JP2001286865A - Immersion type solid-liquid separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the effect of chemical washing to a filter membrane immersed into a membrane immersion tank, also to eliminate various troubles caused during chemical washing, and to facilitate operation control. SOLUTION: This membrane immersion type solid-liquid separator is provided with a liquid collecting part 6 on the bottom of the membrane immersion tank 1A, a taking-out means 13 for taking out the liquid in this liquid collecting part 6, and a sensor LS for detecting a liquid level of the liquid collecting part 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for immersing a filtration membrane in raw water containing an organic suspension having a concentration of suspended solids (SS) of 500 mg / L or more, represented by activated sludge. The present invention relates to a membrane immersion type solid-liquid separation device that obtains filtered water by performing membrane filtration, and in particular, enhances the effect of chemical cleaning of a filtration membrane immersed in a membrane immersion tank and solves various troubles that occur simultaneously during chemical cleaning. The present invention relates to a membrane immersion type solid-liquid separation device which facilitates operation management.

[0002]

2. Description of the Related Art It has been known that, as a method for directly filtering raw water containing a high concentration of an organic suspended substance, it is effective to immerse a filtration membrane in a water tank and perform filtration by external pressure. I have. According to this method, since the flow path of the liquid to be filtered in the tank can be widened, the liquid to be filtered is concentrated into a gel or cake, and the flow path of the liquid to be filtered or the membrane surface is formed. This is because it is possible to reduce the problem of obstruction.

FIG. 3 (a) is a sectional view showing a conventional membrane immersion type solid-liquid separation apparatus, and FIG. 3 (b) is a plan view of the same membrane immersion tank.

In FIG. 3, reference numeral 1 denotes a membrane immersion tank, in which membrane modules 3A and 3B having partition plates 2A and 2B having upper and lower openings on both sides are immersed in the center. The partition plates 2A and 2B are for aerating only the inside thereof with a blower B by an aeration tube 4 provided below the membrane module 3B, thereby promoting an upward flow due to the aeration.

[0005] Reference numeral 5 denotes an overflow port, which is used to overflow an excessively concentrated liquid to be filtered.

[0006] Raw water is supplied to the membrane immersion tank 1 from a pipe 11 provided with a pump P1, and membrane filtered water (permeated water) is taken out from a pipe 12 as treated water. The pipe 12 includes a self-priming pump P2, and a pressure gauge PI for measuring a filtration pressure is provided on a suction side of the pump P2, and a flow meter FI is provided on a discharge side.

LS is a liquid level detector (level switch), which detects three levels of liquid levels L-1, L-2 and L-3.
The liquid level L-1 is used for withdrawing the liquid in the tank, the liquid level L-2 is used for injecting the chemical, and the liquid level L-3 is used for the abnormal stop condition of the pump P2.

Reference numeral 13 denotes a pipe for extracting the liquid in the tank, which is provided with a pump P3 interlocked with the level switch LS. 14
Is a pipe for supplying a chemical solution, and has a pump P4. It should be noted that the pumps P3 and P4 may be used in common, and the liquid in the tank may be extracted and the flow path for supplying the chemical solution may be switched by switching the valve.

In such a membrane immersion type solid-liquid separation device, an MF (microfiltration) membrane or a UF (ultrafiltration) membrane is usually used as a filtration membrane for the membrane modules 3A and 3B.
An external pressure type hollow fiber membrane or flat membrane of the MF membrane is suitably used.

In the membrane filtration step, the liquid to be filtered in the membrane immersion tank 1 is aerated or agitated by a stirring means, whereby the concentration of the substance to be filtered (SS) on the membrane surface is suppressed and the clogging of the membrane is reduced. I do. In this case, as shown in FIG. 3, the membrane modules 3A, 3A
B, two partition plates 2A and 2B having upper and lower openings are provided in the vicinity of the side surface, and the membrane modules 3A and 3B inside the partition plates 2A and 2B are provided.
In many cases, a method is used in which only the lower part of the partition is aerated to generate an upward flow in the partition plates 2A and 2B by an air lift.

