JP2009011982A - Treatment apparatus and treatment method of low-concentration polychlorinated biphenyl - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment apparatus and a treatment method of low concentration polychlorinated biphenyl which have advantages such as firstly freedom from wasting of hydrogen peroxide, high efficiency, freedom from uselessness, and excellent running cost, secondly excellent post-treatment cost, thirdly easy control of dose of chemicals, and fourthly excellent treatment stability, initial cost, space and the like. <P>SOLUTION: In this treatment apparatus 2 and treatment method, low-concentration polychlorinated biphenyl 1 contained in an object treatment water 3 is oxidized and decomposed by a Fenton method. The whole amount of an aqueous hydrogen peroxide solution is added by a hydrogen peroxide addition means 6 to the treatment water 3 supplied to a treatment tank 4 in an early stage of the reaction. An iron ion addition means 7 adds a divalent iron ion solution to the object treatment water 3, contained in the treatment tank 4, in divisions. Every time when the iron ion solution is added in divisions to the object treatment water 3 to be supplied and the supplied object treatment water 3, a pH adjustment means 8 adds a pH adjustor to maintain the object treatment water 3 at a pH value of about 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a processing apparatus and processing method for low-concentration polychlorinated biphenyl. That is, the present invention relates to a processing apparatus and a processing method for oxidizing and decomposing low-concentration polychlorinated biphenyl based on the Fenton method.

《Technical background》
Polychlorinated biphenyl (PCB) is a general term for organic compounds in which hydrogen atoms of the aromatic ring of biphenyl are substituted with chlorine atoms, and there are many isomers depending on the number and position of substituted chlorine atoms.
Polychlorinated biphenyl has been widely used as a heat medium, insulating oil, etc. from around 1950 in view of its physical properties and chemical stability. However, since the 1970s, strong toxicity has been recognized, and production is prohibited. Import banned and use suspended.
Thus, polychlorinated biphenyl has become one of the environmental hormones and organic pollutants, and it tends to remain without being decomposed, resulting in a great social problem. In particular, since its manufacture has been banned and discontinued, it has been sequentially collected and stored on the business side, and there is concern about environmental pollution risks, and its reliable processing technology is anxious.

<Conventional technology>
Various treatment techniques for such polychlorinated biphenyls are being studied. For example, the following techniques have been developed.
First, adsorption / desorption methods were developed. That is, after the polychlorinated biphenyl is adsorbed on an adsorbent such as activated carbon and then desorbed in a desorbing solvent such as dichloromethane or acetone, the desorbed liquid is collected in a collection tank, and then the oxidizing agent, ozone, A processing technique for oxidizing and decomposing by ultraviolet irradiation or the like has been developed.
In addition, ozone, hydrogen peroxide, and ultraviolet methods have been developed. That is, a treatment technique has been developed in which polychlorinated biphenyl-containing water is oxidized and decomposed by OH radicals generated by ozone, hydrogen peroxide, ultraviolet irradiation, etc. after adding a flocculant or alkali.

《Information on prior art documents》
Examples of the adsorption / desorption method include those disclosed in Patent Document 1 below. Examples of the ozone / hydrogen peroxide / ultraviolet ray method include those disclosed in the following Patent Document 2.
JP 2003-10842 A Japanese Patent Application Laid-Open No. 2001-129569

About the problem
By the way, the following problems have been pointed out with regard to such conventional polychlorinated biphenyl processing technology.
In other words, problems have been pointed out in processing performance, initial cost, running cost, installation space, etc., and these points are a major bottleneck in the application of scale-up to large-scale treatment and large-capacity treatment of polychlorinated biphenyl, that is, practical application. It was.
For example, regarding the adsorption / desorption method, problems have been pointed out in terms of reduction in processing capacity due to breakthrough of activated carbon, stability of processing, replacement cost of activated carbon, installation space for tanks, etc. In addition, regarding the ozone / hydrogen peroxide / ultraviolet method, problems have been pointed out due to poor OH radical production efficiency, excessive equipment, power consumption cost, UV lamp degradation, and the like.
Other similar processing techniques of this type have also been pointed out. In particular, with regard to the technology that generates OH radicals with hydrogen peroxide to oxidize and decompose polychlorinated biphenyl, the ratio that hydrogen peroxide is decomposed and wasted into water and oxygen without generating OH radicals. Was expensive.
In order to cover this point, an extremely large amount of hydrogen peroxide was previously added in excess, but there was a problem that the efficiency was poor, the waste was high, and the running cost was increased. It was. Furthermore, it has also been pointed out that the residual content of hydrogen peroxide in the waste liquid after treatment increases, and post-treatment costs for neutralization treatment increase.

<< About the present invention >>
The processing apparatus and processing method for low-concentration polychlorinated biphenyls of the present invention have been made in order to solve the above-described problems of the conventional examples in view of such circumstances.
And, according to the present invention, firstly, hydrogen peroxide is not wasted, it is efficient, has no waste, is excellent in running cost, secondly, is excellent in post-processing cost, and thirdly, it is easy to control the amount of chemical addition Fourthly, an object of the present invention is to propose a processing apparatus and a processing method for low-concentration polychlorinated biphenyl, which are excellent in processing stability, initial cost, space and the like.

<About Claim>
The technical means of the present invention for solving such a problem is as follows. First, claim 1 is as follows.
The low concentration polychlorinated biphenyl treatment apparatus according to claim 1 oxidizes and decomposes the low concentration polychlorinated biphenyl contained in the water to be treated by the Fenton method. A treatment tank and a treatment water supply means, a hydrogen peroxide addition means, an iron ion addition means, and a pH adjustment means attached to the treatment tank are provided.
The treated water supply means supplies treated water containing low-concentration polychlorinated biphenyl to the treatment tank. The hydrogen peroxide adding means adds hydrogen peroxide to the water to be treated in the treatment tank. The iron ion adding means adds divalent iron ions to the water to be treated in the treatment tank.
The pH adjusting means maintains the water to be treated at a predetermined weak acidity by adding a pH adjuster to the water to be treated supplied from the treated water supply means to the treatment tank and the water to be treated in the treatment tank. It is characterized by this.

