WO2009113521A1

WO2009113521A1 - Method of pretreating porous filtration membrane and method of water filtration with pretreated porous filtration membrane

Info

Publication number: WO2009113521A1
Application number: PCT/JP2009/054515
Authority: WO
Inventors: 展征近藤; 隆志大橋
Original assignee: 株式会社クレハ
Priority date: 2008-03-12
Filing date: 2009-03-10
Publication date: 2009-09-17
Also published as: JPWO2009113521A1

Abstract

A method of water filtration, characterized in that pretreated water containing coagulated particles formed by the mixing of a coagulant is passed through a porous filtration membrane comprising a synthetic resin and, during the passing, a pretreatment which is physical washing comprising back washing with treated water or/and washing by aeration is conducted at least once, before the water to be treated is passed and filtered. As a result, water pressure can be inhibited from increasing with time in the water filtration which is accompanied by physical washing and in which a porous synthetic-resin filtration membrane is used.

Description

Pretreatment method for porous filtration membrane and drainage treatment method using pretreated porous filtration membrane

The present invention relates to a pretreatment method for a synthetic resin porous filtration membrane used for sterilization of water and sewage, contamination purification, and the like, and a filtrate treatment method using a porous filtration membrane thus pretreated.

In view of the limited water resources and increasing water demand, in addition to conventional precipitation, flotation separation, sand filtration, etc., in addition to conventional precipitation, flotation separation, sand filtration, etc. There is also an increasing demand for a membrane filtration method using a porous filtration membrane made of a synthetic resin that can be reliably removed.

However, the problem with membrane filtration is that the increase in water pressure due to clogging (fouling) of the membrane due to suspended substances and organic substances in the raw water accompanying the continued operation is inevitable. However, there is a problem that periodic physical cleaning (back cleaning and air cleaning (also referred to as air scrubbing or air bubbling)) and cleaning of the membrane by chemical cleaning in a longer unit are necessary. In particular, the synthetic resin constituting the porous filtration membrane used for water purification is generally hydrophobic, and the membrane cleaning effect by physical cleaning cannot be obtained as expected, and there is a problem that the frequency of chemical cleaning increases.

On the other hand, in order to form a surface state in which fouling is unlikely to occur on the filtration membrane, a method of pre-coating a filter aid such as iron oxide (Patent Document 1), diatomaceous earth agglomerated with polyaluminum chloride, etc. A method of pre-coating a filter aid (Patent Document 2), pre-coating inorganic fine particles such as powdered activated carbon, and performing a filtration operation. When the liquid permeation amount decreases, back washing or air washing is performed to peel off the inorganic fine particles from the filter membrane. And a method for pre-coating the agglomerated particles obtained by adding a flocculant as necessary to the backwash waste water as a filter aid (Patent Document 3). Yes.

However, these conventional methods are not necessarily effective in consideration of physical washing such as back washing or air washing, which is required in normal drainage treatment. That is, in the methods of

Patent Documents

1, 2, and 4, there is a high possibility that the precoated filter aid is removed by physical washing, and the sustainability of the effect tends to be reduced. Further, in the method of Patent Document 3, collection and reuse of the precoated filter aid is scheduled, but there is a difficulty in that the operation and apparatus system of the collection and reuse are complicated.
JP-A-1-180205 JP 61-38611 A JP-A-4-114722 Japanese Patent Application Laid-Open No. 2005-118608.

DISCLOSURE OF THE INVENTION In view of the above circumstances, the main object of the present invention is to simplify and suppress the increase in filtrate pressure over time during drainage treatment with physical cleaning using a porous filtration membrane made of synthetic resin. It is an object of the present invention to provide an effective pretreatment method and a filtered water treatment method using a porous filtration membrane pretreated in this manner.

The pretreatment of the filtration membrane of the present invention has been developed in order to achieve the above-mentioned object, and more specifically, a porous filtration membrane made of a synthetic resin is allowed to pass water containing agglomerated particles by mixing a flocculant. It is characterized by performing physical cleaning consisting of backwashing and / or air cleaning at least once in the middle of the water treatment.