When membrane filtration is performed in such a manner, since a so-called cross-flow flux of the liquid to be filtered cannot be made high, the membrane flux is set at 1 in order to prevent membrane clogging.
It is set to be not more than m ³ / m ² / day. Further, in order to prevent the flow path of the liquid to be filtered from being blocked, it is necessary to provide a relatively large space between the membranes. Therefore, as a result, the membrane module requires a relatively large occupied area, and the membrane immersion tank also has a relatively large capacity. For example, in order to obtain treated water 100 m ³ / day are usually films volume of the immersion tank 1 10 to 50 m ³
(For example, as shown in FIG. 3, 3000 mm × 3800 mm ×
About 4000 mm).

By the way, in such a membrane immersion type solid-liquid separation apparatus, it is necessary to perform membrane cleaning for removing SS and the like adhering to the surface of the filtration membrane. However, as described above, the membrane modules 3A and 3B are used. Since the membrane immersion tank 1 is large and has a large capacity, for chemical cleaning of the membrane, the pump P1 is stopped to stop the flow of the raw water, and the liquid to be filtered in the membrane immersion tank 1 is moved out of the tank from the pipe 13. A method has been proposed in which, after being extracted, a cleaning chemical is introduced into the membrane immersion tank 1 from the pipe 14 to perform chemical cleaning while the membrane is installed in the membrane immersion tank 1 (for example, Japanese Patent Application Laid-Open No. HEI 1-1990).
0-309595). In this case, the liquid to be filtered in the membrane immersion tank 1 is treated as a waste liquid, or is evacuated to another water tank. In particular, when applied to activated sludge, a method is often employed in which the free board of the preceding biological treatment tank is taken high and returned to the biological treatment tank.

During the chemical cleaning, it is effective to agitate the membrane surface by using aeration or agitating means in the same manner as in the ordinary membrane filtration step to remove contaminants on the membrane surface.

[0014]

When the above-mentioned conventional chemical cleaning method was carried out, it was found that there were practically the following problems.

[Problem 1] When the liquid to be filtered was extracted from the inside of the membrane immersion tank, about 5% of the liquid to be filtered remained in the water tank.
The liquid level of the remaining liquid to be filtered (in the present specification, “liquid level” refers to the height from the bottom of the tank) is about 200 mm, and it is usually difficult to lower the liquid level further. . This is because it is difficult to sense the liquid level, and the liquid feed pump may draw air and cause a failure. In other words, if the pump used to extract the liquid in the tank continues to operate even after all the liquid has been sucked, there is a risk that the pump will be damaged by so-called emptying, and even if damage does not occur, air will remain inside the pump. There is a problem that it takes a long time to start up because the liquid is not sucked in smoothly at the next use.

Further, the suspended substance which settled and became sludge remained on the bottom surface of the membrane immersion tank. When the cleaning solution was introduced without removing the residue and the film surface was aerated, the following problem occurred. (1-1) Intense foaming occurred, and it was necessary to add a large amount of antifoaming agent of several tens mg / L. In particular, when the residual amount of the liquid to be filtered is as large as about 10%, the defoaming agent cannot completely suppress the foaming, and the foam overflows from the water tank, so that it is necessary to stop the aeration. In this case, the defoamer is a costly drug,
In addition, since it is necessary to provide an antifoaming agent injection facility, running costs and initial costs increase.

Further, since a highly alkaline chemical mainly composed of a high concentration of caustic soda is usually used as a cleaning chemical for the membrane, the foaming and overflowing of the chemical significantly deteriorates the safety of work.

Further, the need to stop the aeration frequently arises, so that the chemical cleaning effect of the membrane is reduced, and it is necessary to extend the cleaning time. In addition, since it is necessary to monitor the state of foaming and control the amount of aeration, the burden on the operator increases. In order to automate this work, it is necessary to install a foaming detection sensor, an aeration amount control valve, and these control circuits, which increases construction costs.

