JPH0938699A - Waste liquid treatment method and waste liquid treatment system - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To perform a stable wastewater treatment by concentrating the generated sludge in a short time after the sedimentation treatment in the activated sludge method, and further, to provide a treatment method capable of maintaining a high permeation flow velocity for a long time. Processing system. SOLUTION: A sludge produced by treating waste liquid in an aeration tank and a final settling tank is concentrated in a sludge concentrating tank, and sludge in the sludge concentrating tank is converted into a membrane separation device equipped with a separation membrane module in the membrane separating tank. It is filtered, concentrated, and returned to the sludge concentrating tank.
Even if a large amount of excess sludge that cannot be processed in the sludge thickening tank is transferred to the sludge thickening tank, water is removed by a membrane separation device that can concentrate excess sludge in a short time.
It is possible to avoid a situation where the sludge thickening tank is out of capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment before discharging wastewater such as human waste and sewage into a river or the like, and more particularly to a method for concentrating sludge produced by the wastewater treatment.

[0002]

2. Description of the Related Art Conventionally, urban wastewater such as human waste and sewage,
Organic wastewater from factories and the like is discharged to rivers and the like after being treated to remove various suspended substances (SS) contained therein.

The general treatment of conventional urban wastewater and organic wastewater is performed by a system as shown in FIG.
First, in the wastewater raw water to be treated, a relatively large suspended substance is precipitated and separated in the initial settling tank. Next, in the aeration tank, activated sludge decomposes water-soluble components such as BOD and COD in the wastewater. Thereafter, the floc of the activated sludge is settled and separated in the final settling tank and then discharged. In addition, sludge separated and separated in the initial settling tank and the final settling tank is collected in a sludge thickening tank, concentrated by gravity settling, and then water is removed by a dehydrator for disposal.

[0004]

By the way, particularly in the case of sewage treatment, the amount of suspended matter contained in the wastewater is not constant, and there are fluctuations in the quality of the wastewater, fluctuations in the water quantity, fluctuations in the water temperature, etc.
If such load fluctuations are large, fluctuations in the amount of excess sludge that occurs will also increase. On the other hand, in the sludge thickening tank, since it is concentrated by gravity settling, it takes a long time to concentrate the sludge. For this reason, if the amount of sludge transferred from the final settling tank to the sludge thickening tank increases, the treatment in the sludge thickening tank will not be in time. When the capacity of the sludge thickening tank is exceeded, the sludge withdrawal from the final sedimentation tank to the sludge thickening tank is stopped, and the sludge is temporarily stored in the aeration tank or the final sedimentation tank. However, if such sludge is retained,
There is a risk that the treatment conditions of the entire system will collapse and flocs will flow into the water discharged from the final settling tank. It is also possible to provide a preliminary tank that temporarily stores the sludge when the amount of sludge to be treated becomes excessive, but it is extremely uneconomical to separately provide a tank that is not used for actual treatment, It requires a vast land for securing facilities.
In addition, various methods of concentration using a separation membrane were studied,
None of them has been put to practical use due to low permeation flow rate or short-time membrane blockage.

The present invention has been made in order to solve the above-mentioned problems, and aims to perform a stable wastewater treatment by concentrating the generated sludge in a short time after the precipitation treatment in the activated sludge method. An object of the present invention is to provide a processing method and a processing system capable of maintaining a high permeation flow rate for a long time.

[0006]

According to the method for treating waste liquid of the present invention, sludge produced in the final sedimentation tank is treated with a sludge thickener while the sludge in the sludge thickener tank is concentrated in a membrane separation tank. It is characterized in that it is filtered by a membrane separator equipped with a separation membrane module, concentrated, and returned to the sludge concentrating tank.

In carrying out the present invention, the efficiency of sludge treatment in the membrane separation device can be increased by adding a coagulant to the membrane separation tank.

As the aggregating agent, any of a cationic, anionic, nonionic or amphoteric polymer aggregating agent can be used.

Further, it is preferable to use a combination of a metal-based floc modifier and an amphoteric polymer flocculant as the coagulant. As the coagulant, the amphoteric polymer flocculant is added after the addition of the metal-based floc modifier. It is possible to further improve the handleability of the sludge floc obtained by using the means for adding.

