JP2003126685A - Method and apparatus for decomposing environmental pollutant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for decomposing environmental pollutants, in which the concentration of the environmental pollutants in a solution is measured, in real time, thereby efficiently decomposing the environmental pollutants and an apparatus therefor. SOLUTION: The solution containing volatile environmental pollutants is charged into a reaction tank 11. The solution in the reaction tank 11 is directed with ultrasonic waves from an ultrasonic wave oscillator 14, and is also irradiated with ultraviolet rays from an ultraviolet lamp 12, thereby decomposing the environmental pollutants. The concentration of the environmental pollutants in a gas phase part G in the reaction tank 11 is measured by a gas sensor 15, and the direction from the ultrasonic wave oscillator 14 and the irradiation from the ultraviolet lamp 12 are controlled by a control device 16 according to the measured concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for decomposing and detoxifying various pollutants in the environment. More specifically, it is an organic solvent such as an organic halogen compound contained in soil, groundwater, industrial wastewater, etc. , And a method and apparatus for easily and efficiently decomposing organic substances, nitrogen / phosphorus compounds, etc. contained in river water, lakes and marshes.

[0002]

2. Description of the Related Art Among organic solvents, organic halogen compounds such as tetrachloroethylene, trichloroethylene and dichloromethane have been used in various manufacturing industries, laundry industries, etc. as detergents having an excellent dissolving power for oils and fats. In recent years, its carcinogenicity has been pointed out and its release to the environment has been restricted. However, pollution of the environment such as air, public waters, and soil with organic chlorine compounds is still unsolved, and use of alternative solvents or detoxification treatment after using solvents is required.

Similarly, fluorocarbons, polychlorinated biphenyls (PCBs), etc., which have been used as refrigerants and insulating oils, and dioxin, which is generated in a dust incinerator in the presence of chlorine compounds at a low incineration temperature, are also organic. It is a type of halogen compound, and its toxicity and persistent properties pose a problem of its residue in the environment.

In this regard, a method of decomposing the above volatile organic halogen compound by irradiating ultrasonic waves into water has been studied in recent years (J. Phys. Chem., 1991, 95, p. 3630-3638).
etc). The reaction mechanism of decomposition by ultrasonic waves is presumed to be two types: thermal decomposition in cavitation bubbles and reaction with radicals generated by cavitation (Environ. Sci. Technol., 1996, 30, p.1133-1138). Such).

That is, first, when water under sound pressure is compressed by positive sound pressure by ultrasonic irradiation into water and then decompressed in a negative pressure cycle, the water is partially torn off and cavitation bubbles are generated. A vacuum cavity (for example, 100 μm or less at a frequency of several tens kHz) is formed. At this time, when the cavitation bubbles are formed, the volatile harmful substance in the solution, such as an organic halogen compound, is vaporized and enters the bubbles. Next, this bubble is crushed by being crushed by the next positive sound pressure, and the water molecules around the bubble rush toward the center of the bubble that is crushed all at once,
Molecules violently collide with each other, and due to momentary adiabatic compression, high temperature and high pressure of several thousand degrees and several thousand atmospheric pressure levels are reached. At this time, the above organic halogen compound or the like is thermally decomposed when the bubbles are compressed into harmless carbon dioxide gas and halogen ions.

On the other hand, the following reaction occurs due to the thermal decomposition of water molecules in the vicinity of the formation of cavitation bubbles, and H radicals and OH radicals are produced. H ₂ O → H ・ + ・ OH Of these, the OH radicals are more oxidative than ozone as shown in Table 1 and have low selectivity of the reactants and high activity, so they become the main component of the reaction and are Substances and non-volatile substances such as ionic substances that are difficult to vaporize and penetrate into cavitation bubbles are oxidized and decomposed into harmless substances.

[0007]

[Table 1]

In this case, although the decomposition rate depends on the frequency of the ultrasonic waves to be irradiated, the formation and crushing of cavitation bubbles, that is, thermal decomposition and oxidative decomposition by radicals are repeated in a cycle of several microseconds to several tens of microseconds. Decomposition is performed efficiently.

However, in the above prior art,
Although it is possible to decompose volatile organic halogen compounds and the like by safe and simple ultrasonic irradiation, it is difficult to put them into practical use as an apparatus because of the following problems.