(1-2) In a membrane immersion tank using activated sludge as a liquid to be filtered, about 2% by weight of caustic soda and about 700 mg / L of available chlorine (sodium hypochlorite) are used as cleaning chemicals.
Was used, the available chlorine was consumed immediately after the start of washing, and the available chlorine concentration became 10 mg / L or less. Effective chlorine concentration effective for chemical cleaning of membrane is 5
The concentration was 00 mg / L or more. To maintain this concentration, it was necessary to supply 3000 mg / L of available chlorine. This amount was equivalent to six times the originally required amount of sodium hypochlorite, and the drug cost increased accordingly.

[Problem 2] When the chemical cleaning is completed, the chemical is taken out of the film immersion tank, and about 5% of the chemical remains in the tank. Raw water was introduced without removing the residue, and filtration was resumed. As a result, the following problems occurred.

(2-1) By mixing the chemical solution and the raw water, when an alkaline chemical solution is used, the liquid to be filtered becomes alkaline, and the treated water obtained through the membrane becomes alkaline. When an acidic chemical was used, the liquid to be filtered became acidic and the treated water became acidic. For this reason, it has been necessary to interrupt the supply or discharge of the treated water to the next process, and to neutralize the liquid in the membrane immersion tank. For this reason, the burden on the operator has increased, and a neutralization operation involving a danger particularly due to acid or alkali has been required. It should be noted that such a problem does not occur with a neutral chemical solution (such as a surfactant). However, a neutral chemical solution has a low cleaning effect and is not practical.

(2-2) In particular, using an alkaline chemical solution,
When the liquid to be filtered became alkaline, the liquid to be filtered foamed violently, and bubbles overflowed from the water tank, so that a large amount of antifoaming agent had to be added. Further, the treated water is colored and COD _Mn
Also rises by several tens of mg / L, and water quality (COD _Mn >
50 mg / L).

The present invention solves the above-mentioned conventional problems, enhances the effect of chemical cleaning of the filtration membrane immersed in the membrane immersion tank, and solves various troubles that occur simultaneously with chemical cleaning, thereby facilitating operation management. It is an object of the present invention to provide a membrane immersion type solid-liquid separation device that performs the following.

[0024]

According to the present invention, there is provided a membrane immersion type solid-liquid separation apparatus, comprising: a membrane immersion tank; a filtration membrane provided in the membrane immersion tank; and a means for discharging permeated water from the filtration membrane. Means for supplying raw water to the membrane immersion tank, means for stopping the supply of raw water,
Means for transferring the liquid in the membrane immersion tank to the outside of the tank, and membrane immersion type solid-liquid separation in which membrane filtration is performed by the filtration membrane immersed in raw water containing an organic suspension to obtain permeated water. In the apparatus, a liquid reservoir provided at a part of the bottom of the film immersion tank, a unit for extracting the liquid in the liquid reservoir, and a sensor for detecting a liquid level in the liquid reservoir are provided. And

The present inventor has been studying to solve the above-mentioned various troubles which occur simultaneously during the chemical cleaning, and in order to solve these troubles, in the chemical cleaning, the residual liquid in the membrane immersion tank is minimized. Was found to be effective.

That is, it is clear from the following findings that the problem described in the [Problem 1] can be solved by reducing the amount of the liquid to be filtered remaining in the membrane immersion tank before the cleaning chemical is introduced.

It is considered that the foaming in the problem 1-1 is caused by the fact that microorganisms in the liquid to be filtered emit a foaming substance when coming into contact with the drug. In particular, it is considered that the content of the cells released by the killing of the cells by the drug is the main cause of the foaming. The fact that microorganisms are generally concentrated to a high concentration in a membrane immersion tank and that microorganisms are deposited on the bottom to form a sludge promotes this phenomenon.

[0028] The consumption of available chlorine in Task 1-2 also
It is thought that the reaction occurred between the microorganisms remaining in the tank and the available chlorine, and the chlorine was consumed.

Therefore, these problems can be reduced or solved by discharging the microorganisms in the membrane immersion tank together with the liquid to be filtered and the sludge at the bottom to make the concentration low.

