JP2000024660A - Water treatment and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve treated water quality by storing once the water to be treated which is supplied to a filter membrane, executing ozone treatment by always discharging a part of the stored water to be treated and circulating the treated water to the original water to be treated. SOLUTION: The water to be treated which is subjected to the ozone treatment and supplied to the filter membrane is stored once in an ozone treated water tank 6, and raw water 1 is supplied to the ozone treated water tank 6 by a raw water supply means 12. After that, a part of the ozone treated water being the water to be treated is discharged from the ozone treated water tank 6 by a circulation means 7 and returned to the ozone treated water tank 6 and also ozone is injected to the ozone treated water whose some part is discharged by an ozone injection means 5. Then the ozone treated water is discharged from the ozone treated water tank 6 and supplied to a membrane module 9. In this way, an advanced treatment of purified water can be executed and the sufficient treated water quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to advanced treatment of purified water,
The present invention relates to a water treatment apparatus for performing membrane filtration using ozone in combination with advanced treatment of sewage such as night soil and domestic wastewater, and industrial wastewater.

[0002]

2. Description of the Related Art As a typical treatment method of conventional water purification treatment, coagulation sedimentation-sand filtration-chlorine disinfection, coagulation sedimentation-sand filtration-activated carbon-chlorine disinfection or coagulation sedimentation-sand filtration-ozone-activated carbon-chlorine disinfection, etc. Is being done. Also, as a typical treatment method for the discharge and reuse of sewage such as human waste and domestic wastewater or industrial wastewater, first sedimentation basin-aeration-final sedimentation basin-chlorination and first sedimentation basin-aeration-final sedimentation basin -Coagulation sedimentation-Sand filtration-Chlorination, etc. have been performed.

On the other hand, water sources such as water storage dams have been developed as a measure against drought due to increased demand for domestic water, disorderly deforestation, abnormal weather, etc. In recent years, the quality of water sources has deteriorated. However, it is becoming impossible to obtain good drinking water by the conventional methods, which is a serious problem. Sewage such as human waste and domestic wastewater or organic wastewater from factories is discharged after removing various suspended substances and organic components contained in the wastewater by the method described above.
In recent years, however, attention has been paid to environmental issues, and such effluents have been required to be treated with even higher water quality. In addition, it has been proposed to reuse sewage and wastewater as water resources for effective use of water.For example, various uses such as park fountains and scenic views, hydrophilic water, miscellaneous water, industrial water, etc. are considered. And especially landscapes,
It has begun to be actually used as hydrophilic water.

Various types of membrane filtration using ultrafiltration membranes or microfiltration membranes have been proposed for the purpose of such advanced water purification treatment and sewage treatment. The problem is a decrease in filtration flux due to clogging,
Preventing membrane clogging is a major issue. Therefore, in the membrane filtration method, it has been proposed to use a cross-flow filtration method (tangent filtration method) for the purpose of preventing membrane clogging. Furthermore, Japanese Patent Application Laid-Open No. 4-108518 proposes performing tangential filtration by adding an oxidizing gas such as ozone into a loop above the membrane to prevent clogging of the membrane.

[0005]

As described above, by using an oxidizing gas such as ozone together, the permeation flux at the time of membrane filtration is several times larger than when not using ozone together, and the installation area of the filtration membrane is reduced. As it becomes smaller, the economics for water treatment also increases. However, when using ozone,
Since generation of ozone requires a large amount of electric power, how to effectively use the generated ozone is important from the viewpoint of economy.

Conventionally, in the case of performing water treatment using ozone, ozone gas is usually converted into raw water using an air diffuser or the like in an ozone contact tower having a height of several meters in order to improve the efficiency of absorbing ozone into water. A method of injecting and sending to a subsequent processing apparatus has been adopted. However, in the normal membrane filtration method, backwashing or air bubbling cleaning with air is performed at regular intervals to clean clogged membranes. During this cleaning operation, filtration is not performed, so that raw water is supplied to the membrane. Stops.
In the case of using the above-mentioned ozone contact tower, even while the membrane filtration is stopped, the raw water is continuously supplied at a constant flow rate for the purpose of keeping the conditions of the ozone injection constant, and the water amount balance with the subsequent membrane filtration device is maintained. Because of the need to take it, wasteful operations such as discarding or returning the water injected with ozone are necessary,
It was not economic.

