JP6329448B2 - Waste water treatment method and waste water treatment equipment - Google Patents

Description

  The present invention relates to a technique for treating waste water containing magnesium ions, fluoride ions, and selenium, and a technique for a treatment apparatus.

  Conventionally, in a thermal power plant using heavy oil or coal containing sulfur as a fuel, sulfur oxides in flue gas have been desulfurized for the purpose of preventing pollution. Various technologies have been proposed for such a flue gas desulfurization method. Among them, a flue gas desulfurization apparatus using a magnesium-based absorbent such as magnesium hydroxide is known. Wastewater discharged from this flue gas desulfurization system contains a large amount of water-soluble salts mainly composed of magnesium salts such as magnesium sulfate, and fluoride ions, selenium, etc. which are listed as wastewater standard items Is also included. Therefore, it is necessary to remove fluoride ions, selenium and the like so as to be below the reference value, and then discharge them to public water areas.

  For example, Patent Document 1 proposes a method for treating fluorine ions (fluoride ions) in flue gas desulfurization waste water. Specifically, suspended solids in flue gas desulfurization wastewater are solid-liquid separated, and then sodium hydroxide is added to the solid-liquid separated solution to a pH of 9 or more. Fluorine ions are removed from the wastewater by liquid separation.

  For example, Patent Document 2 proposes a method for treating selenium in flue gas desulfurization waste water. Specifically, flue gas desulfurization waste water having a pH of 3 or higher is passed through a tower packed with iron metal, the iron metal and the waste water are brought into contact with each other, selenium is adsorbed on the iron hydroxide generated from the iron metal, and solidified. Liquid separation separates selenium from the wastewater.

  For example, Patent Document 3 proposes a method for treating hexavalent selenium in waste water. Specifically, while adjusting the pH of the wastewater to 6 or less, iron ions were added, and then a metal was added, and then an alkaline agent was added to adjust the pH to 8 to 10 to obtain the obtained water. By separating the oxide into solid and liquid, hexavalent selenium is removed from the waste water.

JP 2000-176241 A Japanese Patent No. 3385137 Japanese Patent No. 3524618

  As a method for removing fluoride ions and selenium in waste water, for example, a combination of Patent Documents 1 and 2 or a combination of Patent Documents 1 and 3 can be considered.

  However, in the combination of Patent Documents 1 and 2, an acid and an alkali agent for obtaining iron hydroxide from iron metal are necessary, a large amount of iron metal for removing selenium is necessary, The sludge generation amount (precipitate generation amount) accompanying it increases, and it cannot be said that it is a realistic combination from problems, such as processing cost.

  Moreover, in the combination of patent documents 1 and 3, since the iron precipitate and the magnesium precipitate are produced | generated simultaneously in the waste_water | drain containing magnesium ion, a low-density deposit produces | generates and sedimentation of the obtained sludge (precipitate) There is a problem that the nature is bad, it is not a realistic combination.

  An object of the present invention is to provide a wastewater treatment method and a treatment apparatus capable of obtaining sludge with high sedimentation concentration while stably treating fluoride ions and selenium in wastewater treatment containing magnesium ions, fluoride ions and selenium. Is to provide.

  In the wastewater treatment method of the present invention, wastewater containing magnesium ions, fluoride ions, and selenium is reacted with an iron salt under the conditions of pH 6.5 to 8.0, and the selenium is added to the generated iron compound-containing precipitate. A first treatment step for adsorbing, a second treatment for causing the waste water containing the iron compound-containing precipitate after the first treatment step to react with an alkaline agent, and adsorbing the fluoride ions to the produced magnesium compound-containing precipitate. And a waste liquid containing the iron compound-containing precipitate and the magnesium compound-containing precipitate after the second treatment step into a sludge and treated water containing the iron compound-containing precipitate and the magnesium compound-containing precipitate. A first solid-liquid separation step of separating.

  In the wastewater treatment method, it is preferable that the sludge separated in the first solid-liquid separation step is returned to the first treatment step.

  In the wastewater treatment method, the treated water separated in the first solid-liquid separation step is reacted with at least one of sodium hydroxide and calcium hydroxide, and the generated magnesium compound-containing precipitate is added to the generated precipitate. A second treatment step for solid-liquid separation of a third treatment step for adsorbing fluoride ions and wastewater containing the magnesium compound-containing precipitate after the third treatment step into sludge and treated water containing the magnesium compound-containing precipitate. It is preferable that the sludge separated by the second solid-liquid separation step is returned to the first treatment step.

Moreover, the wastewater treatment apparatus of the present invention reacts wastewater containing magnesium ions, fluoride ions, and selenium with iron salt under the conditions of pH 6.5 to 8.0, and the generated iron compound-containing precipitates A first treatment tank for adsorbing selenium, a waste water containing the iron compound-containing precipitate discharged from the first treatment tank, and an alkali agent are reacted, and the fluoride ions are adsorbed to the generated magnesium compound-containing precipitate. A wastewater containing the iron compound-containing precipitate and the magnesium compound-containing precipitate discharged from the second treatment tank, and a sludge containing the iron compound-containing precipitate and the magnesium compound-containing precipitate. comprising a first solid-liquid separation away means for solid-liquid separation and treated water, the.

  Moreover, it is preferable that the waste water treatment apparatus further includes a first return means for returning the sludge separated by the first solid-liquid separation means to the first treatment tank.

  In the wastewater treatment apparatus, the treated water separated by the first solid-liquid separation means is reacted with at least one of sodium hydroxide and calcium hydroxide, and the generated magnesium compound-containing precipitate is added to the fluoride. A third treatment tank that adsorbs fluoride ions, and wastewater containing the magnesium compound-containing precipitate discharged from the third treatment tank is separated into sludge and treated water containing the magnesium compound-containing precipitate. It is preferable to include a second return means for returning the sludge separated by the second solid-liquid separation means to the first treatment tank.

