JPH06269778A - Method for purifying water by using membrane module - Google Patents

Abstract

PURPOSE:To provide a water purifying method by which a hydrate secondary Mn having an accumulable property on an inner wall of a treating water tank and an inner wall of a back washing piping and besides on an inner wall of a membrane module does not deposit. CONSTITUTION:Raw water incorporating turbid substance is treated by passing it through the membrane module 4 and the permeated water is introduced into a washing water tank 11, and when the membrane module was clogged, a chlorine type oxidizer is further added to the treating water introduced from the washing water tank to perform back washing of 15, 16, 17 and the membrane module 14 and the permeated water quantity through the membrane module is recovered, and then the raw water is again passed through the membrane module, thus these processes are repeated and the organic substance or inorganic substance incorporated in the raw water are removed to supply it to beverage. When the feed water is passed through the membrane module after the completion of the back washing, the back washing water remaining within the membrane module is introduced to another system without introducing it into the washing water tank.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating water by removing turbidity contained in raw water by using a membrane module and using the raw water for drinking.

[0002]

2. Description of the Related Art Membrane treatment is used for desalination of seawater and production of pure water.
It is a well-known treatment method used for excrement treatment and retreatment of sewage treatment water. If such a treatment method is used for water purification treatment, fine suspended solids such as colloids can be directly separated, and no coagulation sedimentation treatment is required. The advantage is that the area is small. Recently, it has become difficult to set up a conventional type water purification plant that requires a large site, so the use of such a membrane has been considered and is beginning to be used. Furthermore, this membrane treatment is a treatment that conventional treatment methods cannot handle,
For example, since it is possible to remove bacteria such as bacteria and viruses, treatments in that respect are also expected and studied. In water purification, fine pores (0.01-0.5μ
m) a membrane material such as polyethylene, polysulfone, polyacrylonitrile, or cellulose acetate into a tube or a hollow fiber, and bundle a few thousand of these to form a module type microfiltration membrane or ultrafiltration membrane. The raw water containing suspended solids and colloidal organic and inorganic substances is pumped and circulated through the membrane module to separate solid and liquid, and the treated water that has passed through the membrane is guided to the wash water tank and overflows from it. The spilled water is sent to the distribution reservoir, but the hypochlorite is sterilized by adding sodium hypochlorite so that various bacteria do not propagate in the overflow water. In such treatment, naturally suspended substances and colloidal substances contained in the raw water adhere to the membrane and cause clogging, and the treatment capacity immediately decreases, but in order to recover this, for example, the amount of permeated water is below the set value or The membrane is cleaned when the pressure difference across the membrane exceeds a set value or periodically.
The membrane is generally washed by using a backwash pump to pump the treated water in the wash water tank in the direction opposite to the filtration direction, and forcibly extruding the particles clogged in the fine pores by the water pressure.
However, sticky cells and their metabolites adhere to the membrane,
If the colloidal iron hydroxide is clogged in the pores, it cannot be completely removed in a short time only with pressure water.
Usually, several ppm of chlorine-based oxidizer such as sodium hypochlorite is added to the treated water for cleaning. Such backwashing is carried out for several tens of seconds, and when the amount of permeated water in the membrane is recovered, the raw water is immediately sent to the membrane module and the permeated water is sent to the wash water tank. Repeat this treatment frequently (in terms of time, 10 minutes to 1 hour of water flow backwash 1
Raw water is treated (at a rate of 5 seconds to 1 minute) to obtain treated water suitable for beverages. By the way, if water is passed immediately after the backwash, the permeated water will contain chlorine used for the backwash, but the treated water is sterilized by chlorine as described above, and the backwash is frequently repeated. Therefore, each time it is discarded, a considerable amount of water is wasted. Therefore, considering the economical aspect, it is sent to the wash water tank as it is.
Further, if the membrane is used for a long period of time, the flux and the differential pressure cannot be recovered only by backwashing, so chemical cleaning is performed at that time. Detergents and citric acid are used as chemicals.

