JP2009207953A - Wastewater treatment apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve effective utilization of calcium in wastewater treatment where fluorine is removed by adding calcium to wastewater containing fluorine to produce calcium fluoride. <P>SOLUTION: A wastewater treatment apparatus 10 is provided with: a chemical tank 15 storing calcium added to water 12 to be treated containing fluorine to produce calcium fluoride; a filtration membrane 13 separating the calcium fluoride from the water 12 to be treated; and an RO filtration device 14 removing fluorine ions from the water 12 to be treated from which the calcium fluoride has been separated. The water 12 to be treated in which calcium unreacted with fluorine is concentrated by the RO filtration device 14 is returned upstream of the filtration membrane 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wastewater treatment apparatus and a wastewater treatment method for removing fluorine from wastewater.

  At present, reducing industrial waste and separating and reusing industrial waste are important themes from an ecological point of view and are urgent corporate issues. Among the industrial wastes, there are various fluids containing the objects to be removed.

  These are expressed in terms of sewage, waste liquid, drainage, etc., but hereinafter, a substance in which a substance to be removed is contained in a fluid such as water or chemicals will be referred to as drainage.

  A large amount of wastewater is generated during the process of manufacturing the semiconductor device. Almost all of the fluorine used in semiconductor factories is discharged as wastewater that is difficult to reuse.

For example, in a dry (plasma) etching apparatus or a plasma CVD apparatus, a wafer processing or carbon tetrafluoride in cleaning the apparatus _(CF 4), hexafluoroethane _{(C 2 F} 6), perfluorocyclobutane Rob Tan _{(C 4} In many cases, a fluorine-based gas such as F ₈ ) is used. Most of these gases are discharged out of the chamber as CF _4. However, since these are substances having a global warming promoting effect (Perfluorocompounds (PFCs) gas), detoxification treatment is required. In this detoxification treatment, fluorine is absorbed by water and dilute hydrofluoric acid wastewater (waste liquid) is discharged. In addition, in wet etching equipment that uses fluorine-based materials (for example, hydrofluoric acid), concentrated hydrofluoric acid wastewater (waste liquid), which is a waste chemical after wafer processing, and dilute hydrofluoric acid wastewater, which is pure water rinse wastewater (Waste liquid) is discharged. Hereinafter, hydrofluoric acid will be referred to as hydrofluoric acid.

  It is known that wastewater with high fluorine concentration will flow out into nature and upset the balance of the ecosystem. Therefore, it is very important in industry to remove fluorine from waste water. For example, the standard value of the discharge conditions for wastewater containing fluorine is determined by the Water Pollution Control Law and local ordinances. Specifically, the concentration of fluorine contained in the waste water must be 8 mg / L or less. Furthermore, there is a possibility that the total amount of fluorine discharged may be regulated.

  On the other hand, the fluorine removed from the waste water can be reused in the semiconductor processing apparatus by using hydrofluoric acid or the like. As an example of the removal method, fluorine can be removed from the waste water as calcium fluoride by reacting wastewater containing fluorine (waste liquid) with a calcium compound to produce calcium fluoride.

  Furthermore, it is also known to perform advanced wastewater treatment by removing the fluorine content contained in the wastewater as calcium fluoride and further performing filtration treatment.

In the following Patent Document 1, a method of treating water containing calcium and fluorine using a cation exchange tower and an RO membrane separation device is disclosed. In particular, referring to FIG. 1 of the publication and the explanation thereof, after adjusting the pH of Ca / F-containing water in the PH adjustment tank 1, Ca is removed by the cation exchange tower 2, and then the RO membrane separation device 3 To remove F. By doing in this way, since Ca in water is removed beforehand by the cation exchange tower 2, blockage of the RO membrane by CaF ₂ is prevented.

Patent Document 2 below discloses a method in which calcium carbonate or the like is added to water to be treated to produce hardly soluble fluoroapatite, and the fluoroapatite is subjected to ion filtration after membrane filtration. Specifically, referring to FIG. 1 and the explanation thereof, first, raw water in which calcium ion-containing water and fluorine ion-containing water are mixed is stored in the raw water tank 1. And fluoroapatite is produced | generated by adding calcium carbonate and phosphoric acid to this raw | natural water. Further, the produced fluoroapatite is removed by the MF membrane filtration device 2, and the treated water is further purified by the RO membrane filtration device 4.
Japanese Patent Laid-Open No. 10-244259 JP 2001-149950 A

  However, the techniques described in Patent Document 1 and Patent Document 2 described above have the following problems.

  That is, in the technique described in Patent Document 1, since a cation exchange tower for removing the Ca component is used, there is a problem that the processing equipment becomes large and the processing operation becomes complicated.

  In addition, in the technique described in Patent Document 2, it is necessary to adjust the pH of the treated water and to add a special additive in order to generate fluoroapatite, which increases the processing cost. was there.

  The waste water treatment apparatus of the present invention includes an adding means for adding calcium to water to be treated containing fluorine to generate calcium fluoride, a first separating means for separating the calcium fluoride from the water to be treated, And second separation means for removing fluorine ions from the treated water from which calcium fluoride has been separated, and the treated water in which the calcium component that has not reacted with the fluorine is concentrated by the second separating means. Is returned before the first separation means.

  In the wastewater treatment method of the present invention, the step of generating calcium fluoride by adding calcium to the water to be treated containing fluorine, and the step of separating the calcium fluoride from the water to be treated by the first separation means. And removing fluorine ions from the water to be treated from which the calcium fluoride has been separated by the second separation means, and the calcium component that has not reacted with the fluorine is concentrated by the second separation means. In addition, the treated water is returned to a stage preceding the first separation means.

  According to the present invention, after the fluorine content is separated in the calcium fluoride state by the first separation means, the fluorine and the unreacted calcium content are concentrated by the second separation means, and returned to the previous stage rather than the first separation means. ing. Therefore, since the calcium content that has not contributed to the generation of calcium fluoride can be reused, the total amount of calcium required to remove the fluorine content is reduced, and the processing cost is reduced accordingly.

  Furthermore, since the fluorine ions are removed by the second separation means after the calcium fluoride is removed by the first separation means, early blockage of the second separation means is suppressed.

  As one embodiment of the present invention, a wastewater treatment apparatus for treating wastewater containing hydrofluoric acid (hydrogen fluoride (HF) aqueous solution) and a hydrofluoric acid wastewater treatment method using the same will be described. Hereinafter, hydrofluoric acid is referred to as hydrofluoric acid.

  With reference to FIG. 1, the structure of the waste water treatment apparatus 10 is demonstrated. The waste water treatment apparatus 10 of the present embodiment includes a first treatment tank 11A (addition means) in which calcium fluoride is generated by adding calcium to treated water 12 containing fluorine, and an immersed filtration membrane A second treatment tank 11B in which calcium fluoride is filtered by 13 (first separation means), and an RO filtration device 14 (second separation means) for further filtering the treated water 12 filtered by the filtration membrane 13; The sixth treatment path P6 mainly returns the treated water 12 concentrated in the RO filtration device 14 to the first treatment tank 11A.