The waste liquid treatment system of the present invention comprises means for transferring the sludge produced by treating the waste liquid in the final settling tank to the sludge thickening tank, and part of the sludge in the sludge thickening tank to the membrane separation device. It has a means for concentrating and a means for returning the sludge concentrated by the membrane separation device to the sludge concentrating tank, wherein the membrane separating device is provided with a separation membrane module arranged in the membrane separating tank. To do.

The membrane separation device used in the waste liquid treatment system of the present invention has a separation membrane composed of hollow fiber membranes composed of a plurality of hollow fibers, and tubular supports provided at both ends of the separation membrane. , A separation membrane module in which the filtrate contained in the hollow fiber can pass through an internal passage formed in the tubular support, and the membrane surface of the separation membrane is arranged inside along the vertical direction, and excess sludge is removed. What has a membrane separation tank for storing and a suction pump communicating with the internal passage of the tubular support can be applied.

As another type of the membrane separation device used in the waste liquid treatment system of the present invention, a separation membrane composed of a plurality of hollow fibers, and a plate-like spacer which is folded back and sandwiched and covered. A tubular support provided at one end of the spacer, both ends of the hollow fiber are located in an internal passage formed inside the tubular support, and the filtrate inside the hollow fiber is inside. A separation membrane module that can pass through the passage, and a membrane separation tank that is disposed inside such that the planar direction of the spacer is along the vertical direction and that stores excess sludge, and that is in communication with the internal passage of the tubular support. Some are equipped with a suction pump.

As another type of the membrane separation device used in the waste liquid treatment system of the present invention, a flat spacer having an internal space and having a plurality of holes formed on the surface for communicating the outside with the internal space, A porous separation membrane that covers the spacer and a tubular support provided at one end of the spacer, and the filtrate that has entered the internal space of the spacer is inside the internal passage formed inside the tubular support. A separation membrane module that can pass through, a membrane separation tank that is arranged inside so that the plane direction of the spacer is along the vertical direction, and that stores excess sludge, and a suction pump that communicates with the internal passage of the tubular support. Some have and.

When operating the membrane separation apparatus of the present invention, by disposing an air diffuser that diffuses gas under the separation membrane, the sludge concentration efficiency in the membrane separation apparatus can be further enhanced. .

In the present invention, a part of the sludge is drawn out from the sludge thickening tank to which the sludge generated in the waste liquid treatment is transferred to the membrane separation device, and only the water in the sludge is suction-filtered through the separation membrane in the membrane separation device. The sludge is concentrated by the method, and the concentrated sludge is returned to the sludge concentration tank again, whereby the sludge concentration in the sludge concentration tank can be well controlled and the dehydration treatment can be efficiently performed. Also, even if the sludge with low concentration in the sludge thickening tank has a large amount of water, it is easy to increase the concentration in the sludge thickening tank due to the combined use of the membrane separator, and the sludge thickening tank has insufficient capacity. Can be prevented. In addition, because it is a concentration method by removing water using a separation membrane, it can respond to load fluctuations due to changes in the amount of concentrated sludge,
Moreover, since filtration is forcibly performed by suction, sludge can be concentrated in a short time.

Further, by arranging the separation membrane module so that the separation membrane surface is along the vertical direction, in cleaning by air scrubbing, the bubbles act almost uniformly on the entire separation membrane surface. And, it becomes easy to smoothly pass above the membrane separation tank.

When the membrane separation by suction filtration is carried out, the sludge concentration in the membrane separation tank tends to increase, and the permeation flow rate of the membrane tends to decrease. However, by adding a coagulant to the membrane separation tank, The fine flocs in the sludge form relatively large and strong flocs, a dense cake layer is not formed on the surface of the separation membrane, and the peelability from the separation membrane is enhanced.
Therefore, even if the sludge concentration is high and the viscosity of the waste liquid is high, it is possible to maintain a high permeation flow rate with a low transmembrane pressure difference.

Further, by using the method of adding the flocculant after the addition of the metal-based floc modifier, the addition of the metal-based floc modifier to the sludge allows the viscous substance layer and the dissolved components in the organic sludge to be removed. By reacting with a metal-based floc modifier, the sludge is modified so that the charge is neutralized, the hydrocolloid is made hydrophobic, and a strong core having a small particle size but a small stickiness is formed. By adding an amphoteric polymer flocculant to this, the amphoteric polymer flocculant has both positive and negative charges by ion dissociation in the liquid phase, and is crosslinked by interposing polymers or metal ions. The converted polymer reacts with the nuclei of sludge particles to form coarse flocs.

