JP2013013900A - Method and apparatus of treating water using fine air bubble - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of an RO membrane and degradation of water treatment efficiency as much as possible by reducing a washing frequency of the RO membrane with a chemical solution.SOLUTION: During filtering operation by an RO membrane device, a part of concentrated water in the RO membrane device is guided to a circulation pathway. In the circulation pathway, the concentrated water is pressurized by a second pump, air is mixed, and water to be treated and air are stirred using a static mixer to generate fine air bubbles in the water to be treated. Then, the concentrated water containing the fine air bubbles is supplied to a water feed pathway which pressurizes the water to be treated by a first pump and feeds the water to be treated to the RO membrane device.

Description

  The present invention relates to a water treatment method and a water treatment apparatus provided with a reverse osmosis membrane used for various water production facilities and the like, wherein the water treatment method and the water treatment are characterized by generating fine bubbles in the water to be treated. It relates to the device.

  Conventionally, water treatment apparatuses (desalination facilities) using reverse osmosis membranes (RO membranes) have been used in various fields such as seawater desalination facilities, ultrapure water production facilities, and industrial water production facilities. As the reverse osmosis membrane, for example, a spiral membrane module is generally used. However, when the reverse osmosis membrane is used for a long time, the membrane surface is clogged with impurities in the water to be treated, and thus the membrane needs to be washed. .

  Here, in the water treatment apparatus using the RO membrane, the permeation of the water to be treated used as the membrane cleaning of the water treatment apparatus using the microfiltration membrane (MF membrane) or the ultrafiltration membrane (UF membrane). It is impossible to perform a so-called backwashing (backwashing) in which a cleaning liquid or air is supplied from the side (secondary side) to the raw water side (primary side) to remove dirt on the membrane surface.

  Therefore, when the RO membrane is washed, flushing that raises the surface flow velocity on the raw water side to remove the dirt and chemical washing that dissolves the dirt with a chemical such as sodium hypochlorite are used. Further, a method for cleaning the RO membrane by supplying fine bubbles at the time of cleaning has been proposed (Patent Document 1).

  In addition, by generating fine bubbles in the raw water containing salts and separating RO water from the raw water containing fine bubbles, a sufficient effective pressure is applied to the RO membrane even if the operating pressure is lowered, and water is efficiently supplied. A desalting method for permeation is disclosed in Patent Document 2.

JP 2006-263501 A JP 2008-307522 A

  If the RO membrane is cleaned with chemicals, the dirt on the membrane surface is removed and the flux is recovered. However, every time chemical cleaning is performed, the operation of the RO membrane device must be stopped to perform chemical cleaning. In addition, after the chemical cleaning, it is necessary to perform a cleaning operation in order to prevent the chemical from being mixed into the treated water of the RO membrane apparatus, and there is a problem that it takes time to return to the normal operation.

  Further, the RO membrane may be deteriorated by the chemical used for chemical cleaning, and the life of the RO membrane may be shortened.

  On the other hand, as disclosed in Patent Document 1, even when fine bubbles are used during RO membrane cleaning, normal operation cannot be performed during the RO membrane cleaning operation using fine bubbles. In addition, although it is possible to shorten the cleaning time compared with chemical cleaning, since the cleaning frequency of RO membrane is not different from that of RO membrane device that performs chemical cleaning, it is necessary to perform cleaning operation frequently There was a point.

  The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to reduce the RO membrane chemical cleaning frequency, thereby suppressing the deterioration of the RO membrane as much as possible. It is to provide a water treatment apparatus capable of extending the service life and an operation method thereof.

  The present inventors mixed the air into the water to be treated and stirred by a static mixer during the filtration operation with the RO membrane, and included the fine bubbles in the water to be treated and supplied to the RO membrane, thereby The present inventors have found that a dirt adhesion suppressing effect can be obtained and have completed the present invention.

