JP4712665B2 - Pure water production method and pure water production apparatus - Google Patents

Description

  The present invention relates to a pure water (or ultrapure water) production method used in an electronic product manufacturing plant such as a liquid crystal or a semiconductor, a power plant, a pharmaceutical manufacturing plant, etc., and is processed by adding an aluminum-based flocculant. The present invention relates to a pure water production method and a pure water production apparatus for preventing a film adhesion substance contained in water to be treated from adhering to a membrane treatment apparatus such as a reverse osmosis membrane or an ultrafiltration membrane.

In water treatment such as production of drinking water (water tap water) and industrial water (industrial tap water) and waste water treatment, agglomeration treatment is widely performed to remove suspended solids, dissolved organic matter, colloidal silica, and the like. In this agglomeration treatment, aluminum-based or iron-based inorganic metal salts such as aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC), ferric sulfate, polyferric sulfate, and ferric chloride are used as the aggregating agent. The aggregating agent is used alone or in combination. Among these, PAC is most widely used because it is inexpensive and has a wide pH range for aggregation (see, for example, Patent Document 1).
JP 2003-103258 A

  However, since an aluminum-based flocculant is used, there is a problem that aluminum remains in the treated water. In Japan, residual aluminum is 0.2 mg / L or less in terms of comfortable water quality in the water quality standards for drinking water, and if a large amount of aluminum-based flocculant is used, this standard may be exceeded. Further, residual aluminum may be accumulated in circulating water such as pool water and bathtub water, and in recent years, nervous system diseases such as Alzheimer's disease due to aluminum are also a concern.

  In addition, since the inorganic metal salt flocculant does not form a sufficiently large floc when used alone, there is a disadvantage that the solid-liquid separation rate is low in the coagulation sedimentation step, the sand film treatment step, etc. Since the range depends on the quality of the water to be treated, aggregation may not occur or all of the flocculant may remain in the treated water without aggregation.

  Therefore, the amount of the flocculant used is always optimally controlled so that the residual aluminum is controlled to 0.2 mg / L or less.

  On the other hand, since there is no such limitation in industrial tap water, the residual aluminum concentration may be higher than 0.2 mg / L, and in some cases, it remains to a concentration exceeding 0.5 mg / L. There is also.

  In the production of pure water or ultrapure water using such tap water or industrial tap water containing aluminum as the raw water, the tap water or industrial tap water is further mixed with a reverse osmosis membrane device (RO), ultrafiltration. Water is passed through a membrane treatment device such as a device (UF), and further, a treatment is performed by combining an ion exchange resin device, an ultraviolet irradiation device, and the like.

  However, residual aluminum in tap water or industrial tap water adheres to a membrane treatment device such as a reverse osmosis membrane device and gradually increases the differential pressure, thereby reducing the performance of the membrane treatment device and shortening the service life. It was to become.

  A method for preventing the adhesion of the flocculant to the filtration membrane by adding a flocculant adhesion inhibitor immediately before the membrane treatment apparatus is known (Japanese Patent Laid-Open No. 2005-224761). However, with this method, when the residual aluminum concentration is high, there is a problem that the amount of chemicals used increases and the operating cost increases.

  In addition, as another technique, a method of operating a reverse osmosis membrane device by adding an acid to tap water or industrial tap water and avoiding a pH to which residual aluminum adheres is conceivable. Since the operation needs to be lowered to about 4 or less, problems such as corrosion / deterioration of membrane treatment equipment, surrounding piping, pumps, etc., and neutralization of drainage are unavoidable.

  Therefore, in the process of producing pure water, the present invention effectively removes the aluminum contained in the raw water by a simple operation, achieves an improvement in water quality, and adheres residual aluminum to the subsequent membrane treatment apparatus. The purpose is to prevent this.

  The present inventor has made extensive studies to solve the above-mentioned problems, and as a result, pretreatment using an iron-based inorganic polymer flocculant, that is, coagulation-precipitation treatment or filtration treatment using a micro floc method, residual aluminum. It was found that can be effectively removed.

