Fluorine-containing wastewater treatment device and method

Abstract

A treatment device for fluorine-containing waste water comprises: a first coagulation treatment unit for performing coagulation treatment on fluorine-containing waste water by using an inorganic coagulant and a calcium compound; the first precipitation treatment unit is used for precipitating and separating the coagulation reaction liquid from the first coagulation treatment unit; a second coagulation treatment unit for performing coagulation treatment by adding an inorganic coagulant to at least a portion of the treated water from the first precipitation treatment unit; the turbidity removal membrane device is used for carrying out membrane separation treatment on the coagulation reaction liquid from the second coagulation treatment unit; a reverse osmosis membrane device which is supplied with the membrane permeated water from the turbidity removal membrane device and separates the membrane permeated water into permeated water and concentrated water; a means for taking out permeated water from the reverse osmosis membrane device; the third coagulation treatment unit is used for performing coagulation treatment on the concentrated water from the reverse osmosis membrane device by using an inorganic coagulant and is separated from the first coagulation treatment unit; and a second precipitation treatment unit for precipitating and separating the coagulation reaction liquid from the third coagulation treatment unit.

Description

Technical Field

[0001] The present invention relates to a treatment device and method for fluorine-containing wastewater. In particular, the present invention relates to a device and method for treating and recovering fluorine-containing wastewater through coagulation treatment, membrane separation treatment, etc. Background Art

[0002] As a treatment device and method for fluorine-containing wastewater discharged from the manufacturing processes of liquid crystals or semiconductors, there are two-stage precipitation treatments including coagulation precipitation treatment using calcium salts and further coagulation precipitation treatment of the treated water using aluminum salts.

[0003] In Patent Documents 1 and 2, there are described methods and devices for further performing membrane separation treatment on the coagulation precipitation treated water of fluorine-containing wastewater.

[0004] In Patent Document 1, fluorine-containing wastewater is coagulated using calcium salts for solid-liquid separation, and the treated water is coagulated using iron salts for solid-liquid separation, and the treated water is subjected to reverse osmosis (RO) treatment.

[0005] In Patent Document 1, there is described a method as follows: A part of the sludge separated by solid-liquid separation is introduced into a Ca reaction tank, a Ca compound is added to modify (densify) the sludge, and it is returned / introduced into the coagulation reaction tank. This method is generally known as the high-density sludge method.

[0006] In Patent Document 2, after coagulation treatment of fluorine-containing wastewater using calcium salts, precipitation treatment is performed, the treated water is subjected to RO treatment, and the permeate is taken out as treated water. The concentrated water of the RO device is transferred to the coagulation tank. In the form of FIG. 2 in Patent Document 2, pipelines for two series of coagulation and precipitation treatments are provided, the precipitation treated water from one series is subjected to RO treatment to be separated into permeate and concentrated water, and the concentrated water is transferred to the coagulation tank of the other series.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 2014-213264

[0010] Patent Document 2: Japanese Patent Laid-Open No. 2018-143919 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] Since the coagulation sedimentation treated water of fluorine-containing wastewater is in a saturated state of calcium fluoride, if RO treatment is carried out, calcium fluoride scale will precipitate in a short time, blocking the RO membrane. In addition, the sedimentation treated water contains colloids or polymer coagulants derived from the coagulant, so the RO membrane is easily blocked by these substances.

[0013] The subject of the present invention is to provide a treatment device and method for fluorine-containing wastewater, which are devices and methods for treating fluorine-containing wastewater by coagulation sedimentation treatment and RO (reverse osmosis) treatment, etc., and can sufficiently inhibit the blockage of the RO membrane, and make the quality of the treated water good. In addition, the RO treated water can also be recycled and reused.

[0014] Technical means for solving the problem

[0015] The gist of the treatment device and method for fluorine-containing wastewater of the present invention is as follows.

[0016] [1] A treatment device for fluorine-containing wastewater, comprising:

[0017] A first coagulation treatment unit that coagulates fluorine-containing wastewater using an inorganic coagulant and a calcium compound; a first sedimentation treatment unit that separates and precipitates the coagulation reaction liquid from the first coagulation treatment unit;

[0018] A second coagulation treatment unit that adds an inorganic coagulant to at least a part of the treated water from the first sedimentation treatment unit for coagulation treatment;

[0019] A turbidity removal membrane device that performs membrane separation treatment on the coagulation reaction liquid from the second coagulation treatment unit;

[0020] A reverse osmosis membrane device that is supplied with the membrane permeate water of the turbidity removal membrane device and separates it into permeate water and concentrated water;

[0021] A unit for taking out the permeate water from the reverse osmosis membrane device;

[0022] A third coagulation treatment unit that coagulates the concentrated water from the reverse osmosis membrane device using an inorganic coagulant and is separately provided from the first coagulation treatment unit; and a second sedimentation treatment unit that separates and precipitates the coagulation reaction liquid from the third coagulation treatment unit.

