JP2000189993A - Activated sludge treatment by membrane separation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a activated sludge treating method by membrane separation capable of performing a stable solid-liquid separation while preventing the excess adsorption of organic materials on the membrane surface of a separation membrane module in an initial operation stage of a waste water treating system. SOLUTION: In the activated sludge treating method by membrane separation capable of performing a biological treatment for degrading organic materials in water to be treated by microorganisms in the activated sludge and a solid- liquid separation treatment by the separation membrane module 3 in the same aerobic tank 6, a method that the activated sludge is previously added into the aerobic tank 6 so that the MLSS concentration of the water to be treated in the aerobic tank 6 is >=2000 mg/l is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a biological treatment for decomposing organic substances in water to be treated by microorganisms in activated sludge,
Regarding the membrane separation activated sludge treatment method in which the solid-liquid separation treatment by the separation membrane module and the solid-liquid separation treatment in the same tank, specifically, to prevent organic substances from adhering to the membrane surface of the separation membrane module in the initial stage of operation of the wastewater treatment system, The present invention relates to a membrane separation activated sludge treatment method capable of performing a solid-liquid separation treatment stably.

[0002]

BACKGROUND ART Highly polluting wastewater (hereinafter referred to as treated water) such as domestic wastewater such as sewage and human waste, and organic industrial wastewater from factories and the like are treated with various suspended substances contained therein. S
S), after being subjected to a process of removing organic substances and the like, is discharged to rivers and the like. In such a wastewater treatment system, for example, as shown in FIG.
Is transferred to an aeration tank 34 provided with a compressed air pump 32 and an air diffuser 33 connected thereto using a transfer pump 35. In the aeration tank 34, biological treatment is performed in which oxygen is supplied to the aerobic microorganisms in the activated sludge to decompose organic substances (BOD components) in the water to be treated. Thereafter, in the sedimentation tank 36, solid-liquid separation is performed by gravity sedimentation,
The separated treated water is discharged into a river or the like, while a part of the separated sludge is returned to the aeration tank 34 as returned sludge,
The remaining sludge is finally disposed of as excess sludge.

However, according to this activated sludge treatment method, if bulking due to filamentous fungi occurs, the sludge in the bulking state floats on the surface of the water to be treated, so that solid-liquid separation by gravity sedimentation in the sedimentation tank 36 is performed. There is a problem that sludge is mixed in the treated water discharged into a river or the like, and deteriorates the water quality. Further, there is a problem that it is difficult to maintain a high concentration of the mixed liquid suspended solid (hereinafter, referred to as MLSS), that is, activated sludge, in the aeration tank 34, and the efficiency of biological treatment is reduced.

As a method for solving such a problem, a separation membrane module connected to a suction pump or a membrane separation activated sludge treatment method using a separation membrane module unit provided with a plurality of the separation membrane modules has recently been proposed. Has been used. As this membrane separation activated sludge treatment method, for example, a method using a system as shown in FIG. 1 can be mentioned. First, the water to be treated stored in the adjustment tank 1 is transferred to an aeration tank 6 provided with a separation membrane module 3 connected to a suction pump 2 and an air diffuser 5 connected to a compressed air pump 4 by a transfer pump 7. Transfer using. In the aeration tank 6, the solid-liquid separation treatment by the separation membrane module 3 and the oxygenation of the aerobic microorganisms in the activated sludge to give organic substances (BOD components) in the water to be treated.
And a biological treatment for decomposing. The water to be treated is filtered by sucking the filtrate side of the separation membrane module 3,
The filtered treated water (filtrate) is discharged to a river or the like. By using such a membrane separation activated sludge treatment method,
Since a sedimentation tank is not required, the quality of the treated water can be kept good, and the MLSS concentration in the aeration tank 6 can be maintained high.

[0005]

However, the above M
LSS is little or no present in the aeration tank at the first start of operation of the conventional wastewater treatment system, and gradually increases to a sufficient concentration, for example, 3000 to 5000 mg / l by continuing operation for a long time. Therefore, in the early stage of operation of the wastewater treatment system, ML
The SS concentration was low, and the ability to decompose BOD components in the aeration tank was insufficient. For this reason, in the wastewater treatment system using the membrane separation activated sludge treatment method as shown in FIG. As a result, there is a problem that the pressure difference between the inside and outside of the separation membrane module 3 increases, so that stable solid-liquid separation processing cannot be performed.

Accordingly, an object of the present invention is to prevent excessive adsorption of organic substances to the membrane surface of a separation membrane module in an initial stage of operation of a wastewater treatment system, and to carry out a solid-liquid separation process stably. It is to provide a sludge treatment method.