The present invention also provides a filtration membrane having a thin layer of agglomerated particles obtained by application of the above pretreatment method. Furthermore, in the filtered water treatment method of the present invention, water containing agglomerated particles by mixing a flocculant is passed through a porous filtration membrane made of a synthetic resin, and backwashing and / or air washing with treated water at least once during the process. After performing the pre-processing which performs the physical washing which consists of, it is characterized by performing water flow and filtration of to-be-processed water.

The inventors will add a few words about how they reached the present invention for the above-mentioned purpose. The surface of the porous membrane of polluted particles that causes the increase in the water flow resistance of the porous filtration membrane accompanying the continuation of the filtered water treatment by repeatedly conducting the drainage treatment of the water to be treated containing organic pollutants by the present inventors When the SEM (scanning electron microscope) observation of the deposited particle layer (cake layer) formed by adhesion and deposition on the surface and the measurement of the water flow resistance were repeated, the cake layer passed water in a relatively loose flock shape. It has been found that there are those that are less likely to cause an increase in resistance, and those that are consolidated in a cake shape and that significantly increase the water flow resistance. In physical cleaning, the floc-like sedimentary particle layer is easily removed, and it is difficult to increase the water flow resistance with continuous drainage treatment. However, the consolidated cake-like sedimentary particle layer is difficult to remove even by physical cleaning. It is considered that the bottom layer is likely to remain, and the water flow resistance increases relatively quickly in the continuation of the filtered water treatment with physical cleaning. Therefore, the idea that pre-treatment that facilitates the formation of a floc-like sedimentary particle layer on the porous filtration membrane prior to the drainage treatment can alleviate the increase in water flow resistance that accompanies the drainage treatment. As a result of examining various pretreatment methods for porous filtration membranes, it was found that formation of an agglomerated particle layer by passing water to be treated with a flocculant added thereto was appropriate. The agglomerated particle layer formed in this way is understood to be the same as the agglomerated particle layer formed when the flocculant is added to the backwash water and the water is formed through the water in Patent Document 4. . However, the porous filtration membrane having the agglomerated particle layer pretreated as described above has a poor effect of preventing increase in water flow resistance in the continuation of the filtered water treatment with physical cleaning.

On the other hand, as a result of further investigations, the present inventors have conducted backwashing with treated water or / at least once during the pretreatment of the porous filtration membrane by passing water to be treated with the above-described flocculant added. And adding a physical cleaning step consisting of air cleaning is effective for suppressing increase in water flow resistance during continuous filtration with physical cleaning, and the above-described pretreatment method for the filtration membrane of the present invention and The drainage treatment method has been reached.

In the method of the present invention, the physical cleaning step is effective during pretreatment by passing water to be treated with a flocculant added (see FIG. 6 showing the results of Examples 3 and 4 and Comparative Example 4 below). Although it is not always clear, the present inventors are considering a mechanism as shown in FIGS. 1 (a) to 1 (c). That is, the agglomerated particle layer formed by one continuous flow of water to be treated to which a flocculant is added tends to be formed in a bridge shape on the surface layer of the porous film as shown in FIG. Many of them are apt to be removed as shown in FIG. 1 (b) when continuing the water treatment with physical cleaning. In contrast, by placing the physical cleaning step at least once during the pretreatment, the agglomerated particle layer formed on the surface layer excluding those adhering to the pore inlet was removed as shown in FIG. As shown in FIG. 1 (c), the water containing the aggregated particles subsequently adheres again to a larger proportion of the surface including the pore inlets, and the filtered water with physical cleaning. It acts as a stable pre-treatment underlayer that contributes to the formation of a floc-like deposited particle layer thereon that is not removed during the continuation of the treatment.

