JP2006320865A - Fluorine-containing wastewater treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment system which is excellent in fluorine and heavy metals-removing effect in wastewater containing heavy metals together with fluorine. <P>SOLUTION: In a fluorine removal method where an aluminum source is added to fluorine-containing wastewater to coprecipitate fluorine with aluminum hydroxide precipitate, the fluorine-containing wastewater is introduced into a reaction tank to generate the above precipitate, and the precipitate slurry is separated from the wastewater. A part of or the whole of the separated slurry is introduced into a conditioning tank. The aluminum source and an alkali agent are added to the precipitate slurry in the conditioning tank, and then the slurry is returned to the reaction tank to adjust pH. Desirably, the pH of the reaction tank is adjusted to 6.5-7.5. Circulation of the precipitate slurry is repeated to reduce fluorine concentration in the wastewater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a treatment method and a treatment apparatus for efficiently removing fluorine contained in waste water, and more particularly, to a treatment method and a treatment apparatus excellent in the effect of removing fluorine and heavy metals for waste water containing heavy metal together with fluorine. The wastewater treatment system of the present invention is particularly useful for a plurality of drainage systems having different fluorine concentrations.

  Conventionally, as a method of removing heavy metals contained in wastewater, by adding slaked lime to the wastewater and adjusting the pH of the wastewater to around 9.5, the heavy metals in the wastewater are insolubilized as hydroxide precipitates, and this is solid-liquid. A slaked lime neutralization method that separates and removes from waste water is known. Also, as a method of removing fluorine in the wastewater, aluminum sulfate is added to the wastewater, the pH of the wastewater is adjusted to around 6.5 to precipitate aluminum hydroxide, and fluorine in the wastewater is adsorbed to this precipitate. The coprecipitation aluminum hydroxide method is known.

For the aluminum hydroxide method, in order to reduce the amount of sludge generated and the amount of chemical used, the pH is adjusted to weak acidity by adding water and sulfuric acid to the solid-liquid separated starch, and fluorine is eluted to separate the liquid. There is known a processing method in which a residue precipitate is reused as a flocculant after separation (Patent Document 1).
JP 09-276875 A

  For wastewater containing heavy metals together with fluorine, the conventional treatment method has a problem that the optimum pH range for precipitation differs, so that the effect of removing them is low. For example, in order to precipitate heavy metals in wastewater as hydroxides, it is necessary to add slaked lime to the wastewater to make the pH alkaline around 9.5. On the other hand, since aluminum is an amphoteric element, aluminum hydroxide dissolves both acidic and alkaline. When the pH of the wastewater is out of the neutral range, the precipitate dissolves, and the fluorine adsorbed or taken into the precipitate is removed. Since it elutes in the wastewater, the fluorine concentration in the wastewater cannot be reduced sufficiently.

  The processing method of Patent Document 1 in which the separated precipitated sludge is reused also has the same problem as described above. Also, in the method of returning the precipitated sludge and the like separated to the neutralization reaction tank for treating the wastewater, if the precipitated sludge etc. is returned as it is and mixed in the same tank as the wastewater, the concentration and settling properties of the starch There is a problem that the remarkably decreases.

  This invention solves the said problem in the conventional processing method, and provides the processing system excellent in these removal effects also with respect to the waste_water | drain containing a heavy metal with a fluorine.

