JPH0638955B2 - Ultrapure water production system sterilization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to ultrapure water for producing extremely high-purity pure water, that is, ultrapure water used in, for example, the electronics industry, medical drug industry, precision machinery industry, and the like. The present invention relates to a sterilization method for a manufacturing system.

[Conventional technology]

In recent years, the technical confidence of the electronics industry in particular has been remarkable, and the ultrapure water used in the manufacturing process is required to have increasingly severe water quality. For example, as shown in Table 1, the quality of ultrapure water required in the electronics industry is as close to theoretical pure water as possible without removing fine particles, bacteria (viable bacteria) and organic substances as well as inorganic ions as impurities. is necessary.

Although various unit operations are combined to remove impurities, broadly speaking, ion exchange resins and reverse osmosis membranes (RO membranes) are used to remove inorganic ions, and fine particles and bacteria are treated with RO or ultrafiltration (UF). ) Or a membrane treatment such as a membrane filter (MF) is mainly used. For example, the flow of the ultrapure water production system is, as shown in FIG. 3, a primary pure water production apparatus comprising the above-mentioned treatment apparatus such as coagulation sedimentation 21 and sand filtration 22 and RO 23 and regenerative mixed bed type ion exchange tower 24, Further, it is composed of an ultraviolet sterilizer 15, a non-regeneration type ion exchange cartridge 16 and a secondary pure water producing device composed of MF or UF20 and the like, and ultrapure water is circulated between the secondary pure water producing device and the point of use 3 It is common to construct a system that circulates through line 4 so as to always maintain its purity.

By the way, bacteria that live in the ultrapure water circulation line (hereinafter referred to as "ultra pure water system") including the secondary pure water production device and the point of use form a slime layer on the wall surface of pipes, devices, etc. Since it tends to proliferate, it is necessary to sterilize the ultrapure water system including the wall surface, and conventionally, this sterilization was performed using a hydrogen peroxide solution. The main reason for using a hydrogen peroxide solution is that it has the advantage that it can be sterilized without bringing extra salts into the ultrapure water line.

[Problems to be solved by the invention]

The sterilizing action of hydrogen peroxide is mainly the sterilizing action of trauma caused by oxidative power. Normally used hydrogen peroxide solution concentration is 1-5V /
V% and immersion time is 1 to 3 hours. However, some bacteria that live in the ultrapure water system have a strong catalase activity as shown in formula (1), and the bactericidal effect of hydrogen peroxide cannot be expected for these bacteria.

2H ₂ O ₂ → 2H ₂ O ₂ + O ₂ (1) In addition, the slime layer that propagates in the ultrapure water system and adheres to the wall and proliferates against the traumatic bactericidal action of hydrogen peroxide, hypochlorous acid, etc. Play a protective material role. Therefore, in the conventional ultrapure water-based sterilization treatment using hydrogen peroxide, it is necessary to set the hydrogen peroxide solution concentration to 5 V / V% or more in order to fully expect the sterilization effect. However, it is not preferable to increase the concentration of the hydrogen peroxide solution because it is dangerous in handling. Moreover, since hydrogen peroxide undergoes self-decomposition, there is a drawback that the hydrogen peroxide solution cannot be stored for a long time.

An object of the present invention is to provide a sterilization method for safely and effectively sterilizing an ultrapure water production system for producing ultrahigh-purity pure water, that is, ultrapure water.

[Means for solving problems]

In order to solve the above problems, the present inventors have investigated a sterilization method that is easy to handle and has a particularly high bactericidal effect on bacteria that live in the ultrapure water system, and uses inorganic nutrient salts that have not been attempted in the past. The present invention has been completed by finding that the sterilization method described above is the most practical.

A feature of the present invention is that a secondary pure water producing apparatus is installed for the purpose of further removing impurities in the outlet water of the primary pure water producing apparatus, and the outlet water (ultra pure water) of the secondary pure water producing apparatus is installed. Part of 2
In an ultrapure water production system having an ultrapure water circulation line that constantly circulates between the secondary pure water production apparatus and the point of use so as to return to the inlet of the secondary pure water production apparatus, the secondary water excluding the non-regenerative ion exchange cartridge A method for sterilizing an ultrapure water production system, which comprises passing an inorganic nutrient salt solution having a concentration of 0.1 W / V% or more through a pure water production apparatus and an ultrapure water circulation line.