[0007]

That is, the membrane separation activated sludge treatment method of the present invention comprises a biological treatment in which microorganisms in activated sludge decompose organic substances in water to be treated and a solid-liquid separation treatment by a separation membrane module. In the membrane separation activated sludge treatment method performed in the same tank, the MLSS concentration of the water to be treated in the tank is set to 2000 mg before the first operation.
Activated sludge is added to the tank so as to be at least / l.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a wastewater treatment system using a membrane separation activated sludge treatment method. First, after a relatively large suspended substance in the water to be treated is removed with a screen (not shown) or the like, the water to be treated stored in the adjustment tank 1 is separated from the separation membrane module 3 connected to the suction pump 2.
And an aeration tank 6 provided with an air diffuser 5 connected to the compressed air pump 4 using a transfer pump 7. This aeration tank 6
Among them, a solid-liquid separation treatment by the separation membrane module 3 and a biological treatment for decomposing organic substances (BOD components) in the water to be treated by supplying oxygen to the aerobic microorganisms in the activated sludge are performed.
The water to be treated is filtered by sucking the filtrate side of the separation membrane module 3, and the filtered treated water (filtrate) is collected by the water collection pipe 8 and discharged to a river or the like.

In the present invention, the active water in the aeration tank 6 is controlled so that the MLSS concentration of the water to be treated in the aeration tank 6 becomes 2000 mg / l or more before the first operation of the wastewater treatment system. The feature is that sludge is added (hereinafter referred to as seeding). MLSS
If the concentration is less than 2000 mg / l, the ability to decompose the BOD component will be insufficient, and a large amount of the BOD component will be adsorbed on the membrane surface of the separation membrane module 3, making it impossible to perform a stable filtration treatment. The MLSS concentration is preferably between 3000 and
It is in the range of 8000 mg / l.

The activated sludge to be seeded into the aeration tank 6 is not particularly limited. For example, surplus sludge or return sludge generated from an existing wastewater treatment system can be used. More preferably, it is activated sludge obtained from a system treating wastewater having similar properties. The seeding method of the activated sludge is not particularly limited,
For example, before the operation of the wastewater treatment system is started, a method of adding the activated sludge to the treatment water in the aeration tank 6 to a position where the activated sludge is sufficiently stirred and mixed, aeration of the activated sludge previously diluted with water, treatment water, or the like is performed. A method such as introduction into the tank 6 may be used.

The separation membrane module 3 is not particularly limited as long as it has a filtration membrane (separation membrane) having a plurality of fine pores. For example, a flat membrane type, a hollow fiber membrane type, a tubular Known separation membranes such as a membrane type and a bag-like membrane type can be applied, and among them, a hollow fiber membrane type is preferable. In addition, as the material, cellulose, polyolefin, polysulfone, polyvinylidene fluoride (P
VDF), polytetrafluoroethylene (PTFE), ceramics, polyacrylonitrile (PAN) and the like. The average pore diameter of the pores of the filtration membrane of the separation membrane module 3 is:
Although not particularly limited, for example, those having an average pore diameter of 0.001 to 0.1 μm generally called an ultrafiltration membrane or those having an average pore diameter of 0.1 to 1 μm generally called a microfiltration membrane can be used.

The separation membrane module 3 includes, for example, a separation membrane 21 composed of a hollow fiber membrane composed of a plurality of hollow fibers, and a tubular support 22 provided at both ends of the separation membrane 21 as shown in FIG. And a hollow fiber separation membrane module having a schematic configuration including: As the hollow fiber, various porous and tubular hollow fibers can be used. For example, the hollow fiber is made of various materials such as cellulose, polyolefin, polyvinyl alcohol, polymethyl methacrylate (PMMA), polysulfone, and PAN. Things can be used. Above all, polyolefin-based hollow fibers such as polyethylene and polypropylene are preferable in consideration of high chemical resistance, high elongation of the film, and the like. Further, although not particularly limited, the outer diameter of the hollow fiber is 20 to 2000 μm, and the pore diameter is 0.01 to 1 μm.
m, the porosity is 20 to 90%, and the thickness of the hollow fiber membrane is 5 to 30.
Those having a thickness of 0 μm are preferred.

The separation membrane 21 is preferably a so-called permanent hydrophilization membrane having a hydrophilic group on the surface. If the surface of the separation membrane 21 is hydrophobic, a hydrophobic interaction acts between the organic matter in the water to be treated and the surface of the separation membrane 21, causing organic matter to be adsorbed on the membrane surface, which leads to membrane surface blockage and filtration. This is because the life is likely to be short and the filtration process cannot be performed stably.

The tubular support 22 has a tubular shape with an internal passage 23 formed therein. One end of the tubular support 22 is closed, and the other end is connected to the water collecting pipe 8. The tubular support 22 shown in FIG. 3 is cylindrical, but is not limited to this. For example, the tubular support 22 may have a square pillar shape. Further, a slit 25 is formed in the side wall 24 of the tubular support 22 along the longitudinal direction thereof. While the end of the separation membrane 21 is inserted into the slit 25,
The separation membrane 21 is closed and firmly supported and fixed by the filled sealing material. Here, the ends of the separation membrane 21 are both ends in the fiber direction of the hollow fiber, and both ends of each hollow fiber are located in the internal passage 23 of the tubular support 22.

