JPH08309369A - Treatment of selenium-containing water - Google Patents

Abstract

PURPOSE: To stably lower the concn. of selenium in final treated water by supplying water after reduction treatment to one surface of a dialytic membrane while supplying selenium- containing water before reduction treatment to the other surface of the dialytic membrane to subject both waters to contact treatment and subjecting both treated waters to flocculation treatment under a specific pH condition. CONSTITUTION: Selenium-containing water is guided to a mixing tank 16 and a reducing agent is supplied to selenium-containing water from a reducing agent storage tank 17 to be mixed therewith and this selnium-containing water is preheated through a heat recovering heat exchanger 18 to be subjected to dialytic treatment along with water to be treated in a acid recovering dialytic device 19 to be lowered in pH. Selenium-containing water is heated to predetermined temp. by a temp. rasing heat exchanger 20 and adjusted to predetermined pH by the acid injected from an acid storage tank 21. Selenium-containing water is further sent to a reducing reaction column 22 to reduce hexavalent selenium to selenium. The water to be treated after reducing reaction is sent to the acid recovering dialytic device 19 and the heat recovering heat exchanger 18 and subsequently guided to a flocculation and neutralization tank 23 and the inorg. flocculant from an inorg. flocculant storage tank 24 and alkali from an alkali storage tank 25 are injected into the water to be treated to adjust the pH thereof to 6-10.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating selenium-containing water. More specifically, the present invention relates to selenium-containing water, particularly wastewater containing hexavalent selenium (SeO ₄ ²⁻ , selenate ion), which is difficult to remove only by aggregating with iron salt, and finally treated water by using a small amount of chemicals. The selenium concentration of 0.
The present invention relates to a treatment method of selenium-containing water which can be 1 mg / liter or less.

[0002]

2. Description of the Related Art Flue gas desulfurization effluents from coal-fired power plants and effluents from oil refineries sometimes contain selenium. In addition, selenium is used as an industrial raw material for decolorizing and coloring agents for glass, high-grade pigments, additives for steel and copper, and as a catalyst during the synthesis of urethane and urea. May also contain selenium. Selenium is rarely contained in high concentration in wastewater, but as selenium is regulated for environmental protection,
It was necessary to treat selenium in the wastewater. Furthermore, Heisei 6
From August, 2012, the drainage standard for selenium based on the Water Pollution Control Law is 0.1 mg / liter. The selenium in the wastewater is usually colloidal selenium, tetravalent selenite ion (SeO ₃ ²⁻ ) or hexavalent selenate ion (Se).
It often exists as O ₄ ²⁻ ). As a method for treating such selenium-containing water, there are a coagulation sedimentation method and an ion exchange method, and Encyclopedia of Envir
operational Control Technology
gy (Gulf Publishing Co., 19
93), Vol. 6, p. 632, for its outline. Many improved methods have been proposed for the treatment of selenium-containing water by the coagulation-sedimentation method, and, for example, JP-A-6-79.
Japanese Patent No. 286 proposes a method of adding ferrous sulfate or ferrous chloride as an iron salt to waste water, and then adding a neutralizing agent, and coprecipitating selenium with iron hydroxide floc to remove it. . However, with this method, the selenium concentration in the final treated water can be reduced only to 0.2 to 0.4 mg / liter, and 0.1 m
The wastewater standard of g / liter cannot be achieved. In addition, R. H. Lien is EPD Cong
r. '90, 334, Chemical a
nd Biological Cyanide Des
truncation and Selenium Rem
oval from Precise Metal
Titled Tailing Pond Water, FeSO ₄ .7H ₂ O or FeCl ₂ .4H ₂ O was added to wastewater containing selenate ions, and Na ₂ SeO ₄ + 6Fe was added.
(OH) ₂ → Se ⁰ + 3Fe ₂ O ₃ + 2NaOH + 5H ₂ O
The method of reducing the selenate ion is proposed according to. However, according to this method, the addition amount of FeSO ₄ .7H ₂ O required to reduce the selenium concentration in the final treated water to 0.1 mg / liter or less is 25 g / liter or more, and a large amount of sludge is generated. Therefore, there are practical and economic problems, and in reality it is difficult to apply. In addition, in order to carry out the reduction treatment efficiently, hydrochloric acid,
It is necessary to add sulfuric acid or the like and treat under acidic conditions.
The present inventors diligently studied the reason why it is difficult to remove selenium in wastewater to 0.1 mg / liter or less by the coagulation sedimentation method, and the cause is that it is difficult to remove the contained hexavalent selenium. It was found that it was because of some reason, or because there was a substance in the wastewater that hinders or interferes with coagulation and sedimentation. Based on this finding, the present inventors have previously invented a method for treating selenium-containing water by adding thiourea to reduce hexavalent selenium at a pH of 2 or less and then performing a coagulation treatment. However, although the selenium concentration in the final treated water can be stably reduced to 0.1 mg / liter or less by this method, when the amount of wastewater to be treated is large,
There is a problem that the amount of the acid used to reduce the water content to 2 or less and the amount of the alkali used to neutralize the water to be treated increase, which affects the treatment cost.

