JP2006167633A - Treating method of fluorine-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating method of fluorine-containing water by which fluorine is removed from the fluorine-containing water. <P>SOLUTION: A calcium compound and an aluminum salt are added to the fluorine-containing water and produced sludge is returned by circulation. In this treating method of the fluorine-containing water, a ratio of a flow rate of returned sludge/a flow rate of sludge discharged outside a system is adjusted by using sludge concentration as an index. By this method, aluminum concentration in the system can be appropriately maintained and fluorine can be stably and efficiently removed even when coagulation property becomes worse due to variation of the fluorine-containing water to be treated or the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for treating fluorine-containing water that removes fluorine from fluorine-containing water. In particular, the present invention relates to a method for treating fluorine-containing water in which a calcium compound and an aluminum salt are added to fluorine-containing water and the resulting sludge is circulated and returned.

As a method of treating fluorine-containing water discharged from electronics industry wastewater, etc., calcium fluoride is generated by adding calcium compounds such as slaked lime, calcium chloride and calcium carbonate to the treated water, and fine particles of calcium fluoride In general, a method of agglomerating the material with an aluminum or iron-based inorganic flocculant and a polymer flocculant, followed by precipitation separation is employed. In general, aluminum-based flocculants that can be used include aluminum salts such as PAC and sulfuric acid band.
These form sparingly soluble aluminum hydroxide, adsorb the remaining fluorine without reacting with calcium, and remove fluorine by agglomerating insolubles such as calcium fluoride by coprecipitation. It is known. And according to this method, the fluorine concentration in the treated water can be reduced to a concentration of 10 to 20 mg · F / L. However, in July 2001, the emission standard value of fluorine was strengthened from 15 mg · F / L to 8 mg · F / L, and it became necessary to further treat fluorine.
However, in order to highly treat fluorine in the coagulation sedimentation method, the amount of aluminum coagulant added must be increased to 2000 to 5000 mg / L, and the sludge produced under such conditions has a dehydrating property. Unfortunately, the amount of dehydrated cake after sludge dehydration is very large.

Therefore, a method called a sludge circulation method is adopted as a means for reducing the amount of dehydrated cake. According to this method, by returning a part of the sludge after solid-liquid separation to the previous Ca reaction tank and the inorganic flocculant reaction tank, the sludge concentration is increased and the density is increased, and the cohesiveness of the sludge is increased. The dehydrating property can be increased, that is, the water content can be decreased. Furthermore, in the sludge circulation method, in order to reduce the amount of inorganic flocculant added, a method is known in which sludge regeneration treatment is performed in which alkali or acid is added to the returned sludge and then returned to the reaction tank ( Patent Document 1: Japanese Patent Publication No. 7-36911). Further, an aluminum recovery apparatus is known for adding an alkali or an acid to aluminum-containing sludge and reusing the aluminum eluate as a flocculant (Patent Document 2: JP-A-11-333500).
In this regeneration treatment, the aluminum hydroxide in the sludge is dissolved by the acid or alkali treatment, and the adsorbed fluorine is released. The released fluorine reacts with calcium in sludge, or slaked lime added for pH adjustment during sludge regeneration or calcium in calcium chloride to form calcium fluoride. The aluminum salt regenerated in this manner is reused in the inorganic reaction tank, so that the aluminum concentration in the inorganic reaction tank is increased and the amount of the flocculant added can be greatly reduced.

Japanese Patent Publication No. 7-36911 JP 11-333500 A

As described above, as a method of treating fluorine-containing water, in order to reduce the amount of inorganic flocculant added, after sludge regeneration treatment in which alkali or acid is added to the sludge to be circulated and returned to the reaction tank, The sludge circulation method for circulation return was sometimes selected. Conventionally, in the sludge circulation method, there are many cases where the sludge discharge flow rate and circulation return flow rate to the outside of the system are constant, but in this case, the discharge amount is too large and the aluminum concentration in the inorganic reaction tank is sufficiently high. Sometimes it didn't go up. On the other hand, if the discharge flow rate is low, the sludge concentration in the sludge may become too high, which may cause clogging of the piping, or the SS concentration in the system will become too high, causing the aggregation failure. There was a case. In addition, even if the discharge flow rate and the circulation return flow rate are set appropriately at the beginning, depending on the state of the fluorine-containing water, the cohesiveness may deteriorate and the floc sedimentation will deteriorate, resulting in a lower sludge concentration. When the sludge concentration is low, the amount of aluminum to be regenerated is reduced, resulting in an adverse effect that the effect of sludge circulation cannot be obtained sufficiently.
Japanese Patent Laid-Open No. 11-333500 (Patent Document 2) discloses an aluminum recovery apparatus in which an aluminum dissolving agent is added to aluminum-containing sludge to dissolve the sludge, and the resulting aluminum eluate is reused as a flocculant. In the aluminum recovery apparatus, the sludge concentration is adjusted to a predetermined concentration range. And in patent document 2, it is described that the said collection | recovery apparatus has the advantage that the aluminum concentration in an aluminum eluate can be made constant. However, Patent Document 2 does not disclose or suggest any method for controlling the return of the aluminum eluate so that fluorine can be appropriately removed from the fluorine-containing water without causing the above-described adverse effects.