The film thickness direction schematic cross section which shows the presumed mechanism of aggregated particle thin layer formation to the porous filtration membrane surface by the pre-processing method of this invention. The schematic arrangement | positioning figure which shows an example of the apparatus system suitable in order to implement the pre-processing method and filtered water processing method of the filtration membrane of this invention. The plot which shows the time-dependent change of the transmembrane differential pressure during the filtered water treatment using the filtration membrane of Example 1 and Comparative Example 1. The plot which shows the time-dependent change of the transmembrane differential pressure during the filtered water treatment using the filtration membrane of Example 2 and Comparative Example 2. The plot which shows the time-dependent change of the transmembrane differential pressure during the filtered water treatment using the filtration membrane of Example 3 and Comparative Examples 3 and 4. The plot which shows the time-dependent change of the transmembrane differential pressure during the filtered water treatment using the filtration membrane of Examples 3, 4 and Comparative Example 3. The schematic arrangement | positioning figure which shows another example of the apparatus system suitable in order to implement the pre-processing method and filtered water processing method of the filtration membrane of this invention. The plot which shows the time-dependent change of the transmembrane differential pressure during the suction filtered water treatment using the filtration membrane of Example 5 and Comparative Example 5.

Hereinafter, preferred embodiments of the pretreatment method and the filtered water treatment method of the filtration membrane according to the present invention will be described in more detail.

(Porous filtration membrane)
In the present invention, the increase in the drainage pressure accompanying the continuation of the filtered water treatment is intended to suppress the organic pollutant particles contained in the water to be treated in the porous filter membrane made of synthetic resin which is generally hydrophobic to some extent. This is caused by adhesion and clogging. Therefore, the method of the present invention can be applied to porous filter membranes made of a wide variety of synthetic resins such as eletin resins, vinylidene fluoride resins, ether sulfone resins, and the like. Vinylidene-based resins are preferred, and particularly vinylidene fluoride-based resins that are excellent in weather resistance, chemical resistance, heat resistance, and strength (that is, vinylidene fluoride homopolymers or copolymers containing 70 mol% or more of vinylidene fluoride) Is preferably used.

Many methods for forming these porous filtration membranes are known for each resin, and these methods may be used. Among them, a stretched porous membrane including a stretching process for increasing the porosity and the fine pore diameter is preferable. Is also preferred for improving the strength and forming the pretreated aggregated particle layer.

As a form of the porous filtration membrane, a flat membrane or a pleated flat membrane shape is not used, but a large membrane area per unit volume of the filtration device is given, and physical washing such as back washing and air washing A hollow fiber membrane shape that can be easily formed into a module shape suitable for the above is more preferable.

The general physical properties of porous filtration membranes suitable for application of the method of the present invention are as follows: Average by half dry / bubble point method (ASTM F316-86 and ASTM E1294-86) The pore diameter is 0.05 to 0.5 μm, preferably 0.08 to 0.25 μm, more preferably 0.13 to 0.25 μm, the maximum pore diameter is 0.1 to 1 μm, preferably 0.15 to 0.5 μm, More preferably 0.2 to 0.4 μm; a film thickness of 0.1 to 0.5 mm, preferably 0.2 to 0.4 mm, more preferably 0.2 to 0.3 mm; a hollow fiber membrane as a preferred form In this case, the outer diameter is 1 to 2.5 mm, preferably 1 to 2 mm, more preferably 1.2 to 1.5 mm; the inner diameter is 0.5 to 2 mm, preferably 0.6 to 1.6 mm, more preferably 0.8-1mm, etc.

(Filter system)
The porous filter membrane as described above is subjected to the pretreatment of the present invention and used for filtered water treatment (filtration operation). FIG. 2 is a schematic layout diagram of an example of an apparatus system suitable for carrying out the pretreatment method and the drainage treatment method of the present invention. Hereinafter, preferred embodiments of the pretreatment method and the drainage treatment method of the present invention will be described more specifically with reference to FIG. 2 as necessary.

