JP2001252536A - Method for cleaning filter membrane and apparatus for filtering seawater using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cleaning cost of a filter membrane while the installation space is small in a membrane filter. SOLUTION: In a method for cleaning the filter membrane 10a of a filter membrane module 10 through which raw seawater 1 is passed, by cleaning the membrane 10a by using the raw water 1 containing a chlorine agent 3 as the first cleaning liquid, organic suspended substances adherent to the membrane 10a are decomposed/removed surely by the first cleaning liquid, and the membrane 10a is cleaned by using the raw water 1 containing an acid 4 as the second cleaning liquid so that inorganic fine particles which exist in the first cleaning liquid and are deposited on the membrane 10a are decomposed/removed surely. In this way, even when seawater is used, the membrane 10a can be made to restore the initial state so that cleaning water with the use of clean water and an apparatus for storing the cleaning water can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning a filtration membrane and a seawater filtration device using the same.

[0002]

2. Description of the Related Art A membrane filtration device using a microfiltration (MF) membrane or an ultrafiltration (UF) membrane is configured such that a raw water supply side of a filtration membrane provided inside a pressure-resistant vessel is a filtered water permeation side. By setting the pressure higher than that, raw water is transmitted through the filtration membrane to obtain filtered water. Such membrane filtration devices include a total filtration method in which the entire amount of raw water is permeated through a filtration membrane for treatment, and a parallel flow filtration method in which raw water is circulated and supplied to permeate a part of the raw water through the filtration membrane. .

[0003] In such a membrane filtration device, an insoluble cake layer is deposited on the surface of the filtration membrane on the raw water supply side as the operation proceeds, and the filtration speed is reduced. Since the pressure difference from the water permeation side increases, causing energy loss and damage to the filtration membrane, NaCl
The filtered water mixed with O or the like is periodically (about 1 to 3 minutes every 20 to 60 minutes) from the filtered water permeation side of the filtration membrane to the raw water supply side, thereby being deposited on the surface of the filtration membrane on the raw water supply side. A washing operation (backwashing) for washing and removing the cake layer to recover the pressure loss of the filtration membrane is performed.

Recently, various studies have been conducted on a seawater filtration apparatus in which such a membrane filtration apparatus is applied to pretreatment of a seawater desalination apparatus. Since seawater contains many suspended substances such as organic substances such as plankton, algae, bacteria, and contaminated oil, and inorganic substances such as sand and clay, a seawater filtration apparatus using the above membrane filtration apparatus is used. Then, the above-mentioned suspended solids cannot be sufficiently removed only by the regular backwashing as described above,
Depending on the season, it may not be possible to maintain driving for about one week in a short time and about several months in a long time.

When the pressure difference between the raw water supply side and the filtrate permeation side of the filtration membrane exceeds the upper limit value (about 1.5 to 2.0 kg / cm ² ), the washing water containing high concentration NaClO or the like. By flowing (tap water) through the filtration membrane, the suspended substances are chemically decomposed and removed.

[0006]

For this reason, a facility for storing cleaning water (clean water) for chemical cleaning must be provided in the seawater filtration device, which not only increases the space required for installation. , Washing costs were also high.

Therefore, it is conceivable to carry out chemical cleaning using seawater as cleaning water. However, when seawater is mixed with NaClO or the like at a high concentration, as shown below, Mg ions and Ca ions in the seawater become alkali. As a result, fine particles are generated as a result of the formation, and the particles are deposited on the surface of the filtration membrane, thereby reducing the cleaning effect.

[0008] _{^{Mg 2+, Ca 2+, CO 3}} - + alkaline _{→ Mg (OH) 2 ↓,} MgCO 3 ↓, Ca (OH) 2 ↓, CaCO 3 ↓

Therefore, it has been strongly desired to reduce the cleaning cost while reducing the installation space.

[0010]

Means for Solving the Problems The first invention for solving the above-mentioned problems is a filtration membrane cleaning method for cleaning a filtration membrane through which seawater has been permeated. After washing the filtration membrane as a first washing liquid, the filtration membrane is washed with seawater containing an acid as a second washing liquid.

