JP2014039895A - Water treatment method and water treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform water treatment at a high water recovery ratio without precipitating substances based on metal ions, silica or the like included in the water to be treated to a reverse osmosis membrane face.SOLUTION: In a state where a reducing agent 16 is added to the water 12 to be treated, and dissolved oxygen is substantially removed, membrane filtering treatment is performed with a membrane filter 20, thus the sticking of insoluble substances to the membrane filter 20 is suppressed, and a drainage volume in a membrane separation device 22 can be reduced. Further, by adding acid 18 to the water 12 to be treated and performing desalting treatment with a reverse osmosis membrane 24 while maintaining pH in a predetermined range, even in the case a concentration rate in the desalting treatment is increased to the solubility of silica or more, the precipitation of silica scale to a reverse osmotic membrane face can be suppressed. Thus, water treatment can be performed at a high water recovery ratio without precipitating substances based on metal ions, silica or the like included in the water 12 to be treated to the reverse osmosis membrane face.

Description

  The present invention relates to a water treatment method and a water treatment apparatus used for water purification, industrial water production, and the like.

  Conventionally, when water to be treated, such as groundwater containing metal ions, silica, and insoluble substances, is desalted using a reverse osmosis membrane, the substance that precipitates on the surface of the reverse osmosis membrane when the water to be treated is concentrated Is previously removed from the water to be treated, followed by a desalting treatment. As a method for removing these substances, iron ions or manganese ions are oxidized in the presence of free chlorine, and then aggregated with an inorganic flocculant such as PAC (polyaluminum chloride), and then precipitated, filtered or filtered. Is common. Furthermore, there is a method of filtering with a microfiltration membrane or an ultrafiltration membrane after precipitation / filtration or filtration. In addition, when these metal oxides are in a low concentration, they may be directly filtered through a microfiltration membrane or an ultrafiltration membrane after adding an inorganic flocculant such as PAC. However, since these methods use many kinds of drugs, there is a problem that the cost of the drugs becomes high and the labor spent on the management of the drugs increases.

  In addition, since groundwater contains silica in a higher concentration than surface water, it is necessary to reduce the concentration factor for desalination so that it does not exceed the solubility of silica, and as a result, water recovery There is also a problem that the rate must be reduced. In contrast, an invention has been devised in which an ultrafiltration membrane is provided in front of a reverse osmosis membrane to remove the colloidal silica component in the water to be treated, thereby increasing the silica concentration of the concentrated water (for example, , See Patent Document 1). However, generally, even if an ultrafiltration membrane is provided before the reverse osmosis membrane, when the silica concentration of the concentrated water reaches 100 to 200 mg / L, silica scale is deposited on the reverse osmosis membrane surface.

  On the other hand, the present inventors relate to a method for desalinating water to be treated such as ground water containing metal ions, silica and insoluble substances using a reverse osmosis membrane, and using a water treatment apparatus 100 as shown in FIG. A method of performing water treatment has been devised (see Patent Document 2). In this method, the treated water 12 is pumped from the well 14 through the raw water supply line L2 by the well pump P2, and the reducing agent 16 is added to the treated water 12 from the reducing agent tank T2 by the reducing agent pump P4. A membrane filtration process is performed by a membrane separation device 22 in which a protective layer is provided on the primary side of the filtration membrane 20 in advance. The amount of the reducing agent 16 added is such that the dissolved oxygen concentration of the concentrated water after the desalting treatment by the reverse osmosis membrane (RO) 24 measured by the dissolved oxygen meter (DO) 26 is maintained at approximately 0 mg / L. It is managed. The treated water 12 subjected to membrane filtration is stored in the intermediate tank T6 through the primary treated water feed line L4, and then supplied to the reverse osmosis membrane 24 through the primary treated water supply line L10 by the booster pump P10. And desalting is performed. According to this method, water treatment is stably performed without depositing a metal oxide on the reverse osmosis membrane surface.

