JP2003145170A - Method and apparatus for treating fluorine-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating fluorine-containing wastewater, capable of easily clearing a new water quality standard. SOLUTION: The method for treating fluorine-containing wastewater includes a reaction process allowing wastewater preliminarily reduced in the concentration of fluorine by primary treatment to flow in a reaction tank 12 and adding an aluminum compound and a polymeric flocculant to wastewater to form flocs, a process allowing wastewater to flow in a floating separation tank 20 and supplying pressurized water in which air is dissolved under pressure to the floating separation tank 20 from the bottom thereof to float flocs by generated fine air bubbles and a process for removing floated flocs.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating fluorine-containing wastewater and an apparatus therefor.

[0002] Factory wastewater, especially wastewater from a plating factory or a semiconductor factory, often contains fluorine-containing wastewater. Usually, for the wastewater treatment of wastewater containing a high concentration of fluorine, a method is adopted in which calcium fluoride is separated by neutralizing with slaked lime. In addition, a coagulation sedimentation method using an aluminum compound and a treatment method using an ion exchange resin in a special case are also adopted.

[0003]

The removal of fluorine by the method using slaked lime can be reduced to a concentration of about 8 to 15 mg / l (ppm). Since the conventional treatment standard was 15 mg / l or less, this method could be used. However, since the treatment standard was recently reviewed and the law was revised to reduce the fluorine concentration to 8 mg / l or less, the treatment using slaked lime is no longer applicable. At present, it is necessary to dilute and deal with it,
There is a problem that the cost will rise. It is not an essential solution.

Even in the coagulation-precipitation method using an aluminum compound, the limit is 8 to 15 mg / l. Depending on the raw water, it is possible to remove fluorine to a considerable extent by using an ion exchange resin. However, this method increases the running cost and is not suitable for treating industrial wastewater. Further, since various ionic species that inhibit ion exchange are mixed in the factory wastewater, it is practically impossible to treat the factory wastewater.

Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a method for treating fluorine-containing wastewater and a treatment apparatus for fluorine-containing wastewater which can easily meet new water quality standards. There is.

[0006]

According to the method for treating fluorine-containing wastewater according to the present invention, the wastewater, which has been subjected to a primary treatment and having a reduced fluorine concentration in advance, flows into a reaction tank, and the aluminum compound and polymer aggregates in the wastewater. A reaction step of adding an agent and forming flocs, and then flowing the waste water into the flotation separation tank, and from the bottom of the flotation separation tank into the flotation separation tank, supplying pressurized water in which air is dissolved to be dissolved, The method is characterized by including a step of levitating the flocs by the generated fine air particles and a step of removing the levitated flocs.

The fluorine concentration of the wastewater subjected to the primary treatment is set to 8
It has to be reduced to ~ 100 mg / l. This is because if the initial concentration is too high, it cannot be removed completely.
Further, it is necessary to adjust the pH in the reaction step to 6 to 7.5. The reaction step may be divided into a first step of adding an aluminum compound to the waste water and a second step of subsequently adding a polymer coagulant. It is preferable that the addition amount of the aluminum compound is 1.1 or more in terms of a molar ratio of aluminum to contained fluorine. A molar ratio of at least 1.1 is required and may be higher, but the removal efficiency is not so improved. The aluminum compound added may be one or more selected from polyaluminum chloride, aluminum hydroxide, aluminum sulfate and sodium aluminate.

Further, in the fluorine-containing wastewater treatment apparatus according to the present invention, the wastewater that has been subjected to the primary treatment and having the fluorine concentration reduced in advance is introduced, and the aluminum compound and the polymer flocculant are added to the wastewater to form flocs. A reaction tank, a flotation separation tank into which the waste water flows from the reaction tank, and a pressurized water supply device for supplying pressurized water obtained by pressurizing and dissolving air from the bottom of the flotation separation tank to the flotation separation tank. However, the flocs are floated and separated by fine air particles generated from the pressurized water. The reaction tank is
First, aluminum compound is added to the inflowing wastewater
And a second tank in which the polymer flocculant is added to the wastewater introduced from the first tank.