[0011] In a second aspect based on the first aspect, the chlorine concentration of the first cleaning solution is 10 to 1000 pp.
m, wherein the acid concentration of the second cleaning solution is 0.1% or less.

[0013] A third invention is a method for cleaning a filtration membrane for permeating seawater, wherein the chlorine concentration is 10%.
The filtration membrane is washed with seawater to which a chlorine agent is added so as to have a pH of not more than 1000 ppm and an acid is added so that the pH is 9 or less.

[0013] In a fourth aspect based on the third aspect, the washing solution is added with the acid to the seawater so as to maintain the pH at 9 or less, and the chlorine concentration is adjusted to 10 to 1000 p.
pm to the seawater to which the chlorine agent is added.

According to a fifth aspect, in any one of the first to fourth aspects, the chlorinating agent is at least one of NaClO or Cl ₂ and the acid is HC
1, H ₂ SO ₄ , and HNO ₃ .

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the FI value of the seawater is 5 or less.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, after allowing the washing liquid to permeate the filtration membrane from a direction in which seawater permeates the filtration membrane,
It is characterized in that the filtration membrane is washed by repeatedly permeating the washing liquid through the filtration membrane from the opposite direction.

An eighth invention is a seawater filtration device utilizing the filtration membrane cleaning method according to any one of the first to seventh inventions, wherein the filtration device main body having the filtration membrane and the filtration device are provided. Raw water supply means connected to one side of the filtration membrane of the main body, for supplying raw water of seawater to one side of the filtration membrane of the filter main body, and connected to the other side of the filtration membrane of the filter main body; And a filtered water collecting means for collecting the filtered water filtered by the filtration membrane, the filtration water being connected to the other side of the filtration membrane of the filter main body, and being provided on the other side of the filtration membrane of the filter main body. And a bypass means connected to one side of the filtration membrane of the filter body and returning the water on the side of the filtration membrane of the filter body to the raw water supply means. , The chlorine agent in at least one of the raw water or the filtered water And chlorine agent addition means for adding, characterized by comprising an acid adding means for adding the acid to at least one of the raw water or the filtered water.

A ninth invention is characterized in that, in the eighth invention, the chlorinating agent adding means adds the chlorinating agent to the raw water, and the acid adding means adds the acid to the raw water. I do.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for cleaning a filtration membrane and a membrane filtration apparatus using the same according to the present invention will be described below, but the present invention is not limited to these embodiments.

First Embodiment A first embodiment of a method for cleaning a filtration membrane and a seawater filtration apparatus using the same according to the present invention will be described with reference to FIG. FIG.
1 is an overall schematic configuration diagram of a seawater filtration device.

The filtration membrane cleaning method according to the present embodiment is a filtration membrane cleaning method for cleaning the filtration membrane 10a of the filtration membrane module 10 through which the raw water 1 of seawater is permeated. After washing the filtration membrane 10a as a first washing liquid, the filtration membrane 10a is washed using the raw water 1 containing the acid 4 as a second washing liquid.

Here, the chlorinating agent 3 is NaClO or Cl
Preferably at least one of the _two . Cl
₂ may be supplied into the raw water 1 from a Cl ₂ cylinder, but can be obtained by electrolyzing the raw water 1.

The acid 4 is HCl, H ₂ SO ₄ , HNO
Preferably at least one of the _three . In particular, the acid 4 is more preferably HCl. Because acid 4 is H
_If it is ₂ SO ₄ , sulfate may be generated depending on components contained in the raw water 1. If the acid 4 is HNO ₃ , the material of the filtration membrane 10 a may damage the filtration membrane 10 a. This is because there is a fear. However, if the filtration membrane 10a has high oxidation resistance, it is better to use HNO ₃ having a high ability to decompose organic substances.

