JP2002248324A - Membrane separation apparatus and its backwashing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a time interval of chemical cleaning work by exfoliating contaminants stuck onto the membrane surface of the primary side of a membrane separation apparatus efficiently by backwashing. SOLUTION: This membrane separation apparatus 2 of an inside-pressurizing hollow fiber type, a tubular type or a spiral type, in which the permeated water is obtained from one side 2B of a separation membrane 2M by supplying raw water to the other side 2A, is provided with means 14, 21 for introducing gas directly from one end of the raw water side 2A, a means 20 for introducing backwashing water into the permeated water side 2B and a gas-liquid discharging means 22 arranged on the other end of the end 2A. The membrane 2M is washed efficiently by supplying backwashing water and the gas at the same time when backwashed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a desalination reverse osmosis (R)
O) membranes, ultrafiltration (UF) membranes and microfiltration (MF) membranes used for water treatment for removing trace organic substances, solid-liquid separation treatment for river water, industrial water or wastewater, or biologically treated water The present invention relates to an internal pressure hollow fiber type, tubular (tubular) type or spiral type membrane separation device and a backwashing method thereof, in particular, which enables efficient backwashing, thereby extending the chemical washing interval. The present invention relates to a membrane separation device capable of improving the operation efficiency of the device and a method for back washing the membrane separation device.

[0002]

2. Description of the Related Art In recent years, TOC components comprising humic acid and fulvic acid, which are microbial metabolites, have increased due to organic contamination of industrial water and water intake water sources, and in water treatment facilities using membranes, membrane contamination has been increasing. It tends to increase.

Generally, a system consisting of coagulation, sedimentation and sand filtration has conventionally been used as a pretreatment for RO membrane treatment. However, when the concentration of organic matter in raw water increases, ferric chloride and polystyrene are used. It is necessary to add a large amount of a coagulant such as aluminum chloride and aluminum sulfate. In this case, if these coagulants are added in excess, a small amount of coagulant in a dissolved state that cannot be coagulated remains in the coagulation treatment water, and the remaining coagulant re-aggregates in the process of being concentrated in the RO membrane. Thus, there is a problem in that the RO film is fixed to the primary side (raw water side) surface and the frequency of chemical cleaning is increased.

In recent years, a pretreatment system using an MF membrane or a UF membrane has been adopted in place of such a pretreatment system based on coagulation and sedimentation. It is possible to remove the colloidal component in the raw water that contaminates the RO membrane without adding a small amount of coagulant or by adding only a small amount of coagulant, thereby suppressing the contamination of the RO membrane and extending the chemical cleaning interval. Thereby, the operation efficiency of the RO membrane can be improved.

However, in the MF membrane or UF membrane used as a pretreatment, the polymeric humic acid or fulvic acid, which is the TOC component in raw water, is adsorbed or deposited on the primary surface of these membranes, and This will increase the filtration resistance of the membrane.
Such membrane contamination due to polymeric humic acid or fulvic acid cannot be removed by general water backwashing, and requires chemical cleaning.

On the other hand, even in the case where sewage or industrial effluent biologically treated water is subjected to membrane separation treatment and reused, the biologically treated water contains TOC components composed of humic acid and fulvic acid, which are microbial metabolites. However, membranes used for membrane separation of such biologically treated water have the same problems as described above.

The present inventor has focused on a cleaning operation using gas in such a membrane separation apparatus, and has devised a method for efficiently removing these membrane contaminants. For example, it has been proposed to introduce a gas during a filtration operation to prevent membrane contamination (JP-A-9-99223 and JP-A-9-99227).

[0008] Further, in the external pressure hollow fiber type membrane separation apparatus, a scrubbing cleaning method in which the membranes are brought into contact with each other to enhance the effect of removing membrane contaminants is known. Also, a gas cleaning method aiming at a similar effect is known.

In these methods, a gas is introduced from one end of a raw water flow path of a membrane module before and after backwashing, and a shear force generated when a gas-liquid interface passes through the membrane surface is used. However, even in such a method, when water having a high organic substance concentration is separated, the cleaning effect is not sufficient, and the film contaminants gradually accumulate, so frequent chemical cleaning is required.

On the other hand, the present inventor has proposed a film cleaning method for reducing the amount of used chemicals by using a gas at the time of chemical cleaning (Japanese Patent Laid-Open No. 2000-167364). However, although this method is effective for improving the chemical cleaning efficiency, it is not effective for suppressing membrane contamination during the filtration operation, and the chemical cleaning interval cannot be extended.

