JP5724390B2 - Method and apparatus for treating dioxane-containing water - Google Patents

Description

  The present invention relates to a method and apparatus for treating dioxane-containing water.

  Dioxane has been confirmed to be acutely toxic to animals and is considered to be irritating to humans and may cause damage to the brain, kidneys and liver. It is the substance that is going to be.

  Since dioxane is a biologically degradable substance and has a low adsorptivity in activated carbon, a physicochemical treatment method centered on an accelerated oxidation method (AOP, Advanced Oxidation Process) has been mainly used as the treatment method. For example, methods for treating dioxane by an accelerated oxidation method, a Fenton oxidation method, and the like are described in JP-A-2005-058854, JP-A-2005-074409, JP-A-2005-103401, JP-A-2008-221151, and JP-A-4553326. .

However, in the AOP treatment, the amount of oxidizing agent (O _3, etc.) added in proportion to the amount of treated water increases, and there is no reaction selectivity for dioxane and it reacts with all the coexisting organic substances, so an excessive amount of oxidizing agent must be added. There is a problem that initial cost and running cost are remarkably increased due to the necessity of performing reduction treatment after the AOP process in order to remove residual oxidant.

JP 2005-058854 A JP 2005-074409 JP-A-2005-103401 JP2008-221151 Japanese Patent No. 4553326

  An object of this invention is to provide the processing method and apparatus which can solve the said problem, can process dioxane containing water at low cost, and can obtain the quality of treated water with high purity.

  The method for treating dioxane-containing water of the present invention (Claim 1) includes an alkali addition step in which alkali is added to dioxane-containing water to make it alkaline, and a reverse flow through the reverse osmosis membrane separation device after the alkali addition step. And an osmotic membrane separation step.

  The method for treating dioxane-containing water according to claim 2 is characterized in that, in claim 1, alkali is added so that the pH becomes 9.5 or more in the alkali addition step.

  A method for treating dioxane-containing water according to claim 3 is characterized in that, in claim 1 or 2, the method comprises a step of neutralizing the permeated water of the reverse osmosis membrane separation device.

  The method for treating dioxane-containing water according to claim 4 is characterized in that, in claim 1 or 2, the method comprises oxidizing the permeated water of the reverse osmosis membrane separation device.

  The method for treating dioxane-containing water according to claim 5 is characterized in that, in any one of claims 1 to 4, the method comprises a step of separating dioxane by subjecting the concentrated water of the reverse osmosis membrane separation device to distillation treatment. Is.

  The method for treating dioxane-containing water according to claim 6 is characterized in that, in claim 5, it comprises a step of neutralizing the bottom water of the distillation separation tower generated in the distillation separation treatment step.

  An apparatus for treating dioxane-containing water according to the present invention (invention 7) comprises an alkali addition means for adding alkali to dioxane-containing water to make it alkaline, and a reverse osmosis membrane for subjecting water from the alkali addition means to reverse osmosis membrane separation treatment And a separation device.

An apparatus for treating dioxane-containing water according to an eighth aspect is characterized in that, in the seventh aspect , the alkali adding means adds an alkali so that the pH is 9.5 or more.

  A dioxane-containing water treatment apparatus according to a ninth aspect is characterized in that, in the seventh or eighth aspect, the apparatus has a neutralization treatment means for neutralizing the permeated water of the reverse osmosis membrane separator.

  A dioxane-containing water treatment apparatus according to a tenth aspect is characterized in that in the seventh or eighth aspect, the apparatus has an oxidation treatment means for oxidizing the permeated water of the reverse osmosis membrane separation apparatus.

  The apparatus for treating dioxane-containing water according to claim 11 has a distillation column according to any one of claims 7 to 10, wherein the concentrated water of the reverse osmosis membrane separator is distilled to separate dioxane. To do.

  A dioxane-containing water treatment apparatus according to a twelfth aspect of the invention is characterized in that in the eleventh aspect, the dioxane-containing water treatment apparatus has a neutralization treatment means for neutralizing the distillation separation tower bottom water generated in the distillation tower.