JP 59-90688 A JP 2010-137209 A

  However, in the water treatment method using the water treatment device 100 of FIG. 3, it is necessary to provide a protective layer in advance on the filtration membrane 20 of the membrane separation device 22. At this time, after supplying and storing tap water from a supply line (not shown) to the intermediate tank T6, the pretreatment pump P20 is operated, and the liquid is fed from the protective agent supply line L30 to the primary side of the membrane separation device 22. The primary treated water of the obtained membrane separation device 22 is collected in the intermediate tank T6, and the tap water can be circulated between the intermediate tank T6 and the membrane separation device 22. During this circulation process, the protective agent 40 is injected into the protective agent supply line L30 from the protective agent tank T20 by the protective agent pump P22, so that the primary side of the filtration membrane 20 of the membrane separation device 22 is A protective layer is formed. Since it is necessary to perform such work as pretreatment, not only is the work complicated, but there is a problem in that costs associated with the use and disposal of the protective agent 40 are generated and the cost increases. .

  The present invention has been made in view of the above problems, and its object is to achieve a high water recovery rate without depositing substances based on metal ions, silica, etc. contained in the water to be treated on the reverse osmosis membrane surface. It is to carry out water treatment.

(Aspect of the Invention)
The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

  (1) A water treatment method in which water to be treated containing metal ions, silica, and insoluble substances is subjected to membrane filtration treatment with a filtration membrane to remove insoluble substances, and then desalted with a reverse osmosis membrane. A state in which dissolved oxygen in the treated water is substantially removed by adding a reducing agent to the water and oxidation precipitation of metal ions is suppressed, and an acid is added to the treated water to adjust the pH of the treated water A water treatment method in which the membrane filtration treatment and the desalting treatment are carried out in a state where is maintained in a predetermined range (Claim 1).

  The water treatment method described in this section is a water treatment method for water to be treated such as ground water containing metal ions, silica, and insoluble materials, and the insoluble material contained in the water to be treated is not particularly limited, When groundwater is used as the water to be treated, examples thereof include metal oxides such as iron oxide and manganese oxide, calcium compounds, soil components, organic substances, and microorganisms. In addition, examples of metal ions include metal ions such as iron, manganese, calcium, and magnesium. And in this water treatment method, a reducing agent and an acid are added with respect to the above-mentioned to-be-treated water. The reducing agent is added so as to substantially remove dissolved oxygen in the water to be treated, thereby suppressing the oxidative precipitation of metal ions in the water to be treated. The acid is added so as to maintain the pH of the water to be treated in a predetermined range. And the to-be-processed water of the state which added the reducing agent and the acid is membrane-filtered by a filtration membrane, and the insoluble substance in to-be-processed water is removed. Furthermore, the water to be treated that has been subjected to membrane filtration is desalted with a reverse osmosis membrane to remove metal ions and silica in the water to be treated.

  In other words, the water treatment method described in this section adds a reducing agent to the water to be treated, and suppresses the oxidative precipitation of metal ions contained in the water to be treated. In addition, the amount of insoluble substances that cause membrane clogging that is difficult to remove will be kept to a minimum, reducing the number of maintenance of the filtration membrane and reducing the amount of drainage. Furthermore, since an acid is added to the water to be treated and the pH of the water to be treated is maintained within a predetermined range, even when the concentration rate in the desalting treatment by the reverse osmosis membrane is increased beyond the solubility of silica, This suppresses the deposition of silica scale on the reverse osmosis membrane surface. Therefore, water treatment is performed at a high water recovery rate without depositing substances based on metal ions, silica and the like contained in the water to be treated on the reverse osmosis membrane surface.

(2) The water treatment method as set forth in (1) above, wherein the amount of the acid added is set so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5.
The water treatment method described in this section is reversed by setting the amount of acid added to the water to be treated so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5. Even when the concentration rate in the desalting treatment by the osmosis membrane is increased to be higher than the solubility of silica, the silica scale deposition on the reverse osmosis membrane surface is stably suppressed.