About Claim 2, it is as follows. According to a second aspect of the present invention, there is provided a processing apparatus for low-concentration polychlorinated biphenyl. In the first aspect, the hydrogen peroxide adding means adds a total amount of an aqueous solution of hydrogen peroxide at the beginning of the reaction. The iron ion addition means repeats a plurality of cycles intermittently after the addition of hydrogen peroxide, and adds the divalent iron ion solution in portions.
The pH adjusting means is characterized in that an acid pH adjuster is added before the addition of hydrogen peroxide, and an alkaline pH adjuster is added every time an iron ion solution is added after the addition of hydrogen peroxide. To do.
About Claim 3, it is as follows. According to a third aspect of the present invention, the iron ion adding means adds an aqueous solution of ferrous sulfate. The pH adjusting means is, for example, adding sulfuric acid or caustic soda to maintain the water to be treated in the treatment tank at about pH 4 to suppress the decomposition reaction of the added hydrogen peroxide into water and oxygen, It is characterized by.
About Claim 4, it is as follows. The low-concentration polychlorinated biphenyl processing apparatus according to claim 4 is the processing apparatus according to claim 2, wherein the hydrogen peroxide added in the whole amount is divided into divalent iron ions dividedly added as a catalyst. It is reduced with each addition to generate OH radicals.
At the same time, the polychlorinated biphenyl contained in the water to be treated is oxidized and decomposed by the OH radicals, and thus is mineralized into a low molecular compound such as water or carbon dioxide gas.

About Claim 5, it is as follows. In the method for treating low-concentration polychlorinated biphenyl according to claim 5, low-concentration polychlorinated biphenyl contained in the water to be treated is oxidized and decomposed based on the treatment process of the Fenton method.
And hydrogen peroxide, a bivalent iron ion, and a pH adjuster are added with respect to the to-be-processed water containing low concentration polychlorinated biphenyl. The total amount of hydrogen peroxide is added at the beginning of the reaction. Divalent iron ions are added in portions by repeating a plurality of cycles intermittently after the addition of hydrogen peroxide.
As for the pH adjuster, an acid pH adjuster is added before the addition of hydrogen peroxide, and after the addition of hydrogen peroxide, an alkaline pH adjuster is added every time an iron ion solution is added. It is characterized by maintaining.

About Claim 6, it is as follows. In the method for treating low-concentration polychlorinated biphenyl according to claim 6, in claim 5, an aqueous solution of ferrous sulfate is added as the divalent iron ion.
At the same time, as the pH adjuster, for example, sulfuric acid or caustic soda is added, so that the water to be treated is maintained at about pH 4 and the decomposition reaction of the added hydrogen peroxide into water and oxygen is suppressed. And
About Claim 7, it is as follows. The method for treating low-concentration polychlorinated biphenyls according to claim 7 is characterized in that the hydrogen peroxide added as a total amount as an aqueous solution is reduced with divalent iron ions added in portions as a catalyst. As a result, OH radicals are generated. Therefore, the polychlorinated biphenyl contained in the water to be treated is characterized by being oxidized and decomposed by the OH radical and mineralized into a low molecular compound such as water or carbon dioxide.
About Claim 8, it is as follows. The method for treating low-concentration polychlorinated biphenyl according to claim 8 is the method according to claim 7, wherein the hydroxide ions produced by the reduction reaction of hydrogen peroxide are further produced by the oxidation reaction of divalent iron ions. It is oxidized by trivalent iron ions to generate OH radicals. Therefore, the polychlorinated biphenyl contained in the water to be treated is characterized by being oxidized and decomposed by the OH radical and mineralized into a low molecular compound such as water or carbon dioxide.

<About the action>
Since the present invention comprises such means, the following is achieved.
(1) The water to be treated containing low-concentration polychlorinated biphenyl is supplied to a treatment apparatus, so that the polychlorinated biphenyl is oxidized and decomposed by a treatment method based on the treatment process of the Fenton method.
(2) First, this processing apparatus includes a processing water supply means, a processing tank, and a post-processing tank. The treatment tank is provided with hydrogen peroxide addition means, iron ion addition means, pH adjustment means, and the like.
(3) Therefore, the water to be treated is supplied to the treatment tank, but before that, sulfuric acid or the like is added from the pH adjusting means to make it weakly acidic at about pH 4.
(4) In the treatment tank, first, all the hydrogen peroxide is added from the hydrogen peroxide addition means to the water to be treated.
(5) Then, a divalent iron ion solution is dividedly added from the iron ion addition means, and caustic soda or the like is added from the pH adjustment means for each divided addition, and the weak acidity of the water to be treated is maintained. .
(6) Now, hydrogen peroxide generates OH radicals using iron ions as a catalyst. In this OH radical generation reaction, first, iron ions are divided and added, so there is no risk of OH radical consumption reaction. Furthermore, since the atmosphere is weakly acidic, the iron ion catalytic function is promoted and excessively charged. It is avoided that hydrogen oxide is decomposed and wasted into water and oxygen, and is thus carried out efficiently.
(7) OH radicals are also generated by the reaction of trivalent iron ions and hydroxide ions generated by the above reaction.
(8) And in the treatment tank, polychlorinated biphenyl in the water to be treated is oxidized and decomposed by the strong oxidizing power of OH radicals, and mineralized into low molecular compounds such as water and carbon dioxide.
(9) After that, the water to be treated is subjected to predetermined post-treatment in the post-treatment tank and drained to the outside.
(10) By the way, in this processing apparatus and processing method, the chemical addition amount is easily calculated from the reaction theoretical value, and the configuration is relatively simple, and stable processing is possible.
(11) The polychlorinated biphenyl treatment apparatus and treatment method of the present invention exhibit the following effects.

