JP2871819B2 - Filtration method using hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to condensate of a nuclear power plant, a thermal power plant or raw water containing an insoluble substance such as heater drain water or other service water or waste water. Regarding the method of filtration in the arranged filtration tower, more specifically, when filtering raw water,
The present invention relates to an improvement in a method for starting filtration of raw water after forming a thin coating film of iron oxide fine particles on the surface of a hollow fiber membrane in advance.

<Conventional technology> When raw water containing an insoluble substance is treated with a filtration tower to obtain filtered water from which the insoluble substance has been removed, a filtration tower conventionally filled with a filter medium, or a filter aid is pre-coated. Various filtration towers such as filtration towers have been used. In recent years, filtration towers using hollow fiber membranes have come to be used particularly for condensate treatment in nuclear power plants and the like. That is, in a filtration tower using a hollow fiber membrane, first, the clad caused by iron oxide, which is an insoluble substance in the condensate, is removed, and then the resulting filtered water is treated with a mixed bed of a cation exchange resin and an anion exchange resin. This is to remove impurity ions.

The filtration tower used for the above-described condensate treatment is usually a hollow fiber module in which a number of hollow fiber membranes are bundled from a partition plate that partitions the inside of the tower into an upper treatment water chamber and a lower filtration chamber. Is suspended in the filtration chamber. For example, when condensate is filtered, the condensate flows from the lower part of the filtration tower into the filtration chamber, and the condensate is filtered from the outside to the inside of each hollow fiber membrane. By filtering the clad caused by iron oxide on the surface of each hollow fiber membrane, obtaining filtered water from which iron oxide has been removed inside each hollow fiber membrane, collecting the filtered water in the treatment water chamber, and taking out the collected water. It is.

Further, when the pressure difference in the filtration tower rises due to the continuation of the filtration operation as described above, the surface of the hollow fiber membrane to which the iron oxide is adhered is bubbled with a gas such as air to remove most of the iron oxide. Then, if necessary, treated water and purified water such as pure water are flowed back from the inside to the outside of the hollow fiber membrane to remove iron oxide remaining on the membrane surface, and the washing and drainage containing a large amount of iron oxide Get. After the completion of the washing, the filtration operation is started again, and thereafter, the filtration and washing are sequentially repeated to perform the treatment.

As described above, since the filtration tower using the hollow fiber membrane directly filters condensate through each hollow fiber membrane, the filtration tower is compared with the conventional precoat filtration tower using a fine powder ion exchange resin or the like as a filter aid. Then, the amount of solid matter contained in the washing wastewater is extremely small, and therefore, it is suitable especially when the solid matter becomes a target of radioactive waste, such as condensing water of a boiling water nuclear power plant.

However, even in a filtration method using a hollow fiber membrane having such advantages, for example, when raw water contains fine organic matter or oil, or a substance having a relatively high viscosity, the surface of the hollow fiber membrane may be reduced. These substances adhered to the surface cannot be completely removed by the above-mentioned washing operation, so that the initial pressure difference increases each time washing is performed, and finally, the filtration process itself may be impaired.

Therefore, the applicant of the present application has proposed that even if such raw materials contain such hard-to-peel substances, they are not allowed to remain on the surface of the hollow fiber membrane during washing, and the A new filtration method that can effectively prevent the phenomenon that the initial differential pressure gradually rises and stably perform the filtration treatment was proposed. (See JP-A-63-252507.) In this method, before filtering raw water with a hollow fiber membrane, water containing iron oxide fine particles having good releasability is passed through the hollow fiber membrane in advance and each hollow fiber membrane is filtered. A thin coating film of the iron oxide fine particles is formed on the surface of the substrate, and then raw water containing an insoluble substance is filtered through the coating film. According to the filtration method, even if the raw water contains an insoluble substance having poor releasability, the insoluble substance is captured by the coating film without directly adhering to the surface of the hollow fiber membrane. Thus, in the cleaning step, almost all the insoluble substances are peeled off when the coating film of the iron oxide fine particles that is easily peeled off is peeled off, and thus the initial pressure difference increases with each washing as described above. Troubles can be effectively prevented.