The acid concentration of the second cleaning solution is 0.1%.
% Is preferable. This acid concentration depends on the filtration membrane 10a.
It is desirable to be as high as possible as long as it is within a range that does not damage. This is because the higher the acid concentration, the more reliably the fine particles can be decomposed and removed. However, if the acid concentration exceeds 0.1%, the filtration membrane 10a may be damaged, which is not preferable.

The chlorine concentration of the first cleaning liquid is 10 to 1
Preferably it is 000 ppm. This is because if the chlorine concentration is less than 10 ppm, the chlorine cleaning effect of the chlorine agent 3 cannot be sufficiently exhibited, and the chlorine concentration is 1000 ppm.
If it exceeds pm, the number of the fine particles generated in the first cleaning liquid is too large, and it becomes difficult to clean (see Table 1 below).

[0026]

[Table 1]

Here, FI is an index indicating the degree of contamination of the water quality at the inlet of the membrane, and specifically, pressure filtration of 2.1 kg / cm ² is performed by a 0.45 μm membrane filter, and the initial filtration is performed. Time required for filtering 500 ml (T ₁ )
, And the filtration time (T ₂ ) of 500 ml was similarly measured after continuously filtering for 15 minutes, and the value was calculated by the following equation.

FI = (1−T ₁ / T ₂ ) × 100/15

It is preferable that the FI value of seawater used as a cleaning liquid is 5 or less. This is because if the FI value of seawater used as the cleaning liquid exceeds 5, the cleaning effect is reduced because the fine particles in the cleaning liquid are deposited simultaneously with the removal of the cake layer by the cleaning.

Further, after allowing the washing liquid to permeate the filtration membrane 10a from the direction in which the raw water 1 permeates the filtration membrane 10a,
It is preferred that the filtration membrane 10a be washed by repeating the permeation of the washing liquid through the filtration membrane 10a from the opposite direction. This is because the raw water supply side of the filtration membrane 10a is more contaminated than the filtration water permeation side, so that it can be efficiently decomposed by starting the cleaning first, and the fine particles formed in the first cleaning liquid can be efficiently decomposed. This is because it is possible to reliably prevent the particles from moving to the filtered water permeation side.

On the other hand, as shown in FIG. 1, the seawater filtration device according to the present embodiment using the above-described filtration membrane cleaning method includes a filtration membrane module 10 which is a filter main body having a filtration membrane 10a, and a filtration membrane module 10. Filtration membrane 10 of membrane module 10
a raw water tank 11 and a feed pump 21 which are connected to a raw water supply side, which is one side of a, and constitute raw water supply means for supplying raw water 1 of seawater to the raw water supply side of the filtration membrane 10a of the filtration membrane module 10. And the filtration membrane 10a of the filtration membrane module 10.
Of the filtration membrane 10a
The filtration water tank 12 and the like constituting the filtration water recovery means for collecting the filtration water 2 filtered by the above and the filtration water permeation side of the filtration membrane 10a of the filtration membrane module 10 are connected to each other. A backwashing pump 8 or the like constituting a filtered water supply means for supplying filtered water 2 to the filtered water permeation side; The pipe 34 and the like constituting a bypass means for returning the raw water 1 and the filtered water 2 and the like on the relevant side of the raw water 10a into the raw water tank 11, and the chlorinating agent adding apparatus 61 constituting the chlorinating agent adding means for adding the chlorinating agent 3 to the raw water Etc.,
An acid addition device 62 constituting an acid addition means for adding the acid 4 to the raw water 1 and a metering pump 2 for adding the chlorinating agent 3 to the filtered water 2
3 and a chlorine agent tank 13.

The structure of the above-described apparatus will be described more specifically.