[0003]

However, when this conventional method is used for a few dozen to several tens of days, the backwashing period is drastically shortened even though it is not the time for chemical cleaning, and backwashing is frequently performed. Even if repeated, the flux of the membrane and the differential pressure did not recover and the amount of permeated water decreased sharply. A close examination of such a phenomenon reveals that hydrated ferric manganese is deposited on the inner wall of the wash water tank, the inner wall of the pipe for backwashing, and the inner wall of the container of the membrane module, and the above-mentioned problems occur. I understood. Therefore, an object of the present invention is to provide a water purification method that does not cause such manganese damage.

[0004]

[Means for Solving the Problems] The above problems are solved by passing raw water for water purification through a membrane module to remove turbidity, guiding the permeated water to a wash water tank, and washing when the membrane module is clogged. A chlorine-based oxidizing agent is added to the treated water introduced from the water tank to backwash the membrane module to regenerate the amount of permeated water in the membrane module, and then the raw water is passed through the membrane module again to repeat the raw water. In the water purification method using a membrane module, which removes the suspended matter contained in the membrane module, and when the raw water is passed through the membrane module after the backwashing, the reverse residual water remaining in the membrane module is used. It is solved by introducing the wash water to another system without introducing it into the wash water tank. If the backwash water remaining in the membrane module at the end of the backwash is not directly discarded but is directly guided to the reservoir, it is economical because it is not wasted. Also, if the supply of the chlorine-based oxidant is stopped immediately before the end of the backwash and only the treated water is sent, the chlorine-based oxidant will not be left in the backwash water supply pipe that connects the wash water tank and the membrane module. More preferable.

[0005]

[Operation] Raw water contains iron to some extent, and manganese ions are contained in a smaller amount.
Since manganese ion has a higher standard reduction potential than iron, it is not oxidized to dissolved oxygen contained in water and passes through the filtration membrane as it is. However, manganese ions oxidize, though very slowly, with the chlorine-based oxidizer used for backwashing.
Oxidized and precipitated hydrated secondary manganese oxide is highly accumulative because it is autocatalytically oxidized and precipitated. Therefore, even if the treated water containing chlorine-based oxidizer is slowly circulated in the system even if the treated water is diluted and the chlorine concentration becomes almost trace, It is not preferable because it increases the contact time with water. According to the present invention, the treated water containing the chlorine-based oxidant is immediately treated in another system without staying in the system for a long time. It rarely occurs in the water tank, backwash water supply pipe and inner wall of the membrane module.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. The raw water that has passed through the pre-filter 1 is first supplied to the supply tank 2 and then supplied from the supply pump 3 to the membrane module 4. The filtration membrane includes an ultrafiltration membrane and a microfiltration membrane, but the present invention may be any filtration membrane, and the filtration membrane may be made of any material that is strong against chlorine-based oxidants. The filtration membrane is usually modularized to increase the throughput per unit volume. In the present invention, a hollow fiber module made of, for example, polyethylene or cellulose acetate is used. When such a hollow fiber is used, raw water is passed from the outside of the membrane to the inside. The membrane module 4 having the filtration membrane therein has three inlets / outlets of a raw water supply port 5, a concentrated water port 6 and a permeated water port 7, and the discharge port of the above-mentioned supply pump 3 is connected to the supply port 5. . Part of the raw water supplied to the membrane module 4 permeates the filtration membrane and flows to the permeated water port 7. Since organic substances and inorganic substances are removed when they permeate, raw water that does not permeate has a high concentration of organic substances and inorganic substances, and such concentrated water is discharged from the concentrated water port 6. This concentrated water is normally returned to the supply port 5 of the membrane module 4 via the circulation pump 8 without being discarded as it is. This is to make effective use of water resources.
Therefore, the membrane module 4 is always supplied with the same amount of raw water as the amount of permeated water from the supply tank 2. This membrane module has a pressure of 0.5 Kgf / cm ² at 25 ° C.
It is capable of treating 14 m ³ / day of water. Further, the concentrated water inlet 6 is provided with an electromagnetic opening / closing valve 9 for discarding backwashed washing water.