  The first treatment tank 11 </ b> A is a tank in which treated water 12 that is wastewater containing fluorine is stored, and calcium fluoride is generated by adding calcium to the treated water 12.

  In this Embodiment, the to-be-processed water 12 is the waste_water | drain containing a fluorine content. This waste water is discharged from a semiconductor processing factory, and is discharged by, for example, an etching process of a semiconductor, glass, metal or the like, a wafer processing process such as formation of a CVD film, or cleaning of a semiconductor processing apparatus.

For example, in a dry (plasma) etching apparatus or a plasma CVD apparatus, a fluorine-based gas such as CF ₄ , C ₂ F ₆ , or C ₄ F ₈ is often used. These gases are also used when cleaning the inside of the chamber after wafer processing. Most of these gases are discharged out of the chamber as CF _4. However, since these are substances having a global warming promoting effect (Perfluorocompounds (PFCs) gas), detoxification treatment is required. Fluorine burned and decomposed in this detoxification treatment is absorbed by water, and dilute hydrofluoric acid wastewater is discharged. Also, wet etching equipment uses hydrofluoric acid to improve the corrosiveness during etching, so concentrated hydrofluoric acid wastewater that is a waste chemical after wafer processing and dilute hydrogen fluoride that is drainage of pure water rinse Acid wastewater is discharged.

In the first treatment tank 11A, hydrogen fluoride (HF) contained in the water to be treated 12 is dissociated by 99.9% or more into hydrogen ions (H ⁺ ) and fluorine ions (F ⁻ ) (the following formula A). . Moreover, in order to promote this dissociation, the to-be-processed water 12 may be stirred with stirring means, such as a propeller, in the inside of the first treatment tank 11A.

HF → H ^{+ +} F ^- (formula A)
The first path P1 is a path through which the treated water 12 discharged from the environment described above is supplied to the first treatment tank 11A. For example, treated water 12 containing fluorine ions (F ⁻ ) is introduced into the first treatment tank 11A via the first path P1. As an example, water to be treated having a fluorine ion concentration of 100 mg / L is supplied from the first path P1 at 10 t / day. Here, the pH of water to be treated containing hydrogen fluoride is, for example, about PH 3 to 4, and is very strong acidic. Therefore, the pH of the water to be treated 12 may be between 7 and 9 by adding NaOH as an alkaline agent.

The chemical tank 15 is a tank in which an aqueous solution of calcium is stored in order to fix the fluorine contained in the water 12 to be treated. As calcium used, calcium chloride (CaCl ₂ ) or calcium hydroxide (Ca (OH) ₂ ) is employed. Here, considering the low cost and the high solubility product, calcium chloride is preferred as the calcium component used. As an example, the chemical tank 15 stores an aqueous solution containing 35% by weight of calcium chloride.

  The aqueous solution stored in the chemical tank 15 is introduced into the first treatment tank 11A via the second path P2 (addition means).

  In the first treatment tank 11A, the fluorine ions contained in the water to be treated 12 introduced from the first path P1 and the calcium content introduced from the second path P2 combine to generate calcium fluoride. Specifically, the fluorine content contained in the water to be treated 12 is fixed as calcium fluoride by the reaction shown in the following formula (B).

2F ⁻ + CaCl ₂ → CaF ₂ + 2Cl ⁻ (Formula B)
Referring to the above formula (B), in order to convert the fluorine ions contained in the water 12 to be treated into calcium fluoride, theoretically, calcium having a mole number that is ½ of the fluorine ions is required. For example, as described above, in order to treat the water to be treated having a fluoride ion concentration of 100 mg / L for 10 t / day, a calcium chloride aqueous solution having a concentration of 35% by weight is required to be 5.5 L / day. However, the total amount of calcium added does not combine with fluorine ions, and a portion of the input calcium does not combine with fluorine ions. Therefore, in the present embodiment, a larger amount of calcium chloride than the theoretically required amount is charged into the water to be treated 12. Specifically, an amount of calcium chloride more than twice the amount theoretically required to immobilize the total amount of fluorine contained in the water to be treated 12 is passed through the second path P2. It has thrown into 1 process tank 11A. By doing in this way, the density | concentration of the fluorine ion contained in the to-be-processed water 12 discharged | emitted from 11 A of 1st process tanks can be 4 mg / L or less, for example. This fluorine ion concentration satisfies the general discharge standard.

  In this embodiment, since a larger amount of calcium fluoride than the theoretical value is added to the water to be treated, the treatment cost may increase. From this, in order to reduce processing cost, the to-be-processed water concentrated by the RO filtration apparatus 14 is returned to the 1st processing tank 11A, and the calcium content is reused. This matter will be described later.

  As described above, the water to be treated 12 in which fluoride ions are fixed as calcium fluoride is introduced into the second treatment tank 11B via the third path P3.

  In the second treatment tank 11B, the calcium fluoride is separated from the treated water 12 by filtering the treated water 12 through the filtration membrane 13 (first separation means). Here, as the filtration membrane 13, a filtration mechanism capable of performing filtration in a fluid can be generally employed. Furthermore, you may isolate | separate from to-be-processed water by precipitating calcium fluoride. In the present embodiment, solid-liquid separation between calcium fluoride and the water to be treated 12 is performed by performing filtration using a self-forming film formed on the surface of the filtration film 13. Details of the self-forming film will be described later.

The treated water 12 filtered by the filtration membrane 13 immersed in the second treatment tank 11B is in a state in which calcium fluoride is almost separated and removed, and the calcium content and unreacted fluorine ions (F ⁻ ) are removed. For example, it contains about 4 mg / L. Furthermore, the fluorine content and unreacted calcium ions (Ca ²⁺ ) are also contained in the filtered water 12 to be treated. Fluorine ions and calcium ions remaining in the water to be treated 12 are removed by the RO filtration device 14 in the next stage.

  The self-forming film described above may be a self-forming film made of an object to be removed containing calcium fluoride generated in the water 12 to be treated. That is, the water to be treated 12 is filtered by the removal object adsorbed on the filtration surface of the filtration membrane 13. Further, when the calcium fluoride is recovered, the self-forming film is also peeled off from the filtration film 13 and recovered.

  The air diffuser 18 has a function of supplying bubbles to the filtration membrane 13 from below in the treated water 12. Specifically, gas is supplied to the air diffuser 18 from a pump (not shown) provided outside to generate bubbles. Bubbles generated from the air diffuser 18 move upward along the filtration surface of the filtration membrane 13. As described above, by generating bubbles from the air diffuser 18, the thickness of the self-forming film formed on the surface of the filtration film 13 can be made constant or less. From this, it becomes possible to filter the water 12 to be treated while suppressing the blockage of the self-forming film and securing a certain amount of flux.

  As the gas generated from the air diffuser 18, an inert gas such as helium, neon, argon, or nitrogen can be employed. When air is supplied from the air diffuser 18 to the water 12 to be treated, carbon dioxide gas contained in the air reacts with fluoride ions contained in the water 12 to be treated, which may reduce the concentration of calcium fluoride. is there. By adopting an inert gas as the gas supplied from the air diffuser 18, the fear can be eliminated.