As shown in FIG. 1, the bottom of a raw water tank 11 for storing raw water 1 for seawater is connected via a pipe 31 to a feed pump 21 for feeding the raw water 1. The feed pump 21 has a microfiltration (MF) membrane and an ultrafiltration (U) inside.
F) It is connected via a pipe 32 below the raw water supply side of the filtration membrane module 10 provided with a filtration membrane 10a such as a membrane. The pipe 32 is provided with a valve 41 and a pressure gauge 51. A drain pipe 33 provided with a valve 42 is connected to the pipe 32 on the filtration membrane module 10 side.
The upper part on the raw water supply side of the filtration membrane module 10 is provided with a valve 4
The raw water tank 11 is connected to the raw water tank 11 through a pipe 34 provided with a pipe 3.

The upper side of the filtration membrane module 10 on the filtration water permeation side is connected to the filtration water tank 12 for storing the filtration water 2 through a pipe 35. A pressure gauge 52 is provided on the filtration membrane module 10 side of the pipe 35, and a valve 44 is provided on the filtration water tank 12 side of the pipe 35. The bottom of the filtered water tank 12 is connected via a pipe 36 to the backwash pump 22 that supplies the filtered water 2. The backwash pump 22 is connected between the pressure gauge 52 of the pipe 35 and the valve 44 via a pipe 37 having a valve 45.

On the other hand, the lower part of the chlorinating agent tank 13 for storing the chlorinating agent 3 such as NaClO
Are connected via The metering pump 23 includes a pipe 39
Is connected to the pipe 36 via a.

Above the raw water tank 11, a chlorinating agent adding device 61 for adding a predetermined amount of the chlorinating agent 3 such as NaClO into the raw water tank 11 and an acid 4 such as HCl are added in a predetermined amount. The acid addition devices 62 are in communication with each other.

In such a seawater filtration apparatus, when the valves 41, 43, 44 are opened, the valves 42, 45 are closed, and the feed pump 21 is operated, the raw water 1 in the raw water tank 11 is changed to the filtration membrane module 10 And a part of the raw water 1 is returned to the raw water tank 11 from the pipe 34 while cleaning the surface of the filtration membrane 10a on the raw water supply side, while the remaining raw water 1 permeates the filtration membrane 10a and passes through the filtration membrane 10a. The filtered water 2 from which the water has been removed is fed into the filtered water tank 12 from the pipe 35 (parallel flow filtration method), and is filtered by the seawater filtration device in this step.

In this way, the raw water 1 is kept for a predetermined time (20 to
60 minutes) After the filtration, the operation of the feed pump 21 is stopped,
While closing the valves 41, 43, 44, the valves 42, 43
When the backwash pump 22 and the metering pump 23 are operated by opening 45, the filtered water 2 to which a predetermined amount of the chlorine agent 3 has been added is added.
Is fed from the filtration water permeation side of the filtration membrane module 10 to the raw water supply side, and the cake layer deposited on the surface of the filtration membrane 10a on the raw water supply side without being washed completely by the parallel flow is washed away. From the drain pipe 33.

After the pressure loss of the filtration membrane 10a is recovered by performing such backwashing for a predetermined time (about 1 to 3 minutes), the process returns to the above-described filtration step of the raw water 1, and the production of the filtered water 2 is performed again. .

As described above, while the regular backwashing is repeatedly performed, as described above, the suspended matter in the raw water 1 cannot be sufficiently removed, and the pressure loss of the filtration membrane 10a can be sufficiently recovered. Instead, the pressure gauge 51 indicates a predetermined value (1.5 kg
/ Cm ² ), feed pump 2
1 is stopped, and the filtered water 2 in the filtered water tank 1 is emptied. Then, the chlorine agent adding device 61 is adjusted so that the chlorine concentration in the raw water 1 in the raw water tank 11 becomes a predetermined value (10 to 1000 ppm). Is operated to add the chlorine agent 3 to the raw water 1 in the raw water tank 11.

Next, the feed pump 21 is operated to feed the raw water 1 (first washing liquid) in the raw water tank 11 in the same manner as in the case of manufacturing the filtered water 2, so that the filtration membrane module 10 is supplied. Is chemically washed from the raw water supply side, and the washing liquid is collected in the filtered water tank 12.
Subsequently, the valves 41, 42 and 44 are closed, and the valve 4 is closed.
3 and 45 are opened, and the backwash pump 22 is operated to supply the washing liquid in the filtrate tank 12 from the filtered water permeation side of the filtration membrane module 10 to the raw water supply side, whereby the filtration membrane 10 a Is chemically cleaned from the raw water supply side, and the cleaning liquid is collected in the raw water tank 11.