The iron oxide fine particles having good releasability used in the filtration method refer to all iron oxide fine particles which can be easily separated in the above-mentioned washing step even if they adhere to the surface of the hollow fiber membrane. Α-Fe ₂ O ₃ (hematite), α-FeOOH (goethite) or Fe ₃ O ₄ (magnetite). Also, like the condensate of the nuclear power plant mentioned above,
When most of the insoluble substances contained are iron oxides, the oxides contained in the raw water can be prepared without special preparation of the iron oxide fine particles in the form described above for forming the coating film. Iron can be used.

That is, the raw water containing iron oxide is directly filtered through the hollow fiber membrane, and then the iron oxide is peeled off from the hollow fiber membrane in the above-mentioned washing step, whereby a washing wastewater containing a large amount of iron oxide is obtained. The iron oxide in the solution is aggregated by being sufficiently stirred by bubbling or the like in the washing step, and physically aggregates, resulting in iron oxide fine particles having good peelability. Therefore, the aggregated iron oxide thus obtained can be used as iron oxide fine particles for forming a coating film.

<Problems to be Solved by the Invention> As described above, in the treatment of condensate or the like in which most of the insoluble substances in the raw water are iron oxide, iron oxide fine particles for forming the coating film must be prepared. At least, the coating film may be formed by using the iron oxide fine particles in the washing wastewater obtained in the washing step, but when the method is performed using a filtration tower having the above-described structure, the following method is used. Do it like this.

That is, the filtration of raw water is stopped due to the increase in the differential pressure,
Filtration water in the treatment water chamber of the filtration tower, and from the state where raw water is filled in the filtration chamber, for example, air flows into the filtration chamber to bubble the filtration chamber and adhere to the surface of the hollow fiber membrane. To remove the iron oxide.

By the bubbling operation, a cleaning wastewater containing a large amount of the separated iron oxide is obtained in the filtration chamber, and a part of the obtained cleaning wastewater is used in the next filtration step to form iron oxide fine particles for forming a coating film. In general, the washing waste liquid is left below the lower end of the hollow fiber module suspended from the partition plate in the lower part of the filtration chamber for use as water. It is discharged outside.

After completion of the washing operation, raw water or filtered water is supplied to the filtration chamber through a raw water inflow pipe connected to the lower portion of the filtration tower or via a water supply pipe for water filling separately provided at the lower portion of the filtration tower.
Water for filling, such as pure water, is allowed to flow in to fill the filtration chamber once. Next, raw water or filtered water, water for coating film formation such as pure water is flown into the filtration chamber from the raw water inflow pipe or the water filling water supply pipe, and the coating film formation water is directed from the filtration chamber to the treatment water chamber. In other words, the water in the filtration chamber is passed through each hollow fiber membrane together with the coating film forming water by flowing the raw water in the same manner as in the case of performing the filtration of the raw water, whereby the surface of each hollow fiber membrane contains the iron oxide fine particles. A coating film is formed. Thereafter, the raw water flows into the filtration chamber through the raw water inflow pipe, and the raw water is filtered through the formed coating film.

