JPH06238135A - Permeated flux recovery method for hollow fiber filter membrane module - Google Patents

Abstract

PURPOSE:To reduce running cost and also to increase recovery and to prevent the clogging of a filter membrane by performing filtration with a circulated quantity and membrane surface linear velocity of specified values and adding a fine particle additive to raw water on the upstream side of a filter membrane module for a prescribed time in normal operation. CONSTITUTION:In a method wherein water is cleaned by the inner pressure type crossflow filtration using a hollow fiber ultrafiltration membrane module (UF module), in normal operation, water is wholly filtered while performing crossflow at circulated quantity to raw water inflow quantity ratios of >=6 exceeding zero and at 0.005-0.5m/sec membrane surface linear velocity. In baskwashing, with permeated water from the UF module 12, etc., the membrane is intermittently backwashed under pressure control or at a specified pressure at a prescribed period. Here in normal operation, a fine particle additive, such as mineral fine particles and fine cellulose fiber is added to raw water from an adding device 20 on the upstream side of the UF module 12 at intervals of at least several days for a prescribed time.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a permeation flow of a filtration membrane module when a water represented by surface water such as river water or lake water is subjected to membrane purification using a hollow fiber type ultra or microfiltration membrane module. Regarding how to recover a bundle.

[0002]

2. Description of the Related Art Conventionally, as a water purification system for obtaining tap water from surface water such as river water and lake water, it is common to go through a coagulation-precipitation-sand filtration-chlorine sterilization process. In order to realize such a process, a coagulation basin, a sedimentation basin, a sand filtration basin, and a chlorine sterilization facility are required, and there is a problem that a large installation space is required. In addition, since water sources such as rivers have been polluted in recent years, development of a new advanced water purification treatment system has been required, and it has been proposed to add an activated carbon treatment system or an ozone treatment system to the above process.

However, adding the above-mentioned activated carbon treatment system and ozone treatment system to the conventional water purification system causes a further increase in the installation space, and there is a new problem that a complicated measurement and control technique is also required. Occurs.

On the other hand, a technique for utilizing a new material called an ultrafiltration membrane or a microfiltration membrane has been proposed in various fields, and as an example, a water purification system using a hollow fiber type ultrafiltration membrane module is put to practical use. Is being considered.

An example thereof will be described with reference to FIG. Figure 7
In the above, raw water such as river water introduced through the check valve 30 is pressurized by the pump 31 and is hollow fiber ultrafiltration membrane module (hereinafter, also referred to as UF module) 3
2 is supplied. Briefly, the UF module 32 is composed of a large number of hollow fiber-shaped ultrafiltration membranes, and when raw water containing turbidity components is supplied to the inside of the hollow fiber membranes, the turbidity components are removed. Permeated water is obtained outside the hollow fiber membrane. In this way, in the UF module 32, the permeated water from which the suspended components have been removed by the filtering action of the ultrafiltration membrane,
It is supplied to the treatment facility of the next stage through the permeated water automatic valve 33.

By the way, in the UF module 32, a turbidity component that cannot be permeated is accumulated on the inner surface of the hollow fiber membrane, which causes a decrease in treatment capacity and eventually an operation stop. is there. This is realized by increasing the speed of the water flow supplied to the hollow fiber membranes of the UF module 32. That is, by applying a high-speed water flow (cross flow) to the inner surface of the hollow fiber membrane in parallel with the length direction of the yarn, the turbid component adhered to the inner surface of the hollow fiber membrane is
So to speak

Therefore, at the outlet communicating with the inside of the hollow fiber membrane in the UF module 32, a path 35 for constantly discharging a part of concentrated water containing a large amount of suspended matter through a concentrated water discharge automatic valve 34. And U to get high speed water flow
A circulation path 36 for returning the raw water supplied to the F module 32 to the suction side of the pump 31 is connected. The circulation flow rate returned to the suction side of the pump 31 is determined by the check valve 3
Compared with the flow rate of raw water supplied through 0, it is usually about 10 times or more, which is far higher. In this way, the UF module 3
The processing method of returning raw water from 2 to the suction side of the pump 31 is called a cross flow method.

Due to such cross flow, the pump 3
The capacity of 1 is much larger than the capacity of the pump in the conventional water treatment system by coagulation-sedimentation-sand filtration, which has the same capacity, and therefore the power consumption is also higher than that of the conventional pump. However, there is a problem that the running cost becomes high. In addition, the concentrated water is continuously discharged. For example, when the inflow of raw water is 1, when the permeated water is 0.3, the ratio of the concentrated water is 0.7, and Since the part is discarded, there is also a problem that the recovery rate is as bad as 30%. Here, the flow rate of the permeated water is P and the discharge rate of the concentrated water is C.
Then, the recovery rate is represented by 100 × P / (P + C) (%).

