JP2003334566A - Method and device for treating drain containing fluorine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the stably permeating water amount and treated water quality of a drain containing fluorine, using a membrane filter. <P>SOLUTION: Calcium salt is added to the drain at an optimal pH value in a reaction tank 1. Next, not more than 1,500 mg/L of PAC (polyaluminum chloride) are added to the drain within the pH range of 6 to 10 in a reaction tank 2 to perform the flocculation process. Further, the drain subjected to the process is filtered through a membrane of the membrane filter 4. In this case, the filtering membrane of the subject device 4 has pores whose diameter is 0.5 to 10 μm. Consequently, the treated water of good quality is obtained, while the permeating water amount of the device 4 is large. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of a large amount of fluorine-containing wastewater discharged in a semiconductor factory or the like, and more particularly to a method and apparatus for obtaining stable treated water by simple operation.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor factory or the like, a large amount of fluorine-containing waste water is discharged because hydrofluoric acid or the like is used in the manufacturing process. It is a general method that calcium is added to the fluorine-containing wastewater to generate sparingly soluble calcium fluoride, and the calcium fluoride is separated. Moreover, since the calcium fluoride generated by the addition of calcium is extremely fine, it is usually an inorganic coagulant (ferric chloride or polyaluminum chloride (PA
C)) and a polymer flocculant are added to generate floc of flocs of calcium fluoride, and the flocs thus generated are separated in a settling tank.

[0003]

However, if a settling tank is used for solid-liquid separation, there is a problem that the site area of the settling tank becomes very large in order to perform sufficient precipitation treatment.

Therefore, it has been proposed to use a membrane filtration device for solid-liquid separation. Membrane filtration device is
There is an advantage that a small and clear treated water can be stably obtained. However, when a membrane filtration device is used to filter flocculated flocs of calcium fluoride, the permeated water amount (filtered water amount) cannot be stably increased for a long time, and it is difficult to put it into practical use.

Japanese Unexamined Patent Publication No. 9-85262 discloses a PAC.
A method has been proposed in which membrane filtration is performed after agglutination using hydrochloric acid and hydrochloric acid as a flocculant. However, even with this method,
The amount of permeated water decreased after 500 hours and has not been put to practical use as an economical treatment.

In the conventional treatment, the floc formation of calcium fluoride is affected by the coexisting substances contained in the waste water, the form of fluorine, the pH at that time, etc.
There is also a problem that stable treatment cannot be performed, the treated water becomes cloudy, and the fluorine concentration of the treated water fluctuates to about 5 to 20 mg / L.

In Japanese Patent Publication No. 7-53276, a calcium compound and an aluminum compound are added to waste water, and p
While adjusting H to the range of 6 to 8, a part of the concentrated liquid generated in the subsequent membrane separation step was added and stirred, and the obtained suspension was introduced into a circulation tank to react with it. Membrane separation has been shown. However, this method adds both calcium and aluminum compounds to the wastewater,
The pH was adjusted within a relatively wide range of 6 to 8, and the production of calcium fluoride and the flocculation by the aluminum compound as a pretreatment for membrane filtration were not properly controlled.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a treatment method and apparatus capable of obtaining a stable permeated water amount and treated water quality by utilizing membrane filtration of fluorine-containing wastewater. .

[0009]

According to the present invention, calcium ions are added to fluorine-containing wastewater, and then the pH is adjusted to 6-10.
Within the range, polyaluminum chloride is added at an addition amount of 1500 mg / L or less, and water is passed through a membrane filtration device for solid-liquid separation.

The present invention also provides a calcium adding means for adding calcium ions to the fluorine-containing wastewater, and an aggregating means for adding polyaluminum chloride at an addition amount of 1500 mg / L or less within a pH range of 6 to 10 after calcium addition. And a membrane filtration device that separates solid-liquid separation by passing waste water after coagulation.

As described above, by setting the addition amount of polyaluminum chloride to 1500 mg / L or less, the flux (permeation flow rate per unit area of membrane) of the membrane filtration treatment in the latter stage.
Can be large enough. Therefore, according to the present invention, it has become possible to put the membrane filtration treatment into practical use for treating fluorine-containing wastewater.