That is, in the case of using only ultrasonic waves, when the volatile substance to be decomposed has a high concentration, the decomposition rate is high, but the decomposition proceeds and the residual concentration gradually decreases. The speed decreases. Therefore, the efficiency of decomposition is reduced, and it takes time to decompose, so that it is difficult to quickly treat a large amount of harmful substances.

This can be explained as follows. First, in a high concentration range of a volatile substance, a large amount of volatile molecules are vaporized and transferred into cavitation bubbles generated by ultrasonic irradiation, and are rapidly thermally decomposed by a high-temperature and high-pressure reaction field. Next, when the decomposition progresses to the medium concentration range, the number of molecules that vaporize and migrate into the cavitation bubbles decrease,
The water around the bubbles is vaporized in a form that compensates for this, and the steam migrates into the bubbles, and OH radicals are generated by the thermal decomposition of the steam. In this region, thermal decomposition of the molecule itself in the bubble and oxidative decomposition by OH radicals competitively occur at the bubble interface.

When the decomposition further progresses to a low concentration range, the volatile molecule exists in the liquid phase in a metastable state in the form of entering into the gap of hydrogen-bonded water molecules (called hydrophobic hydration). As a result, molecules that vaporize and migrate into the cavitation bubbles almost disappear, and the rate of water vapor entering the bubbles increases, while the amount of OH radicals generated at the bubble interface increases while volatile substances existing at the bubble interface. The following recombination reactions occur and hydrogen peroxide is generated in the liquid phase due to the fact that the number of molecules is small and the lifetime and diffusion distance of OH radicals are extremely short due to high activity. Will be the main body of decomposition. OH + .OH → H ₂ O ₂ From Table 1, the oxidizing power of hydrogen peroxide is weaker than that of OH radicals and ozone, so that the decomposition rate decreases at the end of the reaction.

In order to solve this problem, the inventors of the present invention have earnestly studied, and as a result, by carrying out a combined treatment of ultrasonic irradiation and ultraviolet irradiation, the hydrogen peroxide generated by ultrasonic irradiation is irradiated with ultraviolet rays, and Since active and low-selective OH radicals are generated, polluted water containing volatile substances such as organic halogen compounds can be easily, reagentless, and efficiently used from a high concentration level to a low concentration range of the environmental emission standard level. Can be decomposed into water, can be discharged to public sewage, or can be used as reused water.
It has been found that even substances such as phosphorus compounds that are difficult to be normally oxidized and decomposed can be decomposed by the high oxidizing power of OH radicals.

[0014]

The decomposition of such environmental pollutants must be carried out until the concentration level reaches the environmental emission standard. However, in order to accurately measure the concentration of environmental pollutants in the solution to be treated, expensive equipment such as a gas chromatograph and a skilled analysis technique are required, and it takes a long time to obtain the analysis result.

Therefore, it is currently difficult to detect / confirm whether or not the environmental pollutants in the solution to be treated have been decomposed to the concentration level of the environmental emission standard. In many cases, ultrasonic waves and ultraviolet rays are irradiated for a certain time and a sufficient time by a timer method or the like, and wasteful time and power are consumed.

In addition, when the initial concentration of the environmental pollutant in the solution to be treated is unknown or fluctuates, or when the time required for decomposition to the environmental emission standard concentration level fluctuates for some reason such as a change in treatment conditions. However, it became difficult to determine the required decomposition time, and it was necessary to successively measure the concentration of environmental pollutants in the liquid in batches, and automation of the treatment was impossible.

Therefore, an object of the present invention is to provide a method and apparatus for decomposing environmental pollutants, which are capable of more efficiently decomposing environmental pollutants by grasping the concentrations of the environmental pollutants in the solution to be treated in real time. To provide.

[0018]

The present inventors have found that many environmental pollutants such as organic halogen compounds are volatile, so that the gaseous environmental pollutants partially volatilized and transferred into the gas phase of the reaction vessel. The experiment was conducted by focusing on the fact that the concentration of slag is related to the residual concentration of environmental pollutants in the solution to be treated, and the concentration of environmental pollutants in the gas phase and liquid phase of the reaction vessel There is a fixed relationship such as a proportional relationship or an exponential relationship between them, and by measuring the concentration of the environmental pollutant in the gas phase part easily and quickly with a gas component detection means such as a gas sensor, the environmental pollutant in the liquid phase part can be measured. Found that the concentration of can be predicted almost accurately in real time,
The present invention has been completed.