Further, in the method for treating fluorine-containing wastewater according to the present invention, wastewater having a reduced fluorine concentration is introduced into a reaction tank, and sodium aluminate and a polymer flocculant are added to the wastewater to form flocs. The method is characterized by including a reaction step, a step of causing the waste water to flow into a settling tank to precipitate flocs, and a step of removing the flocs.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present invention aims to treat raw water containing various heavy metals and fluorine, such as factory wastewater. This raw water is primarily treated. In the primary treatment, a sulfur compound such as sodium sulfide and a polymer flocculant are added to the raw water to precipitate and remove heavy metals as sulfides, and calcium hydroxide is added to precipitate fluorine as calcium fluoride, thereby removing fluorine. Remove.

By this primary treatment, fluorine of 8 to 15 m
It can be reduced to about g / l, and conventionally, the standard could be cleared by this primary treatment. Depending on the raw water, fluorine may not be reduced to 15 mg / l or less even if this primary treatment is performed, but in this case, it was usual to dilute it with water and release it below the standard. However, it has been impossible to stably treat fluorine to a new standard of 8 mg / l or less only by this primary treatment.

The present inventors have tried to further subject the above-mentioned primary treated wastewater to a secondary treatment by the coagulating sedimentation method which is the same means as the primary treatment. That is, the aluminum compound is added to the wastewater subjected to the primary treatment to form flocs, and the flocs are precipitated and removed. However, even if the secondary treatment was carried out by the coagulation-sedimentation method in which such an aluminum compound was added, fluorine could be slightly reduced, but it was not stably reduced to the new standard of 8 mg / l or less. .

The inventors of the present invention have tried to treat the above-mentioned primary wastewater by a pressure flotation treatment method which has been generally used conventionally for treating wastewater containing oil lighter than water. This pressurized flotation process is not normally performed for treating wastewater containing heavy metals. As a result, surprisingly, the new standard of fluorine was 8 mg / l.
It was found below that stable reduction can be achieved.

That is, in the present invention, first, the wastewater, which has been subjected to the primary treatment and whose fluorine concentration has been reduced in advance, flows into the reaction tank, and the aluminum compound and the polymer coagulant are added to the wastewater to form flocs (reaction Process). Next, the waste water is introduced into the flotation separation tank, pressurized water obtained by pressurizing and dissolving air is supplied into the flotation separation tank from the bottom of the flotation separation tank, and flocs are levitated by the generated fine air particles ( Pressure levitation treatment). By removing the floating flocs, the drainage of the middle layer of the flotation separation tank is 5
It was found that the fluorine concentration was around mg / l and the new standard could be cleared.

As described above, even if the same aluminum compound is added to form flocs containing fluorine, and the flocs are precipitated and removed, the fluorine cannot be sufficiently removed, but this flocculation-precipitation method is not used. , It is possible to stably remove fluorine below the new standard by levitating the flocs by the pressure levitation method and removing these flocs, which means that the flocs are generated due to the fine air particles generated by the pressure levitation method. It is further promoted, and it is considered that a large amount of fluorine is included in the flocs and the removal rate is improved.

Usually, the wastewater in the factory contains fluorine in the range of several thousand to tens of thousands ppm, and even if it is subjected to the pressure floating process as it is, the fluorine cannot be reduced. It is important to reduce the fluorine concentration to about 8 to 100 mg / l by the above-mentioned primary treatment and then perform the above-mentioned pressure-levitation treatment of the above-mentioned secondary treatment. That is, if the fluorine concentration of the starting waste water is too high, it cannot be removed even by the secondary treatment, so it is necessary to reduce it to the above concentration by the primary treatment in advance.

In the reaction step of adding the aluminum compound, for example, caustic soda or the like is added to the waste water to remove p from the waste water.
It is necessary to adjust H to 6-7.5. Further, in the reaction step, the aluminum compound and the polymer coagulant may be added at the same time, but the aluminum compound is added in the first tank and the polymer coagulant is slowly added in the second tank. It is preferable to form flock.