Further, when adding calcium ions to the fluorine-containing wastewater, it is preferable to add calcium ions while adjusting the pH to a predetermined value within the range of 4 to 10.

Thus, by adding calcium ions while adjusting the pH to a predetermined value within the range of 4 to 10, floc formation of calcium fluoride can be effectively performed. As a result, excessive addition of polyaluminum chloride in the next step can be avoided.
Then, the fluorine concentration of the membrane filtration treated water can be made sufficiently low.

The membrane filtration device has a pore size of 0.5 to 1
It is preferable to perform the filtration treatment using a 0 μm filtration membrane. By using a membrane having a pore size of 0.5 to 10 μm, the permeated water amount per unit area of the membrane can be sufficiently increased while maintaining the fluorine concentration of the treated water at a low concentration.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of an embodiment of the present invention. Fluorine-containing wastewater is first introduced into a reaction tank 1. Calcium salt is added to the reaction tank 1, and the waste water and the calcium salt are mixed by the stirrer 1a. In this reaction tank 1, sparingly soluble calcium fluoride is generated and its flocs (fine particles) are deposited. As the calcium salt to be added, calcium chloride, calcium hydroxide and the like are suitable. Furthermore, in this reaction tank 1, p
An H adjuster is added to adjust the pH to a predetermined value (set pH).

This set pH is a predetermined value within the range of pH 4 to 10 which is determined for each target wastewater from the floc formation state, treated water quality, etc. Specifically, the jar test is conducted within the range of 4 to 10. , The floc formation state (especially size) at that time, the turbidity of the treated water (supernatant water) in the jar test, and the treated water quality after filter paper filtration are considered and set to the optimum values.

As described above, in this embodiment, when adding a calcium salt to the fluorine-containing wastewater, the optimum pH is examined according to the target wastewater, and the calcium salt is added to the wastewater while adjusting the optimum pH. To do. As a result, calcium fluoride can be effectively produced and good fluorine removal is ensured.

In FIG. 1, 8 is a pH adjusting agent storage tank, 9 is an injection pump for supplying the pH adjusting agent stored in the pH adjusting agent storage tank 8 into the reaction tank 1, and 1
Reference numeral 0 is a pH sensor attached to the reaction tank 1. And
The pH sensor 10 and the injection pump 9 are instrumentally connected, and the pH of the liquid in the reaction tank 1 measured by the pH sensor 10 is measured.
The supply amount of the infusion pump 10 is controlled so that becomes a predetermined value.

The waste water to which the calcium salt has been added is then introduced into the reaction tank 2. Polyaluminum chloride (PAC), which is an inorganic coagulant, is added to the reaction tank 2, and PAC is mixed with the waste water by the stirrer 2a to form coagulated flocs in which calcium fluoride flocs are coagulated.
Further, a pH adjusting agent is added to the reaction tank 2 to adjust the pH within the range of 6 to 10. At this time, the addition amount of PAC is less than that of the conventional method.
Set within the range of 00 mg / L. Although it depends on the fluorine concentration of the waste water, etc., it is usually preferably in the range of 200 to 750 mg / L. Further, in the present invention, the addition amount of PAC is the addition amount as an aqueous solution containing 10 to 11% of the active ingredient Al ₂ O ₃ .

Here, if the amount of PAC added is small, the diameter of the flocs produced may be small and may pass through the filtration membrane in the next step. Meanwhile, PAC is 1500 mg /
When L or more is added, the amount of permeated water in the membrane filtration device in the next step decreases. Although the detailed mechanism of this is not clear, if the amount of PAC added is too large, the viscosity of the liquid increases, it easily adheres to the filtration membrane, and the cleaning property deteriorates. It is thought that it will become low. Further, by using the membrane filtration device, it becomes unnecessary to add the organic polymer coagulant, which is conventionally required. Therefore, it is possible to reduce the chemical cost and the amount of sludge.

