TW202308948A - Method for treating fluorine-containing water - Google Patents

Abstract

Provided is a method for treating fluorine-containing water, which can control the amount of a calcium compound added to a sludge modification tank to a proper amount in a fluorine-containing water treatment device in which a part of sludge separated in a solid-liquid separation tank is introduced into a modification tank, and a calcium compound is added thereto, followed by circulation to a reaction tank. In a first reaction tank 1, modified sludge from a sludge modification tank 5 and, if required, a calcium compound and a pH adjuster are added to raw water, and the resultant is introduced into a flocculation tank 3 through a second reaction tank 2 and subjected to flocculation treatment. Flocculation treatment water in the flocculation tank 3 is subjected to solid-liquid separation in a precipitation tank 4, and a part of the separated sludge is introduced into the sludge modification tank 5. A calcium compound-containing liquid is added to the sludge modification tank 5 via a control valve 13. The amount of the calcium compound added is controlled on the basis of the flow rate and fluorine concentration of raw water and the calcium concentration in the second reaction tank 2.

Description

How to deal with fluoride water

The present invention relates to a method for treating fluorine-containing water for removing fluorine from fluorine-containing water.

As a method for removing fluorine from fluorine-containing water, a method of adding calcium compounds such as hydrated lime and calcium chloride to fluorine-containing water in a reaction tank to adjust the pH to 6 to 10, and to precipitate precipitates including calcium fluoride , adding a polymer coagulant in the coagulation tank for coagulation reaction, and carrying out precipitation and separation in the precipitation tank.

However, in this treatment method, since the generated flocs are gel-like hydroxides containing a large amount of water, the settleability is poor. In addition, the generated sludge has poor dehydration properties, and its treatment is not easy. In addition, the fluorine concentration of the treated water cannot be sufficiently reduced.

As a method for improving the above-mentioned aspects, Patent Document 1 describes a fluorine removal method that uses a reaction tank that reacts fluorine-containing water with a calcium compound, a raw water channel that introduces fluorine-containing water into the reaction tank, and transfers fluorine from the reaction tank. A coagulation device for coagulation by adding a polymer coagulant to the reaction liquid, and a solid-liquid separation tank for introducing a mixed liquid containing flocs formed in the coagulation device for solid-liquid separation. A part of the sludge is introduced into the reforming tank, and after adding the calcium compound, it is circulated to the reaction tank.

Patent Document 2 and Patent Document 3 also describe similar fluorine-containing water treatment methods. [Prior art literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 10-479 [Patent Document 2] Japanese Patent Laid-Open No. 2007-190517 [Patent Document 3] Japanese Patent Laid-Open No. 2009-233568

[Problem to be Solved by the Invention] The amount of the calcium compound to be added to the sludge reforming tank was measured by measuring the flow rate and the fluorine concentration of the raw water, and controlling based on the results.

However, when the calcium compound is poorly soluble such as slaked lime (calcium hydroxide), calcium carbonate, etc., the concentration of the calcium compound aqueous solution cannot reach the set value, and the added amount of the calcium compound may deviate from the target value.

When the addition of the calcium compound to the sludge reforming tank is insufficient, the removal of fluorine from the fluorine-containing water becomes insufficient. Conversely, when the calcium compound is added excessively, not only the chemical cost is high, but also when the treated water is reused, treatment for reducing the calcium concentration in the treated water is required.

The object of the present invention is to provide a method for treating fluorine-containing water, which introduces a part of the sludge separated in the solid-liquid separation tank to the sludge reforming tank, and circulates it to the reaction tank after adding a calcium compound, In addition, in the treatment method of the above-mentioned fluorine-containing water, the addition amount of the calcium compound to the sludge reforming tank can be controlled so that it becomes an appropriate amount. [Means to solve the problem]

The treatment method of fluorine-containing water of the present invention uses a treatment device for fluorine-containing water, and the treatment device for said fluorine-containing water includes: a reaction tank, which reacts raw water containing fluorine-containing water and a calcium compound to generate a reaction liquid; a raw water passage, Introduce raw water into the reaction tank; coagulation device, transfer the reaction liquid from the reaction tank, and add a polymer coagulant for coagulation; solid-liquid separation tank, introduce the mixed liquid containing flocs formed in the coagulation device and perform solid-liquid separation and a circulation path for introducing a part of the sludge separated in the solid-liquid separation tank to the sludge reforming tank, and adding a calcium compound through the calcium compound adding part to circulate it to the reaction tank, and the fluorine-containing The water treatment method is characterized in that the addition amount of the calcium compound to the sludge reforming tank is controlled based on the fluorine concentration of raw water, the flow rate of raw water, and the calcium concentration in the reaction liquid.

In one aspect of the present invention, as the reaction tank, there are provided: a first reaction tank into which raw water and sludge from the sludge reforming tank are introduced; and a second reaction tank into which the The effluent of the first reaction tank is added with a pH adjuster, and in the form, based on the fluorine concentration of the raw water and the flow rate of the raw water, and the reaction liquid in or out of the second reaction tank Calcium concentration to control the amount of calcium compound added to the sludge reforming tank.

In one aspect of the present invention, the standard addition amount is determined so as to be equivalent to the amount of fluorine introduced into the first reaction tank, and is based on the reaction in the second reaction tank or outflow from the second reaction tank. The detected calcium concentration in the solution is used to correct the base addition amount.

In one aspect of the present invention, regarding the correction, when the calcium concentration in the reaction solution is lower than a preset calcium concentration target value, the addition of the calcium compound is increased according to the difference between the calcium concentration target value and the detected calcium concentration. When the detected calcium concentration in the reaction solution is higher than the preset calcium concentration target value, the added amount of the calcium compound is reduced according to the difference between the detected calcium concentration and the calcium concentration target value.

In one aspect of the present invention, calcium hydroxide slurry (slurry) is added as the calcium compound. [Effect of the invention]

In the method for treating fluorine-containing water of the present invention, the addition amount of the calcium compound to the sludge reforming tank is controlled based not only on the fluorine concentration in the raw water but also on the calcium concentration in the reaction solution, so the concentration of the calcium compound can be appropriately controlled. Add amount. Thereby, the water quality of the treated water is also improved. In addition, since calcium scale in the treated water is low and calcium scale is suppressed, biological treatment can be applied in the latter stage of this treatment.

Hereinafter, an embodiment will be described with reference to FIG. 1 .

Fig. 1 is a system diagram showing an embodiment of a fluorine-containing water treatment device for carrying out the method of the present invention. In Fig. 1, 1 represents a first reaction tank into which raw water is introduced via a raw water pipe 1a, and 2 represents a second reaction. Tank, 3 denotes coagulation tank, 4 denotes sedimentation tank, 5 denotes sludge reforming tank. The raw water pipe 1a is provided with a raw water flowmeter 21 and a fluorine sensor 16 including a fluorine ion electrode for detecting the fluorine concentration of the raw water.

In FIG. 1 , the reaction between raw water and calcium compounds is carried out in a first reaction tank 1 and a second reaction tank 2 arranged in series in two stages. That is, the modified sludge from the sludge reforming tank 5 is added to the first reaction tank 1, and at the same time, a calcium compound and a pH value regulator are added as needed, preferably at a pH of 4 to 10, more preferably at a pH of 6 The fluorine in the raw water is almost insoluble at ~6.5. The effluent from the first reaction tank 1 is introduced into the second reaction tank 2, and a pH adjuster is added if necessary, preferably at a pH of 4-10, more preferably at a pH of 6-6.5 to insolubilize residual fluorine. In addition, in order to further insolubilize fluorine in the second reaction tank 2, a calcium compound may be added in addition to the pH adjuster.

A calcium sensor 9 such as a calcium ion sensor for detecting the concentration of calcium ions is provided in the second reaction tank 2 . Furthermore, besides the second reaction tank 2, the calcium sensor 9 may be installed on the piping 2a between the second reaction tank 2 and the coagulation tank 3, or the piping 4a through which the treated water of the sedimentation tank 4 passes.

The effluent from the second reaction tank 2 is introduced into the coagulation tank 3, and a polymer coagulant is added thereto for coagulation treatment. The polymer coagulant is not particularly limited as long as it is used for coagulation treatment of suspended wastewater, for example, a polyacrylamide-based polymer coagulant or the like is used. In addition, in order to improve the coagulation effect, it is also possible to add a polymer coagulant after adding an inorganic coagulant such as poly aluminum chloride (Poly aluminum chloride, PAC) or aluminum sulfate.

The coagulation-treated water in the coagulation tank 3 is then introduced into the sedimentation tank 4 via the pipe 3a, subjected to solid-liquid separation, and the separated water is discharged outside the system as treated water. Part of the separated sludge is sent to the sludge reforming tank 5 as return sludge, and the remaining part is discharged out of the system as excess sludge.

By adding and mixing a calcium compound in the sludge reforming tank 5 , at least a part of the calcium compound adheres to the surface of the sludge by adsorption or the like, and the sludge is reformed. When the modified sludge is introduced into the first reaction tank 1, the calcium compound on the sludge surface reacts with the fluorine in the raw water, and the sludge particles grow. The sludge grown in this way is efficiently settled in the sedimentation tank 4 because of its good settling property.

The calcium compound is added to the sludge reforming tank 5 in the form of a calcium compound-containing liquid (for example, an aqueous slurry of slaked lime (calcium hydroxide) or calcium carbonate, or an aqueous solution of calcium chloride). The calcium compound-containing liquid is preferably slaked lime slurry, and its concentration is less than 20 wt%, ideally 10 wt%. Aqueous calcium chloride solutions are used at standard concentrations (eg 35 wt%).

The calcium compound-containing liquid is added to the sludge reforming tank 5 through the piping 10, the on-off valve 11, the piping 12, the control valve 13, and the piping 14 by a pump or the like.

The control valve 13 is configured to be able to continuously change the opening degree (that is, the calcium compound supply amount), and the opening degree is controlled by the controller 15 . The controller 15 is based on the detection signal of the calcium sensor 9, the fluorine sensor 16 including a fluorine ion electrode for detecting the fluorine concentration of the raw water, the detection signal of the raw water flow meter 21 of the raw water piping, and the The detection signal of the flow meter 17 is used to control the opening of the control valve 13 .

The amount of calcium compound to be added is basically determined so that it is equivalent to the amount of fluorine introduced into the first reaction tank 1 (obtained from the product of the flow rate of raw water and the fluorine concentration of raw water). The calcium concentration detected by the device 9 is determined by correcting the reference addition amount. In one example of the correction, when the calcium concentration detected by the calcium sensor 9 is lower than the preset calcium concentration target value, the calcium compound addition amount is increased according to the difference between the calcium concentration target value and the detected calcium concentration. On the contrary, when the calcium concentration detected by the calcium sensor 9 is higher than the preset calcium concentration target value, the added amount of the calcium compound is reduced according to the difference between the detected calcium concentration and the calcium concentration target value.

Furthermore, in the above-described embodiment, in order to prevent clogging of the control valve 13 , washing water can be supplied to the pipe 12 through the pipe 19 having the valve 18 . By closing the valve 11 and opening the valve 18, washing water is introduced into the control valve 13, and the control valve 13 is washed with the washing water to prevent clogging. The washing of the control valve 13 using the washing water is preferably performed regularly by using a timer, for example, once every 5 minutes to 24 hours, especially about once an hour, and at a frequency of once. The passing time of the purified water is 1 minute to 10 minutes, especially about 2 minutes and 30 seconds, but it is not limited thereto. As washing water, tap water, industrial water, etc. can be used.

Thus, in this embodiment, since the calcium compound addition amount is corrected using the detection value of the calcium sensor 9, even if the calcium compound concentration of the calcium compound solution fluctuates, appropriate calcium compound addition control is performed. Thereby, treated water with good water quality can be obtained, and for example, the fluorine concentration and calcium concentration in the treated water can be reduced. In addition, this makes it easy to reuse the treated water.

In the above-described embodiment, since the control valve 13 is washed with washing water, clogging of the control valve 13 is prevented and stable treatment can be performed.

Although this indication was demonstrated in detail using the specific form, it is clear to those skilled in the art that various changes can be made without deviating from the intention and range of this indication. This application is based on Japanese Patent Application No. 2021-135698 filed on August 23, 2021, the entirety of which is incorporated by reference.

1: The first reaction tank 1a: Raw water piping 2: The second reaction tank 2a, 3a, 4a, 10, 12, 14, 19: Piping 3: Agglutination tank 4: Sedimentation tank 5: Sludge reforming tank 9: Calcium sensor 11: On-off valve 13: Control valve 15: Controller 16: Fluorine sensor 17, 21: flow meter 18: valve

FIG. 1 is a configuration diagram of a treatment apparatus for fluorine-containing water according to an embodiment.

1: The first reaction tank

1a: Raw water piping

2: The second reaction tank

2a, 3a, 4a, 10, 12, 14, 19: Piping

3: Agglutination tank

4: Sedimentation tank

5: Sludge reforming tank

9: Calcium sensor

11: On-off valve

13: Control valve

15: Controller

16: Fluorine sensor

17, 21: flow meter

18: valve

Claims (5)

A treatment method for fluorine-containing water is characterized in that a treatment device for fluorine-containing water is used, and the treatment device for fluorine-containing water comprises: A reaction tank for reacting raw water containing fluorine-containing water with a calcium compound to generate a reaction solution; Raw water channel, importing raw water to the reaction tank; The agglutination device transfers the reaction liquid from the reaction tank, and adds a polymer agglutinant for agglutination; a solid-liquid separation tank, which introduces the mixed liquid containing flocs formed in the coagulation device and performs solid-liquid separation; and a circulation path for introducing a part of the sludge separated in the solid-liquid separation tank to the sludge reforming tank, and adding a calcium compound through the calcium compound adding part to circulate it to the reaction tank, and The method for treating fluorine-containing water controls the amount of calcium compound added to the sludge reforming tank based on the fluorine concentration of raw water, the flow rate of raw water, and the calcium concentration in the reaction liquid. The method for treating fluorine-containing water according to Claim 1, wherein, as the reaction tank, there is provided: a first reaction tank into which raw water and sludge from the sludge reforming tank are introduced; and a second reaction tank A reaction tank, in which the effluent of the first reaction tank is introduced and a pH adjuster is added, the treatment method of the fluorine-containing water is based on the fluorine concentration of the raw water and the flow rate of the raw water, and the fluorine concentration in the second reaction tank or from the The calcium concentration in the reaction solution flowing out of the second reaction tank is controlled to control the amount of calcium compound added to the sludge reforming tank. The method for treating fluorine-containing water according to claim 2, wherein the standard addition amount is determined in such a manner that it is equivalent to the amount of fluorine introduced into the first reaction tank, and is based on the amount in the second reaction tank or from the The calcium concentration detected in the reaction solution flowing out of the second reaction tank is used to correct the base addition amount. The method for treating fluorine-containing water as described in claim 3, wherein regarding the correction, when the calcium concentration in the reaction solution is lower than the preset calcium concentration target value, according to the difference between the calcium concentration target value and the detected calcium concentration Poor, increase the amount of calcium compound added, when the detected calcium concentration in the reaction solution is higher than the preset calcium concentration target value, reduce the added amount of calcium compound according to the difference between the detected calcium concentration and the calcium concentration target value. The method for treating fluorine-containing water according to any one of claim 1 to claim 4, wherein calcium hydroxide slurry is added as the calcium compound.

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