JP2003053164A - Removing method of pathogenic protozoa and separating membrane used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a removing method of pathogenic protozoa and a separating membrane used therein which reliably removes pathogenic protozoa such as Cryptospolidium and Dialdia, enhances filtration speed and, moreover, drastically reduces equipment cost and running cost. SOLUTION: In this removing method of pathogenic protozoa and a separating membrane used therein, the separation membrane of which the fraction grain size is >=1 μm, the perfect removal grain size is <=2.9 μm and the permeation rate of pure water is >=30000 L/m<2> /hr/98 kPa is used, thereby, the filtration is performed and the pathogenic protozoa is removed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing pathogenic protozoa such as Cryptosporidium and Giardia from raw water and a separation membrane used therefor.

[0002]

2. Description of the Related Art Since the occurrence of collective diarrhea caused by Cryptosporidium in Ogose Town, Saitama Prefecture in 1996, there has been a strong demand for safety measures against tap water. Therefore, advanced treatment such as ozone treatment and introduction of membrane filtration method have been introduced. Are rapidly spreading.

[0003] By the way, there are about 2 water purification facilities throughout the country where the quality of tap water is good and water is supplied only by disinfection.
There are 600 water purification plants, and there are more than 6000 water purification plants that do not filter sand with simple water. Even in these water purification facilities, when raw water includes subsurface water or groundwater (shallow well) that flows when underground water flows into the ground temporarily, protozoa such as Cryptosporidium and Giardia may exist in the raw water. It became clear that in August 1999, in Yamagata Prefecture, Cryptosporidium was detected in the raw water of a water purification plant that was supplying underground water only by sterilization, and water supply was suspended for about 10 days. Several cases have occurred so far, and even if the quality of the raw water is relatively good, technical measures against contamination of pathogenic protozoa are urgently required.

As a countermeasure for pathogenic protozoa in existing water purification systems, it is common to use physical filtration techniques such as rapid sand filtration, slow sand filtration, and separation membrane filtration. In particular,
Since separation membrane filtration is mainly used for turbidity and sterilization, it has a separation performance of 0.2 μm or less, and its precision is significantly better than that of other physical filtration. Cryptosporidium, Giardia, etc. Animals can also be removed almost completely.

[0005]

However, in the conventional separation membrane filtration, it is possible to remove pathogenic protozoa such as Cryptosporidium, but the filtration rate is overwhelmingly lower than that of sand filtration, etc. Since a high-pressure raw water pump of 200 kPa or higher is required, when using it at a water purification plant, it is necessary to modify or expand the power receiving equipment to increase the power of the raw water pump, and the equipment cost and running cost also increase significantly. However, this is an obstacle to the widespread use of separation membrane filtration.

[0006] On the other hand, sand filtration has a higher filtration rate than separation membrane filtration and can keep equipment costs and running costs low, but it is not always sufficient in the removal performance of pathogenic protozoa such as Cryptosporidium. , There is a problem with safety.

[0007] That is, as a safety measure against tap water, pathogenic protozoa such as Cryptosporidium can be reliably removed, filtration speed can be increased, and equipment costs and running costs can be significantly reduced. There is a social demand for a method and a separation membrane used therefor.

In view of the above-mentioned problems, the present invention can almost certainly remove pathogenic protozoa such as Cryptosporidium and Giardia, can increase the filtration rate, and can significantly reduce equipment costs and running costs. It is an object to provide a method for removing protozoa and a separation membrane used for the method.

