JP2003326258A - Water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method by which water can be treated stably without deteriorating the filtration performance of a membrane for a long period of time by improving the cleaning efficiency of the membrane and in which membrane filtration is used. <P>SOLUTION: In this water treatment method, such a cycle is repeated that membrane filtration is performed for a prescribed time by making the water to be treated pass through a membrane module 3 from the primary side to the secondary side and then the used module 3 is backward washed. When the module 3 is backward washed, ozone gas from an ozone gas generating apparatus 10 is introduced from the primary side of the module 3 while the module 3 is backward washed by supplying hydrogen peroxide to backward washing water from a hydrogen peroxide tank 7 by using a chemical injecting pump 8 to obtain hydrogen peroxide-containing water and making the obtained hydrogen peroxide-containing water pass through the module 3 from the secondary side to the primary side so that the introduced ozone is brought into contact with the supplied hydrogen peroxide in the membrane. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water supply system, a sewer system,
The present invention relates to a water treatment method in which a membrane is washed every predetermined time when contaminants are separated and removed from water to be treated such as industrial water and various wastewaters by a membrane treatment.

[0002]

2. Description of the Related Art As a method for removing pollutants in water to be treated, a water treatment method utilizing membrane filtration is known. In the water treatment using this membrane filtration, as the water treatment operation is continued, an adhered layer of pollutants is generated on the surface of the membrane, clogging, fouling such as flow path clogging due to solid matter occurs, and filtration performance is improved. There is a problem that the amount of treated water decreases and a stable amount of treated water cannot be obtained.

In order to solve the above problems, cleaning of the membrane is regularly performed. Methods of cleaning this membrane include physical cleaning and chemical cleaning. Physical washing includes backwashing (backwashing) in which membrane filtered water flows back, flushing with water flow on the primary side of the membrane, air scrubbing that vibrates the membrane with air, etc. to remove adhering substances by physical action. There is.

On the other hand, chemical cleaning is a cleaning method in which substances that cannot be completely removed by physical cleaning are decomposed or dissolved by chemicals to be removed, and the filtration capacity of the membrane can be restored to almost the initial state. However, it is desirable to reduce the number of times as much as possible from the viewpoint of costly chemical cleaning and wastewater treatment.

As one of the methods for solving these problems, a method of cleaning the film using ozone or water containing ozone has been proposed. This is a method in which ozone is used as an oxidant to oxidatively decompose, remove, and remove substances adhering to the filtration membrane, thereby efficiently recovering membrane performance.

[0006] For example, in Japanese Patent Laid-Open No. 2000-107777, as a water treatment method for reducing the ozone supply amount, the concentration of dissolved ozone in membrane filtration water is continuously measured, and the membrane filtration treatment is performed based on the measured value. A method of controlling the amount of ozone supplied so that the concentration of dissolved ozone in water is within a predetermined range is described, and it is disclosed that clogging of the film can be suppressed by this method.

Further, in Japanese Patent Laid-Open No. 2000-350988, as a method for treating human waste sewage, solid-liquid separation is performed after biological treatment, and a coagulant is added to the permeated liquid, followed by sedimentation separation. In the method of performing solid-liquid separation treatment by the membrane filtration device, it is described that the accelerated oxidation treatment is performed between the sedimentation separation tank and the circulation tank or the membrane supply tank to the membrane filtration device. The combined use of ozone and hydrogen peroxide as a treatment is disclosed.

Further, Japanese Patent Laid-Open No. 6-238136 discloses a filtration membrane while purifying water represented by surface water such as river water and lake water by cross flow filtration using an ultra or microfiltration membrane module. In the method of cleaning a module, it is disclosed that an oxidizing bactericidal agent selected from hydrogen peroxide, ozone and the like is used as a bactericidal agent in clean water for backwashing a membrane.

[0009]

However, in the method described in the above-mentioned Japanese Patent Laid-Open No. 2000-107777, since the cleaning is performed only with ozone or ozone-containing water, the cleaning effect is limited and the running cost is low. In view of the above, there is a problem that a large amount of ozone is required to maintain the cleaning effect. It is also possible to increase the time of physical cleaning, but in that case,
Since the membrane filtration time is reduced, the recovery rate of filtered water is reduced.