  In the method and apparatus for treating dioxane-containing water of the present invention, after adding alkali to dioxane-containing water to adjust the pH to alkaline, preferably 9.5 or higher, a reverse osmosis membrane separator (hereinafter sometimes referred to as RO). ).

  The reason for adjusting the pH of the dioxane-containing water (RO feed water) to be alkaline is as follows.

  Dioxane has high removal characteristics by RO. When the membrane surface is new, the RO membrane surface removal rate of dioxane is about 96% regardless of the pH of the RO feed water. However, when the RO membrane is changed (deteriorated or contaminated), the dioxane removal rate is significantly reduced when the RO water supply is neutral or lower. On the other hand, when the RO water supply is alkaline, the dioxane removal rate becomes high due to the electric repulsion between the dioxane and the RO membrane even in the case of a deteriorated RO membrane or a contaminated RO membrane. That is, dioxane (1,4-dioxane) has a boat-type structure as represented by the following formula, and is negatively charged from the structure.

  Moreover, the membrane surface of the RO membrane is also negatively charged, and its polarity increases as the pH value increases (shifts to the negative side). Therefore, by setting the pH of the dioxane-containing water supplied to the RO to be alkaline, preferably 9.5 or more, the state of the RO membrane is changed (deteriorated or contaminated) due to the repulsive force between the dioxane and the RO membrane. Even in the case, the dioxane removal rate can be kept high.

  In addition, by adjusting the pH of the RO water supply to alkaline, preferably 9.5 or higher, the growth of microorganisms on the membrane surface can be suppressed, slime troubles on the RO membrane surface can be prevented, and the RO permeate flow rate can be reduced. It is also possible to suppress adhesion of a nonionic surfactant that may be caused to adhere to the RO membrane surface.

  In this invention, when the dioxane density | concentration in RO water supply is high, since dioxane leaks to RO permeate water side, it is preferable to process the dioxane in permeate water. As a method for treating dioxane in the RO permeated water, an oxidation treatment is suitable, and an accelerated oxidation treatment is suitable as the oxidation treatment.

In this accelerated oxidation treatment method, an oxidizing agent such as O ₃ or H ₂ O ₂ is added to the water to be treated. Since this oxidant generally reacts with all organic substances in water, a large amount of oxidant (O ₃ , H ₂ O ₂ ) must be injected when treating wastewater with a high organic substance concentration. However, in RO, not only dioxane but also coexisting organic substances are removed, and the organic substance concentration in the permeated water is low. Therefore, when the accelerated oxidation method is applied to the RO permeated water, the accelerated oxidation method without the RO treatment is performed. In comparison, the amount of oxidant can be reduced to about 1/20 to 1/50.

In addition, when O ₃ or H ₂ O ₂ is added, the radical initiation reaction of OH radicals that contribute to the organic matter decomposition reaction proceeds in the alkaline region. When the pH of the RO feedwater is high, the pH of the RO permeate is also high, and the dioxane decomposition efficiency is increased by adding O ₃ or H ₂ O ₂ to this high pH RO permeate.

  In the present invention, reverse osmosis membrane concentrated water may be distilled to separate dioxane.

  In general, dioxane is concentrated to the condensation side by azeotropic distillation. Most of the initial cost in the distillation method depends on the size (column diameter, height) of the distillation column, and most of the running cost depends on the amount of blown steam. Since these are substantially proportional to the amount of water supplied, the initial cost and running cost decrease as the amount of water supplied to the distillation tower decreases. Therefore, dioxane is separated and concentrated by RO, and the distillation tower feed water amount is set to, for example, 1/4 (RO 75% recovery) to 1/20 (RO 95% recovery), and then distilled and separated to significantly reduce the cost of the dioxane treatment apparatus. Reduction is possible.