By repeating the above operation a plurality of times,
After both sides of the filtration membrane 10a of the filtration membrane module 10 are washed with chlorine, organic suspended substances such as plankton, algae, bacteria, and contaminated oil adhering to the filtration membrane 10a are surely decomposed and removed (first Washing), and the washing solution is drained into a drain pipe 33.
And discharged to the outside for detoxification.

At this time, the above-mentioned cleaning liquid is added to the chlorinating agent 3 in seawater.
, Inorganic fine particles as described above are generated in the cleaning liquid, and are deposited on the raw water supply side of the filtration membrane 10a.

For this reason, after the chlorine washing is completed, the raw water 1 is fed again into the raw water tank 1 and the acid addition device 62 is controlled so that the acid concentration of the raw water 1 in the tank 11 becomes 0.1% or less. To add the acid 4 to the raw water 1.

Next, using the raw water 1 (second cleaning liquid), the filtration membrane module 10 using the first cleaning liquid described above is used.
In the same manner as the washing procedure of the filtration membrane 10a.
Oa is acid washed (second wash).

Thus, the inorganic fine particles deposited on the filtration membrane 10a are dissolved and removed, and the filtration membrane 10a
Is restored to the initial size.

That is, when the chlorine concentration is 10 to 1000 ppm
After the filtration membrane 10a is subjected to chlorine washing with the first cleaning liquid, the organic suspended substances adhering to the filtration membrane 10a are surely decomposed and removed, and then the acid concentration is 0.1% or less. By acid-cleaning the filtration membrane 10a with the cleaning liquid, inorganic fine particles in the first cleaning liquid deposited on the filtration membrane 10a are surely decomposed and removed.

Therefore, even if seawater is used, the filtration membrane 10a of the filtration membrane module 10 can be restored to the initial state.

[0049] Therefore, since there is no need for cleaning water using tap water or equipment for storing the same, it is possible to greatly reduce the installation space and the cleaning cost.

Here, in order to confirm the above-mentioned effects, a chlorine agent 3 was added to the raw water 1 so that the chlorine concentration became 500 ppm.
In the case where the filtration membrane 10a of the filtration membrane module 10 is simply washed (first washing) using the first washing liquid to which (NaClO) is added (comparative example), the raw water 1 is added so that the chlorine concentration becomes 200 ppm. Filtration membrane 1 of filtration membrane module 10 using a first cleaning solution to which chlorine agent 3 (NaClO) has been added.
After washing (a first washing), the filtration membrane 10a is again washed (a second washing) using a second washing solution in which an acid 4 (HCl) is added to the raw water 1 so that the acid concentration becomes 0.1%. The filtration pressure before and after the cleaning of the filtration membrane 10a when (one experiment) was performed (experimental example) was determined. Fig. 2 (Comparative example)
And FIG. 3 (Experimental example).

As can be seen from FIGS. 2 and 3, in the case of the comparative example, the filtration pressure of the filtration membrane 10a is set to the initial value (about 0.2 kg).
/ Cm ² ), it is not possible to sufficiently recover the pressure, and even if the filtration is performed for a while, the filtration pressure is greatly increased. On the other hand, in the case of the experimental example, not only does the filtration pressure of the filtration membrane 10a return to the initial value, but also the filtration pressure does not greatly increase after washing.

From the above, it was confirmed that the filtration membrane washing method of the present invention can sufficiently obtain the desired effects.

[Second Embodiment] The second embodiment of the filtration membrane cleaning method and the seawater filtration device using the same according to the present invention will be described below. However, for the same parts as in the first embodiment described above,
The description is omitted by using the same reference numerals as in the first embodiment described above.

