JPH1119663A - Removing method for organic matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amt. of an oxidizing agent by adding oxygen and persulfuric acid and/or persulfate as the oxidizing agent to raw water, then subjecting the water to heat treatment, in the case that total org. carbon components in the raw water are decomposed by heat-treating the raw water in the presence of the oxidizing agent, then subjecting the water to a deionizing treatment. SOLUTION: At the time of removing the total org. carbon TOC at a production stage, etc., of ultrapure water, the raw water subjected to a pre-treatment is introduced into a treating vessel 1, and after bubbling the oxygen or an oxygen rich air, the water is introduced into a thermally decomposing reactor 3 with a pump 2 after adding the oxidizing agent. The addition of the persulfate, etc., as the oxidizing agent is preferably within the range of 15-35 pts.wt. as S2 O8 <2-> per 1 pts.wt. TOC in the raw water. The oxygen is added to the raw water having >=4 ppm TOC when IPA is an object matter as the TOC component so that a dissolved oxygen concn. may be >=8 ppm, then the persulfate, etc., are preferably added so that S2 O8 <2-> concn. per 1 pts.wt. TOC may be 20-35 pts.wt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing organic substances, and more particularly, to TOC in ultrapure water or ultrapure water production process.
(Total organic carbon) The present invention relates to a method for removing organic substances with greatly improved removal efficiency.

[0002]

2. Description of the Related Art In the production of ultrapure water used mainly for cleaning semiconductor substrates and liquid crystal substrates, the removal of TOC is very important as is the removal of other impurities (fine particles, ions, etc.). In addition, especially when cleaning semiconductor substrates and liquid crystal substrates and collecting and reusing rinse wastewater, protecting the processing equipment from bacterial fouling and maintaining stable operation are also important.
It is very important to reduce the TOC before removing impurities by another unit device.

[0003] For this reason, in order to obtain treated water whose TOC is reduced to a target level, a two-stage reverse osmosis membrane separation treatment, a low-pressure ultraviolet oxidation treatment using an ion exchange tower in combination, a biological treatment and the like are performed. In addition, in order to reduce the processing cost and to further reduce the TOC, the present applicant has filed an application for a thermal decomposition type TOC removal method using an oxidizing agent (WO094 / 18127). According to this method, raw water containing TOC on the order of several ppm can be highly processed to several ppb-TOC in a single-stage process. Applicant also concluded that persulfuric acid or persulfate is the most suitable oxidizing agent to be used in this TOC removal method, and that the amount of S ₂ O ₈ per 1 part by weight of TOC in raw water
It has been confirmed that it is appropriate to use 20 to 45 parts by weight in terms of ^2- , and a patent application was filed earlier (Japanese Patent Application Laid-Open No. 8-1739).
No. 78).

[0004] In this TOC removal method by the thermal decomposition method, (a) TOC can be removed to a low level with a simple device. (b) According to the TOC concentration of the raw water, it can be dealt with only by adjusting the amount of the oxidizing agent added. (c) Since there is a heating step, it prevents the growth of bacteria,
Organic matter as a nutrient source is reduced, and bacterial fouling can be reduced. There is such an excellent advantage.

[0005]

However, in the above-mentioned conventional thermal decomposition method, when treating raw water having a TOC of about 1 ppm, there is not much problem.
In the case of raw water of ppm or more, TOC could not be reduced to the target water quality unless the amount of the oxidizing agent was considerably increased.

[0006] The oxidizing agent added by this method, for example, sodium persulfate, is present as sulfuric acid and sodium sulfate after the decomposition reaction of the TOC component. Therefore, the need for a large amount of the oxidizing agent causes not only a rise in the cost of the chemical, but also a problem of an increase in the load on the downstream equipment.

The present invention solves the above-mentioned conventional problems, and heat-treats raw water in the presence of an oxidizing agent to decompose the TOC component in the raw water, followed by deionization to remove organic substances in the raw water. In a method, an object of the present invention is to provide a method for removing organic substances, which greatly reduces the amount of an oxidizing agent used.

[0008]

According to the method for removing organic substances of the present invention, raw water is heat-treated in the presence of an oxidizing agent to remove T from raw water.
In a method of removing organic matter in raw water by deionizing after decomposing an OC component, oxygen is added to raw water,
After adding persulfuric acid and / or persulfate as an oxidizing agent, heat treatment is performed. In the following, persulfate and persulfate may be referred to as “persulfate or the like”.