[0009]

As described above, the filtration rate by the conventional membrane filtration method is overwhelmingly lower than that of sand filtration. The reason for this is that the fractionated particle size of sand filtration is 5-10.
It has a high pure water permeation rate of 5 μm, and the size is 5 μm even if impurities or suspended substances are present in the raw water.
If it is m or less, it will be permeated, so that resistance to impurities and the like is less likely to occur, and a high filtration rate can be maintained, whereas a microfiltration membrane or an ultrafiltration membrane with a fractional particle size of 0.2 μm or less In the conventional separation membrane, which is the mainstream, the pure water permeation rate is originally low due to the small fractional particle size, and most of the impurities and suspended substances present in the raw water are trapped in the separation membrane, and the resistance of these impurities, etc. It will be even lower with. From this, if the separation particle size of the separation membrane is made close to the maximum particle size that can remove pathogenic protozoa such as Cryptosporidium, it will be filtered while reliably removing pathogenic protozoa such as Cryptosporidium. It is thought that the speed can be increased.

On the other hand, the smallest confirmed pathogenic protozoa is Cryptosporidium,
The size of the oocyst is said to be 4 to 5 μm. However, Cryptosporidium has elasticity like rubber, and may deform and become smaller in size when pressure is applied when it is filtered by a separation membrane.
As a result of examining the correlation between the removal performance of standard particles and the crypto removal performance for removing Cryptosporidium, the present inventors have found that the removal performance of 2.9 μm standard particles and the crypto removal performance are relatively consistent. I found it. That is, it can be presumed that Cryptosporidium is transformed into a small size of about 2.9 μm during filtration, and if this minimum pathogenic protozoa can be removed, all pathogenic protozoa can be removed. Therefore, by setting the maximum removal particle size of the separation membrane to 2.9 μm or less, the pathogenic protozoa containing Cryptosporidium can be removed almost certainly, and the fractionation particle size of the separation membrane can be increased at a high filtration rate. When the maximum removal particle diameter is within 1 μm and the maximum removal particle diameter is within 2.9 μm, the filtration rate can be correspondingly increased. The present invention has been completed based on the above findings. Furthermore, by using the separation membrane of the present invention, nematodes and rotifers and their eggs, which have become a problem of leakage from biological activated carbon filtration layers, and their eggs, parasites that may be found in tap water raw water It is clear that microorganisms larger than Cryptosporidium can also be removed, such as worms such as worms such as Echinococcus.

The separation membrane for removing pathogenic protozoa of the present invention is a separation membrane used for removing pathogenic protozoa existing in raw water by membrane filtration, and has a fractional particle size of 1
the particle size of completely removed particles is 2.9 μm or less,
And the pure water permeation rate is 30,000 L / m ² / hr / 98k
Pa or higher. The method for removing pathogenic protozoa of the present invention is a method for removing pathogenic protozoa existing in raw water by membrane filtration, wherein the fractional particle size is 1 μm or more,
It is characterized by performing filtration using a separation membrane having a completely removed particle size of 2.9 μm or less and a pure water permeation rate of 30,000 L / m ² / hr / 98 kPa or more.

The term "pathogenic protozoa" as used in the present invention refers to, for example, Cryptosporidium and Giardia, which are microorganisms that cannot be easily killed by chlorine sterilization and may exist in tap water raw water.

The fractional particle size means the particle size (S) of particles having a rejection rate of 90% by the hollow fiber membrane,
The rejection rate of at least two kinds of particles having different particle diameters was measured, and the value of S at which R was 90 was determined in the following approximate expression (1) based on the measured values, and this was used as the fractional particle diameter. It is what R = 100 / (1-m · exp (−a · log (s))) (1) In the above formula (1), a and m are constants determined by the hollow fiber membrane and are two or more types. It is calculated based on the measured rejection rate.

The completely removed particle size means standard latex particles such as polystyrene having a constant particle size (concentration: 10 ⁶ particles / mL).
The above shows the maximum removal particle size when no particles are removed when filtered through a separation membrane (filtration speed 5 m ³ / m ² / d). Determine by observing the presence or absence of particles with a microscope or fluorescence microscope.

The pure water permeation rate is measured by measuring the water permeation rate per hour under the conditions of filtration pressure of 20 kPa and temperature of 25 ° C., using pure water as raw water. The numerical value converted into the permeation rate per pressure is shown. When the separation membrane is a hollow fiber membrane, an open-ended hollow fiber membrane module having an effective length of 3 cm is used to filter the hollow fiber membrane from the outside to the inside (external pressure filtration) to measure the amount of water permeation.