The filtration membrane cleaning method according to the present embodiment is a filtration membrane cleaning method for cleaning the filtration membrane 10a of the filtration membrane module 10 through which the raw water 1 of seawater has passed, and the chlorine concentration is 10 to 1000 ppm. Is to wash the filtration membrane 10a using the raw water 1 to which the chlorinating agent 3 is added and the acid 4 so that the pH is 9 or less as a washing liquid.

Here, when the pH of raw water 1 exceeds 9, F
It is not preferable because the I value exceeds 5.

The washing solution is added with acid 4 so as to keep the pH at 9 or less, and the chlorine concentration is adjusted to 10 to 10%.
It is preferable that the chlorine agent 3 is added so as to be 00 ppm. This is because if a predetermined amount of the chlorine agent 3 is added to the raw water 1 and then the acid 4 is added so that the pH is 9 or less, a large amount of chlorine gas is generated and released out of the system.

On the other hand, the seawater filtration device according to the present embodiment using the above-described filtration membrane cleaning method has the same configuration as the seawater filtration device described with reference to FIG. 1 in the first embodiment described above. It has become.

In such a seawater filtration device, the filtration treatment of the raw water 1 and the regular backwashing of the filtration membrane 10a are performed in the same manner as in the first embodiment described above.

On the other hand, as described above, the suspended matter in the raw water 1 cannot be sufficiently removed, and the pressure loss of the filtration membrane 10a cannot be sufficiently recovered. Once 1.5kg / cm ² or so) so more than,
After the feed pump 21 is stopped and the filtered water 2 in the filtered water tank 1 is emptied, p of the raw water 1 in the raw water tank 11 is reduced.
The acid 4 is added to the raw water 1 from the acid addition device 62 so that H is 9 or less (preferably about 5.5 to 7). continue,
The chlorinating agent 3 is added to the raw water 1 from the chlorinating agent adding device 61 so that the chlorine concentration in the raw water 1 becomes 10 to 1000 ppm. With the addition of the chlorine agent 3, the pH of the raw water 1
Therefore, the acid 4 is appropriately added so that the pH of the raw water 1 is always kept within the above range.

Thus, the chlorine concentration is 10 to 1000
ppm and a pH of 9 or less (preferably 5.5 to 5.5).
7), the filtration membrane 10a of the filtration membrane module 10 is washed in the same manner as in the first embodiment described above.

At this time, since the pH of the cleaning solution is 9 or less, the presence of the inorganic fine particles as described above is negligible, so that the filtration membrane 10a should be cleaned without any problem. Can be.

That is, when the chlorine concentration is 10 to 1000 ppm
And a washing liquid having a pH of 9 or less.
By washing the organic material, organic suspended matter adhering to the filtration membrane 10a is surely decomposed and removed without almost any inorganic fine particles.

Therefore, even if seawater is used, the filtration membrane 10a of the filtration membrane module 10 can be restored to the initial state.

Therefore, as in the case of the first embodiment described above, washing water using tap water and equipment for storing the washing water are not required, so that the installation space can be greatly reduced. In addition, the cleaning cost can be significantly reduced.

Here, in order to confirm the above-mentioned effects, a chlorine agent 3 was added to the raw water 1 so that the chlorine concentration became 500 ppm.
The case where the filtration membrane 10a of the filtration membrane module 10 is only washed (first washing) using the first washing liquid to which (NaClO) is added (comparative example: the same as the case of the first embodiment) And chlorine agent 3 so that the chlorine concentration becomes 50 ppm.
And the filtration membrane 10a of the filtration membrane module 10 was washed using the raw water 1 to which the acid 4 was added so that the pH became 5.5 to 6 (experimental example). When the filtration pressure before and after washing was determined, almost the same results as in the case of the first embodiment described above were obtained.

That is, in the case of the comparative example, the filtration membrane 10
In the case of the experimental example, the filtration pressure of “a” cannot be sufficiently restored to the initial value (approximately 0.2 kg / cm ² ). Thus, not only did the filtration pressure of the filtration membrane 10a return to the initial value, but also the filtration pressure did not increase significantly after washing.