That is, in the method for decomposing environmental pollutants of the present invention, a solution to be treated containing a volatile environmental pollutant is introduced into a reaction vessel, and ultrasonic waves are applied to the solution to be treated stored in the reaction vessel. In the method of decomposing the environmental pollutants by irradiating with ultraviolet rays, the concentration of the environmental pollutants existing in the gas phase portion of the reaction vessel is detected, and the irradiation of ultrasonic waves and ultraviolet rays is controlled according to the detected concentration. It is characterized by doing.

Further, the apparatus for decomposing environmental pollutants of the present invention irradiates the reaction vessel for storing the solution to be treated containing the volatile environmental pollutant and the solution to be treated in the reaction vessel with ultrasonic waves. In the apparatus for decomposing environmental pollutants, including means and means for irradiating the solution to be treated in the reaction vessel with ultraviolet rays, a gas sensor for detecting the concentration of environmental pollutants present in the gas phase portion of the reaction vessel is provided. A control means for controlling the irradiation of the ultrasonic wave irradiation means and the ultraviolet light irradiation means based on the detected concentration of the gas sensor is provided.

According to the present invention, by detecting the concentration of the environmental pollutant existing in the gas phase portion of the reaction container, the concentration of the environmental pollutant in the liquid phase can be predicted almost accurately in real time, and the concentration can be predicted. Since the irradiation of ultrasonic waves and ultraviolet rays can be controlled so as to be below a certain level, it is possible to efficiently decompose the environmental pollutants so as to satisfy the concentration level of the environmental emission standard.

The method and apparatus for decomposing environmental pollutants of the present invention are particularly suitable for treating a liquid to be treated containing an organic halogen compound as an environmental pollutant.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1 shows an embodiment of the apparatus for decomposing environmental pollutants of the present invention. This disassembly device 10
It has a cylindrical reaction vessel 11, and an ultraviolet lamp 12 is arranged at the center of the inside thereof. At the bottom of the reaction vessel 11,
A ring-shaped vibrator 13 is attached so as to be located on the outer periphery of the ultraviolet lamp 12 when viewed from above. The oscillator 13 is oscillated by the ultrasonic oscillator 14.

A gas sensor 15 is attached to the gas phase portion G of the reaction vessel 11, and the gas sensor 15 is connected to the control device 16. The detected concentration of environmental pollutants measured by the gas sensor 15 is converted into an electric signal and sent to the control device 16. The control device 16 is connected to the ultraviolet lamp 12 and the ultrasonic oscillator 14, and controls the operations of the ultraviolet lamp 12 and the ultrasonic oscillator 14 based on the detected concentration.

As the gas sensor 15, for example, a semiconductor system for detecting a change in electric resistance when a gas component is adsorbed on the surface of a metal oxide, or an increase in weight when the gas component is adsorbed on a quartz oscillator to which a gas adsorbing molecule is attached. It is possible to use a crystal oscillator system or the like that detects a change in the frequency by decreasing the frequency. The gas sensor 15 is commercially available and, for example, one manufactured by FIS Co., Ltd. or one manufactured by Figaro Giken Co., Ltd. can be used.

Next, an embodiment of the method for decomposing environmental pollutants according to the present invention using the above decomposing device will be described.

The environmental pollutant targeted by the present invention is not particularly limited as long as at least a part thereof is volatilized when it is irradiated with ultraviolet rays or ultrasonic waves. Specifically, organic pollutants such as tetrachloroethylene and trichlorethylene are used. Halogen compounds are mentioned and they are particularly suitable for treating dry cleaning waste liquids containing these organic halogen compounds.

The solution L to be treated containing the above environmental pollutants is stored in the reaction vessel 11 and is irradiated with ultraviolet rays from the ultraviolet lamp 12 and is also irradiated with ultrasonic waves W by the vibrator 13 operated by the ultrasonic oscillator 14. The environmental pollutants in the solution L to be treated are decomposed.

In this case, the solution L to be treated is preferably adjusted to pH 2 to 6 by adding a pH adjuster or the like. As a result, the oxidative power of OH radicals formed by irradiation of ultrasonic waves and ultraviolet rays can be increased, and the decomposition efficiency of environmental pollutants can be increased.