To solve such a problem, a method may be considered in which the supply of raw water is stopped while the membrane filtration is stopped, and the generation of ozone is stopped at the same time. In the case of generation, it takes at least several seconds until a required generation amount is obtained, and this membrane filtration cannot be performed. Further, in an ozone generator using oxygen obtained from air by a PSA method (pressure swing method) and using it as an ozone gas raw material, once ozone generation is stopped, it takes several minutes before ozone is generated again. Not economic.

The present invention has been made to solve such problems, and an object of the present invention is to provide sufficient treated water quality in performing advanced treatment of purified water and advanced treatment of sewage. An object of the present invention is to provide an economical water treatment method that can maintain a high filtration flux with a low ozone injection amount because ozone can be effectively used.

[0009]

Means for Solving the Problems As a result of diligent studies on the ozone injection method, the present inventors have found that by always injecting ozone into raw water before the membrane filtration, a high filtration flow rate with a substantially small ozone amount can be obtained. Find that you can get a bunch,
The present invention has been completed. That is, in the present invention, in a method (1) in which raw water is treated with ozone and then treated with a filtration membrane, the present invention is suitable for water purification treatment and sewage treatment. In the water treatment method, a part of water is always extracted and subjected to ozone treatment and circulated to the original water to be treated. (2) In the method of treating raw water with ozone and then treating it with a filtration membrane, After injecting ozone, temporarily store it before supplying it to the filtration membrane,
Further, a part of the stored ozonized water is always extracted, mixed with raw water, and circulated to the original ozonated water after ozone treatment. For supplying raw water to the tank 6
A circulating means 7 for taking out a part of the ozonized water from the tank 6 and returning it to the tank 6; a means 5 for injecting ozone into the ozonized water partly taken out; The present invention relates to a water treatment apparatus having means 8 for taking out and supplying it to a membrane module 9.

The details of the present invention will be described below. As shown in FIG. 1, an example of a specific process of the advanced treatment method for purified water, sewage, and wastewater according to the present invention is as follows.
After ozone (O ₃ ) is added to raw water 1 consisting of lake water, stored water or secondary sewage water or industrial wastewater, and ozone treatment 2 is performed to ozone decompose suspended substances and organic substances in the raw water 1, Filtration is performed using a membrane having ozone resistance.

Conventionally, when raw water consisting of river water, underground water, lake water, reservoir water or secondary sewage water or industrial wastewater is simply filtered through a membrane, the suspended substance contained in the raw water and the pore size of the membrane to be used are exceeded. As a result, the organic substance in the raw water clogs the membrane, or adsorbs on the network inside the membrane, and the resulting membrane is formed. The filtration flux decreased from one-several to several-tenths of the filtration flux of the clarified water, resulting in an increase in membrane filtration cost and reduced economic practicality.

[0012] However decomposition is filtered in the presence of an oxidizing agent such as ozone (O ₃₎ to the raw water in the membrane filtration method, an organic substance adhering or clogging the membrane using an oxidizing agent such as ozone (O ₃₎ It is possible to obtain a very high filtration flux while filtering. That is, ozone (O ₃₎ filtration membrane in the presence, in order to attack repeatedly organics adhering to the membrane by ozone (O ₃₎ which passes through the membrane, will be performing filtration while continuously self-cleaning, the As a result, a filtration method capable of obtaining a high filtration flux is obtained.

[0013] The addition of ozone (O ₃ ) also makes the raw water 1
Microorganisms living therein, such as viruses, bacteria, molds, and protozoa, can be sterilized and removed. The water treatment apparatus according to the present invention for performing such advanced water treatment includes an ozonated water tank 6, a means 12 for supplying raw water to the tank 6, and a part of the ozonized water from the tank 6. It has a circulating means 7 for taking out and returning to the tank 6, a means 5 for injecting ozone into the partially-treated ozonized water, and a means 8 for taking out ozonized water from the tank 6 and supplying it to the membrane module 9. It is characterized by the following.