  According to the present invention, in a wastewater treatment containing magnesium ions, fluoride ions, and selenium, a wastewater treatment method and a treatment apparatus capable of obtaining sludge having high sedimentation concentration while stably treating fluoride ions and selenium. Can be provided.

It is a schematic diagram which shows an example of a structure of the waste water treatment apparatus which concerns on this embodiment. It is a schematic diagram which shows another example of a structure of the waste water treatment apparatus which concerns on this embodiment. It is a schematic diagram which shows another example of a structure of the waste water treatment apparatus which concerns on this embodiment.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  FIG. 1 is a schematic diagram illustrating an example of a configuration of a wastewater treatment apparatus according to the present embodiment. The waste water treatment apparatus 1 shown in FIG. 1 includes a first treatment tank 10, a second treatment tank 12, a first flocculant reaction tank 14, and a first solid-liquid separation tank 16. Further, the waste water treatment apparatus 1 includes an iron salt tank 18, an iron salt addition device provided with an iron salt supply line 20, a pH adjuster tank 22, a pH adjuster addition device provided with a pH adjuster line 24, and a first alkaline agent tank 26. , An alkaline agent addition device including the first alkaline agent supply line 28, a first flocculant tank 30, and a flocculant addition device including the first flocculant supply line 32.

  A drain line 34 is connected to the first treatment tank 10. Between the first treatment tank 10 and the second treatment tank 12, between the second treatment tank 12 and the first flocculant reaction tank 14, and between the first flocculant reaction tank 14 and the first solid-liquid separation tank 16. Are connected by a drain line (not shown). A treated water line 36 and a sludge discharge line 38 are connected to the first solid-liquid separation tank 16. One end of the iron salt supply line 20 is connected to the first treatment tank 10, the other end is connected to the iron salt tank 18, one end of the pH adjuster line 24 is connected to the first treatment tank 10, and the other end is adjusted to pH. It is connected to the agent tank 22. One end of the first alkaline agent supply line 28 is connected to the second treatment tank 12, and the other end is connected to the first alkaline agent tank 26. One end of the first flocculant supply line 32 is connected to the first flocculant reaction tank 14, and the other end is connected to the first flocculant tank 30.

  An example of the operation of the wastewater treatment apparatus 1 according to this embodiment will be described.

  The wastewater to be treated in this embodiment is not particularly limited as long as it contains magnesium ions, fluoride ions, and selenium. Examples of the wastewater include flue gas desulfurization wastewater. The flue gas desulfurization waste water is, for example, waste water discharged from a flue gas desulfurization device that absorbs and removes sulfur oxides in exhaust gas with a magnesium-based absorbent such as magnesium hydroxide.

Wastewater containing magnesium ions, fluoride ions, and selenium (hereinafter sometimes referred to as raw water) is supplied to the first treatment tank 10 through the drainage line 34. The iron salt in the iron salt tank 18 is supplied from the iron salt supply line 20 to the first treatment tank 10, and the pH adjuster in the pH adjuster tank 22 passes through the pH adjuster line 24 to the first treatment tank 10. It is supplied and the pH in the 1st processing tank 10 is adjusted to the range of 6.5-8.0. In the first treatment tank 10, precipitates containing iron compounds such as iron hydroxides (Fe (OH) ₂ , Fe (OH) ₃ etc.) and iron oxides (FeO, Fe ₂ O ₃ etc.) are generated. The selenium is mainly adsorbed on the generated precipitate (first treatment step). Next, the waste water in the first treatment tank 10 is supplied to the second treatment tank 12 together with the precipitate containing the iron compound on which selenium is adsorbed. Then, the alkaline agent in the first alkaline agent tank 26 is supplied from the first alkaline agent supply line 28 to the second treatment tank 12. At this time, in the second treatment tank 12, a precipitate containing a magnesium compound such as magnesium hydroxide (Mg (OH) ₂ or the like) or magnesium oxide (MgO or the like) is generated, and the generated precipitate is included in the generated precipitate. Fluoride ions are mainly adsorbed (second processing step). The formation mechanism of the precipitate is not clear, but first, the magnesium compound is precipitated using the precipitate containing the iron compound adsorbed with selenium as the nucleus, and fluoride ions are adsorbed on the surface of the precipitate containing the magnesium compound. . Thus, it is considered that the precipitate containing the magnesium compound and the precipitate containing the iron compound are integrated after the second treatment step to form a precipitate having a high density. For this reason, it is thought that the sedimentation concentration property of the sludge containing the said deposit improves in a solid-liquid separation process of a latter stage. On the other hand, when the second treatment step is performed before the first treatment step, that is, when a precipitate containing a magnesium compound is generated and a fluoride ion is adsorbed, then a precipitate containing an iron compound is formed, an iron salt At the time of addition, the precipitate containing the magnesium compound is dissolved by the acidic iron salt, the fluoride ions adsorbed on the precipitate containing the magnesium compound are eluted, and the fluoride ion concentration in the treated water increases. Moreover, when it is going to suppress elution of fluoride ion, it is necessary to add more alkali agents, the amount of precipitates increases, and the amount of sludge generated increases. Furthermore, since it does not become a precipitate having a precipitate containing an iron compound as a nucleus, it becomes a sludge having a low sediment concentration property.