<< First effect >>
First, hydrogen peroxide is not wasted, and OH radicals are efficiently generated without waste.
In the Fenton method according to the treatment apparatus and treatment method of the present invention, the water to be treated is maintained at a weak acidity of about pH 4, for example. The total amount of hydrogen peroxide and divalent iron ions added in portions promotes the production of OH radicals as expected without being wasted, and is therefore toxic polychlorine. Biphenyl chloride is reliably oxidized, decomposed and removed. Furthermore, OH radicals are also generated by the reaction of trivalent iron ions and hydroxide ions.
Accordingly, it is not necessary to add an excessive amount of hydrogen peroxide as in the above-described conventional polychlorinated biphenyl processing technique, and the cost of using chemicals is reduced.
As a result, the Fenton method according to the present invention is easy to apply to scale-up, ie, practical use, for large-scale treatment and large-volume treatment of low-concentration polychlorinated biphenyl.

<< Second effect >>
Secondly, the residual content of hydrogen peroxide is very low, and the post-treatment cost with the neutralizing agent is also reduced.
In the Fenton method according to the treatment apparatus and treatment method of the present invention, as described above, OH radicals are efficiently generated as expected with hydrogen peroxide, and low-concentration polychlorinated biphenyl is oxidized, decomposed, and removed. The Accordingly, hydrogen peroxide is not added excessively as in the conventional treatment technique of this type, so that the water to be treated has a very small residual amount of hydrogen peroxide after the treatment, and the post-treatment with the neutralizing agent. Processing costs are greatly reduced.
In view of this, the Fenton method according to the present invention also reduces the cost of using chemicals from this aspect, and opens up the path to large-scale treatment and low-volume treatment of low-concentration polychlorinated biphenyl, that is, practical application. .

《Third effect》
Third, chemical addition control is easy. In the Fenton method according to the treatment apparatus and treatment method of the present invention, the addition amount of chemicals can be controlled easily and reliably.
That is, the addition amount of hydrogen peroxide corresponding to the content of polychlorinated biphenyl in the water to be treated, the addition amount of divalent iron ions corresponding to the addition amount of hydrogen peroxide, and the addition of a suitable pH adjuster The amount and the like are easily calculated from the theoretical reaction value to obtain the required number of moles. Therefore, it is possible to add an appropriate amount of chemicals without excess or deficiency, and these automatic controls are easy.
With respect to the divalent iron ion, there is no situation where the quantitative property cannot be ensured and the residue remains or is insufficient, and the instability of the processing performance is avoided.
In view of this, the Fenton method according to the present invention can be easily applied to scale-up, ie, practical application of low-concentration polychlorinated biphenyl to large-scale treatment and large-capacity treatment.

<< 4th effect >>
Fourth, it is excellent in processing stability, initial cost, running cost, space, and the like.
The Fenton method according to the treatment apparatus and treatment method of the present invention is compared with the above-described conventional polychlorinated biphenyl treatment techniques, such as adsorption / desorption method, ozone / hydrogen peroxide / ultraviolet method, etc. Excellent processing stability, initial cost, running cost, installation space, etc.
That is, the problems pointed out in this type of conventional processing technology such as reduction of processing capacity due to use over time, replacement cost of activated carbon, equipment installation space, OH radical generation efficiency, equipment overload, power waste cost, UV lamp deterioration, etc. Is resolved.
Therefore, the Fenton method according to the present invention also supports the application of scale-up to large-scale treatment and large-capacity treatment of low-concentration polychlorinated biphenyl, that is, practical use from these aspects.
As described above, the effects exerted by the present invention are remarkably large, such as all the problems existing in this type of conventional example are solved.

《About drawing》
Hereinafter, the processing apparatus and processing method of the low concentration polychlorinated biphenyl of this invention are demonstrated in detail based on the best form for implementing invention shown in drawing.
FIG. 1 is a configuration flowchart for explaining the best mode for carrying out the present invention.

<About polychlorinated biphenyl 1>
First, the polychlorinated biphenyl 1, which is a treatment target of the treatment apparatus and treatment method of the present invention, will be described.
Polychlorinated biphenyl (PCB) 1 is any one of 10 hydrogen atoms (H) for two aromatic rings of biphenyl (molecular formula C ₁₂ H ₁₀ , structural formula C ₆ H ₅ -C ₆ H ₅ ). It is a general term for organic compounds in which 10 to 10 are substituted with chlorine atoms (Cl). Depending on the number of substituted chlorine atoms and the substitution position, there are over 100 isomers, with 2,6-dichlorobiphenyl, 2,2′dichlorobiphenyl, 2,3,5-trichlorobiphenyl being typical.
And it was excellent in heat-resistant stability and electrical insulation, and was used for a heat medium, insulating oil, transformer oil, a capacitor, etc. However, in view of the strong toxicity to the human body and the environment and the risk of dioxin generation when incinerated, production was prohibited and use was discontinued. At present, its indegradability and persistence are problems, and it is known as environmental hormones and organic pollutants, and there is a concern about the risk of environmental pollution.
Biphenyl is known to be insoluble in water, but polychlorinated biphenyl 1 is slightly soluble in water depending on the amount of substitution with chlorine atoms, and low-concentration, water-dispersed polychlorinated biphenyl 1 The existence of
The present invention treats such a low concentration polychlorinated biphenyl 1 as a treatment target. That is, water that contains a small amount of polychlorinated biphenyl 1 is used as a treatment target. Specifically, water containing polychlorinated biphenyl 1 up to about several hundred ppm, particularly water containing polychlorinated biphenyl 1 up to about 100 ppm, for example, polychlorinated biphenyl of several tens of ppm is treated. Water containing 1 is treated.
The present invention treats such a low concentration polychlorinated biphenyl 1 as a treatment target.

<< Outline of Processing Apparatus 2 and Processing Method >>
The treatment apparatus 2 and the treatment method of the present invention oxidize and decompose the low-concentration polychlorinated biphenyl 1 contained in the water to be treated 3 based on the treatment process of the improved Fenton method.
That is, in the treatment apparatus 2 and the treatment method of the present invention, the water to be treated 3 is water containing low-concentration polychlorinated biphenyl 1. Then, the contained polychlorinated biphenyl 1 is oxidized with OH radicals generated using hydrogen peroxide (H ₂ O ₂ ) and divalent iron ions (Fe ²⁺ ), which are Fenton's reagent. Decomposes into water (H ₂ O) and carbon dioxide (CO ₂ ). The present invention is an improvement of such a Fenton process.
And the processing apparatus 2 and the processing method of this invention are the processing tank 4, the treated water supply means 5, the hydrogen peroxide addition means 6, the iron ion addition means 7, and the pH adjustment means 8 which were attached to the processing tank 4. Have.
Hereinafter, these will be described in detail.