Further, in the method disclosed in Japanese Patent Laid-Open No. 2000-350988, the accelerated oxidation treatment in which ozone and hydrogen peroxide are used in combination is performed on the raw water before filtration, whereby the load on the filtration membrane is increased. This is for reducing the water content, and is not a combination of ozone treatment and hydrogen peroxide used as cleaning water for the membrane itself.

Further, in the method described in JP-A-6-238136, a high cleaning effect cannot be expected when hydrogen peroxide and ozone are used alone as cleaning water used for backwashing. Even when hydrogen peroxide and ozone are combined, it is necessary to mix ozone and hydrogen peroxide in advance. For this reason, the reaction between ozone and hydrogen peroxide is already completed by the time the mixed solution reaches the inside of the film, so that there is a problem that the synergistic effect of ozone and hydrogen peroxide cannot be obtained.

The present invention has been made in view of the above-mentioned problems of the prior art. In the cleaning process of the membrane, the fouling substance attached to the filtration membrane is decomposed, peeled and removed more efficiently to improve the membrane performance. It is an object of the present invention to provide a water treatment method using membrane filtration that enables stable water treatment for a long period of time without recovering the filtration performance by recovering water.

[0013]

[Means for Solving the Problems] That is, the water treatment method of the present invention is a membrane filtration treatment in which water to be treated is passed from the primary side to the secondary side of the membrane to remove contaminants. Is a water treatment method in which a cycle of cleaning the film is repeated after a predetermined time, and in cleaning the film, ozone gas or ozone-containing water formed by dissolving the ozone gas is formed from one side of the film. It is characterized in that hydrogen peroxide gas or hydrogen peroxide-containing water is introduced from the other side of the film to bring the ozone and hydrogen peroxide into contact with each other in the film.

According to the water treatment method of the present invention, since ozone and hydrogen peroxide are combined in the film cleaning so that they are brought into contact with each other in the film, hydroxyl radicals and the like having a stronger oxidizing power than ozone can be obtained. Radicals are generated. Further, since the radical promotes the oxidation, the fouling substance can be efficiently decomposed, peeled and removed, and the cleaning effect of the film can be enhanced.

Further, in general, the lifetime of the above-mentioned generated radicals is very short, so even if ozone and hydrogen peroxide are mixed in advance, the radicals will disappear before they reach the film surface. Since hydrogen oxide is individually introduced from both sides of the film, the above radicals can be efficiently generated in the film.

In the present invention, at the time of cleaning the membrane, it is preferable to introduce the ozone gas from the primary side of the membrane while passing the hydrogen peroxide-containing water from the secondary side to the primary side of the membrane.

According to this, since hydrogen peroxide is a liquid at room temperature and normal pressure, hydrogen peroxide is mixed with the backwash water at the time of backwashing the membrane and passed from the secondary side to the primary side of the membrane. Therefore, hydrogen peroxide can be used as it is in a normal backwash system.

Further, by introducing ozone as a gas from the primary side of the film on the opposite side, it is possible to distribute ozone more uniformly over the entire membrane module as compared with the case where it is introduced as ozone-containing water, and at the film surface. The contact with hydrogen peroxide can be facilitated. Furthermore, since the amount of water used for cleaning does not increase, the recovery rate of membrane-filtered water does not decrease.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the water treatment method of the present invention will be described below with reference to FIG. FIG. 1 is a schematic configuration diagram showing an embodiment of the water treatment method of the present invention.

As shown in FIG. 1, this water treatment apparatus has a membrane filtration means provided with a membrane module 3 for performing membrane filtration treatment of raw water which is water to be treated, and peroxidation of the treated water subjected to the membrane filtration treatment. A backwash means for backwashing the membrane module 3 by mixing the hydrogen peroxide from the hydrogen tank 7 to produce hydrogen peroxide-containing water and feeding the water with the backwash pump 5. It mainly comprises an ozone gas supply means for supplying the ozone gas from the ozone gas generator 10.