As the aluminum compound, one kind or two or more kinds of polyaluminum chloride, aluminum hydroxide, aluminum sulfate and sodium aluminate can be used. The addition amount of this aluminum compound is preferably 1.1 or more in terms of a molar ratio of aluminum to contained fluorine. The polymer coagulant may be a coagulant that is usually used and is not particularly limited.

FIG. 1 is an overall schematic view of the processing apparatus 10.
A reaction tank 12 is composed of a first tank 13 and a second tank (precipitation tank) 14. Factory wastewater containing heavy metals, fluorine, etc. is subjected to primary treatment into the first tank 13, and wastewater in which heavy metals and fluorine have been reduced in advance is introduced. An aluminum compound is added to the first tank 13. As a result, a floc containing fluorine is formed. In the first tank 13, caustic soda or the like is appropriately added to adjust the pH to 6 to 7.5. Reference numeral 15 is a stirrer.

The drainage is naturally flowed from the first tank 13 into the second tank 14 through the pipe 16. A polymer flocculant is added to the second tank 14, whereby flocs grow larger. Reference numeral 17 is a stirrer.

The waste water is naturally flown from the second tank 14 into the floating separation tank 20 from the bottom through the pipe 18. The slurry can be extracted from the bottom of the floating separation tank 20. The floating separation tank 20 is composed of an inner tank 20a and an outer tank 20b.
It has a tank structure, and both tanks communicate with each other in the middle, and the treated water is discharged from the outer tank 20b through the pipe 21.
Reference numeral 22 denotes a scraping blade, which is rotated by a motor 23 around a shaft 24 on the surface of water so that the floating flocs can be scraped off toward a discharge shooter 25. It is preferable to return a part of the scum discharged to the discharge shooter 25 to the first tank 13 by a return pipe (not shown).

Reference numeral 27 is a pressurized water supply device. 28 is a pressurizing pump, and through the pipes 29 and 30, the outer tank 20b
A part of the drainage from the tank is sent to the pressurized water tank 31. 32
Is an air compressor, and the compressed air is connected to the pipe 29 by the pipe 33.
Send to. The compressed air is taken into the drainage, pushed into the drainage by the pressurizing pump 28, melted in the drainage, and sent to the pressurized water tank 31.

The pressurized water in the pressurized water tank 31 is pipe 3
2. It is supplied to the bottom of the flotation tank 20 through the pipe 18 via the valve 33. Since the floating separation tank 20 is at atmospheric pressure, the air dissolved in the pressurized water floats as a large number of fine air particles. The fine air particles are floated and separated in the separation tank 20.
The lighter flock that adheres to the inner flock emerges. Further, as described above, it is considered that the fine air particles promote the formation of flocs, and thus it is considered that a larger amount of fluorine is held in the flocs and the removal rate of fluorine is increased.

It has been found that among the aluminum compounds, in the case of sodium aluminate, fluorine can be sufficiently removed not only by the pressure floating method but also by the usual coagulating sedimentation method. That is, wastewater having a reduced fluorine concentration is introduced into a reaction tank in advance, sodium aluminate and a polymer coagulant are added to the wastewater to form flocs, and then the wastewater is introduced into a sedimentation tank to precipitate the flocs. Then, the flocs are removed. Sodium aluminate is the alkali _{solution, [Al (OH) 4]} -, or [(HO) ₃
It is dissociated into Al-O-Al (OH) ₃ ] ^2- . Although the mechanism is not clear, in the case of sodium aluminate, fluorine could be sufficiently removed even by the coagulation sedimentation method.

[0025]

EXAMPLE (Example 1) Processing was carried out by the processing apparatus shown in FIG. Factory wastewater (raw water) was subjected to a primary treatment, and the fluorine concentration in this primary treated water (effluent) was 12.3 mg / l. The flow rate of this primary treated water into the first tank 13 is 7 m ³ /
Then, polyaluminum chloride (PAC) was supplied to the first tank 13 at 0.9 l / h for reaction. p
H was adjusted to 7 to 8 with caustic soda. The waste water was allowed to flow into the second tank 14 by natural inflow from the first tank 13, and the polymer flocculant was added to the waste water in the second tank 14 to generate flocs. Further, this drainage was supplied into the flotation separation tank 20, and pressurized water was supplied from the pressurized water tank 31 to the flotation separation tank 20 to float and separate the flocs. The fluorine concentration in the discharged water could be reduced to 1.5 mg / l.