  That is, the pure water production method of the present invention includes a removal step of adding an iron-based inorganic polymer flocculant to raw water treated with an aluminum flocculant to remove residual aluminum, and a treated water that passes through the removal step. And a membrane treatment process for passing water through the membrane treatment apparatus.

  Further, the pure water production apparatus of the present invention includes a flocculant addition means for adding an iron-based inorganic polymer flocculant to raw water treated with an aluminum-based flocculant, and the added iron-based inorganic polymer flocculant. An aluminum removing means for removing the agglomerated residual aluminum, and a membrane treatment device for passing treated water from which the residual aluminum has been removed.

  The pure water production method and the pure water production apparatus of the present invention can of course be applied to the production of ultrapure water depending on the apparatus configuration, and are used in a factory for manufacturing electronic products such as liquid crystals and semiconductors. Such a method and apparatus for producing ultrapure water are also included.

  According to the pure water production method and the pure water production apparatus of the present invention, in the case of using tap water or industrial tap water treated with an aluminum-based flocculant as raw water, residual aluminum contained in the raw water is effectively used. By removing the water, the quality of pure water is improved, aluminum is prevented from adhering to the film processing apparatus, the increase in the differential pressure is suppressed, the performance of the film processing apparatus is suppressed, and the film processing apparatus Can extend the lifespan.

  The pure water production method of the present invention includes an aluminum removal step of adding an iron-based inorganic polymer flocculant to raw water treated with an aluminum flocculant to remove residual aluminum, and treated water that has passed through the aluminum removal step. Is a two-step process called a membrane treatment step for passing water through a membrane treatment apparatus.

  Here, in the aluminum removal step, an iron-based inorganic polymer flocculant is added to the raw water to cause aluminum flocs contained in the raw water to be removed as aggregates. The raw water used here is treated with an aluminum-based flocculant and remains with aluminum, for example, treated with an aluminum-based flocculant such as PAC and sulfuric acid band such as tap water and industrial tap water. If present, this step can be applied as it is. When raw water is not yet treated with an aluminum-based flocculant, a step of adding an aluminum-based flocculant may be provided before this step.

Examples of the iron-based inorganic polymer flocculant added here include a polymer compound that is an iron-based flocculant and includes a repetition of the basic structure, such as polyiron and polysilica iron. The degree of polymerization can be 2 or more, and is preferably 10 or more. Here, polyiron is ferric sulfate, and its molecular formula is [Fe ₂ (OH) _n (SO ₄ ) _{3−n / 2} ] _m (where 0 <n ≦ m / 2 and m> 10). Specific examples of products that can be used as the polyiron include polyiron-D, polyiron-C (manufactured by Nittetsu Mining Co., Ltd., trade name), and the like.
The molecular formula of polysilica iron is [SiO ₂ ] _n · [Fe ₂ O ₃ ], and a molecular weight of about 500,000 daltons is effective. Specific products that can be used as the polysilica iron include PSI-025, PSI-050, and PSI-075 (above, manufactured by Seiko Kiko Co., Ltd., model number).

  At this time, the addition amount of the iron-based inorganic polymer flocculant should be appropriately added in accordance with the residual aluminum concentration contained in the raw water. In the case of tap water, the residual aluminum concentration However, when the raw water is industrial tap water of 0.2 ppm or less, the residual aluminum concentration is about 0.1 to 0.5 ppm, and the iron-based inorganic polymer flocculant is, for example, 10 to 100 ppm. It is preferable to add to the raw water so as to have a concentration. By processing in this way, the residual aluminum concentration can be reduced to an extremely low level of 0.01 ppm or less.

  In addition, before or simultaneously with the addition of the iron-based inorganic polymer flocculant, or at the same time, a bactericidal agent for suppressing the growth of viable bacteria can be added. Examples of the bactericidal agent include sodium hypochlorite and potassium hypochlorite. And hypochlorite compounds such as calcium hypochlorite.

  In this aluminum removal step, after adding the iron-based inorganic polymer flocculant, the aluminum is removed using a known filtration means such as a known agglomeration settling device such as an inclined plate sedimentation basin or a sand filtration device. To be removed. When a coagulation sedimentation apparatus is used, residual aluminum may be further removed using a rapid filtration apparatus or the like.