Specifically, the present invention
A water treatment method for treating water to be treated by a reverse osmosis membrane device,
At the time of filtration operation by the reverse osmosis membrane device, branch the concentrated water path of the reverse osmosis membrane device and lead a part of the concentrated water to the circulation path,
After pressurizing the concentrated water by the second pump, air is mixed in, and after the fine water bubbles are generated in the concentrated water by stirring the concentrated water and air using a static mixer,
After supplying the concentrated water containing fine bubbles to the water supply path that pressurizes the treated water with the first pump and supplies it to the reverse osmosis membrane, the treated water containing fine bubbles in the circulation path is supplied to the reverse osmosis membrane device. Supply,
The present invention relates to a water treatment method.

The present invention also provides:
A reverse osmosis membrane device for treating water to be treated;
A water supply path for supplying treated water to the reverse osmosis membrane device;
A first pump for pressurizing the water to be treated in the water supply path;
A branch path branched from the concentrated water path of the reverse osmosis membrane device and connected to the water supply path upstream of the reverse osmosis membrane device,
Here, the circulation path is
A second pump for pressurizing the concentrated water;
Air input means for mixing air into the pressurized concentrated water;
Stir the concentrated water and the mixed air, in order with a static mixer to make concentrated water containing fine bubbles,
The present invention relates to a water treatment apparatus that supplies concentrated water containing fine bubbles from a circulation path to a water supply path, and then supplies treated water containing fine bubbles in the circulation path to a reverse osmosis membrane device.

  In the membrane separation apparatus using the RO membrane, the water to be treated is pressurized to a pressure suitable for the treatment with the RO membrane and then supplied to the primary side of the RO membrane separation apparatus. At this time, a part of the concentrated water of the RO membrane device is pressurized to mix air, and the concentrated water and air are agitated by a static mixer, whereby fine bubbles (micro bubbles) are generated in the concentrated water.

  Concentrated water containing fine bubbles is supplied to the RO membrane device through the water supply path for supplying water to be treated, so that the RO membrane separation device has an appropriate void ratio (volume ratio of gas in gas-liquid two-phase flow) ) Makes it possible to supply water to be treated containing fine bubbles. As a result, contamination of the RO membrane during normal operation can be prevented, the number of times of RO membrane chemical cleaning can be reduced, and the processing efficiency of the RO membrane separation apparatus can be increased.

  The void ratio of the water to be treated containing fine bubbles supplied to the reverse osmosis membrane device is preferably 0.01% or more and 1% or less.

  If the void ratio is less than 0.01%, the amount of fine bubbles contained in the treated water supplied to the reverse osmosis membrane device is too small, and therefore, RO membrane contamination cannot be effectively prevented. On the other hand, if the void ratio exceeds 10%, there are too many fine bubbles contained in the water to be treated, so that it does not exist as a bubbling flow and has a cleaning effect because it becomes a slag flow. In order to prevent bubbles from accumulating in the RO membrane device and not reduce the processing efficiency, and to prevent the bubbles from coalescing before the membrane, the void ratio should be 1% or less. Ideal. Therefore, the void ratio in the water to be treated is preferably 0.01% or more and 10% or less, and more preferably 0.01% or more and 1% or less.

  Here, the void ratio means the void ratio of the water to be treated when supplied to the RO membrane separation apparatus, that is, the void ratio of the water to be treated actually processed by the RO membrane separation apparatus.

  It is preferable to provide a gas-liquid separator in the concentrated water path to remove bubbles in the concentrated water.

  The water supply pressure in the water supply path is 1.0 MPa or more and 3.0 MPa or less, and the pressure of concentrated water containing fine bubbles when supplying from the circulation path to the water supply path is higher than the pressure in the water supply path in the range of 5 kPa to 100 kPa. Thus, it is preferable to adjust the pressure of the concentrated water by adjusting the output of the second pump.

  In the case of a low-pressure RO membrane separator, the water to be treated is pressurized to a pressure range of 1.0 MPa to 3.0 MPa, but part of the concentrated water of the RO membrane separator is pressurized by the second pump in the circulation path Contains fine bubbles by pressurizing a part of the concentrated water so that the pressure of the circulation path after passing through the static mixer is at least 5 kPa higher than the water to be treated flowing through the piping of the water supply path It becomes easy to supply the concentrated water to the water supply path and mix it with the water to be treated that does not contain fine bubbles. In addition, since there is a slight differential pressure, when mixed with the water to be treated flowing through the pipe of the water supply path, it is mixed over the entire surface of the pipe cross section of the water supply path, so that fine bubbles are not biased in the treated water after mixing. Mixed.