In the membrane filtration means, the pipe from the raw water tank 1 for storing the raw water to be treated has the operation pump 2,
It is configured to be connected to the primary side inlet of the membrane module 3 via the valve 19. The amount of water flowing into the raw water tank 1 is preferably controlled by a water level sensor or the like installed in the water tank.

The pipe from the outlet of the secondary side of the membrane module 3 is connected to the membrane filtration water tank 4 through the valve 15, and the pipe from the membrane filtration water tank 4 serves as membrane filtration water in the next step. It is connected so that water can flow to. A drain drain 14 for discharging water in the membrane module before the start of cleaning is provided below the membrane module 3.

The piping from the primary outlet of the membrane module 3 is connected to the circulation pump 13 via a valve 18,
From here, it joins so that it may join between the valve 19 and the primary side inlet of the membrane module 3. As a result, raw water can be circulated from the circulation pump 13 through the membrane module 3 to the circulation pump 13 via the valve 18, and cross flow can be performed. A drain 9 for discharging the backwash water in the pipe is provided between the valve 18 and the circulation pump 13.

The membrane module 3 is not particularly limited,
Hollow fiber-shaped, spiral-shaped, tubular-shaped, flat membrane-shaped porous membranes and the like can be used. Further, the pore size of the porous membrane can be appropriately selected and is not particularly limited. The material of the film and the adhesive layer of the film are preferably made of a material having ozone resistance and hydrogen peroxide resistance in order to come into contact with ozone and hydrogen peroxide. Examples of the material for such a film include an ozone-resistant organic resin such as vinylidene fluoride polymer resin,
Alternatively, an inorganic material such as ceramic can be used.

Further, the filtration method of the membrane module 3 may be a total volume filtration method or a cross flow filtration method. When the cross-flow filtration method is used, the circulation flow can be achieved by circulating the raw water on the primary side of the membrane module 3 by the circulation pump 13. Further, the method of passing water to the membrane module 3 may be an external pressure type or an internal pressure type.

Next, the backwashing means will be described. From the membrane filtration water tank 4, the backwashing pump 5 and the valve 17 are used so as to join the secondary side outlet of the membrane module 3 and the valve 15. The backwash pipe 6 is connected so that part of the membrane filtration water can be used for backwashing.

The pipe from the hydrogen peroxide tank 7 is connected to the backwash pipe 6 through the chemical injection pump 8 and the valve 16. The chemical injection pump 8 and the valve 16 can be controlled in flow rate by a control device (not shown).
As a result, water containing hydrogen peroxide at a predetermined concentration can be used as backwash water.

Next, the ozone gas supply means will be described. A pipe for supplying ozone gas to the primary inlet of the membrane module 3 is connected from the ozone generator 10 via a valve 20. As the ozone generator 10, a conventionally known one can be appropriately used.

The pipe from the primary outlet of the membrane module 3 is connected to the exhaust ozone treatment device 12 via the valves 18 and 11.
It is connected to the. The exhaust ozone treatment device 12 is a device for discharging excess ozone gas to the outside of the system when ozone-containing water is formed in the membrane module 3.
The types of the exhaust ozone treatment device 12 are activated carbon type, thermal decomposition type,
Any form such as catalytic type may be used.

Next, a water treatment method using this water treatment apparatus will be described. First, the valve 19 is opened, and the operation pump 2 is controlled by a signal from a flow sensor (not shown) or the like to supply raw water, which is water to be treated, from the raw water tank 1 to the primary inlet of the membrane module 3 for constant flow filtration. Start. The membranous filtered water is stored in the membranous filtered water tank 4 from the secondary outlet of the membrane module 3 via the valve 15, and is passed to the next step as necessary.

In the present invention, the inorganic substances represented by manganese and iron contained in the raw water are the membrane module 3
It is preferably removed before being introduced into. The concentration of each metal after removing the manganese and iron is preferably less than 0.005 mg / L. As such a method of removing manganese and iron, an ion exchange treatment method, a method of performing an oxidation treatment by adding an oxidizing agent such as air aeration and sodium hypochlorite,
Examples thereof include a biological treatment method using iron bacteria and the like, a contact filtration method using a manganese contact filter such as manganese sand, and the like.