According to the present invention, the following wastewater treatment method and treatment apparatus are provided.
(1) In a fluorine removing method in which an aluminum source is added to wastewater containing fluorine to coprecipitate fluorine together with aluminum hydroxide precipitation, the precipitate is produced by introducing fluorine-containing wastewater into a reaction vessel, and the precipitate slurry Is separated from the waste water, and a part or all thereof is introduced into a conditioned tank, and after adding an aluminum source and an alkaline agent to the precipitation slurry, the pH is adjusted by returning to the reaction tank. A wastewater treatment method characterized by repeating circulation to reduce the fluorine concentration in the wastewater.
(2) The waste water treatment method according to (1), wherein the pH of the waste water in the reaction tank is adjusted to 6.5 to 7.5.
(3) In the treatment method described in (1) or (2) above, fluorine-containing wastewater is introduced into the first reaction tank, the aluminum source and fluorine are reacted under stirring, and this wastewater is further fed into the second reaction tank. And the reaction is carried out, the waste water is extracted from the second reaction tank and introduced into the sedimentation tank, and the sedimentation slurry is separated from the wastewater in the sedimentation tank, and a part or all of this precipitation slurry is introduced into the condition tank. In this condition tank, after adding an aluminum source and an alkaline agent to the precipitation slurry, the pH is adjusted by returning to the first reaction tank, and the waste slurry is treated by repeating circulation of the precipitation slurry to reduce the fluorine concentration in the waste water. .
(4) For wastewater containing heavy metal together with fluorine, after removing fluorine by the treatment step described in any of (1) to (3) above, an alkaline agent is added to the wastewater to adjust the pH to 9-10. Wastewater treatment method that adjusts to precipitate heavy metals in wastewater and removes it from the wastewater.
(5) In the treatment method described in any one of (1) to (3) above, the wastewater treatment method in which wastewater extracted from the reaction tank is introduced into a coagulation tank and a coagulant is added to promote precipitation. .
(6) A reaction tank for reacting fluorine in the waste water with the aluminum source, draining water extracted from the reaction tank, adding a flocculant and extracting from the agglomeration tank for promoting precipitation. A settling tank for separating the precipitate slurry from the waste water containing the precipitate, a condition tank for introducing a part or all of the separated precipitate slurry and adding the aluminum source and the alkaline agent, and a circulation for returning the set slurry to the reaction tank. A wastewater treatment apparatus characterized by having a path.
(7) In the processing apparatus of (6), the first reaction tank, the second reaction tank, the pH meter provided in the second reaction tank, the coagulation tank for introducing the waste water extracted from the second reaction tank, and the coagulation tank A settling tank for separating the precipitate slurry from the waste water containing the precipitate, a condition tank for introducing a part or all of the separated precipitate slurry and adding the aluminum source and the alkali agent, and the settling slurry in the condition tank for the first reaction tank A wastewater treatment apparatus having a circulation path for returning to the waste water.
(8) Precipitation tank for adding heavy metal in waste water in the pH range of 9 to 10 by adding an alkaline agent to the waste water after the fluorine removing step described in (6) or (7), waste water containing starch Wastewater treatment apparatus including a heavy metal removal step having a tank for solid-liquid separation.

  In the treatment method of the present invention, the precipitate slurry (returned sludge) is first conditioned so as not to be mixed in the same tank as the processing raw waste water when circulating the precipitate slurry incorporating fluorine in the waste water into the reaction tank. Since it is introduced into the tank, the alkali agent and aluminum source are added, and the sludge properties are adjusted and then introduced into the reaction tank, the concentration and sedimentation of the starch that is finally extracted is extremely good, greatly increasing the processing time. The amount of sludge can be significantly reduced, and the processing equipment can be downsized.

  Specifically, for example, the sedimentation rate of sludge is about 9 to 10 times faster than the conventional treatment method, the treatment time is greatly shortened, and the capacity of the thickener used for solid-liquid separation of sludge is about 1/9. The size can be reduced to 1/10. Incidentally, when a thickener having a diameter of about 21 m is conventionally required, a thickener having a diameter of about 6.6 to 7.0 m is sufficient according to the processing method of the present invention.

  The treatment method of the present invention has a first-stage fluorine removal process and a second-stage heavy metal removal process for wastewater containing heavy metals together with fluorine, and in the first stage, precipitates are generated in the neutral region. Incorporating fluorine and precipitating heavy metals in the alkaline region in the second stage, so fluorine and heavy metals are insolubilized in the optimum pH range, and are excellent in removing fluorine and heavy metals. Fluorine concentration in waste water and heavy metals Any of the concentrations can be greatly reduced.

The present invention will be specifically described below.
The treatment method of the present invention is a fluorine removal method in which fluorine is co-precipitated with aluminum hydroxide by adding an aluminum source to fluorine-containing wastewater. The slurry of the precipitate is separated from the waste water, a part or all of the slurry is introduced into a conditioned tank, and after adding an aluminum source and an alkaline agent to the precipitated slurry in the conditioned tank, the pH is adjusted by returning to the reaction tank. The wastewater treatment method is characterized in that the starch slurry is repeatedly circulated to reduce the fluorine concentration in the wastewater.

  In the present invention, the drainage refers to water that is subject to removal treatment of fluorine or heavy metals contained in the wastewater, and is not limited to general domestic wastewater, factory wastewater, drainage water, and industrial water and agricultural water. , Including groundwater, river and lake water, seawater, mine water, and water in dams such as rivers. The heavy metal contained in the waste water refers to a metal element containing heavy metals such as selenium, cadmium, hexavalent chromium, lead, zinc, copper, nickel, arsenic, and antimony. The treatment system of the present invention has an excellent removal effect with respect to any one or more of the heavy metals that are the sources of contamination contained in the waste water and the like.