According to the present invention, unlike the separation membrane which has been used for tap water for the purpose of removing turbidity and sterilization,
Pure water permeation rate is at least 10 times higher, and fractionation particle size is at least 5 times larger. By applying a separation membrane, turbidity and sterilization are not sufficient, but pathogenic protozoa such as Cryptosporidium and Giardia The animal can be almost certainly removed, and the clogging is suppressed by permeation of the fine particles trapped in the conventional separation membrane, and the high filtration rate can be maintained for a long time.

In particular, a separation membrane having a large fractional particle size of 1.5 μm or more and a high pure water permeation rate of 80,000 L / m ² / hr / 98 kPa or more is preferable. The transmembrane pressure difference, which is the difference between the pressure on the inlet side (inlet) and the secondary side (outlet), is 0.1 to 30 kPa, enabling a long-term filtration operation with a very small pressure difference, and the water level held by the water purification plant. The difference can be used as the driving pressure for filtration. As a result, with the conventional separation membrane, as described above, 200 k
A high-pressure raw water pump of Pa or higher is indispensable, and accompanying modification or construction of the power receiving equipment is required, but the present invention does not require a raw water pump at all, and it is possible to greatly reduce both construction costs and running costs. Become.

In the present invention, the fractional particle size of the separation membrane is
At least 1 μm or more is preferable to increase the filtration rate, and smaller is preferable for turbidity or sterilization. Therefore, within the range of 1 μm or more and 2.9 μm or less, it is almost certain that pathogenic protozoa are The desired filtration rate, filtration drive pressure, and turbidity
It will be decided by weighing the effect of sterilization.

The separation membrane material applied to the present invention is not particularly limited, and includes cellulose type polymers, acrylonitrile type polymers, polyimide type polymers, polyamide type polymers, polysulfone type polymers, polyvinyl alcohol type polymers, vinyl chloride type polymers, and fluorine type polymers. Materials such as and modified polymers and mixtures thereof are used. Among these, it is preferable to use a polysulfone-based polymer that is excellent in heat resistance, acid / alkali resistance, strength physical properties, and oxidant resistance. As a representative example of polysulfone-based polymer,
Examples thereof include those having a repeating unit represented by the following general formula (I) or (II).

[Chemical 1]

[Chemical 2]

The base film material may contain a hydrophilic polymer in order to impart functionality such as water wettability and stain resistance. Examples of hydrophilic polymers include polyvinyl alcohol, ethylene / vinyl alcohol copolymer, ethylene / vinyl acetate copolymer, polyvinylpyrrolidone, polyethylene oxide, polyvinyl acetate, polyacrylic acid, and modified polymers thereof. Among the hydrophilic polymers, polyvinyl alcohol having a large number of modified products is preferable because it is easy to impart functionality according to the purpose.
The content of the hydrophilic polymer is 1 to 10 wt% in order to provide the functionality without impairing the properties of the base polymer.
% Range is preferred.

The separation membrane can be applied to any of a flat membrane, a tubular membrane, and a hollow fiber membrane. Among them, the hollow fiber membrane has a feature that the space per unit membrane area can be made the most compact, and particularly, in the treatment amount. It is preferable because it is advantageous in a large application. For hollow fiber membranes, the inner diameter is typically 0.2-2 mm,
The outer diameter is 0.4 to 5 mm.

The structure of the separation membrane has a fine porous structure such as a mesh structure, a honeycomb structure, and a fine gap structure, and can be applied to both a symmetrical structure and an asymmetric structure. Further, a so-called finger-like structure or void structure may be present inside the separation film. The fine porous structure inside the separation membrane is one of the factors that determine the fractionated particle size and the pure water permeation rate.

