JPS6331592A - Method for making ultrapure water - Google Patents

Abstract

PURPOSE:To suppress the lowering of flux, by biologically treating recovered water in an ultrapure water treatment system and subsequently injecting hydrazine to water before performing membrane separation. CONSTITUTION:Water passing through the ultraviolet oxidizing apparatus 4 of a recovery system A is introduced into a bioreactor 13 to be biologically treated under an aerobic condition. By this method, organocarbon becomes CO2 or is taken in a bacterial cell. Further, a hydrazine tank 15 for supplying hydrazine and a chemicals injection pump 6 are provided to a piping system for supplying treated water from the bioreactor 13 to the RO membrane separation apparatus 7 of an ultrapure water making system B to continuously or intermittently inject hydrazine. By this method, it can be prevented that bacteria are adhered to the RO membrane of the separation apparatus 7 to form a gel layer.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing ultrapure water, and particularly relates to a method for producing ultrapure water that incorporates biological treatment means to suppress the growth of microorganisms in water. .

[Background Art and Prior Art] In the manufacture of LSIs and VLSIs, large amounts of pure water and ultrapure water are used. Ultrapure water is pure water having a specific resistance of 17 to 18 MΩ·cm, which is extremely close to the specific resistance of theoretically pure water (water consisting only of H2O), which is 18.24 MΩ·cm.

- In the shell, the ultrapure water production process is composed of activated carbon, ion exchange resin, ultraviolet (UV) oxidation, reverse osmosis membrane (R○), ultrafiltration membrane (UF), etc.

For example, the ultrapure water production process in the process of recovering cleaning waste liquid from a semiconductor wafer cleaning system using ultrapure water is as shown in FIG. In the device shown in Figure 2,
The wastewater from the semiconductor cleaning process 1 is first subjected to activated carbon adsorption treatment in the activated carbon adsorption tower 2 of the recovery system A, and then treated and desalted in the ion exchange tower 3, and then further treated with a reverse osmosis membrane device (not shown) when necessary. The ultraviolet oxidation device 4 is used to process the ultraviolet light. In the ultraviolet oxidation device 4, in order to almost completely oxidize and decompose organic substances, hydrogen peroxide is generally added as an oxidizing agent, and the treatment is performed by irradiating ultraviolet rays in the presence of hydrogen peroxide.

The treated water from the recovery system A consisting of the activated carbon adsorption tower 2, ion exchange tower 3, and ultraviolet oxidation device 4 is returned to the pure water production system. This pure water production system B
is pre-treatment system C (I collection tank 5 and 24a filter 6
Consisting of ), primary pure water system D (reverse osmosis membrane device 7,
It consists of a deaerator 8 and an ion exchanger 9. ) and subsystem E (consisting of an ultraviolet sterilizer 10, a mixed bed ion exchange device 11, and an ultrafiltration membrane device 12).

Microorganisms are present even in oligotrophic water such as ultrapure water or pure water obtained by such pure water production equipment, although in very small amounts. Proliferates and causes trouble in pure water production equipment such as RO equipment.

In order to solve the problems caused by the growth of microorganisms in conventional pure water production equipment, the applicant has developed an ultrapure water production equipment that includes a membrane treatment device and an ion exchange tower.
Furthermore, in order to remove the energy source and/or nutrient source of @ amount, as shown in FIG.
We have discovered an ultrapure water production device in which a biological treatment means F consisting of a bacterial cell separator 14 for separating and removing bacterial cells grown in this biological reaction tank is added to the device as shown in FIG.
I applied for a patent earlier (Patent application 1985-231738゜ and below)
It is called "first-to-file." ) That is, the earlier application was filed based on the following knowledge.

Biological treatment of water containing relatively large amounts of organic matter, such as sewage and industrial wastewater, belongs to conventional technology.

However, biological treatment of extremely oligotrophic water such as ultrapure water has never been carried out in the past. Furthermore, biological treatment was originally thought to be impossible.

In addition to the fact that the mechanism of biological growth under oligotrophic conditions such as ultrapure water has not been fully elucidated, biological treatment of such water means adding microorganisms; This was because it was thought to be a contaminant.

Therefore, in the research of the previous application, as a result of studying the behavior of microorganisms in the conventional pure water production process, it was found that although most of the organic carbon is removed in this process, about 50 PPb (TOCa degree) is present in the treated water. Organic matter still remains, and microorganisms are responsible for the TOC in the water.
If it exists, by assimilating it, it will grow to 4-5x 103N/mλ in bioassay value, and the TOC will be 50
It has been found that when Ppb remains, it becomes about 2xlO5N/mfL, which causes clogging of R○, UF membranes, etc., and has an adverse effect on pure water production. In fact, measurements have shown that there is enough organic matter remaining in ultrapure water for microorganisms to grow to a bacterial count of 103 to 10'N/mλ, and in addition, phosphorus from equipment such as piping and resin remains. Alternatively, when phosphorus or the like is added due to nitrogen elution or cleaning chemicals, it has been confirmed that microorganisms proliferate even more easily and reach a rate of 105 N/mλ or more.