  The fourth path P4 is a path through which filtered water filtered by the filtration membrane 13 passes. A storage tank 15C is provided in the branched path in the middle of the fourth path P4.

  In the storage tank 15C, a part of the filtrate water filtered by the filtration membrane 13 is stored. The position of the storage tank 15C is set above the liquid level of the water 12 to be treated stored in the separation tank 11C. The filtered water or tap water stored in the storage tank 15C is used by causing the fourth path P4 to flow backward when the self-forming film formed on the surface of the filtration film 13 is peeled off.

  The seventh path P7 is a path for transporting the object to be removed containing precipitated calcium fluoride from the second treatment tank 11B to the filter press 17. Specifically, the object to be removed deposited on the surface of the filtration membrane 13 and the object to be removed deposited at the lower part of the second treatment tank 11 </ b> B are transported to the filter press 17. The treated water 12 to be transported contains calcium fluoride with high purity. Moreover, when the neutralization process of the to-be-processed water 12 is performed, the neutralization salt is also contained in the to-be-processed water 12 transferred.

  The object to be removed containing calcium fluoride is supplied to the filter press 17 through the seventh path P7, and the water content of the object to be removed is reduced by performing the dehydration process. The water content of the object to be removed that has been dehydrated by the filter press 17 is, for example, about 50% by weight. Further, when the object to be removed is dried, a block (solid matter) having a calcium fluoride purity of about 85% by weight is obtained. Calcium fluoride contained in the object to be removed with high purity is reused as a fluorine source.

  The eighth path P8 is a path for injecting water into the filter press 17 to wash the neutralized salt contained in the object to be removed housed in the filter press 17. For example, about 15% by weight of neutralized salt (NaCl) is contained in the object to be removed in the water to be treated whose pH has been adjusted. By injecting water into the filter press 17 from the eighth path P8, most of the neutralized salt is discharged from the filter press 17 to the outside. Further, calcium fluoride having a size larger than that of the neutralized salt remains in the filter press 17. That is, by injecting water into the filter press 17, the purity of calcium fluoride contained in the object to be removed stored in the filter press 17 can be improved.

  In the receiving tank 19, water injected into the filter press 17 is temporarily stored. The treated water stored in the receiving tank 19 is returned to the second processing tank 11B through the ninth path P9 and filtered.

  Here, the first processing tank 11A and the second processing tank 11B described above may be the same processing tank. This makes it possible to fix fluoride ions and separate the solid and liquid in the same tank, simplify the configuration of the entire facility and reduce the size. Furthermore, since the number of tanks is reduced, initial cost and running cost are also reduced.

  The pump 20 has been refurbished in the middle of the fourth path P4, and filtration by the filtration membrane 13 is performed by the suction pressure generated by the pump 20, and the RO filtration device 14 (the first filter is generated by the applied pressure generated by the pump 20). The treated water 12 is filtered by the two separation means. In this way, by using the pump 20 together for the filtration of the filtration membrane 13 and the RO filtration device 14, the number of pumps required is reduced, so that the cost required for the facility is reduced.

  The RO filtration device 14 is a device that filters a fluid using a RO (Reverse Osmosis Membrane) membrane. In the present embodiment, the RO filtration device 14 has a function of further filtering and purifying the water to be treated 12 filtered by the filtration membrane 13. Specifically, the RO filtration device 14 is composed of a filtration membrane having pores with a diameter of several nanometers, and can separate impurities such as fluorine ions and calcium ions from the water to be treated 12. Specifically, by treating the treated water 12 containing 4 mg / L of fluorine ions with the RO filtration device 14, the concentration of the treated water 12 can be reduced to 1 mg / L. In the RO filtration device 14, calcium ions and chloride ions are removed from the water to be treated 12 in addition to fluorine ions. Furthermore, instead of the RO filtration device 14, a filtration device provided with an NF (Nanofiltration Membrane) membrane may be employed.

  The treated water 12 filtered by the RO filtration device 14 is discharged out of the system of the wastewater treatment device 10 via the fifth path P5. The treated water 12 released through the fifth path P5 is in a state in which impurities such as fluorine ions are highly removed, and can be used as cleaning water in the semiconductor manufacturing process. Furthermore, since the concentration of the fluorine ions contained is extremely low, it can be directly discharged into the natural world such as a river.

  On the other hand, the treated water 12 remaining in the RO filtration device 14 is in a state where impurities such as fluorine ions, calcium ions, chloride ions are concentrated. In the present embodiment, the concentrated water 12 to be treated is returned to the first treatment tank 11A via the sixth path P6. This makes it possible to reuse fluorine ions and unreacted calcium ions as calcium components for producing calcium fluoride. As a result, it is possible to increase the concentration of calcium ions in the first treatment tank 11A while reducing the amount of consumed calcium chloride.

  Here, in the sixth path P6, which is a path through which the treated water is returned from the RO filtration device 14 to the first treatment tank 11A, the concentration of chloride ions is measured by measuring the conductivity of the treated water. A conductivity meter 32 is interposed. Here, as a means for measuring the concentration of chloride ions, a chloride ion concentration meter can be adopted in addition to the conductivity meter 32, but the conductivity meter 32 that can be used in-line is more suitable. Preferred as a means.

  When the wastewater treatment apparatus 10 having the above-described configuration is continuously operated, calcium ions contained in the added calcium chloride are combined with fluorine ions in the water to be treated and consumed for the production of calcium fluoride. On the other hand, chloride ions separated from calcium chloride do not contribute to the formation of calcium fluoride and remain in the water to be treated. For this reason, the concentration of chloride ions contained in the water to be treated becomes very high with the progress of the waste water treatment, which may impede the filtration treatment by the RO filtration device 14. Therefore, when the concentration of chloride ions measured by the measuring means provided in the path through which the water to be treated is circulated (for example, the sixth path P6) is a certain level or more, the circulating water to be treated is replaced. good.

  Here, the means for measuring the concentration of chloride ions can be interposed in a place other than the sixth path P6 as long as it is a path through which the water to be treated is circulated. It can also be prepared on the way. However, for example, if the conductivity meter 32 is interposed in the middle of the third path P3, the water to be treated passing through the third path P3 contains a large amount of suspended solids (SS). 32 makes it difficult to obtain the chloride ion concentration with high accuracy. On the other hand, in the sixth path P6, the water to be treated 12 from which SS or the like has been removed by the RO filtration device 14 passes, so that the concentration of chloride ions can be obtained with high accuracy. Furthermore, since the water to be treated that passes through the sixth path P6 contains chloride ions at a high concentration, the value of the detected chloride ions is less affected by the sensitivity of the sensor (conductivity meter 32), The concentration of chloride ions can be obtained with high accuracy.