When the separation membrane module as shown in FIG. 4 is used in the waste liquid treatment system of the present invention, sludge in the membrane separation tank is solid-liquid separated by the separation membrane to remove water, and is taken into the hollow fiber. The filtrate passes through the hollow fiber, enters the inner passage of the tubular support from its end, passes through the inner passage, and is discharged.
In this waste liquid treatment system, one tubular support may be used for one separation membrane, and cost reduction and miniaturization can be promoted. Further, by disposing the spacers between the folded separation membranes, there is no adhesion between the separation membranes, and the filtration performance does not deteriorate due to the separation membranes being bundled.

When the separation membrane module as shown in FIG. 5 is used in the waste liquid treatment system of the present invention, the sludge in the membrane separation tank is solid-liquid separated by the separation membrane to remove water, and the filtrate permeated through the separation membrane. Are taken into the inner space of the spacer through holes formed in the spacer, enter into the inner passage of the tubular support through the inner space, and are discharged through the inner passage. In this waste liquid treatment system, one tubular support may be used for one separation membrane, and cost reduction and miniaturization can be promoted. Further, by disposing the spacers between the folded separation membranes, there is no adhesion between the separation membranes, and the filtration performance does not deteriorate due to the separation membranes being bundled. In addition, a material other than the hollow fiber membrane can be used as the separation membrane, and the range of choice of the separation membrane can be expanded.

In the waste liquid treatment system of the present invention, when the air scrubbing treatment is introduced into the membrane separation tank, the membrane separation membrane can be washed properly and the separation performance can be prevented from lowering.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but it should be understood that the present invention is not construed as being limited thereto.

[First Embodiment] In the waste liquid treatment method of the present embodiment, as shown in FIG. 1, first, the waste liquid raw water to be treated is introduced into an initial settling tank. In this initial settling tank, a relatively large suspended solid is separated by settling. Then, the treated water is treated with activated sludge water in the aeration tank, and the generated sludge is transferred to the sludge thickening tank. BO in wastewater by activated sludge in aeration tank
After water-soluble components such as D and COD are decomposed, flocs of the activated sludge are precipitated and separated in the final settling tank. And
The treated water is discharged and the generated sludge is transferred to the sludge thickening tank. In the sludge thickening tank, conventional sludge concentration processing is performed by gravity settling, and the concentrated sludge is then disposed of by removing water with a dehydrator. Furthermore, in the waste liquid treatment of this embodiment, the sludge thickening tank is connected to the membrane separation device. Then, a part of the sludge is transferred from the sludge thickening tank to the membrane separation device and concentrated in the membrane separation device.

As the membrane separating device, the one having the structure shown in FIG. 2 can be applied. The membrane separation device 10 shown in FIG. 2 has a membrane separation tank 12 for storing sludge, a separation membrane module 14 arranged in the membrane separation tank 12, and a suction pump 16 connected to the separation membrane module 14. It is schematically configured. The separation membrane module 14 is as shown in FIG. 3, and includes a separation membrane 18 composed of a hollow fiber membrane composed of a plurality of hollow fibers,
It has a tubular support 20 provided at both ends of the separation membrane 18. As the hollow fiber, various porous and tubular hollow fibers can be used, and for example, those made of various materials such as cellulose, polyolefin, polyvinyl alcohol, PMMA, and polysulfone can be used. Of these, materials having high elongation such as polyethylene and polypropylene are preferable. Further, although not particularly limited, the outer diameter of the hollow fiber is 20 to 2000 μm, and the pore diameter is 0.0.
The thickness is preferably 1 to 1 μm, the porosity is 20 to 90%, and the thickness of the hollow fiber membrane is 5 to 300 μm.

The separation membrane is preferably a so-called permanent hydrophilization membrane having a hydrophilic group on the surface. If the surface of the separation membrane is hydrophobic, a hydrophobic interaction between the organic substances in the water to be treated and the surface of the separation membrane will occur, causing adsorption of organic substances on the membrane surface, which leads to clogging of the membrane surface and the filtration life. This is because it tends to be short. In addition, clogging caused by adsorption is generally difficult to recover filtration performance even by membrane surface cleaning. However, by using the permanent hydrophilization membrane, the hydrophobic interaction between the organic matter and the surface of the separation membrane can be suppressed, and the adsorption of the organic matter can be suppressed. Furthermore, when the air scrubbing process described later is performed on a hydrophobic film, the film surface may be in a dry state due to air bubbles, which further enhances hydrophobicity and may cause a decrease in flux. The flux is unlikely to be reduced even when the film is dried.