<< About treated water supply means 5 etc. >>
First, the treated water supply means 5 and the like used in the treatment apparatus 2 and the treatment method will be described. The treated water supply means 5 supplies the treated water 3 containing the low-concentration polychlorinated biphenyl 1 to the treatment tank 4 as a treatment target.
That is, the treated water 3 is introduced into the treated water tank 9 of the treated water supply means 5, and the treated water 3 is supplied to the treated tank 4 via the treated water tank 9. The treated water 3 introduced into the treated water tank 9 is subjected to pretreatment such as dust sludge removal and biological treatment in advance as necessary.
In the illustrated example, the water to be treated 3 is supplied to the treatment tank 4 via the pH adjustment tank 10. In the pH adjusting tank 10, a pH adjusting agent is added from the attached pH adjusting means 8. That is, the pH adjusting means 8 adds a pH adjusting agent to the treated water 3 being supplied from the treated water tank 9 of the treated water supply means 5 to the treated tank 4 to make the treated water 3 a predetermined weak acidity. After adjusting, it is supplied to the treatment tank 4.
The treated water 3 from the treated water tank 9 is often pH 6 or higher, for example, so that an acid pH adjuster such as sulfuric acid is used as a pH adjuster to adjust the pH to about pH 5 to about 3, for example about pH 4. . The reason for adjusting the pH in advance in this way is to make the OH radical production reaction with hydrogen peroxide and divalent iron ions efficiently as expected, as will be described later.
In addition, such pH adjustment tank 10 is, for example, a large-scale large-capacity treatment of water 3 to be treated, a continuous treatment, a treatment of polychlorinated biphenyl 1 having a relatively high concentration although it is a low concentration, Used in the case of etc. On the other hand, it is also possible to carry out the above-described pH adjustment in the treated water tank 9 instead of using the pH adjustment tank 10 in a substitute or combined manner.
The treated water supply means 5 and the like are as described above.

<About hydrogen peroxide addition means 6>
Next, the hydrogen peroxide adding means 6 attached to the processing tank 4 used in the processing apparatus 2 and the processing method will be described.
The hydrogen peroxide addition means 6 adds a total amount of an aqueous solution of hydrogen peroxide (H ₂ O ₂ ) to the treated water 3 in the treatment tank 4 at the beginning of the reaction. Hydrogen peroxide becomes a source of OH radicals, which oxidize and decompose polychlorinated biphenyl 1.
The amount of hydrogen peroxide added per reaction depends on the specific content and specific concentration of the low-concentration polychlorinated biphenyl 1 contained in the water 3 to be treated. The actual required amount (necessary number of moles) calculated based on the above is added all at once at the beginning of the reaction. The next addition is when hydrogen peroxide is exhausted from the water 3 to be treated in the treatment tank 4, that is, at the next reaction, and the whole amount is added in the same manner. Thus, in this specification, the addition of the whole amount means that the amount of the drug necessary for the reaction is added all at once.
In this way, the entire amount of hydrogen peroxide is added from the hydrogen peroxide addition means 6.

<< About iron ion addition means 7 >>
Next, the iron ion addition means 7 attached to the processing tank 4 used in this processing apparatus and processing method will be described.
Iron ion adding means 7, relative to the water to be treated 3 of the processing tank 4 after the hydrogen peroxide has been added by the above intermittently repeated multiple cycles, divalent iron ions (Fe ²⁺⁾ solution added portionwise To do.
That is, substances that generate divalent iron ions in the liquid, such as ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O), are typically used as such iron salts, but other anhydrous Salts and hydrated salts such as iron chloride (FeCl ₂ ) and hydrates thereof can also be used. The divalent iron ion functions as a catalyst for the OH radical generation reaction of hydrogen peroxide.
The amount of iron ion added per reaction is calculated based on the theoretical reaction value, but the actual required amount is larger, for example, about 0.5 mole per mole of hydrogen peroxide. .
Moreover, this iron ion is divided and added in multiple times. That is, the necessary amount for one reaction is not added in the whole amount, but is divided into about 3 to 7 times, for example, 5 times, and is added sequentially. As for the addition timing for each time, the next time is added at the stage where the previous addition is gone. Thus, in this specification, divided addition means that the amount of drug necessary for the reaction is added in multiple portions.
The reason for the divided addition is as follows: a, b, c. First a. If the total amount is added, in the chemical reaction to be described later, the OH radical is wasted at the same time as the intended positive reaction from the original system using hydrogen peroxide as a reactant to the production system using OH radical as a product. A reaction, that is, a reaction in which surplus OH radicals are returned to water easily occurs, resulting in loss. Therefore, the iron ions used for generating OH radicals are wasted. On the other hand, when the addition is divided, such a reaction is suppressed and the waste of iron ions is eliminated.
B. OH radicals are present only momentarily due to the vigorous reaction, and when they are added in a divided amount rather than in the total amount, OH radicals are generated and spread everywhere, and oxidation of polychlorinated biphenyl 1 occurs. , Decomposition is more reliable, efficient and faster.
C. When the addition is divided, the remaining hydrogen peroxide is smaller than the total addition, and accordingly, the post-treatment cost by the neutralizing agent is reduced accordingly.
Thus, divalent iron ions (Fe ²⁺ ) and the like are dividedly added from the iron ion adding means 7.