  The eleventh path P11 has one end communicating in the middle of the fourth path P4 and the other end communicating in the middle of the sixth path P6. When the water to be treated passes through the eleventh path P11, the water to be treated filtered by the filtration membrane 13 is not supplied to the RO filtration device 14 but returned to the first treatment tank 11A and circulated. The eleventh path P11 is provided with a turbidimeter 30 for measuring the turbidity of the water to be treated that has passed through the filtration membrane 13. And if the turbidity of the to-be-processed water detected by the turbidimeter 30 is above a certain level (if the amount of to-be-removed substance contained in the to-be-processed water is large), the to-be-processed water will be supplied to the RO filtration apparatus 14. Instead, it is returned to the first processing tank 11A via the eleventh path P11. On the other hand, if the turbidity of the water to be treated detected by the turbidimeter 30 is below a certain level, the water to be treated is supplied to the RO filtration device 14. By doing in this way, it prevents that the to-be-processed water containing to-be-removed things, such as a large amount of calcium fluoride, approachs into RO filtration device 14, and the filter membrane of RO filtration device 14 is clogged early. Is done. Here, instead of the turbidimeter 30, an optical sensor, a conductivity meter, or the like that can detect the quality of the water to be treated can also be employed. However, there is SDI (Silt Density Index) as an index indicating the turbidity of water to be treated introduced into the RO filtration device 14, and the output of the turbidimeter 30 is easily correlated with SDI. Therefore, from this viewpoint, the turbidimeter 30 is suitable as a means for detecting the turbidity of the water to be treated.

  The twelfth path P12 has one end connected to the middle of the fifth path P5 and the other end connected to the storage tank 15C. A portion of the water to be treated filtered by the RO filtration device 14 is transferred to the storage tank 15C through the twelfth path P12 and stored as filtered water 16. The filtered water 16 is flowed back to the filtration membrane 13 and used to peel the self-forming membrane constituting the filtration membrane 13. Therefore, it is necessary to prepare pure water with low turbidity as the filtered water 16, and the tap water is stored in the storage tank 15C during the first period in which the waste water treatment apparatus 10 is operated. And after the steady driving | operation with which filtration by the filtration membrane 13 and the RO filtration apparatus 14 is started, a part of to-be-processed water filtered by the RO filtration apparatus 14 is stored in the storage tank 15C.

  In addition, the head of the filtered water 16 stored in the storage tank 15C is higher than the head of the treated water 12 stored in the second treatment tank 11B. Therefore, when the self-forming film formed on the surface of the filtration membrane 13 is peeled off, it is stored in the storage tank 15C using the hydraulic head difference of the fluid stored in both tanks without using a driving force such as a pump. The filtered water 16 can be made to flow backward to the filtration membrane 13. Therefore, power such as a pump is not required for peeling the self-forming film, and the running cost of the processing apparatus is reduced.

  The tenth path P <b> 10 has one end connected to the fourth path P <b> 4 upstream of the pump 20 and the other end connected to the fourth path P <b> 4 subsequent to the pump 20. That is, the tenth route P10 is a bypass route of the fourth route P4. An adjustment valve 36 is provided in the tenth path P10, and the adjustment valve 36 is adjusted according to the output of the pressure gauge 34 that detects the pressure inside the fourth path P4. As a result, the suction pressure applied to the filtration membrane 13 by the pump 20 and the applied pressure applied to the RO filtration device 14 are adjusted to predetermined values. In the present embodiment, when the calcium component charged from the chemical tank 15 is combined with fluorine ions to be calcium fluoride, the first treatment tank 11A → the second treatment tank 11B → the RO filtration device 14 → It is circulated in the order of the first treatment tank 11A. Therefore, almost the entire amount of calcium added can be used for the production of calcium fluoride.

  Furthermore, in this Embodiment, the to-be-processed water 12 from which the calcium fluoride was removed by the filter membrane 13 is further filtered by the RO filtration apparatus 14. Therefore, since there is no possibility that the pores of the fine filtration membrane of the RO filtration device 14 are clogged with calcium fluoride, the RO filtration device 14 can be used continuously for a long period of time.

  With reference to FIG. 2, the detail of the above-mentioned RO filtration apparatus 14 is demonstrated. A plurality of the RO filtration devices 14 are arranged in series with respect to the path through which the water to be treated 12 is treated. Specifically, from the first RO filtration device 14A, the second RO filtration device 14B, and the third RO filtration device 14C. The RO filtration device 14 is configured. Each RO filtration device is configured to include an RO filtration membrane 28 inside. Further, here, filtration by the first RO filtration device 14A, the second RO filtration device 14B, and the third RO filtration device 14C is performed by applying a pressurizing force by the pump 20.

  The first RO filtration device 14A is provided in the foremost stage, and the treated water 12 from which calcium fluoride has been removed by being filtered by the filtration membrane 13 (see FIG. 1) is introduced into the first RO filtration device 14A. The The first RO filtration device 14A is filtered by the pressure applied by the pump 20, and the treated water that has passed through the RO filtration membrane 28 is free from impurities such as fluorine ions and calcium ions in the fifth path. Released to the outside via P5. On the other hand, the treated water that does not pass through the RO filtration membrane 28 of the first RO filtration device 14A is transported to the second RO filtration device 14B in a state where impurities such as fluorine ions and calcium ions are concentrated. In the first RO filtration device 14A, for example, 55% of the introduced water to be treated is filtered by the RO filtration membrane 28, and the remaining 45% of the water to be treated is transported to the second RO filtration device 14B.

  In the 2nd RO filtration apparatus 14B, the to-be-processed water is filtered by RO filtration membrane similarly to 1st RO filtration apparatus 14A. Again, the treated water that has passed through the RO filtration membrane is taken out from the fifth path P5. On the other hand, the water to be treated that has been concentrated without passing through the RO filtration membrane is transported to the third RO filtration device 14C in a state where fluorine ions and calcium ions are further concentrated. Here, the amount of treated water that passes through the RO filtration membrane of the second RO filtration device 14B and is discharged to the outside is about 25% of the treated water that flows into the RO filtration device 14. Then, about 20% of the water to be treated is introduced into the third RO filtration device 14C in a state of being further concentrated without being filtered by the second RO filtration device 14B.

  In the third RO filtration device 14C, the water to be treated is further filtered in the same manner as the first RO filtration device 14A and the like described above. Accordingly, the treated water that has passed through the RO filtration membrane of the third RO filtration device 14C is discharged to the outside, and the treated water that has not passed through the RO filtration membrane is further concentrated and then the first treatment via the sixth path P6. It is returned to the tank 11A (see FIG. 1). As an example, the amount of water to be treated that passes through the RO filtration membrane of the third RO filtration device 14 </ b> C is about 11% with respect to the total amount of water to be treated introduced into the RO filtration device 14. And about 9% of to-be-processed water does not permeate | transmit the RO filtration membrane of the 3rd RO filtration apparatus 14C, and the 1st treatment tank 11A (refer FIG. 1) in the state by which the density | concentration of calcium ion was concentrated about 10 times. ).

  In the present embodiment, as described above, a plurality of RO filtration devices 14 are arranged in series with respect to the path of the water to be treated, thereby preventing clogging of individual RO filtration devices and performing advanced filtration treatment. Can do. Specifically, for example, by increasing the permeated water ratio, it is possible to filter a large amount of water to be treated using one RO filtration device. However, in this case, sufficient filtration with the RO membrane is not performed, and the conductivity increases and the removal rate decreases. Furthermore, problems such as a shortened life of the RO membrane and frequent cleaning of the RO membrane occur.

