JP5943176B2 - Method and apparatus for treating harmful substance-containing water. - Google Patents

Description

The present invention relates to a method and apparatus for treating water containing harmful substances, and more specifically, a treatment system for removing these harmful substances from waste water containing harmful substances such as fluorine, boron, nitrogen compounds, phosphorus and heavy metals. In addition, the present invention relates to a treatment system that is excellent in solid-liquid separation of sludge incorporating toxic substances, and that sludge settles in a short time to remove toxic substances.

A method for removing harmful substances contained in waste water by taking them into layered double hydroxides is conventionally known. For example, Japanese Patent Application Laid-Open No. 2003-285076 (Patent Document 1) discloses that a layered double hydroxide is generated by adding a divalent metal ion and a trivalent metal ion to a wastewater containing fluorine to form the layered double hydroxide. A treatment method for incorporating fluorine between the two layers is described.

In International Publication WO2005-087664 (Patent Document 2), an acidic solution containing aluminum ions and magnesium ions and an alkaline solution containing alkali are mixed, and after mixing of the acidic solution and the alkaline solution is completed, no time is left. By immediately removing or neutralizing water, the general formula: Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O (A ⁿ⁻ is an anion) The hydrotalcite-like substance is formed, and a treatment method is described in which fluorine or the like is taken into the substance and fixed.

JP 2003-285076 A International Publication WO2005-087664

The conventional treatment method described above is a method of removing fluorine by producing a layered double hydroxide such as hydrotalcite, but has a problem that the treatment time is prolonged due to poor sedimentation of the produced sludge. Further, the treatment method of Patent Document 1 focuses on the recovery of the fluorine-containing emulsifier, and the removal of heavy metals is unclear. Moreover, in the processing method of patent document 2, although the anion exchange ability is improved by controlling the crystallite size of a hydrotalcite-like substance to 20 nm or less, the adsorption effect with respect to chromium is shown about heavy metal ion. However, heavy metals other than chromium are unknown.

The present invention solves the problem of inferior sedimentation of the produced sludge in the above-described conventional treatment method, and provides a treatment system excellent in the adsorption effect on fluorine and the sedimentation of the produced sludge. Moreover, the removal effect of boron, a nitrogen compound, phosphorus, and heavy metals is also excellent, Preferably, the processing system excellent in the removal effect of harmful substances, such as a boron, a nitrogen compound, phosphorus, and heavy metals, with fluorine is provided.

The present invention relates to a method for treating harmful substance-containing water having the following constitution.
[1] A step of adding a hardly soluble metal oxide and a soluble metal compound, which are components of the layered double hydroxide, to harmful substance-containing water, and under the liquidity of pH 7 to 11, the surface of the hardly soluble metal oxide is The above-mentioned layered double hydroxide produced by the reaction of the dissolved hardly soluble metal oxide and the soluble metal compound generates sludge formed on the surface of the hardly soluble metal oxide undissolved portion while dissolving and leaving the undissolved portion . The reaction process, the solid-liquid separation process in which the sludge is settled and solid-liquid separated to remove harmful substances incorporated in the sludge out of the system, and part or all of the solid-liquid separated sludge is returned to the reaction process. A method for treating toxic substance-containing water, comprising a sludge returning step of using the returned sludge to form a layered double hydroxide.
[2] A second addition tank is provided in the sludge return process, a hardly soluble metal oxide is added in the second addition tank, and the sludge to which the hardly soluble metal oxide is added is returned to the reaction process to contain harmful substance-containing water. The method for treating toxic substance-containing water as described in [1] above, which is added to the water.
[3] The method for treating toxic substance-containing water according to the above [1] or [2], wherein when the produced sludge slurry is allowed to stand, the stable volume after 30 minutes is 40% or less.
[4] The poorly soluble metal oxide is magnesium oxide, the soluble metal compound is a soluble aluminum salt, magnesium oxide and a soluble aluminum salt are added to harmful substance-containing water, and this is reacted under alkalinity to produce magnesium oxide. The toxic substances described in any one of [1] to [3] above, wherein sludge in which harmful substances are taken into hydrotalcite is formed by forming hydrotalcite on the surface of the slag, and the sludge is solid-liquid separated. Method for treating substance-containing water.
[5] The above-mentioned [1] to [[1] above, wherein the harmful substance is any one or more of fluorine, boron, nitrogen compound, phosphorus, and heavy metals, and sludge incorporating the harmful substance is generated and solid-liquid separated. [4] The method for treating toxic substance-containing water according to any one of [4].
[6] Addition of 0.05 to 10 g / L of magnesium oxide and soluble aluminum salt to 10 to 1000 mg / L of water in water for 1 L of harmful substance-containing water with a fluorine concentration of 1 to 50 mg / L Then, the method for treating toxic substance-containing water according to any one of [1] to [5] above, wherein the reaction is carried out at a pH of 7 to 11 in a reaction tank.
[7] A pre-treatment step is provided for reducing harmful substances and interfering substances contained in harmful substance-containing water (raw water), and the pre-treated raw water contains a hardly soluble metal oxide that becomes a component of the layered double hydroxide; The method for treating toxic substance-containing water according to any one of [1] to [6] above, wherein a soluble metal compound is added.
[8] The method for treating toxic substance-containing water according to any one of [1] to [7], wherein a step of post-treating treated water obtained by solid-liquid separation of sludge is provided.