However, in the above-mentioned conventional method, when the filtration chamber is filled with water, the filling water is caused to flow into the filtration chamber as an ascending flow from below the surface of the coating iron oxide fine particle water that was present at the lower portion of the filtration chamber. In addition, at this time, the filtration chamber is filled with water so as not to allow water in the filtration chamber to pass through each hollow fiber membrane. Although they are dispersed to some extent in the filtration chamber, most of them are raised in the filtration chamber with the inflow of water for filling, and are not trapped on the surface of the hollow fiber membrane during this time. As a result, when the filtration chamber becomes full of water, relatively large amounts of iron oxide fine particles for forming a coating film are present in the water in the upper part of the filtration chamber, and iron oxide fine particles are present in the water below the filtration chamber. There is not much.
Therefore, from this state, the coating film forming water is caused to flow into the filtration chamber in ascending flow, and the coating film forming water is caused to flow from the filtration chamber to the treatment water chamber. When the membrane is allowed to pass from the outside to the inside, a relatively large amount of iron oxide fine particles is captured on the upper surface of each hollow fiber membrane of the hollow fiber module suspended in the filtration chamber from the partition plate in the longitudinal direction. The lower the lower part, the smaller the trapped amount of iron oxide fine particles. Therefore, the surface of each hollow fiber membrane becomes relatively thick at the upper part and becomes thinner toward the lower part, resulting in an uneven coating film. . As a result, uniform filtration is not performed, and a problem occurs in that the intended purpose is not achieved because the thickness of the coating film is too thin below the hollow fiber membrane. In order to form a coating film having a predetermined thickness, it is necessary to use extra iron oxide fine particles for forming the coating film. However, when forming the coating film, a relatively small amount of coating iron oxide fine water containing a required amount of iron oxide fine particles is present in the lower portion of the filtration chamber in advance, and then the iron oxide is formed on the surface of the hollow fiber membrane through a water filling operation. The above-described method of forming a coating film of fine particles can be applied even when iron oxide is not present in the raw water to be treated, and therefore, special preparation of iron oxide fine particles for forming the coating film is required. However, in such a case, it goes without saying that the smaller the amount of iron oxide fine particles required for forming the coating film, the more economically advantageous.

The present invention provides, as described above, a method of forming a coating film of iron oxide fine particles having good releasability on the surface of a hollow fiber membrane prior to filtration of raw water, and then filtering raw water through the coating film. And a coating film having a required thickness can be uniformly formed on the surface of the hollow fiber membrane by using a minimum necessary amount of the iron oxide fine particles. It is an object of the present invention to provide a filtration method capable of performing a good filtration treatment through a covering film.

<Means for Solving the Problems> The present invention made to achieve the above-mentioned object provides a large number of hollow fiber membranes from a partition plate that partitions the inside of a tower into an upper treated water chamber and a lower filtration chamber. Using a filtration tower formed by suspending the bundled hollow fiber modules in the filtration chamber, by flowing raw water containing insoluble substances from the filtration chamber and passing the raw water from the outside to the inside of each hollow fiber membrane, Before the filtration operation of obtaining filtered water from the treated water chamber, water containing iron oxide fine particles having good releasability is passed through the hollow fiber membrane to form a thin coating film of the iron oxide fine particles on the surface of each hollow fiber membrane. In the filtration method, when forming a coating film of iron oxide fine particles on the surface of each hollow fiber membrane, an oxidizing solution for coating containing an amount of iron oxide fine particles necessary for forming the coating film in the lower part of the filtration chamber. Pre-existing iron fine particle water, then iron oxide for coating Filling the filtration chamber with water for flooding into the filtration chamber from a position above the surface of the fine particle water by allowing the majority of the iron oxide fine particles to flow into the lower portion of the filtration chamber,
Thereafter, the coating film forming water is allowed to flow into the filtration chamber from the lower portion thereof and the water in the filtration chamber is passed through each hollow fiber membrane to form a coating film of iron oxide fine particles on the surface of each hollow fiber membrane, Thereafter, a filtration method using a hollow fiber membrane is characterized in that raw water is filtered through the coating membrane.

<Operation> Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment.

FIG. 1 is a sectional view showing an example of a hollow fiber module used in the present invention, and FIG. 2 is a flow explanatory diagram showing an example of a filtration tower used in the present invention.

The hollow fiber module 1 shown in FIG.
Outer diameter 0.3-4mm, inner diameter 0.2-3mm with ~ 1.0μ micropore
About 100 to 50,000 hollow fiber membranes 2 are housed in the outer cylinder 3, and the upper end of the hollow fiber membranes 2 is adhered to the upper joint portion 4 without closing the hollow portion. Is closed at the lower joint portion 5 with the lower end closed. It is a so-called one-end water collecting type. In addition to providing flow ports 6A and 6B at the upper part and the lower part of the outer cylinder 3, respectively, providing the opening 7 at the lower joint part 5, A skirt 8 is provided.