(3) A water treatment method according to (1) or (2) above, wherein the reducing agent is added so that dissolved oxygen is not substantially contained in the concentrated water or permeate accompanying the desalting treatment (claim 3). ).
The water treatment method described in this section is to add a reducing agent to the water to be treated so that dissolved oxygen is not substantially contained in the concentrated water or permeate accompanying the desalting treatment. Alternatively, a reducing agent is added so as to keep the dissolved oxygen concentration of the permeated water at 0.1 mg / L or less. In this description, “so that dissolved oxygen is not substantially contained” means that the dissolved oxygen in the concentrated water or the permeated water is determined according to the dissolved oxygen concentration of the concentrated water or the permeated water measured with a dissolved oxygen meter or the like. This shows that a reducing agent is added in an amount that can be removed sufficiently and sufficiently in the calculation. In order to perform this, for example, a dissolved oxygen meter may be installed in the concentrated water flow line, and the dissolved oxygen may be measured. Thus, by adding a reducing agent so that dissolved oxygen is not substantially contained in the concentrated water or permeated water, it is possible to stably suppress the oxidative precipitation of metal ions contained in the water to be treated. is there.

(4) The water treatment method according to (1) to (3) above, wherein the acid is added after the reducing agent is added (claim 4).
In the water treatment method described in this section, by adding a reducing agent to the water to be treated and then adding an acid, the pH is kept within a predetermined range with respect to the water to be treated whose pH has been changed by the addition of the reducing agent. Since the acid is added to maintain the pH of the water to be treated within a predetermined range by adding the acid while substantially removing dissolved oxygen in the water to be treated by adding a reducing agent. Will be maintained.

(5) In the above items (1) to (4), a water treatment method using a microfiltration membrane or an ultrafiltration membrane as the filtration membrane (claim 5).
The water treatment method described in this section sufficiently removes insoluble substances in the water to be treated by using a microfiltration membrane or an ultrafiltration membrane as a membrane for performing membrane filtration. . Here, any microfiltration membrane or ultrafiltration membrane can be used regardless of water flow method (internal pressure type, external pressure type, etc.), membrane material (organic, inorganic, etc.), membrane shape, etc. In order to prevent membrane clogging of the reverse osmosis membrane used for the treatment, it is preferable to use a membrane having a membrane pore diameter of 0.1 μm or less. As the filtration method, the dead end method is preferable because it can reduce the dissolution of oxygen, and the frequency of reverse water flow is appropriately determined from the ability of the microfiltration membrane or ultrafiltration membrane and the properties of the water to be treated.

(6) The water treatment method according to (1) to (5) above, wherein sodium bisulfite is used as the reducing agent.
The water treatment method described in this section uses sodium bisulfite as a reducing agent to be added to the water to be treated, so that it reacts with dissolved oxygen in the water to be treated at an appropriate rate to substantially remove the dissolved oxygen. Is what you do.

(7) The water treatment method using hydrochloric acid or sulfuric acid as the acid in the above items (1) to (6).
The water treatment method described in this section is often used for pH adjustment as an acid to be added to the water to be treated, and the pH of the water to be treated is maintained by using hydrochloric acid or sulfuric acid, which is relatively easily available. Is easily performed.

  (8) A water treatment apparatus for treating water to be treated containing metal ions, silica, and insoluble substances, comprising a reducing agent adding means for adding a reducing agent to the water to be treated, and an acid in the water to be treated. And adding an acid addition means for maintaining the pH of the water to be treated in a predetermined range, and subjecting the water to be treated to which the reducing agent and the acid have been added to a membrane filtration treatment to remove insoluble substances. The water treatment apparatus (Claim 6) including the filtration membrane for this and the reverse osmosis membrane for performing a desalination process to the said to-be-processed water after the said membrane filtration process.

(9) In the above item (8), the acid addition means adds the acid so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5 (Claim 7). ).
(10) In the above items (8) and (9), the reducing agent addition means is a water to which the reducing agent is added so that dissolved oxygen is not substantially contained in the concentrated water or permeated water accompanying the desalting treatment. A processing device (claim 8).
(11) In the above items (8) to (10), the reducing agent adding means adds the reducing agent to the water to be treated before the acid is added (claim 9). .

(12) The water treatment device according to (8) to (11) above, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane (claim 10).
(13) The water treatment device according to (8) to (12) above, wherein the reducing agent is sodium bisulfite.
(14) The water treatment device according to the above (8) to (13), wherein the acid is hydrochloric acid or sulfuric acid.

  And the water treatment apparatus as described in (8) to (14) term is an apparatus for implementing the water treatment method as described in said (1) to (7) term, respectively (1) to ( The equivalent action corresponding to the item 7) is exhibited.