  The inventors of the present invention have studied a control method that does not cause the above problems when treating fluorine-containing water with a sludge circulation method, and using the sludge concentration as an index, the flow rate of returned sludge / discharged outside the system. It has been found that by controlling the ratio of the flow rate of the sludge to be generated, fluorine can be appropriately removed from the fluorine-containing water without causing the above-mentioned adverse effects. The present invention has been made in view of such circumstances. In the case where fluorine-containing water is treated by the sludge circulation method, the sludge flow rate is returned to the outside of the system using the sludge concentration as an index. By controlling the ratio of the sludge flow rate, the amount of inorganic flocculant added can be reduced without causing problems such as a decrease in fluorine removal capacity, clogging of pipes, and agglomeration failure due to fluctuations in the sludge concentration returned by circulation. It aims at providing the processing method of fluorine-containing water which can remove a fluorine stably and efficiently.

In the present invention, as a first aspect, a calcium compound is added to fluorine-containing water to form calcium fluoride to produce a first treated water containing the calcium fluoride, and aluminum is added to the first treated water. A salt is added to form an insolubilized product, and a second process for producing a second treated water containing the insolubilized product is separated; a sludge containing the insolubilized product is separated from the second treated water; and the final treated water And a third step of generating sludge, and a part of the sludge is discharged out of the system, and acid or alkali is added to the remaining sludge to regenerate the sludge, and then the regenerated sludge is recovered in the first step. Sludge in the sludge in a method for treating fluorine-containing water that includes the fourth step of returning to the second step and / or returning to the second step and adding to the fluorine-containing water in the first step and / or the first treated water in the second step concentration As an index, in the fourth step, and adjusting the ratio of the flow rate of the sludge discharged out of the flow rate / system of the sludge sent back, provides a method of treating fluorine-containing water.
As a second aspect of the present invention, the adjustment of the ratio of the flow rate of returned sludge / flow rate of sludge discharged out of the system using the sludge concentration in the sludge as an index in the fourth step is 1) returned. The sludge flow rate is constant and the sludge concentration in the sludge is used as an index to adjust the flow rate of sludge discharged outside the system. 2) The sludge flow rate discharged outside the system is constant. Either by adjusting the flow rate of the returned sludge using the sludge concentration in the sludge as an index, or 3) using the sludge concentration in the sludge as an index, The method for treating fluorine-containing water is provided by adjusting both the flow rate of the discharged sludge.
As a third aspect, the present invention provides the method for treating fluorine-containing water, wherein in the second step, the aluminum concentration in the second treated water is 50 mg / L or more.
This invention provides the processing method of the said fluorine-containing water by which adjustment in a 4th process is performed so that the sludge density | concentration in sludge may become the range of 1%-15% as a 4th aspect.

  The present invention relates to a method for treating fluorine-containing water by a sludge return method using a calcium compound and an aluminum salt, and using the sludge concentration in the sludge as an index, the flow rate of returned sludge / the flow rate of sludge discharged outside the system. By adjusting the ratio, the second step, which was caused by excessive sludge discharge, which was caused by circulating and returning a certain amount of sludge and discharging a certain amount of sludge out of the system, which was performed by the conventional method. Can reduce the concentration of aluminum during formation of insolubilized materials and decrease fluorine removal capability, and blockage of pipes due to excessive sludge discharge and aggregation failure due to increased SS concentration in the system. It has the advantageous effect that appropriate fluorine removal can be achieved with the added amount. In addition, the present invention has been unable to cope with the conventional method of circulating and returning a certain amount of sludge and discharging a certain amount of sludge out of the system. Even when the cohesiveness of the inorganic flocculant in the second step varies, there is an advantageous effect that appropriate fluorine removal can be achieved with a small amount of the inorganic flocculant added.

  In the method for treating fluorine-containing water according to the present invention, first, a first step is performed in which a calcium compound is added to fluorine-containing water to form calcium fluoride to produce first treated water containing the calcium fluoride. . FIG. 1 is a schematic view showing an example of a flow that can be used in the method for treating fluorine-containing water of the present invention, and the present invention will be described in detail based on this.

  In the first step, the calcium compound is added to the fluorine-containing water. The calcium compound is added to the fluorine-containing water using any known apparatus and method as long as calcium fluoride is formed. Can be done. In the first step, from the viewpoint of removing fluorine, the residual fluorine ion concentration after the treatment is preferably 20 mg / L or less, more preferably 15 mg / L or less, and most preferably 10 mg / L or less. is there. In the first step, first treated water containing calcium fluoride generated by the reaction of fluorine in the fluorine-containing water with calcium in the calcium compound is produced, and this first treated water is provided to the second step. . The pH of the reaction system when calcium compound and optionally regenerated sludge are added to the fluorine-containing water in the first step to form calcium fluoride is preferably maintained in the range of 3 to 12, more preferably 4. Maintained in the range of ~ 11.

  Moreover, in 1 aspect of this invention, the sludge by which the reproduction | regeneration process returned in a 4th process (it is also called regenerated sludge in this specification) is returned to a 1st process, and is added to fluorine-containing water. In the method of the present invention, the return of the regenerated sludge may be performed in either the first step or the second step, or both, so when the regenerated sludge is returned only in the second step, Regenerated sludge may not be added to the fluorine-containing water in one step. When the regenerated sludge is returned to the first step, the order of addition of the regenerated sludge and the calcium compound to the fluorine-containing water is not particularly limited, and may be added simultaneously or sequentially. . Moreover, the addition of the regenerated sludge to the fluorine-containing water can also be performed using any known apparatus and method.