When the TOC component in the raw water is all isopropyl alcohol (IPA: C ₃ H ₇ OH, this IPA is typically used for recovering semiconductor cleaning wastewater and obtaining pure water using the same as raw water, which is included in the cleaning wastewater. It is assumed that this is a typical substance), and this is converted into Na ₂ S ₂ O as a persulfate.
_In the case of treating by the thermal decomposition method using ₈ , a decomposition reaction occurs according to the following reaction formula.

C ₃ H ₇ OH + 9Na ₂ S ₂ O ₈ + 9H ₂ O → 3CO ₂ + 4H ₂ O
+ 9Na ₂ SO ₄ + 9H ₂ SO ₄ As is clear from the above reaction formula, 9 mol of Na ₂ S ₂ O ₈ is required for 1 mol of IPA (3 mol of carbon). In terms of the concentration, oxidative decomposition of 1 ppm of TOC requires 59.5 ppm of Na ₂ S ₂ O ₈ (67.5 ppm for K ₂ S ₂ O ₈ ). Therefore,
It is considered that addition of about 70 mg / L of persulfate per 1 mg / L of TOC is preferable.

However, in the ordinary thermal decomposition treatment, it is necessary to add about 30 ppm of Na ₂ S ₂ O ₈ lower than 59.5 ppm to 1 ppm of TOC (ie, about 50% of the above theoretical amount). And good treated water can be obtained.

The present inventors conducted a more detailed study on the required addition amount of persulfate and the like / TOC ratio of raw water to reduce the TOC in the treated water to a level of several tens of ppb or less by this thermal decomposition method. However, it was confirmed that this ratio was not constant, but increased when the TOC concentration in the raw water rose above a certain range, and that a large amount of persulfate and the like had to be added to decompose the unit amount of TOC. . As a result of further intensive analysis of this phenomenon, the TO
In the C decomposition, it was found that not only persulfate as an oxidizing agent but also dissolved oxygen in raw water contributed.

Based on this finding, the present inventors have found that in the thermal decomposition treatment of TOC in raw water, the required added amount of persulfate or the like / TOC of raw water is increased by increasing the dissolved oxygen concentration of the raw water in advance. The present inventors have found that the ratio can be kept equal to that in the treatment of raw water having a low concentration of TOC, and that the amount of persulfate and the like can be significantly reduced as compared with the prior art, thus completing the present invention.

The method of the present invention is particularly suitable for the TOC
Is effective for treating raw water having a relatively high TOC concentration of 4 to 5 ppm or more, but even with raw water having a TOC of about 1 to 2 ppm, the required amount of persulfate and the like can be effectively reduced.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the oxygen adding means in the organic matter removing method of the present invention.

In the organic matter removing method of the present invention, oxygen and a persulfate as an oxidizing agent are added to raw water which has been subjected to pretreatment, if necessary, followed by thermal decomposition treatment, followed by deionization treatment. Further post-processing is performed as necessary. In addition, oxygen is
It may be added before the oxidizing agent is consumed in the thermal decomposition treatment, and may be added before or after the oxidizing agent is added.

As the raw water, recovered water from the semiconductor or liquid crystal cleaning process, industrial water, city water, well water and a mixture thereof are generally used. For the recovered water from the semiconductor cleaning process, an appropriate pretreatment is used. After passing through the process, it is preferable to introduce into the thermal decomposition process.

As the pretreatment step, any means can be provided according to the quality of the raw water, and for example, means such as coagulation, filtration, flotation, adsorption, and ion exchange can be employed. Specific pretreatment steps include the following (i) to (iii). In particular, with respect to the recovered water from the semiconductor washing step, after the H ₂ O ₂ contained in the activated carbon adsorption tower is removed by the pretreatment of the following (iii), fluorine is removed in the strong anion exchange tower to perform thermal decomposition. Preferably, it is introduced into the processing step.

(I) Coagulation / pressure flotation / filtration device (ii) Ion exchange column (iii) Activated carbon adsorption column → anion exchange column In the present invention, a method of adding oxygen to raw water to increase the dissolved oxygen concentration is as follows. For example, the following method can be used.