  Next, the membrane treatment process refers to a process of removing the impurities such as various ions and organic substances by subjecting the water to be treated which has passed through the aluminum removal process to a water treatment treatment by a membrane treatment apparatus. As a film treatment apparatus used here Examples include a reverse osmosis membrane device and an ultrafiltration device.

  In this membrane treatment process, since the aluminum contained in the raw water is agglomerated in the previous stage, the adhesion of residual aluminum to the membrane treatment apparatus used here is effectively suppressed, and other impurities due to the membrane treatment are removed. Removal can be performed efficiently. By not attaching residual aluminum to the membrane treatment apparatus in this way, the lifetime of the membrane treatment apparatus can be extended, and accordingly, the cost of the entire water treatment can be effectively saved.

  In addition, in this invention, you may make it perform the process by the other apparatus used in manufacture of a pure water other than this aluminum removal process and a film | membrane process, for example, a 2 bed 3 tower type ion exchange apparatus, Examples of the treatment include a known apparatus used for producing pure water or ultrapure water such as an ion exchange apparatus such as a cation exchange apparatus or an anion exchange apparatus, an ultraviolet irradiation apparatus, or a deaeration apparatus. These other apparatuses may be provided after the iron-based inorganic flocculant is added and before the residual aluminum is removed, and the addition of the flocculant and the removal of the residual aluminum are not necessarily processed continuously. Also good.

  Moreover, in order to prevent adhesion of aluminum to the film processing apparatus of the present invention, an aluminum adhesion inhibitor can be used in combination with the iron-based inorganic polymer flocculant. this is. Abnormal increase of aluminum in raw water (often occurs immediately after typhoon, heavy rain, etc., or immediately after deterioration of raw water quality to waterworks), or when conditions such as coagulation device malfunction, flow rate change Can also be supported. When this aluminum adhesion inhibitor is used, adhesion of residual aluminum to a membrane treatment apparatus such as a reverse osmosis membrane apparatus can be more effectively suppressed.

（ここで、Ｒは炭素数２〜６の直鎖状又は分枝鎖状のアルキレン基である。）又はその塩を含有する凝集剤付着抑制剤が挙げられる。ちなみに、この化合物の分子量は、４００〜１００００の範囲である。 As this aluminum adhesion inhibitor, for example, a compound represented by the following general formula (I) as described in JP-A-2005-224761

(Here, R is a linear or branched alkylene group having 2 to 6 carbon atoms) or a flocculant adhesion inhibitor containing a salt thereof. Incidentally, the molecular weight of this compound is in the range of 400-10000.

  Hereinafter, the present invention will be described by reference examples, examples and comparative examples. Note that the present invention is not limited to these descriptions.

(Reference example)
First, the flocculating agent which can be used for the coagulation sedimentation was investigated using the jar test. The test method is as follows.

〔Test method〕
In a 500 mL beaker, raw water (Tsukuba city industrial water in Ibaraki Prefecture: residual aluminum concentration: 0.1-0.3 ppm, conductivity 270 μS / cm) was added, and the flocculant was added and the pH was adjusted. Then, after stirring at 100 rpm for 3 minutes and then at 30 rpm for 5 minutes, the mixture was allowed to stand for 10 minutes and the state was observed. The pH was adjusted to the optimum pH for flocculation of the flocculant used by adding caustic soda or hydrochloric acid.
As the flocculant, PAC (manufactured by Nitto Chemical Industry Co., Ltd., trade name: pack), FeCl ₃ (manufactured by Kanto Chemical Co., Ltd., trade name: iron chloride), polysilica iron (manufactured by Waterworks Engineering Co., Ltd., model number: PSI-025) ), Poly iron (manufactured by Nippon Steel Mining Co., Ltd., trade name: poly iron-D). The supernatant was filtered through a sand filtration column (2.5 mmφ, filtered sand particle diameter 0.6 mm) (SV = 10 (1 / h)), and the water quality was analyzed. The results are shown in Table 1.