  In addition, when the pressure of the concentrated water flowing through the circulation path after passing through the static mixer is lower than the pressure of the water to be treated flowing through the water supply path, a backflow may occur. On the other hand, if the pressure of the concentrated water flowing through the circulation path is too large compared to the pressure of the water to be treated flowing through the water supply path, there is a possibility of backflow when the water supply path piping and the circulation path piping are merged. This is not preferable because the load on the first pump increases.

  In addition, due to the pressure difference during mixing, the gas dissolved in the concentrated water flowing through the circulation path may foam due to the pressure drop and coalesce to generate coarse bubbles. It is preferable to pressurize the water to be treated by adjusting the output of the second pump so that the pressure of the concentrated water passing through the circulation path is equal to or lower than 100 kPa compared to the pressure of the water to be treated flowing through the water supply path.

  The water treatment apparatus of the present invention is provided with a first pressure measuring device that measures the pressure of the water supply path upstream of the reverse osmosis membrane apparatus, and a second pressure that measures the pressure of the circulation path downstream of the static mixer in the circulation path. It is preferable to provide a measuring device and pressurize the concentrated water by the second pump so that the differential pressure between the second pressure measuring device and the first pressure measuring device is 5 kPa to 100 kPa.

  The water treatment apparatus of the present invention preferably further includes a flow rate adjusting means for adjusting the supply amount of concentrated water containing fine bubbles to the water supply path in the circulation path.

  By providing the flow rate adjusting means, it is possible to adjust the void ratio of the treated water after returning to an appropriate range when supplying concentrated water containing fine bubbles to the water supply path. In addition, a flow volume adjustment means means the well-known means which can control the supply amount to a water supply path | route, for example like the combination with a flowmeter and a flow volume adjustment valve.

  According to the present invention, since the frequency of RO membrane chemical cleaning can be reduced, the cost for chemical cleaning can be reduced. In addition, by reducing the frequency of cleaning, it is possible to prevent the RO membrane from being deteriorated by chemicals, thereby extending the life of the RO membrane. Furthermore, the treatment efficiency of the water to be treated by the RO membrane is high.

It is a schematic block diagram of the water treatment apparatus of the reference example 1 similar to this invention. It is a schematic block diagram of the water treatment apparatus currently disclosed by patent document 1. FIG. It is a schematic block diagram of the water treatment apparatus (reference example 2) similar to this invention. It is a schematic block diagram of the water treatment apparatus (Example 1) of this invention. It is a schematic block diagram of the water treatment apparatus (Example 2) of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, this invention is not limited to the following description.

(Reference Example 1)
A schematic diagram of a water treatment apparatus similar to the present invention is shown in FIG. The water treatment apparatus of Reference Example 1 includes a first pump 1, a water supply path 2, an RO membrane apparatus 3, a circulation path 4, a second pump 5, a compressor 6 (air input means), and a static mixer 7.

  Further, the water supply path 2 and the circulation path 4 are respectively provided with a second pressure gauge 50 (second pressure measurement device) and a first pressure gauge 51 (first pressure measurement device). The pump 5, the compressor 6, the second pressure gauge 50 and the first pressure gauge 51 are each electrically connected to the control device 52.

  The raw water (treated water) is pressurized by the first pump 1 provided in the water supply path 2 and supplied to the RO membrane device 3. The permeated water of the RO membrane device 3 is supplied outside the system through the treated water path 8. On the other hand, the concentrated water of the RO membrane device 3 is drained through the concentrated water path 9. The raw water in the present invention is preferably fresh water such as factory effluent, river water, lake water, etc., or water having a low salinity concentration, and usually by a coagulation precipitation treatment or membrane treatment (MF membrane or UF membrane) as a pretreatment. Primary treated water is used.

  A circulation path 4 is connected to the water supply path 2, and a part of the raw water pressurized by the first pump 1 is supplied to the circulation path 4. The raw water supplied to the circulation path 4 is further pressurized by the second pump 5. This is because it is necessary to pressurize the raw water in the circulation path 4 more than the pressure loss in the circulation path 4 in order to return the raw water containing fine bubbles to be described later from the circulation path 4 to the water supply path 2.