That is, it is a well-known fact that the saturated dissolved oxygen concentration of water is generally about 8 ppm at room temperature, which is in equilibrium with the air component which is a mixed system with nitrogen (and other trace components). Is the dissolved oxygen concentration at Therefore, if the oxygen partial pressure of the gas in contact with the raw water is increased by any means, the dissolved oxygen concentration can be easily increased to 8 ppm or more. In addition, since the raw water is pressurized on the outlet side (reactor side) of the pump that feeds the raw water to the thermal decomposition apparatus, the gas can be dissolved to a degree higher than the solubility under atmospheric pressure. By injecting oxygen or air into the high-pressure section, the dissolved oxygen concentration of the raw water can also be increased. Note that oxygen or air does not necessarily need to be completely dissolved in raw water. That is, the oxygen in the gas remaining undissolved in the thermal decomposition apparatus is dissolved in water in parallel with the consumption of dissolved oxygen during the thermal decomposition reaction, and has the effect of maintaining the dissolved oxygen concentration.

Therefore, in the present invention, as a means for adding oxygen to raw water, for example, the following method I-VI can be mentioned. The following I-VI shows an example of the oxygen adding means according to the present invention, and the present invention is not limited to these methods. I A method of introducing raw water into the treatment tank 1 and bubbling oxygen or oxygen-enriched air as shown in FIG. This raw water is then introduced into the thermal decomposition reactor 3 by the pump 2 after adding the oxidizing agent.

II. As shown in FIG. 1 (b), a method in which raw water is introduced into a gas permeable membrane module 4 and oxygen or oxygen-enriched air is injected into the module 4. This raw water is then introduced into the thermal decomposition reactor 3 by the pump 2 after adding the oxidizing agent.

Prior to the means I and II, the concentration of all dissolved gases (particularly dissolved nitrogen) in the raw water may be reduced by vacuum degassing or degassing with a gas permeable membrane module. It is effective in increasing the oxygen dissolving efficiency. Further, a method of supplying oxygen while depressurizing the gas phase portion of the gas permeable membrane module is also suitable as the preliminary treatment. These methods are suitable for processing upstream of the water pump 2 to the reactor 3.

III As shown in FIG. 1C, a method of injecting an oxygen-containing gas such as compressed air into the raw water by a compressor or the like at the outlet side of a pump 2 for introducing the raw water into the thermal decomposition reactor 3. IV A method in which air or oxygen at normal pressure or pressure is sucked into the piping on the inlet side of the pump 2 for introducing raw water into the thermal decomposition reactor 3 using an ejector or the like. V A method in which the thermal decomposition reaction section is multi-staged, and the intermediate portion of each stage is open to the atmosphere to increase dissolved oxygen. VI In the above-mentioned V, the above-mentioned I or
How to do II.

In the present invention, the amount of oxygen added to the raw water varies depending on the TOC concentration in the raw water, the reduction ratio of the amount of the oxidizing agent added, the target treated water TOC, and other various conditions. TOC4 when targeted
In the case of raw water of not less than ppm, the dissolved oxygen concentration in the raw water should be 8 ppm or more, which is the saturated concentration in equilibrium with the atmosphere (supersaturated).
It is preferable to set the addition amount so that
If the dissolved oxygen concentration is less than 8 ppm, the effect of reducing the oxidizing agent according to the present invention cannot be sufficiently obtained. The amount of oxygen added may be measured by measuring the dissolved oxygen concentration of the raw water after oxygen addition with a dissolved oxygen concentration meter, and controlling the dissolved oxygen concentration based on the measured value.

In the present invention, oxidizing agents include sodium peroxydisulfate (Na ₂ S ₂ O ₈ ), potassium peroxydisulfate (K ₂ S ₂ O ₈ ), and ammonium peroxydisulfate ((NH ₄ ) ₂ S ₂ O). ₈₎ persulfates or persulfuric acid (H ₂ S ₂ O ₈₎ can be mentioned, such as but, Na ₂ S
Persulfates such as ₂ O ₈ and K ₂ S ₂ O ₈ are preferred.

The addition amount of persulfate or the like as an oxidizing agent varies depending on the concentration of dissolved oxygen in the raw water due to the above-mentioned addition of oxygen, but is 15 to 35 weight% as S ₂ O ₈ ^2- per 1 part by weight of TOC in the raw water. The range is preferably in the range of parts. TOC1
If the added amount of persulfate or the like in terms of S ₂ O ₈ ^2- per part by weight is less than this range, the oxidizing agent becomes insufficient, and a large amount of TOC remains. It becomes excessive and places a load on the downstream device, causing problems such as elution of the TOC component from the downstream device.