  Since this invention was comprised in this way, it becomes possible to perform a water treatment with a high water recovery rate, without precipitating the substance based on the metal ion, silica, etc. which are contained in to-be-processed water on a reverse osmosis membrane surface.

It is a schematic diagram which shows typically the water treatment apparatus which concerns on embodiment of this invention. It is a flowchart which shows an example of the water treatment method performed using the water treatment apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the conventional water treatment apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, parts that are the same as or correspond to those in the prior art are denoted by the same reference numerals, and detailed description thereof is omitted.
Drawing 1 is a mimetic diagram showing typically water treatment equipment 10 concerning an embodiment of the invention. The water treatment apparatus 10 according to the embodiment of the present invention is largely different from the conventional water treatment apparatus 100 shown in FIG. 3 in the following points. First, in the water treatment device 10 according to the embodiment of the present invention, the protective layer is not formed on the filtration membrane 20 of the membrane separation device 22 which is performed in the conventional water treatment device 100, and the protective layer is formed. Not equipped for. Moreover, after adding the reducing agent 16 with respect to the to-be-processed water 12 pumped from the well 14, the acid 18 is further added and the installation for that is added.

  In FIG. 1, a water treatment line that is a main water treatment path is used for solid-liquid separation of insoluble substances in the water to be treated 12 by membrane filtration, and then metal ions and silica remaining in the water to be treated 12 are removed. This is a line for desalting. Specifically, as shown in FIG. 1, the groundwater (treated water 12) pumped from the well 14 is transferred to the membrane separation device 22, and the primary treated water obtained after membrane separation is reversed via the intermediate tank T6. It refers to a line from the transfer to the osmosis membrane 24 to the transfer of the desalted permeated water to the treated water tank T8.

Next, with reference to FIG.1 and FIG.2, the water treatment apparatus 10 which concerns on embodiment of this invention, and the water treatment method using the same are demonstrated in detail. This description will be made along the flowchart shown in FIG. 2 by taking as an example the case where groundwater is used as treated water, and for the configuration of the water treatment apparatus 10, refer to FIG. 1 as appropriate. FIG. 2 is an example of a flowchart illustrating a water treatment method using the water treatment apparatus 10 for each treatment process for the water to be treated 12.
S10 (groundwater pumping): Groundwater which is the treated water 12 is pumped from the well 14 by the well pump P2 through the raw water supply line L2.

S20 (reducing agent addition): The reducing agent 16 is added to the water to be treated 12 in the raw water supply line L2 by the reducing agent adding means including the reducing agent tank T2 and the reducing agent pump P4. Thereby, the dissolved oxygen in the to-be-processed water 12 is removed substantially. The reducing agent 16 is not particularly limited as long as it can remove dissolved oxygen in the water 12 to be treated. For example, sodium sulfite, sodium bisulfite, sodium thiosulfate, or the like is used. From the aspect, sodium bisulfite is preferred.
The amount of the reducing agent 16 added is determined by measuring concentrated water accompanying desalination treatment by a reverse osmosis membrane (RO) 24, which will be described later, with a dissolved oxygen meter (DO) 26 provided in the concentrated drainage line L16, and measuring the concentrated water. Is set so that the dissolved oxygen concentration is always around 0 mg / L. At this time, for example, when the measurement data of the dissolved oxygen meter 26 is sent to a control unit (not shown) and the measured value exceeds a predetermined value (for example, 0.1 mg / L) for a certain time (for example, 120 seconds), the reducing agent. You may comprise so that the reducing agent pump P4 may be instruct | indicated so that the addition amount of 16 may be increased. In this case, the increasing amount of the reducing agent 16 is, for example, an amount corresponding to the increased oxygen amount (reaction equivalent) or an amount exceeding this, and when the dissolved oxygen concentration returns to a predetermined value, the reducing agent 16 is added. You may comprise so that the quantity may be returned to the initial addition amount. In addition, data such as the amount of dissolved oxygen contained in the water to be treated 12, the amount of oxygen mixed during the main water treatment process, the amount of consumption of the reducing agent 16 consumed in addition to the reaction with oxygen are collected, and the data is collected. Based on this, the amount of the reducing agent 16 required may be calculated, and the reducing agent 16 greater than the calculated value may be added.