  From this, in this invention, as shown in FIG. 2, RO filtration apparatus is arrange | positioned in three steps in series. Thus, for example, even if the permeated water ratio of each RO filtration device is 55%, filtered water is taken out from each RO filtration device, so that the water recovery rate of the entire device can be increased to about 90%. Furthermore, since the water recovery rate becomes high, the water to be treated having a very high concentration of calcium ions contained therein can be obtained from the third RO filtration device 14C. Accordingly, since the amount of water to be treated returned for reuse is reduced, the efficiency of the first separation means (filtration membrane 13) is increased, and the cost can be reduced accordingly.

  Furthermore, in one RO filtration device, the proportion of fluorine ions captured is about 80%. By arranging the RO filtration devices in three stages in this way, the proportion of fluorine ions supplemented is a theoretical value. It can be raised to about 99%.

  Moreover, although the 1st RO filtration apparatus 14A etc. are provided in 3 steps | paragraphs in series with respect to the path | route of a treated water, the number of RO filtration apparatuses provided may be 2 steps | paragraphs or 4 steps | paragraphs or more.

  Here, you may provide the monitoring means which monitors the density | concentration of the calcium ion contained in the to-be-processed water 12 stored in 11 A of 1st process tanks. That is, an aqueous solution of calcium chloride is supplied from the chemical tank 15 via the second path P2 only when the concentration of calcium ions measured by this monitoring means is below a certain level. By doing in this way, the quantity of the calcium chloride consumed can be reduced, making the density | concentration of the calcium content contained in the to-be-processed water 12 stored in 11 A of 1st process tanks more than fixed.

  The above is the configuration of the waste water treatment apparatus 10 according to the present embodiment.

  Next, a wastewater treatment method using the wastewater treatment apparatus 10 having the above-described configuration will be described with reference to FIGS. 1 and 3. As shown in the flowchart of FIG. 3, the wastewater treatment method of the present embodiment includes step S1 for generating calcium fluoride, step S2 for performing solid-liquid separation of calcium fluoride by filtration, and further filtration. This step mainly includes step S3 for removing fluorine ions, step S4 for returning the calcium content concentrated in step S3, and step S5 for recovering calcium fluoride.

Step S1: Step of generating calcium fluoride With reference to FIG. 1, first, the treated water 12 containing the fluorine content discharged from the semiconductor manufacturing process or the like is supplied to the first treatment tank 11A via the first path P1. To introduce. This treated water 12 contains fluorine ions at a concentration of about 100 mg / L, for example. Since the water to be treated 12 containing hydrofluoric acid exhibits extremely strong acidity, neutralization is performed in the first treatment tank 11A or in the previous stage of the first treatment tank 11A, and the pH of the water to be treated 12 is set to, for example, 7 to 9 It may be controlled to the value of.

  Next, the calcium content is added from the chemical tank 15 to the first treatment tank 11A via the second path P2. Here, an aqueous solution of calcium chloride is added from the chemical tank 15 to the first treatment tank 11A. Theoretically, the amount of added calcium is required to be 1/2 the number of moles of fluorine ions contained in the water 12 to be treated. However, since a part of the input calcium content does not bind to fluorine ions, in this embodiment, a larger amount of chloride (for example, 2 times or more, more preferably 5 times or more) than the amount theoretically required. Calcium is added.

  By introducing an aqueous solution of calcium chloride into the first treatment tank 11A, fluorine ions and calcium ions contained in the water to be treated 12 are combined and fixed as calcium fluoride. The treated water 12 in which calcium fluoride is generated is transferred to the second treatment tank 11B via the third path P3.

Step S2: Step of separating calcium fluoride from the water to be treated by membrane filtration In this step, the calcium fluoride generated in the previous step is separated from the water to be treated 12. As a device for separating calcium fluoride from the water 12 to be treated, a filter capable of filtration can be employed. As an example, a flat membrane filter having a pore diameter of 0.2 μm is employed as the filtration membrane 13. Further, as the filtration film 13, a self-forming film made of a deposited object to be removed (calcium fluoride) is employed. The filtered water filtered by the filtration membrane 13 is transported to the RO filtration device 14 via the fourth path P4. The filtration membrane 13 used in this step is a filtration membrane that blocks the passage of calcium fluoride, but allows the passage of fluorine ions at the atomic level. Accordingly, fluorine ions remain at a concentration of about 4 mg / L in the water to be treated 12 filtered by the filter membrane 13. This fluorine ion is not bonded to the calcium component in the previous step S1.

  Moreover, a part of the to-be-processed water 12 filtered by the filter membrane 13 is stored in the storage tank 15C. The filtered water 16 stored in the storage tank 15C is used to peel off the self-forming film attached to the surface of the filtration film 13. Specifically, by continuously performing filtration through the filtration membrane 13, the self-forming membrane attached to the surface of the filtration membrane 13 is blocked and the flux gradually decreases. And when the quantity of this flux becomes below fixed, filtration by the filter membrane 13 is stopped. Further, the filtered water 16 stored in the storage tank 15 </ b> C is caused to flow back to the filtration membrane 13 to peel off the self-forming membrane attached to the surface of the filtration membrane 13. Furthermore, after that, the self-forming film is formed again on the surface of the filtration membrane 13 by restarting the filtration by the filtration membrane 13 and circulating the water to be treated.

  In the initial stage of operating the apparatus, tap water is stored in the storage tank 15C. In the steady operation, the water to be treated filtered by the RO filtration device 14 may be stored in the storage tank 15C via the twelfth path P12.

  Further, while filtering the water 12 to be treated by the filtration membrane 13, bubbles are passed through the surface of the filtration membrane 13 by the air diffuser 18. As a result, it is possible to control the film thickness of the self-forming film formed on the surface of the filtration film 13 and maintain the filtration capacity.

  The filtration in this step is performed by the suction force of the pump 20 interposed in the fourth path P4. This pump 20 is also used in the next step as a pressurizing means. As a method for controlling filtration by the filtration membrane 13 by the pump 20, the rotation of the pump 20 may be controlled so that the suction pressure is constant, or the flow rate of the water to be treated filtered by the filtration membrane 13 is constant. You may control as follows. A tenth path P10 that bypasses the fourth path P4 before and after the place where the pump 20 is provided is provided, and an adjustment valve 36 is interposed in the tenth path P10. In this step, by adjusting the adjustment valve 36 according to the pressure value measured by the pressure gauge 34, the suction pressure acting on the filtration membrane 13 and the applied pressure acting on the RO filtration device 14 are set to appropriate values. Is controlling.

