Treatment apparatus for waste water from exhaust gas treatment facility

Abstract

To provide a treatment apparatus for waste water from an exhaust gas treatment facility capable of suppressing blockage of an RO apparatus for brine recovery and stably increasing a recovery rate of waste water from the exhaust gas treatment facility.SOLUTION: A treatment apparatus for waste water from an exhaust gas treatment facility includes a first RO apparatus 4 separating fluorine-containing waste water from an exhaust gas treatment facility into first permeate water and first concentrated water by reverse osmosis treatment, a coagulation sedimentation apparatus 14 precipitating and separating calcium fluoride by adding calcium compounds and coagulants to the first concentrated water, a second RO apparatus 15 separating separated water from the coagulation sedimentation apparatus 14 into second permeate water and second concentrated water by reverse osmosis treatment, and a return piping 16 returning the second permeate water to the pre-stage of the first reverse osmosis membrane apparatus 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for treating wastewater from an exhaust gas treatment facility (abatement device) for treating gases containing PFCs and the like by abatement combustion or the like.

[0002] PFCs (Perfluorocompounds) are 4 , C 2 F 6 , C 4 F 8 ,SCIENCE FICTION 6 , W.F. 6 In this specification, in addition to these perfluoro compounds, CH 2 F 2 , Cl 2 , BCl 3 , F 2 , HF, SiH 4 , N.H. 3 , PH 3 , TEOS (tetraethoxysilane), TRIS (triethoxysilane), TiCl 4 This refers to all harmful, flammable, greenhouse gases used in deposition, etching, cleaning, and other processes. [Background technology]

[0003] In the manufacturing processes of semiconductors, liquid crystals, LEDs, solar cells, etc., large quantities of the above-mentioned PFCs, such as perfluoro compounds, are used. Factories that use perfluoro compound gases are equipped with exhaust gas treatment equipment called abatement devices that render these gases harmless. In abatement devices, perfluoro compounds are converted to fluorine (F) through combustion (oxidation) or thermal decomposition reactions using combustion, electrical heating, plasma, etc. 2 After the desorption of F, the exhaust gas is washed with a water scrubber installed in the device, and the F in the gas is removed. 2 Absorb and remove.

[0004] In addition to HF, scrubber wastewater contains organic hydrocarbon compounds (TOC components) derived from the organic skeletons of perfluorochemical molecules. Therefore, the scrubber wastewater is treated by being led to an organic matter decomposition means such as a biological treatment device (Patent Document 1).

[0005] The reason for installing organic matter removal equipment such as biological treatment equipment to treat wastewater from abatement processes is to save energy in the abatement equipment and to separate C-F bonds, which are harmful, flammable, and contribute to global warming, through low-temperature decomposition. This is because the scrubber wastewater contains total organic hydrocarbon compounds (TOC), as the hydrocarbon skeleton is not completely combusted.

[0006] The amount of wastewater from the semiconductor manufacturing process, particularly wastewater from decontamination, exceeds the amount of ultrapure water used in the process. Therefore, in order to efficiently recover and reuse wastewater in facilities that have semiconductor manufacturing processes, it is necessary to treat and reuse the wastewater with a high recovery rate.

[0007] Fig. 2 is a flow diagram showing an example of a conventional decontamination wastewater treatment device. Decontamination wastewater from a water scrubber of the decontamination device is introduced into a pH adjustment tank (not shown) where a pH adjuster is added to adjust the pH to neutral. Water from the pH adjustment tank is introduced into a pretreatment device 1 having a biological treatment tank, a coagulation tank, etc., and treated there.

[0008] Treated water from the pretreatment device 1 passes through a relay tank 2 and is filtered by a safety filter 3, and is then supplied to a first RO (reverse osmosis) device 4. The permeated water (first permeated water) that has permeated the RO membrane of the first RO device 4 is supplied to a water scrubber of the decontamination device.

