manner as in Example except that a 2.0 wt% citric acid aqueous solution (pH = 2) was used as the acid solution. (Washing 2) and water washing (washing 3) were performed.

Comparative Example 2 Acid cleaning with an inlet operating pressure of 1.5 kg / cm ² (cleaning 1) was carried out in the same manner as in Example except that a 2 wt% aqueous citric acid solution adjusted to pH = 5 with sodium hydroxide was used as the acid solution. ), Alkali cleaning (cleaning 2), and water cleaning (cleaning 3).

Comparative Example 3 Acid washing was carried out using a 2 wt% aqueous citric acid solution adjusted to pH = 4 with sodium hydroxide as an acid solution in the same manner as in Example except that the inlet operating pressure was 2.5 kg / cm ^2. (Washing 1), alkali washing (washing 2), and water washing (washing 3) were performed.

Comparative Example 4 Acid washing was carried out by using a 2 wt% aqueous citric acid solution adjusted to pH = 4 with sodium hydroxide as an acid solution in the same manner as in Example except that the inlet operation pressure was 3.5 kg / cm ^2. (Washing 1), alkali washing (washing 2), and water washing (washing 3) were performed.

Comparative Example 5 In the cleaning steps 1 and 2, the inlet operation pressure was 1.5 kg / cm in the same manner as in Example except that the immersion cleaning for 20 hours with circulation of 4 hours was not performed.
² , acid cleaning (cleaning 1), alkaline cleaning (cleaning 2),
Washing with water (washing 3) was performed.

The changes in water permeability according to the above Examples and Comparative Examples 1 to 5 are shown in Table 1 and FIGS. 2 and 3.

Cleaning solution A: Acid solution adjusted to pH = 4 by adding sodium hydroxide to a 2 wt% citric acid aqueous solution B; Acid adjusted to pH = 5 by adding sodium hydroxide to a 2 wt% citric acid aqueous solution Solution C: 2 wt% citric acid aqueous solution, pH = 2 C; sodium hypochlorite aqueous solution containing 200 mg / l of available chlorine and sodium hydroxide added, pH = 12 Example; A + D Comparative Example 1; C + D Comparative Example 2; B + D Comparative Example 3; A + D Comparative Example 4; A + D Comparative Example 5; A + D

[0037]

[Table 1]

From Table 1 and FIGS. 2 and 3, the inlet operation at the time of low pH as in Comparative Example 1, the high pH as in Comparative Example 2, and the washing operation as in Comparative Examples 3 and 4 It is understood that when the pressure is high or when the immersion cleaning is not performed as in Comparative Example 5, the permeability of the membrane 8 cannot be sufficiently restored.

On the other hand, in the examples, the pH of the acid chemical solution is 3.5 to 4.5, preferably pH = 4, which is close to the pH range of the coagulation treatment.
Since it was adjusted to, it is possible to prevent denaturation of aggregated organic substances due to pH change during acid washing, and to dissolve and remove inorganic deposits while keeping organic substances in an aggregated state so that organic substances can be smoothly removed by alkali washing. Next, 200 available chlorine
By using the alkaline chemical solution containing mg / l, the decomposition power of the aggregated organic matter remaining in the membrane is promoted by utilizing the oxidizing power of effective chlorine, and a high amount of permeated water is obtained. Further, in the examples, since the inlet operation pressure is low, it is understood that the contaminants in the cleaning waste liquid are extruded without re-adhering to the membrane surface and the cleaning effect is promoted.

[0040]

According to the invention of claim 1, since the membrane is immersed in the same aqueous solution and allowed to stand still after the circulation cleaning with the acid aqueous solution or the circulation cleaning with the alkaline aqueous solution,
The substances that are easily peeled off and adhered to the film can be removed by circulation cleaning, the substances that are strongly adhered can be removed by immersion cleaning, and the burden of immersion cleaning is only the firmly adhered substances, and the chemical solution penetrates from the inner and outer surfaces of the film. Effectively decomposes, exfoliates, and dissolves the film-adhering substance, and then effectively extrudes and discharges with water, which can improve the cleaning effect.In addition, citric acid has a pH of 3.5 to 4.5, so Deterioration can be prevented, and it becomes easy to remove inorganic adhering substances by acid washing and organic adhering substances by alkaline washing.

[0041] According to the invention described in claim 2, it is prevented from film inlet operation pressure of contaminants during extrusion for low and 1kg / cm ² ~2kg / cm ² is reattached to the film surface.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the amount of permeated water of a membrane module and pH.

FIG. 3 is a characteristic diagram showing the relationship between the amount of permeated water of the membrane module and the inlet pressure of the circulating cleaning liquid.

[Explanation of symbols]

 7 membrane module 8 membrane

Claims (2)

[Claims] 1. A method for cleaning a membrane module in which a coagulant is added to organic wastewater to cause coagulation, and solid-liquid separation is performed between coagulated flocs and treated water. .5 ~ 4.5
The citric acid aqueous solution is circulated and washed, then the membrane is immersed in the same aqueous solution, and the citric acid aqueous solution remaining in the membrane is extruded and washed with water, and then an effective chlorine-containing alkaline aqueous solution is circulated and washed, Then immerse the membrane in the same aqueous solution,
Next, a method of cleaning a membrane module, which comprises cleaning with water. 2. The membrane inlet operating pressure during extrusion and circulation cleaning with water, an aqueous citric acid solution and an aqueous sodium hypochlorite solution is 1 kg / cm ^{2 to 2} kg / cm ² , and a membrane surface velocity is 1 m / s. The method for cleaning a membrane module according to claim 1, wherein the membrane module is cleaned.