  An example of an apparatus configuration based on the processing method of the present invention is shown in FIG. The processing system of the present invention shown in the figure has a first stage fluorine removal step and a second stage heavy metal removal step. For wastewater with a low concentration of heavy metals, the first fluorine removal step is sufficient.

  The first stage fluorine removal step has a reaction tank for reacting fluorine in the waste water with the aluminum source. In the example shown in the figure, the reaction tank into which the treatment raw waste water is introduced is preferably provided in two stages of the first reaction tank 10 and the second reaction tank 11 so as to prevent the short pass of the waste water and advance the reaction reliably. ing. The second reaction tank 11 is provided with a pH meter (not shown). Moreover, it is preferable to provide a stirring means in these reaction tanks 10 and 11.

  Further, the treatment system of the present invention introduces waste water extracted from the second reaction tank 11 and adds a flocculant to promote precipitation, and precipitates from the waste water containing precipitate extracted from the aggregation tank 12. A settling tank 13 for separating the slurry, a condition tank 14 for introducing a part or all of the separated precipitate slurry and adding an aluminum source and an alkaline agent, and circulation for returning the set slurry in the condition tank 14 to the first reaction tank 10 It has a path 15.

  In the treatment system, fluorine-containing wastewater or wastewater containing heavy metal together with fluorine is introduced into the first reaction tank 10 to react the aluminum source and fluorine, and this wastewater is further introduced into the second reaction tank 11 to react the reaction. To proceed. The aluminum source is added in the condition tank 14 together with the alkaline agent. The precipitation slurry containing the aluminum source and the alkali agent is introduced into the first reaction vessel 10. Although aluminum sulfate is generally used as the aluminum source, it is not limited to this. Moreover, although slaked lime is generally used as an alkaline agent, it is not restricted to this.

  The treated raw waste water is stirred and mixed with the precipitation slurry sent from the condition tank 15 in the first reaction tank 10 and reacts with the aluminum source contained in the precipitation slurry to produce aluminum hydroxide precipitate. It introduce | transduces into the 2nd reaction tank 11, a reaction is advanced, a fluorine is taken in into aluminum hydroxide precipitation, and is coprecipitated.

  A pH meter is provided in the reaction tank, and the pH in the reaction tank is controlled to 6.5 to 7.5, preferably 6.8 to 7.2. In the illustrated example, a pH meter is provided in the second reaction tank 11 (not shown). For example, this pH adjustment is performed by adjusting the amount of slaked lime or aluminum sulfate added in the condition tank 15 according to the properties and the amount of the treated raw wastewater introduced into the first reaction tank 10. good. If the pH in the reaction tank is out of the above range, the aluminum hydroxide precipitate starts to dissolve, so the fluorine in the precipitate elutes and the effect of removing the fluorine decreases, which is not preferable.

  The waste water containing the precipitate is extracted from the reaction tank (second reaction tank 11 in the illustrated example) and introduced into the aggregation tank 12. In addition, the aspect which extracts drainage from a reaction tank, a coagulation tank, and a sedimentation tank is not restrict | limited. An overflow may be sufficient, and the aspect discharged | emitted from the tank bottom may be sufficient. A polymer flocculant is added to the agglomeration tank 12 to agglomerate the precipitate in the waste water. Common flocculants can be used. The waste water to which the flocculant is added is introduced into the settling tank 13, and the slurry containing the precipitate is separated from the waste water. A thickener or the like is used as the settling tank 13. The precipitation slurry may be a solid content concentration that can be pumped.

  All or a part of the precipitated slurry separated from the waste water is introduced into the condition tank 14 through the circulation path 15, where an aluminum source such as aluminum sulfate and an alkaline agent such as slaked lime are added. As described above, these addition amounts are adjusted so that the pH in the reaction tank is 6.5 to 7.5, preferably 6.8 to 7.2. The precipitation slurry to which the aluminum source and the alkali agent are added is sent from the condition tank 14 to the reaction tank (first reaction tank 10 in the illustrated example) through the circulation path 15 and mixed with the raw material wastewater. The circulation process of returning to the reaction tank again through the tank and the condition tank is repeated. Depending on the nature of the precipitate, a part of the precipitate is extracted out of the system.

