JP2004074039A - Water treatment equipment and method for fluoride-containing waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment equipment for fluoride-containing waste water which can be stably operated over a long period of time. <P>SOLUTION: The water treatment equipment for fluoride-containing waste water is provided with a first reaction tank 11 (a first reactor) where acid or alkali and a flocculant are added to the fluoride-containing waste water, a membrane separation apparatus 14 (a membrane separation means) which is installed downstream of the first reaction tank 11 and separates deposited aggregate formed by the reaction of fluorides and the flocculant from the waste water, and a circulation tank 13 installed between the first reaction tank 11 and the membrane separation apparatus 14. The waste water to which the acid or the alkali and the flocculant have been added is supplied and the separated deposited aggregate is returned to the tank 14. The water treatment equipment also has a second reaction tank (a second reactor) to which the waste water flowing out from the first reaction tank 11 is supplied, between the first reaction tank 11 and the circulation tank 13. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a fluoride-containing wastewater treatment apparatus and a fluoride-containing wastewater treatment method for removing fluoride from fluoride-containing wastewater.
[0002]
[Prior art]
Wastewater from thermal power generation using coal as fuel may contain coal-derived fluoride. Therefore, in wastewater treatment in a thermal power plant, water treatment for removing fluoride is performed.
As a water treatment for removing fluoride, a flocculant such as slaked lime, a sulfuric acid band, or polyaluminum chloride (PAC) is added to pH-adjusted wastewater to precipitate and aggregate fluoride, followed by filtration. The method is general. In such a fluoride removing method, for example, a wastewater containing fluoride is reacted with a flocculant to precipitate a fluoride, a reaction tank for flocculating, and a fluoride is precipitated, and a flocculated precipitate and water are aggregated. Coagulation sedimentation and membrane separation are used.
[0003]
[Problems to be solved by the invention]
When membrane separation is used to separate precipitated aggregates and water, unreacted fluoride and coagulant are separated by membrane when the reaction between fluoride and coagulant in the reaction tank becomes insufficient. In some cases, the solution reached the means and reacted and precipitated and aggregated on the film surface. As a result, the precipitated aggregates adhere to the membrane surface and block the pores of the membrane, so that the membrane separation performance is greatly reduced and the operation is destabilized.
[0004]
Therefore, Japanese Patent Publication No. 7-53276 proposes a method for treating wastewater that promotes the reaction between a fluoride and a flocculant. FIG. 5 shows a water treatment apparatus used in this treatment method. The water treatment apparatus 50 includes a reaction tank 52 in which a calcium compound or an aluminum compound is added to wastewater containing fluoride via a supply pipe 51, and wastewater flowing out of the reaction tank 52 and returned from a membrane separation unit 54 described later. And a membrane separation means 54 for separating wastewater flowing out of the circulation tank 53 into concentrated water containing fluoride precipitated and coagulated by the coagulant and permeated water. ing. In the water treatment device 50, not only the concentrated water is returned to the circulation tank 53, but also a part of the concentrated water is returned to the reaction tank 52, and the precipitates and aggregates contained in the concentrated water are used as seed crystals. Thus, the precipitation reaction in the reaction tank 52 is promoted. As a result, the calcium compound or the aluminum compound as the coagulant sufficiently reacts with the fluoride, so that the reaction on the membrane surface of the membrane separation device 54 is suppressed, and a decrease in filtration performance is prevented. .
[0005]
However, in such a treatment method, it is necessary to control the amount of the coagulant added and the amount of the concentrated liquid circulated, and it has been difficult to perform an efficient operation when the fluorine concentration in the raw water changes. For example, when the concentration of fluorine in the raw water is reduced, if the amount of the coagulant added is reduced in proportion thereto, the fluorine removal performance and the operation performance of the membrane treatment apparatus may be reduced.
[0006]
In addition to the above-mentioned treatment method, it is also conceivable to lengthen the residence time of the reaction tank or the circulation tank, lengthen the reaction time between the fluoride and the flocculant, and increase the degree of progress of the precipitation reaction. However, in this case, in order to allow the precipitation reaction to proceed to a sufficiently satisfactory level, it was necessary to greatly increase the residence time and increase the reaction tank volume. Therefore, there has been a problem that the installation area increases and the equipment cost also increases.