(Pre-processing method)
In accordance with the present invention, pretreatment water for pretreatment by passing water through the porous filtration membrane as described above is generally obtained by adding a flocculant to water (raw water) containing insoluble organic substances. It is done. Raw material water in which aggregated particles are formed by adding a flocculant in surface water (river water, lake water) or the like is preferable. For example, when used in the apparatus system shown in FIG. 2, it is generally easy to use the water to be treated (raw water) to be purified by the filtration operation as long as it contains the necessary insoluble organic matter. In tank 2, a flocculant such as sulfuric acid band, polyaluminum chloride, ferric chloride, polysilica iron, etc. was added and held for about 10 minutes to 1 day with stirring as necessary, and formation of aggregated particles was confirmed visually. Later, water can be passed for pretreatment. The addition amount of the flocculant is about 0.5 to 100 mg / L, and it is preferable to select optimum aggregated particle forming conditions by a preliminary test (jar test) according to the raw material water and the flocculant used. If necessary, a flocculant may be added after adjusting the pH of the raw material water to a suitable one for aggregation. However, turbidity such as domestic wastewater is high, and there are many soluble organic substances (for example, MLSS (suspended substance concentration) is 1000 mg / L or more or / and soluble COD (chemical oxygen demand) is 10 mg / L or more. ) When filtering the water to be treated (Example 5 etc. described later), it is preferable to separately use pretreated water obtained by adding a flocculant to surface water or the like.

The pretreated water thus prepared generally has a turbidity (JIS K0101) of 0.1 or more, preferably 0.1 to 200, more preferably 1 to 5. Further, the chromaticity (JIS K0101) is preferably 0 to 100, more preferably 0 to 30, and still more preferably 0 to 20.

The prepared pretreated water is sent from the tank 6 to a porous filtration membrane disposed in a filtration device 8 (in this case, a vertical cylinder type module) for pretreatment. The apparatus may be either a pressure type or an immersion type, and the porous filtration membrane can be used in the form of a module or an element, but is basically arbitrary.

As an operation method during the pretreatment, referring to FIG. 2, a total amount filtration method for sending treated water to the treated water tank 10 through the whole amount pipe 9 or a circulating filtration method for returning a part of the treated water to the raw water tank 6 through the pipe 12. Either of these is acceptable.

While observing the increase in filtrate pressure (transmembrane differential pressure) during water flow (filtration treatment) for pretreatment, backwashing the treated water stored in the treated water tank 10 from the filtrate side of the membrane in a timely manner. In general, it is necessary to remove aggregated particles that are excessively deposited and deposited on the stock solution side of the membrane by air flow (to the stock solution side) or air cleaning (supplying air from the bottom pipe 13 to the stock solution side of the membrane to cause bubbling). Yes, if this is not done, the filtration pressure will increase excessively during pretreatment. In particular, in the method of the present invention, it is necessary to perform physical cleaning consisting of backwashing and / or air washing at least once during the pretreatment. This is because, by performing physical cleaning as described above, the state shown in FIG. 1A changes from the state shown in FIG. 1B to the state shown in FIG. 1B, thereby increasing the probability that the aggregated particles effectively adhere to the pore surface. it is conceivable that. In addition, the aggregate particle layer when backwashing and air washing are both performed during pretreatment is about 0.1 μm, which is thinner than about 3 μm when only backwashing is performed. There is not so much difference (see the results of Examples 3 and 4 shown in FIG. 6 below). That is, the effect of suppressing the increase in the filtered water pressure by the pretreatment of the present invention is a thin layer of about 0.1 μm (SEM-EDX (Scanning ElectronｓEnergyDispersive X-ray) adhering to the surface of the filtration membrane formed during the pretreatment. It is presumed that the layer of aggregated particles) is most contributing by spectroscopic analysis.

Physical washing conditions include, for example, 1 minute of backwashing for 30 minutes of filtration; 3 minutes of air washing for 3 hours of filtration, but when the turbidity of the pretreatment water (flocculating agent added water) is high It is preferable to suppress the increase in drainage pressure during pretreatment by increasing the frequency of each cleaning, or improving the cleaning efficiency by increasing the amount of air in backwashing flux or air cleaning. The waste water from the physical washing is discharged from the bottom of the apparatus 8 to the outside of the system.