<About pH adjusting means 8>
Next, the pH adjusting means 8 attached to the processing tank 4 used in the processing apparatus 2 and the processing method will be described.
As described above, the pH adjusting means 8 is a pH adjusting agent for the water to be treated 3 before being supplied from the treated water supply means 5 to the treatment tank 4 and the water to be treated 3 after being supplied to the treatment tank 3. Is added to maintain the water to be treated 3 at a predetermined weak acidity of about pH 4, for example.
That is, the pH adjusting means 8 adds an acid pH adjusting agent such as sulfuric acid before the addition of hydrogen peroxide, and after the addition of hydrogen peroxide, after each addition of the above iron ions, an alkaline pH such as caustic soda. Add modifier.
Maintaining the water to be treated 3 at about pH 3 to about pH 5, typically about pH 4, first comprises a. As will be described later, it functions to suppress a wasteful decomposition reaction of hydrogen peroxide into water and oxygen that inhibits the intended reaction. With this, b. It functions to promote electron donation of iron ions to hydrogen peroxide. Based on these a and b, the generation of OH radicals proceeds efficiently as expected.
On the other hand, the treated water 3 from the treated water tank 9 of the treated water supply means 5 often has a pH of 6 or more, for example, and as described above, for example, sulfuric acid is added in advance from the pH adjusting means 8, for example, The pH is adjusted to about 4. After the fact, when iron ions are added, the pH of the water to be treated 3 is lowered as it is, so that, for example, caustic soda is added each time the iron ions are dividedly added, and the water to be treated 3 is reduced to about pH 4, for example. The pH is adjusted.
The pH adjusting means 8 is as described above.

<< About the reaction (the 1) in the processing tank 4 >>
Next, a chemical reaction (part 1) in the treatment tank 4 will be described. In the treatment apparatus 2 and the treatment tank 4 of the treatment method, firstly, the water to be treated 3 was stirred and flowed down, and the added hydrogen peroxide (H ₂ O ₂ ) was added as a catalyst. Reduction with divalent iron ions (Fe ²⁺ ) generates OH radicals (.OH).
Secondly, in the treatment tank 4, OH radicals are generated as described above, and hydroxide ions (OH ⁻ ) generated by the reduction reaction of hydrogen peroxide are divalent iron ions. It is oxidized by trivalent iron ions (Fe ³⁺ ) generated by the oxidation reaction of (Fe ²⁺ ) to generate OH radicals.
The generation of OH radicals based on such a Fenton process will be described in further detail.
First, in the treatment tank 4, OH radicals are generated by the chemical reaction formulas of the following chemical formulas 1 and 2.

That is, in the reaction formula of Chemical Formula 1, the divalent iron ions (Fe ²⁺ ) added sequentially and sequentially from the iron ion addition means 7 are easy because the water 3 to be treated is maintained in a weakly acidic atmosphere having a pH of about 4, for example. In addition, as a catalyst, electrons (e ⁻ ) are sequentially donated to the hydrogen peroxide of the chemical formula 2 and self is oxidized to trivalent iron ions (Fe ³⁺ ).
Therefore, reduction in the second reaction formula, initially the total amount added hydrogen peroxide from the hydrogen peroxide addition means 6 (H 2 _{O 2),} the electronic based on 1 reaction formula of (e ^-) are sequentially donor, Accordingly, OH radicals (.OH) and hydroxide ions (OH ⁻ ) are generated each time.
By the way, in such a reaction, since the to-be-processed water 3 is maintained in the weakly acidic atmosphere as mentioned above, it is suppressed that hydrogen peroxide is decomposed | disassembled into water and oxygen, and wasted. On the other hand, if the atmosphere is not maintained in a weakly acidic atmosphere, hydrogen peroxide becomes water molecules (H ₂ O) while generating oxygen (O) in the nascent stage, according to the following reaction formula 3. According to the reaction formula of the chemical formula 2, it will be wasted without generating OH radicals. It should be noted that oxygen (O) in such a nascent stage is out of the system as oxygen molecules (O ₂ ) when there is no oxidation target.

Second, OH radicals (.OH) can also be generated by the following reaction formulas of Chemical Formula 4 and Chemical Formula 5. That is, in the treatment tank 4, first, OH radicals are generated according to the above-described reaction formulas of Chemical Formula 1 and Chemical Formula 2, but secondly, OH radicals can also be generated according to the following reaction formula. It is.

That is, the trivalent iron ion (Fe ³⁺ ) generated in the chemical formula 1 is converted from the hydroxide ion (OH ⁻ ) generated in the chemical formula 2 according to the chemical formula 4 and chemical formula 5 Takes electrons (e ⁻ ) to generate OH radicals ( ^.OH ), and returns itself to divalent iron ions (Fe ²⁺ ).
Thus, if not only the reaction formulas of Chemical Formula 1 and Chemical Formula 2 but also the chemical formulas of Chemical Formula 4 and Chemical Formula 5 occur in a chain-balanced manner, OH radicals are generated very efficiently.
In the treatment tank 4, OH radicals are generated in this way.

<< About the reaction (2) in the processing tank 4 >>
Next, the chemical reaction (part 2) in the treatment tank 4 will be described. In the treatment tank 4, the low-concentration polychlorinated biphenyl 1 contained in the water to be treated 3 is oxidized and decomposed by the OH radicals generated in this way to be mineralized.
These will be described in more detail. First, OH radical, that is, hydroxy radical (.OH) has a strong oxidizing power as is well known. That is, it has an extremely strong electron (e ⁻ ) deprivation ability, oxidation ability, that is, activation ability and decomposition ability, which is unparalleled as an active oxygen species, and is highly reactive with radicals.
OH radicals are generated every time iron ions are added to hydrogen peroxide, but the presence of the OH radicals is instantaneous due to the intense reaction, and the lifetime is short.
Now, the OH radical dispersed in the aqueous phase oxidizes the low-concentration polychlorinated biphenyl 1 contained in the water to be treated 3 and eventually decomposes. In other words, the OH radical covers the organic structure of polychlorinated biphenyl 1, for example, the π electron of the double bond of the aromatic ring, the π electron of the hydrogen atom H next to the chlorine atom Cl, the carbon atom C, etc. Are added or substituted with an OH group. Based on these, a chain process in which the carbon chain, organic bond, and molecular bond of polychlorinated biphenyl 1 are sequentially cut, decomposed, and broken is followed, so that polychlorinated biphenyl 1 is finally converted into inorganic water ( Oxidized, decomposed and mineralized into H ₂ O) and carbon dioxide (CO ₂ ).
In addition, since chlorine gas (Cl ₂ ) is decomposed and generated in a very small amount and a low concentration (for example, in the example described later, it is only 1 mol with respect to 32 mol of water and 12 mol of carbon dioxide gas), particularly post-treatment. Etc. are not required. In the treatment tank 4, it exists as hydrochloric acid (HCl) because of acidity, and when sodium hydroxide is added from the pH adjusting means 8, sodium chloride (NaCl) is generated. Without being separated, it is discharged to the outside as it is.
In the treatment tank 4, the low concentration polychlorinated biphenyl 1 is thus oxidized, decomposed and mineralized.