[0023] [2] The treatment device for fluorine-containing water according to [1], which has a bypass unit for sending the treated water from the first sedimentation treatment unit to the third coagulation treatment unit when the second coagulation treatment unit, the turbidity removal membrane device and the reverse osmosis membrane device stop operating.

[0024] [3]The treatment device for fluorine-containing water according to [1] or [2], wherein a dilution water supply unit is provided on the primary side of the reverse osmosis membrane device.

[0025] [4]A method for treating fluorine-containing water, which uses the treatment device for fluorine-containing drainage water according to any one of [1] to [3] to treat fluorine-containing water.

[0026] Effects of the invention

[0027] In the treatment device and method for fluorine-containing drainage water of the present invention, an inorganic flocculant and a calcium compound are used to perform flocculation and precipitation treatment on the fluorine-containing drainage water. Then, after performing flocculation treatment with an inorganic flocculant, solid-liquid separation treatment is carried out for RO treatment, and RO permeate water is recovered. In addition, the RO concentrate water is further subjected to flocculation and precipitation treatment with an inorganic flocculant.

[0028] Since RO treatment is carried out after two-stage flocculation and solid-liquid separation treatment in the above manner, clogging of the RO membrane can be suppressed. The permeate water treated by RO can be recovered and reused.

[0029] Since the RO concentrate water is further subjected to flocculation and solid-liquid separation treatment (the third-stage flocculation and solid-liquid separation treatment), the fluorine concentration in the treated water is sufficiently low.

[0030] In an embodiment of the present invention, when the pipeline of the second-stage flocculation-solid-liquid separation treatment and the RO treatment is stopped, the flocculation-solid-liquid separation treatment water of the first stage is sent to the third-stage flocculation-solid-liquid separation treatment, whereby treated water with a low fluorine concentration can be produced. Description of the drawings

[0031] Figure 1 Figure 1 is a flowchart of the treatment device for fluorine-containing drainage water of the embodiment. Detailed implementation manners

[0032] Figure 1 is a flowchart showing an embodiment of the treatment device for fluorine-containing drainage water of the present invention.

[0033] The fluorine-containing drainage water to be treated in the present invention is preferably fluorine-containing drainage water discharged from the electronic industry fields such as electronic displays and semiconductors. The fluorine concentration in the fluorine-containing drainage water is usually 20 mg-F / L to 1000 mg-F / L, especially about 150 mg-F / L to 800 mg-F / L.

[0034] ​​Raw water (fluoride-containing wastewater), Fe salts such as FeCl3 and FeSO4, Al salts such as poly aluminum chloride (PAC) and aluminum sulfate, anionic polymer (organic polymer) flocculants, pH adjusters, and modified sludge that has been densified by reaction with a calcium compound and recycled from the first chemical reaction tank 3 are added to the first reaction-flocculation tank 1, and treatment is carried out at pH 8 to 11, thereby generating insoluble substances such as calcium fluoride.

[0035] As the acids and bases used as pH adjusters, those commonly used in ordinary water treatment can be used. For example, acids such as hydrochloric acid and sulfuric acid; bases such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide can be used.

[0036] Subsequently, the flocculated liquid from the first reaction-flocculation tank 1 is subjected to solid-liquid separation using the first sedimentation tank 2. The excess sludge in the separated sludge after solid-liquid separation is sent to the sludge treatment process, and a part of the separated sludge is transported to the first chemical reaction tank 3 and mixed with a calcium compound. The modified sludge that has been densified by the reaction of the sludge with the calcium compound is recycled to the first reaction-flocculation tank 1.

[0037] As the calcium compound, calcium hydroxide, calcium chloride, etc. can be used. The addition amount of the calcium compound is preferably 120% to 1500%, particularly about 130% to 280% of the reaction equivalent of the fluoride ions flowing into the first reaction-flocculation tank 1. However, in the case where substances that consume calcium such as phosphoric acid or sulfuric acid are contained in the raw water, it is preferable to consider the consumption caused by them.

[0038] The first solid-liquid separation water (supernatant) obtained by solid-liquid separation using the first sedimentation tank 2 is transported to the second reaction-flocculation tank 5 via the relay tank 4. The F concentration in the first solid-liquid separation water is preferably about 5 mg / L to 50 mg / L. The flow rate of the first solid-liquid separation water is preferably 30 m 3 / h to 500 m 3 / h or so.