  From this test result, it was confirmed that residual aluminum cannot be removed by PAC. In addition, in any of the iron-based polymer flocculants of polyiron and polysilica iron, any flocculant has sufficient removal ability for residual aluminum. It was confirmed that there was.

Example 1
[Coagulation precipitation method]
The treatment was performed by the pure water production apparatus shown in FIG. Here, the pure water production apparatus 1 shown in FIG. 1 includes a coagulating sedimentation apparatus 2 that adds an iron-based inorganic polymer coagulant to raw water treated with an aluminum coagulant to coagulate and precipitate residual aluminum. It was comprised from the rapid filtration apparatus 3 which filters a floating solid substance, and the reverse osmosis membrane apparatus 4 which removes various ion and organic substance, The raw | natural water was taken out as treated water through these apparatuses.

The treatment amount of the raw water was 200 m ³ / day, the coagulating sedimentation apparatus 2 was operated using an inclined plate sedimentation basin, and the surface area load factor was 14 mm / min. Polysilica iron (manufactured by Suido Kiko Co., Ltd., model number: PSI-025) was used as a flocculant and added at an addition rate of 10 mg / L. The coagulating sedimentation apparatus 2 has a coagulant adding means for injecting the coagulant into the apparatus.

  Next, as a rapid filtration apparatus, a single-layer filtration apparatus having a silica sand particle size of 0.6 mm, a silica sand layer height of 400 mm, and a supporting gravel layer of 300 mm was used, and water was passed at a filtration flow rate of 150 m / day.

  The reverse osmosis membrane device (RO) was implemented with 10 Toray SU720s, an operating pressure of 0.9 MPa, and a water recovery rate of 75%. The raw water used was industrial tap water in Tsukuba City, Ibaraki Prefecture (residual aluminum concentration 0.1-0.3 ppm, conductivity 270 μS / cm).

  Table 2 shows the measurement results of the residual aluminum concentration at the RO inlet. It was confirmed that aluminum was almost completely removed by coagulation precipitation. It was also confirmed that the removal of aluminum was almost completely performed even when the aluminum concentration of the raw water was high.

  Moreover, the time-dependent change of the reverse osmosis membrane apparatus (RO) inlet pressure in Example 1 is shown in FIG. As shown in FIG. 2, in the case of Example 1, it was confirmed that the operating pressure of the reverse osmosis membrane device did not increase and could be stably operated for a long time.

(Example 2)
(Micro floc method only)
The treatment was performed by the pure water production apparatus shown in FIG. Here, the pure water production apparatus 10 shown in FIG. 3 includes a sand filtration apparatus 11 that removes the aggregate after adding the coagulant to the raw water treated with the aluminum-based coagulant to aggregate the residual aluminum, and various ions. And a reverse osmosis membrane device 12 for removing organic substances, and raw water was taken out as treated water through these devices.

The treatment amount of the raw water was 200 m ³ / day, and the sand filtration device had a filtration sand particle size of 0.6 mm, a filling amount of 833 L, and SV = 10 (1 / h). Prior to sand filtration, a chemical injection device was installed, and polysilica iron (manufactured by Seiko Kiko Co., Ltd., model number: PSI-025) was used as a flocculant and added at an addition rate of 10 mg / L.

  The reverse osmosis membrane device (RO) was implemented with 10 Toray SU720s, an operating pressure of 0.9 MPa, and a water recovery rate of 75%. As the raw water, industrial tap water (residual aluminum concentration is 0.1 to 0.3 ppm, conductivity 270 μS / cm) was used in Tsukuba City, Ibaraki Prefecture.

(Example 3)
[Micro flock method + chemicals]
In Example 2, a chemical injection device was installed immediately before the reverse osmosis membrane device, and Isoban (manufactured by Kuraray Co., Ltd., model: 600SF35) was injected with a concentration of 5 ppm. Otherwise, the same processing as in Example 2 was performed.