The membrane may be chemically cleaned by adding chemicals such as sodium hypochlorite to the backwash water. If the concentration is 50 ppm or less, the aggregated particle thin layer is hardly removed. The same applies to radical physical cleaning. The effect of strong adhesion of the agglomerated particle thin layer to the porous membrane is thought to be strengthened by increasing the pretreatment time or by repeating backwashing, air washing, etc. It has also been confirmed by pretreatment for 1 hour including backwashing (Example 2 described later).

(Water treatment)
The filtered water treatment itself using the porous filtration membrane pretreated as described above is not particularly different from general filtered water treatment. In the apparatus system shown in FIG. 2 described above, treated water (raw water) directly supplied to and stored in the tank 6 is supplied to the filtered membrane after the pretreatment held in the apparatus 8 via the pump 7. Drained.

The operation itself is the same as that in the pretreatment except that conditions under which the filtrate pressure hardly rises can be set independently of the pretreatment conditions according to the quality of the raw water. While performing the backwashing and air washing with the treated water stored in the tank 10 as necessary while observing the increase in the filtrate pressure, the low concentration chemical cleaning agent can be mixed in the backwashing water as well. It is.

Hereinafter, the pretreatment method and drainage treatment method of the porous filtration membrane of the present invention will be described more specifically with reference to Examples and Comparative Examples.

<< Example of Porous Filtration Membrane Production >>
(Production Example 1)
A hollow fiber porous membrane made of polyvinylidene fluoride (PVDF) was produced as follows.

Main polyvinylidene fluoride (PVDF) (powder) having a weight average molecular weight (Mw) of 4.12 × 10 ⁵ and polyvinylidene fluoride (PVDF) (powder) for crystal property modification having an Mw of 9.36 × 10 ⁵ Were mixed at a ratio of 95% by weight and 5% by weight, respectively, using a Henschel mixer to obtain a PVDF mixture having an Mw of 4.38 × 10 ⁵ .

Adipic acid polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.) as the aliphatic polyester and N-methylpyrrolidone (NMP) as the solvent were 77.5 wt% / 22.5 wt% The mixture was stirred and mixed at room temperature to obtain a plasticizer / solvent mixture.

Using a co-rotating meshing twin screw extruder (“BT-30” manufactured by Plastic Engineering Laboratory Co., Ltd., screw diameter 30 mm, L / D = 48), powder provided at a position 80 mm from the most upstream part of the cylinder A PVDF mixture is supplied from the supply unit, and a plasticizer / solvent mixture heated to a temperature of 160 ° C. from a liquid supply unit provided at a position 480 mm from the most upstream part of the cylinder is PVDF mixture / plasticizer / solvent mixture = 35. 7 / 64.3 (% by weight) is supplied and kneaded at a barrel temperature of 220 ° C. The kneaded product is hollow fiber-shaped at a discharge rate of 7.6 g / min from a nozzle having a circular slit with an outer diameter of 7 mm and an inner diameter of 5 mm. Extruded to. At this time, air was injected into the hollow portion of the yarn at a flow rate of 4.2 mL / min from a vent provided in the center of the nozzle.

The extruded mixture is maintained in a molten state at a temperature of 40 ° C. and is led to a water cooling bath having a water surface at a position 280 mm away from the nozzle (ie, an air gap of 280 mm), and is cooled and solidified (in the cooling bath). Was taken up at a take-up speed of 5 m / min, and then wound around a case having a circumference of about 1 m to obtain a first intermediate molded body.

Next, the first intermediate molded body is immersed in dichloromethane at room temperature for 30 minutes while being vibrated, then the dichloromethane is replaced with a new one and immersed again under the same conditions to extract the plasticizer and the solvent, and then Heating was performed in an oven at 120 ° C. for 1 hour to remove dichloromethane and heat treatment was performed to obtain a second intermediate molded body.