[0039] Fe salts such as FeCl3 and FeSO4, Al salts such as PAC and aluminum sulfate, anionic polymer (organic polymer) flocculants, and pH adjusters are added to the second reaction-flocculation tank 5, and coagulation treatment is carried out by adjusting to pH 5 to 9.

[0040] After the condensate is de-turbidified using a turbidity removal membrane device 6 such as a microfiltration (MF) membrane or an ultrafiltration (UF) membrane, a phosphonic acid such as 2-phosphonobutane-1,2,4-tricarboxylic acid or a scale dispersant such as polyacrylic acid is added. Subsequently, RO treatment is performed using an RO device 7, and it is separated into permeate water and concentrated water. The recovery rate (permeate water / influent water × 100%) of the RO device 7 is preferably about 50% to 90%. The permeate water can be reused in the form of equipment water or raw water for producing ultrapure water. The addition amount of the scale dispersant to the turbidity removal treated water of the turbidity removal membrane device 6 is about 10 mg / L to 1000 mg / L.

[0041] The turbidity removal membrane device 6 includes a backwashing mechanism and performs backwashing intermittently. The backwash drainage is sent to the first reaction-coagulation tank 1.

[0042] The RO device 7 can be an RO device with a flushing mechanism based on dilution water. If it is an RO device with a flushing mechanism, the attachment of CaF2 scale can be suppressed by flushing.

[0043] The flushing is preferably carried out by introducing dilution water into the primary side of the RO membrane device for about 5 minutes to 60 minutes in such a way that the membrane surface flow velocity becomes about 0.001 m / s to 1 m / s. As the dilution water, it is preferably an unsaturated solution with a saturation index of less than zero for the scale species (here calcium fluoride), and it is the permeate water of the RO membrane device, but pure water, tap water, industrial water, etc. prepared separately can also be used. The pH of the dilution water is preferably set to 3.2 or less.

[0044] The flushing can be carried out at predetermined regular intervals, and it is preferably carried out at the time point when scale is generated in the RO membrane device.

[0045] The concentrated water of the RO device 7 is sent to the third reaction-coagulation tank 8, and Fe salts such as FeCl3 and FeSO4, Al salts such as PAC and aluminum sulfate, an anionic polymer (organic polymer) coagulant, a pH adjuster, modified sludge from the second chemical reaction tank 10, and calcium salts as needed are added to the third reaction-coagulation tank 8, and treatment is carried out at pH 8 to 11, thereby generating insoluble substances such as calcium fluoride.

[0046] Subsequently, the condensate from the third reaction-coagulation tank 8 is subjected to solid-liquid separation using the second sedimentation tank 9. The excess sludge in the separated sludge after solid-liquid separation is sent to the sludge treatment process, and a part of the separated sludge is transported to the second chemical reaction tank 10 and mixed with a pH adjuster such as NaOH. By mixing with NaOH in the second chemical reaction tank 10, the sludge reacts with NaOH to form densified modified sludge. The modified sludge is recycled to the third reaction-coagulation tank 8.

[0047] The supernatant obtained by solid-liquid separation using the second sedimentation tank 9 is sent to the discharge process. In the discharge process, it is adjusted to a neutral pH using a pH adjustment tank (not shown) and discharged into a river or the like via a monitoring tank (not shown).

[0048] In the above-described embodiment, a bypass pipeline 20 is provided, and the bypass pipeline 20 is used to transfer the water in the relay tank 4 to the third reaction-coagulation tank 8 when the second reaction-coagulation tank 5, the turbidity removal membrane device 6, and the RO device 7 are not operating. When the second reaction-coagulation tank 5, the turbidity removal membrane device 6, and the RO device 7 are not operating, the linear velocity (LV) of the water flow in the second sedimentation tank 9 is preferably about 0.5 m / h to 4 m / h.

[0049] Based on the fluorine-containing wastewater treatment apparatus configured as described above and the treatment method using the apparatus, the fluorine-containing wastewater is treated by the first coagulation sedimentation treatment using the first reaction-coagulation tank 1, the first sedimentation tank 2, and the first chemical reaction tank 3. Then, the supernatant from the first sedimentation tank 2 is coagulated using the second reaction-coagulation tank 5, the coagulated liquid is treated using the turbidity removal membrane device 6, and RO treatment is performed using the RO device 7. Therefore, the F concentration of the treated water (permeate water) from the RO device 7 becomes sufficiently low. In addition, since the influent water of the RO device 7 is water that has undergone two-stage coagulation treatment and solid-liquid separation treatment, clogging of the RO membrane can be suppressed. In particular, by configuring the RO device 7 as a device with a flushing mechanism or adding a scale inhibitor to the RO influent water, the scale risk of the RO device 7 can be further reduced.