  For example, in the embodiment of FIG. 1, a calcium reaction tank 1 is provided as a place where a calcium compound is added to fluorine-containing water. The calcium reaction tank 1 is connected with a fluorine-containing water supply line 2 for supplying fluorine-containing water and a calcium compound supply line 3 for supplying a calcium compound. In the calcium reaction tank 1, fluorine in the fluorine-containing water and the calcium compound The calcium inside reacts to form calcium fluoride. After the formation of calcium fluoride, the first treated water containing calcium fluoride is supplied to the inorganic reaction tank 6 via the first treated water supply line 5. Moreover, although the stirring means is provided in the calcium reaction tank 1, this installation is arbitrary. Further, in the embodiment of FIG. 1, a sludge return line 4 is connected to the calcium reaction tank 1, and the regenerated sludge is supplied to the calcium reaction tank 1 through the sludge return line 4 and added to the fluorine-containing water. The Rukoto.

The fluorine-containing water in the present invention may be water of any origin as long as it contains fluorine. For example, wastewater discharged from the electronics industry including the semiconductor-related industry, the power plant, the aluminum industry, etc. Although it is mentioned, it is not limited to these. The fluorine contained in the fluorine-containing water can exist in any state. For example, fluorine may exist in a form such as fluorine ion (F ⁻ ) or an ionized compound containing a fluorine element, or form as a part of a molecule such as hydrogen fluoride (HF). However, the present invention is not limited to these. The amount of fluorine contained in the fluorine-containing water is not particularly limited, but is preferably 3000 mg · F / L or less, more preferably 1000 mg · F / L or less. Further, the fluorine-containing water in the present invention may contain any other element other than fluorine in the form of any compound or ion.

  The calcium compound is not particularly limited as long as it can form calcium fluoride by reacting with fluorine in fluorine-containing water, and examples include, but are not limited to, calcium hydroxide, calcium chloride, and calcium carbonate. Is not to be done. The calcium compound can be used in any form including a solution, a slurry, and a dry solid.

  The amount of the calcium compound added to the fluorine-containing water can be appropriately set, but at least the amount of fluorine: calcium = 2: 1 in molar ratio with respect to the fluorine contained in the fluorine-containing water, that is, the weight. It is desirable that the ratio of fluorine: calcium = 1: (20/19). From the viewpoint of removing fluorine contained in fluorine-containing water as calcium fluoride, it is preferable that calcium is present excessively with respect to the amount of calcium required by the weight ratio of the above formula, and the weight ratio of the above formula The concentration in the reaction field (calcium reaction tank in the embodiment of FIG. 1) is preferably 100 to 600 mg · Ca / L excess, more preferably 200 to 400 mg · Ca / L. A calcium compound is supplied so that it may become excess.

In the present invention, following the first step, a step of adding an aluminum salt to the first treated water to form an insolubilized product and generating a second treated water containing the insolubilized product is performed.
In the second step, an aluminum salt that is an inorganic flocculant is added to the first treated water, but the addition of the aluminum salt to the first treated water is any known as long as an insolubilized product is formed. It is possible to carry out using this apparatus and method. In the second step, calcium fluoride in the first treated water is aggregated by the added aluminum salt to produce an insolubilized product, and this second treated water is supplied to the third step. The pH of the reaction system when the aluminum salt and optionally regenerated sludge are added to the first treated water in the second step to form an insolubilized material is preferably maintained in the range of 5 to 8.5, more preferably. Is maintained in the range of 6-8.

  Moreover, in 1 aspect of this invention, the reproduction | regeneration sludge returned in a 4th process may be returned to a 2nd process, and may be added to a 1st treated water. In the method of the present invention, the return of the regenerated sludge may be performed in either the first step or the second step, or both, and therefore when the regenerated sludge is returned only in the first step, Regenerated sludge does not need to be added to the first treated water in the two steps. When the regenerated sludge is returned to the second step, the order of adding the regenerated sludge and the aluminum salt to the first treated water is not particularly limited, and may be added simultaneously or sequentially. good. Moreover, the addition of the regenerated sludge to the first treated water can also be performed using any known apparatus and method.

  For example, in the aspect of FIG. 1, the inorganic reaction tank 6 is provided as a place where an aluminum salt is added to the first treated water. The inorganic reaction tank 6 is connected to a first treated water supply line 5 for supplying first treated water and an aluminum salt supply line 7 for supplying aluminum salt. In the inorganic reaction tank 6, fluorination of the first treated water is performed. Calcium is agglomerated by the aluminum salt to form an insolubilized product. After the insolubilized material is formed, the second treated water containing the insolubilized material is supplied to the polymer reaction tank 10 via the second treated water supply line 8. Moreover, although the inorganic reaction tank 6 is provided with the stirring means and the pH adjuster supply line 9 which supplies a pH adjuster in an inorganic reaction tank, these installations are arbitrary. Further, in the embodiment of FIG. 1, the sludge return line 4 is connected to the inorganic reaction tank 6, and the regenerated sludge is supplied to the inorganic reaction tank 6 through the sludge return line 4 and added to the first treated water. Will be. In addition, in the aspect of FIG. 1, although the sludge return line 4 is connected to both the calcium reaction tank 1 and the inorganic reaction tank 6, the aspect by which the sludge return line 4 is connected to either one may be sufficient. .