  The ratio supplied to the circulation path 4 (amount of water flowing through the circulation path 4 / amount of water flowing through the water supply path 2 before branching) is preferably 20% or less, and more preferably 10% or less. This is because if the amount of water supplied to the circulation path 4 is increased, the second pump 5 must be enlarged and the pipe diameter is also increased.

  The second pump 5 is configured so that the pressure of the water to be treated flowing through the circulation path 4 after passing through the static mixer 7 is 5 to 100 kPa lower than the pressure of the water to be treated flowing through the water supply path 2. It is preferable to pressurize the raw water. In the water treatment apparatus of the present invention, the second pump 5 has a structure in which a part of the water to be treated in the water supply path 2 pressurized by the first pump 1 is taken out and returned to the water supply path 2 again. Since it is sufficient to pressurize the pressure loss in the static mixer 7, the power of the pump can be small.

  In the pressure adjustment, the control device 52 calculates the differential pressure from the measured values of the first pressure gauge 51 provided in the water supply path 2 and the second pressure gauge 50 provided in the circulation path 4, and the second pump 5 This is done by controlling the output of.

  The raw water further pressurized by the second pump 5 is mixed with air by a compressor 6 provided in the circulation path 4. Thereafter, the raw water and air are stirred by the static mixer 7, and the air mixed into the raw water becomes fine bubbles. An ejector can also be used as the air input means.

  The compressor 6 is also electrically connected to the control device 52 and is controlled in accordance with the output of the second pump 5. Specifically, the air pressure discharged from the compressor 6 is controlled to be higher than the pressure of the water to be treated that has passed through the second pump 5, and air is supplied to the circulation path 4.

  Here, as a means for stirring raw water and air to generate fine bubbles, Patent Document 1 uses an ejector, and Patent Document 2 uses a compressor and an injector, but in the present invention, a static mixer 7 is used. In a pressure dissolution type fine bubble generator such as an ejector, bubbles are generated according to the amount of air to be dissolved, and it is difficult to generate sufficient fine bubbles. In other words, in the prior art, after the gas (air) is completely dissolved in the water once under pressure, the pressure of the water to be treated is reduced, and the gas dissolved in the water to be treated cannot be completely dissolved to form bubbles. Therefore, the gas that does not dissolve in the water remains coarse even if air is simply put in the ejector. For this reason, it is difficult to obtain only fine bubbles unless these coarse bubbles are removed.

  In addition, since all the air introduced by the compressor does not become fine bubbles, it is very difficult to adjust the void ratio, which will be described later, wasteful power is applied, and a sufficient amount of fine bubbles is generated. I can't.

  In contrast, in Reference Example 1, sufficient static bubbles can be generated by using the static mixer 7. This is because all the air introduced by the compressor 6 is refined by the static mixer 7. For this reason, the amount of air supplied to the water to be treated through the compressor 7 and the amount of fine bubbles are linked, so that it is possible to sufficiently obtain fine bubbles of a certain size or less and to easily adjust the void ratio.

  The raw water containing fine bubbles is returned from the circulation path 4 to the water supply path 2. At this time, it is preferable to adjust the void ratio of the raw water in the water supply path 2 after returning, in other words, the raw water actually supplied to the RO membrane device 3 to be 0.01% or more and 1% or less.

  Since the raw water pressure in the circulation path 4 is higher than the raw water pressure in the water supply path 2, the fine bubbles in the raw water returned to the water supply path 2 are slightly lower in pressure than in the circulation path 4. Void rate changes. For this reason, the amount of water returned from the circulation path 4 to the water supply path 2 is adjusted so that the void ratio of the raw water in the water supply path 2 after returning is 0.01% or more and 1% or less, and the flow rate is adjusted using a flow meter, a flow control valve, etc. It is preferable to adjust by means (not shown).

  The raw water containing fine bubbles supplied to the RO membrane device 3 is prevented from adhering to the surface of the RO membrane due to the fine bubbles, and the RO membrane is not easily clogged even if the same raw water amount is processed. As a result, the chemical cleaning frequency of the RO membrane decreases, and the raw water treatment efficiency can be maintained higher than before.