The ozonated water tank 6 is a tank for storing the ozone-treated liquid to be supplied to the filtration membrane. The raw water supply means 12 supplies the raw water 1 to the tank 6, and is composed of a liquid feed pump and the like. The circulating means 7 has a function of taking out a part of the liquid in the tank 6 and returning it to the tank 6 again. The circulating path including the circulating means 7 is provided with the ozone injection means 5. As an ozone injection means, an ejector, an air diffuser or the like is used. Also, the tank 6 and
A supply unit 8 for sending the liquid to be treated to the membrane module 9 is provided between the membrane module 9 having a built-in filtration membrane. Means for returning the liquid not filtered by the membrane to the tank 6 may be further provided. Further, a gas pressurizing means such as a compressor for air bubbling can be installed below the membrane module 9. Further, means for supplying the membrane filtered water to the membrane module 9 for backwashing can be provided.

As the membrane module 9, a module in which an ozone-resistant membrane is housed in a casing is used. The ozone-resistant membrane is not particularly limited as long as it is a filtration membrane that is not deteriorated by ozone (O ₃ ). For example, an inorganic membrane such as a ceramic having ozone resistance, polyvinylidene fluoride (PVD)
F) membrane, polytetrafluoroethylene (PTFE) membrane, ethylene-tetrafluoroethylene copolymer (ETFE) membrane,
An organic film such as a fluorine resin film such as a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) film can be used. It is particularly preferable to use a polyvinylidene fluoride (PVDF) film.

The ozone resistant membrane is preferably a hollow fiber membrane. The pore size provided in such an ozone-resistant membrane is determined by ultrafiltration (UF) membrane to microfiltration (M
F) The pore size range of the membrane may be used, but it is preferred to use a microfiltration (MF) membrane because the filtration flow rate of the membrane is basically high. For example, the pore size of the membrane is preferably 0.001 to 1 μm, and more preferably 0.05 to 1 μm.

The filtration may be performed by a cross-flow filtration method or a dead-end filtration method.
It is preferable to leave ozone at 0.05 ppm or more in the filtered water. Air bubbling, after filtration for a certain time,
The filtration is stopped, gas is sent to the membrane surface, and the membrane is washed by vibrating the membrane surface. Organic substances originally adsorbed on the membrane surface are decomposed by ozone and become non-adsorbent, and in the presence of ozone, non-adsorbable substances (organic and inorganic substances) that block the pores of the membrane are effectively eliminated by air bubbling. Great cleaning effect can be obtained.

The air bubbling may be used in combination with the backwashing, or in the order of filtration-air bubbling-backflow washing, or filtration-backflow washing-air bubbling, filtration- (air bubbling simultaneous backwashing). May be. Air bubbling is preferably performed for 1 second to 6 minutes. If the time is less than 1 second, the effect is small, and no filtration is performed during air bubbling.

FIG. 2 shows a specific example of the water treatment method of the present invention.
This will be described with reference to FIG. Raw water 1 is supplied to an ozonated water tank 6. A part of the raw water is extracted from the ozonized water tank 6 by a circulation means (hereinafter referred to as a supply pump) 7, and ozonized air generated by the ozone generator 4 is injected by an ozone injection means (hereinafter referred to as an ejector) 5. It is returned to the ozonated water tank 6 again. The raw water thus ozone-treated is supplied from a tank 6 to a membrane module 9 by a supply means (hereinafter referred to as a circulation pump) 8 to obtain a membrane filtered water 10. In the case of cross-flow filtration, the ozonated water supplied to the membrane module 9 is partially returned to the ozonated water tank 6 as shown by the broken line in FIG. In the case of dead-end filtration, the raw water supplied to the membrane module 9 is not returned to the ozone-treated water tank 6 but is entirely converted into membrane filtered water 10. While the membrane filtration is stopped by a washing operation such as backflow washing or air bubbling, the supply of raw water is stopped by the automatic valve 11 linked to the amount of water in the circulation tank, but the supply pump 7 is always operated, and the ozone-treated water is stopped. Ozone is continuously injected into the raw water in the tank 6.