In the present invention, in particular, IP as a TOC component
After adding oxygen so that the dissolved oxygen concentration becomes 8 ppm or more to the raw water having a TOC of 4 ppm or more in the case of A, the amount of S ₂ O ₈ ² per 1 part by weight of TOC is adjusted to 20 to 35 parts by weight. It is preferable to add a sulfate or the like.

In the present invention, the heating temperature in the thermal decomposition treatment after the addition of the oxidizing agent is 90 ° C. or higher, particularly 110 to 15 ° C.
The temperature is preferably 0 ° C., and the heat decomposition reaction time is as follows:
Although it depends on the heating temperature, the raw water TOC, the dissolved oxygen concentration, and the amount of the oxidizing agent added, it is usually preferably 1 to 15 minutes.

In the thermal decomposition treatment, a platinum-based oxidation catalyst such as a platinum-supported catalyst or a platinum plating catalyst may be brought into contact with the catalyst.

It should be noted that although there is no particular need to adjust the pH conditions of the heat decomposition treatment, TOC is more easily decomposed on the acidic side. Usually, when persulfate or the like is added to neutral raw water, H ₂ SO ₄ is generated due to oxidative decomposition of the TOC component or self-decomposition of the oxidizing agent, and the pH becomes acidic.
There is no particular need for pH adjustment.

The thermally decomposed water is then subjected to a deionization treatment. Prior to the deionization treatment, an oxidizing agent removal treatment is performed as necessary.

That is, when the excess oxidizing agent in the pyrolysis process is contained in the pyrolysis water and flows into the deionization process, the reverse osmosis membrane and the ion exchange resin in the deionization process are oxidatively degraded, and the degraded resin is degraded. This causes problems such as an increase in TOC and a reduction in the life of the apparatus due to elution of the methane.

In the present invention, since the amount of persulfate and the like as an oxidizing agent is small, the amount of persulfate and the like contained in the water subjected to the thermal decomposition treatment is small. Although not performed, the effect of the oxidizing agent on the deionization process can be reliably prevented by performing the oxidizing agent removing process.

As the oxidizing agent removing means, a packed column filled with activated carbon and / or a suitable catalyst can be employed.

The activated carbon may be granular, powdery or fibrous, but granular or fibrous ones are particularly advantageous in terms of water flow efficiency. There is no particular limitation on the type of activated carbon (coconut-based, coal-based, etc.). On the other hand, as the catalyst, various catalysts such as generally used platinum-based catalyst and palladium-based catalyst can be used.

The above-mentioned activated carbon and catalyst can attain the object by using only one of them, but depending on the case,
You may use both together. In addition, as the oxidizing agent removing means, ultraviolet irradiation can be employed.

The oxidizing agent removal treatment conditions are such that persulfate and the like remaining in the heat decomposition treatment water are removed to a sufficiently low concentration that the ion exchange resin and the reverse osmosis membrane in the subsequent deionization treatment step are not oxidatively degraded. Any condition can be used as long as it is possible, and it is appropriately determined according to the concentration of the residual persulfate and the like in the heat decomposition water and the specification of the oxidizing agent removal step, that is, the shape, particle size, filling amount, etc. of the activated carbon and the catalyst. For example, when pyrolysis water containing 10 ppm of residual Na ₂ S ₂ O ₅ is treated in a 20/40 mesh granular activated carbon packed tower, SV = 40.
It is preferable to be about hr ^-1 or less.

Since the heat-decomposed water is usually acidic with a pH of 4 or less, in order to protect such a residual oxidizing agent removing apparatus from corrosion, a pH between the heat-decomposing step and the oxidizing agent removing step is reduced. It is preferable to provide an alkali injection means for adjustment, neutralize the acidic water, and then introduce it to the oxidizing agent removing step.

In the present invention, an ion exchange tower, a reverse osmosis membrane separation device, or the like can be used in combination as a deionization means as required. That is, for example, an ion exchange tower → a reverse osmosis membrane separator, a reverse osmosis membrane separator → an ion exchange tower, or a reverse osmosis membrane separator → a reverse osmosis membrane separator can be used.

