JPH0724264A - Filtering method using hollow fiber membrane module - Google Patents

Abstract

PURPOSE:To efficiently clean membranes of the whole module and to suppress decrease in the effective membrane area by arranging a sheet-type planer hollow fiber membrane module in such a manner that the sheets of the module are vertically arranged when a liquid is filtered while the module is scrubbed with air from the lower side of the module. CONSTITUTION:When a liquid is filtered while the sheet-type planer hollow fiber membrane module 2 is scrubbed with air introduced from the lower side of the module through a diffuser pipe 4. The module 2 is arranged with the sheet plane vertically disposed. Thereby, whole of the module can efficiently be cleaned so that decrease in the effective membrane area or clogging of the membrane can be suppressed. Especially, for filtering highly polluted water, the cleaning efficiency is improved and clogging of the membrane is suppressed so that a high filtering flow rate can be maintained for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration method using a hollow fiber membrane module, and more particularly to a filtration method suitable for filtering a highly polluted liquid with a hollow fiber membrane module.

[0002]

2. Description of the Related Art Conventionally, hollow fiber membrane modules have been manufactured using sterile water,
It has been widely used in the field of so-called microfiltration such as the production of drinking water and high-purity water and the purification of air, but in recent years it has been highly polluted by secondary treatment, tertiary treatment in sewage treatment plants and solid-liquid separation in septic tanks Various studies have been conducted for use in water treatment applications.

Since the hollow fiber membrane module used for such an application has a large clogging of the hollow fiber membrane during the filtration treatment, after the filtration treatment for a certain period of time, air is sent to vibrate the hollow fiber membrane and the membrane surface is cleaned. The membrane surface is repeatedly washed, for example, by passing treated water in the opposite direction to the filtration treatment.

However, the hollow fiber membrane module used in these fields is of a cylindrical type in which hollow fiber membranes are concentrically arranged in a circular shape or a concentric circle which has been used in the field of conventional microfiltration. Was almost all.
Further, even if improvements are made, many of them merely change the filling rate or filling form of the hollow fiber membrane.

[0005]

Highly polluted water (for example, ss ≧ 5) is obtained by using such a conventional hollow fiber membrane module.
When the filtration treatment (0 ppm, TOC ≧ 100 ppm) is performed, the hollow fiber membranes are fixed (adhered) and integrated with each other through the deposits such as organic substances attached to the surface of the hollow fiber membranes during use. As a result, the effective membrane area of the hollow fiber membrane in the module was reduced, and the filtration flow rate was rapidly reduced.

Further, even when the hollow fiber membrane module in which the hollow fiber membranes are fixed and integrated as described above is regularly subjected to membrane surface cleaning or backwashing, it is not easy to recover the function of the module once fixed and integrated. However, there was a decrease in cleaning efficiency.

As a solution to this problem, a hollow fiber membrane module is replaced with a concentrating hollow fiber membrane module, and the hollow fiber membranes are arranged in a sheet form.
A hollow fiber membrane module in which one end or both ends of a hollow fiber membrane are fixed by fixing members in one or two different housings while maintaining open states, respectively, and are perpendicular to the hollow fiber membrane of the fixing member. There has been proposed a hollow fiber membrane module in which all the cross-sectional shapes are elongated and substantially rectangular.

In such a sheet-shaped flat hollow fiber membrane module, the hollow fiber membranes can be evenly arranged in the inner and outer layers with a space between layers, and the surface of the hollow fiber membranes can be cleaned during membrane surface cleaning. It is a module suitable for filtering highly polluted water because it makes it extremely easy to wash it evenly, and can prevent the deterioration of filtration efficiency as it has been so far.

The membrane surface of the flat type hollow fiber membrane module is washed by a method such as vibrating the yarn by air scrubbing.
When stacking and fixing a plurality of modules vertically with the seat surface horizontal, and sending air from below the modules to perform scrubbing cleaning, air bubbles hit one to three modules from the bottom. However, for the modules above it, it is difficult for air bubbles to pass between the hollow fibers, and because the air bubbles pass through the outside of the module, that is, the part without the hollow fiber membrane, the membrane surface cleaning is efficient in the module above. Sometimes it's not done well.

Therefore, in order to perform air scrubbing uniformly on each module, the modules are not laminated,
If the seat surfaces are horizontal and they are arranged side by side, the can body and tank will be larger than necessary.