Removal of pathogenic protozoa is achieved by filtration on a separation membrane by known methods. If filtration is continued, the filtration speed will decrease due to clogging.
The filtration of the separation membrane is performed while performing physical cleaning and chemical cleaning at regular intervals. These washings can be performed automatically or manually.

Examples of physical cleaning include backwashing of permeated liquid for returning the filtrate to the raw water side, bubbling cleaning for feeding air to the raw water side for bubbling, and gas for permeating gas from the filtrate side to the raw water side for cleaning. Examples include backwashing and washing combining these. Among these, the gas backwashing is preferable because the gas jetting effect and the vibration effect overlap with each other and the backwashing effect is enhanced. In the separation membrane applied to the present invention, since the particle size of fractionated particles is large, the gas backwashing can be easily performed at 200 kPa or less.

Examples of the chemical cleaning include oxidizing agents such as sodium hypochlorite, alkalis such as caustic soda, acids such as hydrochloric acid and oxalic acid, and combinations thereof. As tap water is legally required to add sodium hypochlorite, it is advantageous to use sodium hypochlorite from the viewpoint of waste liquid treatment after chemical cleaning and contamination risk of tap water by chemicals. Is. Examples of chemical cleaning with sodium hypochlorite include methods that constantly add to raw water and also perform cleaning while filtering, methods that add during backwashing, and sodium hypochlorite of relatively high concentration every 1 to several months. Examples include a method of washing.

If necessary, known treatment techniques such as ozone, activated carbon, coagulation sedimentation or pressure floating, ultraviolet treatment, and physical filtration such as sand filtration can be combined as the pretreatment or the posttreatment. . In combination with such conventional processing technology, if you want to further enhance safety from a multi-defensive perspective in consideration of possible damage to the separation membrane, or if you want to further suppress clogging of the separation membrane, etc. It is effective.

[0027]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

Examples 1 to 3 and Comparative Examples 1 and 2 are separation membranes made of a hydrophilized polysulfone hollow fiber membrane having an outer diameter / an inner diameter of 1.3 / 0.8 mm, which have the following characteristics. Is used. Here, the 2.9 μm particle removal rate is
Logarithmic reduction value (LRV) log ₁₀ (“raw water particle number” /
"Number of filtered water particles"). In other words, when no particles fall out in the filtered water, the number of filtered water particles is set to 1 and ≧ LRV.

Example 1: Fractionated particle size 2.0 μm, pure water permeation rate 152000 L / m ² / hr / 98 kPa,
2.9 μm particle removal rate ≧ 7.4. Example 2: Fractionated particle size 1.7 μm, pure water permeation rate 1
26000 L / m ² / hr / 98 kPa, 2.9 μm particle removal rate ≧ 7.4. Example 3: Fractionated particle size 1.2 μm, pure water permeation rate 4
5000 L / m ² / hr / 98 kPa, 2.9 μm particle removal rate ≧ 7.4. Comparative Example 1: Fractionated particle diameter 2.3 μm, pure water permeation rate 1
65000 L / m ² / hr / 98 kPa, 2.9 μm particle removal rate 5.1. Comparative Example 2: Fractionated particle size 2.5 μm, pure water permeation rate 1
78000 L / m ² / hr / 98 kPa, 2.9 μm particle removal rate 3.4.

In Examples 1 to 3 and Comparative Examples 1 and 2,
2.9 μm polystyrene fluorescent standard particles (G-300, D
The removal rate of Cryptosporidium and the removal rate of Cryptosporidium were examined. 1.2 μm and 2.
Standard particles of 0 μm and 3.2 μm cross-linked methyl methacrylate (PM-3KV, PM-4KV, PM-5K, respectively).
V, manufactured by Toshin Chemical Co., Ltd.) and calculated. The results are shown in Table 1.

[Table 1]

As shown in Table 1, the separation membranes of Examples 1 to 3 capable of completely removing 2.9 μm particles were also able to completely remove Cryptosporidium.