[0011]

As described above, conventionally, a conventional RO membrane for desalination, a water treatment for removing a trace amount of organic substances, a solid-liquid separation treatment for river water, industrial water or wastewater, or biologically treated water. No effective method has been provided for extending the chemical cleaning interval of a UF film, an MF film, or the like used for the above.

Accordingly, an object of the present invention is to extend the chemical cleaning interval by efficiently removing contaminants adhering to the primary film surface by backwashing. To generate a strong shear force due to the movement of the gas-liquid interface during backwashing to reduce the amount of backwash water and simplify the backwash operation. It is an object of the present invention to provide a membrane separation device capable of performing the method and a back washing method thereof.

[0013]

The membrane separation device of the present invention comprises:
In an internal pressure hollow fiber type, tubular type, or spiral type membrane separation device that supplies raw water to one side of the separation membrane and obtains permeated water from the other side, gas is directly introduced from one end of the raw water side of the separation membrane. Means for introducing backwash water to the permeated water side of the separation membrane, and gas-liquid discharge means provided on the other end side of the raw water side of the separation membrane away from the gas introduction means. Further, the separation membrane can be washed by simultaneously supplying backwash water and gas.

The backwashing method of the present invention backwashes an internal pressure hollow fiber type, tubular type or spiral type membrane separation device which supplies raw water to one side of a separation membrane and obtains permeated water from the other side. In the method, a gas is directly introduced from one end of the raw water side of the separation membrane, and in parallel with this, backwash water is introduced into a permeated water side of the separation membrane, and the gas is supplied to the raw water side of the separation membrane. It is characterized in that backwash water and gas are discharged from gas-liquid discharge means provided on the other end side remote from the introduction means.

In the present invention, a gas such as air is introduced into the raw water side (primary side) of the separation membrane at the time of back washing (back pressure washing), and back washing water is introduced into the permeated water side (secondary side). Perform backwash.

For this reason, when the backwash water passes through the membrane from the secondary side to the primary side of the membrane, the contaminants adhering to the membrane surface are peeled off, and at the same time, the air introduced into the primary side is moved at a high speed. By passing through the inside of the membrane module and generating not only the above-mentioned backwashing effect but also a shearing effect at the gas-liquid interface, a separating effect that is more than each of the individual effects is brought about.

[0017] That is, as shown in FIG. 2 (a), only the air introduced to the primary side 10A of the membrane 10, the fluid passage rate occurring on the membrane surface is only dependent on the air passing speed U _G, while FIG. as shown in 2 (b), alone backwashing passing the backwash water from the secondary side 10B of the membrane 10 to the primary side 10A, the fluid passage rate caused the film surface is only backwash water discharging speed U _L but, as shown in FIG. 2 (c), by introducing air into the primary side simultaneously film the backwash water during backwashing, substantially fluid passing speed U ₀ of the membrane surface backwash water discharging speed U _L and the air Passing speed U
_G, and a high peeling effect can be obtained with a strong shearing force due to rapid movement of the gas-liquid interface. In FIG. 2, P indicates a contaminant attached to the surface of the primary side 10A of the film 10.

As described above, in the present invention, the flow rate of the gas introduced into the primary side of the membrane and the flow rate of the backwash water are combined to generate a high flow rate on the primary side of the membrane, and the dirt on the membrane surface is removed by high shearing force. Although effectively removed, such a high flow rate is achieved when the flow path on the raw water side is a restricted space, such as an internal pressure hollow fiber type, a tubular type, or a spiral type. You. In a space having a wide raw water side such as an external pressure hollow fiber type, the flow rate of gas or backwash water is reduced, and the object of the present invention cannot be achieved.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a membrane separation apparatus and a backwashing method according to the present invention will be described in detail with reference to the drawings.

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

[0021] In FIG. 1, 1 is raw water tank, 2 membrane module 3 is transmitted water tank, 4 denotes a compressor, _{P 1} is the raw water pump, _{P 2} is a backwashing pump. Each code | symbol of 11-22 shows a piping. V _{1 to} V ₆ are open / close valves.

In this membrane separation apparatus, after filtering raw water for a predetermined time, backwashing is performed, and the filtration step and the backwashing step are alternately repeated.

In the step of filtering raw water, the valves V ₁ , V ₂ ,
With V ₃ open and valves V ₄ , V ₅ , V ₆ closed, the raw water pump P ₁ is operated, and the raw water introduced from the pipe 11 is introduced into the membrane module 2 via the raw water tank 1 and the pipes 12, 13, 14. I do. The permeated water of the membrane module 2 is stored in the permeated water tank 3 via the pipes 17 and 18 and taken out from the pipe 19 as needed. On the other hand, the concentrated water circulates through the pipes 15 and 16 to the raw water introduction side. In this filtration step, the valve V ₆
May be opened, and a part of the concentrated water may be discharged from the pipe 22 to the outside of the system.