Next, the second intermediate molded body was passed through a 60 ° C. water bath at a first roll speed of 8.0 m / min, and the second roll speed was set at 17.6 m / min to achieve the longitudinal direction. The film was stretched 2.2 times. Next, the sample was passed through a warm water bath controlled at a temperature of 90 ° C., and the third roll speed was reduced to 15.1 m / min, whereby a 14% relaxation treatment was performed in warm water. Further, a 4% relaxation treatment was performed in the dry heat bath by passing it through a dry heat bath (2.0 m length) controlled to a space temperature of 140 ° C. and dropping the fourth roll speed to 14.5 m / min. This was wound up to obtain a polyvinylidene fluoride hollow fiber porous membrane (third molded body) according to the method of the present invention.

The obtained PVDF hollow fiber porous membrane had an outer diameter of 1.275 mm, an inner diameter of 0.836 mm, a porosity of 69.9%, and an average pore diameter Pm (half dry method) = 0.135 μm.

(Production Example 2)
The ratio of both in the plasticizer / solvent mixture is 82.5% / 17.5% by weight, the raw material discharge rate is 16.7 g / min, and the air flow rate from the vent provided in the center of the nozzle is 9.5 mL / min. Minutes, water bath temperature 40 ° C, take-up speed 11.0 m / min, draw ratio 1.85 times, first stage relaxation wet heat 90 ° C 8%, second stage relaxation dry heat 140 ° C 4% A PVDF hollow fiber porous membrane was obtained in the same manner as in Production Example 1 except that each was changed. The obtained PVDF hollow fiber porous membrane had an outer diameter of 1.368 μm, an inner diameter of 0.878 μm, a porosity of 71.1%, and an average pore diameter Pm = 0.115 μm.

<< Example >>
Example 1
A portion corresponding to a membrane area of 5 m ² on the basis of the outer surface of the PVDF hollow fiber porous membrane obtained in Production Example 2 is inserted into the external pressure type vertical cylindrical module 8 of the apparatus system shown in FIG. went.

<Pretreatment>
As raw water to be used, the surface water of turbidity 1-2 degrees (Shikawa River, Iwaki City, Fukushima Prefecture) was put into mixing tank 2 with

stirrer

4, and 20 ppm of polyaluminum chloride (Daimei Chemical Industry Co., Ltd.) was added. By mixing for about 1 hour with stirring, pretreated water with turbidity of 2 to 3 degrees was obtained. This pretreated water is sent to the filtration membrane in the module 8 with a filtration flux of ² m ³ / m ² / day, and the external pressure type total filtration is continued for 30 minutes, and the filtration flux of 1.5 is filtered with the treated water in the tank 10. Repeat the operation of backwashing at the double flow rate for 1 minute and discharging the washing drainage from the bottom pipe 14, and air at a flow rate of 30 L / min from the bottom of the module 8 instead of backwashing once every 3 hours of filtration. After feeding, cleaning (scrubbing) was performed for 3.5 minutes. Pretreatment for a total of 1 day was performed by repeating the pretreatment of the above cycle.

<Drainage treatment>
The river surface water with a turbidity of 1 to 2 equivalent to that used in the pretreatment is supplied to the raw water tank 6 as it is, and the water in the tank 6 is further supplied to the module 8 including the filtration membrane after the pretreatment. A filtered filtration operation was performed in which filtered water treatment was performed and 15% of the treated water was returned to the raw water tank 6. Filtration was continued for 30 minutes at a feed water flux of 1.75 m ³ / m ² / day to membrane 8 and then backwashed for 1 minute with 1.5 times the flux until another 3 hours Air washing was performed at a flow rate of 30 L / min for 4 minutes every time. With the above as one cycle, the filtration operation was performed for about 6 days.

(Comparative Example 1)
Using the apparatus system shown in FIG. 2, the PVDF hollow fiber membrane obtained in Production Example 2 was inserted into the vertical cylinder module 8 in the same manner as in Example 1, and directly without performing pretreatment with flocculant-added water, Filtration operation was continued under the same conditions as in Example 1 using river surface water having a turbidity of 1 to 2 equivalent to that used in Example 1 stored in tank 6.