As the post-treatment means, any means can be adopted according to the required quality of the treated water.
Sterilization by UV oxidation, TOC decomposition, or ion exchange, reverse osmosis membrane separation, microfiltration membrane separation, ultrafiltration membrane separation equipment, etc., generally equivalent to the secondary pure water production process (subsystem) in ultrapure water production Process, ie, low-pressure ultraviolet irradiation equipment (organic matter decomposition) → mixed-bed ion exchange tower (non-regenerating ion exchanger: removal of decomposition products) → ultrafiltration membrane separation equipment (ion exchange flowing out of the ion exchange tower) (Separation of resin fine particles) is employed.

Specific examples of the deionization step and the post-treatment step include the following (i) to (v).

(I) Decarbonation tower → anion exchange tower → reverse osmosis membrane separator → secondary pure water production process (ii) Reverse osmosis membrane separator → low pressure reverse osmosis membrane separator → secondary pure water production process (iii) ) Cation exchange tower → decarbonation tower → anion exchange tower → reverse osmosis membrane separator → secondary pure water production process (iv) Weak anion exchange tower → strong cation exchange tower → strong anion exchange tower → secondary pure water production process ( v) Reverse osmosis membrane separation equipment → ion exchange tower (mixed bed type ion exchange tower or (strong cation exchange tower → strong anion exchange tower))
→ Secondary pure water production process The equipment for these deionization and post-treatment processes removes the TOC component by heat treatment in advance, and has a small amount of persulfate as an oxidizing agent. It is reduced and a small capacity small device can be adopted.

The method for removing organic substances according to the present invention is as follows.
In particular, the TOC is 4 to 5 ppm or more and the relative T
This is effective when treating water having a high OC concentration, and can significantly reduce the required amount of an oxidizing agent.
Even with raw water of about 1 ppm C, the effect of reducing the amount of the oxidizing agent can be sufficiently obtained.

[0046]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 and Comparative Example 1 As a simulated liquid of organic wastewater, water obtained by dissolving a reagent grade IPA in ultrapure water was used as raw water, and Na ₂ S ₂ O ₈ was used as an oxidizing agent.
, And a thermal decomposition experiment of TOC was performed.

The reaction temperature was 130 ° C., the reaction time was 5 minutes,
The raw water TOC was fixed at 9 ppm, and the amount of Na ₂ S ₂ O ₈ injected and the Na with respect to the raw water TOC required to reduce the TOC of the treated water to 20 ppb or less under the following dissolved oxygen concentration conditions.
The ratio of the ₂ S ₂ O ₈ injection amount was examined, and the results are shown in Table 1.

Comparative example of dissolved oxygen concentration Comparative example 1: no dissolved oxygen adjustment (dissolved oxygen concentration 7.2 pp
m) Example 1: Dissolved oxygen concentration of raw water was increased to 12 ppm by oxygen bubbling Example 2: Dissolved oxygen concentration of raw water was increased to 24.5 ppm by oxygen bubbling

[0050]

[Table 1]

As is apparent from Table 1, the required amount of the oxidizing agent can be reduced by increasing the dissolved oxygen concentration of the raw water by bubbling. In particular, in Example 2, the oxidizing agent can be reduced by about 31% as compared with Comparative Example 1 in which no treatment with dissolved oxygen is performed.

Examples 3-6, Comparative Examples 2-5 The actual wastewater containing several kinds of organic substances derived from the substrate cleaning chemicals was used as raw water, Na ₂ S ₂ O ₈ was used as an oxidizing agent, and T
An OC thermal decomposition experiment was performed.

When the reaction temperature is 130 ° C., the reaction time is 5 minutes, and the TOC raw water shown in Table 2 is treated under the following dissolved oxygen concentration conditions, the Na required to reduce the TOC of the treated water to 20 ppb or less is obtained. ₂ S ₂ O ₈ injection amount and raw water TOC
The ratio of the amount of Na ₂ S ₂ O ₈ injected to the mixture was determined. The results are shown in Table 2.

Dissolved oxygen concentration conditions Comparative Examples 2 to 5: no dissolved oxygen adjustment (dissolved oxygen concentration 7.0 p
pm) Examples 3 to 6: Compressed air (0.8 MPa) by a compressor was quantitatively injected between the outlet of the pressurizing pump and the reactor by 0.5 volume (normal pressure conversion) per 1 volume of raw water (dissolved oxygen) Supersaturated).