Moreover, this invention relates to the processing apparatus of the harmful | toxic substance containing water which consists of the following structures.
[9] An addition tank for adding a chemical to toxic substance-containing water, a reaction tank for reacting the added chemical to produce sludge, and a solid-liquid separation tank for separating the produced sludge are sequentially connected by a pipe line. In addition, each supply tank is provided with a means for supplying harmful substance-containing water and a soluble metal compound, and each reaction tank is provided with a supply means for a hardly soluble metal oxide and a pH adjuster. The tank is connected to the separated sludge and the treated water discharge pipe, respectively, and is further provided with a return pipe from the solid-liquid separation tank to the reaction tank, in which the soluble metal compound was added in the addition tank. Hazardous substance-containing water is introduced into the reaction tank, and the hardly soluble metal oxide and the pH adjuster are added in the reaction tank. The surface of the hardly soluble metal oxide dissolves and reacts with the soluble metal compound under alkalinity. Soluble metal oxide Sludge layered double hydroxide is formed on the dissolved portion surface is generated and sedimentation is introduced into the sludge solid-liquid separation tank, some or all of the sludge subjected to solid-liquid separation of the reaction vessel through the return conduit A device for treating water containing hazardous substances, which is returned to the factory.
[10] The treatment apparatus according to [9], wherein a second addition tank for adding a hardly soluble metal oxide to the separated sludge is provided in the middle of the return conduit.

In the treatment system (treatment method and treatment apparatus) of the present invention, the sludge produced is excellent in sedimentation, for example, when the produced sludge slurry is allowed to stand, the stable volume after 30 minutes is 40% or less, Since it settles in a short time, solid-liquid separation can be performed in a short time, and a solid-liquid separation tank can be reduced in size.

The treatment system of the present invention is excellent in the effect of removing fluorine, and easily reduces the fluorine concentration in the wastewater to below the drainage standard [fluorine 8 mg / L (public water area other than sea area), fluorine 15 mg / L (sea area)]. Can be reduced. Furthermore, by returning the separated sludge to the reaction step, the effect of removing fluorine can be enhanced, and the fluorine concentration in the waste water can be easily reduced to the environmental standard (0.8 mg / L or less). In addition, harmful substances such as boron, nitrogen compounds, phosphorus, and heavy metals can be removed simultaneously with fluorine.

SEM photograph of sludge by the treatment method of the present invention Component analysis diagram inside sludge (Fig. 1 (A) b) Component analysis diagram near the surface of the sludge (Fig. 1 (A) b) Photograph showing sludge sedimentation for the treatment method of the present invention and the conventional treatment method Process drawing showing the processing method of the present invention Process drawing which shows the example which provided the 2nd addition tank in the processing method of this invention Process drawing which shows the processing method of this invention which provided the pre-processing process and the post-processing process XRD analysis chart of sludge by the treatment method of the present invention

Hereinafter, the present invention will be specifically described based on embodiments.
Processing method of the present invention, the step of adding a sparingly soluble metal oxide becomes a component of the layered double hydroxide and the soluble metal compound to the pollutant water under liquid property of PH7～11, flame soluble metal oxide The layered double hydroxide formed by the reaction of the dissolved hardly soluble metal oxide and the soluble metal compound was formed on the surface of the undissolved part of the hardly soluble metal oxide while dissolving the surface of the product and leaving the undissolved part . A reaction process for generating sludge, a solid-liquid separation process for removing harmful substances taken into the sludge by allowing the sludge to settle and solid-liquid separation, and reacting part or all of the solid-liquid separated sludge This is a method for treating toxic substance-containing water, characterized by having a sludge returning step of returning to the process and using the returned sludge for forming a layered double hydroxide.

Preferably, the treatment method of the present invention includes a step of returning a part or all of the solid-liquid separated sludge to the reaction step and utilizing the returned sludge for forming the layered double hydroxide in the above treatment method. This is a method for treating substance-containing water.

In the present invention, toxic substance-containing water broadly means water containing toxic substances, and includes various types of wastewater and wastewater generated naturally and artificially, such as factory effluent and sewage, seawater, river water, Lakes and ponds, surface pools, rivers and other dams, underground running water and pools, underdrains, etc. that contain harmful substances or soil contaminated by harmful substances Wastewater with high salt concentration such as seawater and leachate from the final disposal site is separated into clear water (fresh water) and concentrated water using reverse osmosis membrane and electrodialysis (desalting treatment) Such as concentrated water.

Examples of harmful substances to be treated include heavy metals, fluorine, boron, nitrogen, and phosphorus. Heavy metals are cadmium, lead, copper, zinc, iron, nickel, selenium, hexavalent chromium, arsenic, manganese, antimony, etc. According to the treatment system of the present invention, these harmful substances contained in water containing harmful substances It has an excellent removal effect on any one or more of the above.

Further, harmful substances include halide ions, various halogen acids (halogen acids, perhalogen acids, halous acids, hypohalous acids, etc.), hexafluorophosphate ions (PF ₆ ⁻ ), borofluoride ions (BF ₄ ^- ), Silicofluoride ions (SiF ₆ ^2- ), organic acids, suspended solids (SS) and organic substances. The treatment system of the present invention has an excellent removal effect on one or more of these harmful substances.