  Next, the waste water in the second treatment tank 12 is supplied to the first coagulant reaction tank 14 together with the precipitate containing the iron compound adsorbed with selenium and the precipitate containing the magnesium compound adsorbed with fluoride ions. The Then, the flocculant in the first flocculant tank 30 is supplied from the flocculant supply line 32 to the first flocculant reaction tank 14. In the first flocculant reaction tank 14, the precipitate on which selenium and fluoride ions are adsorbed is flocked. The waste water in the first flocculant reaction tank 14 is supplied to the first solid-liquid separation tank 16 together with the flocked precipitates (precipitates on which selenium and fluoride ions are adsorbed), and the first solid-liquid separation is performed. In the tank 16, solid-liquid separation is carried out into sludge containing precipitates on which selenium and fluoride ions are adsorbed and treated water, the treated water is discharged out of the system from the treated water line 36, and the sludge is discharged from the sludge discharge line 38. It is discharged out of the system (solid-liquid separation process).

  Below, the detail of each processing process of this embodiment is demonstrated.

<First treatment process>
The first treatment step is a step in which raw water and an iron salt are reacted under a condition of pH 6.5 to 8.0, and selenium is adsorbed on a precipitate containing the generated iron compound. The reaction pH may be in the range of 6.5 to 8.0, but the pH of the raw water is preferably in the range of 7.0 to 7.5 in terms of sludge sedimentation concentration, selenium removal rate, and the like. When the pH of the raw water satisfies the above range, generation of a precipitate containing a magnesium compound can be suppressed, an iron salt can be precipitated as an iron compound, and selenium can be efficiently adsorbed on the precipitate. On the other hand, if the pH of the raw water is less than 6.5, the precipitation of iron compounds in the first treatment step is small, the core precipitates in the reaction of the second treatment step are small, and the density of the second reaction step is low. It is considered that a relatively low precipitate is generated, and sludge having low sedimentation concentration is generated as compared with the case where the above range is satisfied. In addition, when the pH of the raw water exceeds 8.0, a precipitate containing an iron compound and a precipitate containing a magnesium compound are generated at the same time, and a precipitate having a relatively low density is generated in which the precipitate containing the iron compound does not become a nucleus. Thus, as compared with the case where the above range is satisfied, sludge with low sedimentation concentration is generated and the selenium removal rate is also reduced.

  In this embodiment, while adding an iron salt or after adding a necessary amount of iron salt, a pH adjuster is supplied to the first treatment tank 10 to adjust the reaction pH to a range of 6.5 to 8.0. Is done. However, since the iron salt shows acidity, even if the pH of the raw water before adding the iron salt is adjusted to 6.5 to 8.0, the pH of the raw water is less than 6.5 by adding the iron salt. It may become. In that case, it is necessary to adjust the pH again so that the pH of the raw water is in the range of 6.5 to 8.0 while adding the iron salt or after adding the iron salt. Therefore, it is desirable to adjust the pH while adding the iron salt or after adding the iron salt. The reaction pH is measured by a pH meter (not shown) installed in the first treatment tank 10. In addition, adjustment of reaction pH is performed as follows, for example. For example, the operator can supply the pH adjusting agent by opening and closing a valve (not shown) provided in the pH adjusting agent line 24 while looking at the value of the pH meter. Further, for example, a control unit electrically connected to an electromagnetic valve (not shown) provided in the pH meter and the pH adjuster line 24 is provided, and the control unit that receives the pH value from the pH meter is based on the pH value. This is done by controlling the opening and closing of the electromagnetic valve.

  For adjusting the pH of the raw water, an acid agent such as hydrochloric acid or a pH adjuster such as an alkali agent such as sodium hydroxide or calcium hydroxide is used.

Examples of the iron salt used in the present embodiment include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, and the like. If the form of selenium in the waste water is only tetravalent selenium (SeO ₂ ²⁻ ), any iron salt may be used, but if hexavalent selenium (SeO ₃ ²⁻ ) is included, Divalent iron salts such as ferrous iron and ferrous sulfate are preferred. By using a divalent iron salt, it is considered that hexavalent selenium is reduced to tetravalent selenium and the tetravalent selenium is adsorbed by the precipitate containing the iron compound.

  The amount of iron salt added is appropriately set depending on the selenium concentration in the raw water, the required selenium concentration in the treated water, and is not particularly limited. For example, the selenium concentration in the raw water If the amount is slightly higher than the reference value (0.1 mg / L) (about 0.2 to 0.3 mg / L), the amount of iron salt added is, for example, about 100 to 500 mgFe / L.

  The reaction time between the raw water and the iron salt in the first treatment step is not particularly limited as long as the time for sufficiently depositing the precipitate containing the iron compound is ensured, for example, 10 minutes to 60 minutes. It is preferable to be in the range. If the reaction time is less than 10 minutes, the generation of the precipitate containing the iron compound is not sufficiently performed, and the process proceeds to the second treatment step, so that the selenium removal rate may be reduced. Since the 1st processing tank 10 of a big capacity | capacitance is needed, it may be unpreferable practically. Moreover, it is preferable to install a stirrer in the 1st processing tank 10 and to make it react, stirring raw | natural water and an iron salt in the point of the production | generation efficiency of the precipitate containing an iron compound.

<Second treatment process>
The second treatment step is a step in which the wastewater containing the iron compound-containing precipitate adsorbing selenium after the first treatment step is reacted with an alkaline agent to adsorb fluoride ions to the produced magnesium compound-containing precipitate.

Examples of the alkaline agent used in the present embodiment include sodium hydroxide (NaOH), calcium hydroxide (Ca (OH) ₂ ), and the like, and calcium hydroxide is preferable in terms of fluorine removal rate. By using calcium hydroxide, fluoride ions are precipitated as calcium fluoride, so that the fluorine removal rate is improved as compared with the case of using sodium hydroxide. Moreover, since calcium fluoride adheres to the precipitate produced | generated at the 1st process process and the 2nd process process, compared with the case where sodium hydroxide is used, the sedimentation concentration property of sludge may improve.