The present invention has been made in view of the above-described circumstances, and allows a fluoride and a coagulant to sufficiently react with each other before reaching the membrane surface of the membrane separation means, and can operate stably for a long period of time. It is another object of the present invention to provide a fluoride-containing wastewater treatment apparatus and a fluoride-containing wastewater treatment method that do not require expensive equipment costs.
[0007]
[Means for Solving the Problems]
The water treatment apparatus for wastewater containing fluoride of the present invention is a first reactor in which an acid or alkali and a coagulant are added to wastewater containing fluoride,
Membrane separation means provided downstream of the first reactor to separate precipitated aggregates formed by the reaction between the fluoride and the flocculant from wastewater;
Circulation provided between the first reactor and the membrane separation means, to which waste water to which an acid or alkali and a coagulant are added is supplied, and the precipitated aggregate separated by the membrane separation means is returned. A water treatment device comprising a tank and a fluoride-containing wastewater,
A second reactor is provided between the first reactor and the circulation tank, to which the wastewater flowing out of the first reactor is supplied.
As described above, since the second reactor is provided between the first reactor and the circulation tank, the fluoride in the wastewater and the flocculant can be sufficiently reacted with each other. It is possible to prevent the compound and the flocculant from reaching the membrane separation device and reacting and precipitating and flocculating on the membrane surface.
[0008]
In the water treatment apparatus for wastewater containing fluoride of the present invention, it is preferable that an acid or an alkali can be added in the second reactor. If the acid or alkali can be added in the second reactor, if the pH adjustment in the first reactor is not sufficiently performed, the acid or alkali is also added to the second reactor to obtain a pH suitable for the reaction. And the reaction between the fluoride and the aggregate can be further promoted. In addition, even if aggregates adhere to the surface of the pH meter installed in the first reactor and the sensitivity is lowered to cause an indication error, the pH suitable for the reaction in the second reactor may be maintained. it can.
[0009]
Further, the water treatment method of the fluoride-containing wastewater of the present invention, a reaction step of reacting the fluoride contained in the wastewater and the coagulant to form a precipitate aggregate,
An aging step for continuing the reaction after the first reaction step;
A circulation step of returning the precipitated aggregate separated in the subsequent membrane separation step to the wastewater after the aging step,
And a membrane separation step of separating precipitated aggregates formed in the reaction step and the aging step from wastewater.
As described above, by continuing the reaction between the fluoride and the flocculant after the first reaction step, the fluoride and the flocculant can be sufficiently reacted, so that the precipitation and aggregation of the fluoride and the flocculant in the membrane separation step can be prevented. .
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a water treatment apparatus and a water treatment method for a fluoride-containing wastewater of the present invention will be described with reference to the drawings.
FIG. 1 shows a water treatment device (hereinafter abbreviated as a water treatment device) of a fluoride-containing wastewater of the present embodiment. The water treatment apparatus 10 includes, from an upstream side, a first reaction tank 11 as a first reactor, a second reaction tank 12 as a second reactor, a circulation tank 13, and a membrane separation unit. And a membrane separation device 14. Hereinafter, each of these components will be described.
In addition, in this specification, "wastewater" is wastewater containing fluoride.
[0011]
In the first reaction tank 11, wastewater is supplied from a wastewater storage tank 15 in which wastewater before treatment is stored via a pipe 16 and a pump 17, and an acid is added to the wastewater via an acid supply pipe 18, and alkali is added to the wastewater. This is a tank to which an alkali is added via a supply pipe 19 and a coagulant is added via a coagulant supply pipe 20. As described above, the flocculant is added to the wastewater, and at least a part of the fluoride is precipitated and aggregated to form a precipitated aggregate. Further, the pH of the wastewater is adjusted to 6 to 8 by adding an acid or an alkali.