In addition, in conventional pure water production equipment, ultraviolet sterilization treatment is performed (10 of subsystem E in the equipment shown in Figure 2), but the ultraviolet irradiation treatment is temporary, and a small amount of microorganisms are removed afterwards. It was found that it was growing again.

As a result of the above-mentioned research on the growth mechanism of microorganisms in pure water, it has been found that microorganisms with very low concentrations of phosphorus, such as 1
It has been found that the plant grows by removing TOC, phosphorus, and other nutrients at a high removal rate until it becomes oppt, and when TOC, phosphorus, or nitrogen becomes deficient, the growth is rapidly suppressed.

The earlier application has such knowledge as the background for completing the invention, and according to the apparatus of the earlier application, biological treatment is carried out aerobically in the presence of an energy source and a nutrient source in the biological treatment means. Since trace amounts of TOC components and/or phosphorus components contained in pure water are almost completely removed, ultrapure water of extremely high quality without the fear of microbial growth can be obtained.

[Problems to be Solved by the Invention] However, in the above-mentioned prior application, since biological treatment is introduced, a bacterial cell separator is required in the process after biological treatment, so there are many equipment, equipment, and treatment steps. It was industrially disadvantageous in terms of equipment costs, maintenance, equipment space, etc.

On the other hand, if the bacterial cell divider is omitted and the biological IA water containing the bacterial cells is directly flowed into the RO device, the bacterial cells will cause the R
A gel layer is formed on the surface of a separation membrane such as an O membrane, causing significant clogging of the membrane, resulting in a problem that the continuous operation period becomes extremely short due to membrane deterioration and decrease in membrane flux.

[Means for Solving the Problems] The present invention makes it possible to omit the bacterial cell separator in the device of the above-mentioned prior application that incorporates biological treatment, and even in this case, the decrease in flux of the membrane separation device can be avoided. This method combines a method of suppressing water pollution, etc., by producing ultrapure water using an ultrapure water production system equipped with a membrane separation device, and collecting the wastewater discharged when the ultrapure water is used at the point of use. In an ultrapure water production method having a recovery system in which the recovered water is used again as raw water for the ultrapure water treatment system, the recovered water is subjected to biological treatment, hydrazine is injected into the obtained biologically treated water, and then a membrane separation device is used. The gist of this paper is a method for producing ultrapure water, which is characterized by supplying ultrapure water to water.

In a preferred embodiment of the present invention, pure water from a pure water production system is treated with biological treatment means to remove TOC components contained in the water. At this time, preferably a nutrient source is added for biological treatment. As mentioned above, since nitrogen eluted from an ion exchange resin or the like is usually dissolved in pure water, it is preferable to add phosphorus as a nutrient source. The amount of phosphorus added is most preferably such that almost all of the phosphorus is consumed when most of the TOC in the pure water is removed, but it may be slightly more or less than this amount.

If the TOC component is sufficiently removed in this way, microorganisms will not proliferate thereafter.

The degree of TOC removal is as follows: TOC in pure water is 10p.
It is preferable that the amount is less than pb, preferably less than Ippb.

In another preferred embodiment of the present invention, treated water from a pure water production system is treated by biological treatment means to remove phosphorus contained in the purified water to 10 ppt or less. If phosphorus is removed in this way, microorganisms will not grow again unless phosphorus is subsequently added to the purified water).

In yet another embodiment of the present invention, treated water from a pure water production system is treated with biological treatment means to remove nitrogen contained in the pure water.

In the present invention, the bacterial species used for biological treatment under such oligotrophic conditions include oligotrophic bacteria.
etc. are suitable. Oligotrophic bacteria are microorganisms that grow in water with extremely low TOC concentrations, such as ultrapure water, and by using them, the TOC concentration in treated water can be reduced to 50 ppb or less, for example 10 to 1 ppb.
It is possible to reduce the phosphorus or nitrogen concentration to about 10 ppt or less.