Next, after a lapse of a predetermined filtration time, the operation pump 2 is stopped, the valve 15 is closed, and the backwashing process is started. First, the drainage drain 14 is opened and the water in the membrane module 3 is discharged. Next, after closing the drainage drain 14, the backwash pump 5 is operated to open the valve 17, and a part of the membrane filtration water in the membrane filtration water tank 4 is passed from the secondary side of the membrane module 3 to the primary side. Then, the backwash water is finally discharged from the drain 9 to the outside of the system through the valve 18.

In the present invention, the chemical injection pump 8 is simultaneously operated at this time to open the valve 16, hydrogen peroxide is supplied from the hydrogen peroxide tank 7 and mixed with the backwash water to a predetermined concentration. Then, the backwash water is used as the hydrogen peroxide-containing water.

Further, at this time, simultaneously with this backwashing, ozone gas generated from the ozone generator 10 is introduced from the primary side of the film through the valve 20.

As a result, due to the synergistic effect of ozone and hydrogen peroxide, OH radicals are formed inside the membrane module 3, particularly near the surface of the membrane, and accelerated oxidation treatment is performed on the membrane surface to enhance the cleaning effect. You can After passing through the primary outlet of the membrane, the excess ozone-containing gas is exhausted from the air vent valve 11 via the exhaust ozone treatment device 12.

Here, it is preferable to supply hydrogen peroxide in the backwashing step so that the concentration thereof is 0.01 to 10,000 mg / L. Hydrogen peroxide concentration is 0.01
If it is less than mg / L, the amount of radicals generated by the reaction is small and the cleaning effect cannot be expected, which is not preferable.
If it exceeds 10000 mg / L, it is not preferable because the economical efficiency is deteriorated. The washing time is preferably 0.5 to 5 minutes.

On the other hand, it is preferable that the ozone gas is supplied so that the ozone gas concentration is 0.1 to 50 g · O ₃ / m ³ . When the ozone gas concentration is less than 0.1 g · O ₃ / m ³ , the amount of radicals generated by the reaction is small,
50g · O
_When it exceeds ₃ / m ³ , the economical efficiency is deteriorated, which is not preferable.

Although the timing of supplying ozone can be set as appropriate, from the viewpoint of shortening the cleaning time, it is preferable to supply ozone at the same time as the start of the backwashing step, and at least until the backwashing step is completed. It is preferably supplied.

In the present invention, ozone gas or ozone-containing water formed by dissolving the ozone gas is introduced from one side of the membrane, and hydrogen peroxide gas or hydrogen peroxide-containing water is introduced from the other side of the membrane. It may be introduced, but since hydrogen peroxide is a liquid at room temperature and atmospheric pressure, it is preferable to supply it as backwash water from the secondary side of the membrane, and therefore it is preferable to supply ozone from the primary side of the membrane.

Further, in this case, ozone supplied from the primary side is not necessarily limited to ozone gas, and it is also possible to supply ozone-containing water.
Ozone is not evenly distributed over the entire membrane, contact with hydrogen peroxide on the membrane surface is likely to be insufficient, and the amount of water used during cleaning increases and the recovery rate of membrane filtration water decreases. It is preferable to supply ozone gas.

In the present invention, in order to further enhance the cleaning effect, an air scribing step of supplying compressed air generated by a compressor (not shown) from the lower part of the primary side of the membrane module 3 and raw water to the membrane module 3. Physical washing such as a flushing step of passing water may be performed together.

The operation time of the above membrane filtration treatment, the cleaning time,
The operating time for one cycle, which is a combination of both, can be appropriately set depending on the water quality of the raw water, the processing capacity of the apparatus, etc., but the operating time for one cycle is usually preferably 15 minutes to 6 hours.

By the above membrane filtration treatment and membrane cleaning, the fouling substance attached to the filtration membrane is decomposed more efficiently,
The film performance can be recovered by peeling and removing. As a result, stable water treatment can be performed for a long period of time without deterioration of filtration performance.

[0044]

EXAMPLES The water treatment method of the present invention will be described in more detail below with reference to examples. The present invention is not limited to the examples below.