[0003]

According to the present invention, wastewater containing selenium, particularly wastewater containing hexavalent selenium, is treated by a reduction reaction and a coagulation-sedimentation separation method. The amount of selenium is reduced and selenium in the wastewater is efficiently removed to reduce the selenium concentration in the final treated water to 0.
It was made for the purpose of providing a method of reducing the amount to 1 mg / liter or less.

[0004]

As a result of intensive studies to solve the above problems, the inventors of the present invention contain selenium and water to be treated in which hexavalent selenium has been reduced under acidic conditions. It was found that the amount of acid required for pH adjustment and the amount of alkali necessary for neutralization treatment can be reduced by performing dialysis treatment between raw water and transferring the acid component to the raw water side. The present invention has been completed based on the above. That is, in the present invention, (1) a reducing agent is added to water containing hexavalent selenium, and the pH is adjusted to 2 at a temperature of 60 to 100 ° C.
In the following, hexavalent selenium is subjected to reduction treatment, water after reduction treatment is supplied to one side of the dialysis membrane, and water containing selenium before reduction treatment is supplied to the other side of the dialysis membrane for dialysis treatment and reduction. The present invention provides a method for treating selenium-containing water, which comprises subjecting treated water and dialysis treatment to coagulation treatment at pH 6 to 10. Further, as a preferred embodiment of the present invention, (2) the method for treating selenium-containing water according to (1), wherein the reducing agent is thiourea, and (3) the concentration of thiourea is 100 to 100%.
The method for treating selenium-containing water according to the item (2), which is added so that the amount is 700 mg / liter, and (4) the reduction treatment time is 5 to 5.
The treatment method of selenium-containing water according to any one of (1) to (3), which is 30 minutes, and (5) the dialysis treatment is a dialysis treatment using an anion exchange membrane. Treatment method of selenium-containing water, (6) dialysis treatment is electrodialysis treatment using an anion exchange membrane, treatment method of selenium-containing water according to (1) to (4), (7) dialysis treatment, A method for treating selenium-containing water according to items (1) to (4), which is an electrodialysis treatment using a cation exchange membrane, (8) between water after reduction treatment and water containing selenium before reduction treatment. And a method for treating selenium-containing water according to items (1) to (7), wherein heat exchange for heat recovery is performed.
(9) Adjust pH to 6 to 10 by adding slaked lime or sodium hydroxide to water that has undergone reduction treatment and dialysis treatment. (1)
To (8), the method for treating selenium-containing water, (10) the method for treating selenium-containing water according to (1) to (9), wherein an inorganic coagulant is added in the coagulation treatment, and (11) In the coagulation treatment, a polymer coagulant is further added (1) to (1
The treatment method of selenium-containing water described in the item 0) can be mentioned.

The method of the present invention can be applied to the treatment of wastewater containing hexavalent selenium. Although the selenium concentration in the wastewater to be treated is not particularly limited, the selenium concentration in the normal selenium-containing wastewater is several mg / liter or less, and according to the method of the present invention, such wastewater is treated for final treatment. The selenium concentration in water can be stably controlled to 0.1 mg / liter or less. In the method of the present invention, a reducing agent is added to the wastewater containing hexavalent selenium. The reducing agent added is 6
There is no particular limitation as long as it can reduce valent selenium, and examples of such a reducing agent include thiourea, hydrazine, sodium thiosulfate (hypo), ferrous sulfate, ferrous chloride and the like. Can be mentioned. Among these, thiourea can be used particularly preferably because it has a faster reduction reaction rate than other reducing agents, requires a small amount of addition, and produces a small amount of sludge. In the method of the present invention, when thiourea is used as the reducing agent, it is preferably added so that the concentration of thiourea is 100 to 700 mg / liter, more preferably 200 to 500 mg / liter. In the method of the present invention, the selenium-containing water added with the reducing agent is subjected to acid recovery in a dialysis device. In the dialysis device, selenium-containing water added with a reducing agent was supplied to one side of the dialysis membrane, and water to be treated that had undergone the reduction treatment was supplied to the other side of the dialysis membrane to perform dialysis treatment, and the reduction treatment was terminated. Recover the acid in the water to be treated. The dialysis membrane to be used is not particularly limited as long as it can recover an acid, and as such a dialysis membrane, for example, a cation exchange membrane, an anion exchange membrane,
Examples thereof include microfiltration membranes, ultrafiltration membranes, porous membranes such as ceramic membranes.