During the filtration operation of Example 1 and Comparative Example 1, 25 ° C. corrected inter-membrane differential pressure, that is, the actual value of the differential pressure generated between the upstream and downstream of the filtration membrane, coefficient: (viscosity of 25 ° water) Next, the corrected transmembrane pressure difference obtained by multiplying / (viscosity of water at the temperature at the time of filtration) was measured successively. The results are summarized and shown as a plot in FIG.

Referring to FIG. 3, in Comparative Example 1 in which the filtration operation was performed immediately using a filtration membrane without pretreatment, the transmembrane differential pressure was low at the beginning of the operation, but the differential pressure rapidly increased thereafter. Thus, in Example 1 using the pretreated filtration membrane, it can be seen that the increase in the transmembrane pressure difference accompanying the continuation of the filtration operation is remarkably suppressed. Regarding Example 1, since the transmembrane pressure difference was measured during the pretreatment, the measured value plot is also shown before the operation time of 0 days.

(Example 2)
The effect of pretreatment in a shorter time was confirmed. That is, as pretreatment water, the same one as in Example 1 and Comparative Example 1 was used, and the PVDF hollow fiber membrane of Production Example 1 was filtered for 30 minutes → backwashed for 1 minute → filtered for 30 minutes → air washed 3 Pre-treatment for 5 minutes was performed. The filtration flux, backwash flux and air flow rate were the same as in Example 1.

About the filtration membrane (membrane area 5m < ² >) after the said pre-processing, the filtration operation was performed on the conditions similar to Example 1. FIG.

(Comparative Example 2)
A filtration operation was performed in the same manner as in Example 2 except that the PVDF hollow fiber membrane of Production Example 1 was used without pretreatment.

The changes over time of the 25 ° C. corrected transmembrane pressure difference in Example 2 and Comparative Example 2 are plotted in FIG. FIG. 4 shows that the effect of the present invention can be sufficiently obtained even with a short pretreatment of 1 hour.

(Example 3)
Except for using the PVDF hollow fiber membrane of Production Example 1, pretreatment and drainage treatment (filtration operation) were performed in the same manner as in Example 1.

(Comparative Example 3)
A filtration operation was performed in the same manner as in Example 3 except that a hollow fiber membrane without pretreatment was used.

(Comparative Example 4)
In the pretreatment, the pretreatment and the filtration operation were performed in the same manner as in Example 3 except that physical washing (back washing and air washing) was not performed.

The changes over time in the transmembrane pressure difference during the pretreatment and filtration operation are shown together in FIG.

In Comparative Example 4 in which physical cleaning was not performed in the pretreatment, it was found that the increase in the transmembrane pressure difference during the pretreatment was remarkable, and the effect of suppressing the increase in the transmembrane pressure difference during the filtration operation was poor.

Example 4
In the pretreatment, pretreatment and filtration operation were performed in the same manner as in Example 3 except that backwashing was performed instead of air washing performed once every 3 hours.

FIG. 6 shows the change over time in the transmembrane pressure difference during the filtration operation together with the results of Example 3 and Comparative Example 3. That is, it can be understood that the effect of suppressing the increase in the transmembrane pressure difference of the present invention can be obtained essentially by only one of the back washing and the air washing.

The thickness of the aggregated particle layer after the pretreatment by SEM observation is about 0.1 μm in the system (Examples 1 to 4) in which backwashing and air washing are used in combination, whereas only the backwashing example. No. 5 is as thick as about 3 μm. In any case, it can be seen that the extremely thin aggregated particle layer formed on the surface layer by the pretreatment shows the effect of suppressing the increase in transmembrane pressure difference during the filtration operation of the present invention.

(Example 5)
A portion equivalent to a membrane area of 0.5 m ² on the basis of the outer surface of the PVDF hollow fiber porous membrane obtained in Production Example 1 above is immersed in a module built-in tank 8A shown in FIG. 7 for pretreatment and drainage treatment. went.

stirrer

4, and 20 ppm of polyaluminum chloride (Daimei Chemical Industry Co., Ltd.) was added. By mixing for about 1 hour with stirring, pretreated water with turbidity of 2 to 3 degrees was obtained. This pretreatment water was sent to the membrane exposure module built-in tank 8A, and continuously filtered with a filtration flux of ² m ³ / m ² / day in a form of water absorption from the inside of the filtration membrane by an operation pump (suction) 7A. During filtration, air 13 was constantly supplied to the cross-sectional area of the tank 8A at a flow rate of 100 m ³ / m ² / h for bubbling, and pretreatment was performed for a total of one day.