[Addition process]
In the treatment system of the present invention, the hardly soluble metal oxide and the soluble metal compound, which are the components of the layered double hydroxide in the addition step, are added to the harmful substance-containing water, and this is reacted under alkaline in the reaction step. Sludge having a layered double hydroxide formed on the surface of the hardly soluble metal oxide is generated.

The hardly soluble metal oxide partially dissolves on its surface and becomes a component source of the layered double hydroxide, and most of it remains as an undissolved part, and the dissolved hardly soluble metal oxide reacts with the soluble metal compound. Thus, a layered double hydroxide is formed on the surface of the hardly soluble metal oxide. Further, the dissolved hardly soluble metal oxide serves as a component source of the layered double hydroxide and serves as an alkali agent.

Examples of the hardly soluble metal oxide include magnesium oxide and calcium oxide. In addition, magnesium oxide is preferable for forming the hydrotalcite of the layered double hydroxide. This magnesium oxide may be one containing magnesium oxide as a part of the component, such as a baked product of dolomite [CaMg (CO ₃ ) ₂ ], or one containing magnesium oxide together with other components, not limited to Ca. it can.

A soluble aluminum salt, a soluble iron salt, etc. can be used as a soluble metal compound. Among these, a soluble aluminum salt is preferable for forming hydrotalcite. Specifically, polyaluminum chloride, aluminum sulfate (sulfuric acid band), aluminum chloride, aluminum nitrate and the like are preferable. In addition, as a soluble aluminum salt, a waste liquid containing a high concentration of aluminum (a recovery waste liquid of a noble metal catalyst, a liquid in which metal aluminum is dissolved, or the like) can be used.

The amount of the soluble aluminum salt added is suitably such that the aluminum concentration in the water is 10 to 1000 mg / L with respect to 1 L of harmful substance-containing water having a fluorine concentration of 1 to 50 mg / L. The amount of magnesium oxide added is suitably 0.05 to 10 g / L with respect to 1 L of harmful substance-containing water having a fluorine concentration of 1 to 50 mg / L.

In the process of adding the hardly soluble metal oxide and the soluble metal compound to the harmful substance-containing water, the addition tank adds the soluble metal compound and the hardly soluble metal oxide to the harmful substance-containing water and introduces it into the reaction tank. Alternatively, a soluble metal compound may be added to the harmful substance-containing water in the addition tank, and this may be introduced into the reaction tank, and a poorly soluble metal oxide and a pH adjuster may be added as necessary in the reaction tank. Moreover, you may add harmful substance containing water and a soluble metal compound in the pipe line which introduces harmful substance containing water to a reaction tank.

[Reaction process]
For example, when magnesium oxide is used as a hardly soluble metal oxide, a soluble aluminum salt is used as a soluble metal compound, and these are added to harmful substance-containing water and reacted under alkaline conditions (preferably pH 7 to 11), Since it is difficult to dissolve, most remains as an undissolved part, but the surface is partially dissolved, and the eluted magnesium reacts with aluminum to form a layered double hydroxide on the surface of magnesium oxide. Specifically, magnesium and aluminum react with the magnesium oxide surface to form hydrotalcite [general formula: Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O ( ^An- is an anion)].

This state is shown in FIGS. When EDX analysis is performed on the inside (a) of the sludge in FIG. 1 (A), it is shown that the magnesium component is predominantly magnesium oxide as shown in FIG. 1 (B). On the other hand, when EDX analysis is performed on the surface (b) of the sludge in FIG. 1 (A), peaks of magnesium and aluminum are detected and hydrotalcite is formed as shown in FIG. 1 (C). I understand.

Since the hardly soluble metal oxide may be hydrated into a metal hydroxide in the reaction process, a layered double hydroxide is formed on the surface of the coexisting substance of the hardly soluble metal oxide and the metal hydroxide. It may be formed.

The layered double hydroxide has a layered structure containing water molecules between layers, and has the property of taking in anions between layers in order to maintain electrical neutrality. Anionic harmful substances such as fluorine, organic acids, oxyanionic boron, nitrogen, phosphorus, selenium, hexavalent chromium, arsenic and antimony contained in this water are taken in between the layers. In addition, harmful heavy metals such as cadmium, lead, copper, zinc, iron, nickel, and manganese are incorporated by replacing some of the magnesium and aluminum forming the layered double hydroxide with cationic heavy metals. It is. The suspended matter (SS) is aggregated and taken in with the sludge containing the layered double hydroxide, and the organic matter is adsorbed and taken in the surface of the sludge containing the layered double hydroxide. Thus, the sludge containing the layered double hydroxide that has taken in the toxic substance settles, and the toxic substance can be removed by solid-liquid separation.

In the reaction step, a pH adjuster can be added as necessary. Examples of the pH adjuster include alkalis such as sodium hydroxide, calcium hydroxide and calcium oxide, and acids such as sulfuric acid and hydrochloric acid. Thereby, it is controlled to pH 7-11. The pH may be adjusted before the reaction, during the reaction, or after the reaction, but it is preferably during or after the reaction because it promotes the formation of the layered double hydroxide.

[Solid-liquid separation process]
The produced sludge is guided to the solid-liquid separation step to be settled and solid-liquid separation is performed. The sludge produced by the treatment method of the present invention has a structure in which a layered double hydroxide is formed on the surface of an undissolved hardly soluble metal oxide (magnesium oxide or the like), and thus has good sedimentation.