  Here, when the turbidity of the water to be treated detected by the turbidimeter 30 does not satisfy a predetermined value, the water to be treated filtered by the filtration membrane 13 is not introduced into the RO filtration device 14, It returns to 11A of 1st process tanks via the 11th path | route P11 and the 6th path | route P6. For example, in the initial stage when the wastewater treatment apparatus 10 is operated, a sufficient self-forming film is not formed on the surface of the filtration membrane 13, so the turbidity of the water to be treated filtered by the filtration membrane 13 is not sufficient. . In this case, the water to be treated filtered by the filtration membrane 13 is returned to the first treatment tank 11A via the eleventh path P11. On the other hand, if the self-forming film is sufficiently formed on the surface of the filtration membrane 13 and the turbidity measured by the turbidimeter 30 satisfies a predetermined value, the water to be treated filtered by the filtration membrane 13 is subjected to RO filtration. Introduced into the device 14.

Step S3: Step of further filtering the treated water from which calcium fluoride has been removed In this step, further filtration by the RO filtration device 14 is performed using the pressure applied by the pump 20, and fluorine ions contained in the treated water Remove. As described above, the filtration membrane 13 that has been filtered in the previous step supplements calcium fluoride having a relatively large particle diameter, but does not supplement ions of atomic size. Therefore, fluorine ions remain at about 4 mg / L in the water to be treated that has passed through the filtration membrane 13. If the concentration of the remaining fluorine ions is about this level, it can be released into the natural environment such as a river as it is, but it is not suitable for use as washing water or the like in a semiconductor manufacturing process. For this reason, in the present embodiment, the filtered water that has passed through the filtration membrane 13 is further purified using the RO filtration device 14. The treated water filtered by the RO filtration device 14 is discharged to the outside via the fifth path P5. On the other hand, the water to be treated in which calcium ions and the like are concentrated without passing through the RO filtration membrane inside the RO filtration device 14 is returned to the first treatment tank 11A via the sixth path P6 and used as a calcium source. Reused.

  The RO filtration device 14 filters the water to be treated by the applied pressure given by the pump 20. As described above, the pump 20 is shared by the filtration membrane 13 and the RO filtration device 14.

  As illustrated in FIG. 2, the RO filtration device 14 includes a plurality of RO filtration devices 14 arranged in series with respect to the treatment path of the water to be treated. Specifically, the first RO filtration device 14A, the second RO filtration device 14B, and the third RO filtration device 14C are arranged from the upstream side of the path where the treated water 12 is treated. And the to-be-processed water is first introduce | transduced into 14 A of 1st RO filtration devices with the pressurization pressure of the pump 20. FIG. The treated water that has passed through the RO filtration membrane 28 inside the first RO filtration device 14A is discharged to the outside via the fifth path P5. On the other hand, in the water to be treated that has not permeated the RO filtration membrane 28, calcium ions and fluorine ions are concentrated and transferred to the second RO filtration device 14B. In the second RO filtration device 14B, filtration by the RO membrane is performed similarly to the first RO filtration device 14A, and the treated water that has been filtered is discharged to the outside via the fifth path P5 and has not been filtered. The treated water is transferred to the third RO filtration device 14C after further concentration. Further, the same filtration by the RO filtration membrane was performed in the third RO filtration device 14C, and the water to be treated that passed through the RO filtration membrane was discharged to the outside via the fifth path P5 and did not pass through the RO filtration membrane. The treated water is reused via the sixth path P6. That is, it is returned to the first processing tank 11A shown in FIG. Here, in the water to be treated which is concentrated by the RO filtration device arranged in three stages and passes through the sixth path P6, calcium ions and fluorine ions are concentrated about 10 times, for example.

Step S4: Returning the concentrated calcium content In this step, the treated water 12 that has not been filtered by the RO filtration device 14 is returned to the first treatment tank 11A via the sixth path P6, and the Reuse to produce calcium fluoride. As described above, in the present embodiment, the amount of calcium content (calcium chloride) added to reduce the amount of fluorine ions remaining in the water to be treated 12 is twice the theoretically required amount. 10 times the range. From this, the to-be-treated water 12 that has passed through the first treatment tank 11A, the second treatment tank 11B, and the RO filtration device 14 contains a large amount of calcium ions that have not been combined with the fluorine content. The treated water 12 is concentrated about 10 times by the filtration device 14.

  The calcium ions contained in the water to be treated returned to the first treatment tank 11A are used to fix the fluorine content contained in the water to be treated introduced from the first path P1 as calcium fluoride.

  Here, in the case where the first treatment tank 11A is omitted and the fluorine content is fixed in the second treatment tank 11B, the water to be treated containing calcium in a high concentration passes through the sixth path P6. 2 Returned to treatment tank 11B.

  By performing the above-described return, the calcium added from the chemical tank 15 to the first treatment tank 11A is circulated through the treatment path of the waste water treatment apparatus 10 except for the part that combines with the fluorine ions to generate calcium fluoride. Will be. Accordingly, most of the calcium supplied from the chemical tank 15 contributes to the fixation of fluorine ions, and there is almost no calcium released to the outside from the fifth path P5. For this reason, the calcium content required for immobilization of fluorine ions is reduced, and the processing cost is reduced.

  Further, the concentration of ions (for example, chloride ions) contained in the water to be treated that passes through the sixth path P6 is measured by the conductivity meter 32. And if the quantity of the measured ion is more than predetermined amount, the to-be-processed water to circulate will be replaced.

  When the above-described steps S1 to S4 are advanced, the generated calcium fluoride is precipitated in the lower part of the second treatment tank 11B. In this embodiment, the following step S5 is performed in order to collect the precipitated calcium fluoride.

Step S5: Step of recovering calcium fluoride precipitated in the second treatment tank 11B In this step, first, an object to be removed containing calcium fluoride precipitated at the bottom of the second treatment tank 11B is passed through the seventh path P7. Then, it is transferred to the filter press 17.

  Next, by injecting water into the filter press 17, the neutralized salt (NaCl) contained in the water 12 to be treated is washed and removed. Since the pH-adjusted water to be treated 12 contains neutralized salt, the object to be removed separated from the water to be treated 12 is also neutralized with calcium fluoride and other calcium salts (for example, Calcium carbonate). Further, for example, in the case of drainage from a wet etching apparatus, silicon may be included. By injecting water into the filter press 17, the neutralized salt is dissolved in water and released to the outside. Since calcium fluoride has a large diameter, it is not released from the filter press 17 to the outside even if washed with water. By doing in this way, the density | concentration of the calcium fluoride contained in a to-be-removed object is improved.

  Next, after the object to be removed is dehydrated by the filter press 17, the object to be removed in a semi-solid state is taken out. In this state, the water content of the object to be removed is about 50% by weight. Next, the object to be removed is dried to form a solid block of the object to be removed. In this embodiment, an object to be removed containing 85% by weight of calcium fluoride is obtained.

  In this embodiment, since solid-liquid separation is performed without using a flocculant such as a polymer flocculant, immobilized calcium fluoride can be obtained with high purity from wastewater containing fluoride ions. . The obtained calcium fluoride can be reused in the semiconductor manufacturing process as hydrofluoric acid by reacting with a strong acid (for example, sulfuric acid).