When disposing the hollow fiber module 1 in the filtration tower, as shown in FIG. 2, a partition plate 10 is provided above the filtration tower 9 and the inside of the tower is separated from the treated water chamber 11 above the partition plate 10 by a lower part. And a large number of hollow fiber modules 1 (three in the figure) from the partition plate 10 into the filtration chamber 12.
Hanging up.

Further, a bubble distribution mechanism 13 is disposed below the inside of the filtration tower 9.
The bubble distribution mechanism 13 includes a bubble distribution plate 14 and the bubble distribution plate.
And a bubble distribution pipe 15 that penetrates the hollow fiber module 1 directly below the skirt 8 of each hollow fiber module 1.
Is arranged.

In addition, one end of the treated water outflow pipe 16 and one end of the compressed air inflow pipe 17A communicate with the upper part of the filtration tower 9, and one end of the raw water inflow pipe 18, one end of the compressed air inflow pipe 17B, and the drain pipe below the filtration tower 9. One ends of the pipes 19 are communicated with each other, and further, one end of the air vent pipe 20 penetrates through a side trunk directly below the partition plate 10. Also,
Apart from the air vent pipe 20, one end of a water filling water inflow pipe 21 is communicated with a side body directly below the partition plate 10. 22 to 28
Denotes a valve, and 29 denotes a baffle plate.

The filtration method of the present invention using the filtration tower 9 will be described below by taking as an example a condensate containing raw material water and an insoluble substance such as iron oxide.

In the present invention, the following operation is performed prior to the filtration of the condensate. That is, the coating film is newly supplied from the outside, or a part of the washing wastewater containing a large amount of iron oxide fine particles obtained in the filtration chamber 12 by washing after the completion of the condensate filtration is left. An iron oxide fine particle water for coating containing an amount of iron oxide fine particles required for formation is previously hollowed in the lower part of the filtration chamber 12 and the water surface L is suspended in the filtration chamber 12 as shown by a dotted line in FIG. In this state, the valves 28 and 25 are opened and the water filling pipe 21 for water filling provided on the side body above the water surface of the coating iron oxide fine particle water is provided. For example, water for filling, such as condensate, flows into the filtration chamber 12 as slowly as possible, for example, so that most of the iron oxide fine particles are maintained below the lower end of the hollow fiber module 1. In the case of a filtration tower having a bubble distribution mechanism 13 below the inside of the filtration tower 9 as in the present embodiment, since the bubble distribution mechanism 13 serves as a baffle plate,
Even if the water for water filling flows in abruptly, the layer of the iron oxide fine particle water for coating is not disturbed, and most of the iron oxide fine particles can be kept below the lower end of the hollow fiber module 1. The flooding water flows into the filtration chamber 12 and rises in the interior of the filtration chamber 12, and then reaches the vicinity of the partition plate 10 and flows out of the filtration tower 9 through the air vent pipe 20 in the side trunk. At this time, since the inside of the filtration chamber 12 is full, the valves 28 and 25 are closed to stop filling.

In the above-mentioned filling operation, instead of flowing water from the lower part of the filtration tower 1 through the raw water inflow pipe 18 from the lower part of the filtration tower 1, that is, from below the water surface L of the iron oxide fine particle water for coating, water filling is performed as in the prior art. Surface L of iron oxide fine particle water
From above, and the majority of the iron oxide fine particles are supplied gently so as to be maintained below the hollow fiber module 1. Therefore, when the filtration chamber 12 becomes full of water, the iron oxide Most of the fine particles can be present below the lower end of the hollow fiber module 1, so that most of the iron oxide fine particles do not rise to the upper part in the filtration chamber 12 unlike the conventional case.