  In the treatment method of the present invention, the slurries with sludge added to the reaction tank are circulated in the reaction tank as described above, so that the precipitate (sludge) is concentrated, and therefore the settling and separation properties are good, and the sludge with a small amount of sludge is obtained. Can be obtained. On the other hand, if the sludge separated without using the condition tank is returned to the reaction tank as it is and mixed with the treated raw wastewater, the reaction with the aluminum source occurs before the pH adjustment by slaked lime etc., so the sludge is not concentrated and the sludge The amount cannot be reduced.

  According to the above-described fluorine removal step of the present invention, for example, with regard to the treated raw wastewater containing several tens mg / l of fluorine, the fluorine concentration of the treated wastewater can be reduced to 5 mg / l or less, preferably 4 mg / l or less. it can. For example, to reduce the fluorine concentration in the treated wastewater to 4 mg / l or less compared to the treated wastewater having a fluorine concentration of 20 mg / l, the pH in the reaction tank is adjusted to about 6.8 to 7.0. The added amount of aluminum sulfate may be 3 to 4 mg / L waste water.

  For wastewater containing heavy metal together with fluorine, the treated wastewater that has undergone the fluorine removal step is subsequently introduced into the second-stage heavy metal removal step to remove heavy metals. In addition, this heavy metal removal process may process the waste water which performed the said fluorine removal process together with the heavy metal containing waste water of another system | strain with low fluorine concentration.

  As shown in the figure, the heavy metal removal step includes a water collection tank 16 for introducing the waste water subjected to the defluorination treatment, reaction tanks 17 and 18 for precipitating heavy metals in the waste water, a coagulation tank 19 for aggregating the generated precipitate, waste water It has a sedimentation tank 20 for separating the sediment in it. You may introduce | transduce the drainage containing heavy metal of another system | strain with a low fluorine concentration into the water collection tank 16. FIG.

  The drainage of the water collection tank 16 is introduced into the third reaction tank 17, and an alkaline agent such as slaked lime is added to adjust the pH in the tank to 9-10, preferably around pH 9.5, and hydroxylate heavy metals in the drainage. And precipitate. This reaction tank is preferably provided in two stages as shown in order to prevent a short path of drainage (a phenomenon in which the drainage flows without sufficiently reacting with the drug). The waste water from the third reaction tank 17 is introduced into the fourth reaction tank 18 to advance the precipitation reaction. Drainage containing a heavy metal hydroxide precipitate is introduced into the coagulation tank 19 and a polymer flocculant is added to coagulate the precipitate to enhance the sedimentation. This waste water is introduced into a settling tank 20 such as a thickener and solid-liquid separation is performed, and sludge is separated from the waste water.

  According to the above treatment step of the present invention, in the first stage fluorine removal step, a precipitate is generated in the neutral region to coprecipitate fluorine, and in the second step heavy metal removal step, the heavy metal is precipitated in the alkali region, Since fluorine and heavy metal are insolubilized in the optimum pH range, the fluorine and heavy metal removal effect is excellent, and both the fluorine concentration and heavy metal concentration in the waste water can be greatly reduced.

Examples of the present invention are shown below together with comparative examples. All of these examples were conducted by batch tests.
[Example 1]
The fluorine-containing wastewater was treated according to the fluorine removal step of the present invention shown in FIG. On the other hand, as a comparative example, the defluorination treatment was advanced based on the conventional starch repetition method in which the precipitated slurry was returned to the first reaction tank as it was without using the condition tank of FIG. In any case, wastewater having a fluorine concentration of 15 to 20 mg / l was used as the raw wastewater for treatment, and the pH of the reaction tank was adjusted to 7.0 to 7.5. The results are shown in FIG.
As shown in FIG. 2, in the sample of the present invention, since the precipitate is concentrated, the sedimentation rate of the precipitate is high, from about 0.5 m / h to about 0.65 m / h. There was a tendency for the sedimentation rate to increase. On the other hand, in the comparative sample, the sedimentation rate of the sludge immediately after the start of the test is high, but the sedimentation rate rapidly decreases due to the repeated sludge, and the sludge sedimentation rate after 3 repetitions is about 0.05 m / h or less. The sludge settling speed in the treatment method of the invention is about 9 to 10 times that of the comparative example.