  Furthermore, it is also possible to use the high purity calcium fluoride obtained in the present application as a flux mixed in steel. In addition, calcium chloride can be obtained by adding hydrochloric acid to the obtained calcium fluoride. Furthermore, since sulfuric acid, hydrochloric acid, etc. added to recycle calcium fluoride are chemicals that are always used in semiconductor factories, it is possible to reuse calcium fluoride without adding new equipment in the factory. It can be performed.

  Next, with reference to FIG. 4 thru | or FIG. 6, the detail of the filtration mechanism (filter apparatus 23) applicable as the above-mentioned filtration membrane 13 is demonstrated. In the following embodiment, a filtration mechanism using a self-forming film will be described, but other forms of filtration devices can be applied to the present invention. For example, a normal filtration membrane made of a polymer compound can be used as the filtration membrane 13.

  With reference to FIG. 4, the filter apparatus 23 removes the to-be-processed water mixed with the to-be-removed object which is calcium fluoride with the filter which consists of a self-forming film | membrane formed from the to-be-removed object.

  More specifically, in the filter device 23 of the present embodiment, a second filter 22 (self-forming film) formed from an object to be removed containing calcium fluoride is formed on the surface of the organic polymer first filter 21. It is a thing. Using the second filter 22 which is this self-forming film, the water to be treated mixed with the material to be removed is filtered.

  The first filter 21 can adopt either an organic polymer type or an inorganic type (ceramic type) in principle if a self-forming film can be attached. Here, a polyolefin polymer film having an average pore diameter of 0.25 μm and a thickness of 0.1 mm was employed. A photograph of the surface of the polyolefin filter membrane is shown in FIG.

  The first filter 21 has a flat membrane structure provided on both sides of the frame 24 and is immersed so as to be perpendicular to the fluid level. By sucking with a pump 26 from the hollow portion 25 of the frame 24, the filtrate 27 (water to be treated) can be taken out.

  Next, the second filter 22 is a self-forming film that is attached to the entire surface of the first filter 21 and solidified by sucking the aggregated particles of the object to be removed. This self-forming film may be agglomerated in a gel or cake form.

  Filtration for forming the second filter 22 that is the self-forming film of the object to be removed and removing the object to be removed will be described.

  Referring to FIG. 5A, the first filter 21 has a number of filter holes 21A, and the self of the object to be removed that is formed in layers in the opening of the filter hole 21A and the surface of the first filter 21. The formed film is the second filter 22. The surface of the first filter 21 has agglomerated particles of the object to be removed made of calcium fluoride. The agglomerated particles are sucked through the first filter 21 by the suction pressure from the pump, and the fluid moisture is sucked out. The second filter 22 is formed on the surface of the first filter 21 by solidifying immediately after drying (dehydration).

  Since the second filter 22 is formed from the aggregated particles of the object to be removed, the film immediately has a predetermined film thickness, and the filtration of the aggregated particles of the object to be removed is started using the second filter 22. Therefore, if the filtration is continued while sucking with the pump 26 (see FIG. 4), a self-forming film of agglomerated particles is laminated on the surface of the second filter 22 to become thick, and the second filter 22 is eventually clogged and filtered. I can't continue. During this time, the calcium fluoride as the object to be removed is solidified, adheres to the surface of the second filter 22, and the treated water passes through the first filter 21 and is taken out as filtered water.

  In FIG. 5A, one side of the first filter 21 has treated water mixed with an object to be removed such as calcium fluoride, and the other side of the first filter 21 passes through the first filter 21. Filtered water is produced. The treated water is sucked and flows in the direction of the arrow, and the agglomerated particles in the treated water 12 are solidified as they approach the first filter 21 by this suction. Further, the self-forming film to which some aggregated particles are bonded is adsorbed on the surface of the first filter 21 to form the second filter 22. The object to be removed in the solution is solidified by the action of the second filter 22 and the water to be treated is filtered.

  In this way, by slowly sucking in the water to be treated through the second filter 22, the water in the water to be treated can be taken out as filtered water, and the object to be removed is dried and solidified and laminated on the surface of the second filter 22. The aggregated particles of the removal object are captured as a self-forming film.

  The first filter 21 is immersed vertically in the water to be treated, and the material to be removed is dispersed in the water to be treated. When the water to be treated is sucked by the pump 26 through the first filter 21 with a weak suction pressure, the aggregated particles of the objects to be removed are combined with each other on the surface of the first filter 21 and adsorbed on the surface of the first filter 21. Is done. The agglomerated particles S1 having a diameter smaller than the filter hole 21A pass through the first filter 21, but there is no problem in the process of forming the second filter 22 because the filtered water is circulated again to the water to be treated.

  Next, the filtration process by the above self-forming film will be described in order.

  First, the water to be treated is filtered by the first filter 21 to form a second filter on the surface of the first filter. In this film forming process, since the water to be treated is sucked with a very weak suction pressure, the agglomerated particles S1 are stacked while forming gaps of various shapes, and the first self-forming film having a very high degree of swelling is formed. Two filters 22 are obtained. Water in the water to be treated permeates through this highly swelled self-forming film and is sucked, passes through the first filter 21 and is taken out as filtered water, and finally the water to be treated is filtered.

  Moreover, the parallel flow is formed in the to-be-processed water along the surface of the 1st filter 21 by sending the bubble A from the bottom face (the diffuser 18 shown in FIG. 1). This is because the second filter 22 adheres uniformly to the entire surface of the first filter 21 and forms a gap in the second filter 22 and adheres softly. Specifically, the air flow rate is set to 1.8 liters / minute, but it is selected depending on the film quality of the second filter 22.

  When the second filter 22 is sufficiently formed by the film formation process described above and the filtered water to be treated has achieved a predetermined transparency, the process proceeds to the filtration process. In this filtration step, the aggregated particles S1 made of calcium fluoride are gradually stacked on the surface of the second filter 22 while being adsorbed by a weak suction pressure. At this time, the purified water permeates the second filter 22 and the further aggregated particles S1 and is taken out from the first filter 21 as filtered water.

  However, if the filtration is continued for a long time, the thick self-forming film adheres to the surface of the second filter 22, so that the above-mentioned gap eventually becomes clogged, and filtered water cannot be taken out. For this reason, it is necessary to remove the laminated self-forming film in order to regenerate the filtration capacity.

  An example of regeneration of the filtration capacity will be described as follows.

  For example, referring to FIG. 4, the hollow portion 25 of the first filter 21 has a negative pressure compared to the outside due to a weak suction pressure, so the first filter 21 has a shape recessed inward. Yes. Therefore, the second filter 22 adsorbed on the surface is similarly recessed inward.

  In the regeneration process, the weak suction pressure is stopped and returned to almost the atmospheric pressure, whereby the first filter 21 returns to the original state. As a result, the second filter 22 and the self-forming film adsorbed on the surface of the second filter 22 are similarly returned to the original state. As a result, since the suction pressure that first adsorbs the self-forming film disappears, the self-forming film loses the adsorbing force to the first filter 21 and receives a force that expands outward. As a result, the adsorbed self-forming film starts to be detached by its own weight.