After completion of such a water filling operation, the valves 26 and 22 are opened to return the condensed water from the raw water inflow pipe 18 into the filtration chamber 12 as a coating film forming water by ascending flow, and the water in the filtration chamber 12 Is passed through each hollow fiber membrane 2. As the water for forming the coating film, water such as filtered water from the filtration tower 9 or pure water stored in advance may be used instead of condensed water. At this time, the iron oxide fine particles for coating existing below in the filtration chamber 12 rise in the filtration chamber 12 by the upward flow of the condensate,
At first, it flows into each hollow fiber module 1 through the opening 7 of each hollow fiber module 1 or through the circulation port 6A located below each hollow fiber module 1. At this time, from the distribution port 6B located above each hollow fiber module 1,
Filtration chamber 12 that does not contain much iron oxide particles for coating
Water flows into each hollow fiber module 1. And
The water containing a large amount of iron oxide fine particles for coating, which has flowed into the hollow fiber module 1 through the opening 7 or the flow port 6A, rises in the hollow fiber module 1 and moves along the length of each hollow fiber membrane 2 while rising inside the hollow fiber module 1. The filtration is performed on the substantially lower half membrane surface in the vertical direction, and accordingly, a coating film of iron oxide fine particles is gradually formed on the substantially lower half membrane surface of each hollow fiber membrane 2. On the other hand, the distribution port 6B
Flowing into the hollow fiber module 1 through the water, the water not containing much iron oxide fine particles flows down the inside of the hollow fiber module 1 and the upper half of the membrane surface in the longitudinal direction of each hollow fiber membrane 2 And filtered. In addition, the filtered water obtained inside each hollow fiber membrane 2 in the above-described operation rises inside each hollow fiber membrane 2 and is collected in the treated water chamber 11 above the partition plate 10, and the treated water outflow pipe Outflow from 16.

While continuing the operation as described above, the iron oxide fine particles for coating in the filtration chamber 12 also gradually rise in the filtration chamber 12 with the inflow of condensate in the ascending flow from the raw water inflow pipe 18, and finally. Reaches the vicinity of the circulation port 6B located above the hollow fiber module 1. When the iron oxide fine particles for covering reach the distribution port 6B, the iron oxide fine particles flow into the hollow fiber module 1 through the distribution port 6B. On the other hand, at this time, almost no iron oxide particles for coating are present in the vicinity of the opening 7 or the circulation port 6A located below the hollow fiber module 1, and the coating oxide is not supplied from the opening 7 or the circulation port 6A. Condensate containing almost no iron particles will flow in.

Then, the water containing the iron oxide particles for coating flowing into the hollow fiber module 1 through the circulation port 6B is substantially upper half in the longitudinal direction of each hollow fiber membrane 2 while descending in the hollow fiber module 1. And the coating film of the iron oxide fine particles is gradually formed on the film surface of almost the upper half of each hollow fiber membrane 2, and finally, the coating film on the lower half Along with the formation, a coating film can be formed on the surface of each hollow fiber membrane 2 more uniformly in the longitudinal direction than in the related art.

In other words, conventionally, the filling water was filled in the ascending flow from below the surface of the coating medium iron fine particle water, which was previously provided in the lower portion of the filtration chamber, so that the filtration chamber was filled with water. It moved upward in the chamber, and there was almost no iron oxide fine particles for coating in the lower part in the filtration chamber. Therefore, when the water for forming the coating film flows into the filtration chamber in an ascending flow thereafter, the iron oxide fine particles for coating almost flow from the opening 7 or the flow port 6A in FIG. 1 located below the hollow fiber module. Most of the iron oxide fine particles for coating
6B flows into the hollow fiber module. Therefore, the coating iron oxide fine particles hardly adhere to the substantially lower half membrane surface in the length direction of each hollow fiber membrane, and conversely, the coating iron oxide fine particles are coated on the substantially upper half membrane surface in the length direction. The result was that it adhered more than necessary. On the other hand, according to the method of the present invention, as described above, initially, the opening 7 or the flow opening 6A located below the hollow fiber module 1 is provided.
The coating iron oxide fine particles flow into the hollow fiber membrane 2 and adhere to the substantially lower half membrane surface in the longitudinal direction of the hollow fiber membranes 2. Thereafter, the coating iron oxide fine particles flow from the distribution port 6 </ b> B located above the hollow fiber module 1. As it flows in, it adheres to the substantially upper half of the surface of each hollow fiber membrane 2 in the longitudinal direction, and as a result, the surface of each hollow fiber membrane 2 is uniformly covered in the longitudinal direction. A film can be formed.