<< About the post-treatment tank 11 >>
Next, the post-treatment tank 11 will be described. A post-treatment tank 11 is attached to the treatment tank 4, and after the polychlorinated biphenyl 1 is oxidized and decomposed as described above, the treated water 3 is discharged, and after the necessary post-treatment, Drained.
Such a post-treatment tank 11 will be further described in detail. The illustrated post-treatment tank 11 includes a neutralization tank 12, a precipitation tank 13, a coagulation sedimentation tank 14, a filtration tank 15, a pH adjustment tank 16, a treatment water tank 17, and the like in order toward the downstream.
First, from the treatment tank 4, the water to be treated 3 after the oxidation and decomposition treatment of the polychlorinated biphenyl 1 is discharged to the neutralization tank 12 of the post-treatment tank 11. In the neutralization tank 12, a pH adjuster such as caustic soda is added to the water 3 to be treated, and the pH is adjusted to the optimum value for the inorganic flocculant. If even a small amount of hydrogen peroxide remains in the water 3 to be treated, a neutralizing agent such as catalase is added to avoid water pollution.
Next, in the precipitation tank 13, the colloidal complex with the iron content contained as a residue in the water to be treated 3 flowing from the neutralization tank 12 is solid-liquid separated and precipitated and removed at the bottom.
In the coagulation sedimentation tank 14, for example, polyaluminum chloride (PAC, Al ₂ (OH) _n Cl _6-n ) is added as an inorganic coagulant to the water to be treated 3 flowing from the upper part of the sedimentation tank 13 and stirred. The Thus, the colloidal complex remaining in the water to be treated 3 without being precipitated in the settling tank 13 is agglomerated and solid-liquid separated to be precipitated and removed.
If necessary, a storage sedimentation tank is provided next to the aggregation sedimentation tank 14 and, for example, an anion is added as a polymer flocculant, thereby further aggregating, blocking, solid-liquid separating the colloidal complex, Then, precipitation and removal may be attempted.
Then, the water 3 to be treated passes through the filtration tank 15, the pH adjustment tank 16, and the treatment water tank 17 of the post-treatment tank 11, and is further purified and adjusted to a pH suitable for external drainage. 17 is drained externally and discharged.
The post-treatment tank 11 is as described above.

《Action etc.》
The processing apparatus 2 and processing method of the low concentration polychlorinated biphenyl 1 of the present invention are configured as described above. Therefore, it becomes as follows.
(1) The treated water 3 containing the low concentration polychlorinated biphenyl 1 is supplied to the treatment apparatus 2. The treatment device 2 purifies the water 3 to be treated by oxidizing and decomposing the polychlorinated biphenyl 1 by a treatment method based on the treatment process of the Fenton method.

(2) The treatment apparatus 2 includes a treatment water tank 9, a pH adjustment tank 10, a treatment tank 4, a post-treatment tank 11 and the like of the treated water supply means 5 in order.
The pH adjusting tank 10 is provided with pH adjusting means 8, and the treatment tank 4 is provided with hydrogen peroxide adding means 6, iron ion adding means 7, pH adjusting means 8, etc. Hydrogen, divalent iron ions, pH adjusters, etc. can be added.

(3) The treated water 3 is then supplied from the treated water tank 9 of the treated water supply means 5 to the treated tank 4.
In addition, before the water 3 to be treated is supplied to the treatment tank 4, in the illustrated example, an acid pH adjuster such as sulfuric acid is added from the pH adjustment means 8 in the pH adjustment tank 10, so that, for example, a predetermined weak value of about pH 4 is obtained. It is considered acidic.

  (4) The treated water 3 supplied to the treatment tank 4 is firstly added with an aqueous solution of hydrogen peroxide from the hydrogen peroxide addition means 6. The total amount of hydrogen peroxide is added at the beginning of the reaction.

(5) In the treatment tank 4, after the hydrogen peroxide is added in this way, a divalent iron ion solution is added from the iron ion addition means 7 to the water to be treated 3. The divalent iron ion is added repeatedly in a plurality of cycles intermittently in a plurality of times by divided addition during the reaction after the addition of hydrogen peroxide.
For each divided addition of iron ions, an alkaline pH adjuster such as caustic soda is added from the pH adjusting means 8, so that the treated water 3 always maintains a predetermined weak acidity of about pH 4. As divalent iron ions, for example, an aqueous solution of ferrous sulfate is added.

(6) Then, in the treatment tank 4, the hydrogen peroxide that has been added in the total amount as described above is reduced by divalent iron ions that are added in a divided manner as a catalyst, and OH radicals are generated at each divided addition. To do. That is, according to the reaction formulas of Chemical Formula 1 and Chemical Formula 2, the divalent iron ion donates an electron to hydrogen peroxide to become a trivalent iron ion. Is generated.
Since OH radicals are dividedly added with iron ions, there is no risk of a reaction that consumes OH radicals, and each OH radical is efficiently generated without waste each time divided addition is performed.
Moreover, this OH radical production reaction is efficiently and reliably carried out as expected even when maintained in a weakly acidic atmosphere having a pH of about 4, for example. That is, under a predetermined weak acid atmosphere, first, electron donation of divalent iron ions is promoted, and further, a reaction in which hydrogen peroxide is decomposed and wasted into water and oxygen according to the chemical formula of Chemical Formula 3 above. Suppressed and avoided, generating full-capacity OH radicals.