  Furthermore, when the filtered water is caused to flow back into the hollow portion 25 in this regeneration step, the first filter 21 is helped to return to its original state, and the hydrostatic pressure of the filtered water is applied and a force that further expands outward is applied. Further, the filtered water oozes out from the inside of the first filter 21 through the filter hole 21 </ b> A (see FIG. 5A) to the boundary between the first filter 21 and the second filter 22 and from the surface of the first filter 21 to the second filter 22. Promotes the release of self-forming films. The reverse flow can be performed by causing the filtered water 16 temporarily stored in the storage tank 15C shown in FIG. 1 to flow into the filtration membrane.

  If the filtration is continued while regenerating the second filter 22 as described above, the concentration of the object to be removed from the water to be treated 12 increases, and the viscosity of the water to be treated 12 eventually increases. Therefore, when the concentration of the object to be removed in the water to be treated 12 exceeds a predetermined concentration, the filtering operation is stopped and left to settle. Then, the concentrated slurry is stored at the bottom of the second treatment tank 11B (FIG. 1), and this cake-like concentrated slurry is recovered. The recovered concentrated slurry is dehydrated using a filter press 17 (see FIG. 1), and further compressed or heat dried to remove the water contained therein and reduce the amount.

  This slurry can be reused as a hydrofluoric acid source. That is, by concentrating the filtered water 16 stored in the storage tank 15C in the reverse direction and repeating the peeling of the self-forming film, it is possible to improve the concentration efficiency of the concentrated slurry that is a raw material of hydrofluoric acid.

  With reference to FIG. 6, the experiment which filtered the to-be-processed water 12 using the filtration membrane 13 shown in FIG. 1 is demonstrated. FIG. 6 is a graph showing the change with time of the flux during the filtration process. In this graph, the horizontal axis indicates the time for which the processing is continuously performed, and the vertical axis indicates the magnitude of the flux.

First, the conditions of this experiment will be described. In this experiment, filtration was performed by applying a suction pressure of 7 kPa to a filtration membrane having an area of 0.1 m ² . In the water to be treated, calcium chloride is added to wastewater containing 1000 mg / L of fluorine ions, and fluoride ions are fixed as calcium fluoride. The diameter of calcium fluoride is about 0.25 μm. And it experimented by measuring regularly the quantity of the to-be-processed water and flax.

  From this experiment, the average flux was 0.4 m / day, and it was proved that the filtration membrane 13 of this embodiment can sufficiently withstand practical use. Furthermore, the concentration of fluoride ions contained in the filtered water obtained by the filtration membrane is 3.5 mg / L, and this value satisfies the general discharge standard.

  The experimental method will be described in detail. First, a self-forming film is formed on the surface of the filtration membrane by circulating an object to be removed such as calcium fluoride, and filtered water having a certain level of transparency can be obtained. At this point, filtration begins.

  The flux at the start of filtration is about 0.7 m / day, and the flux gradually decreases as filtration continues. This is because the self-forming film is blocked as the filtration progresses. The flux at the time when 130 minutes have passed since the start of filtration is about 0.2 m / day. At this point, the self-forming membrane is peeled off from the filtration membrane, and the removal target concentrated in the water to be treated is recovered.

  When peeling of the self-forming film and recovery of the object to be removed are completed, a new self-forming film is formed on the surface of the filtration film, and the water to be treated is filtered again. By repeating the above steps, the object to be removed containing calcium fluoride can be separated from the water to be treated.

  From the above experiment, it was found that sufficient flux can be secured by periodically peeling and regenerating the self-formed film.

It is a figure which shows the waste water treatment apparatus of this invention. It is a figure which shows the RO filtration apparatus with which the waste water treatment apparatus of this invention is equipped. It is a flowchart which shows the waste water treatment method of this invention. It is a figure explaining the filter apparatus applied to the waste water treatment apparatus of this invention. It is a figure explaining the (A) operation principle of the filter apparatus applied to the waste water treatment equipment of the present invention, and (B) is an enlarged view of the first filter. It is a characteristic view for demonstrating the characteristic of the filtration apparatus applied to the waste water treatment apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wastewater treatment apparatus 12 Water to be treated 13 Filter membrane 14 RO filtration apparatus 14A First RO filtration apparatus 14B Second RO filtration apparatus 14C Third RO filtration apparatus 15 Chemical tank 16 Filtered water 17 Filter press 18 Aeration apparatus 19 Receiving tank 20 Pump 21 First 1 filter 22 second filter 23 filter device 24 frame 25 hollow portion 26 pump 27 filtrate 28 RO filtration membrane 30 turbidity meter 32 conductivity meter 34 pressure gauge 36 regulating valve P1 first path P2 second path P3 third path P4 4th path P5 5th path P6 6th path P7 7th path P8 8th path P9 9th path P10 10th path P11 11th path P12 12th path

Claims (10)

An adding means for adding calcium to the water to be treated containing fluorine to generate calcium fluoride;
First separation means for separating the calcium fluoride from the treated water;
A second separation means for removing fluorine ions from the water to be treated from which the calcium fluoride has been separated, and
The waste water treatment apparatus, wherein the water to be treated in which the calcium component that has not reacted with the fluorine is concentrated by the second separation means is returned to a stage prior to the first separation means. A plurality of the second separation means are arranged in series with respect to a path for treating the water to be treated.
The wastewater treatment apparatus according to claim 1, wherein the water to be treated that has been concentrated by the two separation means arranged at the rearmost stage is returned to the front stage rather than the first separation means.   The wastewater treatment apparatus according to claim 1, wherein the second separation unit is a filtration device including an RO membrane or an NF membrane.   The waste water treatment apparatus according to claim 1, wherein the first separation means is a self-forming film containing the calcium fluoride laminated on a filtration membrane. A storage tank for storing a fluid flowing back to the first separation means;
The wastewater treatment apparatus according to claim 4, wherein the treated water filtered by the second separation means is stored in the storage tank. The first separation means is a suction type filtration device, and the second separation means is a pressure type filtration device,
A suction pressure is applied to the first separation means and a pressure is applied to the second separation means by a pump interposed in a path between the first separation means and the second separation means. The waste water treatment apparatus according to claim 1. Further comprising a bypass path for bypassing the path where the pump is interposed;
The wastewater treatment apparatus according to claim 6, further comprising an adjustment valve that adjusts an amount of the water to be treated that passes through the bypass path.   The wastewater treatment apparatus according to claim 1, further comprising ion concentration measuring means for measuring a concentration of ions contained in the water to be treated in a path through which the water to be treated is circulated. Comprising turbidity detection means for detecting the turbidity of the water to be treated that has passed through the first separation means,
The wastewater treatment apparatus according to claim 1, wherein if the turbidity of the water to be treated detected by the turbidity detecting means is below a certain value, the water to be treated is supplied to the second separation means. . Generating calcium fluoride by adding calcium to the water to be treated containing fluorine; and
Separating the calcium fluoride from the treated water by a first separating means;
Removing fluorine ions from the water to be treated from which the calcium fluoride has been separated by the second separation means,
A wastewater treatment method characterized in that the water to be treated in which the calcium component that has not reacted with the fluorine is concentrated by the second separation means is returned to a stage prior to the first separation means.

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