From this, it was confirmed that the method for cleaning a filtration membrane of the present invention can sufficiently obtain the intended effect.

[0068]

The first invention is a filtration membrane cleaning method for cleaning a filtration membrane through which seawater has passed, wherein the filtration membrane is washed with seawater containing a chlorine agent as a first cleaning liquid. Since the filtration membrane is washed with seawater containing an acid as the second washing liquid, the suspended matter of the organic substance adhering to the filtration membrane can be reliably decomposed and removed by the first washing liquid, and Inorganic fine particles present in one cleaning liquid and deposited on the filtration membrane can be reliably decomposed and removed by the second cleaning liquid, so that the filtration membrane can be restored to its original state even with seawater. Can be. This eliminates the need for cleaning water using tap water and equipment for storing the same, so that the installation space can be significantly reduced and the cleaning cost can be significantly reduced.

According to a second aspect, in the first aspect, the chlorine concentration of the first cleaning solution is 10 to 1000 pp.
m, and the acid concentration of the second cleaning solution is 0.1% or less, so that the above-described effects can be reliably obtained without damaging the filtration membrane.

The third invention is a filtration membrane cleaning method for cleaning a filtration membrane through which seawater has passed, wherein the chlorine concentration is 10%.
A chlorine agent is added so as to be about 1000 ppm, and the filtration membrane is washed with seawater to which an acid is added so that the pH becomes 9 or less, so that inorganic fine particles are almost completely contained in the washing liquid. Since the organic suspended matter adhering to the filtration membrane can be reliably decomposed and removed without being present, the filtration membrane can be restored to the initial state even if seawater is used. This eliminates the need for cleaning water using tap water and equipment for storing the same, so that the installation space can be significantly reduced and the cleaning cost can be significantly reduced.

In a fourth aspect, in the third aspect, the washing solution is added with the acid to the seawater so as to keep the pH at 9 or less, and the chlorine concentration is adjusted to 10 to 1000 p.
Since the seawater is obtained by adding the chlorine agent to the seawater so as to be set to pm, the amount of chlorine released from the cleaning liquid to the outside of the system can be suppressed.

In a fifth aspect, in any one of the first to fourth aspects, the chlorinating agent is at least one of NaClO and Cl ₂ and the acid is HC.
1, H ₂ SO ₄ , and HNO ₃ , so that the above-described effects can be reliably obtained.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, since the FI value of the seawater is 5 or less, the above-described effects can be surely obtained.

A seventh aspect of the present invention is the liquid crystal display device according to any one of the first to sixth aspects, wherein after allowing the washing liquid to permeate the filtration membrane from a direction in which seawater permeates the filtration membrane,
Since the filtration membrane is washed by repeating the permeation of the cleaning liquid through the filtration membrane from the opposite direction, the above-described effects can be reliably obtained.

An eighth invention is a seawater filtration device using the filtration membrane cleaning method according to any one of the first to seventh inventions, wherein the filtration main body having the filtration membrane, Raw water supply means connected to one side of the filtration membrane of the main body, for supplying raw water of seawater to one side of the filtration membrane of the filter main body, and connected to the other side of the filtration membrane of the filter main body; And a filtered water collecting means for collecting the filtered water filtered by the filtration membrane, the filtration water being connected to the other side of the filtration membrane of the filter main body, and being provided on the other side of the filtration membrane of the filter main body. And a bypass means connected to one side of the filtration membrane of the filter body and returning the water on the side of the filtration membrane of the filter body to the raw water supply means. , The chlorine agent in at least one of the raw water or the filtered water And chlorine agent addition means for adding, since with an acid adding means for adding the acid to at least one of the raw water or the filtered water, it is possible to easily implement the filtration membrane cleaning method according to the present invention.