FIG. 4 is a graph showing an example of the relationship between the TOC concentration in ultrapure water (horizontal axis) and the growth rate of oligotrophic bacteria (vertical axis). In this example, acetic acid is used as a substrate, and by changing the amount added, the TOC in water can be adjusted from 0 to 35 degrees.
It changes between ppb. As shown, in this example, TO
As the C concentration decreases, the growth rate μ (hr-') also gradually decreases, and when the TOC concentration becomes 5 ppb or less, the growth rate μ decreases.
decreases linearly. On the other hand, even if the TOC concentration increases, the rate of increase in μ gradually decreases, and the maximum growth rate μmax
was 0.24h, r-'. From this example, when acetic acid is used as a substrate, oligotrophic bacteria proliferate at a growth rate of 0.12 to 0.24 hr-', and the TOC concentration in pure water decreases at a fairly rapid rate to below 5 ppb. It is acknowledged that this can be done.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a system diagram showing a pure water production apparatus suitable for carrying out the present invention. In FIG. 1, the configurations of the systems AlC, D, and E are the same as those in FIG. 2, so the same members are given the same reference numerals and the explanation of the configurations will be omitted.

In FIG. 1, water that has passed through the ultraviolet oxidizer 4 of the recovery system A is introduced into a biological reaction tank 13 and subjected to aerobic biological treatment. That is, the biological reaction tank 13 contains biological fixing means,
For example, it contains a fixed bed such as a honeycomb tube made of ceramic material, or a fluidized bed such as ceramic granular material. Therefore, elution of inorganic or organic substances from these fillers can be ignored. Then, the reaction is carried out for a period longer than necessary for the microorganisms to sufficiently propagate (multiply) in the presence of the energy source and nutrient source for the microorganisms. Note that since there is usually several ppm of dissolved oxygen in pure water, this reaction proceeds aerobically, but when dissolved oxygen is low, it is necessary to aerate with pure oxygen to provide aerobic conditions. is necessary. This reaction activates the microorganisms and assimilates the TOC components in the water. Thus, for example, this biological reaction continues until the TOC component contained in the water in the biological reaction tank 13 is almost completely eliminated.

In addition, in the apparatus shown in FIG. 1, the phosphorus or nitrogen concentration of the water from the ultraviolet oxidizer 4 is ToC? If the degree of IA is significantly lower than the IA degree, the rate of biological treatment in the biological reaction tank 13 will be extremely slow. In such a case, a small amount of phosphorus or nitrogen may be added to the artificial part of the biological reaction tank so that living organisms can proliferate and assimilate organic carbon. In this case, phosphorus is BOD in weight ratio to the amount of BOD components in water.
It is preferable to add so that the ratio of /phosphorus # is about 100/1 and the ratio of nitrogen is about 10015.

Further, in the present invention, a biological reaction may be performed so that no phosphorus or nitrogen remains. In this case, it is preferable that the entire pure water production device be made of a material that does not pose a risk of leaching phosphorus or nitrogen.

Furthermore, in the present invention, when performing biological treatment, the phosphorus and/or TOC components may be adjusted so that almost all of the phosphorus and TOC components are digested by microorganisms.

Due to the reaction in the biological reaction tank 13, organic carbon becomes CO2
Or it becomes a fungal body. Therefore, in the present invention, hydrazine is injected into the biological reaction treated water containing the bacterial cells. That is, as shown in FIG. 1, in the piping system that supplies treated water from the biological reaction tank 13 to the RO membrane separation device 7 of the ultrapure water production system B, there are a hydrazine pipe 15 for supplying hydrazine into the system, and A drug injection pump 16 is provided to inject hydrazine continuously or intermittently.

In this case, the amount of hydrazine to be injected is determined as appropriate depending on the quality of the treated water, the purpose of treatment, etc., but it is usually preferable to inject the hydrazine so that the concentration of hydrazine at the inlet of the RO membrane separation device 7 is equal to or higher than ippm. . Further, the pH in the system is preferably 6.5 or higher in order to maintain the effect of hydrazine well, and it is preferable to adjust the pH appropriately as necessary.

Since hydrazine has the effect of inhibiting the growth of bacteria, by injecting hydrazine, the R
It is possible to prevent bacteria from adhering to the O membrane and forming a gel layer, and the problems of membrane deterioration and flux reduction are resolved.

Therefore, when the biologically treated water into which hydrazine has been injected in this way is then supplied to the RO membrane separation device, it is efficiently subjected to membrane separation treatment, making it possible to produce high-quality ultrapure water.

In the above explanation, an example was explained in which the water discharged from the semiconductor cleaning process was treated and regenerated into ultrapure water.
Naturally, the present invention can be applied to various other types of equipment, such as equipment for treating water recovered from other processes, and processes for producing pure water from certain aqua regia, well water, etc.

[Function] The water obtained from the pure water treatment means has a low content of TOC components and salts, and can be used in semiconductor cleaning steps and the like. However, as mentioned above, microorganisms tend to multiply if left as is. Therefore, this treated water is further treated in a biological treatment tank.

In this biological treatment tank, biological treatment is performed aerobically in the presence of an energy source and a nutrient source, and trace amounts of TOC components and/or phosphorus components contained in pure water are almost completely removed.