  The addition amount of the alkaline agent may be an amount capable of forming a precipitate containing a magnesium compound sufficient to remove fluoride ions. The addition amount of the alkaline agent is appropriately set depending on the magnesium ion concentration and fluoride ion concentration of the raw water and the required fluoride ion concentration in the treated water. When calcium hydroxide is used as the alkaline agent, the amount of the alkaline agent added is preferably, for example, 2000 to 4000 mg / L if the raw water is 100 to 300 mgF / L.

  The pH of the waste water in the second treatment step is preferably 9 or more, preferably in the range of 9.0 to 10.0, and more preferably in the range of 9.2 to 9.7. . In the case of less than 9.0, the precipitate containing the magnesium compound is not sufficiently generated, and the fluoride ion removal rate may be reduced. The amount of generated sludge may become excessive.

  The reaction time of the waste water and the alkaline agent in the second treatment step is not particularly limited as long as the time for sufficiently depositing the precipitate containing the magnesium compound is secured, but for example, 10 minutes to 60 minutes It is preferable to be in the range. If the reaction time is less than 10 minutes, the precipitate containing the magnesium compound is not sufficiently generated and the process proceeds to the solid-liquid separation treatment step, and the fluoride ion removal rate may be reduced. When it exceeds, since the 2nd processing tank 12 of a big capacity | capacitance is needed, it may not be practically preferable. Moreover, it is preferable to install a stirrer in the 2nd processing tank 12 and to make it react, stirring a waste_water | drain and an alkaline agent in the point of the production | generation efficiency of the deposit containing a magnesium compound.

  As described above, by performing the second treatment step after the first treatment step as in the present embodiment, a precipitate to which a precipitate containing an iron compound and a precipitate containing a magnesium compound are attached is obtained. For this reason, sludge with high sedimentation concentration property is obtained, removing selenium and fluoride ion efficiently. On the other hand, when the first treatment step is performed after the second treatment step, that is, when the iron salt is added after the precipitate containing the magnesium compound is first generated, one of the magnesium precipitates that have adsorbed the fluorine ions. Since the portion dissolves, the fluoride ion removal rate may decrease, or the amount of alkali agent added may increase. Eventually, as described above, a high-density precipitate having a precipitate containing an iron compound as a core is not generated, and sludge having a low sediment concentration property may be formed. In addition, in the case of wastewater treatment in which only the first treatment step is performed without providing the second treatment step, when the reaction pH is adjusted to 6.5 to 8.0, a precipitate containing a magnesium compound is not generated. In some cases, the fluoride ion removal rate may be significantly reduced. In addition, in the case of wastewater treatment in which only the first treatment step is performed without providing the second treatment step, a precipitate containing a magnesium compound is not generated even when the reaction pH is adjusted to less than 6.5. The removal rate may be significantly reduced. When the reaction pH is adjusted to more than 8.0, a precipitate containing an iron compound and a precipitate containing a magnesium compound are generated at the same time, and a high-density precipitate having a precipitate containing an iron compound as a nucleus is formed. Because it is difficult, it may become sludge with poor sedimentation concentration.

<Solid-liquid separation process>
In the solid-liquid separation treatment step, it is desirable to perform a solid-liquid separation treatment after adding a flocculant to the waste water after the second treatment step to flock the precipitate in the waste water. As the flocculant, conventionally known inorganic flocculants, polymer flocculants and the like are used.

  In the solid-liquid separation treatment of this embodiment, a solid-liquid separation tank (precipitation tank) that separates precipitates that have adsorbed fluoride ions and selenium from wastewater into sediment and separates the sludge containing the precipitates and treated water. As explained in the example, it is not limited to this as long as it is separated into sludge containing precipitates adsorbing fluoride ions and selenium and treated water. Good. The sludge containing the solid-liquid separated deposits is discharged out of the system, and is disposed, for example, after being concentrated and dehydrated.

  FIG. 2 is a schematic diagram illustrating another example of the configuration of the waste water treatment apparatus according to the present embodiment. In the waste water treatment apparatus 2 shown in FIG. 2, the same components as those in the waste water treatment apparatus 1 shown in FIG. The waste water treatment apparatus 2 shown in FIG. 2 includes a sludge return line 40, one end of the sludge return line 40 is connected to the sludge discharge line 38, and the other end is connected to the first treatment tank 10. The sludge obtained by the solid-liquid separation tank 16 through the first treatment step and the second treatment step shows alkalinity. For this reason, in the wastewater treatment apparatus 2 shown in FIG. 2, the sludge that has been subjected to the solid-liquid separation treatment (precipitate that has adsorbed fluoride ions and selenium) is supplied from the sludge return line 40 to the first treatment tank 10. It becomes possible to utilize as an alkaline agent which adjusts pH in 1 processing tank 10 to the range of 6.5-8.0. As a result, it is possible to reduce the amount of alkaline agent used for pH adjustment in the first treatment step. In addition, the fluoride ion removal rate may be improved by circulating the sludge.

  FIG. 3 is a schematic diagram illustrating another example of the configuration of the waste water treatment apparatus according to the present embodiment. In the waste water treatment apparatus 3 shown in FIG. 3, the same code | symbol is attached | subjected about the structure similar to the waste water treatment apparatus 1 shown in FIG. 1, and the description is abbreviate | omitted. The waste water treatment apparatus 3 shown in FIG. 3 includes a third treatment tank 42, a second flocculant reaction tank 44, and a second solid-liquid separation tank 46. An alkali agent addition device including a second alkali agent tank 48, a second alkali agent supply line 50, a second flocculant addition device including a second flocculant tank 52, and a second flocculant supply line 54 are provided.