The tubular support 20 has a tubular shape with an internal passage 24 formed therein, one end of which is closed and the other end of which is connected to the suction pump 16 and a pipe 22. The tubular support 20 shown in FIG. 3 has a cylindrical shape, but the present invention is not limited to this. For example, the outer shape may be a square pole. Furthermore, this tubular support 2
A slit 28 is formed along the length of the side wall 26 of No. 0. The end of the separation membrane 18 is inserted into the slit 28 and is closed by the sealing material to be filled, so that the separation membrane 18 is firmly supported and fixed. That is, in the separation membrane module 14, both ends of the separation membrane 18 are supported by the two tubular supports 20, respectively. In this case, the ends of the separation membrane 18 are both ends of the hollow fiber in the fiber direction, and both ends of each hollow fiber are located in the internal passage 24 of the tubular support 20.

The width of the slit 28 is preferably 30 mm or less, and more preferably 10 mm or less. This is because by narrowing the width of the slit 28, it becomes easier to arrange the hollow fibers constituting the separation membrane 18 in one row in a more orderly manner. If the hollow fibers are not aligned and the hollow fiber membrane is disturbed and formed, a plurality of hollow fibers will be bundled and adhered and integrated due to the adhesion of sludge, etc., and the surface area as a separation membrane cannot be used effectively, resulting in a decrease in separation performance. Resulting in. The length of the slit is not particularly limited, but if it is too short, the membrane area of the separation membrane cannot be increased, and the separation performance cannot be improved. If the length is too long, the production becomes difficult. 100 to 2000 mm is appropriate.

The sealing material bundles and fixes each hollow fiber of the separation membrane 18 in the slit 28 while keeping the end of the hollow fiber open, and makes the inner passage 24 of the tubular support 20 liquid-tight from the outside. The partition 28 is formed by filling the slit 28 with a liquid epoxy resin, unsaturated polyester resin, polyurethane, or the like and curing it. Also,
If the separation membrane is inserted and fixed in two or more rows for one slit, or if two or more slits are formed in one tubular support and the separation membrane is inserted and fixed in each slit,
A plurality of separation membranes 18 can be formed per one separation membrane module 14. As the number of the separation films 18 increases, the overall film area can be increased, and the processing performance can be improved. However, if three or more separation membranes are provided, the washing effect of the separation membrane located inside cannot be enhanced at the time of washing the separation membrane described later. Therefore, two separation membranes are appropriate.

A plurality of separation membrane modules 14 having such a structure can be arranged in one membrane separation tank 12. By arranging a plurality of separation membrane modules 14, the membrane area as a whole can be increased and the processing performance can be improved. Also, in consideration of the compactness of the separation tank and the washing efficiency of the separation membrane described later, it is preferable that the interval between the adjacent separation membrane modules 14 is small. However, if the interval is too narrow, clogging with sludge is likely to occur, and bubbles may not easily pass between the separation membrane modules. For this reason,
The spacing between each separation membrane module should be selected in consideration of the size of the separation membrane module occupying the separation membrane module, the number of separation membrane modules, the thickness of the tubular support, the conditions such as air scrubbing and backwashing. Are required, and the interval is 5-1.
The range of 00 mm is preferable, and the range of 5 to 70 mm is more preferable.

The internal passage 24 of each tubular support 20 is connected to the suction pump 16 by a pipe 22. Therefore, by operating the suction pump 16, the permeated liquid that has entered the internal passage 24 is forcibly transferred and discharged out of the system.

In the membrane separation tank 12, below the separation membrane 18, it is preferable to arrange an air diffuser 30 for diverging gas. The air diffuser 30 is a hollow body having a large number of pores, and is connected to a pneumatic pump 32. By operating the compressed air pump 32, air bubbles are emitted from the air diffuser 30. By using this air diffuser 30, air scrubbing can be performed. That is, the hollow fiber membrane oscillates due to bubbles rising from the air diffuser 30 and the hollow fibers rub against each other due to this oscillating, or the relative flow of the hollow fiber and water causes the surface of the hollow fiber to move. The attached sludge will be removed.