The permeate treated by the membrane module is pipe 10
The water is once received by the washing water tank 11 through the above in order to secure clean water for washing. Therefore, the wash water tank 11 is sized so that water necessary for back washing and chemical washing can be secured, for example, about 200 liters. The bottom portion of the wash water tank 11 is connected to the pipe 10 through a backwash water supply pipe 12, a backwash pump 13, and an electromagnetic opening / closing valve 14, and the permeate port 7 of the membrane module 4 is connected.
Is in communication with. Permeate water port 7 and electromagnetic on-off valve 1
An oxidant tank 15 in which a chlorine-based oxidant is dissolved is connected to the No. 4 via an oxidant supply pump 16 in order to supply the chlorine-based oxidant during backwashing. Although sodium hypochlorite was used in the examples, chlorine gas, highly exposed powder, or the like can be used instead of this.

In the present invention, when the raw water is passed through the membrane module after the backwash and the operation is restarted, the wash water remaining in the membrane module is passed through another system without being put in the wash water tank 11, so that the backwash water is supplied. An electromagnetic three-way valve 17 is provided upstream of the cleaning water tank 11 at a downstream of the junction between the pipe 12 and the pipe 10.
Is provided. One of the ports is naturally connected to the wash water tank 11, but the other port is connected to another system so that the wash water cannot directly enter the wash water tank 11. Normally, the overflow water in the wash water tank 11 is sterilized with chlorine and then sent to the distribution reservoir. Since the wash water originally contains chlorine and does not need to be sterilized with chlorine, the other port is directly connected to the reservoir in the embodiment. This way,
The processing efficiency can be the same as the conventional one.

Now that the apparatus used in the present invention has been described, the method of the present invention will be described in detail with reference to this apparatus. Groundwater may contain a relatively large amount of iron and manganese ions, but even river surface water contains trace amounts of manganese ions, in addition to organic matter and colloidal or particulate iron hydroxide. include. Manganese has a higher standard reduction potential than iron and is not oxidized by dissolved oxygen in neutral solution. Therefore, since most of the raw water is dissolved in the state of manganese ions, the pre-filter 1 removes coarse particles from the raw water and the supply tank 2
After being put into the membrane, the feed pump 3 pressure-feeds it to the membrane module 4, and most of the organic substances and iron hydroxide contained in the raw water are removed by the above-mentioned filtration membrane, but manganese ions pass through the filtration membrane as they are and washed. Enter the water tank 11. The treated water that overflows from the wash water tank 11 is sent to a distribution reservoir after being sterilized with chlorine on the downstream side.

When the raw water corresponding to the amount of permeated water is supplied to the supply port 5 while circulating the concentrated water by the circulation pump 8, the clogging of the filtration membrane gradually progresses, and the differential pressure between the supply port 5 and the permeated water port is increased. growing. Periodically, that is, every 10 to 60 minutes, or at a predetermined value, for example, 1.5 Kgf / cm ² where this differential pressure is, in anticipation of the time when this differential pressure does not become extremely large.
When this occurs, backwashing is usually started automatically to restore the flux of the filtration membrane. First, the electromagnetic opening / closing valve 9 at the concentrated water inlet 6 is opened. Next, the three-way valve 17 is closed, and the electromagnetic opening / closing valve 14 of the backwash system is opened. In this state, the backwash pump 13 and the chlorine-based oxidant supply pump 16 are driven. Normally, the chlorine concentration in the wash water is 3
Sodium hypochlorite is added to reach ppm. In the above example, the backwash time is about 30 to 45 seconds and the amount of water is 4
Although it is about 5 to 60 liters, immediately before that, the chlorine-based oxidant supply pump 16 is stopped and only treated water is supplied to the membrane module 4 from the permeated water port 7. This is because the treated water containing the chlorine-based oxidizer after the backwash is the cleaning system 12 and the piping system 1.
It was set to 0 as little as possible. The washing liquid obtained by backwashing the filtration membrane passes through the concentrated water port 6 and is discharged to the outside of the system through the electromagnetic opening / closing valve 9. When the backwash is completed in this way, the backwash pump 13 is automatically stopped and the electromagnetic opening / closing valves 14 and 9 are closed. Then, when the backwashing is completed and the operation is restarted, the above-described three-way valve 17 is not the washing water tank 11 but is automatically and temporarily switched to another system. This switching time is the time for discharging the residual cleaning water and varies depending on the size of the membrane module 4 and the capacity of the supply pump 3. In the embodiment, since the residual cleaning water is sent to the distribution reservoir, it takes about 15 minutes as long as possible. When this switching time elapses, the three-way valve 17 is switched to the wash water tank 11 side. And
The above process is repeated to produce purified water to be used for beverages.