(7) In addition to this, OH radicals are water generated by reduction reaction of hydrogen peroxide with trivalent iron ions generated by oxidation reaction of divalent iron ions in the treatment tank 4. Oxide ions are also generated by oxidation. That is, the trivalent iron ions and hydroxide ions generated by the chemical formulas 1 and 2 are also generated by the chemical formulas 4 and 5.
Therefore, also from this aspect, OH radicals are efficiently generated. And the production | generation of this OH radical is each produced | generated in a chain | strand every time the addition addition of an iron ion is divided.

  (8) Now, the OH radicals thus generated have a very strong oxidizing power. Therefore, in the treatment tank 4, the polychlorinated biphenyl 1 contained at a low concentration in the water to be treated 3 is oxidized by the OH radicals and thus mineralized into low molecular compounds such as water and carbon dioxide. End up.

(9) In the water 3 to be treated, the polychlorinated biphenyl 1 contained therein is mineralized into water, chlorine gas, and carbon dioxide gas in this way, and is discharged from the treatment tank 4 to the post-treatment tank 11. The The illustrated post-treatment tank 11 includes a neutralization tank 12, a sedimentation tank 13, a coagulation sedimentation tank 14, a filtration tank 15, a pH adjustment tank 16, a treated water tank 17, and the like.
Since hydrogen peroxide is effectively used for generating OH radicals as described above, the residual amount after the treatment is very small, and the use of the neutralizing agent in the neutralization tank 12 is negligible or absent ( For example, the residual peroxide ion concentration is about 0 to 3% or less of the hydrogen peroxide used).
And the to-be-processed water 3 is adjusted to the state which can be drained by passing through the post-treatment tank 11, and is drained outside.

(10) In this treatment apparatus 2 and treatment method, as described above, based on the treatment process of the Fenton method, the polychlorinated biphenyl 1 that is a toxic organic compound contained in the water to be treated 3 is converted into a low molecular weight compound. This is easily and easily realized.
That is, the required amount of chemicals such as hydrogen peroxide, divalent iron ions, and pH adjusters can be easily calculated from the theoretical reaction values. For example, about several times larger than the theoretical reaction value is added as an actual required amount, so that the addition amount is optimized.
The treatment apparatus 2 is provided with a treatment water tank 9 and a post-treatment tank 11 with a treatment tank 4 as a center, and a hydrogen peroxide addition means 6, an iron ion addition means 7, a pH adjustment means 8 and the like. It consists of the structure which was made. That is, this processing method can perform stable processing by using the processing device 2 having a relatively simple configuration.
The operation of the present invention is as described above.

<< Examples of oxidation and decomposition reactions >>
Hereinafter, an example of the processing apparatus 2 and the processing method of the present invention will be described. That is, the theoretical support for an example of the oxidation and decomposition reaction of polychlorinated biphenyl 1 in the treatment tank 4 (that is, the example described above as reaction 2 in the treatment tank 4) will be explained. Keep it.
In this example, as polychlorinated biphenyl 1, two hydrogen atoms (H) were substituted with two chlorine atoms (Cl) for biphenyl (C ₆ H ₅ -C ₆ H ₅ ) which is a symmetric body. C ₆ H ₄ (Cl) -C ₆ H ₄ (Cl) is the target. The chlorine atom substitution positions are both symmetrical and inside.
Now, the polychlorinated biphenyl 1 of this example has 2 mol of a chlorinated phenyl group (C ₆ H ₄ (Cl) —) as an aromatic ring. Therefore, first, the oxidation / decomposition reaction by OH radical is verified for either one of the phenyl chloride groups (C ₆ H ₄ (Cl) —).
First, the oxidation and decomposition reactions proceed sequentially by following the chain processes (1), (2), (3), (4), and (5) shown in the following reaction formulas.

The reaction formula of the above chemical formula 6 is as follows. By sequentially following the chain processes (1) to (5) in each reaction formula of Chemical Formula 6, oxidation and decomposition by a predetermined OH radical proceed respectively.
That is, the starting material consisting of a phenyl chloride group (C ₆ H ₄ (Cl) —) is (1) C ₆ H ₂ (Cl) (OH) ₂ −, → (2) a divalent cyclic ketone C ₆ H _2. (Cl) (O) _2- , → (3) Divalent carboxylic acid HOOC-C (Cl) = C * —CH═CH—COOH, → (4) Activated carbon group —C (Cl) = C * -CH = CH-, (5) OH-C (Cl) (OH) -C * (OH) -CH (OH) -CH (OH) -OH, and then C (Cl) (OH) _2- C ※ (OH) -CH (OH ) become a -CH (OH) _2, is alcohol reduction.
In such a chain process, water (H ₂ O) and carbon dioxide (CO ₂ ) are decomposed and generated as needed. OH radicals are often attributed to water by reaction.
In the processes (3), (4) and (5), C * is C ₆ H ₄ (Cl) -C ₆ H ₄ (Cl) which is a symmetric body of polychlorinated biphenyl 1 in this example. This is a carbon atom bonded to the other phenyl chloride group (C ₆ H ₄ (Cl)) (the same applies to each reaction formula of Chemical Formula 7 described later).

In this example, following the chain processes (1) to (5) of each reaction formula of Chemical Formula 6, the chain processes (6) to (11) of the following chemical formulas of Chemical Formula 7 are followed.

The reaction formula of the above chemical formula 7 is as follows. By sequentially following the chain process (6) or (7) to (11) of each reaction formula of Chemical Formula 7 from the alcohol of the chain process (5) described above, oxidation and decomposition by a predetermined OH radical can be performed, respectively. proceed.
First, since the alcohol of (5) is divided at (6) and the active hydrogen H is returned to water by OH radicals, the reaction formula of process (6) is rewritten as the reaction formula of process (7). Then (7) OC-CHO, (8) divalent aldehyde OCH-OC-CO-CHO, (9) divalent carboxylic acid HOOC-OC-CO-COOH, (10) oxalic acid HOOC -COOH → (11) Eventually returned to carbon dioxide and water.
Even in such a chain process, water and carbon dioxide gas are decomposed and generated as needed.