In FIG. 1, 11 is a pH adjusting agent storage tank, and 12 is the pH stored in the pH adjusting agent storage tank 11.
An injection pump for supplying a regulator into the reaction tank 2 and a pH sensor 13 attached to the reaction tank 2. The pH sensor 13 and the infusion pump 12 are instrumentally connected, and the infusion pump 1 is so adjusted that the pH of the liquid in the reaction tank 2 measured by the pH sensor 13 becomes a predetermined value.
Control the supply amount of 2.

Thus, calcium salt and PA
The drainage in which the aggregated flocs of calcium fluoride aluminum are formed by the addition of C is supplied to the membrane filtration device 4 at a predetermined pressure by the pump 3. The membrane filtration device 4 is divided into a raw water chamber 4b and a treated water chamber 4c by a filtration membrane 4a. The raw water is supplied to the raw water chamber 4b, and the treated water that has passed through the filtration membrane 4a is fed to the treated water chamber 4c. can get. The filtration membrane 4a of the membrane filtration device 4 is a microfiltration membrane (M
F) and an ultrafiltration membrane (UF) are used, and those having a pore size in the range of 0.5 μm to 10 μm are particularly preferably used as this membrane. By using the filtration membrane 4a having such a pore size, it is possible to perform stable filtration processing while maintaining a high filtration rate.

Here, the pore size of the membrane filtration device (MF) currently put to practical use in water treatment is mainly 0.2 to 0.4 μm, and 0.5 μm is conventionally used for the treatment of fluorine-containing wastewater.
Studies have been made with less than filtration membranes. For example, JP-A-1
0-202272, JP 2001-259656.
Japanese Patent Laid-Open No. 2,137,852 and the like describe such a membrane filtration device (MF). However,
Suspended substances are reliably removed with a filtration membrane of less than 0.5 μm, but the amount of permeated water per unit area of the membrane is small,
Or, since it is unstable, the cost of the relatively large-scale fluorine wastewater treatment in which the flow rate of the wastewater is 1 m ³ / hr or more becomes high and it has not been put to practical use.

As a result of the particle size distribution of the suspended substance added with calcium fluoride and PAC, the present inventor has found that the particle size has a peak of 0.6 μm or more and 3 μm or less and a particle size of 4 μm or more and 50 μm or more.
It was confirmed that there was a peak of μm or less. It is assumed that the former peak is derived from calcium fluoride and the latter is derived from calcium fluoride and PAC flocs.

Therefore, for the purpose of practical application of wastewater treatment on a scale of 1 m ³ / hr or more, the present inventor has used a filtration membrane having a pore size of 0.5 μm or more, which has not been used in the field of water treatment in the past. And conducted a thorough study on the quality of treated water. As a result, even if the filtration membrane has a relatively large pore size of 0.5 μm or more, by using depth type microfiltration (Nominal Filtration), it can be clarified while maintaining a flux that is about 2 to 20 higher than in the past. It became clear that various filtered water could be obtained, and it became possible to put it into practical use for wastewater treatment.

Regarding the pore diameter of the filtration membrane 4a,
It is preferably 5 μm to 10 μm. The pore size of the filtration membrane is 0.5μ
If it is less than m, an industrially sufficient flux cannot be obtained, and if the pore size exceeds 10 μm, fine particles pass through the membrane and the treated water becomes clouded.

Here, the type of the membrane module of the membrane filtration device 4 is not particularly limited, but for example, a hollow fiber type or spiral type module can be used. Further, the material of the film is not limited, but polypropylene, polyester, polyacrylonitrile, polyolefin, polyvinylidene fluoride, ceramic or the like can be used.

Further, the operation of the membrane filtration device 4 is performed by the filtration membrane 4a.
In order to suppress the clogging of, the accumulation of solid matter on the film surface,
The cross-flow method is preferable, and the cross-flow method is used in this embodiment. That is, part of the raw water is extracted from the raw water chamber 4b and returned to the inlet side of the membrane filtration device 4 by the circulation pump 5. The circulating water amount is preferably about 5 to 50 times the inflowing water amount of the membrane filtration device 4. A part of the circulating water is discharged outside the system as concentrated waste water and treated separately.