In addition, at the place where the air bubbles do not pass, there is a problem that the suspended substance settles, deposits, or adheres to the sheet surface to reduce the effective membrane area and promote clogging.

The present invention solves such a problem in the filtration of a liquid, particularly highly polluted water, using a sheet-shaped flat hollow fiber membrane module. An object of the present invention is to provide a filtration method using a membrane module, which is capable of efficiently cleaning the entire membrane surface of the module and suppressing the reduction of the effective membrane area and the progress of clogging of the membrane surface. .

[0013]

Means for Solving the Problems That is, the gist of the present invention is that when a liquid is filtered from below a sheet-like flat hollow fiber membrane module while continuously or intermittently scrubbing with air, the sheet surface is vertical. The module is arranged so that

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing an example of a method for supporting a hollow fiber membrane module in a filtration method using a sheet-shaped flat hollow fiber membrane module according to the present invention, in which a sheet surface is made vertical in a can or a tank, It is a perspective view when a module is fixed with the longitudinal direction of the hollow fiber membrane horizontal and three modules are arranged side by side. 1 is a water collecting pipe,
Reference numeral 2 is a hollow fiber membrane, 3 is a hollow fiber membrane focusing end portion, and 4 is an air diffuser.

In the flat hollow fiber membrane module used in the present invention, the hollow fiber membranes arranged in a sheet shape are fixed by potting resin with both ends or one end kept open, and the hollow fiber membrane openings Is connected to a water collection pipe.

The hollow fiber membrane is not limited to one in which only one end is open and connected to the water collecting pipe, but the hollow fiber membrane is fixed in a state where both ends are kept open and has water collecting pipes at both ends. It doesn't matter. That is, in each drawing, the hollow fiber collecting end portion 3 may be a water collecting pipe.

When fixing the module, the hollow fiber membrane 2 needs to be appropriately relaxed, but if the relaxation is taken too much, the hollow fiber membrane becomes buoyant and bowed, and the width of vibration of the hollow fiber membrane increases. By doing so, the stress due to buckling at the potting resin cured part that fixes the hollow fiber converging end and the base of each hollow fiber membrane becomes large, and the strength of the interface part decreases, so that the resin cured part and the hollow fiber membrane are reduced. The hollow fiber membrane may be cracked or cut in between. Relaxation rate when fixed is 3%
It is more preferable to be within 1%.

As a method of fixing the module, any method such as a method of fixing with a stand or a clamp in the tank or the inside of the can or a method of fixing with a dedicated jig can be used, but the module moves during air scrubbing or the like. It does not matter if it is a fixing method that does not occur.

The air diffusing plate 4 is used for air scrubbing, but any air diffusing plate 4 may be used as long as the air bubbles hit the entire module.

Therefore, although the diffuser plate is shown in the figure, it is also possible to use a diffuser pipe having a hole or a porous pipe made of a porous material. A blower is connected to an air diffuser or an air diffuser, and bubbling is performed by continuously or intermittently blowing air from the blower during the filtration operation to clean the membrane surface.

As shown in FIG. 1, when a plurality of modules are arranged side by side in a lateral direction and fixed, adjacent ones are considered in order to make a can body and a processing tank compact and to perform efficient air scrubbing. It is preferable that the distance between the modules is small, but if the distance is too narrow, it may be difficult for the air valve to pass between the modules.

Therefore, an appropriate gap is required between the modules, and the gap is preferably in the range of 30 to 100 mm. In practice, the intervals between the modules can be selected in consideration of the size of the modules, the number of modules, and backwashing conditions such as air scrubbing.

As the hollow fiber membrane 2, for example, cellulose type, polyolefin type, polyvinyl alcohol type, PM
Materials made of various materials such as MA-based and polysulfone-based materials can be used, and materials having high strength and elongation such as polyethylene and polypropylene are particularly preferable.

If it can be used as a filtration membrane,
The pore diameter, porosity, film thickness, outer diameter, etc. are not particularly limited, but in view of securing a membrane area per removal object or volume and the strength of the hollow fiber membrane, a preferable example is a pore diameter of 0. 01
˜1 μm, porosity 20 to 90%, film thickness 5 to 300 μm,
The outer diameter may be in the range of 20 to 2000 μm.

Further, in the case of removing bacteria, it is essential that the pore size is 0.2 μm or less, and in the case of removing organic substances and viruses, the molecular weight cutoff is limited to tens to hundreds of thousands. An outer filtration membrane may be used.