[0050] In addition, in the above-described embodiment, since the influent water of the RO device 7 is water obtained by removing turbidity from the coagulated liquid of the second reaction-coagulation tank 5 using the turbidity removal membrane device 6, clogging of the membrane caused by residual colloid components or polymers derived from the polymer coagulant can be suppressed.

[0051] In the above-described embodiment, the RO concentrated water can be treated using the third reaction-coagulation tank 8, the second sedimentation tank 9, and the second chemical reaction tank 10 to obtain the discharged water with a sufficiently reduced F concentration.

[0052] In addition, in the above-described embodiment, when the second reaction-coagulation tank 5, the turbidity removal membrane device 6, and the RO device 7 are stopped, the designed LV of the second sedimentation tank 9 is set to 0.5 m / h to 4 m / h, whereby the F concentration of the supernatant from the second sedimentation tank 9 can be made sufficiently low.

[0053] In the present invention, a plurality of RO devices 7 can be arranged in parallel. In such a case, during the period of producing desalted water by introducing the water to be treated (the de-turbidified water of the de-turbidification membrane device 6) into a part of the RO devices, dilution water is introduced from the dilution water tank into other RO devices for cleaning, and the cleaning drainage water is returned to the dilution water tank.

[0054] When the water quality of the dilution water in the dilution water tank becomes on the side of a salt concentration higher than the specified value, a part of the dilution water is discharged and made to converge with the raw water tank or the relay tank, and at the same time, new dilution water is replenished. As the dilution water, the permeated water of the RO device can be used.

[0055] In the above-described embodiment, both the first reaction-coagulation tank 1 and the third reaction-coagulation tank 8 are coagulation tanks based on the high density sludge (HDS) method, but either one or both of the reaction-coagulation tanks can be a simple coagulation tank that does not return the sludge from the sedimentation tank. When the first reaction-coagulation tank 1 is a simple coagulation tank, a calcium compound such as calcium hydroxide can be added to the first reaction-coagulation tank 1.

[0056] The present invention has been described in detail using a specific form, but those skilled in the art clearly understand that various changes can be made within the scope of achieving the effects of the invention.

[0057] This application is based on Japanese Patent Application 2023-050168 filed on March 27, 2023, and the entire content thereof is incorporated herein by reference.

[0058] Explanation of reference numerals

[0059] 1: First reaction-coagulation tank

[0060] 2: First sedimentation tank

[0061] 3: First chemical reaction tank

[0062] 5: Second reaction-coagulation tank

[0063] 6: De-turbidification membrane device

[0064] 7: RO device

[0065] 8: Third reaction-coagulation tank

[0066] 9: Second sedimentation tank

[0067] 10: Second chemical reaction tank

[0068] 20: Bypass pipeline

Claims

1. A treatment device for fluorine-containing water drainage, comprising: A first coagulation treatment unit that coagulates the fluorine-containing drainage using an inorganic coagulant and a calcium compound; a first precipitation treatment unit that precipitates and separates the coagulation reaction liquid from the first coagulation treatment unit; A second coagulation treatment unit that adds an inorganic coagulant to at least a part of the treated water from the first precipitation treatment unit for coagulation treatment; A turbidity removal membrane device that performs membrane separation treatment on the coagulation reaction liquid from the second coagulation treatment unit; A reverse osmosis membrane device that is supplied with the membrane permeate water from the turbidity removal membrane device and separates it into permeate water and concentrated water; A unit that extracts the permeate water from the reverse osmosis membrane device; The third coagulation treatment unit that coagulates the concentrated water from the reverse osmosis membrane device using an inorganic coagulant and is separately provided from the first coagulation treatment unit; and a second precipitation treatment unit that precipitates and separates the coagulation reaction liquid from the third coagulation treatment unit.

2. The treatment device for fluorine-containing water according to claim 1, which has a bypass unit for sending the treated water from the first precipitation treatment unit to the third coagulation treatment unit when the second coagulation treatment unit, the turbidity removal membrane device, and the reverse osmosis membrane device are stopped.

3. The treatment device for fluorine-containing water according to claim 1 or 2, wherein, A dilution water supply unit is provided on the primary side of the reverse osmosis membrane device.

4. A treatment method for fluorine-containing water that treats fluorine-containing water using the treatment device for fluorine-containing drainage according to claim 1 or 2.

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