  As the aluminum salt, any known one can be used as long as it functions as a flocculant capable of aggregating calcium fluoride, and examples thereof include PAC, sulfate band and the like, but are not limited thereto. Is not to be done. In the present specification, the “aluminum salt” added in the second step is different from the recycled sludge to be returned.

  In the method of the present invention, in order to sufficiently obtain the effect of circulating sludge, the inventors of the present invention are the places where the aluminum salt and the regenerated sludge are added to the first treated water in the second step, that is, in FIG. In the embodiment, it has been found that the aluminum concentration in the inorganic reaction tank 6, that is, the aluminum concentration in the second treated water is preferably 50 mg · Al / L or more, more preferably 100 mg · Al / L or more. The “place where the aluminum salt and the regenerated sludge are added to the first treated water in the second step” means that the regenerated sludge already added in the first step is contained in the first treated water. It may be an aspect brought about in two steps, or may be an aspect in which regenerated sludge is newly added in the second step.

  The amount of aluminum salt added to the first treated water in the second step depends on the flow rate of the regenerated sludge added to the second treated water, the aluminum content in the regenerated sludge, the amount of fluorine in the fluorine-containing water, etc. The fluorine content in the final treated water can be appropriately set so that it falls within an appropriate range. In the present invention, the amount of aluminum salt added in the second step can be reduced by controlling the ratio of the flow rate of returned sludge / the flow rate of sludge discharged outside the system using the sludge concentration as an index. For example, the amount of the aluminum salt added in the second step is not particularly limited, but is often in the range of 5 to 50 mg · Al / L in terms of the aluminum concentration in the second treated water.

  When the pH is adjusted in the first step and the second step, any known acid or alkali can be used as long as it is not contrary to the object of the present invention. For example, sulfuric acid, hydrochloric acid, nitric acid, Sodium hydroxide or the like can be used.

  For the second treated water generated from the second step, a polymer flocculant is optionally added before the third step for producing sludge containing insolubilized material and final treated water, and the insoluble material is aggregated. You may perform the process which improves property. The polymer flocculant addition treatment can be performed using any known apparatus and method as long as the polymer flocculant improves the aggregability of the insolubilized material. For example, in the embodiment of FIG. 1, the second treated water is supplied to the polymer reaction tank 10 via the second treated water supply line 8. A polymer flocculant supply line 11 is connected to the polymer reaction tank 10, and the polymer flocculant supplied from the polymer flocculant supply line 11 enters the second treated water in the polymer reaction tank 10. Added and mixed. Moreover, although the polymer reaction tank 10 is provided with a stirring means, this installation is arbitrary. The second treated water to which the polymer flocculant has been added and the insolubilized matter has been increased in cohesiveness is supplied to the settling tank 12 via the second treated water supply line 8 '.

As the polymer flocculant, any polymer that improves the agglomeration property of the insolubilized product generated by adding the aluminum salt in the second step can be used. For example, anionic polymer organic flocculant, nonionic property Examples thereof include a polymer organic flocculant and a polymer organic flocculant having a cationic group. The amount of the polymer flocculant added to the second treated water is not particularly limited, but is generally 0.1 to several tens mg / L, preferably 2 to 5 mg / L. .
Examples of the anionic polymer organic flocculant include alginic acid or a salt thereof, carboxymethylcellulose, a polymer of acrylic acid or a salt thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, acrylamide and 2-acrylamide-2- Examples include copolymers of methylpropane sulfonate, terpolymers of acrylic acid or salts thereof with acrylamide and 2-acrylamido-2-methylpropane sulfonate, and partial hydrolysates of polyacrylamide. It is not limited. The range of the weight average molecular weight of the anionic polymer organic flocculant is not particularly limited, but a range of 5 million to 20 million is preferable. These anionic polymer organic flocculants can be used alone or as a mixture.

  Examples of the nonionic high molecular organic flocculant include, but are not limited to, a polymer of acrylamide. The range of the weight average molecular weight of the nonionic polymer organic flocculant is not particularly limited, but a range of 5 million to 20 million is preferable. These nonionic high molecular organic flocculants can be used alone or as a mixture. The anionic polymer organic flocculant and the nonionic polymer organic flocculant can also be used as a mixture.

The polymer organic flocculant having a cationic group is a polymer organic flocculant containing a cationic group in the molecular structure. The cationic organic coagulant, the cationic polymer organic flocculant, and the amphoteric polymer organic flocculant Agents.
The cationic organic coagulant is an organic coagulant containing a cationic group in the molecular structure, for example, a polycondensate of dimethylamine and epichlorohydrin, polydimethylallyl ammonium chloride, polyethyleneimine, dicyandiamide and formalin. A polycondensate of dimethylaminoethyl methacrylate and styrene, a polycondensate of melamine and formalin, or a copolymer comprising a monomer constituting these and a nonionic monomer such as acrylamide. It is not limited to these. The range of the weight average molecular weight of the cationic organic coagulant is not particularly limited, but is preferably in the range of tens of thousands to several millions. These cationic organic coagulants can be used alone or as a mixture.