FIG. 1 is an explanatory diagram of a dialysis treatment using an anion exchange membrane. In the figure, the raw water containing selenium before pH adjustment is supplied to the liquid passage 2 on one side of the anion exchange membrane 1, and the acidic water to be treated after the reduction treatment is supplied to the liquid passage 3 on the other side. Supply so that they flow counter-currently to each other. When the acidic water to be treated contains, for example, hydrochloric acid or sulfuric acid as an acid, hydrogen ions and chlorine ions or sulfate ions pass from the liquid passage 3 through the anion exchange membrane 1 to the liquid passage 2. However, the pH of the raw water drops. Anion exchange membranes block the migration of cations and allow anions such as chloride ions and sulfate ions to pass through, but since hydrogen ions are small, they pass through the anion exchange membrane along with chloride ions, sulfate ions, etc. It moves to the side and the acid is recovered. FIG. 2 is an explanatory diagram of an electrodialysis treatment using an anion exchange membrane. In this figure, the raw water containing selenium before pH adjustment is supplied to the liquid passage 5 on one side of the anion exchange membrane 4, and the acidic water to be treated after the reduction treatment is supplied to the liquid passage 6 on the other side. Supply so that they flow counter-currently to each other.
The passage 5 for the liquid of raw water is further in contact with an electrolytic solution chamber 8 filled with an electrolytic solution such as sodium sulfate with a bipolar membrane 7 composed of a cation exchange membrane portion and an anion exchange membrane portion separated. A cathode 9 is provided in the passage 6 of the acidic water to be treated, and an anode 10 is provided in the electrolytic solution chamber 8. Chloride ions in the acidic water to be treated are attracted to the anode 10, move to the raw water side through the anion exchange membrane 4, are blocked by the cation exchange membrane portion of the bipolar membrane 7, and remain in the raw water. Hydrogen ions in the acidic water to be treated become hydrogen gas at the cathode 9. Water between the bipolar membranes is dissociated into hydrogen ions and hydroxyl ions, and the hydrogen ions move to the raw water side through the cation exchange membrane portion of the bipolar membrane 7. As a result, the concentration of hydrogen chloride in the raw water increases and the pH increases. descend. The hydroxyl ions pass through the anion exchange membrane portion of the bipolar membrane 7 and generate oxygen gas at the anode. FIG. 3 is an explanatory diagram of an electrodialysis treatment using a cation exchange membrane. In this figure, raw water containing selenium before pH adjustment is supplied to the liquid passage 12 on one side of the cation exchange membrane 11, and acidic treated water whose reduction treatment has been completed is supplied to the liquid passage 13 on the other side. Supply so that they flow counter-currently to each other. A cathode 14 is provided in the passage 13 of the acidic water to be treated, and an anode 15 is provided in the passage 12 of the raw water. The raw water usually contains salts, and the cation components of the salts, such as sodium ions and calcium ions, are attracted to the cathode 14 and passed through the cation exchange membrane 11 into the acidic water to be treated which has completed the reduction treatment. Although it migrates, anion components of salts, such as chloride ions and sulfate ions, are blocked by the cation exchange membrane 11 and remain in the raw water. On the other hand, in the raw water passage 12, the hydroxyl ions generated by the dissociation of water become oxygen gas and water at the anode 15, and the hydrogen ions are blocked by the cation exchange membrane 11 and remain in the raw water.
The pH of raw water decreases.