Note that, in the above-described embodiment, the case of the hollow fiber module having the flow ports only below and above the outer cylinder has been described as an example, but a number of flow ports are provided almost uniformly in the vertical direction around the outer cylinder. In the case of the hollow fiber module, the iron oxide fine particles for coating gradually flow in the filtration chamber while gradually ascending in the filtration chamber by the upward flow of water for forming the coating film, and sequentially flow into the respective membrane surfaces of the hollow fiber membranes. Become attached. Therefore, also in this case, the hollow fiber membrane is generally directed upward from below.
A coating film having a substantially uniform thickness can be formed.

After forming the coating film, the following filtration operation is continuously performed.

That is, the condensate containing the insoluble substance flows from the raw water inflow pipe 18 with the opening of the valve kept as it is. The double water flows into the inside of each hollow fiber module 1 through the opening 7 and the flow ports 6A and 6B of each hollow fiber module 1 in the same manner as in the step of forming the coating film. Through each hollow fiber membrane 2 from outside to inside. As a result, insoluble substances contained in the condensate are captured by the coating film,
An insoluble substance will adhere to the upper part of the coating film.

The filtered water in each hollow fiber membrane 2 rises inside, is collected in the treated water chamber 11, and flows out from the treated water outflow pipe 16.

By continuing such a filtration operation, when the differential pressure of the filtration tower 9 reaches a specified value, the filtration is stopped and the following washing is performed.

That is, while the valve 22 and the valve 26 are closed, the condensate flowing into the filtration chamber 12 below the partition plate 10 and the filtered water into the treated water chamber 11 above the partition plate 10 are filled with the filtered water 24 and the valve 24. 25 is opened, and compressed air flows in from the compressed air inflow pipe 17B. The compressed air rises in the filtration tower 9 as bubbles and is once received above the bubble receiver 14, and forms an air layer between the upper wall of the bubble receiver 14 and the lower end of the bubble distribution pipe 15. The bubbles rise in the skirt portion 8 of the hollow fiber module 1 through the lower end of the layer and the bubble distribution pipe 15, and then flow into each hollow fiber module 1 through the opening 7. Each hollow fiber membrane 2 vibrates due to the rise of the air bubbles, and the water in the hollow fiber module 1 is stirred, and the coating film attached to the surface of each hollow fiber membrane 2 is peeled off, and the insoluble substance is also peeled off. You. Note that the bubbles flow out of the hollow fiber module 1 through the flow port 6B of the hollow fiber module 1 and then out of the filtration tower 9 through the air vent pipe 20.

After sufficient stirring by such bubbles, the valve 24 is closed while the valve 25 is open, the valve 23 is opened, and the hollow fiber membrane 2 is opened.
The cleaning waste liquid mainly containing iron oxide peeled off from the drain pipe 19 flows out, and at this time, a part of the cleaning waste liquid is removed from the filtration chamber 12.
The remaining washing wastewater is used as water containing iron oxide fine particles having good releasability in the next formation of a coating film on the surface of the hollow fiber membrane 2.

After the above-described stirring with the compressed air and the partial discharge of the cleaning waste liquid are completed, the formation of the above-described coating film using the iron oxide fine particles in the cleaning waste liquid remaining in the filtration chamber 12 and the filtration are performed. I do.

After the cleaning drainage blow is completed, the valve 25 and the valve 27 are opened as necessary, the other valves are closed, and compressed air flows in from the compressed air inflow pipe 17A to enter the treated water chamber 11. An operation may be performed in which the existing treated water is caused to flow back through each hollow fiber membrane 2 by the air pressure, and iron oxide fine particles slightly remaining on the outer surface of each hollow fiber membrane 2 are washed off.