S30 (acid addition): The acid 18 is added to the water to be treated 12 to which the reducing agent 16 has been added in S20 by an acid addition means including an acid tank T4 and an acid pump P6. Thereby, the pH of the to-be-processed water 12 is maintained in the predetermined range, for example, about pH 4.5-5.5. In order to execute this, for example, the pH of the concentrated water accompanying the desalination treatment by the reverse osmosis membrane 24 to be described later is converted into a pH measuring device (pH) provided in the path of the concentrated water, in the concentrated drainage line L16 in the example of FIG. The acid 18 is added so that the pH of the measured concentrated water is always 4.5 to 5.5. Alternatively, data such as pH value of groundwater pumped as treated water 12 in S10, pH change due to addition of reducing agent 16 in S20, pH change in the main water treatment process until subsequent desalting treatment, etc. It is good also as calculating the addition amount of the acid 18 that the pH of concentrated water always becomes 4.5-5.5 based on the data collected, and adding the acid 18 of the addition amount. As the acid 18, hydrochloric acid, sulfuric acid or the like is used.
S40 (membrane filtration treatment): In S20 and S30, the water to be treated 12 to which the reducing agent 16 and the acid 18 are added is subjected to membrane filtration treatment by a membrane separation device (MS) 22 including the filtration membrane 20. As the filtration membrane 20, an ultrafiltration membrane or a microfiltration membrane is used. The concentrated water generated by the membrane filtration process is re-filtered by the membrane separation device 22 or drained through the drain line L8.
S50 (intermediate tank storage): In S40, the water to be treated 12 subjected to membrane filtration by the membrane separation device 22 is stored in the intermediate tank T6 via the primary treated water feed line L4. When performing reverse water flow to the membrane separation device 22, the treated water 12 is supplied from the intermediate tank T6 to the secondary side of the membrane separation device 22 via the reverse water flow line L6 by the backwash pump P8. The drainage is discharged from the drainage line L8.

S60 (desalting treatment): The treated water 12 is supplied from the intermediate tank T6 to the reverse osmosis membrane (RO) 24 via the primary treated water supply line L10 by the booster pump P10, and the desalting treatment is performed. And about the to-be-processed water 12 (permeated water) obtained as the permeated water after a desalting process, it transfers to S70, About the to-be-processed water 12 (concentrated water) used as the concentrated water after a desalting process, The process proceeds to S90.
S70 (Conductivity measurement): In S60 described above, the conductivity of the treated water 12 (permeated water) obtained as the permeated water after the desalting treatment is measured by the conductivity meter (CD) 28. And about the to-be-processed water 12 (below predetermined value) whose measurement result is a predetermined value (for example, 70 microS / cm) or less, it transfers to S80. In addition, the water to be treated 12 whose conductivity exceeds a predetermined value (exceeding the predetermined value) is returned to the intermediate tank T6 via the treated water circulation line L18 (returned to S50).
S80 (Treatment water tank storage): In S70, the treated water 12 (below the predetermined value) whose conductivity is not more than a predetermined value is stored in the treatment water tank T8 via the treatment water line L12. Thereby, the ground water made into drinking water will be stored in the treated water tank T8.

S90 (concentrated water branch): In S60 described above, the water to be treated 12 (concentrated water) that has become the concentrated water after the desalting treatment is branched into circulation and drainage. And the to-be-processed water 12 (for circulation) branched as the concentrated water for circulation is supplied again to the reverse osmosis membrane 24 via the circulation line L14 (return to S60). Moreover, about the to-be-processed water 12 (for drainage) branched as the concentrated water for drainage, it transfers to S100.
S100 (Measurement of dissolved oxygen): In S90 described above, the dissolved oxygen concentration of the treated water 12 (for wastewater) branched as concentrated water for wastewater is measured by a dissolved oxygen meter (DO) 26. And this measurement result is reflected in the addition amount of the reducing agent 16 in said S20. In the example of FIG. 1, the dissolved oxygen meter 26 is provided in the concentrated drainage line L <b> 16, but is not limited to this position, and the permeated water or concentrated water path separated by the reverse osmosis membrane 24 (for example, , L12, L14, L18, etc.).
S110 (drainage): In S100, the water to be treated 12 as the concentrated water for drainage after measuring the dissolved oxygen concentration is drained through the concentrated drainage line L16.