[0055]

[Table 2]

As is clear from Table 2, by injecting pressurized air and increasing the dissolved oxygen concentration of the raw water, the oxidizing agent could be reduced by 9 to 45% as compared with the case where no dissolved oxygen was treated. The effect of reducing the required amount of the oxidizing agent added by increasing the dissolved oxygen concentration was more remarkable as the raw water TOC concentration was higher, but it was confirmed that the effect was exhibited even in raw water having a lower TOC concentration.

Example 7 The following raw water was passed through the pure water production system shown in FIG.

Raw water: Raw water 1 (IPA dissolved ultrapure water, TO
C: 20.2 ppm) and Raw Water 2 (Atsugi City Water, TOC:
0.8 ppm) and raw water 1: raw water 2 = 1: 2 (TOC: 7 ppm, DO: 7.0 ppm) In the system of the present embodiment, raw water is heated by the heat exchanger 11 , Oxygen and then Na ₂ as oxidant
S ₂ O ₈ is added, and the thermal decomposition of the TOC is performed in the thermal decomposition reactor 12. The heat-decomposed water is then supplied to the cooling heat exchanger 1
After cooling in 3, NaOH for neutralization is added, and residual Na ₂ S ₂ O ₈ is removed in the activated carbon tower 14. Next, water was passed through a reverse osmosis membrane separator 16 and an ion exchange tower 17 sequentially through a flow rate adjusting tank 15 to obtain treated water. The specifications and processing conditions of each part are as follows. In addition, in FIG. 2, the numerical value in a parenthesis is the flow rate of each part. Indicates a sampling point.

Oxygen injection amount: dissolved oxygen concentration after oxygen injection 1
5 ppm Na ₂ S ₂ O ₈ addition amount: 217 ppm Thermal decomposition reactor: Reactor capacity = 10 liters Reaction temperature = 130 ° C Average residence time = 5 minutes Activated carbon tower: Activated carbon = Kurikol WG-160 manufactured by Kurita Water Industries Ltd.
SV / 40 hr ^-1 reverse osmosis membrane separator: equipment = "NTU 729 HRS2" manufactured by Nitto Denko Corporation Permeate recovery rate = 70% Ion exchange tower: Ion exchange resin = Mitsubishi Chemical ( Ltd. “Diaion SM”
500 ml of N-UP "(mixture of a strongly acidic cation exchange resin and a strongly basic anion exchange resin) SV = 29.4 hr ^-1 Water quality collected at each part was analyzed, and the results are shown in Table 3. .

Comparative Example 6 A treatment was carried out in exactly the same manner as in Example 7 except that oxygen was not injected, and the results are shown in Table 3.

[0061]

[Table 3]

As shown in Table 3, in Example 7 in which oxygen was injected, T
The addition amount of Na ₂ S ₂ O _{8 to 1} part by weight of OC is S ₂ O ₈
It is clear that a thermal decomposition treatment of about 25 parts by weight in terms of ^2- yields pure water with extremely low TOC. On the other hand, in Comparative Example 6, in which oxygen was not injected, the oxidizing agent was insufficient, so that TOC could not be sufficiently removed.

[0063]

As described above in detail, according to the organic matter removing method of the present invention, the amount of persulfate or the like as an oxidizing agent is reduced in the thermal decomposition of TOC, thereby reducing cost and efficiency. Processing can be performed. Further, since the added amount of persulfate and the like is small, as a result, the influence on the deionization treatment step after the thermal decomposition treatment by excess persulfate and the like is prevented, and the persulfate derived from the added persulfate and the like Since the concentrations of sulfate and sulfuric acid in the heat decomposition treatment water are low, the scale of the apparatus in the deionization treatment step can be reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an oxygen adding means in an organic matter removing method of the present invention.

FIG. 2 is a flowchart illustrating a pure water production system according to a seventh embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing tank 2 Pump 3 Heat decomposition reactor 4 Gas permeable membrane module 11 Heating heat exchanger 12 Heat decomposition reactor 13 Cooling heat exchanger 14 Activated carbon tower 15 Tank 16 Reverse osmosis membrane separator 17 Ion exchange tower

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Morita 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Kurita Kogyo Co., Ltd. (72) Inventor Yoshiharu Obata 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo No. Kurita Kogyo Co., Ltd. (72) Inventor Ryohei Miwa 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A method for removing raw material organic matter in raw water by subjecting raw water to heat treatment in the presence of an oxidizing agent to decompose TOC components in the raw water, and then deionizing the raw water. A heat treatment after adding persulfuric acid and / or persulfate.