In addition, the following problems can be solved by reducing the amount of the chemical remaining in the membrane immersion tank after chemical cleaning and before introducing the liquid to be filtered, based on the following findings. did.

The acidification or alkalinization of the liquid to be filtered in the problem 2-1 is performed when the acid component or the alkali component of the chemical solution remaining in the membrane immersion tank exceeds the interference ability of the raw water charged into the membrane immersion tank. Occurs. Therefore, this fluctuation in pH can be suppressed by reducing the amount of the chemical remaining in the film immersion tank.

The problem of the problem 2-2 is that the microorganisms in the liquid to be filtered are killed by the alkali, and this is
It is considered that the liquid to be filtered is foaming due to a foaming substance which is a component and is released from the cells at that time. Therefore, this problem can be reduced or solved by reducing the amount of the chemical solution remaining in the film immersion tank and suppressing the pH fluctuation.

As described above, it is effective to minimize the amount of liquid remaining in the film immersion tank during chemical cleaning.

As in the membrane immersion type solid-liquid separation apparatus of the present invention, a liquid reservoir is provided on the bottom surface of the membrane immersion tank, means for extracting the liquid in the liquid reservoir, and a sensor for detecting the liquid level in the liquid reservoir. By interlocking these, the pump can be prevented from being emptied, and the liquid in the tank can be withdrawn to a depth of 200 mm or less. As a result, the amount of the residual liquid in the film immersion tank can be reduced to a very small amount, so that the trouble caused by the residual liquid can be effectively eliminated or reduced.

[0035]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 (a) is a sectional view showing an embodiment of a membrane immersion type solid-liquid separation apparatus of the present invention, and FIG. 1 (b) is a plan view of the same membrane immersion tank. FIG. 2 is a sectional view showing another embodiment of the membrane immersion type solid-liquid separation device of the present invention. In FIGS. 1 and 2, members having the same functions as the members shown in FIG. 3 are denoted by the same reference numerals.

In the membrane immersion type solid-liquid separation apparatus shown in FIG. 1, a concave portion serving as a liquid reservoir 6 is provided at one corner of the bottom surface of the membrane immersion tank 1A, and a pipe 13 provided with a suction pump P3 for extracting liquid in the tank. Is located near the bottom surface of the liquid reservoir 6, an air purge type liquid level detector (level switch) LS is provided in the liquid reservoir 6, and a supply pipe 15 for rinsing liquid is further provided. Unlike the conventional membrane immersion type solid-liquid separation device shown in FIG. 3, the other components have the same configuration.

The means for extracting the liquid in the tank provided in the liquid reservoir 6 may be any known means such as a submersible pump or the like in addition to the pipe 13 having the suction pump P3 as shown in FIG. It must be resistant to cleaning chemicals.

The liquid level detecting sensor provided in the liquid reservoir 6 may be of any type known in the art, but is preferably one which is not affected by scum or bubbles. The liquid reservoir 6 is located at the bottom of the membrane immersion tank 1A and tends to accumulate sludge. In particular, air is constantly supplied and the air level is detected by the pressure of the air. An expression level switch is preferred. In addition, a friction type level switch can also be suitably used.

The liquid reservoir 6 may be of any type as long as it does not hinder the operation of such a liquid extracting means and the operation of the liquid level detecting sensor, and its shape is not limited. If it is excessively large, the liquid remains in the liquid reservoir. Normally 250-5
The size is preferably about 00 mm square. Further, the position where the liquid reservoir 6 is installed is preferably a portion where the liquid flows without stagnation. Specifically, it is desirable that the distance from the bottom projection position of the aeration tube 5 be within 2000 mm, particularly within 1000 mm.

As shown in FIG. 1, when the partition plates 2A and 2B are provided to partition the swirling flow rising portion and the descending portion, the distance between the bottom surfaces of the partition plates 2A and 2B is 1500 mm or less, particularly 600 mm or less. Is preferred.

If the bottom surface of the film immersion tank 1A is completely flat, the liquid is likely to remain. The inclination of this inclination is preferably 3 to 100 per mil, particularly 5 to 2
It is good to use 0 per mil.