Considering the air scrubbing process by the air diffuser 30, it is desirable to arrange the separation membrane module 14 so that the membrane surface of the separation membrane 18 extends in the vertical direction. By arranging the membrane surface along the vertical direction, bubbles rising from below act uniformly on the entire membrane surface of all the separation membranes 18 and easily pass over the membrane separation tank 12 smoothly. Because. On the other hand, when the separation membrane module is arranged with the separation membrane 18 lying horizontally, the diverged air bubbles hit the separation membrane arranged at the lowermost portion and then move outward along the separation membrane in the horizontal direction. , And the air scrubbing process cannot be effectively performed on the separation membrane disposed on the upper portion.

In the waste liquid treatment system of the present embodiment in which the membrane separation device 10 is connected to the sludge thickening tank, the sludge accumulated in the sludge thickening tank is processed in the sludge thickening tank while the sludge thickening tank It is also flowed in and stored. Then, the suction pump 16 is operated. Then, the membrane separation tank 1
Excess sludge in 2 is suction-filtered by the separation membrane 18, only sludge is captured on the surface of the separation membrane 18, and water and sludge are separated. The water (filtrate) from which sludge has been removed in this way passes through each hollow fiber constituting the separation membrane 18 by the suction pump 16 and passes through the internal passage 24 and the pipe 22 of the tubular support 20 provided at the end thereof. And is released. Therefore, only water is removed at high speed in the membrane separation tank, and the sludge is concentrated. Excess sludge that has been condensed by removing water is returned to the sludge concentrating tank using a pump or the like. In this way, the sludge is circulated between the sludge thickening tank and the membrane separation device 10, and the moisture in the sludge thickening tank is gradually removed to increase the sludge concentration.

Further, by appropriately washing the separation membrane by the air scrubbing treatment, it is possible to prevent the separation performance from being lowered. The separation membrane can be washed not only by air scrubbing but also by backwashing. That is, by using the suction pump 16 also as a pumping pump, clean water is passed through the hollow fiber through the internal passage 24 of the tubular support 20 and discharged from the surface of the separation membrane 18 to thereby release the surface of the separation membrane 18. Suspended substances adhering to the can be removed. Alternatively, a method in which a granular material such as a sponge ball is sprayed in a membrane separation tank and brought into contact with the separation membrane, or the separation membrane is vibrated by applying ultrasonic vibration can be applied. Further, the surface of the separation membrane can be cleaned by chemical cleaning. Although chemical cleaning is expensive, the amount of chemical used can be reduced by using air scrubbing or backwashing together.

Washing by air scrubbing or backwashing is carried out in a state where the filtering process by suction and the addition of the coagulant described later are stopped. Incidentally, when backwashing is not required due to the nature of the waste liquid, it is also possible to perform cleaning by air scrubbing during the waste liquid filtering process.

According to the waste liquid treatment system and method of this embodiment, while the excess sludge circulates between the sludge thickening tank and the membrane separation device connected thereto, the water content in the excess sludge is increased by the membrane separation device. Since it can be separated and removed in a short time, the excess sludge in the sludge thickening tank and the removal of water can be performed at high speed. In particular, it is possible to flexibly deal with a load change due to a change in the amount of sludge, and by reducing the water content of the sludge transferred to the sludge thickening tank, it is possible to prevent the capacity of the sludge thickening tank from being exceeded. Therefore, the situation where the sludge withdrawal from the settling tank to the sludge thickening tank is not stopped is prevented, the entire system can be stably processed, and the outflow of flocs from the final settling tank can be prevented.

The sludge flowing into the membrane separation tank may contain fine flocs of activated sludge. Such fine flocs containing activated sludge tend to cause the separation membrane to adhere to the surface of the membrane or between the separation membranes, and reduce the permeation flux as the separation membrane. Therefore, it may be necessary to frequently repeat the film surface cleaning such as the air scrubbing process or the backwashing process. In such a case, it is effective to add a flocculant into the membrane separation tank. When a flocculant is added to the membrane separation tank, fine flocs in the treated water become relatively large and have high strength, and a dense cake layer is not formed on the surface of the separation membrane. Peelability is improved. Therefore, the high permeation flux of the separation membrane can be maintained.

That is, the more membrane separation is performed by suction filtration,
Although the sludge concentration in the membrane separation tank tends to increase, and the permeation flux of the membrane tends to decrease, the addition of a coagulant will increase the sludge concentration, and even if the viscosity of the waste liquid is low, It becomes possible to maintain a high permeation flux with a differential pressure.