(Example 2) Fluorine concentration was 10.1 mg /
When the primary treated water (1) was treated by the same pressure floating method as in Example 1, the fluorine concentration could be reduced to 2.7 mg / l.

(Example 3) Fluorine concentration was 19.8 mg /
When 1 liter of the primary treated water was treated by the same pressure floating method as in Example 1, the fluorine concentration could be reduced to 4.1 mg / l.

Example 4 150 ppm of sodium aluminate as an aluminum component was added to primary treated water having a fluorine concentration of 20 ppm, the pH was adjusted to 7.0 with hydrochloric acid, and a polymer flocculant was added to the flocs. And the flocs are removed by precipitation to reduce the fluorine concentration to about 1 pp.
It was possible to reduce to m.

(Example 5) To the primary treated water having a fluorine concentration of 20 ppm, 50 ppm of sodium aluminate was added as an aluminum content, the pH was adjusted to 7.0 with hydrochloric acid, and a polymer flocculant was further added to the flocs. Fluorine concentration of about 2ppm
Could be reduced to

Example 6 150 ppm of sodium aluminate as an aluminum component was added to primary treated water having a fluorine concentration of 45 ppm, the pH was adjusted to 7.0 with hydrochloric acid, and a polymer flocculant was added to the flocs. And the flocs are removed by sedimentation to reduce the fluorine concentration to about 1.5.
It could be reduced to ppm.

Comparative Example 1 50 ml of the same primary treated water as in Example 1 was placed in a beaker, 0.05 ml of polyaluminum chloride was added thereto, and the pH was adjusted to 7 to 8 with caustic soda.
Then, a polymer flocculant was added to form flocs. The fluorine concentration of the filtrate obtained by filtering this precipitate was 7.4 mg / l.

Comparative Example 2 When the same primary treated water as in Example 3 was treated in the same manner as in Comparative Example 1, the fluorine concentration was 10.
It could only be reduced to 8 mg / l.

(Comparative Example 3) Raw water having a fluorine concentration of several thousand ppm was prepared with hydrofluoric acid, and calcium hydroxide was added to the raw water for primary treatment, whereby the fluorine concentration was 12.9 mg /
It was reduced to 1. This primary treated water was treated by the same coagulation-sedimentation method as in Comparative Example 1, but the fluorine concentration was 9.3 mg.
It was only reduced to / l.

(Comparative Example 4) The fluorine concentration was adjusted to 2 with hydrofluoric acid.
After adding sulfuric acid to the solution adjusted to 2.6 mg / l to adjust the pH, calcium hydroxide and a polymer coagulant are added to precipitate calcium fluoride, and the filtrate has a fluorine concentration of 17. It was 8 mg / l.

Comparative Example 5 The liquid of Comparative Example 4 (22.6 mg)
/ L fluorine concentration), adding polyaluminum chloride,
Adjust the pH with caustic soda, add a polymer flocculant to form flocs, and filter the filtrate with a fluorine concentration of 1
It was 1.6 mg / l.

Comparative Example 6 The liquid of Comparative Example 4 (22.6 mg)
/ L fluorine concentration), adding polyaluminum chloride,
Adjust the pH with caustic soda, add a polymer flocculant,
Further, air was blown in to form flocs, and the filtrate had a fluorine concentration of 11.5 mg / l. As described above, in all the examples, the fluorine concentration could be significantly reduced, but in all the comparative examples, the fluorine concentration could not be sufficiently reduced. In Comparative Example 6, air was blown in for comparison (aeration), but with large air particles, the fluorine concentration cannot be reduced to a satisfactory level as compared with the pressure floating method. From this, it is considered that the reduction of the fluorine concentration requires not only the action of air but also the action of promoting generation of flocs when the flocs are floated by fine air particles.