The temperature of the solution L to be treated is 40-60.
It is preferably adjusted to ° C. Thereby, the vapor pressure of the volatile environmental pollutants in the solution to be treated can be increased, the number of molecules of the environmental pollutants transferred into the cavitation bubbles can be increased, and the decomposition rate can be improved.

The temperature of the solution L to be treated can be adjusted by providing heating and / or cooling means in the reaction vessel 11. However, a temperature sensor is provided to keep the temperature of the solution L to be treated within a predetermined range. The ultrasonic oscillator 14 and the ultraviolet lamp 12 may be intermittently turned on / off so as to be maintained.

Further, hydrogen peroxide may be added to the solution L to be treated for treatment. According to this, since the added hydrogen peroxide is decomposed by the ultraviolet rays to generate OH radicals, the environmental pollutants can be decomposed more efficiently.

In this way, the solution L to be treated is stored in the reaction vessel 11, preferably pH and temperature are adjusted, and a decomposition aid such as hydrogen peroxide is added if necessary, and then ultraviolet rays are irradiated from the ultraviolet lamp 12. Together with the ultrasonic oscillator 14
The ultrasonic wave W is irradiated by the vibrator 13 operated by the above to decompose the environmental pollutants. Ultraviolet irradiation and ultrasonic irradiation are preferably performed at the same time, but ultraviolet irradiation can also be performed after ultrasonic irradiation. For example, it is also possible to arrange a plurality of reaction vessels 11 and sequentially irradiate ultraviolet rays and ultrasonic waves in each vessel while sequentially flowing the solution L to be treated into each vessel.

A feature of the present invention is that the concentration of the environmental pollutant transferred to the gas phase G above the reaction vessel 11 is measured by the gas sensor 15 during the above-mentioned ultraviolet irradiation and ultrasonic irradiation.
The ultraviolet lamp 12 and the ultrasonic oscillator 14 are controlled based on the measured concentration. That is, when the concentration of the environmental pollutant in the gas phase G is high, it is predicted that the concentration of the environmental pollutant in the solution L to be treated is also high, so that the ultraviolet ray and the ultrasonic wave are continuously irradiated to the gas phase G. When the concentration of the environmental pollutant becomes less than a predetermined value, the irradiation of ultraviolet rays and ultrasonic waves is stopped and the solution to be treated is allowed to flow out as waste water.

That is, the control device 16 controls the gas sensor 1
When the concentration of the environmental pollutant in the gas phase G is equal to or higher than the predetermined value in response to the measurement signal from 5, the operating signal is sent to the ultraviolet lamp 12 and the ultrasonic oscillator 14 to set the concentration of the environmental pollutant to the predetermined value. When the following occurs, a stop signal is sent to the outside lamp 12 and the ultrasonic oscillator 14, and a discharge valve (not shown) is opened to let the solution to be treated flow out as waste water.

However, the control method by the controller 16 is as follows.
Not limited to the above method, for example, the output of the ultraviolet lamp 12 and the ultrasonic oscillator 14 or ON / OFF may be controlled according to the concentration of the environmental pollutant in the gas phase G.

By such a method, environmental pollutants such as organic halogen compounds contained in the solution to be treated can be efficiently decomposed and safely discharged to a predetermined concentration or less determined by the environmental emission standard. In addition, the processing efficiency can be improved without spending more processing time and energy consumption than necessary.

The structure of the disassembling apparatus is not limited to the structure shown in FIG. 1, and various structures can be adopted. For example, the vibrator 13 of the ultrasonic oscillator 14 may be arranged in the center of the bottom of the reaction vessel 11, and the ultraviolet lamp 12 may be arranged so as to surround the outer circumference of the vibration path of the ultrasonic waves output by the vibrator 13.
Further, it may have a structure in which processing devices including an ultrasonic oscillator and an ultraviolet irradiation lamp are provided in a plurality of stages, and the solution to be processed is sequentially passed through the processing sections of the plurality of stages.