According to a ninth aspect, in the eighth aspect, the chlorinating agent adding means adds the chlorinating agent to the raw water, and the acid adding means adds the acid to the raw water. The method for cleaning a filtration membrane according to the second invention can be easily carried out.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a seawater filtration device according to the present invention.

FIG. 2 is a graph showing a relationship between a filtration time and a filtration pressure in a comparative example.

FIG. 3 is a graph showing a relationship between a filtration time and a filtration pressure in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water 2 Filtrated water 3 Chlorine 4 Acid 10 Filtration membrane module 11 Raw water tank 12 Filtration water tank 13 Chlorine tank 21 Feed pump 22 Backwash pump 23 Metering pump 31, 32, 34-39 Pipe 33 Drain pipe 41-45 Valves 51, 52 Pressure gauge 61 Chlorine addition device 62 Acid addition device

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hideo Iwahashi 1-1 1-1 Akunoura-cho, Nagasaki-shi, Nagasaki F-term in Nagasaki Shipyard, Mitsubishi Heavy Industries, Ltd. 4D006 GA06 GA07 JA53Z JA55A JA57A JA67Z KA16 KA63 KC02 KC03 KC12 KC13 KC16 KD11 KD12 KD23 KD24 KE07Q KE08P KE11R KE12P KE15R KE22Q KE23Q KE24Q KE30P KE30R MB12 PA01 PB03 PB24

Claims (9)

[Claims] 1. A method for cleaning a filtration membrane through which seawater has been permeated, comprising the steps of: washing the filtration membrane with a seawater containing a chlorine agent as a first washing liquid; A method for washing a filtration membrane, comprising washing the filtration membrane as a second washing liquid. 2. The method for cleaning a filtration membrane according to claim 1, wherein the chlorine concentration of the first cleaning solution is 10 to 1000 ppm, and the acid concentration of the second cleaning solution is 0.1% or less. . 3. A method for cleaning a filtration membrane through which seawater has passed, wherein a chlorine agent is added so that the chlorine concentration becomes 10 to 1000 ppm and an acid is added so that the pH becomes 9 or less. Washing the filtration membrane by using seawater to which the water is added as a washing liquid. 4. The method according to claim 3, wherein the washing solution is added with the acid to the seawater so as to keep the pH at 9 or less, and the chlorine concentration is 10 to 1000 ppm.
A method for cleaning a filtration membrane, wherein the seawater is added with the chlorine agent. 5. The method according to claim 1, wherein the chlorinating agent is at least one of NaClO and Cl ₂ , and the acid is at least one of HCl, H ₂ SO ₄ and HNO _3. A method for cleaning a filtration membrane, comprising: 6. The method for cleaning a filtration membrane according to claim 1, wherein the FI value of the seawater is 5 or less. 7. The method according to claim 1, wherein the cleaning liquid is passed through the filtration membrane in a direction that allows seawater to pass through the filtration membrane, and then the cleaning liquid is passed through the filtration membrane in a direction opposite to the direction. A method for washing a filtration membrane, comprising washing the filtration membrane by repeating permeation. 8. A seawater filtration device using the filtration membrane cleaning method according to any one of claims 1 to 7, wherein one of the filtration body having the filtration membrane and the filtration membrane of the filtration body. And a raw water supply means for supplying raw water of seawater to one side of the filtration membrane of the filter main body; and A filtered water collecting means for collecting the filtered water, and a filtered water feeder connected to the other side of the filtration membrane of the filter main body and feeding the filtered water to the other side of the filtration membrane of the filter main body. Supply means, bypass means connected to one side of the filtration membrane of the filter body, and returning water on the side of the filtration membrane of the filter body to the raw water supply means; and the raw water or the filtered water. Adding a chlorinating agent to at least one of A seawater filtration device comprising: an addition unit; and an acid addition unit that adds the acid to at least one of the raw water and the filtered water. 9. The seawater filtration device according to claim 8, wherein the chlorinating agent adding unit adds the chlorinating agent to the raw water, and the acid adding unit adds the acid to the raw water.