<Example> Using the water treatment apparatus having the structure shown in FIG. 1, water treatment was carried out using river water as raw water.

The membrane module 5 has a nominal pore size of 0.
Using a hollow fiber membrane made of polyvinylidene fluoride of 1 μm material, a constant flow rate filtration of 4 m ³ / (m ² · day) was carried out, and the operation was performed under the condition that the recovery rate of the membrane filtration water was 95%. The transmembrane pressure difference at the beginning of the operation was 32 kPa.

The backwash water during backwash was adjusted to have a temperature of 25 ° C. and a hydrogen peroxide concentration of 20 mg / L by adjusting the chemical injection pump 8 and the valve 16. Further, the ozone generation amount from the ozone generator 10 was adjusted so that the ozone generation amount was 15 g · O ₃ / m ³ .

As the operation cycle of the water treatment device, a total of 63 minutes including constant flow filtration for 60 minutes and backwash time for 3 minutes was set as one cycle, and this cycle was repeated.

<Comparative Example> Backwash water was added using sodium hypochlorite instead of hydrogen peroxide so that the residual chlorine concentration in the backwash wastewater was 1 ppm. Water treatment was carried out under the same conditions as in the example except that an air compressor was used for the above and an air scribing step was used instead of the ozone gas supplying step.

<Test Example> Under the above conditions, the water treatment devices of Examples and Comparative Examples were continuously operated, and the transmembrane pressure difference, which was the pressure difference between the primary side and the secondary side of the membrane module 3, was measured. The result is shown in FIG.

As shown in FIG. 2, in the example, it is understood that the increase in transmembrane pressure difference is suppressed as compared with the comparative example. The amount of increase in transmembrane pressure difference after continuous operation for 5 days (after 120 hours) was 8 kPa in Example, and no large increase in transmembrane pressure was observed, whereas in Comparative Example, continuous operation was performed for 5 days. The amount of increase in the transmembrane pressure difference afterward was 78 kPa, which was larger than that in the example.

[0052]

As described above, according to the present invention,
In the membrane cleaning process, by using hydrogen peroxide and ozone so that they contact each other in the membrane, the fouling substances adhering to the filtration membrane are more efficiently decomposed, peeled and removed to restore the membrane performance. Can be made. This makes it possible to provide a water treatment method utilizing membrane filtration, which enables stable water treatment without lowering the filtration performance for a long period of time, and can also reduce equipment costs and treatment costs.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a water treatment method of the present invention.

FIG. 2 is a chart showing the relationship between operating time and transmembrane pressure difference in an example of the present invention.

[Explanation of symbols]

1: Raw water tank 2: Operation pump 3: Membrane module 4: Membrane filtered water tank 5: Backwash pump 6: Backwash piping 7: Hydrogen peroxide tank 8: Chemical injection pump 9: Drain 10: Ozone generator 11: Air bleeding valve 12: Waste ozone treatment device 13: Circulation pump 14: Drainage drain 15, 16, 17, 18, 19, 20: Valve

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Noriaki Kadokawa             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 4D006 GA06 GA07 HA01 HA21 HA41                       HA61 JA53Z JA56Z KA61                       KC03 KC13 KC14 KC16 KD21                       KD22 KE11Q KE22Q KE23Q                       KE24Q KE28Q MA01 MC29X                       PA01 PB02 PB06 PB08

Claims (2)

[Claims] 1. A cycle in which when a contaminant is removed by a membrane filtration treatment in which treated water is passed from the primary side to the secondary side of the membrane, the membrane filtration treatment is performed for a predetermined time and then the membrane is washed. In the cleaning of the film, ozone gas or ozone-containing water formed by dissolving the ozone gas is introduced from the one side of the film, and the hydrogen peroxide gas is supplied from the other side of the film. Alternatively, a water treatment method is characterized in that hydrogen peroxide-containing water is introduced to bring the ozone and hydrogen peroxide into contact with each other in the film. 2. The water treatment according to claim 1, wherein the ozone gas is introduced from the primary side of the membrane while the hydrogen peroxide-containing water is passed from the secondary side to the primary side of the membrane at the time of cleaning the membrane. Method.