[0024] In the backwash process, stop the raw water pump _{P 1,}
The valves V ₁ , V ₂ , V ₃ are closed, the valves V ₄ , V ₅ , V ₆ are opened, the backwash pump P ₂ and the compressor 4 are operated, and the permeated water in the permeated water tank 3 is supplied to the pipe 2.
Pressure is introduced into the secondary side 2B of the membrane module 2 via 0 and 17, and the backwash water permeates through the membrane 2M from the secondary side 2B of the membrane module 2 and flows into the primary side 2A. The air pressurized by the compressor 4 at the time of the back pressure cleaning is supplied to the pipes 21 and 14.
Through the membrane module 2 from one end to the primary side 2A.

Thus, the primary side 2A of the membrane module 2
As shown in FIG. 2 (c), as shown in FIG. 2 (c), a high fluid velocity by backwash water and air is obtained, a strong shearing action is obtained by rapid movement of the gas-liquid interface, and adheres to the surface of the primary side 2A of the membrane 2M. The contaminants thus removed are effectively removed and removed. And the peeled contaminants, together with the gas-liquid mixture of backwash water and air,
It is discharged out of the system via pipes 15 and 22.

The backwash step after the end stops backwash pump _{P 2} and the compressor 4, the valve _{V 4,} V 5, _{V 6} with the closed actuates the raw water pump _{P 1, V 1,} V ₂ ,
Resume filtration step the V ₃ is opened.

The backwash conditions (backwash frequency, backwash time,
The backwash water flow rate and air flow rate) vary depending on the type of membrane module, raw water quality, filtration operation conditions, etc., but a UF membrane module or MF membrane module for solid-liquid separation in various types of water treatment, or an RO for desalination. 15 for membrane modules
It is preferable to perform backwashing for about 10 to 60 seconds at every filtration step of about 180 minutes, and the backwash water flow rate at this time is the flow rate at the outlet of the raw water primary-side flow channel of the membrane module ([the backflow supplied per unit time). Water amount] / [cross-sectional area of primary flow path]).
The air flow velocity is about 0.1 to 2.0 m / sec, and the flow velocity at the outlet of the raw water primary flow path ([air amount supplied per unit time] / [cross-sectional area of primary flow path]) is 0.1. ~ 1.
It is preferably about 0 m / sec.

In the membrane separation apparatus shown in FIG. 1, a raw water introduction pipe 14 of the membrane module 2 is provided at one end of the primary side 2A of the membrane module 2, while pipes 15 and 22 for discharging concentrated water and backwash wastewater are provided. Is provided at the other end of the primary side 2A, the raw water introducing pipe 1 and the pipes 15 and 22 for discharging the concentrated water and the backwash wastewater are used to make the raw water introducing pipe 1
4 is connected to a pipe 21 for introducing air as gas introducing means, and pipes 15 and 22 for discharging concentrated water and backwash drainage are used as gas-liquid discharging means. The gas introducing means and gas-liquid discharging means are separately provided. It may be provided as an independent pipe. In addition, a pipe 2 for introducing air is connected to a pipe 22 for discharging concentrated water and backwash wastewater.
1 may be connected as gas introduction means, and a branch pipe branched from the raw water introduction pipe 14 may be provided as gas-liquid discharge means.

Generally, the membrane separation device is provided with a backwash water introduction pipe and a backwash drainage discharge pipe, and the raw water introduction pipe and the concentrated water and the backwash wastewater discharge pipe are spaced apart from each other. Because of this, as shown in FIG. 1, it is preferable to connect an air introduction pipe to the raw water introduction pipe 14 and use it as a gas introduction means. With such a membrane separation apparatus, simply use an existing membrane separation apparatus. It can be easily implemented simply by providing an air introduction pipe and a compressor.

The present invention is particularly effective for a UF membrane separator or MF membrane separator for solid-liquid separation or an RO membrane separator for desalination used in various water treatments, and is an efficient reverse-separation device. By performing the washing, the chemical washing interval can be greatly extended, and the operation efficiency of the membrane separation device can be increased.

[0031]

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

Example 1 Using the membrane separation apparatus shown in FIG. 1, an experiment was conducted to examine the effect of the present invention in which surface water with advanced organic pollution was used as raw water and gas was introduced together with backwash water to perform backwash.