[0012]
Here, the flocculant is a chemical agent for precipitating and coagulating fluoride in wastewater, for example, calcium compounds such as calcium hydroxide and calcium oxide, aluminum sulfate (sulfate band), and aluminum such as polyaluminum chloride. And the like. These may be used alone or in combination of two or more. When the flocculant is a calcium compound, a precipitated flocculant mainly composed of calcium fluoride is formed. When the aggregating agent is an aluminum compound, a precipitated aggregate in which fluoride is mainly adsorbed to the aluminum compound is formed. Further, the coagulant that has not reacted with the fluoride may precipitate and agglomerate to form a precipitate agglomerate.
The amount of such a coagulant added is usually determined according to the amount of fluoride in the wastewater.
Examples of the acid include hydrochloric acid, and examples of the alkali include sodium hydroxide. When an aluminum compound is used as a coagulant, precipitation and coagulation of fluoride are promoted if the pH of the wastewater is adjusted to 6 to 8 by such an acid or alkali.
[0013]
The wastewater flowing out of the first reaction tank 11 is supplied to the second reaction tank 12 via a pipe 21. Then, in the second reaction tank 12, the fluoride in the wastewater is brought into sufficient contact with the flocculant added in the first reaction tank 11. As described above, by providing the second reaction tank 12 between the first reaction tank 11 and the circulation tank 13, the reaction between the fluoride and the flocculant can be continued to increase the reaction time. As a result, it is possible to increase the yield of precipitated aggregates before reaching the membrane separation device 14.
The residence time in the second reaction tank 12 is desirably 5 minutes to 2 hours, preferably 15 minutes to 1 hour. If the residence time is 5 minutes or more, the fluoride and the flocculant can be reliably reacted. Further, even if the residence time is increased to 2 hours or more, the reaction does not proceed as compared with the residence time.
[0014]
Also in the second reaction tank 12, an acid can be added through an acid supply pipe 22, and an alkali can be added through an alkali supply pipe 23. If an acid or alkali is added to the second reaction tank 12, even if the pH of the wastewater is out of the range of 6 to 8 in the second reaction tank 12, the pH can be adjusted to 6 to 8; Precipitation and aggregation can be further promoted.
[0015]
The circulation tank 13 is a tank in which the wastewater flowing out of the second reaction tank 12 is supplied through a pipe 24, and the precipitated aggregate separated in the membrane separation device 14 is returned through a return pipe 25. . Here, the purpose of returning the deposited aggregates to the circulation tank 13 is to increase the solid content concentration and reduce the liquid amount when supplying the sludge separation device.
[0016]
The membrane separation device 14 is a device having a membrane, in which wastewater is supplied from the circulation tank 13 through a pipe 26 and a pump 27, and separates precipitated aggregates from the wastewater. The water permeated through the membrane separator 14 (hereinafter referred to as permeated water) is subjected to another water treatment in the next step 28.
As the membrane separation device 14, for example, a hollow fiber membrane module or the like is used. When a hollow fiber membrane module is used, wastewater containing precipitated aggregates is in contact with the outside of the hollow fiber membrane. The pores formed in the hollow fiber membrane prevent the precipitated aggregates from entering the inside of the hollow fiber membrane and allow water to permeate into the hollow fiber membrane. As a result, the separated aggregates are separated from the wastewater, and the permeated water is obtained.
[0017]
As described above, the precipitated aggregate separated by the membrane separation device 14 is returned to the circulation tank 13. At that time, the water is returned to the circulation tank 13 as concentrated water together with the water that has not passed through the hollow fiber membrane. In other words, concentrated water containing a high concentration of precipitated aggregates is returned from the membrane separation device 14 to the circulation tank 13. A part of the concentrated water is discharged out of the water treatment device via the drain pipe 29, and the fluoride contained in the concentrated water is treated as sludge in a separate step by the sludge separation device.
The membrane separation device 14 may be provided with a sludge extracting means (not shown) so that unnecessary sludge can be extracted. The sludge extracted by the sludge extraction means is transferred to a sludge separation device via a pipe 29.
Further, the first reaction tank 11, the second reaction tank 12, and the circulation tank 13 described above are provided with a stirring blade 32 driven by a motor 31, and the wastewater is stirred in each tank.