Example 4 Using the separation membrane of Example 1, a tap water filtration test was carried out under the following operating conditions. Raw water: Dedicated tap water (water sterilized from underground water with sodium hypochlorite) Raw water turbidity: 0.05 to 0.2 degree Separation membrane area: 7.2 m ² Treatment amount: 36 m ³ / d Filtration speed: 5 m ³ / m ² / d Filtration method: Total external pressure filtration (constant flow rate filtration) Backwash method: Sodium hypochlorite injection (5 mg / L) + Air backwash (Backwash pressure 70 kPa) Backwash interval: Once every 30 minutes For 10 seconds

The test results are shown in FIG. The differential pressure could be kept below 4 kPa for a long period of about 5 months, and a high filtration rate could be maintained with an extremely low differential pressure.

[0034]

Industrial Applicability As described above, according to the present invention, pathogenic protozoa such as Cryptosporidium and Giardia can be reliably removed, and the filtration rate can be increased. Both costs can be significantly reduced. Therefore, it can greatly contribute to the improvement of the safety of tap water and the suppression of the rise of water charges.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an example of a tap water filtration test result according to the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinji Komori             3-1, Nihonbashi, Chuo-ku, Tokyo, 6 shares             Inside the ceremony company Kuraray (72) Inventor Katsumi Kabazawa             Water 16-48, Sakuragaoka, Setagaya-ku, Tokyo             Dokiko Co., Ltd. (72) Inventor Takuya Onizuka             Water 16-48, Sakuragaoka, Setagaya-ku, Tokyo             Dokiko Co., Ltd. (72) Inventor Yoshitsugu Jimbo             Water 16-48, Sakuragaoka, Setagaya-ku, Tokyo             Dokiko Co., Ltd. F-term (reference) 4D006 GA07 HA01 HA21 HA41 KE03Q                       KE06Q MA01 MA02 MA03                       MA22 MB02 MB20 MC11 MC27                       MC33 MC39 MC54 MC58 MC62                       PA01 PB06 PB70

Claims (10)

[Claims] 1. A separation membrane used for removing pathogenic protozoa existing in raw water by membrane filtration, which has a fractional particle size of 1 μm or more and a completely removed particle size of 2.9 μm or less. And the pure water permeation rate is 30,000 L / m ² / h
A separation membrane for removing pathogenic protozoa having a r / 98 kPa or higher. 2. The fractional particle size is 1.5 μm or more, the completely removed particle size is 2.9 μm or less, and the pure water permeation rate is 80000 L / m ² / hr / 98 kPa or more. Separation membrane for the removal of pathogenic protozoa from. 3. The separation membrane for removing pathogenic protozoa according to claim 1 or 2, wherein the shape of the separation membrane is a hollow fiber. 4. The separation membrane for removing pathogenic protozoa according to claim 1, wherein a water level difference is used as a driving pressure for filtration. 5. The separation membrane for removing pathogenic protozoa according to claim 4, wherein the transmembrane pressure difference is in the range of 0.1 to 30 kPa. 6. A method for removing pathogenic protozoa existing in raw water by membrane filtration, wherein the particle size of fractionated particles is 1 μm or more, the particle size of completely removed particles is 2.9 μm or less, and the pure water permeation rate is A method for removing pathogenic protozoa, which comprises filtering using a separation membrane having a rate of 30,000 L / m ² / hr / 98 kPa or more. 7. A separation membrane having a fractional particle size of 1.5 μm or more, a completely removed particle size of 2.9 μm or less, and a pure water permeation rate of 80000 L / m ² / hr / 98 kPa or more. Item 7. A method for removing a pathogenic protozoa according to Item 6. 8. The method for removing pathogenic protozoa according to claim 6 or 7, wherein the shape of the separation membrane is a hollow fiber. 9. The method for removing pathogenic protozoa according to claim 6, wherein a water level difference is used as a driving pressure for filtration. 10. The method for removing pathogenic protozoa according to claim 9, wherein the transmembrane pressure difference is filtered in the range of 0.1 to 30 kPa.