The used membrane modules are as follows. Manufacturer: Kuraray Co., Ltd. Type: MU-6305 (Internal pressure hollow fiber type UF membrane module) Inner diameter: 0.7 mm Material: Polysulfone Membrane filtration is constant flow filtration of a fixed amount by cross flow filtration (0.3 m / s) And filtration was performed under the operating conditions shown in Table 1.

The rate of increase of the transmembrane pressure difference ΔP was used to determine the degree of membrane fouling (kPa / day), and the rate of increase of the transmembrane pressure difference ΔP and the water recovery rate when filtration was continued for 14 days. And the results are shown in Table 1.

Comparative Example 1 Filtration was carried out in the same manner as in Example 1 except that air was not introduced at the time of backwashing.
The rise rate of water and the water recovery rate were examined, and the results are shown in Table 1.

Comparative Example 2 In Example 1, filtration was carried out in the same manner as in Example 1 except that the introduction of air was carried out after the introduction of the backwash water, and that the flow of water was 20 minutes, the introduction of the backwash water was 45 sec, and the introduction of air was 45 sec. The rate of increase of the transmembrane pressure ΔP and the water recovery rate were examined, and the results are shown in Table 1.

[0037]

[Table 1]

As is evident from Table 1, in Comparative Example 1 in which only the backwash water was not used, and the air was not introduced, the rate of increase of ΔP was 7.40 kPa / day, and ΔP increased in a very short time. Chemical cleaning was required in about a week. In Comparative Example 2 in which air was introduced after the introduction of the backwash water, the ΔP increasing rate was reduced to 0.67 kPa / day due to the gas cleaning effect, and the number of days that filtration could be continued until the chemical cleaning was estimated to be about 100 days. However, in Comparative Example 2, the backwashing time was long, and the water recovery rate was reduced by 2%.

On the other hand, in Example 1 in which gas was introduced during backwashing, the rate of increase of ΔP was 0.01 kPa / day.
It was estimated that the number of days that filtration could be continued until chemical cleaning would be extended to one year or more.

The reason for this is that in the example 1, the flow velocity _{U L} backwash water
= 0.6 m / sec, and the air flow rate U _G = 0.4 m / s
In the _{ec, U L + U G =} 0.6 + 0.4 = 1.0m / s
It is considered that by obtaining a substantial flow rate of ec, contaminants on the film surface are effectively removed by a high shearing separation effect.

[0041]

As described above in detail, according to the membrane separation apparatus and the backwashing method of the present invention, the backwash water is introduced at the time of backwash and the gas is introduced into the primary side of the membrane, so that the gas-liquid A high shearing action due to the rapid movement of the interface can be exhibited, and contaminants attached to the film surface can be efficiently peeled and removed.

Accordingly, since a high backwashing effect can be obtained, the chemical cleaning interval can be greatly extended, and the time required for backwashing and the amount of backwash water can be greatly reduced.

In the present invention, such an effective backwash can be easily carried out only by operating a valve, and application to an existing membrane separation apparatus is extremely easy.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a membrane separation device and a backwashing method of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating an action of removing contaminants on a film surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Membrane module 3 Permeate tank 4 Compressor 10 Membrane 10A Primary side 10B Secondary side

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 63/06 B01D 63/06 63/10 63/10 C02F 1/44 C02F 1/44 H K (72) Inventor Naoki Matsukei 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Kurita Kogyo Co., Ltd. 4D006 GA03 GA06 GA07 HA01 HA18 HA21 HA61 JA51A JA53A JA55A JA57A JA67A KC03 KC14 PA01 PB03 PB08 PC63

Claims (2)

[Claims] 1. An internal pressure hollow fiber type, tubular type or spiral type membrane separation device for supplying raw water to one side of a separation membrane and obtaining permeated water from the other side, wherein one end of the separation membrane on the raw water side is provided. Means for directly introducing a gas from the membrane, means for introducing backwash water to the permeated water side of the separation membrane, and gas-liquid provided at the other end of the raw water side of the separation membrane that is separated from the gas introduction means. A membrane separation device, comprising: a discharge means; and supplying backwash water and gas simultaneously to enable the separation membrane to be washed. 2. A method for backwashing an internal pressure hollow fiber type, tubular type or spiral type membrane separation apparatus in which raw water is supplied to one side of a separation membrane and permeate is obtained from the other side. A gas is directly introduced from one end of the raw water side, and backwash water is introduced into the permeated water side of the separation membrane in parallel therewith, and the raw water side of the separation membrane is separated from the gas introduction means. A backwash method for a membrane separation device, comprising discharging backwash water and gas from gas-liquid discharge means provided on an end side.