JP2006212540A - Treatment method of chemical-washing waste liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of suitably and low-costly treating a chemical-washing waste liquid containing a chelate agent. <P>SOLUTION: When the chemical-washing waste liquid containing the chelate agent is treated, the waste liquid is concentrated by using a reverse osmosis membrane and thereafter the concentrated waste liquid is further concentrated by heating or decompressing to be recovered as a salt containing the chelate agent, in particular as a solid containing the chelate agent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for treating a chemical cleaning waste liquid generated by removal of equipment at a nuclear power plant, and more particularly to a method for treating a chemical cleaning waste liquid containing a chelating agent.

  Chemical cleaning of equipment is performed for the purpose of reducing radioactivity during removal and maintenance of equipment used in nuclear power plants, etc., or removing accumulated sludge. This chemical cleaning generally generates a waste liquid containing a high concentration chelating agent (citric acid, EDTA, etc.).

  The waste liquid containing such a chelating agent is difficult to solidify as it is because the elution rate of the radioactive substance from the solidified body increases when the radioactive waste liquid is solidified (such as concrete solidification). For this reason, it is necessary to perform a solidification process after separating the chelating agent by a separation process or a decomposition process.

As a method for decomposing / separating a chelating agent, a method of combining oxidative decomposition treatment and biological treatment (Patent Document 1), a method of depositing with calcium hydroxide (Patent Document 2), and the like are known.
JP 2000-176462 A Japanese Patent Laid-Open No. 11-352289

  However, when cleaning large equipment (such as a steam generator), the amount of waste liquid generated becomes enormous, and therefore concentration and volume reduction are required prior to the decomposition treatment. Although the evaporative concentration method can be applied, evaporating and concentrating the whole amount of a large amount of waste liquid is expensive and not practical. If a reverse osmosis membrane is used, it is possible to concentrate the chelating agent, but in order to reduce the volume, it is necessary to concentrate the chelating agent to a concentration of 5% or more, desirably 10% or more. Since the reverse osmosis membrane has the property that the solute leaks to the permeate side when the concentration of the solute in the raw water increases, the water quality of the permeate (treated water) becomes a problem when concentrated to a high concentration as described above. .

  That is, when the waste liquid is in a large amount, the treated water is usually continuously discharged by an existing waste water treatment facility and then discharged or collected. In the case of direct discharge, the permeated water needs to satisfy the drainage standard value, so it cannot be concentrated above a certain concentration. In addition, when released or reused after being treated in the desalting tower, the chelating agent contained in the permeated water becomes a load of the ion exchange resin, which makes it difficult to dispose of the ion exchange resin or to solidify the recycled waste liquid. Absent. In order to prevent these problems, it is necessary to use a membrane with a high salt rejection rate, for example, a reverse osmosis membrane for seawater desalination. Since it is necessary to do, it becomes expensive.

  Accordingly, an object of the present invention is to provide a method capable of appropriately treating a chemical cleaning waste liquid containing the above chelating agent at low cost.

  In order to solve the above-mentioned problems, the present inventors have studied a means for concentrating waste liquid at a low cost using a general reverse osmosis membrane (that is, a reverse osmosis membrane that does not require a special high-pressure specification for the entire apparatus). The present invention has been completed. That is, in the method for treating chemical cleaning waste liquid according to the present invention, when processing chemical cleaning waste liquid containing a chelating agent, the waste liquid is concentrated using a reverse osmosis membrane, and then the concentrated waste liquid is further concentrated by heating or decompression. And a salt containing a chelating agent (particularly, a solid containing a chelating agent).

  In such a chemical cleaning waste liquid treatment method, a chemical cleaning waste liquid containing a chelating agent such as citric acid or EDTA is concentrated to a high concentration using a reverse osmosis membrane and then heated or reduced in pressure to solidify the chelating agent. By collecting it as a waste, it becomes possible to temporarily store the waste at a low cost.

  Moreover, in the said process, since a highly purified permeated water is obtained by concentrating a waste liquid with a reverse osmosis membrane of at least 2 steps | paragraphs, it becomes possible to discharge or reuse a treated water substantially continuously. However, when the permeated water that can be continuously discharged or reused is obtained by the one-step reverse osmosis membrane treatment, the two-step or more reverse osmosis membrane treatment is not necessarily required.

  Moreover, in the said process, it is preferable to monitor TOC or COD of the permeate of a reverse osmosis membrane substantially continuously. That is, the chelating agent in the permeated water can be continuously monitored by a TOC meter or a COD meter, and therefore, mixing into an existing processing apparatus can be prevented.

  The chemical cleaning waste liquid in the present invention is not particularly limited, but the present invention is suitable for the treatment of chemical cleaning waste liquid from a nuclear power plant.

  According to the method for treating a chemical cleaning waste liquid according to the present invention, it is possible to obtain a high-purity permeated water quality even when a reverse osmosis membrane having a low rejection rate is used, thereby reducing the cost of the reverse osmosis membrane. In addition, since it is not necessary to use a reverse osmosis membrane for high osmotic pressure, that is, high pressure, the design pressure of the entire apparatus can be kept low, and the concentration apparatus can be downsized. It becomes possible.

  Further, by continuously discharging or collecting the permeated water while monitoring the chelating agent in the permeated water with a TOC meter or a COD meter, a large-capacity waste liquid storage tank becomes unnecessary. Moreover, the load of the chelating agent on the ion exchange resin can be reduced. Furthermore, the chelating agent recovered as a solid is easy to store, and final processing such as decomposition processing and incineration processing is easy.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic equipment system for carrying out a method for treating a chemical cleaning waste liquid according to Example 1 of the present invention, and FIG. 2 shows a method for treating a chemical cleaning waste liquid according to Example 2 of the present invention. 1 shows a schematic equipment system for implementation. The form shown in FIG. 1 is a case where the waste liquid is concentrated by a two-stage reverse osmosis membrane, and the form shown in FIG. 2 is a case where the waste liquid is concentrated by a one-stage reverse osmosis membrane.

  1 and 2, reference numeral 1 denotes raw water containing a chelating agent as a waste liquid to be treated, and 2 denotes a raw water tank that stores the raw water 1. The raw water 1 in the raw water tank 2 is supplied to the first-stage reverse osmosis membrane 4 (reverse osmosis membrane device) by the pump 3 and concentrated there. In the present embodiment, two first-stage reverse osmosis membranes 4 (reverse osmosis membrane devices) are installed in parallel in consideration of the case of processing a large amount of waste liquid.

  In the embodiment shown in FIG. 2, the first-stage reverse osmosis membrane concentrated water 6 concentrated by the first-stage reverse osmosis membrane 4 is returned to the raw water tank 2 to reach a predetermined concentration, or as it is or It is transferred from the raw water tank 2 to another storage tank, further concentrated by heating or decompression, and recovered as a solid containing a chelating agent salt. Since it is further concentrated by heating or depressurization, it is not necessary to concentrate to a particularly high concentration as the concentration treatment by the first-stage reverse osmosis membrane 4, and it is necessary to use a reverse osmosis membrane of a special high pressure specification for the reverse osmosis membrane treatment. However, a normal reverse osmosis membrane can be used. Therefore, it is not necessary to design the entire apparatus to a special high pressure specification.

  In the embodiment shown in FIG. 1, the first-stage reverse osmosis membrane concentrated water 6 concentrated by the first-stage reverse osmosis membrane 4 is returned to the raw water tank 2, and the first-stage reverse osmosis membrane 4 is treated by the first-stage reverse osmosis membrane 4. The first-stage reverse osmosis membrane permeate 8 is supplied to the second-stage reverse osmosis membrane 5 (reverse osmosis membrane device) at the subsequent stage, where it is concentrated. In this embodiment, the first-stage reverse osmosis membrane permeated water 8 supplied to the second-stage reverse osmosis membrane 5 is less than the amount of raw water 1 supplied to the first-stage reverse osmosis membrane 4, so A second-stage reverse osmosis membrane 5 (reverse osmosis membrane device) is installed.

  The second-stage reverse osmosis membrane concentrated water 7 concentrated by the second-stage reverse osmosis membrane 5 is returned to the raw water tank 2 together with the first-stage reverse osmosis membrane concentrated water 6 from the first-stage reverse osmosis membrane 4, After being concentrated, the raw water tank 2 is transferred to another storage tank as it is, further concentrated by heating or decompression, and recovered as a solid containing a salt of a chelating agent. Also in this aspect, normal reverse osmosis membranes can be used for the first-stage reverse osmosis membrane 4 and the second-stage reverse osmosis membrane 5, and the entire apparatus does not need to be designed to a particularly high pressure specification.

  The first-stage reverse osmosis membrane permeated water 8 in the embodiment shown in FIG. 2 or the second-stage reverse osmosis membrane permeated water 9 in the embodiment shown in FIG. 1 is obtained by, for example, using a TOC meter or a COD meter as the chelating agent in the permeated water. It is continuously discharged or collected while it is confirmed by monitoring that the concentration is below a predetermined concentration. Therefore, a large-capacity waste liquid storage tank is unnecessary.

  As a result of processing using the apparatus according to Example 1 shown in FIG. 1 and the apparatus according to Example 2 shown in FIG. 2, good results as shown in Table 1 were obtained. The operating conditions are as shown below.

[Example 1]
・ Raw water: EDTA 4210ppm, adjusted to pH 9 with ammonia ・ First stage reverse osmosis membrane: inlet pressure 2 MPa, permeate pressure 1 MPa, recovery 50%
Second-stage reverse osmosis membrane: inlet pressure 1 MPa, permeate pressure; atmospheric pressure, recovery rate 90%

[Example 2]
-Raw water: EDTA 4210ppm, adjusted to pH 9 with ammonia-1st stage reverse osmosis membrane: inlet pressure 1 MPa, permeate pressure; atmospheric pressure, recovery 50%

  The method for treating chemical cleaning waste liquid according to the present invention can be applied to the treatment of any chemical cleaning waste liquid containing a chelating agent, and is particularly suitable for the treatment of a large amount of chemical cleaning waste liquid generated by removal of equipment of nuclear power plants. Is something.

It is a schematic equipment system diagram for carrying out the processing method of the chemical cleaning waste liquid concerning Example 1 of the present invention. It is a schematic apparatus system diagram for enforcing the processing method of the chemical cleaning waste liquid concerning Example 2 of the present invention.

Explanation of symbols

1 Raw water containing chelating agent as waste liquid to be treated 2 Raw water tank 3 Pump 4 First stage reverse osmosis membrane (reverse osmosis membrane device)
5 Second stage reverse osmosis membrane (reverse osmosis membrane device)
6 1st stage reverse osmosis membrane concentrated water 7 2nd stage reverse osmosis membrane concentrated water 8 1st stage reverse osmosis membrane permeated water 9 2nd stage reverse osmosis membrane permeated water

Claims (5)

  When treating a chemical cleaning waste liquid containing a chelating agent, the waste liquid is concentrated using a reverse osmosis membrane, and then the concentrated waste liquid is further concentrated by heating or decompression and recovered as a salt containing a chelating agent. , Chemical cleaning waste liquid treatment method.   The method for treating a chemical cleaning waste liquid according to claim 1, wherein the waste liquid is concentrated by a reverse osmosis membrane of at least two stages.   The method for treating a chemical cleaning waste liquid according to claim 1 or 2, wherein the TOC or COD of the permeated liquid of the reverse osmosis membrane is substantially continuously monitored.   The method for treating a chemical cleaning waste liquid according to any one of claims 1 to 3, wherein the permeated liquid of the reverse osmosis membrane is discharged or collected.   The chemical cleaning waste liquid treatment method according to claim 1, wherein chemical cleaning waste liquid from a nuclear power plant is treated.

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