Another specific example of the water treatment method according to the present invention is shown in FIG. The raw water 1 contains an ozone generator 4
The ozonized air generated in the above is injected by the ejector 5 and supplied to the ozonated water tank 6. A part of the ozonized water in the ozonated water tank 6 is withdrawn by the supply pump 7, mixed with the raw water 1, and then ozonized air is injected again by the ozone generator 4 and the ejector 5,
It is processed. The ozonated water in the ozonated water tank 6 is supplied to the membrane module 9 by the circulation pump 8 to obtain the membrane filtered water 10. In the case of cross-flow filtration, as shown by the broken line in FIG.
Is returned to the ozonated water tank 6. In the case of dead-end filtration, all of the ozonated water supplied to the membrane module 9 is taken out as membrane filtered water 10. While the membrane filtration is stopped by a washing operation such as backwashing or air bubbling, the supply of raw water is stopped by the automatic valve 12 linked to the amount of water in the circulation tank, but the supply pump 7 is always operated and the ozone-treated water is stopped. And continue to inject ozone into the mixture of raw water.

It is preferable that a part of the circulating water of the supply pump 7 which extracts a part of the ozonized water from the tank 6 and returns it to the ozonated water tank 6 after the ozone treatment is larger, because the contact with the ozonized air increases as the amount increases. If it is too large, energy loss is not preferred. Usually, the supply amount of the raw water 1 is preferably 0.2 to 10 times. In the ozone treatment 2, ozone (O ₃ ) to be added may be ozone alone or ozonized air, and ozone (O ₃ ) may be introduced via an ejector, a line mixing method, a diffuser tube, or the like.

[0022] Ozone (O ₃₎ filtration membrane in the presence, in order to attack repeatedly organics adhering to the membrane by ozone (O ₃₎ which passes through the membrane, will be performing filtration while continuously self-cleaning, As a result, a high filtration flux can be obtained. In order to increase the filtration rate, the concentration of ozone remaining in the filtered water is generally preferably 0.05 ppm or more. On the other hand, the concentration of ozone added to raw water for sterilizing microorganisms and removing odorous substances depends on the quality of the raw water, but is generally 0.1%.
5 ppm or more.

On the other hand, if the ozone concentration is too high, the economic efficiency is reduced.
About 0 ppm is preferable, and more preferably 0.1 to 30 p.
It is preferable to add ozone (O ₃ ) at a concentration of pm. The contact time between the water to be treated and ozone (O ₃ ) does not need to be particularly considered as long as the organic matter and ozone water adhering to the surface of the film structure are continuously supplied. Usually, a contact time of 1 second to 30 minutes is common.

In addition to the ozone treatment, the oxidizing power is further increased,
For the purpose of performing accelerated oxidation, addition of hydrogen peroxide, irradiation of ultraviolet rays, or an accelerated oxidation catalyst such as titanium oxide may be used in combination. At the time of membrane filtration, when the pore size of the membrane is in the microfiltration (MF) region, the pore size increases, so that suspended substances (SS), bacteria, and the like in the raw water 1 enter the membrane. Therefore, in the case of raw water that is high in suspended solids and bacteria, a large amount of ozone injection is required to obtain a high filtration flux. In order to reduce the amount of ozone added, polyaluminum chloride (PAC), bansulfate, ferrous chloride,
A flocculant such as ferric chloride may be used.

The coagulant may be added to the ozone-treated water tank 6 or may be added by a line mixing method using a static mixer or the like in the middle of a pipe for guiding the raw water 1 to the ozone addition place. Is also good. The amount of the flocculant added must be such that the suspended substance contained in the raw water 1 can be flocculated, and generally 1 to 1 per liter of the raw water 1.
00 mg may be added, and more preferably, 1: 1 of raw water 1
What is necessary is just to add 2 to 50 mg per liter.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the advanced water treatment method according to the present invention will be specifically described with reference to the drawings. An example of the process of the advanced treatment method for purified water, sewage, and wastewater according to the present invention is as follows.
As shown in FIG. 1, an ozone treatment 2 for adding ozone to raw water 1 to ozone decompose suspended substances and organic substances in the raw water 1.
After that, membrane filtration treatment 3 using an ozone-resistant membrane is performed.
FIG. 1 shows only a basic process. If necessary, a treatment such as an activated carbon treatment or a reverse osmosis membrane treatment may be performed after the membrane filtration treatment using an ozone-resistant membrane.