Next, the water treatment method using the water treatment apparatus 10 according to the embodiment of the present invention shown in FIG. 1 will be described more specifically with examples.
In this example, sodium metasilicate pentahydrate, kaolin, ferrous chloride tetrahydrate, manganese (II) chloride tetrahydrate, 65% sulfuric acid were added to groundwater (well water), and the pH was 4 Simulated raw water prepared to have a silica concentration of 50 mg / L, an iron concentration of 1 mg / L, and a manganese concentration of 0.1 mg / L was used as the feed raw water (treated water 12). . And groundwater was made into drinking water under the following conditions.

  First, the prepared raw water is transferred from the well pump P2 to the membrane separation device 22 via the raw water supply line L2 (S10 in FIG. 2), and during this time, the reducing agent is supplied to the treated water 12 in the raw water supply line L2. Reductant 16 was added by a reducing agent supply means having a tank T2 and a reducing agent pump P4, and sulfuric acid was added as an acid 18 by an acid addition means having an acid tank T4 and an acid pump P6 (S20 and S30 in FIG. 2). ). Further, the concentrated waste water after desalting by the reverse osmosis membrane 24 is measured by the dissolved oxygen meter 26 (S100 in FIG. 2), and the amount of the reducing agent 16 added is controlled according to the obtained measurement value, and the concentrated waste water The dissolved oxygen concentration was kept almost stable at 0.0 mg / L. The dissolved oxygen meter 26 includes an industrial dissolved oxygen meter manufactured by HORIBA Advanced Techno Co., Ltd. (model name: HD-480, measurement method: galvanic cell method, resolution 0.01 mg / L, repeatability ± 0.5%, linear Sex ± 0.5%) was used.

And the membrane filtration process was performed with the membrane separator 22 (S40 of FIG. 2), and the to-be-processed water 12 after the obtained membrane filtration process was stored in the intermediate tank T6 through the primary treated water feed line L4 ( (S50 in FIG. 2). The membrane separator 22 was an ultrafiltration membrane “Well Pure S” manufactured by Welsey, Inc., and set so that water could pass through at a membrane filtration flow rate of 2.4 m / day.
Next, the treated water 12 was supplied from the intermediate tank T6 to the reverse osmosis membrane 24 through the primary treated water supply line L10 by the booster pump P10, and the desalting treatment was performed (S60 in FIG. 2). Then, the obtained permeated water is measured by the conductivity meter 28 (S70 in FIG. 2) and stored in the treated water tank T8 through the treated water line L12 under the condition of 70 μS / cm or less (S80 in FIG. 2). , And set to be returned to the intermediate tank T6 via the treated water circulation line L18 under conditions exceeding 70 μS / cm. A part of the concentrated water was supplied to the booster pump P10 through the circulation line L14, and the rest was drained through the concentrated drainage line L16 (S90 and S110 in FIG. 2).

Here, the membrane used as the reverse osmosis membrane 24 is BW30-4040 manufactured by Dow, and was set so that the recovery rate could be 90%. Further, the reverse water flow of the ultrafiltration membrane of the membrane separation device 22 was evaluated under the condition that the water flow time during normal operation (water treatment operation) was performed after 24 hours and 48 hours, respectively.
As a result of drinking water from groundwater under the above conditions, the transmembrane differential pressure of the ultrafiltration membrane of the membrane separator 22 is 1 from the initial value even if the water flow time is 48 hours. %, The reverse osmosis membrane 24 increased only to 0.8%, and it was confirmed that stable operation was achieved even when the feed water containing various metals and silica was highly concentrated. Further, no precipitation of crystals or the like occurred in the concentrated water obtained, and the silica concentration was analyzed and confirmed to be 510 mg / L.