[0009] The concentrated water (first concentrated water) from the first RO device 4 is supplied to a second RO device 15 for recovering brine. The permeated water (second permeated water) from the second RO device 15 is returned to the relay tank 2 through a return pipe 16 as a return line, and the concentrated water (second concentrated water) is sent to a wastewater treatment facility (not shown). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2022-70608 Summary of the Invention [Problem to be solved by the invention]

[0011] In order to further increase the recovery rate of the decontamination wastewater, if the brine (first concentrated water) from the first RO device 4 is further treated in the second RO device 15, the second RO device 15 is likely to be clogged with precipitates, resulting in a decrease in flow rate. In addition, the frequency of cleaning and replacement of the membrane will increase.

[0012] An object of the present invention is to provide an apparatus for treating effluent from an exhaust gas treatment facility, which can suppress clogging of an RO device for recovering brine and can stably increase the recovery rate of effluent from an exhaust gas treatment facility. [Means for solving the problem]

[0013] The device for treating effluent from an exhaust gas treatment facility of the present invention comprises a first reverse osmosis membrane device which subjects fluorine-containing exhaust gas treatment facility effluent to reverse osmosis and separates it into a first permeate and a first concentrated water, a coagulation and sedimentation device which adds a calcium-based compound and a coagulant to the first concentrated water to precipitate and separate calcium fluoride, a second reverse osmosis membrane device which subjects the separated water from the coagulation and sedimentation device to reverse osmosis and separates it into a second permeate and a second concentrated water, and a return line which returns the second permeate to the upstream stage of the first reverse osmosis membrane device.

[0014] In one aspect of the present invention, the coagulation and sedimentation apparatus comprises a reaction tank, a coagulation tank, a sedimentation tank, a sludge return path for returning sludge containing calcium fluoride separated in the sedimentation tank to the reaction tank via a sludge modification tank, and a calcium-based compound adding means for adding a calcium-based compound to the sludge modification tank.

[0015] In one embodiment of the present invention, the first permeate from the first reverse osmosis membrane device is recovered as water for a water scrubber of the exhaust gas treatment facility. Effect of the Invention

[0016] In the exhaust gas treatment system effluent treatment apparatus of the present invention, the first concentrated water from the first RO device is subjected to fluoride removal treatment before being supplied to the second RO device, thereby preventing clogging of the second RO device and enabling a stable high water recovery rate in the exhaust gas treatment system effluent treatment apparatus.

[0017] According to the present invention, since the deposition of reaction products of fluorine with Al, Mg, etc. is suppressed in the second RO unit, it becomes possible to maintain the flux (amount of treated water under standard pressure and temperature conditions) of the second RO unit higher than that of conventional equipment, improve the water recovery rate of the entire plant, and control the amount of wastewater discharged below the regulated value. In addition, the number of RO membranes can be reduced, and the total cost including the construction of recovery equipment and operation management such as membrane replacement and chemical cleaning can be reduced. [Brief description of the drawings]

[0018] [Figure 1] 1 is a configuration diagram of a treatment device for wastewater from an exhaust gas treatment facility according to an embodiment. [Diagram 2] FIG. 1 is a configuration diagram of a conventional wastewater treatment device for exhaust gas treatment equipment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing an example of a treatment device for wastewater from an exhaust gas treatment facility according to the present invention. The same reference numerals are used to designate members common to Fig. 2.

[0020] The decontamination wastewater from the water scrubber of the decontamination device is introduced into a pH adjustment tank (not shown) where a pH adjuster is added to adjust the pH to 5 to 8, particularly 6 to 7. The pH adjustment tank may be omitted. As the pH adjuster, NaOH or the like is used.

[0021] The water from the pH adjustment tank is introduced into a pretreatment device 1 having a biological treatment tank and the like, where it is biologically treated to decompose the organic matter. As the biological treatment tank, an aerobic biological treatment tank using an aeration means or a biological activated carbon tower is suitable. Note that if the amount of organic matter is small, the biological treatment tank may be omitted.