  Examples of the cationic high molecular organic flocculant include chitosan, a dimethylaminoethyl (meth) acrylate tertiary salt and / or a quaternary salt (for example, methyl chloride quaternary salt) polymer, dimethylaminoethyl (meth). Copolymer of acrylate tertiary salt and / or quaternary salt (for example, methyl chloride quaternary salt) and acrylamide, N-vinylacrylamidine salt unit-containing polymer organic flocculant (for example, JP-A-5-192513, High molecular organic flocculants disclosed in JP-A-8-155500, JP-A-8-243600, JP-A-9-87323, etc.), polyvinyl imidazolic acid or salts thereof, and Mannich modified products of polyacrylamide. However, it is not particularly limited to these. The range of the weight average molecular weight of the cationic polymer organic flocculant is not particularly limited, but a range of several million to 10 million is preferable. These cationic polymer organic flocculants can be used alone or as a mixture.

  As the amphoteric polymer organic flocculant, for example, one or more cationic monomers selected from dimethylaminoethyl (meth) acrylate tertiary salt and / or quaternary salt (for example, methyl chloride quaternary salt) and the like. And amphoteric polymer organic flocculants such as copolymers of acrylamide and one or more anionic monomers selected from acrylic acid and its salts, etc. is not. The range of the weight average molecular weight of the amphoteric polymer organic flocculant is not particularly limited, but a range of several million to 10 million is preferable. These amphoteric polymer organic flocculants can be used alone or as a mixture.

In this invention, following the 2nd process, the 3rd process which isolate | separates an insolubilized material from 2nd treated water and produces the sludge containing an insolubilized material and final treated water is performed.
The third step can be performed using any known apparatus and method as long as the insolubilized material is separated from the second treated water to generate sludge and final treated water. Examples include, but are not limited to, separation, membrane separation, and pressure levitation separation. For example, in the embodiment of FIG. 1, the second treated water is supplied to the sedimentation tank 12 via the second treated water supply line 8 ′. A sludge extraction line 13 is connected to the settling tank 12, and sludge that has settled and separated is extracted from the settling tank 12 through the sludge extraction line 13. In addition, the final treated water generated by separating the insolubilized material is discharged from the final treated water discharge line 14.

  The final treated water produced in the third step has reduced fluorine. In the method of the present invention, the fluorine concentration in the final treated water is preferably adjusted to 8 mg · F / L or less, more preferably 5 mg · F / L or less. It is possible to reduce. The final treated water may be discharged out of the system as it is depending on the fluorine concentration, pH, etc., and further treatment may be performed as appropriate.

In the present invention, following the third step, a part of the sludge is discharged out of the system, and acid or alkali is added to the remaining sludge to regenerate the sludge. A fourth step of returning to the first step and / or the second step and adding to the fluorine-containing water in the first step and / or the first treated water in the second step is performed.
In the fourth step, a part of the sludge separated in the third step is discharged out of the system, and this sludge can be discharged out of the system using any known apparatus and method. There is no particular limitation. For example, in the embodiment of FIG. 1, an excess sludge extraction pump 15 is interposed in the sludge extraction line 13, and a portion of the sludge is discharged out of the system by the excess sludge extraction pump 15.

  In the fourth step, a portion other than the sludge discharged out of the system among the sludge separated in the third step is returned to the first step and / or the second step as recycled sludge. This sludge can be returned using any known apparatus and method as long as the sludge can be returned to the first step and / or the second step as regenerated sludge, and is not particularly limited. Absent. For example, in the embodiment of FIG. 1, the sludge extraction line 13 is connected to the sludge return line 4 between the excess sludge extraction pump 15 and the settling tank 12, and the sludge return line 16 is connected to the sludge return line 4. It is disguised. This sludge return pump 16 returns the portion of the sludge drawn out from the settling tank 12 to the first step and / or the second step via the sludge return line 4 except for the sludge discharged outside the system. Sludge is added to the calcium reaction tank 1 and / or the inorganic reaction tank 6.

  The regenerated sludge is prepared by adding an acid or alkali to the sludge separated in the third step and regenerating it. When the regeneration treatment is performed by adding an acid to sludge, the acid used is not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, and nitric acid. When acid is used in the regeneration treatment, the pH of the sludge is preferably 4 or less, and more preferably the pH of the sludge is 3-4. Moreover, when a regeneration process is performed by adding an alkali to sludge, the alkali used is not specifically limited, For example, sodium hydroxide, calcium hydroxide, etc. are mentioned. When alkali is used in the regeneration treatment, the pH of the sludge is preferably 9 or more, and more preferably the pH of the sludge is 10-12. Preferably, the regeneration treatment is performed using calcium hydroxide (slaked lime), which can be made alkaline by adding calcium hydroxide to sludge and using calcium hydroxide as a calcium source. This is because the fluorine released from the dissolved aluminum can be converted to calcium fluoride.

  In the fourth step, any known apparatus and method can be used as long as the sludge can be regenerated by adding acid or alkali as a regenerant to the sludge. For example, acid or alkali can be used in the sludge return line. It is also possible to connect the line to which the material is added and perform the regeneration process in the sludge return line. Further, as shown in FIG. 1, a sludge regeneration tank 17 is interposed in the sludge return line 4, and the sludge returned from the sludge return line 4 is stored in the sludge regeneration tank 17, and the sludge regeneration tank 17 In this case, the sludge may be regenerated by adding and mixing acid or alkali through the regenerant addition line 19. When the sludge regeneration tank 17 is used, the sludge regeneration tank 17 may be provided with any known device such as a stirring device as shown in FIG.