  One end of the treated water line 36 is connected to the first solid-liquid separation tank 16, and the other end is connected to the third treatment tank 42. Further, the third treatment tank 42 and the second flocculant reaction tank 44 and the second flocculant reaction tank 44 and the second solid-liquid separation tank 46 are connected by a drain line (not shown). A final treated water line 56 and a sludge discharge line 58 are connected to the second solid-liquid separation tank 46. One end of the sludge return line 40 is connected to the sludge discharge line 58, and the other end is connected to the first treatment tank 10.

  The treated water discharged from the first solid-liquid separation tank 16 is supplied to the third treatment tank 42 through the treated water line 36. The alkaline agent in the second alkaline agent tank 48 is supplied to the third treatment tank 42 through the second alkaline agent supply line 50. In the third treatment tank 42, the treated water reacts with the alkaline agent, so that magnesium ions remaining in the treated water are deposited as precipitates containing a magnesium compound, and adsorb fluoride ions remaining in the treated water (third). Processing step). Thereby, treated water with a lower fluoride ion concentration is obtained.

  Examples of the alkaline agent used in the third treatment step include sodium hydroxide and calcium hydroxide. Moreover, the addition amount of the alkaline agent in the third treatment step may be an amount capable of forming a precipitate containing a magnesium compound sufficient to remove fluoride ions, and the treatment discharged from the final treated water line 56. It is desirable to adjust the addition amount of the alkaline agent while confirming the fluoride ion concentration in water.

  The waste water in the third treatment tank 42 is supplied to the second flocculant reaction tank 44 together with the precipitate containing the magnesium compound on which fluoride ions are adsorbed. Then, the flocculant in the second flocculant tank 52 is supplied from the second flocculant supply line 54 to the second flocculant reaction tank 44. In the second flocculant reaction tank 44, the precipitate on which fluoride ions are adsorbed is flocked. Then, the waste water in the second flocculant reaction tank 44 is supplied to the second solid-liquid separation tank 46 together with the flocked precipitate, and the precipitate in which fluoride ions are adsorbed in the second solid-liquid separation tank 46. Solid-liquid separation into sludge containing waste and treated water. The treated water is discharged from the final treated water line 56 to the outside of the system. Further, the sludge is discharged out of the system from the sludge discharge line 58 (solid-liquid separation processing step), and is supplied to the first treatment tank 10 through the sludge return line 40.

  In the wastewater treatment apparatus 3 shown in FIG. 3, sludge (precipitate that has adsorbed fluoride ions) subjected to solid-liquid separation in the second solid-liquid separation tank 46 is supplied to the first treatment tank 10 through the sludge return line 40. And is used to adjust the pH of the raw water to a range of 6.5 to 8.0. This makes it possible to reduce the amount of alkaline agent used for pH adjustment in the first treatment step. In addition, the fluoride ion removal rate may be improved by circulating the sludge. In the waste water treatment apparatus 3 shown in FIG. 3, the sludge return line 40 is provided in the second solid-liquid separation tank 46, but may be provided in the first solid-liquid separation tank 16, and the first solid-liquid separation tank 16 and the first solid-liquid separation tank 16 may be provided. It may be provided in both of the two solid-liquid separation tanks 46.

  In each wastewater treatment device, for example, fluoride ions and selenium concentrations of 0.1 to 1.0 mg / L, selenium concentrations of 2000 to 15000 mg / L, and fluoride ions and Selenium can be reduced to a wastewater standard (fluoride ion concentration of 15 mg / L or less, selenium concentration of 0.1 mg / L or less), and sludge with high sedimentation concentration can be obtained.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
Using the treatment apparatus shown in FIG. 1, treatment of simulated waste water containing magnesium ions, fluoride ions, and selenium (tetravalent) was performed. The simulated waste water is prepared by referring to the desulfurization waste water quality described in Patent Document 1. However, selenium was adjusted to a value sufficiently higher than the wastewater standard value. Table 1 shows the composition and pH of the simulated waste water.

  The processing of Example 1 was performed as follows. Ferric chloride was added to 1000 mL of simulated waste water so as to be 500 mgFe / L, and then calcium hydroxide was added so as to be 400 mgCa / L, and the pH of the wastewater was adjusted to 7.5, followed by stirring for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1800 mgCa / L (at this time, the pH of the wastewater was 9.2). The waste water was stirred for 15 minutes to react calcium hydroxide with the waste water (second treatment step). Next, 5 mg / L of a polymer flocculant (Orglock M-4020 manufactured by Organo Co., Ltd.) was added and stirred for 10 minutes for aggregation treatment. The SS concentration in the waste water after the coagulation treatment was measured by glass fiber filter paper filtration.

  Next, the waste water after the coagulation treatment is settled and separated in a solid-liquid separation tank, and after 30 minutes, the treated water in the solid-liquid separation tank is collected, and the pH is measured with a pH meter (HM-30P, manufactured by Toa DKK) The chloride ion concentration was measured by lanthanum-alizarin complexone spectrophotometry, and the selenium concentration was measured by ICP mass spectrometry. Further, the volume ratio of sludge accumulated in the solid-liquid separation tank (volume% of sludge with respect to the amount of treated water) was measured by a scale carved on the separation tank wall surface. Each said process was performed in the state which maintained waste_water | drain at 40 degreeC. Table 2 summarizes the chemical addition amount and drainage pH in Example 1.

(Comparative Example 1-1)
After adding calcium hydroxide slurry to 1000 mL of simulated waste water to 1800 mg Ca / L and adjusting the drain pH to 9.2, the waste water and calcium hydroxide were reacted with stirring for 15 minutes (alkali reaction step). . Next, after adding ferric chloride to 500 mgFe / L, calcium hydroxide was added to 400 mgCa / L, and the waste water and ferric chloride were reacted with stirring for 15 minutes ( Iron salt reaction process). The pH of the waste water at this time was 9.2. Next, 5 mg / L of a polymer flocculant (manufactured by Organo Corp., M-4020) was added and stirred for 10 minutes for aggregation treatment. The SS concentration in the waste water after the coagulation treatment was measured.