Hereinafter, embodiments of the present invention will be described in detail.

[0028]

Example 1 Raw water 1 has a turbidity of 3 to 4 degrees and COD
(Chemical oxygen demand) Using river surface water with a value of 2 mg / L and a water temperature of 12 ° C., using the apparatus shown in FIG.
Ozone treatment 2 → filtration treatment 3 with an ozone resistant membrane was sequentially performed, and further activated carbon treatment was performed at a later stage.

In the filtration treatment 3 using an ozone-resistant membrane, a microfiltration (MF) membrane made of PVDF (polyvinylidene fluoride) having a pore diameter of 0.1 μm and manufactured according to JP-A-3-215535 was used as the ozone-resistant membrane. The PVDF hollow fiber module having a pore diameter of 0.1 μm has a diameter of 0.7 mmφ and a diameter of 1.25 mmφ for 1800 mm.
This is an external pressure type module bundled in a 3 inch diameter PVC (polyvinyl chloride) casing and has a membrane area of 7.
At 0 m ² and a clarified water flux of 1.8 m ³ / h, the module filtration pressure is 0.5 kgf / cm ² .

The filtration was carried out by a constant flow rate filtration of a cross flow system. The raw water 1 is transferred to the ozonated water tank 6 at a rate of 1.5 hours / hour.
supplies an amount of m ^3, the raw water per hour 4.5 m ³ from the ozone-treated water tank 6 withdrawn at feed pump 7, the ozone generator 4 via the ejector 5, hourly ozonized air as the amount of ozone 2g Injected.

On the other hand, ozone-treated water is supplied from the tank 6 to the PVDF hollow fiber module at a rate of 2.5 m ^{3 /} h through the circulation pump 8, and filtered water is supplied at a filtration flux of 1.5 m ^{3 /} h. Take out and remove non-permeate liquid at 1 m ^{3 /} h
To return to the ozonated water tank 6. At this time, the concentration of residual ozone in the filtered water was 0.2 ppm. The activated carbon treatment tank used was designed so that the LV (linear velocity) was 250 m / day and the SV (space velocity) was 10 / Hr.

The operation conditions were as follows: the operation of performing filtration for 10 minutes and then performing backwashing for 15 seconds was repeated, and air of 2 Nm ^{3 /} h was supplied from the lower part of the module every 12 hours to perform air bubbling for 120 seconds. During the backwashing and air bubbling, the circulation pump 8 was stopped and the automatic valve 12 was closed to stop the supply of the raw water. However, the supply pump and the ozone generator were always operated, and the injection of ozone was continued.

As a result, the level of the filtration flux could be maintained at the initial value of 1.5 m ³ / h for 12 months, during which the pressure increase was 0.03 kg / cm 2. As a result of analyzing the water from the activated carbon treatment tank, the COD (chemical oxygen demand) value was 0.4 mg / L, the turbidity was 0.02 degrees, and E. coli,
No general bacteria were detected, and the other items sufficiently met the criteria for drinking water.

[0034]

Example 2 Raw water 1 has a turbidity of 10 degrees, a COD (chemical oxygen demand) of 13 to 20 mg / liter, and a BOD
(Biological oxygen demand) value is 20-30mg / l,
Using the sewage secondary treatment water having a water temperature of 25 ° C., raw water 1 → ozone treatment 2 → filtration treatment 3 using an ozone resistant membrane was sequentially performed using the apparatus shown in FIG.