The aggregating agent is not particularly limited as long as it allows fine flocs to have a suitable size, and cationic, anionic, nonionic or amphoteric polymer aggregating agents can be used. Of these, cationic synthetic polymer flocculants are suitable. When only the polymer flocculant is added, the amount of the polymer flocculant used is 0.1 to 1 part by weight based on 100 parts by weight of the suspended solid (SS) in the sludge, although the amount used depends on the properties of the sludge. Is preferred, and 0.1 to 0.8 part by weight is particularly preferred. If the amount is less than 0.1 part by weight, the formation of flocs becomes insufficient. On the other hand, if the amount is more than 1 part by weight, the flocs may be redispersed or the adhesion of the flocs to the separation membrane may increase, which is not preferable.

It is more preferable to add an amphoteric polymer flocculant after adding a metal floc modifier such as iron or aluminum. Here, as the metal-based floc modifier, a sulfuric acid band, ferric chloride, ferrous sulfate, polyiron sulfate, or the like is used, and among them, an iron-based inorganic coagulant is preferable.

The amphoteric polymer flocculant is a polymer flocculant having a cationic group and an anionic group in one molecule. Examples of the cationic group include tertiary amines, neutralized salts thereof, quaternary salts and the like, and examples of the anionic group include a carboxyl group, a sulfone group and salts thereof.
Particularly, an amphoteric polymer flocculant having a carboxyl group is preferable. Further, a nonionic component may be contained in addition to these ionic components. More specifically, examples of the anionic monomer unit include acrylic acid, methacrylic acid, and alkali metal salts thereof. Examples of the cationic monomer unit include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, allyldimethylamine, and neutralized salts thereof.
Grade salts and the like. Examples of the nonionic monomer unit include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide and the like.

As described above, as a means for adding the flocculant after the addition of the metal-based floc modifier, the metal-based floc modifier is added in the pipe in which the sludge flows from the sludge thickening tank into the membrane separator. Means for adding the coagulant to the membrane separation tank may be adopted.

According to the method of adding such a metal-based floc modifier and a coagulant, first, by adding the metal-based floc modifier, the viscous substance layer in the organic sludge and the dissolved component are metal. By reacting with the floc modifier, the charge is neutralized and the hydrocolloid is rendered hydrophobic. Thus, the sludge is modified so as to form a strong core having a small particle size but a small tackiness. After that, when the amphoteric polymer flocculant is added, the amphoteric polymer flocculant ionically dissociates in the liquid phase and has both positive and negative charges, and at the same time, the polymers are crosslinked with each other or metal ions. Then, the crosslinked polymer reacts with the core of the sludge particles to generate coarse flocs. The generated flocs become stronger and more hydrophobic and contracted by stirring or the like. Further, there is almost no residual metal ion or polymer in the liquid phase, and the liquid phase is free from viscous drainage and has good releasability. Therefore, even if it is difficult to dehydrate sludge, it becomes easy to perform coagulation treatment.

As described above, by adding the coagulant to the membrane separation tank, it is possible to remarkably suppress the increase in pressure loss over time in suction filtration using a separation membrane, and to obtain a long-term permeation flux under filtration conditions with small pressure loss. Can be kept high. Therefore, it is possible to stably separate and remove moisture, and to reduce the area of the separation membrane to be used. further,
It is also possible to reduce the load on the separation membrane and extend the life of the separation membrane. Further, since the flocs adhering to the separation membrane are easily separated, the frequency of cleaning the membrane surface can be reduced, and in particular, the chemical cleaning treatment can be reduced. In addition, although the example which performed suction filtration was shown in the said example, pressure filtration can also be applied.

[Embodiment 2] The same system as the waste liquid treatment system of Embodiment 1 is used except that the separation membrane module shown in FIG. 4 is used. As shown in FIG. 4, the separation membrane module used in this embodiment has a separation membrane 34 composed of a plurality of hollow fibers, a plate-shaped spacer 36, and a tubular support 38 having an internal passage formed therein. Composed.
The spacer 36 is covered with the separation film 34, and the sheet-shaped separation film is folded back so that the spacer 36 is sandwiched between them.
Is bonded by using heat seal or an adhesive to form a bag. Further, the end of the portion corresponding to the opening of the bag is fixed by the tubular support 38, and the end of each hollow fiber constituting the separation membrane is positioned in the internal passage 24 of the tubular support 38. To

In the separation membrane module having this structure, the sludge in the membrane separation tank is solid-liquid separated by the separation membrane 34 by operating the suction pump communicating with the internal passage 24 of the tubular support 38, and the hollow fiber The filtrate taken in passes through the hollow fiber, enters the internal passage 24 of the tubular support 38 from the end thereof, passes through the internal passage 24, and is discharged through the suction pump.