<Drainage treatment>
Activated sludge water (MLSS: 7000 mg / L, soluble COD: 13 mg / L) from general domestic wastewater is used as the filtered raw water 11, and this raw water is supplied to the membrane in the tank 8 A and filtered at 0.8 m / day. The filtered water treatment operation was performed with the flux. Filtration was performed in a cycle in which the operation pump (suction) 7 was subjected to suction filtration for 13 minutes and then rested for 1 minute. At a flow rate of 100m ³ / ^m 2 / h for the during operation the cross-sectional area of the constantly air 13 tank 8A, was blown into.

(Comparative Example 5)
Using the system shown in FIG. 7, a vertical membrane exposure module having a membrane area of 0.5 m ² formed in the same manner as in Example 5 is immersed in the tank 8A and the same as in Example 5 except that no pretreatment is performed. Water treatment was performed.

FIG. 8 shows changes in filtrate pressure (corrected transmembrane pressure difference) during the drainage operation in Example 5 and Comparative Example 5 described above. According to FIG. 8, in Example 5 which performed the pre-processing, it turns out that the raise of the filtrate pressure accompanying continuation of drainage operation is remarkably reduced.

As described above, according to the present invention, a simple and effective pretreatment method for suppressing an increase in filtrate pressure over time in a drainage treatment involving physical cleaning using a porous filtration membrane made of a synthetic resin, and A filtered water treatment method using the porous filtration membrane pretreated in this way is provided.

Claims

Pretreatment water containing agglomerated particles by mixing a flocculant is passed through a porous filtration membrane made of a synthetic resin, and at least once in the middle, physical washing consisting of backwashing with treatment water and / or air washing is performed. A pretreatment method for a filtration membrane.
The pretreatment method for a filtration membrane according to claim 1, wherein the synthetic resin comprises a vinylidene fluoride resin.
The pretreatment method for a filtration membrane according to claim 1 or 2, wherein the porous filtration membrane has a hollow fiber shape.
The pretreatment method according to any one of claims 1 to 3, wherein the turbidity of the pretreatment water is 0.1 or more.
The pretreatment method according to any one of claims 1 to 4, wherein the porous filter membrane has an average pore size of 0.05 to 0.5 µm.
A filtration membrane having a thin layer of aggregated particles formed by the method according to any one of claims 1 to 5.
Pretreatment water containing aggregated particles resulting from mixing of a flocculant is passed through a porous filtration membrane made of a synthetic resin, and at least once during the pretreatment, physical washing consisting of backwashing with treatment water and / or air washing is performed. The filtered water treatment method is characterized in that after treatment, water to be treated is passed and filtered.
The drainage treatment method according to claim 7, wherein the synthetic resin is a vinylidene fluoride-based resin.
The filtered water treatment method according to claim 7 or 8, wherein the porous filtration membrane has a hollow fiber shape.
The filtered water treatment method according to any one of claims 7 to 9, wherein an air washing treatment is performed during the pretreatment in addition to the backwashing with the treatment water.
The filtered water treatment method according to any one of claims 7 to 10, wherein the water containing the aggregated particles by mixing the flocculant is obtained by mixing the flocculant in the water to be treated.
The filtered water treatment method according to any one of claims 7 to 11, wherein backwashing and / or air washing treatment with treated water is performed when water to be treated is passed and filtered.
The filtered water treatment method according to any one of claims 7 to 12, wherein the pretreated water is obtained by adding aggregated particles to water to be treated comprising natural surface water.
The filtered water treatment method according to any one of claims 7 to 12, wherein the pretreated water is obtained by adding aggregated particles to natural surface water, and the water to be treated has a turbidity greater than that of the pretreated water. .