It is a flowchart of the processing method and apparatus of dioxane containing water which concern on embodiment of this invention. It is a flowchart of the processing method and apparatus of dioxane containing water which concern on embodiment of this invention. It is a flowchart of the processing method and apparatus of dioxane containing water which concern on embodiment of this invention. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

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

  FIG. 1 is a system diagram showing an embodiment of the processing method and apparatus of the present invention.

  In FIG. 1, an aqueous alkali solution is added to the dioxane-containing wastewater by means of a chemical injection device 1 as an alkali addition means, preferably a pH of 9.5 or more, for example, 9.5 to 11, particularly preferably 10.5 to 11, The RO device 2 is supplied to perform RO processing.

  Examples of the dioxane-containing water include various factory effluents such as the chemical industry and textile industry, leachate from waste landfills, and household effluent.

  The alkali agent used is preferably sodium hydroxide or potassium hydroxide, but is not limited thereto.

  Further, as the RO membrane to be used, an alkali resistant membrane such as a polyetheramide composite membrane, a polyvinyl alcohol composite membrane, an aromatic polyamide membrane is suitable. The RO membrane may be new or may be a used membrane that has been used to some extent.

  In the present invention, in order to suppress membrane surface scale formation in RO, the scale dispersant is added to the RO water supply in an amount not less than 5 times (weight times) the metal concentration in the RO water supply, for example, 5 to 50 times the amount. Is preferred.

  The scale dispersant to be used is not particularly limited as long as it is a chelating agent such as ethylenediaminetetraacetic acid that is easily dissociated in an alkaline region and complexed with a metal ion.

  When the metal concentration is high, the dioxane-containing water may be subjected to a cation exchange treatment in a cation exchange tower as a pretreatment for the scale dispersant addition treatment. The cation exchange tower is not particularly limited, and any cation exchange resin such as H-type or Na-type or chelate resin can be used, and the water flow method may be any of a fixed bed and a fluidized bed.

  When the water to be treated contains suspended substances, the dioxane-containing water is treated with pretreatment equipment such as coagulation filtration, coagulation flotation filtration, coagulation sedimentation filtration, UF, MF membrane pretreatment, etc. to separate and remove suspended substances. You may go.

  When the water to be treated contains a BOD component, a biological treatment may be installed as a pretreatment for the purpose of reducing the organic matter concentration in the RO permeated water. As the biological treatment method, either an aerobic method or an anaerobic method is applicable. Various treatment methods such as an activated sludge method and a carrier method can be employed.

  When performing bacterial cell separation after biological treatment, MBR (immersion membrane) or the like can be used as the bacterial cell separation means in addition to the above pretreatment equipment.

FIG. 2 is a system diagram showing another embodiment of the present invention. In this embodiment, in the flow of FIG. 1, an oxidizing agent such as O ₃ or H ₂ O ₂ is added to the permeated water of the RO device 2 from the oxidizing agent adding means 4 to react dioxane mixed in a small amount in the permeated water. Oxidative decomposition treatment is performed in a reactor such as the tower 3. The addition amount of O ₃ is preferably 5 times or more, for example, 5 to 20 times, particularly 6 to 12 times the TOC concentration in the RO permeated water.

As the oxidizing agent, both O ₃ and H ₂ O ₂ may be added. The preferable amount of O ₃ added in this case is the same as described above. The amount of H ₂ O ₂ added is preferably such that O ₃ / H ₂ O ₂ (weight ratio) is 2 to 10. The reaction system of the reaction tower 3 may be either a bubble tower or an ejector method.

The treated water that has been subjected to the accelerated oxidation treatment with O ₃ / H ₂ O ₂ can be subjected to a reduction treatment and then neutralized to be discharged or recovered as facility water. The reduction treatment is not particularly limited as long as it can remove the residual oxidizing agent such as an activated carbon method or a reducing agent addition method such as NaHSO ₃ . In FIG. 2, a reducing agent is added to the reduction reaction tank 5 by the addition means 6 to perform a reduction treatment, and this reduction treated water is introduced into the neutralization tank 7 and an acid is added by the addition means 8 for neutralization. However, the processing method is not limited to this.