As the fine iron oxide particles having good releasability used in the present invention, the same fine particles as those described above as the prior art can be used. Iron oxide fine particles that can be easily peeled off in the washing step, for example, α-Fe ₂ O ₃ (hematite), α-FeOOH (goethite) and Fe ₃ O ₄ (magnetite) particles having a particle size of 1 to 10 μm. Can be mentioned.

The iron oxide fine particles are non-adhesive, and can be peeled off very easily in the washing step even if a thin coating layer is formed on the surface of the hollow fiber membrane. It should be noted that even with such iron oxide fine particles, fine particles having a particle size of 1 μ or less are not preferable because the releasability is deteriorated, and even if a coating film is formed with the fine particles having a particle size of 10 μ or more, There is a problem that iron oxide in raw water having a small target particle size passes through the coating film.

In addition, as in the case of the above-described condensate treatment, when most of the insoluble substances contained in the raw water are iron oxide,
As already described, iron oxide contained in the raw water can be used as the iron oxide fine particles having good releasability in the present invention.

Next, the thickness of the coating film of the iron oxide fine particles will be described. The present invention has a completely different technical idea from the so-called precoat filtration in which a filter aid is pre-coated on a conventional filter support. In this case, the thickness of the coating film is extremely reduced as compared with the case of the precoat type filtration.

That is, in the conventional precoat type filtration, a precoat layer is formed on a filtration support, and insoluble substances are removed by volume filtration in the precoat layer, so that the precoat layer can be subjected to volume filtration. For example, a relatively thick layer of about 10 mm is required, but the present invention simply prevents the insoluble substance that is difficult to peel off from directly adhering to the surface of the hollow fiber membrane. May be extremely thin, and usually 100 μm or less can sufficiently achieve its purpose. The thickness of the coating film can be obtained by adhering 0.5 to 10 g of the iron oxide fine particles per 1 m ² of the surface area of the hollow fiber membrane.

<Effects> As described above, according to the method of the present invention, a coating film of iron oxide fine particles can be formed on the surface of each hollow fiber membrane with a more uniform thickness in the length direction than in the related art.
Uniform filtration through the coating membrane can be performed on the entire surface of each hollow fiber membrane, and the thickness of the coating membrane becomes too thin in almost the lower half of the length direction of the hollow fiber membrane as in the related art. In this part, the problem that the intended purpose of forming the coating film cannot be achieved is solved.

The method of the present invention can be applied not only to the hollow fiber module having the structure shown in FIG. 1 but also to a hollow fiber module having any structure. Even in the case of a hollow fiber module provided with a circulation port, or a structure in which both ends of each hollow fiber membrane are opened, and filtered water obtained inside each hollow fiber membrane is taken out from both ends of each hollow fiber membrane, The present invention can be applied to a so-called double-end collecting hollow fiber module.

<Examples> Examples and comparative examples will be described below to further clarify the effects of the present invention.

Example 1.2 mm outer diameter with a micropore of about 0.2μ, inner diameter 0.7mm,
170 hollow fiber membranes having a length of 2.0 mm are bundled in an outer cylinder having a diameter of 25 mm to form a hollow fiber module as shown in FIG. 1, and one such hollow fiber module is disposed in a filtration tower. A small experimental filtration tower was constructed according to the flow shown in FIG. 2, and the following experiment was performed.

That is, ² g per 1 m ^{2 of} hollow fiber membrane,
Water (iron oxide fine particle water for coating) in which ₃ O ₄ is dispersed is preliminarily inserted into the lower part of the filtration chamber of the pre-filtration tower such that the water level is lower than the lower end of the front hollow fiber module, and then the oxidation for coating is performed. When pure water was supplied from a position above the water surface of the iron fine particle water to fill the filtration chamber, most of the iron oxide fine particles were still present in the lower part of the filtration chamber. Then, in order to form a coating film of the iron oxide on the surface of each hollow fiber membrane,
Pure water is flowed into the filtration chamber through the raw water inflow pipe connected to the lower portion of the filtration tower as water for forming a coating film, and the pure water flows from the filtration chamber toward the treatment water chamber to form a coating film. As a result of the forming operation, a substantially uniform coating film of iron oxide fine particles was formed on the surface of the hollow fiber membrane as shown in FIG. In FIG. 3, reference numeral 2 denotes a hollow fiber membrane, and reference numeral 30 denotes a formed coating film.