[0022] In the pretreatment device 1, the biologically treated water is coagulated as necessary, and the coagulated water is filtered to separate SS (suspended solids) and bacteria. As the filtration device, an MF membrane device, a UF membrane device, or the like is used. The pretreated water from the pretreatment device 1 is supplied to a first RO device 4 via a relay tank 2 and a safety filter 3. As the safety filter 3, an MF membrane device, or the like is used.

[0023] The permeate from the first RO device 4 is sent to a decontamination device and used as scrubber water, etc. The concentrated water from the first RO device 4 passes through a water receiving tank 5 and is subjected to fluorine removal treatment by coagulation sedimentation in a coagulation sedimentation device 14.

[0024] The coagulation and settling device 14 includes a reaction tank 6, a coagulation tank 7, a settling tank 8, a sludge reforming tank 12, and a calcium-based compound adding means 13, etc.

[0025] The water in the water receiving tank 5 is adjusted to acidic, for example, pH 2.5 to 3.0, by adding a pH adjuster as necessary, and then introduced into the reaction tank 6 of the coagulation sedimentation device 14 and mixed with the modified sludge introduced from the sludge modification tank 12, where the fluorine in the water reacts with calcium compounds to produce calcium fluoride. At least a part of the calcium fluoride is produced on the surfaces of the sludge particles, causing the sludge particles to grow.

[0026] This reaction liquid is then fed to a flocculation tank 7, where a polymer flocculant is added by a polymer flocculant adding means for flocculation treatment, and then solid-liquid separation is performed in a settling tank 8. The supernatant water from the settling tank 8 is fed to a second RO device 15. The permeated water from the second RO device 15 is returned to the relay tank 2 by a return pipe 16. The concentrated water from the second RO device 15 is sent to a wastewater treatment facility (not shown).

[0027] The sludge that has settled and separated in the settling tank 8 is withdrawn by a pump 9. A portion of the withdrawn sludge is returned to the sludge reforming tank 12 via a sludge return line 11, and the remainder is discharged to an external sludge or wastewater treatment facility.

[0028] In the sludge reforming tank 12, a slaked lime dissolution / dispersion liquid (a liquid in which part of the slaked lime is dissolved and the rest is dispersed) supplied from slaked lime addition means 13 as a calcium-based compound addition means is mixed with the returned sludge. This mixed liquid (modified sludge) is supplied to the reaction tank 6. The reaction in this reaction tank 6 is preferably carried out within a predetermined pH range (for example, 6 to 11, particularly 6 to 8), and the amount of slaked lime supplied to the sludge reforming tank 12 is adjusted based on the pH detected by a pH meter 6a provided in the reaction tank 6 so as to achieve this pH range.

[0029] In this wastewater treatment device for exhaust gas treatment equipment, the concentrated water from the first RO device 4 is treated to remove fluorine in the coagulation sedimentation device 14 and then supplied to the second RO device 15. 3 AlF 6 ) and Mg-based materials (NaMgF 2 This suppresses the precipitation of compounds such as urea, which allows the second RO unit 15 to operate stably and increases the water recovery rate.

[0030] The coagulation-sedimentation device 14 used as fluorine removal equipment in the present invention does not need to remove fluorine to the discharge standard value; it is sufficient if it removes fluorine to the extent that cryolite and the like do not precipitate on the membrane surface of the second RO device 15.

[0031] The calcium-based compound is injected in excess from the addition means 13 and is converted into a Ca-based compound (CaF 2 , CaCO 3 , Ca(OH) 2 In order to prevent the precipitation of calcium compounds (Ca(OH), etc.), a hardness meter is installed at the outlet of the coagulation settling device 14, and the hardness of the water is measured so that the detected hardness value is equal to or less than the reference value. 2 or CaCl 2 It is desirable to control the amount of injection of

[0032] In this way, by suppressing the precipitation of compounds of fluorine with Al, Mg, etc. in the second RO unit 15, it is possible to maintain the flux (the amount of treated water under standard pressure and temperature conditions) of the second RO unit 15 more stably and higher than that of conventional facilities.

