JPS59177199A - Suppression of propagation of bacteria in piping - Google Patents

Abstract

PURPOSE:To remove bacteria adherent onto the inner wall of piping for inhibiting the propagation of bacteria in highly demineralized water, in the transportation of highly demineralized water containing the very small amount of fine particles, by abruptly raising the flow speed of said highly demineralized water flowing through the piping at least one time a day. CONSTITUTION:In manufacturing highly demineralized water, raw water is sent to a primary demineralizing system A at first and then sequentially subjected to coagulation 1, treatment 2 with a reverse osmosis membrane and ion-exchanging treatment 4. Then, the water is supplied to a sub-system B, subjected to ultraviolet irradiation 5 and polishing treatment 6 to annihilate microbes existent in the water, and then converted into highly demineralized water by a reverse osmosis or ultrafiltration method 7 to remove organic substance and fine particles from the water. The demineralized water is sent to a using site 8 through piping made of fluororesin, e.g. trifluoroethylene, or high-density polyethylene. Hereon, bacteria adherent onto the inner wall of the piping are removed by raising the speed of transportation of the highly demineralized water twice or more about one time a day, to inhibit the propagation of bacteria in the highly demineralized water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suppressing bacterial growth in piping for supplying ultrapure water with extremely low particulate content.

In recent years, the demand for ultrapure water (generally refers to water with an electrical resistivity of 5 to IOMΩ·0111 or more) has been increasing in fields such as the electronic industry and the pharmaceutical manufacturing industry.

For example, if the water used in the manufacturing process of semiconductor devices contains impurities such as fine particles, the resulting products will have poor characteristics due to the occurrence of lattice defects, a decrease in electrical resistivity, short circuits, etc. For this reason, the water used is required to have high purity.

In particular, recently, there has been a trend toward higher and higher integration density of semiconductor devices, and ultrapure water with even higher purity is required.

Conventionally, ultrapure water has been supplied by purifying raw water, such as tap water, industrial water, or river water, by a combination of operations such as coagulation treatment, filtration treatment, reverse osmosis membrane treatment, and ion exchange treatment.

An example of a typical manufacturing process for ultrapure water is shown in the flow sheet of FIG. In this manufacturing process, the raw water is first
Next, the purified water is supplied to system A, where it is sequentially subjected to coagulation treatment.
After being subjected to reverse osmosis membrane treatment 2, degassing treatment 3, and ion exchange treatment 4, the water is supplied to subsystem B. The water supplied to subsystem B is subjected to ultraviolet irradiation treatment 5 to kill microorganisms in the water, and polylasha (mixed bed ion exchange device) treatment 6, and then finally subjected to reverse osmosis or ultrafiltration. Organic matter and fine particles in the water are removed by Method 7, resulting in ultrapure water. The ultrapure water thus obtained is transported via piping to its point of use (referred to as a point of use), and is made available for use from the terminal piping. Here, some unused ultrapure water is returned to the beginning of subsystem B again. Note that this closed channel that circulates through subsystem B is called the main loop. On the other hand, used ultrapure water is regenerated in wastewater recovery system C and circulated to the first treatment process.

However, with such conventional ultrapure water supply methods, it has been extremely difficult to remove fine particles, particularly microorganisms (bacteria), from the water. This is because even if pure water has been sufficiently sterilized, some microorganisms (bacteria) will normally appear in the tank, main loop 9, and terminal piping when it becomes stagnant due to the end of operations.

In order to suppress the growth of bacteria, it is necessary to remove as much of the bacterial nutrients present in the water as possible.

However, according to experiments conducted by the present inventors, even in ultrapure water with an organic matter content of 50 ppb or less as carbon, bacterial growth of about 104 bacteria/ml was observed if the water was allowed to stand. Therefore, it is technically difficult to suppress bacterial growth simply by removing nutrients.

Therefore, it has been desired to develop a method for effectively suppressing the growth of bacteria in piping by a method other than removing nutrients.

An object of the present invention is to provide a method for inhibiting the growth of bacteria in piping for inexpensively supplying ultrapure water with a low content of fine particles.

As a result of intensive research to achieve the above object, the present inventors have found that by periodically drastically changing the flow rate of water in the pipe, bacteria adhering to the inner wall of the pipe are removed, and as a result, the bacteria inside the pipe is removed. The present invention was completed by discovering the fact that the growth of bacteria can be suppressed.

The method for inhibiting the growth of bacteria in piping according to the present invention is characterized by significantly changing the flow rate of ultrapure water flowing through the piping at least once a day.

In the following, the invention will be explained in more detail.

The method of the present invention shows that bacteria proliferate in water when the total organic carbon TOC is large, but in water with an extremely small total organic carbon TOC, they grow only by adhering to solid surfaces, and they grow in the liquid. Taking advantage of the fact that they hardly proliferate, bacteria adhering to solid surfaces are periodically moved into the liquid using hydraulic power, thereby suppressing the proliferation of bacteria.