[Action]

As a result of detailed examination of the bacteria inhabiting in ultrapure water, it was confirmed that the bacteria group that optimizes extremely low nutritional environment other than the conventionally said bacteria group is the dominant species. Such low-concentration nutritive bacteria grow in the presence of a small amount of organic matter, but do not grow in the presence of a large amount of organic matter. Similarly, inorganic nutrients have extremely low salt tolerance and It was found to be highly sensitive.

The action of the inorganic nutrient salts on the bacterium of the present invention is different from the conventional traumatic bactericidal action of hydrogen peroxide, hypochlorous acid, etc., as described above, due to the osmotic shock and the salt on the extremely low salt tolerance bacterium. It impairs physiological function. Inorganic nutrient salts are used against conventional bacteria such as hydrogen peroxide and hypochlorous acid, which are hard to be killed by oxidizer-based bactericides, or bacteria that form a protective substance such as slime on the outer wall of cells. However, it has a sufficiently high bactericidal action.

As the inorganic nutrient salts used in the present invention, various ones can be used, but Nacl, sodium salts such as Na ₂ SO _4, preferably salt is good, and heavy metals are sterilized, and wastewater treatment of sterilized wastewater is performed. There is a lack of economy because it is necessary. In addition, as the concentration of the inorganic nutrient salt solution,
0.1 W / V% or more, and this inorganic nutrient salt solution has a pore size of 1 μm
It is also preferable to use after membrane filtration with the following MF or UF, and further before dissolving the inorganic nutrient salts in water.
By performing dry heat sterilization at 0 ° C. or higher, preferably 200 ° C. or higher, the inorganic nutrient salts to be used and the bacteria brought into the ultrapure water system from the aqueous solution in which the inorganic nutrient salts are dissolved can be sterilized or sterilized in advance. It can be completely sterilized.

Further, the present invention will be described in detail with reference to FIG. 1 showing an embodiment thereof. In a normal operation without sterilization, a required amount of primary pure water is supplied from the primary pure water introducing pipe 2 to the secondary pure water. The water that has flowed into the pure water production apparatus 1 and has become ultrapure water by the secondary pure water production apparatus 1 is partially passed through the use point 3 by the ultrapure water circulation line 4 to the secondary pure water production apparatus 1 Returned to the entrance. When sterilization is performed, the valve 7 provided on the upstream side of the secondary pure water production apparatus 1 is opened, and the inorganic nutrient salt solution prepared in advance in the inorganic nutrient salt tank 6 to a concentration of 0.1 W / V% or more is dosed. It is injected into the inlet of the secondary pure water producing apparatus 1 via the pump 5. Here, regarding the concentration of the inorganic nutrient salt solution, consider an appropriate dilution ratio so that the concentration of the inorganic nutrient salt in the system including the secondary pure water production apparatus 1 and the ultrapure water circulation line 4 can be maintained at 0.1 W / V% or more. Any concentration may be used. Furthermore, in order to further enhance the bactericidal effect, it is preferably performed at 0.5 W / V% or more. However, by switching the non-regenerative ion exchange cartridge to bypass etc. before performing sterilization treatment,
Contact with inorganic nutrient solutions must be prevented in advance. That is, if the non-regeneration type ion exchange cartridge is brought into contact with the inorganic nutrient salt solution, an ion exchange reaction naturally occurs, the ion exchange capacity of the ion exchange resin is reduced, and eventually a break occurs.

In addition, by filtering the inorganic nutrient solution with MF or UF10 before injecting it into the secondary pure water producing apparatus 1, bacteria and particles brought in from the inorganic nutrient solution are also removed to unnecessarily enter the ultrapure water system. By preventing the introduction of impurities, the bactericidal effect can be further improved. Furthermore, when using salt, for example, since halophilic bacteria are present in low-quality salt, 160% before use.
By using salt that has been sterilized by dry heat at a temperature of not lower than 200.degree. C., preferably not lower than 200.degree. C., even low-quality salt can be easily sterilized and clean.

The sterilization time in the ultrapure water system may be about 1 to 3 hours, which is almost the same as when using the conventional hydrogen peroxide solution. At this time, the valve 8 shown in FIG. 1 may be opened to circulate in the ultrapure water system, or the valve 9 may be opened to discharge a part or all of the inorganic nutrient solution outside the system. The cleaning step is to wash out residual inorganic nutrient salts, and the cleaning time is about 3 to 5 hours. Even if the conventional hydrogen peroxide is used, at least 3 hours or more is required, so that the cleaning time of the present invention using the inorganic nutrient salts is not particularly long as compared with the conventional method. Moreover, when using an inorganic nutrient salt unlike hydrogen peroxide, the end point of washing can be easily known by measuring the specific resistance or the electrical conductivity. From this point, it can be said that the combined use of hydrogen peroxide and inorganic nutrients makes it possible to easily know the end point of washing even by the conventional method.