In this separation membrane module, one tubular support may be used for one separation membrane, and cost reduction and miniaturization can be promoted. Further, by disposing the spacers between the folded separation membranes, there is no adhesion between the separation membranes, and the filtration performance does not deteriorate due to the separation membranes being bundled.

[Embodiment 3] The waste liquid treatment system of Embodiment 1 has the same system except that the separation membrane module shown in FIG. 5 is used. As shown in FIG. 5, the separation membrane module of Embodiment 3 is composed of a flat spacer 42, a separation membrane 44 covering the spacer 42, and a tubular support 38 provided at one end of the spacer 42. The spacer according to the third embodiment is a box-shaped spacer having an internal space formed therein, and an opening 46 is formed on one of the six surfaces constituting the spacer 42, and the surface of the other surface is formed. Are formed with a plurality of holes, and the holes communicate the outside and the internal space. The opening 46 is connected to the internal passage 24 of the tubular support 38. The separation membrane 44 is provided so as to cover the spacer 42 as in the second embodiment, but the separation membrane 44 in the third embodiment does not need to be made of a hollow fiber and is a porous material that does not allow sludge to pass through. If there are any, various ones can be applied.

In the membrane separation device provided with the separation membrane module having this structure, the excess sludge in the membrane separation tank is separated into the separation membrane 44 by operating the suction pump communicating with the inner passage 24 of the tubular support 38. The filtrate that has undergone solid-liquid separation by passing through the separation membrane 44 is taken into the internal space of the spacer 42 through the holes formed in the spacer 42, passes through the internal space,
From the opening 46, it enters the internal passage 24 of the tubular support 38, passes through the internal passage 24, and is discharged via a suction pump.

In this separation membrane module, one tubular support 38 may be used for one separation membrane 44, and cost reduction and miniaturization can be promoted. Further, since the spacers 42 are arranged between the folded separation membranes, the separation membranes do not adhere to each other, and the filtration performance does not deteriorate due to the separation membranes being bundled. In addition, a material other than the hollow fiber membrane can be used as the separation membrane, and the range of choice of the separation membrane can be expanded.

[Test Example] The separation membrane module shown in FIG. 3 having a membrane area of 4 m ² was arranged in parallel in a membrane separation tank having a capacity of 0.5 m ^{3 so} that the membrane surface was parallel to the vertical direction. Configured the device. Then, while supplying sludge from the final settling tank into the membrane separation tank at 5 (l / min), suction filtration was performed so that the permeation flow rate of the separation membrane module was also 26 (l / min) to obtain the membrane permeated water. It was The sludge concentration was 10,000 mg / l and the temperature was 15 ° C. In addition, air was emitted as bubbles at 30 m ³ / hr from an air diffuser provided at the bottom of the membrane separation tank.
Immediately before the start of suction filtration dehydration treatment, 0.7 parts by weight of cationic polymer flocculant was added to 100 parts by weight of sludge solid content in the membrane separation tank. The change with time of the differential pressure was measured for those with and without the addition of this coagulant. The measurement result is shown in FIG. In addition, in FIG.
-□-indicates the measurement result of the example in which the coagulant was added, and -X-x- indicates the measurement result of the example in which the coagulant was not added. From FIG. 6, when the coagulant was not added, the adhesion amount of sludge on the surface of the separation membrane increased with the treatment time, and the pressure difference increased.
With a flocculant added, the differential pressure is about 0.2 kgf / cm
^It can be seen that it stabilizes at ² and does not continue to increase.

[0052]

According to the present invention, even in a situation where a large amount of sludge that cannot be treated in the sludge thickening tank is transferred to the sludge thickening tank, the sludge thickening treatment can be performed in a short time. Since the device removes water, it is possible to avoid a situation where the sludge thickening tank has insufficient capacity. In particular, because it uses a membrane separation device, it is possible to cope with load fluctuations of excess sludge and remove water at high speed. Therefore, it is not necessary to stop the withdrawal of sludge from the settling tank to the sludge thickening tank, or to temporarily store sludge in the aeration tank or settling tank, and it is possible to stabilize the processing of the entire system, The outflow of flocs can be suppressed. Further, there is no need to provide a spare tank, and the membrane separation device does not require a small and large installation area, so that the site can be effectively used.