  Next, the waste water after the coagulation treatment was settled and separated in a solid-liquid separation tank, and after 30 minutes, treated water in the solid-liquid separation tank was collected, and pH, fluoride ion concentration, and selenium concentration were measured. Moreover, the sludge volume ratio (volume% of sludge with respect to the amount of treated water) of the sludge accumulated in the solid-liquid separation tank was measured. Each said process was performed in the state which maintained waste_water | drain at 40 degreeC. Table 3 summarizes the chemical addition amount and drainage pH of Comparative Example 1-1. In addition, the measuring method and measuring equipment of each item are the same as Example 1.

(Comparative Example 1-2)
The test was performed under the same conditions as in Comparative Example 1-1 except that ferric chloride was added to 500 mgFe / L and calcium hydroxide was added to 3200 mgCa / L. Table 3 summarizes the chemical addition amount and drainage pH of Comparative Example 1-2. The pH after ferric chloride and calcium hydroxide addition reaction was 9.5.

(Comparative Example 2-1)
After adding calcium hydroxide slurry to 1000 mL of simulated waste water so as to be 2200 mgCa / L and adjusting the pH of the waste water to 9.2, the waste water and calcium hydroxide were reacted with stirring for 15 minutes (alkali reaction step). . Next, after adding ferric chloride to 500 mgFe / L (the pH of the wastewater is 9.0), the wastewater and ferric chloride were reacted with stirring for 15 minutes (iron salt reaction step) . Subsequent operations were performed under the same conditions as in Comparative Example 1-1. Table 4 summarizes the chemical addition amount and drainage pH of Comparative Example 2-1.

(Comparative Example 2-2)
After adding calcium hydroxide slurry to 1000 mL of simulated waste water so as to be 5000 mgCa / L and adjusting the drainage pH to 9.4, the wastewater and calcium hydroxide were reacted while stirring for 15 minutes (alkali reaction step). . Next, after adding ferric chloride to 500 mg Fe / L (the pH of the wastewater was 9.2), the wastewater and ferric chloride were reacted with stirring for 15 minutes (iron salt reaction step) . Subsequent operations were performed under the same conditions as in Comparative Example 1-1. Table 4 summarizes the chemical addition amount and drainage pH of Comparative Example 2-2.

(Comparative Example 3-1)
After adding ferric chloride to 1000 mL of simulated waste water to 500 mgFe / L and simultaneously adding calcium hydroxide slurry to 2200 mgCa / L (drain pH is 9.2), stirring for 30 minutes The waste water was reacted with ferric chloride and calcium hydroxide (iron salt alkali reaction step). Then, the aggregation process and the sedimentation-separation process were performed similarly to the comparative example 1-1. Table 5 summarizes the chemical addition amount and drainage pH of Comparative Example 3-1.

(Comparative Example 3-2)
A test was conducted under the same conditions as in Comparative Example 3-1, except that ferric chloride was added to 1000 mL of simulated waste water so as to be 1000 mgFe / L. Table 5 summarizes the chemical addition amount and drainage pH of Comparative Example 3-2.

  PH of treated water of Example 1 and each comparative example, fluoride ion concentration and selenium concentration, SS concentration in waste water after coagulation treatment, sludge volume ratio of sludge separated into solid and liquid (volume% of sludge with respect to treated water amount) The results are summarized in Table 6.

In Example 1 in which wastewater and iron salt were reacted under the condition of pH 7.5 and then reacted with an alkaline agent (pH 9.2), the fluoride ion concentration in the treated water was 13 mg / L, and the selenium concentration was 0. 0.05 mg / L. Moreover, the cumulative amount of Ca (OH) ₂ added is 2200 mgCa / L, the SS concentration in the waste water after the coagulation treatment (generated solid matter concentration) is 10500 mg / L, and the sludge volume ratio of the sludge separated into solid and liquid is 29%.

After reacting the waste water and the alkaline agent under the condition of pH 9.2, among the Comparative Examples 1-1 and 1-2 reacted with the iron salt, the cumulative amount of Ca (OH) ₂ added was Example 1. In Comparative Example 1-1, which was the same as in Example 1, the selenium concentration in the treated water was the same as that in Example 1, but the fluoride ion was 31 mg / L, which was higher than that in Example 1. Further, the SS concentration after the coagulation treatment was almost the same as in Example 1, but the sludge volume ratio of the solid-liquid separated sludge was 46%, which was higher than that in Example 1. It can be said that the higher the sludge volume ratio, the worse the sludge is. Next, in Comparative Example 1-2 in which the cumulative amount of Ca (OH) ₂ added was about twice that of Example 1, the selenium concentration and fluoride ion concentration in the treated water were similar to those in Example 1. However, the SS concentration after the coagulation treatment is about 21 times 21700 mg / L compared with Example 1, and the sludge volume ratio of the solid-liquid separated sludge is 60%, which is higher than that of Example 1. The sludge was poorly settled and concentrated.

After reacting the waste water and the alkaline agent at pH 9.2 or 9.4, the cumulative addition of Ca (OH) _{2 was} carried out among Comparative Examples 2-1 and 2-2 that were reacted with iron salt without adjusting the pH. In Comparative Example 2-1, the amount of which was the same as in Example 1, the selenium concentration in the treated water was similar to that in Example 1, but the fluoride ion was 38 mg / L. It was expensive. The SS concentration after the coagulation treatment was almost the same as in Example 1, but the sludge volume ratio of the sludge separated into solid and liquid is 46%, which is higher than that in Example 1 and has poor sedimentation concentration. Met. Next, in Comparative Example 2-2 in which the cumulative amount of Ca (OH) ₂ added was about twice that in Example 1, the selenium concentration and fluoride ion concentration in the treated water were comparable to those in Example 1. However, the SS concentration after the coagulation treatment is 24400 mg / L, which is more than twice that in Example 1, and the sludge volume ratio of the solid-liquid separated sludge is 67%, which is higher than that in Example 1. The sludge was poorly settled and concentrated.