  The present invention is characterized in that the ratio of the flow rate of returned sludge / the flow rate of sludge discharged outside the system in the fourth step is adjusted using the sludge concentration in the sludge as an index. In the present specification, the sludge concentration refers to the concentration of sludge solids contained in the sludge. In the present invention, the sludge discharged outside the system and the first step and / or the second step before the regeneration treatment. Since the sludge returned to is the same sludge, the sludge concentration of any sludge may be measured and the measured value may be used as an index. In addition, acid or alkali is added in the regeneration treatment. If the amount of acid or alkali added to the amount of sludge does not substantially change the sludge concentration, the sludge concentration measured in the regenerated sludge is left as it is. It can also be used as an index for the sludge concentration in the sludge. Furthermore, in the preparation of regenerated sludge, when the addition of acid or alkali substantially changes the sludge concentration in the sludge, the sludge concentration measured in the regenerated sludge is corrected by the amount of acid or alkali added. It is also possible to calculate the sludge concentration in the sludge and use this calculated value as the sludge concentration in the sludge.

  The measurement of the sludge concentration in the sludge can be usually performed using an arbitrary device such as a sludge concentration meter used for measuring the sludge concentration. For example, in the embodiment of FIG. 1, a sludge concentration meter 18 is installed in the sludge regeneration tank 17, and the value measured by the sludge concentration meter 18 is corrected as it is or with the addition amount of acid or alkali to obtain the sludge concentration. Is possible. In addition to this, a mode in which the sludge concentration in the sludge passing through the sludge extraction line 13 is measured by interposing a sludge concentration meter on the sludge extraction line 13 may be used. The aspect which measures the sludge density | concentration in the sludge which passes the sludge return line 4 by interposing a sludge concentration meter on the previous sludge return line 4 may be sufficient.

  In the present invention, the ratio of the flow rate of the returned sludge / the flow rate of the sludge discharged outside the system in the fourth step is adjusted using the sludge concentration in the sludge as an index. In the present invention, the adjustment method is not particularly limited as long as the ratio of the flow rate of returned sludge / the flow rate of sludge discharged outside the system can be adjusted. For example, 1) A mode in which the flow rate of returned sludge is constant and the flow rate of sludge discharged outside the system is adjusted using the sludge concentration in the sludge as an index, and 2) discharged outside the system. A mode in which the flow rate of the sludge is constant and the flow rate of the returned sludge is adjusted using the sludge concentration in the sludge as an index, or 3) sludge returned using the sludge concentration in the sludge as an index The aspect performed by adjusting both the flow volume of this and the flow volume of the sludge discharged | emitted out of the system is mentioned. From the viewpoint that the ratio of the flow rate of the returned sludge / the flow rate of the sludge discharged outside the system can be adjusted more easily by adjusting one of the flow rates, the above 1) or 2) This embodiment is preferred.

  When the flow rate of the returned sludge is constant, for example, 0.5 to 30% of the flow rate of fluorine-containing water (that is, the flow rate of raw water) introduced into the treatment system in which the method of the present invention is performed, preferably 1 It can be set to -10%. Further, when the flow rate of sludge discharged outside the system is constant, for example, 0.1 to 30% of the flow rate of fluorine-containing water (that is, the raw water flow rate) introduced into the treatment system in which the method of the present invention is performed. Preferably, it can be set to 0.5 to 10%. Further, the sludge discharge is not necessarily continuous, and it can be performed intermittently by performing on / off control and repeating the stop and discharge.

  Adjustment of the flow rate of sludge to be returned and / or the flow rate of sludge discharged outside the system is performed using the sludge concentration in the sludge as an index. It is possible to carry out with this apparatus and method. For example, in the embodiment of FIG. 1, the sludge discharge flow rate by the excess sludge extraction pump 15 interposed in the sludge extraction line 13 is determined according to the sludge concentration value measured by the sludge concentration meter 18 provided in the sludge regeneration tank 17. By controlling, the method of the present invention can be carried out by adjusting the flow rate of sludge discharged outside the system. Moreover, in another aspect, according to the sludge density | concentration value measured by the sludge concentration meter 18 provided in the sludge reproduction | regeneration tank 17, the return flow rate of the sludge by the sludge return pump 16 interposed by the sludge return line 4 is controlled. Thus, the method of the present invention can be carried out by adjusting the flow rate of the returned sludge. Furthermore, in another aspect, according to the sludge concentration value measured by the sludge concentration meter 18 provided in the sludge regeneration tank 17, the sludge return flow rate by the sludge return pump 16 interposed in the sludge return line 4 is controlled. In addition, by controlling the sludge discharge flow rate by the excess sludge draw pump 15 interposed in the sludge draw line 13, both the flow rate of returned sludge and the flow rate of sludge discharged outside the system are adjusted. Thus, the method of the present invention can be carried out. In any of the above embodiments, the control of the excess sludge extraction pump 15 and / or the sludge return pump 16 by the sludge concentration value can be automatically controlled by a computer or manually, and is not particularly limited.