Comparative example

Next, a comparative example performed for comparison with the above-described embodiment will be described.
In the first comparative example, the addition amount of the reducing agent 16 is set to an amount corresponding to the dissolved oxygen concentration in the feed raw water, and the dissolved oxygen concentration in the concentrated waste water after the desalination treatment by the reverse osmosis membrane 24 is continued. The water flow and regeneration were carried out under conditions where removal of dissolved oxygen was not sufficient, including the state of 0.2 mg / L or more, and the frequency of reverse water flow through the ultrafiltration membrane was 24 hours. Except for the points described above, drinking water for groundwater was obtained under the same conditions as in the examples.
As a result of the above conditions, in the first comparative example, when the water flow time has elapsed for 24 hours, the transmembrane pressure difference of the ultrafiltration membrane of the membrane separation device 22 is compared with the initial value. The result was a 20% increase. In addition, the reverse osmosis membrane 24 had a reduced flow rate due to the blockage of the membrane separation device 22, resulting in a decrease in the amount of supplied water and a high concentration of 90%. At that time, the silica concentration of the concentrated water obtained by the reverse osmosis membrane 24 showed 450 mg / L, but the differential pressure increased gently.

Subsequently, in the second comparative example, groundwater was made into drinking water under the same conditions as in the example except that the pH of the treated water 12 was not adjusted by adding the acid 18.
As a result of the above conditions, in the second comparative example, the ultrafiltration membrane of the membrane separation device 22 was 2% of the initial transmembrane pressure even when the water passage time was 48 hours. Only a slight increase in the degree, stable operation was performed. However, the reverse osmosis membrane 24 was operated for 24 hours, resulting in a 50% increase in the initial transmembrane pressure difference, and the operation was stopped.

  Now, according to the embodiment of the present invention configured as described above, the following operational effects can be obtained. That is, the water treatment method using the water treatment apparatus 10 according to the embodiment of the present invention is a water treatment method for water to be treated 12 such as ground water containing metal ions, silica, and insoluble substances. Then, as shown in FIGS. 1 and 2, reducing agent 16 is added to the water 12 to be treated by reducing agent adding means including a reducing agent tank T2 and a reducing agent pump P4 (S20), and further, an acid. The acid 18 is added by the acid addition means including the tank T4 and the acid pump P6 (S30). The reducing agent 16 is added so as to substantially remove dissolved oxygen in the water to be treated 12, thereby suppressing oxidative precipitation of metal ions in the water to be treated 12. The acid 18 is added so as to maintain the pH of the water 12 to be treated in a predetermined range. And the to-be-processed water 12 of the state which added the reducing agent 16 and the acid 18 is membrane-filtered by the filtration membrane 20 of the membrane separator 22, and the insoluble substance in the to-be-processed water 12 is removed (S40). Further, the water to be treated 12 subjected to the membrane filtration is desalted by the reverse osmosis membrane 24 to remove metal ions and silica in the water to be treated 12 (S60).

  That is, in the water treatment method according to the embodiment of the present invention, the reducing agent 16 is added to the water to be treated 12 to suppress the oxidative precipitation of metal ions contained in the water to be treated 12. It is possible to minimize the amount of insoluble substances adhering to the filter membrane 20 and causing membrane clogging that is difficult to remove even by chemical cleaning, etc., reducing the number of times the filter membrane 20 is maintained and reducing the amount of drainage. Can do. Furthermore, since the acid 18 was added to the water 12 to be treated and the pH of the water 12 to be treated was maintained within a predetermined range, the concentration rate in the desalting treatment by the reverse osmosis membrane 24 was increased to be higher than the solubility of silica. Even in this case, the deposition of silica scale on the reverse osmosis membrane surface can be suppressed. Therefore, it is possible to perform water treatment at a high water recovery rate without depositing substances based on metal ions, silica and the like contained in the water to be treated 12 on the reverse osmosis membrane surface.

In the water treatment method according to the embodiment of the present invention, the acid 18 added to the water to be treated 12 is added so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5. By setting to, the silica scale deposition on the reverse osmosis membrane surface can be stably suppressed even when the concentration rate in the desalting treatment by the reverse osmosis membrane 24 is increased to the silica solubility or higher.
Furthermore, in the water treatment method according to the embodiment of the present invention, the water to be treated 12 is reduced so that the concentrated water or permeated water accompanying the desalting treatment by the reverse osmosis membrane 24 does not substantially contain dissolved oxygen. The agent 16 is added. For example, as in the example, the reducing agent is added so that the dissolved oxygen concentration of the concentrated water is kept almost stable at 0.0 mg / L. In order to execute this, as shown in the example of FIG. 1, a dissolved oxygen meter 26 may be installed in the concentrated drain line L16 to measure dissolved oxygen in the concentrated water (S100). Thus, by adding the reducing agent 16 so that the dissolved oxygen is not substantially contained in the concentrated water or the permeated water, the oxidative precipitation of the metal ions contained in the water to be treated 12 is stably suppressed. be able to.