(Comparative Example 1)
[Chemicals only]
In Example 2, a chemical injection device is installed immediately before the reverse osmosis membrane device, and isoban (Kuraray Co., Ltd., model: 600SF35) is injected with a concentration of 5 ppm, and the sand filtration device is bypassed. In this way, the treatment was carried out without using a flocculant (polysilica iron).

(Comparative Example 2)
[Sand filtration device + reverse osmosis membrane device only]
In Example 2, the same treatment was performed except that no flocculant was added.

(Test example)
FIG. 4 shows changes with time in the reverse osmosis membrane device (RO) inlet pressure in the case of Example 2, Example 3, Comparative Example 1, and Comparative Example 2. Only in the case of Example 2 and 3, it turns out that the raise of inlet pressure can be suppressed completely.

  The results of measuring the residual aluminum concentration at the raw water and the RO inlet in the case of Example 2 are shown in FIG. In the case of Example 2, it can be seen that the RO inlet residual aluminum concentration is kept low regardless of the concentration of residual aluminum in the raw water.

  The result of measuring the residual aluminum concentration in the raw water and the RO inlet in the case of Example 3 is shown in FIG. Also in this case, it can be seen that the residual aluminum concentration at the RO inlet is kept low regardless of the concentration of residual aluminum in the raw water.

  The results of measuring the residual water concentrations at the raw water and the RO inlet in Comparative Examples 1 and 2 are shown in FIGS. 7 and 8, respectively. In the case of these comparative examples, there is no significant difference in the residual aluminum concentration between the raw water and the RO inlet, and it can be seen that the aluminum in the raw water has not been removed.

It is the schematic which showed the structure of the pure water manufacturing apparatus in Example 1 of this invention. It is the figure which showed the fluctuation | variation of the operating pressure in Example 1. FIG. It is the schematic which showed the structure of the pure water manufacturing apparatus in Example 2 of this invention. It is the figure which showed the fluctuation | variation of the operating pressure in Examples 2, 3 and a comparative example. FIG. 6 is a diagram showing fluctuations in residual aluminum concentration in Example 2. FIG. 6 is a graph showing fluctuations in residual aluminum concentration in Example 3. FIG. 6 is a diagram showing fluctuations in residual aluminum concentration in Comparative Example 1. FIG. 6 is a diagram showing fluctuations in residual aluminum concentration in Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pure water manufacturing apparatus, 2 ... Coagulation sedimentation apparatus, 3 ... Rapid filtration apparatus, 4 ... Reverse osmosis membrane apparatus, 10 ... Pure water manufacturing apparatus, 11 ... Sand filtration apparatus, 12 ... Reverse osmosis membrane apparatus

Claims (8)

An aluminum removal step of adding an iron-based inorganic polymer flocculant to raw water treated with an aluminum flocculant to remove residual aluminum;
A membrane treatment step of passing treated water through the aluminum removal step to a membrane treatment device;
A method for producing pure water, comprising:   2. The pure water production method according to claim 1, wherein the iron-based inorganic polymer flocculant is polyiron or polysilica iron.   The pure water production method according to claim 1 or 2, wherein the addition amount of the iron-based inorganic polymer flocculant is 10 to 100 ppm.   The pure water manufacturing method according to any one of claims 1 to 3, wherein a residual aluminum concentration of treated water at an outlet of the membrane treatment step is 0.01 ppm or less.   The method for producing pure water according to any one of claims 1 to 4, wherein the membrane treatment device is a reverse osmosis membrane device. A flocculant addition means for adding an iron-based inorganic polymer flocculant to raw water treated with an aluminum flocculant;
An aluminum removing means for removing residual aluminum aggregated by the added iron-based inorganic polymer flocculant;
A membrane treatment device for passing treated water from which residual aluminum has been removed;
An apparatus for producing pure water, comprising:   7. The pure water production apparatus according to claim 6, wherein the flocculant adding means and the aluminum removing means are an aggregating and precipitating apparatus having an aggregating agent adding means for injecting an iron-based inorganic polymer flocculant therein.   The pure water production apparatus according to claim 6 or 7, wherein the membrane treatment device is a reverse osmosis membrane device.

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