In chemical cleaning, the film immersion tank 1A
The liquid level detection sensor is preferably provided as low as possible in the membrane immersion tank 1A in order to reduce as much as possible the liquid to be filtered and sludge remaining therein, and the liquid level detection sensor is interlocked with the liquid extracting means in the tank. Is preferred.

As the rinsing liquid, clear water such as tap water, medium water, industrial water, or treated water is usually used. SS is 500mg /
If it is L or less, raw water can be substituted, but clear water is preferred as much as possible.

Accordingly, the rinsing liquid supply means may be provided with piping such as tap water or working water via a valve, or may supply treated water pressurized by a pump as needed via a valve. You may do it. Preferably, the rinsing liquid is interlocked with the liquid level detection sensor and automatically stops when the rinsing liquid is supplied to the rinsing liquid level. In this case, it is preferable to use an automatic valve as the valve of the rinsing liquid supply means. In addition, the rinsing liquid supply means includes the pipe 14 of the chemical liquid supply means and the pump P4.
And can be shared via a valve. When raw water is used as the rinsing liquid, a raw water supply unit can be used. In this case, it is not necessary to provide a separate rinsing liquid supply unit.

The means for supplying the rinsing liquid is preferably one capable of supplying a water amount of 20% or more of the capacity of the membrane immersion tank 1A within one hour, and desirably one capable of supplying water within 20 minutes. Further, the supply amount of the rinsing liquid is preferably at least three times, particularly preferably at least seven times the amount of the liquid remaining in the film immersion tank 1A. The liquid level is preferably about 50 to 700 mm. However, if added excessively, the cost of the rinsing liquid rises, the amount of waste liquid increases, or the time required for the membrane cleaning step increases, so that it is preferable to set the volume at most to half or less of the capacity of the membrane immersion tank. . It is preferable that the rinsing liquid extracted after being put into the membrane immersion tank be treated as a waste liquid, returned to the raw water tank, or put into the activated sludge treatment tank if there is an activated sludge treatment tank in the preceding stage. It is preferable that the rinse solution mixed with the chemical solution to form a diluted chemical solution is introduced into a step in which the chemical solution can be neutralized or neutralized in advance in a film immersion tank and then discharged. When the neutralization is performed in advance in the membrane immersion tank, the water level is low. Therefore, it is preferable to introduce the neutralizing agent into the circulation line while circulating the liquid in the tank by pumping. At this time, it is preferable that an instrument (such as a pH meter or an ORP meter) for detecting neutralization is also provided in the circulation line. The pump used for circulation is preferably shared with the pump used for extracting the liquid in the tank.

In the membrane immersion type solid-liquid separation apparatus shown in FIG.
1 is operated to supply raw water from the pipe 11 to the membrane immersion tank 1A, and the membrane P is extracted by the pump P2 through the pipe 12 as treated water. The chemical cleaning after the membrane filtration step can be preferably performed by the following procedure.

After stopping the blower B to stop the aeration and stopping the pumps P1 and P2 to stop the supply of the raw water and the removal of the treated water, the pump P3 is operated to extract the liquid in the tank from the pipe 13. . In extracting the liquid in the tank, in the membrane-immersion type solid-liquid separation device of the present invention, since the liquid reservoir 6 is provided on the bottom surface of the membrane immersion tank 1A, the tank is lowered to a considerably lower liquid level than in the prior art. Internal fluid can be extracted. The extraction of the liquid in the tank is performed 100 mm from the bottom surface 1a of the membrane immersion tank 1A by interlocking with the level switch LS.
It is preferable to perform the process so that the liquid level drops to the following.

After the liquid in the tank is extracted, a rinsing liquid is supplied from the pipe 15 and extracted from the pipe 13 together with the liquid remaining in the tank 1A. At this time,
It is preferable to perform the process so that the liquid level drops to 100 mm or less from the bottom surface 1a of the membrane immersion tank 1A. By supplying and extracting the rinsing liquid in this manner, the sludge at the bottom of the tank can be smoothly extracted, and adverse effects on chemical cleaning can be prevented. The supply and withdrawal of the rinsing liquid may be performed twice or more.