  FIG. 3 is a system diagram showing still another embodiment of the processing method of the present invention. In this embodiment, in the flow of FIG. 1, the concentrated water concentrated and separated by RO is introduced into the distillation column 10 to further separate and concentrate dioxane. Steam (steam) is blown into the distillation tower. The amount of steam is preferably 15% or more of the amount of water passing through the distillation tower, for example, about 15 to 30%, but is not limited thereto. Further, the packing material in the tower is not particularly limited, such as regular packing, irregular packing, or a combination thereof.

  The dioxane concentrated in the distillation column condensed water obtained from the condenser 11 may be treated as industrial waste or supplied to the reuse process. On the other hand, the tower bottom water is mixed with the RO permeated water and then neutralized by adding an acid by the acid addition means 13 in the neutralization tank 12. The neutralized water can be recovered as discharge or facility water.

  The above embodiment is an example of the present invention, and the present invention may be other than the above. For example, RO concentrated water may be distilled and separated in FIG. The tower bottom water may be mixed with other water (RO permeated water, oxidized water, etc.) and neutralized. Moreover, although tower bottom water is mixed with RO permeated water in FIG. 3, you may neutralize only tower bottom water, without mixing. In FIG. 3, the RO permeate may be oxidized and reduced.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Examples 1 and 2]
After dioxane was dissolved in ultrapure water to a dioxane concentration of 50 mg / L, the pH was adjusted to 9.5 (Example 1) or 10.5 (Example 2) using NaOH, and the used product having a NaCl removal rate of 98%. The RO membrane device filled with the RO membrane (RO membrane ES-20 manufactured by Nitto Denko Co., Ltd., used for 3 years) was subjected to RO treatment by passing water under conditions of a recovery rate of 25%.

[Comparative Examples 1 and 2]
The RO treatment test was performed under the same conditions as in Example 1 except that the pH of the RO water supply was 7 (Comparative Example 1) or 4 (Comparative Example 2). In Comparative Example 2, sulfuric acid was added to adjust the pH to 4. In Comparative Example 1, neither acid nor alkali was added.

[Examples 3 and 4, Comparative Examples 3 and 4]
The RO treatment test was carried out under the same conditions as in Examples 1 and 2 and Comparative Examples 1 and 2, except that a new RO membrane (Nitto Denko RO membrane ES-20) with a NaCl removal rate of 99.5% was used.

  The test results are shown in FIG.

<Discussion>
As shown in FIG. 4, when a new RO membrane is used, the dioxane removal rate is about 96% regardless of the pH value of the RO feed water. On the other hand, when a used RO membrane having a NaCl removal rate of 98% is used, the dioxane removal rate extremely decreases as the pH value of the RO water supply decreases. It was confirmed that the dioxane removal rate was almost constant under the condition that the pH value of the feed water was 9.5 or more, and the dioxane removal rate comparable to that of a new RO membrane could be maintained.

[Example 5]
The wastewater containing 100 mg / L of dioxane and 30 mg / L of TOC was subjected to RO treatment under the conditions of feed water pH 10 and recovery rate 75% using the same RO apparatus as in Example 1. In this RO permeated water (dioxane concentration 7 mg / L, TOC 5 mg / L, pH 10.5), O ₃ and H ₂ O ₂ were O ₃ / TOC = 5, O ₃ / H ₂ O ₂ = 5 (both weight ratio). Then, the accelerated oxidation treatment was performed.

[Examples 6 and 7]
The accelerated oxidation treatment was performed under the same conditions as in Example 5 except that the pH of the RO permeate was changed to pH 7 (Example 6) or 4 (Example 7) using H ₂ SO ₄ .

[Examples 8, 9, and 10]
The accelerated oxidation treatment was performed under the same conditions as in Example 5 except that the O ₃ / TOC ratio was 1 (Example 8), 3 (Example 9), or 10 (Example 10).

[Examples 11, 12, 13, 14]
Accelerated oxidation under the same conditions as in Example 5 except that O ₃ / H ₂ O ₂ was set to 1 (Example 11), 2 (Example 12), 10 (Example 13), or 15 (Example 14). Processed.