  Here, the schematic block diagram of the desalination processing apparatus currently disclosed by patent document 1 is shown in FIG. In this apparatus, the raw water is pressurized by the pump 11 provided in the path 12, air is mixed into the raw water by the bubble generating device 13, and the raw water containing fine bubbles is processed by the RO membrane device 15.

  In the apparatus of FIG. 2, since air is mixed in the entire raw water, it is extremely difficult to adjust a void ratio that is preferable as supply water to the RO membrane apparatus 15. Moreover, since all the raw | natural water is supplied to the bubble production | generation apparatus 15, the motive power for generating a fine bubble must be large.

  On the other hand, in the water treatment apparatus of Reference Example 1 shown in FIG. 1, a part of the raw water is extracted into the circulation path 4, and raw water containing fine bubbles is prepared using the static mixer 7. Since it is set as the structure which returns, it is possible to control the void rate of the raw | natural water supplied to RO membrane apparatus 3 to a suitable range by adjusting the amount of water returned to the water supply path | route 2. FIG.

  In addition, the water treatment method of Reference Example 1 can be easily applied to existing facilities by providing a circulation path.

(Reference Example 2)
The schematic block diagram of another water treatment apparatus similar to the water treatment apparatus of this invention is shown in FIG. Since the raw water treatment by the RO membrane device is the same as the water treatment device of FIG. 1, only the differences will be described here.

  In the water treatment apparatus of FIG. 3, raw water is directly taken into the circulation path 26, and the raw water is pressurized to a pressure higher than that of the first pump 21 by the second pump 27. Thereafter, air is mixed into the raw water using the compressor 28, and the raw water and air are stirred using the static mixer 29, thereby generating fine bubbles.

  The water treatment apparatus of FIG. 3 can obtain the same effect as the water treatment apparatus of Reference Example 1, but the second pump 27 must have a higher pressurizing power than the first pump 21, so that the first pump 1 The power consumption of the second pump 27 is larger than that of the water treatment apparatus of FIG. 1 that only needs to pressurize the pressurized raw water to the pressure loss of the static mixer 29 by the second pump 5.

Example 1
The schematic block diagram of the water treatment apparatus of this invention is shown in FIG. Since the raw water treatment by the RO membrane device is the same as the water treatment device of FIG. 1, only the differences will be described here.

  In the water treatment apparatus of FIG. 4, air is not mixed into the raw water to generate fine bubbles, but the concentrated water of the RO membrane device is collected, and the fine water is included in the concentrated water and mixed with the raw water. A part of the concentrated water of the RO membrane device 33 discharged from the concentrated water system path 35 is taken into the circulation path 37 and pressurized by the second pump 36. Thereafter, air is mixed into the concentrated water pressurized using the compressor 38, and the raw water and air are stirred using the static mixer 29, thereby generating fine bubbles.

  The concentrated water of the RO membrane device 33 has a pressure of 0.5 MPa to 2.5 MPa, for example, depending on the number of stages of the RO membrane device when the raw water pressure in the water supply path 31 is 1.0 MPa or more and 3.0 MPa. For this reason, the water treatment apparatus of FIG. 4 has the advantage that the pressurizing power of the second pump 36 can be small.

  The amount of water supplied from the circulation path 37 to the water supply path 31 and the amount of water absorbed from the concentrated water path 35 to the circulation path 37 are adjusted by a flow rate adjusting means (not shown) to actually supply the RO membrane device 33. The void ratio in the treated water (mixed water of raw water and concentrated water) can be controlled within a suitable range.

  In the water treatment apparatus of FIG. 4, since the fine bubbles are also contained in the concentrated water of the RO membrane device 33, the fine bubbles are collected together with the concentrated water. For this reason, the amount of air to be mixed using the compressor 38 can be reduced during steady operation, and the compressor 38 may be small.

(Example 2)
The schematic block diagram of another water treatment apparatus of this invention is shown in FIG. Since it is the same as that of the water treatment apparatus of FIG. 4 except having the gas-liquid separator 40 in the concentrated water path 35, only a different point is demonstrated here.