After the rinsing, the pump P 4 is operated to supply a chemical solution from the pipe 14 to perform chemical cleaning. After the chemical cleaning, the chemical solution in the film immersion tank 1 is extracted from the pipe 13.
At the time of this chemical cleaning, it is preferable to perform aeration at about ^{20 to} 100 m ³ / m ² / hr.

After the chemical cleaning, a rinse liquid is supplied in the same manner as described above, and the rinse liquid is extracted from the pipe 13 together with the chemical liquid remaining in the film immersion tank 1A. At this time, if necessary, the chemical is neutralized as described above. By supplying the rinsing liquid and extracting the rinsing liquid together with the chemical liquid in this manner, the amount of the chemical liquid remaining in the membrane immersion tank 1A can be significantly reduced, and adverse effects on the membrane filtration step can be prevented.

After the above rinsing, raw water is introduced from the pipe 11 and the membrane filtration is restarted. At this time, it is preferable that after supplying raw water into the membrane immersion tank 1A, filtration is started after elapse of a certain time while aeration is performed. That is, chromaticity and COD
May increase with the passage of time, particularly when the raw water is activated sludge.
The components can be partially biodegraded again by continuing the aeration. Further, when the cleaning liquid is alkaline and the raw water becomes alkaline, the aeration dissolves carbon dioxide in the atmosphere and has an effect of neutralizing the alkali. In addition, when the raw water is activated sludge and the activated sludge is circulated to and from the aeration tank provided at the preceding stage, normalization of pH, chromaticity, and COD can be reduced by the diffusion effect. Here, the waiting time is preferably about 30 minutes to 1 week, particularly preferably 1 hour to 1 day. In particular, when circulation is performed with another treatment tank, the residence time of the membrane immersion tank with respect to the amount of circulating water is 1 to 6 times, particularly 2 times.
~ 3 times is preferred.

The membrane-immersion type solid-liquid separation device shown in FIG. 1 is an example of an embodiment of the present invention, and the present invention is not limited to the illustrated one as long as it does not exceed the gist.
For example, there is no particular limitation on the shape and position of the liquid pool,
As shown in FIG. 2, the liquid pool 6A can be formed with the bottom surface of the film immersion tank 1B as an inclined surface.

[0054]

The present invention will be described more specifically with reference to comparative examples and examples.

Comparative Example 1 The amount of treated water was about 300 by using one aeration tank (capacity: 380 m ³ ) and three conventional membrane immersion tanks (capacity: 45 m ³ ) shown in FIG.
In a system in which a membrane activated sludge treatment was performed at m ³ / day, chemical cleaning of the membrane was performed. About 750 m ³ / day of activated sludge was pumped from the aeration tank to each membrane immersion tank by a pump, and about 650 m ³ / day of activated sludge was overflowed from the membrane immersion tank and returned to the aeration tank.

One of the membrane immersion tanks (tentatively referred to as tank A)
The activated sludge solution was temporarily stopped, and chemical cleaning was performed in the following procedure.

First, the activated sludge in the A tank was withdrawn using a self-priming slurry pump (hereinafter, referred to as a “pump for chemical washing”), and charged into an aeration tank. In this step, the friction type level switch provided below the tank A was automatically stopped by detecting a low water level, and there was no problem with the operation itself. However, about 300 mm of activated sludge remained at the bottom without being extracted.

Caustic soda 2 was added to tank A while sludge remained.
% By weight, and a membrane cleaning solution consisting of an effective chlorine concentration of 1000 mg / L (using sodium hypochlorite) was introduced, and 65 m ³ /
When the aeration was started at m ² / hr, the height of the foam became 2 m or more in about 30 minutes, and the foam began to overflow from the helicopter in the water tank. Therefore, the aeration was temporarily stopped, and an antifoaming agent equivalent to 10 mg / L was charged. . Thereafter, the aeration was restarted, but the foam rose to the helicopter in the water tank again in about 30 minutes, and the aeration was stopped again.
Thereafter, even if an antifoaming agent was added up to 50 mg / L, foaming could not be suppressed.