Further, even if the cross-flow is performed as described above, if the filtration membrane is used for a long period of time, the treatment capacity thereof is gradually reduced. It is presumed that the cause of this is that organic substances and the like (hereinafter referred to as “adhered substances”) in the raw water, which are difficult to remove by ordinary crossflow, adhere to the surface of the filtration membrane. Since the filtration membrane is usually used for a long period of time, it is necessary to take measures to remove such deposits.

Various techniques have been heretofore known in this field as techniques for not reducing or recovering the treatment capacity of a filtration membrane. Japanese Unexamined Patent Publication No. 4-176327 discloses a filtration device including an external pressure type hollow fiber membrane module in which a carrier present in a filtration device is moved by a water flow to bring the deposits into contact with the deposits to remove the deposits. A cleaning method is disclosed. As the carrier, spherical such as polyethylene,
It is tubular or sponge-like and has a size of about 0.5 mm to 30 mm. Japanese Patent Publication No. 56-28563 discloses a method of removing scales generated and attached to a permeable membrane filter medium by mixing solid particles in a treatment liquid only at the time of washing and positively colliding with the surface of the filtration membrane. The technology is disclosed. Japanese Patent Application Laid-Open No. 62-29986 discloses a method of separating a biotechnologically produced useful substance from a cell suspension by cross-flow microfiltration.
A technique of adding 0.05 to 1% by weight of a solid component of 0 μm or less is disclosed. As a solid component, fibrous cellulose is most suitable, and it is described that solid materials such as sodium aluminum silicate and iron hydroxide have no effect. Further, Japanese Patent Application Laid-Open No. 4-15013 discloses a technique of recovering the filtering performance by depositing fine particles on a filtration membrane, and Japanese Patent Application Laid-Open No. 4-114722 discloses a technique of using a hollow fiber membrane precoated with inorganic fine particles to remove organic substances. The liquid containing is filtered, and when the permeation amount of the liquid is lowered, the filtration is stopped for a short time, the inorganic fine particles are peeled off by backwashing and taken out of the system, and the inorganic fine particles are pre-coated on the membrane again to regenerate the filtration membrane. Japanese Patent Laid-Open No. 4-90831 discloses a method for forming a coating film of iron oxide fine particles on the surface of an external pressure type hollow fiber membrane and filtering raw water. Each is disclosed.

[Problems to be Solved by the Invention]

An object of the present invention is to reduce the running cost and increase the recovery rate in a water membrane purification treatment system using the hollow fiber type ultrafine or precision filtration membrane module, and the filtration membrane surface. It is an object of the present invention to provide a method for effectively removing the deposits adhered to the surface to recover the permeation flux.

[0012]

According to the first aspect of the present invention,
In the method of purifying water by internal pressure type cross flow filtration using a hollow fiber type ultra-precision filtration membrane module,
In normal operation, the circulation rate is more than 0 and less than 6 times the raw water inflow rate, and the membrane surface velocity is 0.005 to 0.5.
The entire amount is filtered while performing cross-flow at m / sec, and when backwashing the filtration membrane module, pressure control or a predetermined cycle is performed by permeated water from the filtration membrane module or clean water supplied separately. The hollow fiber filtration is characterized in that a particulate additive is added to the raw water on the upstream side of the filtration membrane module for a predetermined time at an interval of several days or more in the normal operation at a predetermined pressure intermittently. A permeation flux recovery method for a membrane module is provided.

In the first aspect of the present invention, the fine particle additive is preferably mineral fine particles. Hereinafter, the present invention will be described in detail.

The fine particle additive used in the present invention is substantially insoluble in water, and preferably has an average particle size in the range of 0.1 to 50 μm. Examples of such fine particles include kaolin, montmorillonite, bentonite, activated clay, acid clay, diatomaceous earth, fine cellulose fiber, wollastonite, dolomite powder, silica, halocytoclay, talc, mica, calcium carbonate, silicate, and oxidation. zinc,
Examples thereof include barium sulfate, calcium sulfate, basic magnesium carbonate, magnesium hydroxide, magnesium oxide, titanium oxide, alumina and aluminum hydroxide, and among them, kaolin, activated clay, acid clay, diatomaceous earth and silicate mineral fine particles. Alternatively, fine cellulose fibers and the like are preferable.

The filtration membrane module is most preferably made of cellulose acetate, and the shape thereof is a hollow fiber type, and an internal pressure system for introducing raw water into the hollow fiber membrane is adopted. .