[0037]

As described above, according to the present invention, the primary treatment wastewater is reacted with the aluminum compound, and then solid-liquid separation is performed by the pressure floating method, whereby fluorine is stably reduced to below the new standard. There is an effect that it can. Even if the same aluminum compound is added to form a floc containing fluorine, and the floc is precipitated and removed, the fluorine cannot be sufficiently removed.However, the floc is not removed by the pressure flotation method, but by this flocculation method. It is possible to stably remove fluorine below the new standard by levitating and removing this floc, which means that the generation of flocs is further promoted by the fine air particles generated by the pressure levitation method.
It is considered that this causes a large amount of fluorine to be entrapped in the flocs, thus improving the removal rate. When sodium aluminate is used as the aluminum compound, fluorine can be sufficiently removed even by the coagulating sedimentation method. Further, according to the device of the present invention, a simple unit type removal device can be used as it is as a conventional chemical agent addition, reaction tank, and solid-liquid separation device.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an entire processing apparatus.

[Explanation of symbols]

10 processor 12 reaction tanks 13 First tank 14 Second tank 15,17 Stirrer 16, 18, 21, 29, 30, 30a, 32 pipes 20 Floating separation tank 28 Pressurizing pump 31 Pressurized water tank 32 air compressor 33 valves

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinsuke Ozaki             Nagano City, Nagano City 4020 Soybean Island 3 Stocks             Company Misuzu Industry (72) Inventor Tetsuro Machida             Nagano City, Nagano City 4020 Soybean Island 3 Stocks             Company Misuzu Industry F-term (reference) 4D015 BA04 BA05 BA19 BA22 BA23                       BB12 CA20 DA03 DA06 DA08                       DA09 DB01 EA14 EA16 EA33                 4D037 AB13 AB14 BA03 CA08                 4D038 AA08 AB42 BA04 BB04 BB13                       BB18

Claims (8)

[Claims] 1. A reaction step in which wastewater, which has been subjected to a primary treatment and has a reduced fluorine concentration in advance, flows into a reaction tank, and an aluminum compound and a polymer coagulant are added to the wastewater to form flocs, and then the wastewater Flowing into the flotation separation tank, supplying pressurized water from the bottom of the flotation separation tank into the flotation separation tank by pressurizing and dissolving the air, and causing flocs to float by the fine air particles generated; And a step of removing the fluorine-containing wastewater. 2. The method for treating fluorine-containing wastewater according to claim 1, wherein the wastewater subjected to the primary treatment has a fluorine concentration of 8 to 100 mg / l. 3. The method for treating fluorine-containing wastewater according to claim 1, wherein the pH in the reaction step is adjusted to 6 to 7.5. 4. The reaction step is divided into a first step of adding an aluminum compound to the waste water and a second step of subsequently adding a polymer coagulant to the waste water. The method for treating fluorine-containing wastewater according to 2 or 3. 5. The aluminum compound to be added is one or more selected from polyaluminum chloride, aluminum hydroxide, aluminum sulfate and sodium aluminate, and any one of claims 1 to 4 is characterized in that The method for treating aluminum-containing wastewater according to the item. 6. A reaction tank which is subjected to a primary treatment and in which wastewater having a reduced fluorine concentration is introduced in advance, and an aluminum compound and a polymer flocculant are added to the wastewater to form flocs, and the wastewater from the reaction tank. And a pressurized water supply device for supplying pressurized water obtained by pressurizing and dissolving air into the flotation separation tank from the bottom of the flotation separation tank. Ascend Flock,
A treatment device for fluorine-containing wastewater, characterized by being separated. 7. The reaction tank comprises a first tank in which an aluminum compound is added to the inflowing waste water, and a second tank in which a polymer coagulant is added to the waste water inflowing from the first tank. 7. The apparatus for treating fluorine-containing wastewater according to claim 6, comprising: 8. A reaction step in which wastewater, which has been subjected to a primary treatment and has a reduced fluorine concentration in advance, flows into a reaction tank, and sodium aluminate and a polymer flocculant are added to the wastewater to form flocs, A method for treating fluorine-containing wastewater, comprising: a step of causing wastewater to flow into a settling tank to precipitate flocs; and a step of removing flocs.