In the adjustment of the ratio of the flow rate of returned sludge / the flow rate of sludge discharged out of the system using the sludge concentration in the sludge as an index in the fourth step of the present invention, the sludge concentration is a constant value or a constant value. The ratio is controlled so as to be in the range of. In one embodiment, when the sludge concentration falls below a predetermined value or the lower limit of the predetermined range, the ratio of the flow rate of returned sludge / the flow rate of sludge discharged out of the system (that is, a numerical value obtained from the equation) The flow rate of returned sludge and the flow rate of sludge discharged outside the system are controlled so as to increase. Further, when the sludge concentration exceeds a predetermined value or the upper limit of the predetermined range, the ratio of the flow rate of returned sludge / the flow rate of sludge discharged out of the system (that is, a numerical value obtained from the equation) is reduced. In addition, the flow rate of returned sludge and the flow rate of sludge discharged outside the system are controlled.
For example, in the embodiment of FIG. 1, when the sludge flow rate returned by the sludge return pump 16 is constant, if the sludge concentration measured by the sludge concentration meter 18 is less than a predetermined value or a lower limit of a predetermined range, surplus When the sludge discharge flow rate from the sludge extraction pump 15 is reduced and the sludge concentration measured by the sludge concentration meter 18 exceeds a predetermined value or an upper limit of a predetermined range, the sludge discharge flow rate from the excess sludge extraction pump 15 The sludge concentration can be adjusted by increasing the value.
In another aspect, when the flow rate of sludge discharged from the system from the excess sludge extraction pump 15 is constant, the sludge concentration measured by the sludge concentration meter 18 is a predetermined value or a lower limit of a predetermined range. The sludge return pump 16 increases the return flow rate of the sludge, and the sludge concentration measured by the sludge concentration meter 18 exceeds the predetermined value or the upper limit of the predetermined range. It is possible to adjust the sludge concentration by reducing the return flow rate.
Furthermore, in another aspect, when the sludge concentration measured by the sludge concentration meter 18 falls below a predetermined value or a lower limit of a predetermined range, the sludge discharge flow rate from the excess sludge extraction pump 15 is reduced, and the sludge return pump When the sludge return flow rate from 16 and the sludge concentration measured by the sludge concentration meter 18 exceeds a predetermined value or the upper limit of the predetermined range, the sludge discharge flow rate from the excess sludge extraction pump 15 is increased, And it becomes possible to adjust a sludge density | concentration by restrict | squeezing the return flow rate of the sludge from the sludge return pump 16, but it is not limited to these aspects.

Preferably, in the present invention, the ratio of the flow rate of sludge to be returned / the flow rate of sludge discharged out of the system is such that the sludge concentration is in the range of 1 to 15% (sludge solid content weight / sludge volume). Adjusted. In other embodiments, preferably the sludge concentration is a predetermined value within the range of 1-15%, such as 1%, 3%, 5%, 8%, 10%, 15%, etc., or a predetermined range, such as The ratio of the flow rate of returned sludge / the flow rate of sludge discharged out of the system may be adjusted so as to be a combination of the predetermined values, for example, 3 to 5% and 8 to 10%. In the present invention, by setting the sludge concentration to 1% or more, even if the amount of aluminum added in the second step is small (for example, 15 mg · Al / L or less), the reaction field in the second step is sufficient. It is possible to maintain a high aluminum concentration. In addition, by setting the sludge concentration to 15% or less, it is possible to prevent inconveniences in apparatus maintenance such as blockage of piping, and it is possible to prevent deterioration of cohesiveness due to an increase in SS concentration in the system. In the method of the present invention, by controlling the system using the sludge concentration as an index, aluminum in the reaction field (inorganic reaction tank in the embodiment of FIG. 1) can be obtained even if the amount of aluminum salt added in the second step is small. The concentration can be maintained in an appropriate range, and fluorine can be appropriately removed.
EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

Examples 1-3
The fluorine removal treatment was performed by the method for treating fluorine-containing water of the present invention using the flow of the embodiment shown in FIG. As the fluorine-containing water to be treated, hydrofluoric acid waste water (fluorine content of about 100 mg · F / L) discharged from a semiconductor manufacturing factory was used, and the raw water flow rate to the treatment system was 100 L / h.
The first step is performed in a calcium reaction tank (25 L) while maintaining pH = 10, slaked lime is used as the calcium compound, and the slaked lime is added so that the dissolved calcium concentration in the first treated water is 400 mg · Ca / L. Added.
The second step is performed in an inorganic reaction tank (25 L) while maintaining pH = 7, using PAC as an aluminum salt and adding so that the concentration of PAC added to the first treated water is 300 mg / L. It was done.
In addition, after the addition of PAC, in the polymer reaction tank (25 L), ORFLOCK OA-23 (manufactured by Organo Corporation) that is a polymer flocculant is added in an amount such that the concentration in the second treated water is 2 mg / L. Added to the second treated water.
In the third step, the second treated water after the addition of the polymer flocculant was solid-liquid separated into final treated water and sludge in the settling tank (100 L).
In the fourth step, the sludge was returned to the second step, and the flow rate of the returned sludge was constant at 5% of the raw water flow rate. In the sludge reaction tank (5 L) interposed in the sludge return line, sludge was regenerated by adding slaked lime to the sludge so that the sludge had a pH of 11. The sludge concentration was measured with a sludge concentration meter (manufactured by Organo Corporation, TS-701D) installed in the sludge reaction tank.

  In Examples 1 to 3, the sludge concentration measured in the regenerated sludge tank was set to 1% (Example 1), 10% (Example 2), or 15% (Example 3), respectively, and regenerated. When the sludge concentration measured by the sludge concentration meter in the sludge tank becomes less than the set concentration, the sludge discharge flow rate from the excess sludge extraction pump is reduced, and when the sludge concentration exceeds the set concentration, the sludge from the excess sludge extraction pump. The sludge concentration was adjusted to each set concentration by controlling the ratio of the flow rate of the returned sludge / the flow rate of the sludge discharged outside the system.