For this reason, the aeration amount was reduced to 30 m ³ / m ² / hr or less per the bottom area of the membrane installation part, and the washing was continued. However, the aeration was interrupted intermittently, and the overflow of bubbles from the water tank was suppressed. Needed.

When the effective chlorine concentration of the cleaning solution was measured, it was found to have dropped to 10 mg / L or less. Sodium hypochlorite equivalent to the effective chlorine concentration of 2000 mg / L was added again, and after 30 minutes, the residual chlorine concentration was again measured. Was measured,
It was about 700 mg / L. After this, the effective chlorine concentration gradually decreased, but 500 mg / L or more could be maintained at the end of the washing.

The chemical cleaning was carried out for a total of 16 hours in this manner. Even after the completion of the cleaning, adhesion of the sludge cake to the membrane surface was recognized, and the recovery rate of the filtration pressure difference was about 80% of that of the new membrane.

After the washing was completed, the aeration was stopped, and the chemical in the tank A was drawn out by a chemical washing pump, and again stopped automatically by a friction type level switch.
About m of the drug solution remained.

When the supply of the activated sludge was resumed from the aeration tank while the chemical liquid remained in the tank A, and the membrane overflowed again from the tank A, the membrane filtration was resumed. The solution had reached the vicinity, the solution was colored brown, and COD _Mn was about 60 mg / L. Therefore, the filtration was stopped, and only the supply and the overflow of the activated sludge were continued for about 3 hours. After that, when the filtration of the membrane was restarted, the pH of the permeated water became 7.6, the coloring became slight, and the COD _Mn became about 20 mg / L. In the aeration tank, pH control was performed by automatic control.

Example 1 In Comparative Example 1, the film immersion tank 1A shown in FIG.
The same operation was performed using. This pool 6 is 40
It has a size of 0 mm × 400 mm × 400 mm, and is provided at a position 700 mm from the bottom projection position of the diffuser tube 4 and 400 mm from the bottom projection position of the partition plate 2B.

In this membrane immersion tank, the suction pump P3 was placed at a position 100 mm from the lower end of the 400 mm square liquid reservoir 6.
The opening of the tip of the pipe 13 communicating with the suction side of the above was arranged, and a friction type level switch LS was installed at a position 350 mm from the lower end thereof, and was linked with the suction pump P3.

As a result, the activated sludge was removed from the tank bottom 1a by 50%.
mm or less, and the foaming during chemical cleaning was drastically reduced. However, it was preferable to add about 10 mg / L of the antifoaming agent. The effective chlorine concentration is also the initial concentration 1
000 mg / L, 600 mg / L immediately after introduction, and 400 mg / L at the end of washing.

It is not necessary to reduce the amount of aeration.
There was no problem even at about m ³ / m ² / hr.

When chemical cleaning was performed in this state for 16 hours, almost all of the sludge cake adhering to the membrane surface was peeled off.
The pressure difference recovered to over 90% of the new membrane.

After the chemical cleaning, the chemical in the tank is pumped by the suction pump P3.
, And stopped in conjunction with the friction type level switch LS. As a result, the chemical solution could be extracted from the bottom to 50 mm or less.

After that, the activated sludge was started to be introduced, and it was confirmed that overflow had started from the membrane immersion tank 1A. Then, the membrane filtration was started. As a result, the pH of the membrane permeated water was 8.4. there were. However, some coloring is recognized,
COD _Mn values rose to 35 mg / L.

Example 2 An operation was performed in the same manner as in Example 1 except that a rinsing step using raw water was performed before and after the chemical cleaning.