Further, when the separation membrane module is arranged so that the separation membrane surface is along the vertical direction, the cleaning by the air scrubbing can be performed substantially uniformly on the entire separation membrane surface.

When the coagulant is added to the membrane separation tank, the increase in pressure loss over time in suction filtration using a separation membrane is significantly suppressed, and the permeation flux is increased for a long time under a filtration condition with a small pressure loss. It becomes possible to keep. Therefore, it is possible to stably separate and remove moisture, and to reduce the area of the separation membrane to be used. Further, the load on the separation membrane can be reduced, and the life of the separation membrane can be extended. Further, since the flocs adhering to the separation membrane are easily separated, the frequency of cleaning the membrane surface can be reduced, and in particular, the chemical cleaning treatment can be reduced.

In the waste liquid treatment system of the present invention, the separation membrane can be appropriately washed by the air scrubbing treatment, and the deterioration of the separation ability can be prevented.

[Brief description of drawings]

FIG. 1 is a flow chart showing a waste liquid treatment system of the present embodiment example.

FIG. 2 is a configuration diagram showing a membrane separation device according to a first embodiment.

FIG. 3 is a perspective view showing a separation membrane module of form example 1.

FIG. 4 is a diagram showing a separation membrane module of Embodiment 2;
4A is a front view, and FIG. 4B is a sectional view taken along the line bb of FIG. 4A.

FIG. 5 is a diagram showing a separation membrane module of Embodiment 3;
5A is a front view, and FIG. 5B is a sectional view taken along the line bb of FIG. 5A.

FIG. 6 is a graph showing changes in differential pressure over time.

FIG. 7 is a flowchart showing a conventional waste liquid treatment system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Membrane separation apparatus 12 Membrane separation tank 14 Separation membrane module 16 Suction pump 18 Separation membrane 20 Tubular support 24 Internal path 28 Slit 30 Air diffuser 34 Separation membrane 36 Spacer 38 Tubular support 42 Spacer 44 Separation membrane

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Wataru Fujii Wataru Fujii 10-1 Daikokucho, Tsurumi-ku, Yokohama-shi, Kanagawa NITTO CHEMICAL INDUSTRIAL CO., LTD. (72) Minor Okada 2-chome, Kiba, Koto-ku, Tokyo No. 3 Mitsubishi Rayon Engineering Co., Ltd. (72) Inventor Shigeru Tanabe No. 3 Kaigan Dori, Toyama City, Toyama Prefecture DIAFLOK Co., Ltd. Technology Development Center (72) Inventor Tsutomu Tsunoda 2-3 Kyobashi, Chuo-ku, Tokyo No. 19 Mitsubishi Rayon Co., Ltd.

Claims (6)

[Claims] 1. A membrane separation device equipped with a separation membrane module in which a sludge produced by treating waste liquid in a final settling tank is transferred to a sludge concentration tank and a part of sludge extracted from the sludge concentration tank is provided in the membrane separation tank. A method for treating waste liquid, which comprises filtering and condensing in step 1 and returning to the sludge concentrating tank. 2. The waste liquid treatment method according to claim 1, wherein a coagulant is added to the inside of the membrane separation tank. 3. The waste liquid treatment method according to claim 2, wherein a combination of a metal floc modifier and an amphoteric polymer flocculant is used as the flocculant. 4. A means for transferring sludge produced by treating waste liquid in a final settling tank to a sludge thickening tank, a means for transferring sludge extracted from the sludge thickening tank to a membrane separating device and concentrating it, and a membrane separating device. And a means for returning the sludge concentrated in 1. to the sludge thickening tank, and the membrane separation device is provided with a separation membrane module arranged in the membrane separating tank. 5. The waste liquid treatment system according to claim 4, wherein the membrane separation device comprises a separation membrane composed of hollow fiber membranes composed of a plurality of hollow fibers, and tubular supports provided at both ends of the separation membrane. And a separation membrane module in which the filtrate contained in the hollow fiber can pass through an internal passage formed in the tubular support, and the membrane surface of the separation membrane is arranged inside along the vertical direction, A waste liquid treatment system comprising: a membrane separation tank for storing sludge; and a suction pump communicating with the internal passage of the tubular support. 6. The waste liquid treatment system according to claim 4, wherein an air diffuser for diverging gas is arranged below the separation membrane in the membrane separation tank.