For example, as shown in FIG. 2, when the sludge slurry generated by the treatment method of the present invention is placed in a graduated cylinder and allowed to stand for 30 minutes, the volume of sludge slurry at the start of standing is 2300 mL. The volume of the later sludge slurry portion is about 550 mL, and the stable volume is 40% or less, preferably 25% or less in a short time. Here, the stable volume is an index calculated by the following equation [1]. A smaller stable volume indicates that sludge can be solid-liquid separated in a short time.
(Sludge slurry volume after a certain period of time) / (initial sludge slurry volume) × 100 ... [1]

The treatment system of the present invention has a small stable volume, so that sludge can be solid-liquid separated in a short time. If a flocculant is added before introducing into the solid-liquid separation tank, solid-liquid separation can be achieved in a shorter time. As the flocculant, inorganic flocculants and anionic, cationic, nonionic and amphoteric polymer flocculants can be used.

In addition, a soluble magnesium salt (such as magnesium chloride) is used instead of magnesium oxide, and this is added to a harmful substance-containing water together with a soluble aluminum salt, and further added with sodium hydroxide to adjust to alkalinity. When the produced sludge slurry is placed in a graduated cylinder and allowed to stand for 30 minutes, as shown in FIG. 2, for example, the initial sludge slurry volume at the start of standing is 2300 mL. The sludge slurry volume is about 2200 mL, and hardly settles in about 30 minutes.

[Sludge return process]
In the treatment method of the present invention, preferably, a part or all of the solid-liquid separated sludge is returned to the reaction step, and the returned sludge is used for forming the layered double hydroxide. By returning some or all of the sludge to the reaction process, the formation of layered double hydroxides is promoted, and a large amount of harmful substances such as fluorine, boron, nitrogen compounds, phosphorus, and toxic heavy metals are taken into the sludge. Thus, the removal effect is improved.

In addition, about the sludge isolate | separated into solid and liquid, it is good to return the sludge concentrated to the thing with much amount of a hardly soluble metal oxide using the difference in a weight, specific gravity, or sedimentation speed to a reaction process. For example, since sludge with a large amount of hardly soluble metal oxides is heavier than other sludges and settles quickly, it is possible to collect sludge at the initial stage of sedimentation and concentrate it to sludge with a large amount of hardly soluble metal oxides. By returning the sludge having a large amount of the hardly soluble metal oxide to the reaction step, the generation of the layered double hydroxide can be promoted. For example, when magnesium oxide is used as the hardly soluble metal oxide, the formation of hydrotalcite can be promoted by concentrating sludge having a large amount of magnesium oxide and returning it to the reaction step.

On the other hand, surplus sludge that is not returned to the reaction process can be recovered and recycled as a cement raw material. Alternatively, excess sludge can be used as a purification material for soil contamination and wastewater treatment.

[Pretreatment process]
In the treatment method of the present invention, a pretreatment step for reducing in advance harmful substances and interfering substances contained in harmful substance-containing water (raw water) can be provided before the reaction step. The pretreatment can further enhance the effect of removing harmful substances. See FIG. The disturbing component is not a harmful substance itself, but is a substance that interferes with the treatment method of the present invention.

Specifically, for example, if the concentration of heavy metals (cadmium, lead, copper, zinc, iron, nickel, manganese, hexavalent chromium, arsenic, etc.) contained in raw water is higher than 20 mg / L, The structure of the incorporated layered double hydroxide may partially collapse, and the removal effect of harmful substances such as heavy metals may be insufficient. Therefore, preprocessing may be performed. The pretreatment method is not limited. As a pretreatment, for example, a neutralizing agent (NaOH, Ca (OH) _2, etc.) is added to adjust the pH of the raw water to a range of 5 to 10 to generate a heavy metal hydroxide precipitate, which is agglomerated and precipitated. After processing, the heavy metal concentration in the raw water may be less than 10 mg / L, or after adding aluminum salt or iron salt to the raw water, neutralizing agents (NaOH, Ca (OH) ₂ etc.) are added to adjust the pH of the raw water. It may be adjusted to a range of 5 to 10 to generate a hydroxide precipitate, which is co-precipitated in the precipitate, and then solid-liquid separated to make the heavy metal concentration of raw water less than 10 mg / L.

In addition, if the phosphate ion of raw water is higher than 50 mg / L, the phosphate ion competes with other harmful substances and is adsorbed on the layered double hydroxide, reducing the effect of removing other harmful substances. There is. Therefore, preprocessing may be performed. The pretreatment method is not limited. As the pretreatment, for example, a calcium salt (Ca (OH) ₂ or the like) is added to the raw water to generate and remove the calcium phosphate salt, and the phosphate ion of the raw water is adjusted to a phosphorus concentration of less than 5 mg / L.

Similarly, if the nitrate ion of raw water is higher than 200 mg / L as the nitrogen concentration, the nitrate ion competes with other harmful substances and is adsorbed on the layered double hydroxide, which may reduce the effect of removing other harmful substances. is there. Therefore, preprocessing may be performed. The pretreatment method is not limited. As the pretreatment, for example, biological treatment (anaerobic denitrification method or the like) is performed, and nitrate ion of raw water is preferably set to a nitrogen concentration of less than 200 mg / L.