It is desirable that the predetermined pressure during the backwash is substantially 1.0 times or more and 3 times or less the operating pressure during the normal operation. More preferably, it is 1.3 times or more.

The water used for the backwash may be membrane-permeated water, or clean water such as tap water finally obtained may be separately supplied. The backwashing may be time control or pressure control according to a predetermined cycle, and in the case of pressure control, it may be operated at substantially 1.3 times the operating pressure or more. The water used for backwashing preferably contains an oxidizing bactericide such as sodium hypochlorite, chlorine, hydrogen peroxide and ozone. In addition to sterilization, they have the effect of decomposing / cleaning the deposits on the film surface.

[0018]

In the present invention, an interval of several days or more, for example, 1
The particulate matter additive is added to the raw water every 0 to 20 days for a predetermined time, for example, 3 hours to remove the deposits.
The addition amount is appropriately determined depending on the degree of reduction in the treatment capacity of the filtration membrane, but is usually preferably about 10 to 50 ppm with respect to the raw water. The added particulate additive does not pass through the filtration membrane and is discharged out of the system together with the concentrated water during backwashing.

In a preferred embodiment of the present invention, in addition to the addition of the fine particle additive, the amount of water (circulation amount) of the crossflow returned to the membrane module during normal operation is reduced to the utmost limit, and the turbid component attached to the surface of the filtration membrane is removed. Is mainly achieved by pressure control or backwashing at regular time intervals. That is, by backwashing, the suspended components adhering to the surface of the filtration membrane are washed away by the backflow from the outer surface side of the hollow fiber membrane. Concentrated water is not discharged during normal operation, and the apparent total amount is filtered, and a fixed amount of cleaning water is discharged outside the system only during backwashing. Therefore, the water membrane purification system to which the present invention is applied can be said to be an apparent total amount filtration system in which a low circulation amount cross-flow filtration system is also used. In this case, if the flow rate of the permeated water is P and the discharge rate of the wash water is C, the recovery rate is 100 × (P−
It is represented by C) / P (%), and it is possible to operate at a recovery rate of 90% or more and 99% or less.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention using a UF module will be described below with reference to the drawings, but the same can be done using a microfiltration membrane module.
FIG. 1 is a schematic diagram showing a configuration example of a treatment system that implements a water purification method to which the permeation flux recovery method of the present invention is applied. A check valve 10, a pump 11, a UF module 12, which is similar to the conventional example, Permeate water automatic valve 13, cleaning water discharge automatic valve 14
In addition to the above configuration, a permeate tank 17 for accumulating permeate, a pump 18 for returning the accumulated permeate to the outlet side of the UF module 12 for backwashing, and a backwash automatic valve 19
And are provided. Furthermore, in order to remove the deposits attached to the filtration membrane, a kaolin adder 20 as a particulate additive is provided in the raw water supply line on the upstream side of the pump 11.

The operation of this processing system is performed as follows. During normal operation, the permeated water automatic valve 13 is opened, the flush water discharge automatic valve 14 and the backwash automatic valve 19 are closed, and the pump 18 is stopped. In this way, the raw water such as river water introduced through the check valve 10 is supplied to the pump 1
It is boosted by 1 and supplied to the UF module 12.
In the UF module 12, the permeated water from which the suspended components have been removed by the filtration action of the ultrafiltration membrane is accumulated in the permeated water tank 17 through the permeated water automatic valve 13. The permeated water accumulated in the permeated water tank 17 overflows and is sent to the next-stage treatment system. During this normal operation, the circulation route 16
Through this, a cross flow of more than zero and less than 6 times the inflow of raw water is performed, but the amount of permeated water is almost equal to the amount of raw water.

The backwashing is performed for 30 to 60 seconds at regular time intervals of, for example, 30 minutes to 1 hour. In this case, the raw water supply is stopped, the permeated water automatic valve 13 is closed, the flush water discharge automatic valve 14 and the backwash automatic valve 19 are both opened, the pump 11 is stopped, the pump 18 and the chemical injection pump 2
Drive 2 and. In this way, a part of the permeated water stored in the permeated water tank 17 is used to utilize the UF module 12
Is backwashed, and the turbid component stripped off from the inner wall of the hollow fiber membrane by the backwash is discharged as wash water to the outside of the system through the wash water discharge automatic valve 14. The amount of backwash water is equal to the amount of wash water discharged. As a result, even in the treatment system to which the present invention is applied, the recovery rate is 100 × P / (P + C), where P is the flow rate of the permeate and C is the discharge rate of the wash water.
Expressed in%.