By the way, the previous application required a bacterial cell separator to separate and remove the bacterial cells contained in the treated water from the biological treatment tank, but in the present invention, by injecting hydrazine into the biological treated water, , the subsequent membrane separation device is provided with a bacterial cell separation function based on the bacterial growth inhibiting effect of hydrazine.

As a result, the present invention does not require a microbial cell separator, and the pure water obtained is of extremely high quality with no fear of microbial growth.

[Example] Examples will be described below.

Example 1 Using the pure water production apparatus shown in FIG. 1, hydrazine was injected according to the present invention to produce pure water.

The quality of the raw water supplied to the RO membrane separation device and the operating pressure of the device were as follows.

Raw water quality Bacteria concentration: 1011 cells/mi Hydrazine concentration: 1-2 ppm pH: a.

Operating pressure = 10 kg/crn' In this case, examine the change in the amount of water permeated through the R○ membrane over time.
The results are shown in Figure 5.

For comparison, the change in the amount of water permeated through the RO membrane was similarly investigated in the case where hydrazine was not injected, and the results are shown in FIG.

As is clear from Figure 5, the ratio of permeated water amount after 500 hours of water flow is 2 in the case of adding hydrazine and the case of no addition.
:1, and the effect of suppressing flux reduction by hydrazine is remarkable.

[Effects of the Invention] As detailed above, the method for producing pure water of the present invention incorporates biological treatment means and utilizes the growth reaction of microorganisms to produce TOCi.
It removes TOC and/or phosphorus components.
Alternatively, the phosphorus component can be removed to an extremely low concentration at low cost. Moreover, since the growth of bacterial cells produced by biological treatment can be effectively suppressed by hydrazine, and the formation of a gel layer on the membrane surface by bacterial cells and membrane deterioration can be prevented, a bacterial cell separator is not required.

Therefore, since the pure water produced according to the present invention has an extremely low concentration of TOC and/or phosphorus components, which are factors for microbial growth, microbial growth is reliably suppressed. Furthermore, the amount of equipment and installation can be reduced, which is extremely advantageous in terms of equipment costs, maintenance management, and equipment space.

Therefore, according to the present invention, the generation of slime due to microbial growth is suppressed, and various equipment troubles such as slime adhesion to the RO or UF membrane surface are prevented. and,
The number of times the RO or UF is cleaned is also reduced, allowing smooth operation of the device and efficient production of pure water.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing a pure water production/recovery system employing a pure water production device suitable for carrying out the present invention, Figure 2 is a system diagram showing a general pure water production/recovery system, and Figure 3 is a system diagram showing a general pure water production/recovery system. is a system diagram showing the biological treatment system according to the earlier application, Fig. 4 is a graph showing the relationship between the TOC concentration of ultrapure water and the growth rate of microorganisms, and Fig. 5 is the amount of water permeated through the RO membrane obtained in Example 1. It is a graph showing the change over time. A... Recovery system, B... Pure water production system, C... Pretreatment system, D... Primary pure water system, E... Subsystem, F... Biological treatment system, 4 ... Ultraviolet oxidation device, 7... Reverse osmosis membrane device, 9... Ion exchange device, 12... Ultrafiltration membrane device, 13... Biological reaction tank, 14... Bacterial cell separator , 15... Hydrazine tank, 16... Chemical injection pump. Agent Patent Attorney Tsuyoshi Shigeno Fig. 3 Primary pure water to synutem D Fig. 4 - TOC concentration (ppb) Fig. 5 RO water flow time (h'')

Claims (6)

[Claims] (1) Ultrapure water is produced using an ultrapure water production system equipped with a membrane separation device, the ultrapure water is used at the point of use, the wastewater discharged is collected, and the recovered water is treated as ultrapure water again. In an ultrapure water production method having a recovery system that is used as raw water for the system, the ultrapure water is characterized in that the recovered water is subjected to biological treatment, hydrazine is injected into the obtained biologically treated water, and then the ultrapure water is supplied to a membrane separation device. Production method. (2) The method for producing ultrapure water according to claim 1, wherein the ultrapure water treatment system includes a membrane separation device and an ion exchange column containing an ion exchange resin. (3) The method for producing ultrapure water according to claim 1 or 2, wherein the biological treatment is a treatment for removing TOC components from water. (4) The method for producing ultrapure water according to claim 1 or 2, wherein the biological treatment is a treatment for removing phosphorus from water. (5) The method for producing ultrapure water according to claim 1 or 2, wherein the biological treatment is a treatment for removing nitrogen from water. (6) The method for producing ultrapure water according to any one of claims 1 to 5, wherein the microorganism used for biological treatment is an oligotrophic bacterium.