  In the water treatment apparatus of FIG. 5, a gas / liquid separator 40 such as a cyclone or stationary separation is provided in the concentrated water path 35. Since the pressure of the concentrated water drained from the concentrated water path 35 is lower than the supply water of the RO membrane device 33, the fine bubbles in the concentrated water are larger than the fine bubbles in the supply water. When bubbles increase, cavitation may occur in the second pump 36, but by providing the gas-liquid separator 40 in the concentrated water path 35, it is possible to remove large bubbles in the concentrated water.

  In FIG. 5, the gas-liquid separator 40 is provided in the concentrated water path 35, but may be installed upstream of the second pump 36 in the circulation path 37.

  The water treatment apparatus and water treatment apparatus of the present invention are useful in fields such as drinking water production and various wastewater treatment.

1, 21, 32: First pump 2, 12, 22, 31: Water supply path 3, 15, 23, 33: RO membrane device 4, 26, 37: Circulation path 5, 27, 36: Second pump 6, 28 , 38: Compressor 7, 29, 39: Static mixer 8, 16, 24, 34: Treated water path 9, 17, 25, 35: Concentrated water path 11: Pump 13: Bubble generating device 14: Path 40: Gas-liquid separation 50: Second pressure gauge 51: First pressure gauge 52: Control device

Claims (9)

A water treatment method for treating water to be treated by a reverse osmosis membrane device,
At the time of filtration operation by the reverse osmosis membrane device, branch the concentrated water path of the reverse osmosis membrane device and lead a part of the concentrated water to the circulation path,
After pressurizing the concentrated water by the second pump, air is mixed in, and after the fine water bubbles are generated in the concentrated water by stirring the concentrated water and air using a static mixer,
After supplying the concentrated water containing fine bubbles to the water supply path that pressurizes the treated water with the first pump and supplies it to the reverse osmosis membrane, the treated water containing fine bubbles in the circulation path is supplied to the reverse osmosis membrane device Supply,
A water treatment method characterized by the above.   The water treatment method according to claim 1, wherein a void ratio of water to be treated containing the fine bubbles supplied to the reverse osmosis membrane device is 0.01% or more and 1% or less.   The water treatment method according to claim 1 or 2, wherein a gas-liquid separator is provided in the concentrated water path to remove bubbles in the concentrated water. The water supply pressure of the water supply path is 1.0 MPa to 3.0 MPa,
The pressure of the second pump is adjusted so that the pressure of the concentrated water containing fine bubbles when supplying from the circulation path to the water supply path is higher in the range of 5 kPa to 100 kPa than the pressure in the water supply path. The water treatment method according to any one of claims 1 to 3. A reverse osmosis membrane device for treating water to be treated;
A water supply path for supplying treated water to the reverse osmosis membrane device;
A first pump for pressurizing the water to be treated in the water supply path;
A branch path branched from the concentrated water path of the reverse osmosis membrane device and connected to the water supply path upstream of the reverse osmosis membrane device,
Here, the circulation path is
A second pump for pressurizing the concentrated water;
Air input means for mixing air into the pressurized concentrated water;
Stir the concentrated water and the mixed air, in order with a static mixer to make concentrated water containing fine bubbles,
A water treatment apparatus that supplies concentrated water containing fine bubbles from a circulation path to a water supply path and then supplies treated water containing fine bubbles in the circulation path to a reverse osmosis membrane device.   The water treatment device according to claim 5, wherein a void ratio of water to be treated containing fine bubbles supplied to the reverse osmosis membrane device is 0.01% or more and 1% or less.   The water treatment apparatus of Claim 5 or 6 further equipped with the gas-liquid separator which removes the bubble in concentrated water in the said concentrated water path | route. A first pressure measuring device for measuring the pressure of the water supply path upstream of the reverse osmosis membrane device;
A second pressure measuring device for measuring the pressure of the circulation path downstream of the static mixer in the circulation path;
The concentrated water is further pressurized by a second pump so that a differential pressure between the second pressure measuring device and the first pressure measuring device is 5 kPa or more and 100 kPa or less. Water treatment equipment.   The water treatment apparatus according to any one of claims 5 to 8, further comprising a flow rate adjusting means for adjusting a supply amount of concentrated water containing the fine bubbles to the water supply path in the circulation path.

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