The treated water of the membrane filtration device 4 is introduced and stored in the treated water tank 6. This treated water may be discharged as it is, but if it is necessary to further reduce the amount of fluorine, it is adsorbed with a fluorine-containing resin such as zirconium forming a complex compound with fluorine ions or an adsorbent such as activated alumina. It can be processed by the tower 7.

Particularly, when solid-liquid separation using a sedimentation tank is conventionally used, fine calcium fluoride particles or the like may be contained in the treated water and a large amount of suspended solids may be contained, and a fluorine adsorption tower was used. In that case, clogging was likely to occur. However, in this embodiment, the membrane filtration device 4 is used for solid-liquid separation. Therefore, the treated water is stable and clear, and the problem of clogging in the fluorine adsorption tower 7 hardly occurs. By using this fluorine adsorption tower 7, the fluorine concentration of the treated water can be stably maintained at a low concentration.

Further, the fluorine adsorption tower 7 needs to be regenerated with an alkaline chemical at a predetermined frequency. Although this recycled wastewater contains fluorine, it can be treated by returning it to the reaction tank 1.

[0033]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Experiments of the following Examples 1, 2 and 3 and Comparative Examples 1, 2 and 3 were conducted using the processing apparatus shown in FIG. The filtration membrane of the membrane filtration device 4 has a polypropylene pore size of 5 μm.
An MF membrane of m (0.2 μm in Comparative Example 3) was used, and it was operated by a cross flow method at an operating pressure of 0.2 MPa. The circulating water amount was 10 times the raw water amount. The filtration membrane 4a was washed by performing an operation in which the permeated water was caused to flow in the opposite direction to the filtration of the raw water, once for each 5 minutes of drainage filtration (15 seconds / time). The amount of permeated water was converted to the amount of permeated water when the water temperature was 25 ° C and shown. Waste water having a pH of 6 and a fluoride ion concentration of 100 mg / L was used as raw water.

Example 1 Calcium chloride was added to raw water 15 times.
00 mg / L was added. At this time, as a result of the jar test, the pH in the reaction tank 1 was controlled such that the treated water had the lowest fluorine concentration of pH 7. p
Sodium hydroxide was used as the H regulator. next,
250, 500, 1000, 150 PAC in reaction tank 2
0 mg / L was added. After confirming that the pH at this time was 6 to 7, water was passed through the membrane filtration device 4.

(Comparative Example 1) Under the same conditions as in Example 1, P
The experiment was conducted with the addition amount of AC being 2000 mg / L.

FIG. 3 shows changes in the amount of permeated water per unit area of the membrane in Example 1 and Comparative Example 1. In this way, by controlling the PAC injection amount after the addition of the calcium salt to 1500 mg / L or less, a stable and high permeated water amount can be obtained in the membrane filtration of the drainage containing the calcium salt and PAC in the fluorine-containing wastewater. It was confirmed that continuous operation for 20 days was possible. The amount of PAC added was 1000 mg /
When it is L or less, the amount of permeated water can be maintained at 0.5 m ³ / m ² / hr or more, which is more preferable.

Example 2 Calcium chloride was added to raw water 15 times.
00 mg / L was added. At this time, as a result of the jar test, the pH in the reaction tank 1 was controlled such that the treated water had the lowest fluorine concentration of pH 7. p
Sodium hydroxide was used as the H regulator. next,
600 mg / L of PAC was added in the reaction tank 2. After confirming that the pH at this time was 6 to 7, water was passed through the membrane filtration device 4.

(Comparative Example 2) 1500 mg / L was added to raw water without adjusting the pH when calcium chloride was added. The pH of the reaction tank 1 at this time was 5.5. Otherwise, the same operation as in Example 2 was performed.

Table 1 shows the fluorine concentration of treated water of Example 2 and Comparative Example 2 and the amount of permeated water of the membrane filtration device 4.

[Table 1]

Thus, by controlling the pH when calcium is added to the optimum pH, the membrane filtration device 4
It was confirmed that the fluorine concentration of the treated water in (2) was stable and the water quality was good.