[0033] As a result, the water recovery rate of the entire factory is improved, and wastewater discharge volume can be controlled to below regulated values. The number of RO membranes can also be reduced, resulting in a reduction in the total costs, including the construction of recovery facilities and operational management such as membrane replacement and chemical cleaning.

[0034] As mentioned above, it is not necessary to treat fluorine at a high removal rate in the fluorine removal coagulation sedimentation unit 14. As for cryolite, an Al-based compound, by simply reducing the fluorine concentration in the raw water by 30%, the precipitation of cryolite is sufficiently suppressed even if the Al concentration in the concentrated water of the second RO unit 15 becomes 10 times higher than before. This can be explained by the solubility product.

[0035] That is, the molecular formula of cryolite is Na 3 ALF 6 Therefore, the allowable soluble concentration of Al is inversely proportional to the sixth power of the fluorine concentration.

[0036] For example, if the fluorine concentration of the abatement wastewater (raw water) is about 200 ppm, the fluorine is concentrated to about 4,000 ppm in the concentrated water of the second RO device 15. In this case, cryolite precipitates even when the Al concentration is about 0.1 ppm.

[0037] Conventionally, in order to prevent such precipitation of cryolite, it has been necessary to reduce the Al concentration in the pretreatment device 1 to the order of 0.01 ppm, but this is extremely difficult in terms of operational management.

[0038] Therefore, in the present invention, the fluorine in the first concentrated water from the first RO device 4 is removed by the coagulation sedimentation device 14 and the first concentrated water is supplied to the second RO device 15, thereby relaxing the allowable Al concentration more than ever before.

[0039] This makes it possible to prevent the precipitation of cryolite and the like in the second RO unit 15 even if the allowable concentration of Al in the raw water is a value that can be achieved through the operational management of the pretreatment unit 1 (about 0.1 to 0.5 ppm).

[0040] Although the coagulation and settling device 14 is a new piece of equipment, it is different from the previous batch-type fluorine treatment equipment in that it is a distributed treatment. 2 Chemical usage amount and CaF 2 This does not mean that the amount of sludge in the subject will increase.

[0041] The above embodiment is one example of the present invention, and the present invention may have other configurations. In the above embodiment, the coagulation sedimentation device 14 is based on a high density sludge method in which sludge is modified and recirculated, but the coagulation sedimentation device may be a device that does not modify or recirculate sludge. [Explanation of symbols]

[0042] 1 Pretreatment Equipment 2 Relay tank 3. Safety Filter 4 1st RO device 6. Reactor 7 Coagulation tank 8 Sedimentation tank 12 Sludge reforming tank 13. Means of adding calcium compounds 14 Coagulation and settling equipment 15 2nd RO device 16 Return piping

Claims

1. a first reverse osmosis membrane device that subjects fluorine-containing wastewater from an exhaust gas treatment facility to reverse osmosis and separates the wastewater into a first permeate and a first concentrated water; a coagulation and sedimentation device for adding a calcium-based compound and a coagulant to the first concentrated water to precipitate and separate calcium fluoride; a second reverse osmosis membrane device that performs reverse osmosis treatment on the separated water from the coagulation sedimentation device to separate the separated water into a second permeate and a second concentrated water; a return line for returning the second permeated water to a stage preceding the first reverse osmosis membrane device; An exhaust gas treatment facility wastewater treatment device having the above structure.

2. 2. The treatment device for wastewater from an exhaust gas treatment facility according to claim 1, wherein the coagulation and sedimentation device comprises a reaction tank, a coagulation tank, a sedimentation tank, a sludge return line for returning the sludge containing calcium fluoride separated in the sedimentation tank to the reaction tank via a sludge reforming tank, and a calcium-based compound adding means for adding a calcium-based compound to the sludge reforming tank.

3. 3. The apparatus for treating wastewater from an exhaust gas treatment facility according to claim 1, wherein the first permeate from said first reverse osmosis membrane device is recovered as water for a water scrubber of said exhaust gas treatment facility.

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