Of Comparative Examples 3-1 and 3-2 in which an iron salt and an alkaline agent were added to the wastewater and reacted, the comparative example in which the iron salt addition amount and the cumulative Ca (OH) ₂ addition amount were the same as in Example 1 3-1, the fluoride ion concentration in the treated water was similar to that in Example 1, but the selenium concentration was 0.17 mg / L, which was higher than that in Example 1. The SS concentration after the coagulation treatment was almost the same as in Example 1, but the sludge volume ratio of the sludge separated into solid and liquid is 35%, which is higher than that in Example 1 and has poor sedimentation concentration. Met. Next, although the cumulative amount of Ca (OH) ₂ added is the same as that in Example 1, Comparative Example 3-2 in which the amount of iron salt added is twice is the same as that in Example 1 in the selenium concentration in the treated water. The fluoride ion concentration was 24 mg / L, which was higher than that of Example 1. Further, the SS concentration after the coagulation treatment is 1.3400 times that of Example 1, 14400 mg / L, and the sludge volume ratio of the solid-liquid separated sludge is 42%, which is compared with Example 1. The sludge was high and poor in sediment concentration.

  From the above results, in the wastewater treatment containing magnesium ions, fluoride ions, and selenium, as in Example 1, the wastewater and iron salt were reacted under the condition of pH 7.5, and then reacted with an alkali agent ( It was confirmed that by adjusting the pH to 9.2), fluoride ions and selenium can be stably treated, and sludge having high sedimentation concentration can be obtained. In Example 1, since the amount of chemicals used was also suppressed, it was possible to reduce the amount of sludge.

(Example 2-1)
Ferric chloride is added to 1000 mL of simulated waste water to 500 mgFe / L, then calcium hydroxide is added to 350 mgCa / L, and the pH of the wastewater is adjusted to 6.5, followed by stirring for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1850 mgCa / L, and the wastewater was stirred for 15 minutes to react calcium hydroxide and wastewater (second treatment step). The pH after the reaction was 9.2. In the following examples and comparative examples, the iron salt addition amount is 500 mg Fe / L, and the cumulative Ca (OH) ₂ addition amount is 2200 mg Ca / L.

  Next, 5 mg / L of a polymer flocculant (manufactured by Organo Corp., M-4020) was added and stirred for 10 minutes for aggregation treatment. The SS concentration in the waste water after the coagulation treatment was measured.

  Next, the waste water after the coagulation treatment was settled and separated in a solid-liquid separation tank, and after 30 minutes, treated water in the solid-liquid separation tank was collected, and pH, fluoride ion concentration, and selenium concentration were measured. Moreover, the sludge volume ratio (volume% of sludge with respect to the amount of treated water) deposited in the solid-liquid separation tank was measured. Each said process was performed in the state which maintained waste_water | drain at 40 degreeC. Table 7 shows the chemical addition amount and drainage pH in Example 2-1. In addition, the measuring method and measuring equipment of each item are the same as Example 1.

(Example 2-2)
Ferric chloride was added to 1000 mL of simulated waste water so as to be 500 mgFe / L, and then calcium hydroxide was added so as to be 400 mgCa / L, and the pH of the wastewater was adjusted to 7.5, followed by stirring for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1800 mgCa / L, and the wastewater was stirred for 15 minutes to react calcium hydroxide and wastewater (second treatment step). The pH after the reaction was 9.2. Subsequent operations were performed under the same conditions as in Example 2-1. Table 7 summarizes the chemical addition amount and drainage pH of Example 2-2.

(Example 2-3)
Ferric chloride is added to 1000 mL of simulated waste water to 500 mgFe / L, then calcium hydroxide is added to 450 mgCa / L, and the pH of the wastewater is adjusted to 8.0, and then stirred for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1750 mgCa / L, and the waste water was stirred for 15 minutes to react calcium hydroxide and the waste water (second treatment step). The pH after the reaction was 9.2. Subsequent operations were performed under the same conditions as in Example 2-1. Table 7 shows the chemical addition amount and drainage pH in Example 2-3.

(Comparative Example 4-1)
After adding ferric chloride to 1000 mL of simulated waste water to 500 mgFe / L (drainage pH is 5.0), the wastewater and ferric chloride were reacted with stirring for 15 minutes (first treatment step) . Thereafter, a calcium hydroxide slurry was added to 2200 mg Ca / L, and the waste water was stirred for 15 minutes to react calcium hydroxide and the waste water (second treatment step). The pH after the reaction was 9.2. Subsequent operations were performed under the same conditions as in Example 2-1. Table 7 shows the chemical addition amount and drainage pH of Comparative Example 4-1.

(Comparative Example 4-2)
Ferric chloride is added to 1000 mL of simulated waste water to 500 mgFe / L, then calcium hydroxide is added to 300 mgCa / L, and the pH of the wastewater is adjusted to 6.0, followed by stirring for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1900 mgCa / L, and the waste water was stirred for 15 minutes to react calcium hydroxide with the waste water (second treatment step). The pH after the reaction was 9.2. Subsequent operations were performed under the same conditions as in Example 2-1. Table 7 shows the chemical addition amount and drainage pH of Comparative Example 4-2.