In the method of the present invention, the selenium-containing water added with the reducing agent is heated to 60 to 100 ° C. The heating temperature is more preferably 80 to 100 ° C., and 95 to
More preferably, it is 100 ° C. When the temperature of the selenium-containing water is lower than 60 ° C., the reduction reaction of tetravalent or hexavalent selenium, particularly hexavalent selenium, is difficult to proceed. 80 ℃
With the above, the rate of the reduction reaction is high, and the reaction can be completed in a short time. When the temperature exceeds 100 ° C., the reaction rate becomes faster, but a pressure vessel is required. In the method of the present invention, heat can be recovered by using a heat recovery heat exchanger and exchanging heat between the high-temperature reduction-treated water and the raw water containing selenium. The position of the heat recovery step by heat exchange is not particularly limited, but usually the raw water containing selenium is preheated by heat exchange before dialysis treatment. The selenium-containing water preheated in the heat recovery heat exchanger is further heated to a predetermined reaction temperature in the temperature rising heat exchanger. In the method of the present invention, the pH is adjusted by dialysis with water containing reduced selenium.
The water containing selenium before reduction treatment in which the pH is lowered is further adjusted to pH 2 or less by adding an acid. The acid used is not particularly limited, and for example, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc., organic acids such as formic acid, acetic acid, etc. can be used, but hydrochloric acid and sulfuric acid are particularly preferably used. be able to. The pH of the selenium-containing water is adjusted to 2 or less, preferably 0.5 to 2 by adding an acid. PH of selenium-containing water is 2
If it exceeds, the reduction of tetravalent or hexavalent selenium, particularly hexavalent selenium may be insufficient. When hydrochloric acid is used as the acid, 1 g of hydrochloric acid per liter of selenium-containing water
With the above addition, the pH of the selenium-containing water can usually be set to 2 or less.

In the method of the present invention, a reducing agent is added,
Selenium-containing water whose pH is adjusted to 2 or less is 60 to 100 ° C.
The selenium having a valence of 4 or 6 is reduced to a simple substance of selenium while being kept heated. The reduction reaction time in the heated state is 5 to
It is preferably 30 minutes, more preferably 10 to 30 minutes. During this period, selenium having a valence of 4 and hexavalent is reduced to a state of selenium alone. If the reduction reaction time is less than 5 minutes, the reduction of tetravalent or hexavalent selenium, particularly hexavalent selenium may be insufficient. In this reduction reaction, it is considered that tetravalent and hexavalent selenium are reduced to simple selenium (Se ⁰ ) according to the following formula. SeO ₄ ^2- + 2H ⁺ + 2e → SeO ₃ ^2- + H ₂ O SeO ₃ ^2- + 6H ⁺ + 4e → Se ⁰ + 3H ₂ O Addition of a reducing agent to water containing hexavalent selenium, dialysis treatment There is no particular limitation on the order of pH adjustment by addition of the acid and acid, and preheating and heating by heat exchange, and the steps can be performed in any order. For example, it is possible to add a reducing agent to selenium-containing water, preheat it by heat exchange, reduce the pH by dialysis treatment, further heat to a predetermined temperature, and then add an acid to adjust the pH to a predetermined value. It is preferable to perform the dialysis treatment after raising the water temperature by preheating, because the dialysis effect is improved. In addition, after selenium-containing water is preheated and heated to a predetermined temperature, dialysis treatment and pH adjustment by addition of an acid are performed, and finally a reducing agent can be added and reacted. Alternatively, the selenium-containing water can be dialyzed to lower the pH, preheated by heat exchange, added with a reducing agent, heated to a predetermined temperature and adjusted to a predetermined pH by adding an acid. It is also possible to add the reducing agent and the acid at the same time.

In the method of the present invention, the water to be treated in which the hexavalent and tetravalent selenium has been reduced by the reduction treatment is subjected to the dialysis treatment to recover the acid component and, if necessary, the heat exchange to recover the heat. After that, a coagulating sedimentation process is performed. In the coagulation-sedimentation treatment, an inorganic coagulant may be added to the water to be treated, if necessary. The inorganic coagulant to be added is not particularly limited, and a known inorganic coagulant can be used. Examples of such an inorganic flocculant include ferrous chloride, ferric chloride, ferrous perchlorate, ferric perchlorate, ferrous sulfate, ferric sulfate, ferrous nitrate, Ferric nitrate, ferrous thiocyanate, ferric thiocyanate, ferrous acetate, ferric oxalate, ferrous ammonium sulfate,
Examples include ferric ammonium sulfate, potassium ferric sulfate, aluminum sulfate, and polyaluminum chloride. Among these, iron salts such as ferrous chloride, ferric chloride, ferrous sulfate and ferric sulfate can be preferably used. The amount of the iron salt to be added is usually preferably such that the concentration of the iron salt in the water to be treated is 50 to 500 mg / liter, and the concentration of the iron salt in the water to be treated is 100 to 3
More preferably, it is added so as to be 00 mg / liter. Reduction of hexavalent selenium with a reducing agent does not proceed to selenium simple substance, and even if some remains as tetravalent selenium, 4
Valuable selenium is removed by a coagulation sedimentation process by the addition of iron salts. In the method of the present invention, tetravalent and hexavalent selenium is reduced to a simple substance of selenium, and water is added to the water to be treated to which an inorganic coagulant is added, and then an alkali is added to adjust the pH to 6 to 10. The alkali to be used is not particularly limited, and for example, sodium hydroxide, slaked lime, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, carbide slag, etc. can be used, but especially hydroxide Sodium and slaked lime can be preferably used. If the pH of the water to be treated is less than 6, the fine particles in the water to be treated may be colloidal and difficult to aggregate. Further, even if the pH of the water to be treated exceeds 10, the aggregating effect may decrease.