Total organic carbon TOC of water flowing through piping in the present invention
shall be 25 ppm or less. When TOc exceeds 25 ppm, bacteria will proliferate in the liquid due to the nutrients, so even if bacteria are moved from the solid surface into the liquid, bacterial growth cannot be suppressed. Examples of materials include fluororesins such as trifluoroethylene, tetrafluoroethylene, and difluoroethylene, high-density or low-density polyethylene resins, polypropylene resins, polysulfone resins, polycarbonate resins,
Examples include vinyl chloride resin, acrylic resin, and glass, and particularly preferred are hydrophobic resins such as fluororesin or high-density polyethylene resin. Bacteria generally have a hydrophilic surface. Therefore, even if bacteria adhere to the surface of the hydrophobic resin, their adhesion is weak, and they are susceptible to mechanical shocks such as drastic changes in water flow velocity. It can be easily peeled off.

Further, it is preferable that the inner wall surface of the pipe is smooth. The smoother the surface, the better. Bacteria are easily removed from solid surfaces by varying the water flow rate.

In the method of the present invention, the flow rate of pure water within the pipe is significantly changed at least once a day in order to suppress the adhesion and growth of bacteria on the inner wall of the pipe.

It is preferable that the rate of change in flow rate is at least twice the steady flow rate. If the rate of change in flow rate is less than twice the steady flow rate, the shearing force of the hydraulic force applied to bacteria is small, making it difficult to move bacteria attached to the inner wall of the pipe into the liquid.

As a means for changing the flow rate, a side light, a known pump, an on-off valve, etc. can be used.

The flow rate shall be changed at least once a day. If the flow rate is changed less than once a day, the effect of preventing bacterial growth on the inner wall of the piping is low. The time for changing is usually 1 minute or more, preferably 5 minutes or more. If the changing time is too short, it will be difficult to move bacteria attached to the inner wall of the pipe into the liquid.

The method of the present invention is generally applied to the piping in the main loop 9 in FIG.

The method of the present invention can effectively suppress the growth of bacteria in pipes, and does not require any special chemicals or equipment, simply by significantly changing the flow rate of pure water in pipes. Since it can be carried out extremely easily and inexpensively, its industrial value is extremely large.

Hereinafter, the method of the present invention will be explained in detail with reference to Examples.

Example Ultra-pure water with a specific resistance of 5 MΩΦcm was poured into a closed channel with a capacity of 3Q, and the water was allowed to flow at a flow rate of 0.3 m/sec. Insert a fluororesin test piece (20mm x?Omm) into the waterway for comparison.
1 mm) was immersed. To compensate for water evaporation, 0.5 ppm of nutrients (peptone) was added as TOC once daily. The temperature was maintained at 10-20'O.
After FJ, the test piece was pulled out, stained, and examined under a microscope, and numerous bacteria were found to have grown attached to it.

The same type of test piece was similarly immersed in another similar waterway. According to the method of the present invention, this person unplugs the water channel once a day and drains the water vigorously (approximately 0.8 m/sec).
At the same time, 311 g of ultrapure water was added from one side and the water was replaced while keeping the test piece from coming out above the water surface. 7th, 14th,
After 28 days, each test piece was stained and examined under a microscope, and no bacterial adhesion was observed.

1 cliff 12 A waterway similar to Example 1 was operated at 0.2 m/sec.

A test piece made of high-density polyethylene resin and having the same size as in Example 1 was immersed. Once a day, evaporated water was replenished and the same trace amounts of nutrients as in Example 1 were replenished. After 7 days, the test piece was pulled out, stained, and examined under a microscope, and numerous bacteria were observed to have grown on it.

The same type of test piece was immersed in another similar waterway. Next, according to the method of the present invention, nutrients are replenished once a day, and at the same time, the plug at the bottom of the canal is removed and the water is rapidly drained. At the same time, 5 drops of pure water are added from one side so that the test piece does not rise above the water surface. I replaced the water. After 7, 14, and 21 days, the test piece was raised, stained, and examined under a microscope, and no bacterial adhesion was observed.

[Brief explanation of the drawing]

FIG. 1 is a float sheet showing a typical manufacturing process of ultrapure water, and is a reference diagram for explaining the positions of piping according to the method of the present invention. 1... Coagulation treatment, 2... Reverse osmosis membrane, 3...
Deaeration treatment, 4.10...Ion exchange treatment, 5.1
1... Ultraviolet irradiation treatment, 6... Polishing treatment, 7... Ultrafiltration treatment, 8... Point of use, 9.
...Main loop, 12...Activated carbon treatment procedure amendment (
Form) July 14, 1980 Director-General of the Patent Office Kazuo Wakasugi 1, Indication of Case 1988 Patent Section No. 49701S. 2. Name of the invention Method for suppressing the growth of bacteria in piping 3. Relationship with the case of the person making the amendment Patent applicant name (106 Nakeda Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A method for inhibiting the growth of bacteria in piping, which comprises significantly changing the flow rate of ultrapure water flowing through the piping at least once a day. 2. The method for inhibiting the growth of bacteria in a pipe according to claim 1, wherein the pipe is made of a fluororesin or a high-density polyethylene resin. 3. The method for inhibiting bacterial growth in piping according to claim 1, wherein the flow rate of the water is changed to a flow rate that is twice or more the steady flow rate.