Comparative Example Using the same small experimental filtration tower as in the example, after the iron oxide fine particle water for coating was previously inserted into the lower part of the filtration chamber under the same conditions as in the example, the iron oxide fine particles for coating via the raw water inflow pipe was used. When pure water was supplied from below the surface of the water by an ascending flow to fill the filtration chamber, the iron oxide fine particles ascended in the filtration chamber and most of them moved to the upper part in the filtration chamber.
Next, when a coating film forming operation was performed in the same manner as in the example, the surface of the hollow fiber membrane 2 was clearly coated with a relatively thick upper portion of iron oxide fine particles in the longitudinal direction, and a lower portion thereof was coated with iron oxide. The particles were hardly coated, and as a result, an uneven coating film 30 as shown in FIG. 4 was formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a hollow fiber module used in the present invention, FIG. 2 is a flow explanatory diagram showing an example of a filtration tower used in the present invention, and FIG. FIG. 4 is a schematic cross-sectional view showing a state of formation of a coating film of iron oxide fine particles of FIG. 4, and FIG. 4 is a schematic cross-sectional view showing a formation state of a coating film in a comparative example. DESCRIPTION OF SYMBOLS 1 ... Hollow fiber module, 2 ... Hollow fiber membrane 3 ... Outer cylinder, 4 ... Upper joint part 5 ... Lower joint part, 6 ... Distribution port 7 ... Opening part, 8 ... Skirt part 9 ... Filtration tower, 10 ... Partition plate 11 ... treated water chamber, 12 ... filtration chamber 13 ... bubble distribution mechanism, 14 ... bubble distribution plate 15 ... bubble distribution pipe, 16 ... treated water outflow pipe 17 ... compressed air inflow pipe, 18 ... raw water inflow pipe 19 ... drain pipe, 20 … Air vent pipe 21… Water filling water inlet pipe, 22-28… Valve 29… Baffle plate, 30… Coating film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 65/08 B01D 63/04 C02F 1/44 B01D 37/02

Claims (3)

(57) [Claims] 1. A filter tower comprising a hollow fiber module, in which a number of hollow fiber membranes are bundled, suspended from a partition plate dividing the inside of the tower into an upper treated water chamber and a lower filter chamber. ,
Raw water containing an insoluble substance flows from the filtration chamber and the raw water passes from the outside to the inside of each hollow fiber membrane. In a filtration method in which water containing iron fine particles is passed through the hollow fiber membrane to form a thin coating film of the iron oxide fine particles on the surface of each hollow fiber membrane, the surface of each hollow fiber membrane is coated with iron oxide fine particles. When forming, in the lower part of the filtration chamber, pre-existing iron oxide fine particle water for coating containing an amount of iron oxide fine particles necessary for the formation of the coating film, then from the surface of the water of the iron oxide fine particle water for coating Filling the filtration chamber with water for filling water into the filtration chamber from the upper position so that most of the iron oxide fine particles are maintained in the lower part of the filtration chamber, and then filtering the coating film forming water. The lower part in the room And the water in the filtration chamber is allowed to pass through each hollow fiber membrane to form a coating film of the iron oxide fine particles on the surface of each hollow fiber membrane. Thereafter, filtration of the raw water is performed through the formed coating film. A filtration method using a hollow fiber membrane. 2. When most of the insoluble substances contained in raw water are iron oxides, the iron oxides obtained by filtering the iron oxides on the surface of each hollow fiber membrane and washing them are reduced in a large amount. The filtration method using a hollow fiber membrane according to claim 1, wherein the washing wastewater contained in (1) is used as iron oxide fine particle water for coating which is previously present in a filtration chamber. 3. The hollow fiber membrane according to claim 1, wherein the iron oxide fine particle water for coating is present in the filtration chamber such that the water level is lower than the lower end of the hollow fiber module suspended in the filtration chamber. Filtration method.