Furthermore, when the borate ions in the raw water are higher than 100 mg / L as the boron concentration, the borate ions compete with other harmful substances and are adsorbed on the layered double hydroxide, and the removal effect of other harmful substances decreases. There is. Therefore, preprocessing may be performed. The pretreatment method is not limited. As the pretreatment, for example, raw water is passed through a chelate resin having a methylglucamine group to adsorb borate ions, and the borate ions of the raw water are adjusted to a boron concentration of less than 100 mg / L.

Further, if the fluorine concentration of the raw water is higher than 50 mg / L, the required amount of the layered double hydroxide increases, so that the amount of drug to be added may increase. Therefore, preprocessing may be performed. The pretreatment method is not limited. As a pretreatment, for example, a calcium salt may be added to form poorly soluble calcium fluoride, which is then solid-liquid separated so that the fluorine concentration is less than 50 mg / L.

In addition, if the concentration of suspended solids (SS) in raw water is higher than 60 mg / L, the structure of the layered double hydroxide that has incorporated suspended solids will partially collapse, resulting in an insufficient removal effect of harmful substances. There is. Therefore, preprocessing may be performed. The pretreatment method is not limited. As the pretreatment, for example, an inorganic flocculant or a polymer flocculant is added to precipitate and separate floating substances, so that the concentration of floating substances in raw water is less than 20 mg / L.

Similarly, when the concentration of the organic substance contained in the raw water is higher than 200 mg / L as COD, the structure of the layered double hydroxide incorporating the organic substance may partially collapse, and the harmful substance removal effect may be insufficient. . Therefore, preprocessing may be performed. The pretreatment method is not limited. As the pretreatment, for example, the organic matter concentration of raw water may be less than 80 mg / L as COD by a biological treatment method (such as activated sludge method) or an accelerated oxidation method (such as ultraviolet oxidation or photocatalyst).

In the pretreatment step, the treatment effect can be further enhanced by removing the disturbing components contained in the raw water. Interfering components include sulfate ions, sulfite ions, chloride ions, carbonate ions, dissolved silica and silicate ions.

For example, if the concentration of sulfate ion contained in the raw water is higher than 1500 mg / L, the sulfate ion competes with the harmful substance and is adsorbed on the layered double hydroxide, and the harmful substance removal effect may be reduced. Therefore, preprocessing may be performed. The pretreatment method is not limited. As a pretreatment, for example, a Ca salt or a Ba salt is added to raw water to form a hardly soluble sulfate, which is solid-liquid separated to lower the sulfate ion concentration. When using a Ca salt, sulfate ions can be reduced to less than 1000 mg / L. When Ba salt is used, sulfate ion can be reduced to less than 5 mg / L.

Further, if the concentration of sulfite ions in the raw water is higher than 50 mg / L, sulfite ions react with aluminum ions, so that a large amount of aluminum may be required. In addition, sulfite ions compete with harmful substances and are adsorbed on the layered double hydroxide, which may reduce the effect of removing harmful substances. Therefore, preprocessing may be performed. The pretreatment method is not limited. As pretreatment, for example, an oxidizing agent such as hydrogen peroxide may be added to raw water to oxidize sulfite ions to sulfate ions, so that the sulfite ions of raw water are less than 10 mg / L.

Furthermore, when the chloride ion concentration in the raw water is higher than 2000 mg / L, chloride ions may be adsorbed on the layered double hydroxide in competition with harmful substances, and the harmful substance removal effect may be reduced. Therefore, preprocessing may be performed. The pretreatment method is not limited. As pretreatment, for example, chlorine may be gasified and removed by electrolytic decomposition, or the chloride ion concentration may be made less than 1000 mg / L by membrane treatment such as reverse osmosis or electrodialysis.

When the carbonate ion concentration of raw water is higher than 500 mg / L, carbonate ions compete with harmful substances and are adsorbed on the layered double hydroxide, which may reduce the harmful substance removal effect. Therefore, preprocessing may be performed. The pretreatment method is not limited. As pretreatment, for example, aeration is performed to disperse carbonate ions, or Ca salt is added to form a hardly soluble carbonate, which is solid-liquid separated so that the carbonate ion concentration is less than 50 mg / L. .

If the dissolved silica and silicate ions in the raw water are higher than 20 mg / L as the Si concentration, the structure of the layered double hydroxide incorporating the dissolved silica and silicate ions will partially collapse, and the removal effect of harmful substances will be insufficient. May be. Therefore, preprocessing may be performed. The pretreatment method is not limited. As pretreatment, for example, an iron salt or an aluminum salt is added, and a neutralizing agent (NaOH, Ca (OH) _2, etc.) is added to adjust the pH of the raw water to a range of 5 to 10 to precipitate hydroxide. It is preferable that dissolved silica and silicate ions are co-precipitated in the precipitate, and this is solid-liquid separated to make the dissolved silica and silicate ions of raw water less than 10 mg / L as Si concentration.

[Post-treatment process]
Furthermore, the processing method of this invention can provide the process of post-processing the liquid component (process water) which isolate | separated sludge. See FIG.

There are cases where organic matter, suspended solids, and nitrogen compounds remain in the liquid component (treated water) from which the sludge has been separated in the solid-liquid separation step, or the pH of the treated water is 9 or more. Therefore, a post-treatment process for treated water may be provided. The post-processing method is not limited.