In the present invention, in order to remove deposits adhering to the filtration membrane, as will be described later, the kaolin adder 20 is operated for a predetermined time at intervals of several days to ten and several days to remove kaolin. Add to raw water. Kaolin has a particle size larger than the pores of the filtration membrane, does not permeate through the filtration membrane, and serves to peel off deposits attached to the filtration membrane.
The peeled deposits and the particulate additive are discharged out of the system together with the concentrated water of the turbid component at the time of backwashing performed at intervals of tens of minutes as described above.

Hereinafter, description will be made with reference to various measurement results obtained by using the membrane cleaning apparatus shown in FIG. 2 to 5 are reference examples for examining the effect of backwashing, and kaolin was not added. FIG. 2 shows the number of operating days on the horizontal axis and the flux per unit area / time, which is also referred to as the flux on the vertical axis (hereinafter simply referred to as “flux”; the unit is liter / m ² · h;
(° C, converted to 1 kg / cm ² ).
As operating conditions, polyethersulfone having a cut-off molecular weight of 30,000 was used as the material of the UF module 12, the membrane area was 2.2 m ² , and the average operating pressure was 1 kg / cm ² .

As is apparent from FIG. 2, when the system was operated by a normal total filtration method without cross flow shown as a comparative reference example (white circled curve B in the figure), turbid components were backwashed. Is not sufficiently removed and clogging occurs, and the flux is markedly reduced over time. In the conventional method (recovery rate of 20%) in which cross-flow is performed at a membrane surface linear velocity of 1 m / sec (a ratio of the circulation rate to the raw water inflow rate is about 8 times), there is no backwash (black triangle in the figure). In curve c), the flux reduction is improved over curve a. On the other hand, when backwashing is performed at a constant cycle while performing crossflow even at a slow membrane surface linear velocity of 0.01 m / sec (circulation magnification of about 0.4 times) (in the figure, a white triangle curve B), a curve The decrease in flux is suppressed more than in b. Further, when backflowing is performed and crossflow is performed at a linear velocity of 0.1 m / sec (circulation ratio of about 4 times) (curve D in the figure, curve D), flux reduction is improved over curve C. .

FIG. 3 shows operating days (horizontal axis) and flux (vertical axis, 1
(Measured at 5 ° C.) showing the influence of the recovery rate on the relationship. As the operating conditions, cellulose acetate was used as the material of the UF module 12, the membrane area was 1.3 m ² , and the average operating pressure was 1 kg. / Cm ² , inflow rate of raw water is 100 liters /
h, membrane circulating water amount is 300 liters / h, backwash pressure is 1.5
It was set to kg / cm ² . When the recovery rate is 98%, this means that the turbidity components in the wash water discharged during backwashing are concentrated about 50 times, and when the recovery rate is 95%, this is discharged during backwashing. It means that the suspended components of the washing water are concentrated about 20 times. It is more preferable to increase the recovery rate and increase the concentration of turbid components in the wash water discharged during backwashing to reduce the amount of wastewater, but increasing the recovery rate accelerates the decline in flux, so there is a recovery rate on balance. It is necessary to set a limit value and maintain this value.
It can be seen that the recovery rate is preferably about 95%. This value represents that the amount of waste water discharged as concentrated water can be significantly reduced as compared with the method described in FIG.

FIG. 4 shows operating days (horizontal axis) and flux (vertical axis, 1
(Measured at 5 ° C.), showing the effect of backwash pressure on the relationship. As operating conditions, cellulose acetate was used as the material of the UF module 12, the membrane area was 1.3 m ² , and the average operating pressure was 1 kg / cm ² , inflow rate of raw water is 100 liters /
h, membrane circulating water amount is 300 liters / h, recovery rate is 94-
It was set to 95%. From these results, it can be understood that the higher the backwash pressure is, the lower the decrease in the flux over time is, and the higher the average operating pressure is. Gyakuarai圧is 1.5 kg / cm ² about the optimum, it can be expected that a sufficient effect of about 1.3 kg / cm ^2, thus preferably set to more than 1.3 times the average operating pressure.

FIG. 5 is a diagram showing the relationship between the number of operating days (horizontal axis) and the change in the flux (measured at 15 ° C., vertical axis) due to the membrane material of the UF module 12. The operating conditions are UF
The average operating pressure of the module 12 was 1 kg / cm ² , the inflow rate of raw water was 100 liter / h, the membrane circulating water rate was 300 liter / h, and the backwash pressure was 1.0 kg / cm ² . As is clear from the figure, it can be understood that cellulose acetate (CA) having a cut-off molecular weight of 150,000 has the highest flux and the decrease with time is also low.