In conclusion, in one example of polychlorinated biphenyl 1, the symmetric chlorophenyl group (C ₆ H ₄ (Cl)-) on one side is linked to the chain shown in the reaction formula of Chemical Formula 6 and Chemical Formula 7. By following the processes (1) to (11), all of them are theoretically oxidized and decomposed into water and carbon dioxide gas. As a symmetrical body remaining chloride phenyl group _{(-C 6 H 4 (Cl)} ) is also exactly the same oxidized and degraded.
Thus, when the places described above are summarized, the following general reaction formula of Chemical Formula 8 is obtained. That is, when the reaction formulas of the chain processes (1) to (5) and the reaction formulas of the chain processes (7) to (11) are added together and doubled (the remaining one side is added to the one side) )

The general reaction formula of this chemical formula 8 is as follows. As reaction formula of 8, 1 is the mole of an example of polychlorinated biphenyls _{1 C 6 H 4 (Cl)} -C 6 H 4 (Cl) is the theory, 56 moles of OH radicals, It is oxidized and decomposed into 1 mol of chlorine gas, 12 mol of carbon dioxide gas and 32 mol of water. However, little chlorine gas is generated.
In this example, 56 mol of OH radicals may be prepared in advance as a theoretical reaction value, but the actual required amount is prepared roughly. Of course, the same applies to hydrogen peroxide, divalent iron ions, and the like, which are OH radical products.
One example of the oxidation and decomposition reaction is as follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration flow diagram for explaining the best mode for carrying out the invention of a low concentration polychlorinated biphenyl processing apparatus and processing method according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polychlorinated biphenyl 2 Treatment apparatus 3 Water to be treated 4 Treatment tank 5 Treatment water supply means 6 Hydrogen peroxide addition means 7 Iron ion addition means 8 pH adjustment means 9 Treatment water tank 10 pH adjustment tank 11 Post-treatment tank 12 Neutralization tank 13 Precipitation tank 14 Coagulation sedimentation tank 15 Filtration tank 16 pH adjustment tank 17 Treated water tank

Claims (8)

A treatment apparatus for oxidizing and decomposing low-concentration polychlorinated biphenyl contained in water to be treated by the Fenton method, a treatment tank, treated water supply means attached to the treatment tank, and hydrogen peroxide addition means , Iron ion addition means, pH adjustment means,
The treated water supply means supplies treated water containing low-concentration polychlorinated biphenyl to the treatment tank, and the hydrogen peroxide adding means adds hydrogen peroxide to treated water in the treated tank. The iron ion addition means adds divalent iron ions to the water to be treated in the treatment tank,
The pH adjusting means maintains the water to be treated at a predetermined weak acidity by adding a pH adjuster to the water to be treated supplied from the treated water supply means to the treatment tank and the water to be treated in the treatment tank. An apparatus for processing low-concentration polychlorinated biphenyl. 2. The processing apparatus for low-concentration polychlorinated biphenyl according to claim 1, wherein the hydrogen peroxide adding means adds the whole amount of an aqueous solution of hydrogen peroxide at the beginning of the reaction, and the iron ion adding means adds hydrogen peroxide. Later, repeated multiple cycles intermittently, divalent iron ion solution was added in portions,
The pH adjusting means is characterized in that an acid pH adjuster is added before the addition of hydrogen peroxide, and an alkaline pH adjuster is added every time an iron ion solution is added after the addition of hydrogen peroxide. A processing device for low-concentration polychlorinated biphenyl. The processing apparatus for low-concentration polychlorinated biphenyl according to claim 2, wherein the iron ion addition means adds an aqueous solution of ferrous sulfate,
The pH adjusting means is, for example, adding sulfuric acid or caustic soda to maintain the water to be treated in the treatment tank at about pH 4 to suppress the decomposition reaction of the added hydrogen peroxide into water and oxygen, An apparatus for processing low-concentration polychlorinated biphenyl, characterized by: 3. The processing apparatus for low-concentration polychlorinated biphenyl according to claim 2, wherein the hydrogen peroxide added in the whole amount is divalent iron ions dividedly added as a catalyst in the treatment tank. Reduced to produce OH radicals,
Polychlorinated biphenyl contained in water to be treated is oxidized and decomposed by this OH radical, and is mineralized into low-molecular compounds such as water and carbon dioxide gas. Biphenyl processing equipment. A treatment method for oxidizing and decomposing low-concentration polychlorinated biphenyl contained in water to be treated based on the Fenton process.
Hydrogen peroxide, divalent iron ions, and a pH adjuster are added to the water to be treated containing low-concentration polychlorinated biphenyl, and hydrogen peroxide is added in its entirety at the beginning of the reaction. Ions are added in portions by repeating multiple cycles intermittently after the addition of hydrogen peroxide,
As for the pH adjuster, an acid pH adjuster is added before the addition of hydrogen peroxide, and after the addition of hydrogen peroxide, an alkaline pH adjuster is added every time an iron ion solution is added. A method for treating low-concentration polychlorinated biphenyl, characterized in that: In the processing method of the low concentration polychlorinated biphenyl according to claim 5, an aqueous solution of ferrous sulfate is added as a divalent iron ion,
As the pH adjuster, for example, sulfuric acid or caustic soda is added, so that the water to be treated is maintained at about pH 4, and the decomposition reaction of the added hydrogen peroxide into water and oxygen is suppressed, Treatment method for low-concentration polychlorinated biphenyl. 6. The method for treating low-concentration polychlorinated biphenyl according to claim 5, wherein hydrogen peroxide added as a total amount as an aqueous solution is reduced by divalent iron ions dividedly added as a catalyst at each divided addition and OH. Radicals are generated,
Therefore, the polychlorinated biphenyl contained in the water to be treated is oxidized and decomposed by this OH radical, and is mineralized into a low molecular compound such as water or carbon dioxide gas. Treatment method of chlorinated biphenyl. 8. The method for treating low-concentration polychlorinated biphenyl according to claim 7, wherein the hydroxide ions produced by the reduction reaction of hydrogen peroxide are further trivalent produced by the oxidation reaction of divalent iron ions. Oxidized with iron ions to generate OH radicals,
Therefore, the polychlorinated biphenyl contained in the water to be treated is oxidized and decomposed by this OH radical, and is mineralized into a low molecular compound such as water or carbon dioxide gas. Treatment method of chlorinated biphenyl.

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