Example 3 Calcium chloride was added to raw water
It was added at 500 mg / L. At this time, the reaction tank 1 was controlled so that the treated water fluorine concentration was the lowest at pH 7 as a result of the jar test. Sodium hydroxide was used as a pH adjuster. Next, PAC was added to the reaction tank 2 at a concentration of 1000 mg / L. After confirming that the pH at this time was 6 to 7, water was continuously passed through the membrane filtration device 4 equipped with an MF membrane having a pore size of 5 μm.

(Comparative Example 3) An experiment was conducted by replacing the filtration membrane of the membrane filtration device 4 with a filtration membrane having a pore size of 0.2 μm.

FIG. 4 shows changes in the amount of permeated water per unit area of membrane in Example 3 and Comparative Example 3. As described above, it was confirmed that the permeated water amount was increased by about 8 times by setting the pore size of the filtration membrane to 5 μm, and the practical application was possible. A batch test was also conducted on a membrane having a pore size of 10 μm, and it was confirmed that sufficient treated water quality could be obtained.

[0045]

As described above, by setting the addition amount of polyaluminum chloride to 1500 mg / L or less, it is possible to obtain a sufficiently large flux in the subsequent membrane filtration treatment. Therefore, according to the present invention, it has become possible to put the membrane filtration treatment into practical use for treating fluorine-containing wastewater.

In the first step, the pH is adjusted to 4-1.
By adding calcium ions while adjusting to a predetermined value within the range of 0, it is possible to avoid the excessive addition of polyaluminum chloride in the next step and effectively form the flocs of calcium fluoride. Then, the fluorine concentration of the membrane filtration treated water can be made sufficiently low.

Further, the membrane filter has a pore size of 0.5 to 10 μm.
By using this membrane, the permeated water amount can be sufficiently increased while maintaining the fluorine concentration of the treated water at a low concentration.

[Brief description of drawings]

FIG. 1 is a block diagram showing a device configuration of an embodiment.

FIG. 2 is a block diagram showing a device configuration when experiments of examples and comparative examples are performed.

FIG. 3 is a diagram showing changes in the amount of permeated water in Example 1 and Comparative Example 1.

FIG. 4 is a diagram showing changes in the amount of permeated water in Example 3 and Comparative Example 3.

[Explanation of symbols]

1, 2 reaction tanks, 3 pumps, 4 membrane filtration devices, 5 circulation pumps, 6 treated water tanks, 7 fluorine adsorption towers.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D006 GA06 GA07 HA95 JA02Z                       KA01 KA12 KB13 KD08 KD11                       KD17 KE15P KE15Q MA22                       MB02 PA05 PB08 PB70                 4D015 BA04 BA19 BB09 BB13 CA17                       DA04 DA22 DA24 DC02 EA03                       EA04 EA06 EA12 EA13 EA14                       EA15 EA16 EA19 EA37                 4D038 AA08 AB40 BA02 BA04 BA06                       BB09 BB13 BB18

Claims (4)

[Claims] 1. Calcium ions are added to fluorine-containing wastewater, and then polyaluminum chloride is added in an amount of 1500 mg / L or less within a pH range of 6 to 10, and water is passed through a membrane filtration device to solidify. A method for treating fluorine-containing wastewater, characterized by liquid separation. 2. A calcium adding means for adding calcium ions to the fluorine-containing wastewater, an aggregating means for adding polyaluminum chloride at an addition amount of 1500 mg / L or less within a pH range of 6 to 10 after adding calcium, and A treatment device for fluorine-containing wastewater, comprising: a membrane filtration device for passing wastewater through to perform solid-liquid separation. 3. The method or apparatus according to claim 1 or 2, wherein pH is adjusted to a predetermined value within a range of 4 to 10 when calcium ions are added to the fluorine-containing wastewater. A treatment method for fluorine-containing wastewater or a treatment apparatus for fluorine-containing wastewater, which comprises adding calcium ions. 4. The method or apparatus according to any one of claims 1 to 3, wherein the membrane filtration device performs filtration using a filtration membrane having a pore size of 0.5 to 10 μm. A method for treating fluorine-containing wastewater or a treatment device for fluorine-containing wastewater.