In addition, in the water treatment method according to the embodiment of the present invention, after the reducing agent 16 is added to the water to be treated 12, the acid 18 is added, whereby the water to be treated 12 whose pH is changed by the addition of the reducing agent 16. On the other hand, since the acid 18 is added so as to maintain the pH within a predetermined range, the addition of the reducing agent 16 substantially eliminates the dissolved oxygen in the water 12 to be treated, but the acid 18 Addition makes it possible to stably maintain the pH of the water to be treated 12 within a predetermined range.
Furthermore, by using a microfiltration membrane or an ultrafiltration membrane as the filtration membrane 20 for performing the membrane filtration treatment, it is possible to sufficiently remove insoluble substances in the water 12 to be treated.

Moreover, the water treatment method according to the embodiment of the present invention uses sodium bisulfite as the reducing agent 16 to be added to the water to be treated 12 so as to react with the dissolved oxygen in the water to be treated 12 at an appropriate rate. The substantial removal of dissolved oxygen can be performed.
Furthermore, as the acid 18 added to the water to be treated 12, it is often used for pH adjustment, and if hydrochloric acid or sulfuric acid, which is relatively easily available, is used, it is easy to maintain the pH of the water to be treated 12. It can be carried out.
Thus, since the water treatment method according to the embodiment of the present invention does not require a large facility, it is possible to save space, and since it is based on a reduction treatment, the amount of chemical solution is reduced. As a result, the processing steps can be simplified. Therefore, according to the method of the present invention, it is possible to stably obtain drinking water with good water quality at a very low cost.

  10: water treatment device, 12: treated water, 16: reducing agent, 18: acid, 20: filtration membrane, 24: reverse osmosis membrane (RO), P4: reducing agent pump, P6: acid pump, T2: reducing agent Tank, T4: Acid tank

Claims (10)

A water treatment method in which water to be treated containing metal ions, silica and insoluble substances is subjected to membrane filtration with a filtration membrane to remove insoluble substances, and then desalted with a reverse osmosis membrane,
A state in which a reducing agent is added to the water to be treated to substantially remove dissolved oxygen in the water to be treated, and oxidation precipitation of metal ions is suppressed, and an acid is added to the water to be treated. A water treatment method comprising performing the membrane filtration treatment and the desalting treatment in a state where the pH of water is maintained within a predetermined range.   The water treatment method according to claim 1, wherein the amount of the acid added is set so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5.   The water treatment method according to claim 1 or 2, wherein the reducing agent is added so that dissolved oxygen is substantially not contained in the concentrated water or permeated water accompanying the desalting treatment.   The water treatment method according to claim 1, wherein the acid is added after the reducing agent is added.   The water treatment method according to any one of claims 1 to 4, wherein a microfiltration membrane or an ultrafiltration membrane is used as the filtration membrane. A water treatment apparatus for treating water to be treated containing metal ions, silica and insoluble substances,
Reducing agent addition means for adding a reducing agent to the treated water;
Acid addition means for adding an acid to the treated water and maintaining the pH of the treated water in a predetermined range;
A filtration membrane for removing the insoluble material by performing membrane filtration on the treated water to which the reducing agent and the acid have been added;
A water treatment apparatus comprising a reverse osmosis membrane for performing a desalting treatment on the treated water after the membrane filtration treatment.   The water treatment apparatus according to claim 6, wherein the acid addition means adds the acid so that the pH of the concentrated water accompanying the desalting treatment is 4.5 to 5.5.   The water treatment according to claim 6 or 7, wherein the reducing agent addition means adds the reducing agent so that dissolved oxygen is substantially not contained in the concentrated water or permeated water accompanying the desalting treatment. apparatus.   The water treatment apparatus according to any one of claims 6 to 8, wherein the reducing agent adding means adds the reducing agent to the water to be treated before the acid is added.   The water treatment device according to any one of claims 6 to 9, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.

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