  The test results are shown in FIGS.

<Discussion>
From FIG. 5, it was confirmed that the dioxane removal rate in the O ₃ / H ₂ O ₂ method was improved in the alkaline region.

From FIG. 6, it was recognized that the dioxane removal rate increased as the ratio O ₃ / TOC of the amount of O ₃ blown into the RO permeate and the TOC increased, but leveled off at 5 or more.

From FIG. 7, it was recognized that the amount of H ₂ O ₂ added relative to the amount of O ₃ blown was maximum when O ₃ / H ₂ O ₂ = 2 to 10. The reason is considered as follows. That is, when the amount of H ₂ O ₂ added is O ₃ / H ₂ O ₂ of 10 or more, the generation efficiency of OH radicals is lowered because the H ₂ O ₂ concentration is low. When O ₃ / H ₂ O ₂ is less than 2, it is estimated that the unreacted H ₂ O ₂ concentration is high and H ₂ O ₂ contributes as a radical scavenger of OH radicals, so that the reaction efficiency decreases.

[Example 15]
In the same manner as in Example 1, dioxane-containing water (dioxane concentration 20 mg / L) was subjected to RO treatment, and RO concentrated water containing dioxane 100 mg / L was passed through a distillation column under the condition of 15% of the raw water amount of steam. The concentration of dioxane in the bottom water was measured.

[Examples 16, 17, 18]
The test was conducted under the same conditions as in Example 13 except that the amount of steam blown into the distillation tower was 10% (Example 16), 20% (Example 17), and 30% (Example 18) relative to the raw water.

  The dioxane concentration in the bottom water is shown in FIG.

  As shown in FIG. 8, when the amount of steam injected was increased, the dioxane concentration in the bottom water was lowered, but it was confirmed that the distillate leveled off at 15% or more (1 mg / L or less).

Claims (12)

An alkali addition step of adding alkali to dioxane-containing water to make it alkaline;
A method for treating dioxane-containing water, comprising: a reverse osmosis membrane separation step of passing water through a reverse osmosis membrane separation device after the alkali addition step.   2. The method for treating dioxane-containing water according to claim 1, wherein, in the alkali addition step, an alkali is added so that the pH is 9.5 or higher.   3. The method for treating dioxane-containing water according to claim 1, further comprising a step of neutralizing the permeated water of the reverse osmosis membrane separation device. 3. The method for treating dioxane-containing water according to claim 1, further comprising a step of oxidizing the permeated water of the reverse osmosis membrane separation device.   The method for treating dioxane-containing water according to any one of claims 1 to 4, further comprising a step of distilling the concentrated water of the reverse osmosis membrane separation device to separate dioxane.   6. The method for treating dioxane-containing water according to claim 5, further comprising a step of neutralizing the distillation separation tower bottom water generated in the distillation separation treatment step. Alkali addition means for adding alkali to dioxane-containing water to make it alkaline,
A device for treating dioxane-containing water, comprising: a reverse osmosis membrane separation device for subjecting water from the alkali addition means to a reverse osmosis membrane separation treatment. 8. The apparatus for treating dioxane-containing water according to claim 7 , wherein the alkali adding means adds an alkali so that the pH is 9.5 or higher.   The apparatus for treating dioxane-containing water according to claim 7 or 8, further comprising neutralization treatment means for neutralizing the permeated water of the reverse osmosis membrane separation device.   The apparatus for treating dioxane-containing water according to claim 7 or 8, further comprising an oxidation treatment means for oxidizing the permeated water of the reverse osmosis membrane separation device.   The apparatus for treating dioxane-containing water according to any one of claims 7 to 10, further comprising a distillation column for distilling the concentrated water of the reverse osmosis membrane separation apparatus to separate dioxane.   12. The apparatus for treating dioxane-containing water according to claim 11, further comprising a neutralization treatment means for neutralizing the distillation separation tower bottom water generated in the distillation tower.

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