[0018]
In the water treatment method of the fluoride-containing wastewater, first, in the reaction step, the fluoride contained in the wastewater and the coagulant are reacted in the first reaction tank 11 to form a precipitate and an aggregate, and then the aging step In, the reaction is further continued in the second reaction tank 12. Next, in the circulation step, the separated aggregates separated in the subsequent membrane separation step are returned to the wastewater after the aging step in the circulation tank 13. Then, in the membrane separation step, the precipitated aggregate formed in the reaction step and the aging step is separated from the wastewater by the membrane separation device 14.
[0019]
In the water treatment apparatus 10 according to the embodiment described above, the second reaction tank 12 is provided between the first reaction tank 11 and the circulation tank 13, and the wastewater is discharged from the second reaction tank 12. And the coagulant added in the first reaction tank 11 sufficiently react and precipitate and coagulate before reaching the membrane separator 14, so that the fluoride coagulates with the fluoride on the membrane surface of the membrane separator 14. It is prevented that the agent reacts and precipitates and aggregates. Therefore, clogging of the membrane surface is prevented, and a decrease in membrane separation performance is suppressed, so that the water treatment apparatus 10 can be stably operated for a long time.
Moreover, providing the second reaction tank 12 between the first reaction tank 11 and the circulation tank 13 is a simple configuration. Therefore, the operation of the water treatment apparatus 10 does not require any special control, and thus is excellent in operability.
Further, even if the residence time in the first reaction tank 11 and the second reaction tank 12 is not significantly increased, the fluoride and the coagulant sufficiently react with each other, so that it is not necessary to provide a large-volume reaction tank. .
[0020]
Note that the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the second reactor is provided as the second reactor, but the second reactor is not provided, and as shown in FIG. Can be divided into an upstream portion 42 and a downstream portion 43 by a partition plate, the upstream portion 42 can be used as a first reactor, and the downstream portion 43 can be used as a second reactor. Further, the inside of the first reaction vessel can be divided into three parts: an upstream part as a first reactor, a downstream part as a second reactor, and an intermediate part therebetween. In this case, the upstream portion becomes the first reactor, and the intermediate portion and the downstream portion become the second reactor.
[0021]
In the above-described embodiment, both the first reactor and the second reactor are tank reactors, but the present invention is not limited to this. For example, the first reactor or the second reactor may be a tubular reactor such as a static mixer. However, in order to secure the reaction time, the length of the tube required for the reaction becomes long. Therefore, the first reactor or the second reactor is preferably a tank reactor.
[0022]
The water treatment apparatus according to the present invention can be used for the treatment of wastewater containing fluoride without any particular limitation. In particular, the wastewater is discharged from a flue gas desulfurization facility or a ash treatment facility of a coal-fired thermal power plant. It can be suitably used for wastewater, wastewater discharged from semiconductor manufacturing equipment, and the like.
[0023]
【Example】
(Example)
From the upstream side, a 10 m ³ first reaction tank (first reactor), a 30 m ³ second reaction tank (second reactor), a 60 m ³ circulation tank, and a hollow fiber membrane module Water treatment of wastewater containing fluoride was performed using a water treatment device for wastewater containing fluoride, which was equipped with a membrane separation device (membrane separation means) equipped with the same. The wastewater to be water-treated had a fluorine content of 20 to 40 mg / l, a pH of 5 to 6, and a suspended solids (SS) amount of 600 to 1200 mg / l. Further, the flow rate of the wastewater was set to 40 m ³ / hour. Therefore, the residence time of the first reaction tank was 0.25 hours, the residence time of the second reaction tank was 0.75 hours, and the residence time of the circulation tank was 1.5 hours. The first reaction tank, the second reaction tank, and the circulation tank are provided with a stirrer.
Then, 1600 mg / l of polyaluminum chloride (PAC) was added to the first reaction tank as a coagulant. Further, sodium hydroxide was added to the first reaction tank to adjust the pH of the wastewater to 6 to 6.5. Further, the SS concentration in the concentrated water returned from the membrane separation device to the circulation tank was adjusted to be 6000 to 12000 mg / l.