The organic matter contained in the treated water may be reduced to a COD concentration of less than 80 mg / L by, for example, a biological treatment method (such as an activated sludge method) or an accelerated oxidation method (such as ultraviolet oxidation or a photocatalyst). In addition, for the suspended matter (SS) contained in the treated water, for example, an inorganic flocculant or a polymer flocculant is added to precipitate and separate the suspended matter, so that the concentration of suspended matter is less than 20 mg / L. Further, for nitrogen compounds contained in the treated water, for example, biological treatment (nitrification denitrification method or the like) may be performed to reduce the nitrogen concentration to less than 60 mg / L.

Since the pH of the treated water may be 9 or more, when the pH is high, sulfuric acid or hydrochloric acid may be added to the treated water and neutralized so that the pH becomes 6-8.

[Processing equipment]
The processing apparatus of the present invention is shown in FIGS.
The illustrated treatment apparatus includes an addition tank 10 for adding a chemical to harmful substance-containing water (raw water), a reaction tank 30 for reacting the added chemical to generate sludge, and a solid-liquid separation tank for separating the generated sludge. 40, and the addition tank 10, the reaction tank 30, and the solid-liquid separation tank 40 are sequentially connected by a pipe 50.

Discharge pipes 51 and 52 for discharging the separated treated water and sludge are connected to the solid-liquid separation tank 40, respectively, and part or all of the separated sludge is sent to the reaction tank 30 in the sludge discharge pipe 52. A return pipeline 53 to be returned is connected. In the processing system shown in FIG. 4, the second addition tank 20 is provided in the middle of the return conduit 53.

To the addition tank 10, a supply pipe 60 for toxic substance-containing water and a supply pipe 61 for a soluble metal compound are connected. Note that the addition tank 10 may be omitted, the pipe 60 and the pipe 61 may be connected, and the soluble metal compound may be added to the raw water in the pipe.

In the example of the apparatus of FIG. 3, the reaction tank 30 is provided with a supply line 62 for a hardly soluble metal oxide and a supply line 63 for a pH adjusting agent. In the example of the apparatus of FIG. 4, a supply line 62 of a hardly soluble metal oxide is provided in the second addition tank 20.

In the addition tank 10, a soluble metal compound such as polyaluminum chloride is added to the harmful substance-containing water, and this is introduced into the reaction tank 30. In the example of FIG. 3, sludge is added to the reaction tank 30 through a pipe 53, and further a hardly soluble metal oxide is added through a pipe 62. In the apparatus example of FIG. 4, the separated sludge is introduced into the reaction tank 30 after the hardly soluble metal oxide is added through the pipe line 62 in the second addition tank 20.

A pH adjuster is added to the reaction tank 30 through the pipe 63, and the inside of the reaction tank is controlled to pH 7-11. The reaction may be an open system or a closed system, but the reaction tank 30 preferably has a structure that hardly absorbs carbon dioxide because it may inhibit removal of harmful substances due to absorption of carbon dioxide. In general, a closed reaction tank is preferred.

In the reaction tank 30, the surface of the hardly soluble metal oxide partially dissolves and reacts with the soluble metal compound under alkalinity (preferably pH 7 to 11), and layered double water such as hydrotalcite is formed on the hardly soluble metal oxide surface. Sludge with oxides formed. The sludge is guided to the solid-liquid separation tank 40, settles and is separated into solid and liquid. A flocculant may be added before being introduced into the solid-liquid separation tank 40. The flocculant may be added in the pipe by connecting the flocculant supply pipe and the pipe 50, or a flocculant addition tank is provided, and sludge is put into the flocculant addition tank through the pipe 50, and The flocculant may be added through the flocculant supply line. Part or all of the separated sludge is returned to the reaction tank 30 through the pipe line 53. Some sludge may be dehydrated and discarded, recovered and recycled as a raw material for cement, or used as a purification material for soil contamination and wastewater treatment.

The processing apparatus of this invention can be made into a portable apparatus which can be mounted on a vehicle or can be separated into units such as an addition tank, a reaction tank, and a solid-liquid separation tank.

Examples of the present invention are shown below together with comparative examples. In each of these examples, the fluorine concentration was measured by the ion electrode method. Further, the boron concentration, chromium (VI) concentration, arsenic concentration, copper concentration, manganese concentration, and zinc concentration were measured by ICP emission spectroscopy. Selenium concentration, cadmium concentration, and lead concentration were measured by ICP mass spectrometry.

[Example 1]
In accordance with the treatment system shown in FIG. 4, the fluorine-containing water was treated as follows. First, fluorine-containing water (fluorine concentration 20 mg / L) was introduced into the addition tank 10, and polyaluminum chloride was added so that the aluminum concentration was 240 mg / L in water. On the other hand, the entire amount of sludge separated in the solid-liquid separation tank 40 was returned to the second addition tank 20, where 1 g / L of magnesium oxide was added to 1 L of fluorine-containing water. This sludge was introduced into the reaction tank 30, mixed with fluorine-containing water added with polyaluminum chloride, stirred for 30 minutes, and reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, sodium hydroxide is added as a pH adjusting agent to adjust the pH to 8.5 to 9.5, and then the generated sludge is introduced into the solid-liquid separation tank 40 (thickener) and left to stand for 20 hours to remove the sludge. Allowed to settle. In addition, 2 mg / L of anionic polymer flocculant was added to the sludge slurry before introducing into the solid-liquid separation tank 40. The whole amount of sludge separated in the solid-liquid separation tank 40 was introduced into the second addition tank 20 as described above, and 1 g / L of magnesium oxide was added to 1 L of fluorine-containing water and returned to the reaction tank 30. This sludge generation was repeated 15 times. The processing conditions are shown in Table 1, and the processing results are shown in Table 2. Moreover, the X-ray analysis chart of sludge was shown in FIG. In FIG. 6, 1st to 10th is the number of repetitions.