[0040]

EXAMPLE Using the decomposition apparatus of FIG. 1, an aqueous solution containing tetrachloroethylene, which is one of volatile organic chlorine compounds, was used as a solution to be treated, and ultrasonic waves of 200 kHz and maximum intensity near a wavelength of 260 nm were applied to the aqueous solution. It was simultaneously irradiated with the ultraviolet rays that it had, and the change with time of the concentration of tetrachloroethylene remaining in the solution L to be treated was measured. The result is shown in FIG.

On the other hand, the tetrachloroethylene concentration in the gas phase G was measured by the gas sensor 15 while treating under the same conditions as above, and the change with time of the tetrachloroethylene concentration in the gas phase G was measured. The result is shown in FIG.

FIG. 4 shows a correlation diagram between the concentration of tetrachloroethylene in the gas phase G and the concentration of tetrachloroethylene in the solution L to be treated. As shown in FIG. 4, a good correlation is recognized between the two, and it can be seen that the concentration in the solution L to be treated can be predicted with sufficient accuracy from the measurement result of the gas phase concentration.

That is, the straight line in FIG. 4 is y = 3.4x × 0.6.
The correlation is recognized in the relationship of γ (correlation coefficient) = 0.9999. Therefore, by obtaining the gas phase concentration, the concentration in the liquid to be treated can be obtained almost accurately.

[0044]

As described above, according to the present invention, by detecting the concentration of the environmental pollutant existing in the gas phase portion of the reaction vessel, the concentration of the environmental pollutant in the liquid phase can be predicted almost accurately in real time. , Because the irradiation of ultrasonic waves and ultraviolet rays can be controlled so that the concentration becomes a certain level or less,
It is possible to efficiently decompose the environmental pollutants so as to satisfy the concentration level of the environmental emission standard.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an apparatus for decomposing environmental pollutants according to the present invention.

FIG. 2 is a chart showing the relationship between the concentration of tetrachloroethylene in the solution to be treated and the treatment time when the environmental pollutants were decomposed by the method of the present invention.

FIG. 3 is a table showing the relationship between the concentration of tetrachlorethylene in the gas phase of a reaction vessel and the treatment time when an environmental pollutant is decomposed by the method of the present invention.

FIG. 4 is a chart showing the correlation between the concentration of tetrachloroethylene in a solution to be treated and the concentration of tetrachloroethylene in a solution to be treated when an environmental pollutant is decomposed by the method of the present invention.

[Explanation of symbols]

10: Decomposing device for environmental pollutants 11: Reaction vessel 12: UV lamp 13: oscillator 14: Ultrasonic oscillator 15: Gas sensor 16: Control device G: Gas phase L: solution to be treated W: Ultrasound

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07B 35/06 C07B 35/06 37/06 37/06 C07C 21/12 C07C 21/12 F term (reference) 2E191 BA15 BB01 BD11 BD17 4D037 AA01 AA05 AA11 AB12 AB14 AB15 BA18 BA26 BB01 BB02 CA14 4G075 AA15 AA22 AA37 AA52 AA65 BA05 CA23 CA33 DA01 EA01 EB01 4H006 AA05 AC13 AC26 BA91 BA95

Claims (4)

[Claims] 1. A solution to be treated containing a volatile environmental pollutant is introduced into a reaction vessel, and the solution to be treated stored in the reaction vessel is irradiated with ultrasonic waves and ultraviolet rays to remove the environmental pollutant. In the method for decomposing, the concentration of the environmental pollutant present in the gas phase portion of the reaction vessel is detected, and the irradiation of ultrasonic waves and ultraviolet rays is controlled according to the detected concentration to decompose the environmental pollutant. Method. 2. The method for decomposing environmental pollutants according to claim 1, wherein the environmental pollutants are organic halogen compounds. 3. A reaction vessel for storing a solution to be treated containing a volatile environmental pollutant, a means for irradiating the solution to be treated in the reaction vessel with ultrasonic waves, and the object to be treated in the reaction vessel. In the apparatus for decomposing environmental pollutants having means for irradiating the solution with ultraviolet rays, a gas sensor for detecting the concentration of the environmental pollutants present in the gas phase portion of the reaction vessel is provided, and based on the detected concentration of the gas sensor, An apparatus for decomposing environmental pollutants, comprising control means for controlling irradiation of ultrasonic wave irradiation means and ultraviolet irradiation means. 4. The apparatus for decomposing environmental pollutants according to claim 3, wherein the environmental pollutants are organic halogen compounds.