That is, after the activated sludge was extracted from the membrane immersion tank, raw water was introduced as rinsing water until the liquid level reached about 300 mm, and was again extracted to the 50 mm position. The flow rate of the raw water was about 10 m3 / hr, and the raw water was supplied for about 20 minutes.
Thereafter, the raw water for rinsing extracted from the inside of the membrane immersion tank was returned to the aeration tank, and then a chemical solution was supplied. Raw water is BOD
The water quality was about 800 mg / L, SS 150 mg / L, and normal hexane extracted substance 50 mg / L. The situation after extracting the raw water was almost the same as in Example 1,
Visual inspection of the bottom of the aquarium showed that the sludge was well discharged. The effective chlorine concentration immediately after the introduction of the chemical is about 750 m
g / L and about 550 mg / L after the completion of washing, it was judged to be better than Example 1.

After the completion of the chemical cleaning, the chemical was taken out, raw water was again charged to a water level of 300 mm, and raw water mixed with the remaining chemical was drawn to a water level of 50 mm. At this time, the raw water mixed with the chemical is 500m in front of the aeration tank.
^It was discharged to a ^three- volume raw water tank.

After that, the introduction of activated sludge into the membrane immersion tank was started, and the membrane filtration was started after the overflow. The pH of the permeated water was 7.6. Since the pH of the activated sludge in the aeration tank was 7.4, it was found that the increase in pH was suppressed to about 0.2. The COD value of the permeated water was about 20 mg / L, and no significant coloring was observed. In addition, the COD value of the membrane permeated water at normal time is 15 to 20.
Since it was about mg / L, it was determined that there was almost no deterioration in water quality of the membrane permeated water due to chemical cleaning.

[0075]

As described above in detail, according to the membrane immersion type solid-liquid separation device of the present invention, chemical cleaning of the membrane in the membrane immersion type solid-liquid separation device is facilitated under the following effects. Operation can be performed efficiently at low cost, and a good chemical cleaning effect can be obtained. Foaming at the time of chemical cleaning of the membrane and at the time of restarting the membrane filtration step after chemical cleaning can be suppressed. Accordingly, it is not necessary to stop the aeration at the time of chemical cleaning, and efficient chemical cleaning can be performed. Since the amount of chemicals used can be reduced, the cost for chemical cleaning can be reduced. After chemical cleaning, deterioration of water quality at the time of resuming the membrane filtration step is prevented, and treated water can be collected early after the resumption of the membrane filtration step.

The solid-liquid separation device of the membrane immersion type according to the present invention comprises water containing microorganisms such as activated sludge, water obtained by coagulating organic wastewater, water containing organic suspended substances such as proteins and starch, and the like. This is particularly effective for the treatment of activated sludge, and a remarkably good effect can be obtained by applying the present invention to an apparatus that performs a filtration operation on activated sludge.

[Brief description of the drawings]

FIG. 1 (a) is a sectional view showing an embodiment of a membrane immersion type solid-liquid separation device of the present invention, and FIG. 1 (b) is a plan view of the same membrane immersion tank.

FIG. 2 is a cross-sectional view showing another embodiment of the membrane immersion type solid-liquid separation device of the present invention.

FIG. 3 (a) is a cross-sectional view showing a conventional membrane immersion type solid-liquid separation device, and FIG. 3 (b) is a plan view of the same membrane immersion tank.

[Explanation of symbols]

 1,1A, 1B Membrane immersion tank 2A, 2B Partition plate 3A, 3B Membrane module 4 Aeration tube 5 Overflow port 6,6A Liquid reservoir

Claims (1)

[Claims] 1. A membrane immersion tank, a filtration membrane provided in the membrane immersion tank, means for discharging permeated water of the filtration membrane, means for supplying raw water to the membrane immersion tank, and supply of raw water A means for stopping, and a means for transferring the liquid in the membrane immersion tank to the outside of the tank, wherein the membrane is filtered by the filtration membrane immersed in raw water containing an organic suspension to obtain permeated water. In the immersion-type solid-liquid separation device, a liquid pool provided at a part of the bottom of the membrane immersion tank, a means for extracting the liquid in the liquid pool, and a sensor for detecting a liquid level in the liquid pool are provided. A membrane immersion type solid-liquid separation device, comprising: