JP2000000438A - Membrane separator and production of permeated water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the leakage of water to be treated to which particulates are added even when hollow fiber membranes are damaged and to suppress the degradation in the quality of permeated water by subjecting the water to be treated to external pressure filtration through the hollow fiber membranes. SOLUTION: The water to be treated side is set at the pressure higher on the outer side of the hollow fiber membranes by using a pressurizing means, such as a pump, and the water to be treated is supplied and is permeated fully or partly to the inner side of the hollow fiber membrane. The impurities larger than the pores of the membranes among the impurities included in the water to be treated are blocked by the skin layers on the outside surfaces of the hollow fiber membranes and are accumulated on the outside surfaces of the hollow fiber membranes. The filtration is continued in this state while the impurities accumulated on the outside surfaces of the hollow fiber membranes are removed by physical washing, such as backflow washing, for passing clean water and gas from the inner side toward the outer side of the hollow fiber membranes and, thereafter, the water contaminated water in the hollow fiber membrane module is once discharged to the outside of the hollow fiber membrane module and the filtration is repeated by again supplying the water to be treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a membrane separation device using a hollow fiber membrane. More specifically, in a membrane separation device that performs an external pressure filtration operation using a hollow fiber membrane, a membrane separation device that adds fine particles to the water to be treated and a fine particle to the water to be treated when water to be treated is supplied. The present invention relates to a method for producing permeated water.

[0002]

2. Description of the Related Art Separation membranes such as microfiltration membranes and ultrafiltration membranes are used in various fields including the food industry, the medical field, water production, and wastewater treatment. Especially in recent years,
Separation membranes have been used in the field of drinking water production, that is, in the purification process.

[0003] By using a separation membrane, it is possible to completely prevent pathogenic microorganisms such as cryptosporidium which are not killed by chlorination, which is a sterilization technique in the conventional water purification treatment, to obtain safe and high quality drinking water. This is because it becomes possible.

[0004] Examples of the form of the separation membrane include a flat membrane lamination type, a spiral type, a tubular type, and a hollow fiber membrane type. In particular, since the treatment amount is large in the water purification treatment, the effective membrane area per unit volume of the device is small. It is common to use a hollow fiber membrane type separation membrane that can be made large.

[0005]

Generally, in order to increase the processing efficiency of the separation membrane, a measure is taken to reduce the thickness of the membrane as much as possible to reduce the transmission resistance. As a result, it has become possible to provide a very efficient and compact system as compared with the coagulation sedimentation, the sand filtration method, and the like, which are conventional techniques. However, the membrane may be damaged due to the small thickness of the membrane, and in this case, the water to be treated leaks through the damaged portion, which is difficult with the conventional method, and the quality of the treated water is reduced. It had dropped significantly. Particularly in the production of drinking water, the above-mentioned Cryptosporidium and the like are mixed in the permeated water, which is a serious problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. Even if the hollow fiber membrane is damaged, the leakage of the water to be treated is stopped so that the quality of the permeated water can be reduced. It is an object of the present invention to provide a membrane separation device and a method for producing permeated water that suppress deterioration.

[0007] That is, the present invention relates to "a method for producing permeated water, characterized in that the water to be treated to which fine particles are added is subjected to external pressure filtration through a hollow fiber membrane." A permeated water producing apparatus having a liquid storage section for water to be treated existing outside the fiber membrane and the hollow fiber membrane, and means for adding fine particles to the water to be treated. "

[0008]

Embodiments of the present invention will be described below.

[0009] External pressure filtration using the hollow fiber membrane of the present invention comprises:
By using a pressure means such as a pump on the side of the water to be treated or a suction means on the side of the permeated water, the pressure outside the hollow fiber membrane is increased, and the water to be treated is supplied. And a clear permeate is taken out from the open end of the hollow fiber membrane. Of the impurities contained in the water to be treated, those larger than the pores of the membrane are blocked by the skin layer on the outer surface of the hollow fiber membrane and accumulate on the outer surface of the hollow fiber membrane. For this reason, the hollow fiber membrane is subjected to physical cleaning such as backwashing in which clear water or gas flows from the inside to the outside of the hollow fiber membrane or air scrubbing washing in which air is introduced into the outside of the hollow fiber membrane to shake the hollow fiber membrane. Filtration is continued while removing impurities accumulated on the outer surface. After the completion of the physical cleaning, once the contaminated water in the hollow fiber membrane module is drained out of the hollow fiber membrane module, the water to be treated is supplied again and the filtration is repeated.

According to the present invention, when fine particles are added to the water to be treated at the time of supplying the water to be treated and the hollow fiber membrane is damaged, the fine particles added to the water to be treated are replaced with the damaged part. And stop the leakage of the water to be treated from the damaged portion, thereby suppressing the deterioration of the quality of the permeated water.

The fine particles to be added need to clog the damaged hollow fiber membrane as quickly as possible. If the size is too small or too large, the damaged portion cannot be quickly clogged. If the particle size is too small, fine particles may leak to the permeation side instead of clogging the damaged portion, thereby deteriorating the quality of permeated water. On the other hand, if it is too large, clogging cannot be performed, and deterioration of permeated water quality cannot be suppressed. The present inventors have repeatedly studied using various fine particles, and as a result, as a preferable range of the minimum projected diameter of the added fine particles, 0.1 to 1.2 times, preferably 0 to 1.2 times the inner diameter of the hollow fiber membrane. It has been found that if it is 0.3 to 1.1 times, and more preferably 0.6 to 1.0 times, the damaged portion can be quickly clogged and deterioration of the permeated water quality can be suppressed. . Naturally, particles having a size other than those described above may be added.

The shape of the fine particles is not particularly limited in view of the gist of the present invention, but a spherical or oval shape having a maximum projected diameter of three times or less the minimum projected diameter is generally available easily. preferable.

The hollow fiber membrane module to which the present invention is applied is generally airtightly sealed (potted) between the hollow fiber membrane and the hollow fiber membrane and between the hollow fiber membrane and the module container. Take the shape that was made. Thereby, the outside and the inside of the hollow fiber membrane can be isolated by the hollow fiber membrane itself, and the separation treatment can be performed through the membrane. As the structure of the hollow fiber membrane module, both ends of the hollow fiber membrane are potted and then opened from both ends.
No. 27, Japanese Utility Model Application Laid-Open No. 2-100636, Japanese Utility Model Application Laid-open No. 3
JP-A-15628, JP-A-3-59028 and the like, “both-end open type”, JP-A-3-1562.
As disclosed in Japanese Patent Application Publication No. 9-1992, etc., a "single-end open type" in which only one end is opened after both ends are potted,
No. 54733, the hollow fiber membrane is formed in a U-shape, and the hollow fiber membrane is opened with only one end of the hollow fiber membrane open.
Character shape ". For the external pressure type total filtration operation, it is preferable to use a “U-shaped”, which facilitates physical cleaning and drainage.

It has been found from various studies that damage to the hollow fiber membrane is extremely high at the interface between the portion where the hollow fiber membrane is bonded and fixed and the portion where the hollow fiber membrane is not fixed, that is, at the root of the hollow fiber membrane. When the shape of the hollow fiber membrane module is “U-shaped”, the root of the hollow fiber membrane is at the top of the module. Therefore, the fine particles to be added in the present invention are preferably present in the vicinity of the damaged portion of the hollow fiber membrane, that is, at the root of the hollow fiber membrane at the upper part of the module. Particles can collect and clog in the damaged area.

Therefore, if the density of the fine particles is smaller than the density of the water to be treated, the fine particles can be present at the upper part of the module, and it is preferable that the density varies depending on the density of the water to be treated, but approximately 0.7 to 1.3 g / cm ³ , Preferably 0.8 to
It is about 1.2 g / cm ³ . Here, the density of the fine particles is not the density of the material itself, but the density of the fine particles themselves, and the density of the fine particles themselves may be reduced by making them hollow or porous.

The material of the fine particles used in the present invention is not particularly limited in terms of the gist of the present invention, but polystyrene, nylon, PMMA, polyethylene, polyester and the like are used in view of the safety and cost of the fine particles. preferable.

The amount of the fine particles to be added depends on the filtration pressure, the filtration flow rate, and the relationship between the inner diameter of the hollow fiber membrane and the diameter of the fine particles, and is determined in view of the effect of the present invention and from the viewpoint of economy. Should. The standard is about 0.001% to 10% by volume, preferably about 0.01% to 1% by volume, based on the volume of the hollow fiber membrane module on the water to be treated.

The separation membrane used in the present invention is not particularly limited in view of the gist of the present invention. However, the separation membrane is used in the field of drinking water production, that is, in a water treatment process such as a water purification treatment process, a water production process and a wastewater treatment process. It is preferable that the separation membrane is classified into a so-called microfiltration membrane or an ultrafiltration membrane having a pore diameter of 1 nm or more and 10 μm or less. Here, the pore diameter of the separation membrane is
It can be measured by the method described below. That is,
From the water permeability (Lp) of the separation membrane and the membrane permeation rate (Jv) of water,
(1) It is calculated by using the relationship of the expression (2). Jv = Lp · ΔP Equation (1) Lp = (H / L) · {Rp ² / (8η)} Equation (2) where (ΔP) is the transmembrane pressure difference, (H) is the water content of the membrane,
(L) is the film thickness, (Rp) is the pore diameter, and (η) is the viscosity of water.

The materials for the separation membrane include polyacrylonitrile, polysulfone, polyphenylene sulfone,
Inorganic materials such as polyphenylene sulfide sulfone, polyvinylidene fluoride, cellulose acetate, polyethylene, polypropylene, and ceramics can be cited, and are not particularly limited in view of the gist of the present invention. Polyacrylonitrile, cellulose acetate, polyphenylene sulfone, and polyphenylene sulfide sulfone, which are hydrophilic materials, are preferred for water treatment applications such as water and wastewater treatment because they are less likely to be stained and have good cleaning recovery properties.

The method of operating the membrane separation device includes a constant flow filtration in which the filtration flow rate is constant and the filtration differential pressure changes, and a constant pressure filtration in which the filtration differential pressure is constant and the filtration flow rate changes. As the filtration is continued and dirt accumulates on the surface of the separation membrane and in the pores of the separation membrane, the filtration resistance (R) of the separation membrane increases. Generally, in a real process, a fixed amount of water is often treated because a fixed amount of water is often treated.
In order to obtain a certain amount of filtered water, the filtration pressure must be controlled. In the case of constant-pressure filtration, the filtration flow rate decreases as the filtration continues. The method of operating the membrane separation device of the present invention may be either constant flow filtration or constant pressure filtration. However, constant flow filtration is a general and preferred method because a constant throughput can be obtained.

The water to be treated according to the present invention is not particularly limited in view of the gist of the present invention. However, river water is used in the field of drinking water production, that is, in the water purification process, water treatment and wastewater treatment. Alternatively, lake water or groundwater is preferred.

In the method for producing permeated water of the present invention, the hollow fiber membrane, the liquid storage section of the water to be treated existing outside the hollow fiber membrane,
Also, a permeated water producing apparatus having means for adding fine particles to the water to be treated can be used. The means for adding the fine particles to the water to be treated may be provided in the liquid storage section, or may be a means for supplying the water to be treated before the liquid storage section.

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

[0024]

Example 1 Lake Biwa water was used by using a module having a hollow fiber membrane of about 1 m in length and an effective membrane area of 12 m ² , bundled with a polyacrylonitrile hollow fiber membrane having an inner diameter of 400 μm and an average pore diameter of 0.01 μm. External pressure type constant flow total filtration was performed. Filtration linear speed is 1m
/ D. At this time, at the time of supplying the water to be treated, polystyrene beads having a diameter of 400 μm, which is equal to the inner diameter of the hollow fiber membrane, are added to the volume of the hollow fiber membrane module on the side of the water to be treated at 1 vol.
%. When the turbidity of the permeated water was measured in this state, it was 0.01 degrees. Once the filtration was stopped, the roots of the ten hollow fiber membranes were cut with a razor, and the same filtration operation was started again. When the turbidity of the permeated water 1 minute after the restart of filtration was measured, it was 0.06 °,
Three minutes after the restart of the filtration, the turbidity of the permeated water became 0.01 degree, which was the same turbidity as when there was no damage to the hollow fiber membrane. Thereafter, the permeated water turbidity was stable at 0.01 degree even after 400 minutes.

COMPARATIVE EXAMPLE 1 Using the same hollow fiber membrane module as in Example 1, an external pressure type constant flow total filtration of Lake Biwa water was performed. Filtration linear velocity is 1m /
d. At this time, no fine particles were added when supplying the water to be treated. The turbidity of the permeated water was measured in this state in the same manner as in Example 1, and was found to be 0.01 degree. Once filtration was stopped, the root of 10 hollow fiber membranes was cut with a razor,
The same filtration operation was started again. When the turbidity of the permeated water 1 minute after the restart of filtration was measured, it was 0.06 °,
Three minutes after the restart of the filtration, the turbidity of the permeated water was 0.09 degrees. Further, after 400 minutes, the turbidity of the permeated water became 0.5 degree, and the quality of the permeated water deteriorated with the elapse of time as the filtration pressure difference increased.

Comparative Example 2 Using the same hollow fiber membrane module as in Example 1, an external pressure type constant flow total filtration of Lake Biwa water was performed. Filtration linear velocity is 1m /
d. At this time, at the time of supply of the water to be treated, polystyrene beads having a diameter of 30 μm, which is 0.075 times the inner diameter of the hollow fiber membrane, are supplied to the hollow fiber membrane module at a volume of 1 V with respect to the volume of the water to be treated.
ol%. The turbidity of the permeated water was measured in this state in the same manner as in Example 1, and was found to be 0.01 degree. Once the filtration was stopped, the roots of the ten hollow fiber membranes were cut with a razor, and the same filtration operation was started again. When the turbidity of the permeated water was measured 3 minutes after restarting the filtration,
It was 0.2 degrees, and the permeated water turbidity became 0.7 degrees 400 minutes after the restart of filtration. It was considered that the polystyrene beads were leaking.

Comparative Example 3 Using the same hollow fiber membrane module as in Example 1, an external pressure type constant flow total filtration of Lake Biwa water was performed. Filtration linear velocity is 1m /
d. At this time, when the water to be treated is supplied, polystyrene beads having a diameter of 1000 μm, which is 2.5 times the inner diameter of the hollow fiber membrane, are applied to the hollow fiber membrane module at a volume of 1 V with respect to the volume of the water to be treated.
ol%. The turbidity of the permeated water was measured in this state in the same manner as in Example 1, and was found to be 0.01 degree. Once the filtration was stopped, the roots of the ten hollow fiber membranes were cut with a razor, and the same filtration operation was started again. When the turbidity of the permeated water was measured one minute after restarting the filtration,
It was 0.05 degrees, and the turbidity of the permeated water was 0.08 degrees after 3 minutes from the restart of the filtration. Further, after 400 minutes, the turbidity of the permeated water becomes 0.5 degree, and the quality of the permeated water deteriorates with the elapse of time with an increase in the filtration pressure difference. Was.

[0028]

According to the present invention, in a membrane separation apparatus which performs an external pressure filtration operation using a hollow fiber membrane, fine particles are added to the water to be treated when the water to be treated is supplied, and the hollow fiber membrane is damaged. In this case, the fine particles added to the water to be treated
Provided is a membrane separation device and a method for producing permeated water, which suppress deterioration of the quality of permeated water by stopping leakage of the water to be treated from the damaged portion by clogging the damaged portion.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B01D 71/68 B01D 71/68 F term (reference) 4D006 GA06 GA07 HA19 JA67Z KA03 KD30 KE02Q LA04 MA06 MA22 MC18 MC39 MC62 MC63 PA01 PB04 PB05 PB08

Claims (10)

[Claims] 1. A process for producing permeated water, comprising subjecting treated water to which fine particles have been added to external pressure filtration through a hollow fiber membrane. 2. The method for producing permeated water according to claim 1, wherein the fine particles are defined as having a minimum projected diameter of 0.1 to 1.2 times the inner diameter of the hollow fiber membrane. 3. The method for producing permeated water according to claim 1, wherein the density of the fine particles is smaller than the density of the water to be treated. 4. The method according to claim 1, wherein the material of the fine particles is polystyrene, nylon, PMMA, polyethylene, or polyester. 5. The amount of the fine particles added to the water to be treated is 0.
The method for imaging permeated water according to claim 1, wherein the amount is from 001 to 10% by weight. 6. The hollow fiber membrane has a pore diameter of 1 nm or more and 10 μm or more.
The method for producing permeated water according to any one of claims 1 to 5, wherein the membrane is a microfiltration membrane or an ultrafiltration membrane having a diameter of not more than m. 7. The method for producing permeated water according to claim 1, wherein the material of the hollow fiber membrane is polyacrylonitrile, cellulose acetate, polyphenylene sulfide, or polyphenylene sulfide sulfone. 8. The method for producing permeated water according to claim 1, wherein a constant flow rate filtration is performed. 9. An apparatus for producing permeated water having a hollow fiber membrane, a liquid storage section for water to be treated existing outside the hollow fiber membrane, and means for adding fine particles to the water to be treated. 10. The method for producing permeated water according to claim 1, wherein the water to be treated is river water, lake water, or groundwater.