[Example 2]
In the fluorine removal step of the present invention shown in FIG. 1, the relationship between the added amount of aluminum sulfate, the pH of the reaction tank, and the fluorine concentration of the treated waste water was examined. In addition, the waste water with a fluorine concentration of 15 to 20 mg / l was used as the treatment raw waste water. The results are shown in FIG.
As shown in the figure, in order to reduce the fluorine concentration in the treated wastewater to 4 mg / l or less, the pH in the reaction vessel is adjusted to about 6.8 to 7.0, and the amount of aluminum sulfate added is 3 to 4 mg / L. It should be drained.

Example 3
The wastewater fluorine was removed according to the fluorine removal step of the present invention shown in FIG. The test conditions are shown in Table 1, and the test results are shown in Table 1 and FIG. As shown in the results of Table 1, by performing the fluorine removal treatment of the present invention, it was possible to remove about 79% to about 92% of fluorine from the raw waste water. Further, as shown in the results of FIG. 4, the starch concentration could be increased to about 550 g / l in the sample A and 250 g / l in the sample B, and a well concentrated starch could be obtained.

Process drawing which shows an example of the processing method of this invention The graph which shows the result of Example 1 The graph which shows the result of Example 2 The graph which shows the result of Example 3

Explanation of symbols

10-first reaction tank, 11-second reaction tank, 12-flocculation tank, 13-sedimentation tank, 14-condition tank, 15-circulation path, 16-water collecting tank, 17-third reaction tank, 18-fourth Reaction tank, 19-flocculation tank, 20-sedimentation tank.

Claims (8)

In a fluorine removal method in which an aluminum source is added to wastewater containing fluorine to coprecipitate fluorine together with aluminum hydroxide precipitation, the fluorine-containing wastewater is introduced into a reaction vessel to form the precipitate, and the slurry of the precipitate is removed from the wastewater. Separately, introduce a part or all of it into a conditioned tank, add an aluminum source and an alkaline agent to the precipitated slurry in the conditioned tank, return to the reaction tank to adjust the pH, and repeat the circulation of the precipitated slurry. A method for treating wastewater, characterized in that the fluorine concentration in the wastewater is reduced.
The method for treating waste water according to claim 1, wherein the pH of the waste water in the reaction tank is adjusted to 6.5 to 7.5.
The treatment method according to claim 1 or 2, wherein the fluorine-containing wastewater is introduced into the first reaction tank, the aluminum source and fluorine are reacted under stirring, and the wastewater is further introduced into the second reaction tank to perform the above reaction. The waste water is extracted from the second reaction tank and introduced into the settling tank. The settling tank separates the precipitated slurry from the wastewater, and a part or all of the precipitated slurry is introduced into the condition tank. A wastewater treatment method in which an aluminum source and an alkali agent are added to the slurry, and then returned to the first reaction tank to adjust the pH, and the circulation of the precipitated slurry is repeated to reduce the fluorine concentration in the wastewater.
For wastewater containing heavy metal together with fluorine, after removing fluorine by the treatment step according to any one of claims 1 to 3, an alkaline agent is added to the wastewater to adjust pH to 9 to 10 in the wastewater. Wastewater treatment method that precipitates heavy metals and removes them from the wastewater.
The treatment method according to any one of claims 1 to 3, wherein the waste water extracted from the reaction tank is introduced into a coagulation tank, and a coagulant is added to promote precipitation.
Includes a reaction tank for reacting fluorine in the waste water with an aluminum source, a waste water extracted from the reaction tank, adding a flocculant to promote precipitation, and a precipitate extracted from the aggregation tank A settling tank for separating the precipitated slurry from the waste water, a condition tank for introducing a part or all of the separated precipitate slurry and adding an aluminum source and an alkaline agent, and a circulation path for returning the set slurry to the reaction tank. Wastewater treatment equipment characterized by that.
In the processing apparatus of Claim 6, the pH meter provided in the 1st reaction tank and the 2nd reaction tank, the 2nd reaction tank, the coagulation tank which introduces the waste_water | drain extracted from the 2nd reaction tank, The precipitation extracted from the coagulation tank is included. A settling tank for separating the precipitate slurry from the waste water, a condition tank for introducing a part or all of the separated precipitate slurry and adding an aluminum source and an alkaline agent, and a circulation path for returning the set slurry to the first reaction tank A wastewater treatment apparatus characterized by comprising:
A precipitation tank for precipitating heavy metals in the wastewater by adding an alkaline agent to the wastewater after the fluorine removing step according to claim 6 or 7, and a tank for solid-liquid separation of the wastewater containing starch. A wastewater treatment apparatus including a heavy metal removing step.

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