As shown in the treatment results, the fluorine concentration of treated water can be reduced to below the drainage standard (8 mg / L) for public water areas other than the sea area at the first iteration, and the treatment can be performed at the 12th iteration. The fluorine concentration of water can be reduced to the environmental standard (0.8 mg / L or less). Moreover, as shown in the X-ray analysis chart of sludge, the peak of hydrotalcite appears with magnesium oxide, and it turns out that the hydrotalcite is formed on the magnesium oxide surface. When the number of repetitions is 1, the hydrotalcite peak is small, but when the number of repetitions is 5 or more, the hydrotalcite peak increases and grows in proportion to the number of repetitions.

[Example 2]
In accordance with the treatment system shown in FIG. 3, the fluorine-containing water was treated as follows. First, fluorine-containing water (fluorine concentration 20 mg / L) was introduced into the addition tank 10, and aluminum sulfate was added so that the aluminum concentration was 240 mg / L in water. This was introduced into the reaction vessel 30. On the other hand, the entire amount of sludge separated in the solid-liquid separation tank 40 was returned to the reaction tank 30. Further, 1 g / L of magnesium oxide was added to 1 L of fluorine-containing water in the reaction tank 30, mixed with fluorine-containing water added with aluminum sulfate, stirred for 30 minutes, and reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, sodium hydroxide is added as a pH adjusting agent to adjust the pH to 8.5 to 9.5, and then the generated sludge is introduced into the solid-liquid separation tank 40 (thickener) and left to stand for 20 hours to remove the sludge. Allowed to settle. In addition, 2 mg / L of anionic polymer flocculant was added to the sludge slurry before introducing into the solid-liquid separation tank 40. The sludge separated in the solid-liquid separation tank 40 was returned to the reaction tank 30 as described above, and 1 g / L of magnesium oxide was added to 1 L of fluorine-containing water. This sludge generation was repeated 15 times. The processing conditions are shown in Table 3, and the processing results are shown in Table 4.

As shown in the treatment results, the fluorine concentration of the treated water can be reduced to a drainage standard (8 mg / L) or less in public water areas other than the sea area by the first repetition. Each time the number of repetitions is repeated, the fluorine concentration in the treated water can be reduced.

Example 3
In accordance with the treatment system shown in FIG. 4, water containing harmful substances containing fluorine and heavy metals was treated as follows. First, toxic substance-containing water (hazardous substance concentration in raw water is listed in Table 5) was introduced into the addition tank 10 and polyaluminum chloride was added so that the aluminum concentration was 240 mg / L in water. This was introduced into the reaction vessel 30. On the other hand, the entire amount of sludge separated in the solid-liquid separation tank 40 was returned to the second addition tank 20, where 1 g / L of magnesium oxide was added to 1 L of harmful substance-containing water. This sludge was returned to the reaction tank 30, mixed with harmful substance-containing water added with polyaluminum chloride, stirred for 30 minutes, and reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, sodium hydroxide is added as a pH adjusting agent to adjust the pH to 8.5 to 9.5, and then the generated sludge is introduced into the solid-liquid separation tank 40 (thickener) and left to stand for 20 hours to remove the sludge. Allowed to settle. In addition, 2 mg / L of anionic polymer flocculant was added to the sludge slurry before introducing into the solid-liquid separation tank 40. The total amount of sludge separated in the solid-liquid separation tank 40 is introduced into the second addition tank 20 as described above, and magnesium oxide is added at 1 g / L to 1 L of harmful substance-containing water and returned to the reaction tank 30. This sludge generation was repeated 5 times. The processing conditions are shown in Table 5, and the processing results are shown in Table 6.

As shown in the treatment results, the fluorine concentration of the treated water can be reduced to a drainage standard (8 mg / L) or less in public water areas other than the sea area by the first repetition. Each time the number of repetitions is repeated, the fluorine concentration in the treated water can be reduced. Concerning other harmful substances, the concentration in the treated water can be reduced, and the concentration can be further reduced as the number of repetitions is repeated.

Example 4
In accordance with the treatment system shown in FIG. 3, the fluorine-containing water was treated as follows. First, fluorine-containing water (fluorine concentration 20 mg / L) was introduced into the addition tank 10, and polyaluminum chloride was added so that the aluminum concentration was 240 mg / L in water. This was introduced into the reaction vessel 30. Thereafter, 1 g / L of magnesium oxide and water added with polyaluminum chloride were mixed in the reaction tank 30, adjusted to pH 8.5 to 9.5 by adding sodium hydroxide as a pH adjuster, and then stirred for 30 minutes. And reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, the produced sludge was introduced into the solid-liquid separation tank 40 (thickener) and allowed to stand for 30 minutes to settle the sludge. The processing conditions and processing results are shown in Table 7.