[0011]

In the prior art, even if manganese ions are oxidized by chlorine, their reaction rate is very slow. Therefore, even if the backwash water remaining in the membrane module is introduced into the wash water tank, However, since the chlorine concentration in the wash water tank becomes almost traces in a short time, the manganese ion is oxidized to accumulate hydration which is likely to accumulate. It was not considered to be secondary manganese oxide.
For this reason, even if the residual backwash water is introduced into the wash water tank, it should not adversely affect the treatment equipment, and rather, it was considered advantageous in terms of treatment efficiency. However, even if the amount becomes very small, the retention time of chlorine in the wash water tank is relatively long, and if backwashing and operation are repeated frequently, a small amount of manganese ions contained in the treated water are gradually oxidized by chlorine. Is deposited. The precipitated hydrated manganese dioxide has an autocatalytic action, so that other manganese ions are further oxidized and precipitated. This autocatalytic action occurs not only during backwashing, but also during the treatment of raw water, so that the deposition amount increases rapidly, and when it reaches a certain amount, it is stimulated by the change in the water flow and peels into powder, Begins to float in the membrane module. Since the suspended matter causes the membrane to be clogged, the number of times of backwashing of the membrane is increased and the life of the membrane is shortened. In the present invention,
As described above, when restarting the operation after backwashing, the cleaning water remaining in the membrane module and the circulation system is temporarily discharged to another system, so that chlorine is not mixed in the cleaning water tank. Therefore, since the oxidation reaction as described above does not occur, hydrated secondary manganese oxide, which has a possibility of accumulation, does not deposit on the inner wall of the membrane module or the pipe of the backwash system and cause the above-mentioned trouble.

[Brief description of drawings]

FIG. 1 is a block diagram of a water purification apparatus used in the present invention.

[Explanation of symbols]

 1 Pre-filter 2 Supply tank 3 Supply pump 4 Membrane module 5 Supply port 6 Concentrated water port 7 Permeate water port 8 Circulation pump 9 Electromagnetic on-off valve 10 Tube 11 Wash water tank 12 Backwash water supply pipe 13 Backwash pump 14 Electromagnetic on-off valve 15 Chlorine Tank in which system oxidant is dissolved 16 Supply pump 17 3 way valve

Claims (1)

[Claims] 1. Processed water led from the wash water tank when purified water is passed through a membrane module to remove suspended solids and the permeated water is led to a wash water tank and when the membrane module is clogged. After further backwashing the membrane module by adding a chlorine-based oxidant to the, regenerate the amount of permeate of the membrane module,
In addition, the raw water is passed through the membrane module, and this is repeated so that the suspended matter contained in the raw water is removed and the beverage is served.
In the water purification method using a membrane module, when the above-mentioned backwashing is finished and the raw water is passed through the membrane module, the backwashing water remaining in the membrane module should be guided to another system without being guided to the wash water tank. A method for purifying water using a membrane module.