(Comparative Example 4-3)
Ferric chloride is added to 1000 mL of simulated waste water to 500 mgFe / L, then calcium hydroxide is added to 500 mgCa / L, and the pH of the wastewater is adjusted to 8.5, followed by stirring for 15 minutes. Then, the waste water and ferric chloride were reacted (first treatment step). Thereafter, a calcium hydroxide slurry was added to 1700 mgCa / L, and the wastewater was stirred for 15 minutes to react calcium hydroxide and the wastewater (second treatment step). The pH after the reaction was 9.2. Subsequent operations were performed under the same conditions as in Example 2-1. Table 7 shows the chemical addition amount and drainage pH of Comparative Example 4-3.

  The pH of the treated water of Example 2 and Comparative Example 4, the fluoride ion concentration and the selenium concentration, the SS concentration in the waste water after the coagulation treatment, the sludge volume ratio of the sludge separated into solid and liquid (volume% of sludge with respect to the treated water amount) Table 8 summarizes.

  In Examples 2-1 to 2-3, the fluoride ion concentration in the treated water was 12 to 13 mg / L, and the selenium concentration was less than 0.1 mg / L. Moreover, SS density | concentration after a coagulation process was 10400-10700 mg / L, and the sludge volume ratio of the sludge solid-liquid-separated was 29-32%. On the other hand, in Comparative Examples 4-1 to 4-2 in which wastewater and iron salt were reacted at a pH of less than 6.5, the fluoride ion concentration and the selenium concentration in the treated water were as in Examples 2-1 to 2-3. The SS concentration after the coagulation treatment was higher than that of Examples 2-1 to 2-3, and the sludge volume concentration of the solid-liquid separated sludge was 38 to 45%. The sludge was high compared with 1-2-3 and poor in sediment concentration. Moreover, in Comparative Example 4-3 in which wastewater and iron salt were reacted at a pH of more than 8.0, the fluoride ion concentration in the treated water was similar to Examples 2-1 to 2-3, but the selenium concentration Was 0.15 mg / L, which was higher than those of Examples 2-1 to 2-3. In addition, the sludge volume density | concentration of the solid-liquid separated sludge was comparable as Examples 2-1 to 2-3. From the above results, it is possible to stably treat fluoride ions and selenium by reacting wastewater and iron salt under the conditions of pH 6.5 to 8.0 and obtain sludge having high sedimentation concentration. confirmed.

  1-3 Wastewater treatment device, 10 1st treatment tank, 12 2nd treatment tank, 14 1st flocculant reaction tank, 16 1st solid-liquid separation tank, 18 Iron salt tank, 20 Iron salt supply line, 22 pH adjuster Tank, 24 pH adjuster line, 26 First alkali agent tank, 28 First alkali agent supply line, 30 First flocculant tank, 32 First flocculant supply line, 34 Drain line, 36 Treated water line, 38 Sludge discharge Line, 40 Sludge return line, 42 3rd processing tank, 44 2nd flocculant reaction tank, 46 2nd solid-liquid separation tank, 48 2nd alkali agent tank, 50 2nd alkali agent supply line, 52 2nd flocculant tank , 54 Second flocculant supply line, 56 Final treated water line, 58 Sludge discharge line.

Claims (6)

A first treatment step in which wastewater containing magnesium ions, fluoride ions, and selenium and an iron salt are reacted under conditions of pH 6.5 to 8.0, and the selenium is adsorbed to the produced iron compound-containing precipitate;
A second treatment step of causing the waste water containing the iron compound-containing precipitate after the first treatment step to react with an alkaline agent, and adsorbing the fluoride ions to the generated magnesium compound-containing precipitate;
The waste water containing the iron compound-containing precipitate and the magnesium compound-containing precipitate after the second treatment step is solid-liquid separated into sludge and treated water containing the iron compound-containing precipitate and the magnesium compound-containing precipitate. A wastewater treatment method comprising: 1 solid-liquid separation step.   The wastewater treatment method according to claim 1, wherein the sludge separated in the first solid-liquid separation step is returned to the first treatment step. Reacting the treated water separated in the first solid-liquid separation step with at least one of sodium hydroxide and calcium hydroxide to adsorb the fluoride ions to the generated magnesium compound-containing precipitate; Processing steps;
A second solid-liquid separation step for solid-liquid separation of the waste water containing the magnesium compound-containing precipitate after the third treatment step into sludge containing the magnesium compound-containing precipitate and treated water;
The wastewater treatment method according to claim 1 or 2, wherein the sludge separated in the second solid-liquid separation step is returned to the first treatment step. A first treatment tank that causes magnesium ion, fluoride ion, selenium-containing wastewater and iron salt to react under conditions of pH 6.5 to 8.0, and adsorbs the selenium to the produced iron compound-containing precipitate;
A second treatment tank in which the wastewater containing the iron compound-containing precipitate discharged from the first treatment tank is reacted with an alkaline agent, and the fluoride ions are adsorbed on the generated magnesium compound-containing precipitate;
Solid-liquid separation of the waste water containing the iron compound-containing precipitate and the magnesium compound-containing precipitate discharged from the second treatment tank into sludge and treated water containing the iron compound-containing precipitate and the magnesium compound-containing precipitate. waste water treatment apparatus, characterized in that it comprises a first solid-liquid separation away means, the for.   The wastewater treatment apparatus according to claim 4, further comprising a first return means for returning the sludge separated by the first solid-liquid separation means to the first treatment tank. A third treatment in which the treated water separated by the first solid-liquid separation means is reacted with at least one of sodium hydroxide and calcium hydroxide and the fluoride ions are adsorbed on the produced magnesium compound-containing precipitate. A tank,
A second solid-liquid separation means for solid-liquid separation of the waste water containing the magnesium compound-containing precipitate discharged from the third treatment tank into sludge containing the magnesium compound-containing precipitate and treated water;
The wastewater treatment apparatus according to claim 4 or 5, further comprising second return means for returning the sludge separated by the second solid-liquid separation means to the first treatment tank.

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