In the method of the present invention, a high molecular flocculant can be added to the water to be treated which has been adjusted to have a pH of 6 to 10 by reducing selenium having a valence of 4 or 6 to a simple substance of selenium. . There is no particular limitation on the polymer flocculant used,
For example, polyacrylamide, polyethylene oxide,
Nonionic polymer flocculant such as urea-formalin resin,
Cationic polymer flocculants such as polyaminoalkylmethacrylate, polyethyleneimine, halogenated polydiallylammonium, chitosan, sodium polyacrylate, polyacrylamide partial hydrolyzate, partially sulfomethylated polyacrylamide, poly (2-acrylamide) -2- Anionic polymer flocculants such as methyl propane sulfate can be used. Among these polymer aggregating agents, the anionic polymer aggregating agent has an excellent aggregating effect, and thus can be used particularly preferably. There is no particular limitation on the method of separating the aggregate from the water to be treated, which is obtained by reducing and aggregating tetravalent and hexavalent selenium by the method of the present invention, and any method such as sedimentation, flotation, filtration, centrifugation, and filtration membrane separation can be used. Solid-liquid separation methods can be used. The agglomerates produced by the method of the present invention have good sedimentation properties and can usually be separated by natural sedimentation. However, in the case of filtration, the filter can use ordinary gravity filtration, pressure filtration or the like. Also, there is no particular limitation on the filter medium used,
For example, sand or anthracite can be used.

FIG. 4 is an example of a process chart for carrying out the method of the present invention. After introducing selenium-containing water to the mixing tank 16 and supplying and mixing a reducing agent such as thiourea from the reducing agent storage tank 17, preheating is performed through the heat recovery heat exchanger 18, and further reduction treatment is performed in the acid recovery dialysis device 19. The pH is lowered by performing dialysis treatment with the water to be treated which has been completed. Preheated,
The selenium-containing water whose pH has been lowered by the acid recovery is heated to a predetermined temperature in the temperature raising heat exchanger 20, and the acid storage tank 21
More acid is injected to adjust the pH to the specified level. Predetermined temperature and pH
The selenium-containing water thus obtained is then sent to the reduction reaction tower 22 and subjected to a reduction reaction to reduce hexavalent selenium to simple selenium. The water to be treated which has completed the reduction reaction is sent again to the acid recovery dialyzer 19, where the acid is recovered by dialysis, and then to the heat recovery heat exchanger 18 for heat recovery. The water to be treated after the acid recovery and the heat recovery is led to the coagulation neutralization tank 23, the inorganic coagulant such as ferrous sulfate is injected from the inorganic coagulant storage tank 24, and the alkaline storage tank 25 further contains slaked lime and sodium hydroxide. PH of 6 by injecting alkali
It is adjusted to 10 and sent to the coagulation sedimentation separation tank 26. If necessary, the polymer flocculant storage tank 2 in the flocculation sedimentation separation tank 26
A polymer flocculant is supplied from No. 7 to form flocs and precipitate sludge. The supernatant water is discharged as the final treated water from which selenium has been removed. According to the method of the present invention, hexavalent selenium, which was difficult to be completely reduced by the conventional method using an iron salt, etc., can be easily reduced to the state of simple selenium, and the amount of sludge generated is Since the volume can be reduced to 1/10 or less as compared with the conventional method, the water quality of the final treated water is improved and sludge treatment becomes extremely easy. Further, in the method of the present invention, by performing the reduction reaction under heating, the acid addition amount is reduced, and since the acid is further recovered by dialysis treatment, the use amount of the acid and the alkali neutralizing agent is reduced, The amount of sludge generated can be further reduced.