The surface characteristics of the hollow fiber membrane are ethylene-
A so-called permanent hydrophilization film having a hydrophilic group on the surface thereof while holding a polymer such as a saponified product of vinyl acetate copolymer is desirable. When the surface is a hydrophobic hollow fiber membrane, hydrophobic interaction works between the organic matter in the water to be treated and the surface of the hollow fiber membrane to cause adsorption of organic matter on the membrane surface, which leads to blockage of the membrane surface and filtration. The life is shortened.

In addition, clogging caused by adsorption is generally difficult to recover the filtration performance by cleaning the membrane surface. By using the permanent hydrophilization membrane, the hydrophobic interaction between the organic matter and the hollow fiber membrane surface can be reduced, and the adsorption of the organic matter can be suppressed.

[0028]

[Function] By fixing the module by making the sheet surface of the sheet-shaped flat hollow fiber membrane module vertical, and particularly when performing filtration with a plurality of modules, by arranging the modules in parallel in the horizontal direction, Air scrubbing can be done evenly for all modules. or,
By making the sheet surface vertical, it is possible to prevent sedimentation and accumulation of suspended substances on the sheet surface.

[0029]

The present invention will be described in detail with reference to the following examples. [Example 1, Comparative Example 1] A flat hollow fiber membrane module having a membrane area of 2 m ² comprising a polyethylene hollow fiber membrane having a saponified product of an ethylene-vinyl acetate copolymer held on the surface was used to fix the module. The difference in the differential pressure during the filtration operation due to the difference was compared.

As a method of fixing and arranging the modules, there are a method of fixing so that the sheet surfaces of the modules are horizontal in the tank and stacking five modules vertically (hereinafter method I), and another method is Fix the module's sheet surface vertically and the hollow fiber membrane's longitudinal direction horizontally,
It was carried out by a method of arranging five modules side by side (hereinafter Method II).

In both Method I and Method II, the distance between adjacent modules was set to 60 mm. 200p in the tank
It was filled with water in which pm yeast was suspended, and this water was used as raw water for filtration.

The filtration method is as follows: the module is completely immersed in raw water, the water collecting pipe is connected to the inlet side of the pump,
Filtration was performed by aspirating with a pump. The filtration flow rate is constant and 330 ml / min (LV = 0.0099 m
/ H), filtration was carried out for 5 minutes, and stopped for 5 minutes (pump stop) as one cycle.

During operation (both during filtration and when stopped), the module is operated from below the seat surface of the lowermost module in Method I and from each of five modules in Method II, both from below. Scrubbing was continuously performed with 35 Nl / min of air.

In the method I, the first and second modules from the bottom were sufficiently air-scrubbed for stable filtration (30 days), but the third module from the bottom was 15
The fourth module and the module at the top were clogged for 8 days, and the filtrate could not be obtained.

On the other hand, in the modules of Method II, the increase in differential pressure was small in all five modules and stable operation was performed for 40 days.

Therefore, it can be seen that the filtration method in Method II can suppress the increase in differential pressure more than Method I, and can maintain stable filtration.

[0037]

EFFECTS OF THE INVENTION The filtration method using the flat hollow fiber membrane module of the present invention is such that during cleaning of the membrane surface by continuous or intermittent air scrubbing during the filtration operation, air is blown over the entire hollow fiber membrane of the module. Therefore, the cleaning efficiency is improved.
Further, since the sheet surface is vertical, it is possible to prevent sedimentation and accumulation of suspended substances on the sheet surface.

Therefore, the progress of clogging of the film surface can be suppressed. Particularly in the filtration of highly polluted water, the cleaning efficiency is improved and clogging of the membrane surface is suppressed, so that a high filtration flow rate can be maintained for a long period of time.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a method for supporting a hollow fiber membrane module in a filtration method using a sheet-shaped flat hollow fiber membrane module of the present invention.

[Explanation of symbols]

 1 Water collecting pipe 2 Hollow fiber membrane 3 Hollow fiber membrane focusing end 4 Air diffuser

Claims (1)

[Claims] 1. When a liquid is filtered from below a sheet-shaped flat hollow fiber membrane module while continuously or intermittently scrubbing with air, the module is arranged so that the sheet surface becomes vertical. A filtration method using a characteristic hollow fiber membrane module.