[0024]
Under such conditions, water treatment was performed so that the fluorine content of the permeated water discharged from the membrane separation device was less than 7 mg / l and the SS concentration was less than 10 mg / l. FIG. 3 is a graph plotting the differential pressure between the outside and the inside of the hollow fiber membrane with respect to the operation time at that time.
In this water treatment apparatus, since the fluoride and the flocculant sufficiently reacted before reaching the membrane separation device by providing the second reaction tank, the blockage due to precipitation and aggregation on the membrane surface of the hollow fiber membrane was achieved. As shown in FIG. 3, the pressure difference between the outside and the inside of the hollow fiber membrane increased only slightly even when the operation time was 700 hours or more. That is, the water treatment device could be operated stably.
[0025]
(Comparative example)
Wastewater treatment was performed in the same manner as in Example except that the second reaction tank was not provided. FIG. 4 is a graph plotting the differential pressure between the outside and the inside of the hollow fiber membrane with respect to the operation time. In this example, as shown in FIG. 4, about 100 hours after the start of operation, the pressure difference between the outside and the inside of the hollow fiber membrane rapidly increased, and the operation became impossible. When the operation of the water treatment device was stopped and the membrane separation device was checked, the aggregates were deposited and clogged on the membrane surface of the hollow fiber membrane, and the reaction proceeded on the membrane surface of the hollow fiber membrane, It is considered that pores on the membrane surface were closed.
[0026]
【The invention's effect】
In the water treatment apparatus for wastewater containing fluoride of the present invention, the second reactor is provided between the first reactor and the circulation tank, and the fluoride and the flocculant are separated before reaching the membrane separation means. Aggregation prevents precipitation and aggregation on the membrane surface of the membrane separation means, so that the membrane separation performance does not decrease. In addition, since the second reactor is provided between the first reactor and the circulation tank, the operability is excellent because of a simple configuration. Also, since the residence time in the reactor does not need to be significantly increased, a large-volume reactor is not required.
[0027]
In the method for treating fluoride-containing wastewater of the present invention, a ripening step of further reacting the fluoride in the wastewater with the flocculant after the reaction step is provided. And agglomerates can be reacted to precipitate and agglomerate, so that precipitation and agglomeration of fluoride and a flocculant in the membrane separation step can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an embodiment of a water treatment apparatus for a fluoride-containing wastewater of the present invention.
FIG. 2 is a diagram schematically showing another embodiment of the water treatment apparatus for fluoride-containing wastewater of the present invention.
FIG. 3 is a graph plotting the differential pressure between the outside and the inside of the hollow fiber membrane with respect to the operation time in Examples.
FIG. 4 is a graph plotting the differential pressure between the outside and the inside of the hollow fiber membrane with respect to the operation time in a comparative example.
FIG. 5 is a view schematically showing a conventional water treatment apparatus for treating wastewater containing fluoride.
[Explanation of symbols]
10 Fluoride-containing wastewater treatment apparatus 11 First reaction tank (first reactor)
12 Second reactor (second reactor)
13 Circulation tank 14 Membrane separation device (membrane separation means)

Claims (3)

A first reactor in which an acid or alkali and a flocculant are added to wastewater containing fluoride;
Membrane separation means provided downstream of the first reactor to separate precipitated aggregates formed by the reaction between the fluoride and the aggregating agent from wastewater;
Circulation provided between the first reactor and the membrane separation means, wherein wastewater to which an acid or alkali and a coagulant are added is supplied, and precipitates separated by the membrane separation means are returned. A water treatment device comprising a tank and a fluoride-containing wastewater,
An apparatus for treating wastewater of fluoride-containing wastewater, comprising a second reactor between the first reactor and the circulation tank to which wastewater flowing out of the first reactor is supplied. The water treatment apparatus according to claim 1, wherein an acid or an alkali is added to the second reactor. A reaction step of reacting the fluoride and the flocculant contained in the wastewater to form a precipitated flocculent,
An aging step for continuing the reaction after the first reaction step;
A circulation step of returning the precipitated aggregate separated in the subsequent membrane separation step to the wastewater after the aging step,
A membrane separation step of separating precipitated aggregates formed in the reaction step and the aging step from the wastewater.

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