[Comparative Example 1]
In accordance with the treatment system shown in FIG. 3, the fluorine-containing water was treated as follows. First, fluorine-containing water (fluorine concentration 20 mg / L) was introduced into the addition tank 10, and polyaluminum chloride was added so that the aluminum concentration was 240 mg / L in water. This was introduced into the reaction vessel 30. Thereafter, 2.4 g / L of magnesium chloride and water added with polyaluminum chloride were mixed in the reaction tank 30 and adjusted to pH 8.5 to 9.5 by adding sodium hydroxide as a pH adjuster. The mixture was stirred for 30 minutes and reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, the produced sludge was introduced into the solid-liquid separation tank 40 (thickener) and allowed to stand for 30 minutes to settle the sludge. The processing conditions and processing results are shown in Table 7.

As shown in the treatment results, both Example 4 and Comparative Example 1 can reduce the fluorine concentration of the treated water to below the drainage standard (8 mg / L) for public water areas other than sea areas, but the stable volumes are comparable. Example 1 is much larger and has poor separation. On the other hand, Example 4 has a small stable volume, good separability, and can perform solid-liquid separation in a short time.

10-addition tank, 20-second addition tank, 30-reaction tank, 40-solid-liquid separation tank, 50-line, 51, 52-discharge line, 53-return line, 60, 61, 62, 63 -Supply line.

Claims (10)

A step of adding a poorly soluble metal oxide and a soluble metal compound, which are components of the layered double hydroxide, to water containing harmful substances, and dissolving the surface of the hardly soluble metal oxide under liquidity of pH 7-11 A reaction step of leaving the undissolved part and generating sludge formed on the surface of the undissolved part of the hardly soluble metal oxide by the layered double hydroxide generated by the reaction of the dissolved hardly soluble metal oxide and the soluble metal compound ; The sludge is settled and solid-liquid separated to remove harmful substances taken into the sludge out of the system, the solid-liquid separation step, part or all of the solid-liquid separated sludge is returned to the reaction step and returned. A method for treating toxic substance-containing water, comprising a sludge return step in which sludge is used to form layered double hydroxides.
A second addition tank is provided in the sludge return process, the hardly soluble metal oxide is added in the second addition tank, and the sludge to which the hardly soluble metal oxide is added is returned to the reaction process and added to the water containing harmful substances. The method for treating toxic substance-containing water according to claim 1. The method for treating toxic substance-containing water according to claim 1 or 2, wherein when the produced sludge slurry is allowed to stand, the stable volume after 30 minutes is 40% or less . The hardly soluble metal oxide is magnesium oxide, the soluble metal compound is a soluble aluminum salt, magnesium oxide and a soluble aluminum salt are added to harmful substance-containing water, and this is allowed to react under alkaline conditions. The treatment of water containing harmful substances according to any one of claims 1 to 3, wherein sludge in which harmful substances are taken into hydrotalcite is formed by forming hydrotalcite, and the sludge is solid-liquid separated. Method. Toxic substances fluorine, boron, nitrogen compounds, phosphorus, not less than one kind or two kinds of heavy metals, any of claims 1 to 4 for separating harmful substances by generating a sludge incorporating solid-liquid Method for treating hazardous substance-containing water described in 1. To 1L of harmful substance-containing water with a fluorine concentration of 1 to 50mg / L, add magnesium oxide 0.05 to 10g / L and soluble aluminum salt so that the aluminum concentration in water is 10 to 1000mg / L. The method for treating toxic substance-containing water according to any one of claims 1 to 5 , wherein the reaction is carried out at a pH of 7 to 11 in a tank. Pre-treatment process to reduce harmful substances and interfering substances contained in harmful substance-containing water (raw water) is provided, and sparingly soluble metal oxides and soluble metal compounds that become components of layered double hydroxides in the pretreated raw water The processing method of the hazardous | toxic substance containing water in any one of Claims 1-6 which add. The method for treating toxic substance-containing water according to any one of claims 1 to 7, further comprising a step of post-treating treated water obtained by solid-liquid separation of sludge. An addition tank for adding chemicals to toxic substance-containing water, a reaction tank for reacting the added chemicals to produce sludge, and a solid-liquid separation tank for separating the produced sludge are connected in order by pipes. Each tank is provided with means for supplying toxic substance-containing water and soluble metal compounds, each reaction tank is provided with means for supplying a hardly soluble metal oxide and a pH adjuster, and each solid-liquid separation tank is provided with The separated sludge and the treated water discharge pipe are connected to each other, and a return pipe from the solid-liquid separation tank to the reaction tank is provided, which contains a toxic substance to which a soluble metal compound is added. Water is introduced into the reaction vessel, a hardly soluble metal oxide and a pH adjuster are added in the reaction vessel, and the surface of the hardly soluble metal oxide dissolves and reacts with the soluble metal compound under alkalinity to cause the hardly soluble metal oxidation. Undissolved thing Sludge layered double hydroxide is formed on the partial surface is generated and sedimentation is introduced into the sludge solid-liquid separation tank, some or all of the sludge subjected to solid-liquid separation in the reaction vessel through the return conduit A device for treating harmful substance-containing water, which is returned.
The processing apparatus according to claim 9, wherein a second addition tank for adding a hardly soluble metal oxide to the separated sludge is provided in the middle of the return conduit.