The above-mentioned sealing material converges and fixes each hollow fiber membrane of the separation membrane 21 to the slit 25 while keeping the end of the hollow fiber membrane in an open state.
Is liquid-tightly partitioned from the outside, and is formed by filling the slit 25 with an epoxy resin, unsaturated polyester resin, polyurethane, or the like in a liquid state, and curing the slit. Also, by inserting and fixing two or more rows of separation membranes in one slit, or by forming two or more slits in one tubular support, and inserting and fixing the separation membrane in each slit, A plurality of separation membranes 21 can be formed in one hollow fiber separation membrane module.

In such a hollow fiber separation membrane module, a plurality of hollow fibers are hardly bundled and fixed by sludge or the like, and thus are difficult to be integrated. Therefore, air bubbles easily enter between the hollow fibers by air scrubbing during the filtration process,
A good cleaning effect can be expected, and it is suitable for a wastewater treatment system using a membrane separation activated sludge treatment method. A plurality of such hollow fiber separation membrane modules can be arranged in the aeration tank 6. By arranging a plurality of hollow fiber separation membrane modules, the processing performance can be improved.

The air diffuser 5 is a hollow body having a large number of pores, and is connected to a pneumatic pump 4 for feeding air into the air diffuser 5. The air can be sent to the separation membrane module 3 in the form of air bubbles. By using the air diffuser 5, oxygen is sent into the activated sludge in the aeration tank 6, and at the same time, the separation membrane of the separation membrane module 3 is subjected to air scrubbing, that is, bubbles rising from the air diffuser 5 and rising. Thus, the separation membrane can be swung by the water flow generated to remove sludge adhering to the membrane surface of the separation membrane, and the solid-liquid separation ability can be maintained high for a long time.

Further, in consideration of the air scrubbing process by the air diffuser 5, it is desirable to arrange the separation membrane module 3 so that the membrane surface of the separation membrane is along the vertical direction. This is because, 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, and easily pass over the aeration tank 6 smoothly. . On the other hand, if the separation membrane module 3 is placed in a state where the separation membrane is lying horizontally, the diverged air bubbles hit the separation membrane arranged at the bottom, and then move outward along the separation membrane in the horizontal direction. As a result, it becomes impossible to effectively perform the air scrubbing process on the separation membrane disposed on the upper portion.

In the wastewater treatment system, a chemical tank and one end communicate with the chemical tank, and the other end is connected to the water collecting pipe 8.
May be provided with a chemical liquid supply pipe communicating with the liquid medicine supply pipe. In such a chemical tank, N.sub.2 for cleaning the separation membrane is provided.
A chemical solution consisting of an aqueous solution of aOCl, NaOH, HCl or the like can be added.

In such a membrane separation activated sludge treatment method, the BOD component in the water to be treated can be sufficiently decomposed in the aeration tank 6 even in the initial stage of the operation of the wastewater treatment system. B on the membrane surface of membrane module 3
Excessive adsorption of the OD component is prevented, and the solid-liquid separation process is performed stably.

[0021]

EXAMPLES Example 1 using the wastewater treatment system of FIG. 1, to the aeration tank 6 of capacity 1 m ³ before starting operation 10000m
g / l of activated sludge was seeded into aeration tank 6
After the MLSS concentration in the
Treatment of the water to be treated was performed at 500 mg / l for the D component and 100 mg / l for SS. The treated water amount is 1 m ³ / day, and the separation membrane module 3 is manufactured by Mitsubishi Rayon Co., Ltd. Stellapore L, UMF824LF (hollow fiber separation membrane module,
A membrane area of 8 m ² and a pore diameter of 0.1 μm) were used. Table 1 shows the measurement results of the suction pressure (differential pressure) of the separation membrane module 3 immediately after the start of the operation, 10, 30, and 90 days later.

[Comparative Example 1] The same operation as in Example 1 was performed, except that seeding of activated sludge was not performed before the start of operation. Table 1 shows the results. When the activated sludge was not seeded, an increase in suction pressure due to clogging of the membrane surface was observed.

[0023]

[Table 1]

[0024]

As described above, the membrane separation activated sludge treatment method of the present invention comprises a biological treatment in which microorganisms in activated sludge decompose organic matter in water to be treated and a solid-liquid separation treatment by a separation membrane module. In the membrane separation activated sludge treatment method performed in the same tank, the MLSS concentration of the water to be treated in the tank is set to 2000 mg / l before the first operation.
Since activated sludge is added to the tank as described above, excessive adsorption of organic substances to the membrane surface of the separation membrane module is prevented, the rise in the differential pressure inside and outside the separation membrane module is suppressed, and the To perform a solid-liquid separation process.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a wastewater treatment system using a membrane separation activated sludge treatment method.

FIG. 2 is a perspective view showing an example of a hollow fiber separation membrane module.

FIG. 3 is a schematic diagram showing an example of a conventional wastewater treatment system using settling separation.

[Explanation of symbols]

 3 Separation membrane module 6 Aeration tank

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Claims (1)

[Claims] 1. A membrane separation activated sludge treatment method in which a biological treatment for decomposing organic substances of water to be treated by microorganisms in activated sludge and a solid-liquid separation treatment by a separation membrane module are performed in the same tank. Before the start, the concentration of the suspended solids (MLSS) of the liquid to be treated in the tank is 2
Activated sludge is added to the tank so as to have a concentration of 000 mg / l or more.