〔Example〕

 Next, FIG. 2 shows the experimental apparatus flow of the embodiment of the present invention.

Referring to FIG. 2, the required amount of primary pure water is supplied to the high pure water tank 11 through the primary pure water introducing pipe 2. The high pure water tank 11 is sealed with N ₂ gas by a nitrogen gas line 13 and communicates with the atmosphere via an air filter 12.

Non-regeneration type ion exchange cartridge 16, 0.6 μm MF 20 and ultrapure water circulation line 4 by the secondary pure water pump 14.
Through this, the ultrapure water returns to the high pure water tank 11. The above experimental apparatus was operated for about 1 month, and then sterilized by using salt according to the present invention. First, the valves 18 and 19 are closed to block the passage of liquid to the non-regeneration type ion exchange cartridge 16,
The valve 17 is opened. Next, the valve 7 was opened, and 0.5 W / V% salt solution prepared in advance in the inorganic nutrient salt tank 6 was passed through the MF 10 having a pore diameter of 0.45 μm by the chemical injection pump 5.
Next, water was injected into the discharge side of the pure water pump 14, the valve 9 was opened, and the saline solution was discharged out of the system. The sterilization time was about 1 hour. Similarly, after the experimental apparatus was operated for about one month, it was sterilized by the conventional method of 1 V / V% hydrogen peroxide solution. The results are summarized in Table 1. Bacteria measurement is ASTM
The membrane filter culture method was used.

As is clear from the results of Table 2, in the present invention, bacteria were not detected after sterilization, but in the conventional method using hydrogen peroxide, 0.1 to 0.2 bacteria / ml of bacteria were measured and sterilization was insufficient. there were. This is because hydrogen peroxide has a small effect on bacteria having a catalase activity or bacteria forming a protective substance such as slime.

〔The invention's effect〕

As is clear from the above, the present invention uses an inorganic nutrient salt, which has not been used for sterilization of ultrapure water, at a concentration of 0.1 W / V% or more, and thus the sterilization effect is extremely enhanced. , More complete and complete sterilization is possible.

[Brief description of drawings]

FIG. 1 is an explanatory view of a flow showing an embodiment of the present invention, FIG. 2 is an explanatory view showing a flow of an experimental apparatus of an embodiment of the present invention, and FIG. 3 shows a flow of an ultrapure water production system. FIG. 1 ... Secondary pure water production device, 2 ... Primary pure water introduction pipe, 3 ... Use point, 4 ... Ultra pure water circulation line, 5 ... Chemical injection pump, 6 ... Inorganic nutrient salt tank, 7, 8, 9 ... Valve, 10 ... MF or UF, 11 ... High pure water tank, 12 ... Air filter, 13 ... Nitrogen gas line, 14 ... Secondary pure water pump, 15 ... UV sterilizer, 16 ... Non-regenerative ion exchange cartridge, 17, 18 , 19 ... Valve, 20 ... MF, 21 ... Coagulating sedimentation, 22 ... Sand filtration, 23 ... RO, 24 ... Regenerative mixed bed type ion exchange tower.

Claims (3)

[Claims] 1. A secondary pure water producing device is installed for the purpose of further removing impurities in the outlet water of the primary pure water producing device, and a part of the outlet water (ultra pure water) of the secondary pure water producing device is installed. In the ultrapure water production system having an ultrapure water circulation line that constantly circulates between the secondary pure water production apparatus and the point of use so as to return the water to the inlet of the secondary pure water production apparatus, the non-regenerative ion exchange cartridge is excluded. 0.
A sterilization method for an ultrapure water production system, which comprises passing an inorganic nutrient salt having a concentration of 1 W / V% or more. 2. The sterilization method for an ultrapure water production system according to claim 1, wherein the inorganic nutrient salt solution is filtered with a membrane filter or an ultrafiltration membrane having a pore size of 1 μm or less. 3. The sterilization method for an ultrapure water production system according to claim 1, wherein the inorganic nutrient salt solution is prepared by dissolving dry sterilized inorganic nutrient salts.