For the final treated water 5 hours after the start of liquid flow, the fluorine ion concentration was measured as the fluorine concentration in the final treated water. The fluorine ion concentration was measured by ion chromatography.
The aluminum concentration in the inorganic reaction vessel was measured. The aluminum concentration was measured by ICP-MS method.

Comparative Examples 1-4
As a comparative example, a conventional sludge circulation method in which both the flow rate of returned sludge and the flow rate of sludge discharged outside the system are constant was performed. That is, in Comparative Examples 1 to 4, the sludge discharge flow rate from the excess sludge extraction pump was 1.0 m ³ / L (Comparative Examples 1 and 2), 0.1 m ³ / L (Comparative Example 3), 5.8 m. ³ / L (Comparative Example 4) was fixed, and the fluorine removal treatment of fluorine-containing water was performed in the same manner as in Examples 1 to 3 except that the control based on the sludge concentration was not performed.

  The results of Examples and Comparative Examples are listed in Table 1 below.

In Comparative Example 1, it was revealed that the sludge discharge flow rate was 1.0 m ³ / L, and the fluorine concentration in the final treated water was 7 mg · F / L, which was a good treatment. However, in Comparative Example 2, the sludge discharge flow rate was 1.0 m ³ / L, which is the same as that in the Comparative Example, but the fluorine concentration in the final treated water was 13 mg · F / L, which is insufficient in terms of fluorine removal. there were. This is wastewater produced in the actual factory by the fluorine-containing water treated in the examples and comparative examples, and the composition thereof is not constant. It was thought that even if the discharge flow rate to the outside of the system was constant, the sludge diminished without being concentrated, thereby reducing the aluminum concentration in the inorganic reaction tank. That is, from the results of Comparative Examples 1 and 2, it has been clarified that the conventional method in which the sludge discharge flow rate is a constant amount cannot sufficiently cope with the deterioration of cohesiveness caused by fluctuations in fluorine-containing water.

  In Comparative Example 3, since the sludge discharge flow rate is too small, it is considered that the sludge concentration in the system is excessively increased to cause cohesion failure. Further, in Comparative Example 4, it is considered that since the sludge discharge flow rate is too large, the aluminum concentration in the system becomes too low and the fluorine removing ability is lowered. This indicates that the sludge discharge flow rate needs to be set to an appropriate value in the conventional method in which the sludge discharge amount is constant.

In each of Examples 1 to 3, the fluorine concentration in the final treated water was 8 mg · F / L or less, indicating a good fluorine removing ability. From this, by controlling the sludge discharge flow rate so that the sludge concentration is constant, it is possible to sufficiently cope with the deterioration of cohesiveness caused by fluctuations in fluorine-containing water as in Comparative Examples 1 and 2. Became clear. Moreover, it became clear that the setting of the discharge flow rate of sludge like the comparative examples 3 and 4 is unnecessary.

FIG. 1 is a schematic diagram showing one embodiment of a flow that can be used in the method for treating fluorine-containing water of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Calcium reaction tank 2 Fluorine containing water supply line 3 Calcium compound supply line 4 Sludge return line 5 1st treated water supply line 6 Inorganic reaction tank 7 Aluminum salt supply line 8, 8 '2nd treated water supply line 9 pH adjuster supply Line 10 Polymer reaction tank 11 Polymer flocculant supply line 12 Sedimentation tank 13 Sludge extraction line 14 Final treated water discharge line 15 Excess sludge extraction pump 16 Sludge return pump 17 Sludge regeneration tank 18 Sludge concentration meter 19 Regenerant addition line

Claims (4)

A first step of adding a calcium compound to fluorine-containing water to form calcium fluoride and producing a first treated water containing the calcium fluoride;
A second step of adding an aluminum salt to the first treated water to form an insolubilized product, and generating a second treated water containing the insolubilized product;
A third step of separating the insolubilized material from the second treated water to produce sludge containing the insolubilized material and final treated water;
A part of the sludge is discharged out of the system, and acid or alkali is added to the remaining sludge. After the sludge is regenerated, the regenerated sludge is returned to the first step and / or the second step. In the method for treating fluorine-containing water comprising the fluorine-containing water in the first step and / or the fourth step added to the first treated water in the second step,
In the fourth step, the method for treating fluorine-containing water is characterized in that the ratio of the flow rate of returned sludge / the flow rate of sludge discharged outside the system is adjusted using the sludge concentration in the sludge as an index.   The adjustment of the ratio of the flow rate of returned sludge / the flow rate of sludge discharged out of the system with the sludge concentration in the sludge as an index in the fourth step is as follows: 1) The flow rate of returned sludge is constant Either by adjusting the flow rate of sludge discharged outside the system using the sludge concentration in the sludge as an index, or 2) the sludge flow rate discharged outside the system is constant and the sludge concentration in the sludge 3) Adjusting the flow rate of the sludge to be returned, or 3) Using both the sludge concentration in the sludge as an indicator, both the flow rate of the returned sludge and the flow rate of the sludge discharged outside the system It is performed by adjusting, The processing method of the fluorine-containing water of Claim 1 characterized by the above-mentioned.   The method for treating fluorine-containing water according to claim 1 or 2, wherein in the second step, the aluminum concentration in the second treated water is 50 mg / L or more. The method for treating fluorine-containing water according to any one of claims 1 to 3, wherein the adjustment in the fourth step is performed such that the sludge concentration in the sludge is in the range of 1% to 15%.

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