Since river water often contains a large amount of hydrophobic turbidity components, it is considered that a hydrophilic membrane material is preferable for removing hydrophobic turbidity components. From the above points, U
As the membrane material of the F module 12, cellulose acetate is preferable.

FIG. 6 is a diagram showing the results of measuring the recoverability of the permeated water flux when kaolin is added to raw water according to the present invention. The operating conditions are polyethersulfone with a molecular weight cutoff of 30,000, a UF module 12 with a membrane area of 2.2 m ² , an average operating pressure of 1 kg / cm ² , a membrane circulating water volume of 300 liters / h, and a backwash pressure of 1.5 kg / cm
² The arrow in the figure indicates that kaolin is 30m against the raw water.
The time point of addition at the rate of g / liter is shown. As is clear from the figure, it is not necessary to add kaolin all the time, and the addition amount may be about 30 mg / liter. In other words,
Kaolin may be added at the time when the flux of permeate decreases, and the standard is 40 liter / m ² · h in this example.
It was confirmed to recover to 0 liter / m ² · h.

Although the embodiments of the present invention have been described above, it goes without saying that the present invention can be applied not only to surface water but also to various kinds of water.

[0032]

As described above by taking the UF module as an example, according to the present invention, since the adhered matter adhered to the filtration film, which is difficult to remove by backwashing, is also removed, it is caused by the adhered matter. It is possible to prevent clogging of the filtration membrane and recover the permeation flux of the permeation membrane module. In addition, in the water film purification system to which the present invention is applied, the amount of wasteful water discharged is extremely small in a system close to the total amount filtration. Moreover,
It is a space-saving type that does not require a coagulation tank or settling tank as in the past, and is easy to install, and the cross flow amount (circulation amount) for the UF module or precision filtration module used is much smaller than that of the conventional method. So U
A pump for supplying the raw water to the F module or the precision filtration module and for performing the cross flow does not need a large capacity pump, but may be a small pump, and the power consumption of the pump can be greatly reduced. Therefore, compared with the conventional cross flow with a large circulation amount, the running cost is reduced and the operation can be performed for a longer time.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a purifying apparatus for purifying a water film to which the present invention is applied.

FIG. 2 is a diagram showing the relationship between the number of operating days and the change in flux when the system shown in FIG. 1 is operated under various conditions.

FIG. 3 is a diagram showing the influence of the recovery rate on the relationship between the number of operating days and the flux when operating under various conditions set in the configuration shown in FIG. 1.

FIG. 4 is a diagram showing the effect of backwash pressure on the relationship between the number of operating days and the flux when operating under various conditions set in the configuration shown in FIG. 1.

FIG. 5 is a diagram showing the UF that affects the relationship between the number of operating days and the flux when various conditions are set in the configuration shown in FIG.
It is a figure showing the influence by the membrane material of module 12.

FIG. 6 is a diagram showing the results of measuring the recoverability of the flux of permeated water when kaolin is added according to the present invention.

FIG. 7 is a schematic diagram showing a configuration for carrying out a conventional purification method using a UF module.

[Explanation of symbols]

 10, 30 Check valve 11, 18, 31, Pump 12, 32 UF module 13, 33 Permeate water automatic valve 14, Wash water discharge automatic valve 17 Permeate tank 19 Reverse wash automatic valve 20 Particulate additive additive 34 Concentrated water Automatic discharge valve

Claims (3)

[Claims] 1. A method of purifying water by internal pressure type cross-flow filtration using a hollow fiber type ultra-fine filtration module or a precision filtration membrane module, wherein in normal operation, the circulation rate exceeds zero with respect to the raw water inflow rate. A total amount of 6 times or less and a cross-flow at a membrane surface linear velocity of 0.005 to 0.5 m / sec while being filtered, and when backwashing the filtration membrane module, permeated water from the filtration membrane module Alternatively, clean water supplied separately performs pressure control or intermittently at a predetermined pressure at a predetermined cycle, and in the normal operation, at a predetermined time at intervals of several days or more, at the upstream side of the filtration membrane module. A method for recovering permeation flux of a hollow fiber type filtration membrane module, which comprises adding a particulate additive to raw water. 2. The permeation flux recovery method for a hollow fiber type filtration membrane module according to claim 1, wherein the fine particle additive is mineral fine particles or fine cellulose fibers. Flux recovery method. 3. The hollow fiber type filtration membrane according to claim 1, wherein the permeated water or the clean water used for the backwash contains an oxidizing bactericide. Permeation flux recovery method for modules.