The filtration was carried out by a constant flow rate filtration of a cross flow system. After injecting 10 g of ozonized air as an ozone amount per hour from the ozone generator 4 into the raw water 1 through the ejector 5, the ozone-treated water is supplied to the ozone-treated water tank 6 at an amount of 2.0 m ³ per hour. 4.0 m ³ of ozone-treated water per hour was withdrawn from the tank 6 by the supply pump 7,
After mixing with raw water in the raw water 1 supply line, ejector 5
And ozone was injected into the tank 6 again.

On the other hand, the ozone-treated water tank 6 is supplied to the PVDF hollow fiber module at a rate of 2.0 m ^{3 /} h through the circulation pump 8, and the filtered water is filtered at a flow rate of 1.0 h / h.
is taken out by the m ^3, it returned the non-permeate per hour 1 m ³ ozone treated water tank 6. At this time, the residual ozone concentration in the filtered water was 0.1 ppm. The operating condition is filtration 1
After the operation was performed for 0 minutes, the operation of supplying air at 2 Nm ³ per hour from the lower part of the module, performing air bubbling for 60 seconds, and performing backwashing for 20 seconds was repeated. During the backwashing and air bubbling, the circulation pump 8 was stopped and the automatic valve 12 was closed to stop the supply of the raw water. However, the supply pump and the ozone generator were always operated, and the injection of ozone was continued. In this case, 6.0 m ^{3 /} hour of ozone-treated water was withdrawn from the ozone-treated water tank 6 by a supply pump, and ozone-treated through the ejector 5.

As a result, the level of the filtration flux was maintained at the initial value of 1.0 m ^{3 /} h for 8 months, and the pressure rise during this period was 0.04 kg / cm 2. The water quality of the obtained filtrate was 0.05 degrees in turbidity, the COD value was 12 mg / liter, and the BOD value was 1 mg / liter, which was sufficient water quality for landscape water and hydrophilic water.

[0038]

According to the present invention, advanced water purification and sewage treatment using ozone can be performed efficiently and economically.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of an advanced treatment method for purified water, sewage, and wastewater according to the present invention.

FIG. 2 is an apparatus diagram showing one embodiment of an advanced treatment method for purified water, sewage, and wastewater according to the present invention.

FIG. 3 is an apparatus diagram showing one embodiment of an advanced treatment method for purified water, sewage, and drainage according to the present invention.

[Description of Signs] 1 ... Raw water 2 ... Ozone treatment 3 ... Filtration treatment by an ozone-resistant membrane 4 ... Ozone generator 5 ... Ozone injection means 6 ... Ozonated water tank 7 ..Circulation means 8 ... Supply means 9 ... Membrane module 10 ... Membrane filtration water 11 ... Automatic valve 12 ... Raw water supply means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/50 560 C02F 1/50 560E 1/78 1/78 F term (Reference) 4D006 GA06 GA07 HA03 HA04 JA25C KA01 KA02 KA43 KA63 KA64 KB12 KC03 KC13 KC14 KD19 KD21 KE02Q MA01 MA22 MB11 MC29 MC30 MC45 PA01 PB04 PB08 PB24 PC51 PC61 4D050 AA02 AA03 AA13 AA15 AB06 AB07 BB02 BD03 BD06 CA09

Claims (3)

[Claims] In a method of treating raw water with ozone and then treating it with a filtration membrane, the treatment water to be supplied to the filtration membrane is temporarily stored, and the stored treated water is always partially extracted to perform ozone treatment. A water treatment method characterized by circulating to the original treated water. 2. A method in which raw water is treated with ozone and then treated with a filtration membrane. After the ozone is injected into the raw water, the raw water is temporarily stored before being supplied to the filtration membrane, and the stored ozonized water is always partially extracted. Water treatment method, wherein the water is mixed with raw water and circulated to the original ozonated water after ozone treatment. 3. Ozone-treated water tank 6, means 12 for supplying raw water to tank 6, circulating means 7 for taking out a part of the ozone-treated water from tank 6, and then returning to tank 6. A water treatment apparatus comprising: means for injecting ozone into the ozone-treated water obtained; and means for extracting ozone-treated water from a tank and supplying it to a membrane module.