[0012]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 Thiourea was added to a flue gas desulfurization wastewater containing 0.51 mg / liter of hexavalent selenium and 0.10 mg / liter of tetravalent selenium so as to have a concentration of 500 mg / liter.
This treated water was passed through a heat recovery heat exchanger made of carbon to raise the temperature from 20 ° C. to 70 ° C., and then a dialysis device provided with an acid recovery dialysis membrane [Asahi Glass Co., Ltd., AMD] was used. Hydrochloric acid was recovered from the water to be treated whose reduction reaction was completed by dialysis treatment. Furthermore, the water to be treated is heated to 80 to 90 ° C. by a carbon heat exchanger for reheating using steam as a heat source, and 600 mg of hydrochloric acid is injected per liter of water to be treated,
The reaction was carried out for 30 minutes in a Teflon-lined reaction tower. The water to be treated which has completed the reduction reaction was subjected to dialysis treatment with the flue gas desulfurization wastewater to which thiourea was added using the above dialysis device, and was further subjected to heat recovery with the above heat recovery heat exchanger. .
This treatment recovered 80% of the hydrochloric acid and 80% of the heat. When the steady state was reached, the hydrochloric acid concentration in the reaction column was 3,000 mg / liter. The water to be treated that had undergone acid recovery and heat recovery had a hydrochloric acid concentration of 600 mg / liter and a temperature of 30 ° C. In the water to be treated, ferrous sulfate to a concentration of 500 mg / liter, and slaked lime as a neutralizing agent to a concentration of 1,000 mg / liter,
Further, an anionic polymer coagulant [Cliflock PA331 manufactured by Kurita Industry Co., Ltd.] was injected at a concentration of 0.5 mg / liter, and coagulation precipitation separation was performed. The total selenium concentration in this final treated water was 0.05 mg / liter. In this example, the amount of hydrochloric acid and slaked lime used for neutralization was reduced to 1/5 and the amount of steam required for heating was reduced to 1/5 as compared with the conventional method in which acid and heat were not recovered. Was done.

[0013]

EFFECTS OF THE INVENTION According to the method of the present invention, it has been difficult to completely reduce by a conventional method using an iron salt or the like.
Valence selenium can be easily reduced to the state of simple selenium, and the selenium concentration in the final treated water can be stably reduced to 0.1 mg / liter or less. Also, by performing the reduction reaction under heating, the amount of acid added is reduced, and since the acid is recovered by dialysis treatment, the amount of acid and alkali neutralizer used is reduced, and the amount of sludge generated is reduced. Therefore, sludge treatment becomes extremely easy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a dialysis treatment using an anion exchange membrane.

FIG. 2 is an explanatory diagram of electrodialysis treatment using an anion exchange membrane.

FIG. 3 is an explanatory diagram of electrodialysis treatment using a cation exchange membrane.

FIG. 4 is an example of a process chart for carrying out the method of the present invention.

[Explanation of symbols]

 1 Anion Exchange Membrane 2 Liquid Passage 3 Liquid Passage 4 Anion Exchange Membrane 5 Liquid Passage 6 Liquid Passage 7 Bipolar Membrane 8 Electrolyte Chamber 9 Cathode 10 Anode 11 Cation Exchange Membrane 12 Liquid Passage 13 Liquid Passage 14 Cathode 15 Anode 16 Mixing tank 17 Reducing agent storage tank 18 Heat recovery heat exchanger 19 Acid recovery dialyzer 20 Temperature rising heat exchanger 21 Acid storage tank 22 Reduction reaction tower 23 Aggregation neutralization tank 24 Inorganic coagulant storage tank 25 Alkali storage tank 26 Aggregation Precipitation separation tank 27 Polymer flocculant storage tank

Claims (1)

[Claims] 1. A reducing agent is added to water containing hexavalent selenium, the hexavalent selenium is reduced at a pH of 2 or less at a temperature of 60 to 100 ° C., and water after the reduction treatment is treated with one of the dialysis membranes. The selenium-containing water before reduction treatment is supplied to the other side of the dialysis membrane for dialysis treatment, and the water subjected to the reduction treatment and dialysis treatment is subjected to coagulation treatment at pH 6 to 10. Treatment method of selenium-containing water.