KR20150030803A

KR20150030803A - method for water treatment using liquid phase plasma reaction

Info

Publication number: KR20150030803A
Application number: KR20130109512A
Authority: KR
Inventors: 정상철; 배영선
Original assignee: 순천대학교 산학협력단
Priority date: 2013-09-12
Filing date: 2013-09-12
Publication date: 2015-03-23

Abstract

The present invention relates to a water treatment method using an underwater plasma reaction, and more particularly, to a method and apparatus for controlling the concentration of dissolved oxygen in a water containing a pollutant by increasing the generation of oxidized species such as OH radicals in a plasma reaction And to a water treatment method capable of decomposing pollutants in water at high speed.
A water treatment method using an underwater plasma reaction according to the present invention comprises a first step of dissolving oxygen in a treatment object water to adjust a dissolved oxygen concentration in the treatment target water and a second step of introducing the treatment target water into a reaction vessel provided with a pair of electrodes And a third step of supplying power to the electrode to decompose the contaminants by generating plasma in the water to be treated which flows into the reaction tank.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment method using an underwater plasma reaction,

The present invention relates to a water treatment method using an underwater plasma reaction, and more particularly, to a method and apparatus for controlling the concentration of dissolved oxygen in a water containing a pollutant by increasing the generation of oxidized species such as OH radicals in a plasma reaction And to a water treatment method capable of decomposing pollutants in water at high speed.

In general, water (water) treatment technology can be roughly divided into physical and chemical treatment, biological treatment, and multistage treatment. However, much research is currently underway to see better water treatment effects beyond these technologies. Much research has been done on technologies called so-called advanced water treatment techniques.

The advanced water treatment techniques described above include electrochemical techniques, water treatment techniques using electricity and magnetics, water treatment techniques using ultraviolet rays, and water treatment techniques using plasma. The present invention belongs to a water treatment technique using plasma, It is possible to treat harmful gases and odors in the air as well as harmful substances in the air.

Conventional water treatment techniques include flocculation treatment, ozone oxidation treatment using ozone, activated carbon adsorption for adsorbing soluble organic compounds and compounds, biological treatment with microorganisms, and Fenton oxidation process. The most commonly used of these is ozone, and efforts are being made to apply ozone to improve the environment and prevent diseases in industrial wastewater and landfill leachate. This is because ozone has a strong oxidizing power and theoretically has the potential to completely decompose organic matter into CO ₂ and H ₂ O and the advantage of not producing any byproducts, but gradually revealing the chemical characteristics and decomposition mechanism of ozone It is known that the reaction between ozone and some organic substances is selectively observed or the reaction rate is slow.

In order to overcome the disadvantages of the conventional ozone treatment and the limitation of the conventional oxidation treatment process, there has been recently proposed an advanced oxidation treatment (a treatment method that can purify contaminated water by promoting the generation of OH radical having a strong oxidizing power in water Advanced Oxidation Process (AOP) is considered to be very effective for water treatment.

O ₃ / highpH, O ₃ / H ₂ O ₂ (Peroxone), O ₃ / UV, H ₂ O ₂ / UV, and the like are examples of AOP that can be applied to water treatment. Plasma discharges are being actively studied.

Plasma-based water treatment technology is different from conventional water treatment technology, and it does not require the input of chemicals, the treatment process is simple, and secondary pollution is not generated. Recently, it has become a new concept of water treatment technology.

Studies on electric discharge for the treatment of water pollutants have been actively carried out in USA, Japan, Netherlands, Czech Republic, Russia and Canada since the late 1980s. When generating a high voltage pulse discharge in water or surface water begins to various physical and chemical processes UV, shock waves, and H ·, O ·, OH · , 1 O 2, HO 2, O - as _2, H ₂ O ₂ And these unstable products react with secondary pollutants or oxygen to form peroxide or a new type of radical, so that a chain oxidative decomposition reaction proceeds, It can be widely applied to purification of water such as sterilization treatment of wastewater.

Korean Patent Publication No. 2006-0124864 discloses an underwater plasma discharge device and an underwater discharge method using the same.

The discharge device described above includes at least one pair of electrodes installed in a reactor into which water is introduced, an air injection unit for injecting air into the reactor to guide the pair of electrodes to be a two-phase space of water and air, And a power supply unit for applying power to the electrode of the plasma display panel. The disclosed technique has a structure for aerating the air into the reactor to form the inside of the reactor into two-phase space of water and air. Aeration is present in the form of bubbles in water.

Since the plasma is discharged in the two-phase space state where air bubbles exist in the water, stable plasma discharge can be maintained, but the generation of oxidized species such as OH radicals is lowered rather than the plasma discharge in the air- There is a problem that the decomposition effect of the pollutant is lowered.

The object of the present invention is to provide a water treatment method capable of dissolving oxygen in the water to be treated to increase the concentration of dissolved oxygen, thereby increasing the generation of oxidized species such as OH radicals and decomposing pollutants in water at high speed .

In order to accomplish the above object, a water treatment method using an underwater plasma reaction according to the present invention comprises: a first step of dissolving oxygen in a treatment target water to adjust a dissolved oxygen concentration in the treatment target water; A second step of introducing the object water to a reaction tank provided with a pair of electrodes; And a third step of supplying power to the electrode to generate plasma in the water to be treated which flows into the reaction tank to decompose contaminants.

Wherein the second step circulates the object to be treated through the reaction vessel and the temperature of the object water flowing into the reaction vessel is cooled to 15 to 25 캜.

In the third step, the power supplied to the electrode is 220 to 300 V, the pulse width is 1 to 5,, and the frequency is 25 to 35 KHz.

The first step is characterized in that the dissolved oxygen concentration is adjusted to 30 to 70 ppm.

As described above, according to the present invention, dissolved oxygen is introduced into the reaction tank after dissolving oxygen in the process water, so that bubbles are prevented from being generated in the reaction tank, and dissolved oxygen in the treated water can be increased.

As described above, the present invention increases the concentration of dissolved oxygen in the water to be treated, thereby increasing the generation of oxidized species such as OH radicals, and thus it is possible to decompose contaminants in water at high speed.

FIG. 1 is a schematic view showing an underwater plasma reaction apparatus applied to an embodiment of the present invention,
FIGS. 2 and 3 are graphs showing OES (Optical Emission Spectra) results of light generated by generating a plasma phenomenon while varying the DO concentration of distilled water. FIG.
4 is a graph showing the decomposition reaction rate of methylene blue according to the DO concentration in the methylene blue aqueous solution,
5 is a graph showing changes in the concentration of methylene blue depending on the presence or absence of a plasma reaction and the DO concentration in a methylene blue aqueous solution.

Hereinafter, a water treatment method using an underwater plasma reaction according to a preferred embodiment of the present invention will be described in detail.

First, an underwater plasma reaction apparatus for generating a plasma in water will be described with reference to FIG.

The illustrated underwater plasma reactor includes a tubular reaction tank 10, a circulation pump 50 for circulating the water to be treated through the reaction tank 10, a circulation pump 50 for circulating the water to be treated into the reaction tank 10, A pair of electrodes 30 provided in the reactor 10; a bipolar pulse power supply 20 for supplying power to the electrodes 30; And oxygen dissolving means (60) for dissolving oxygen in the water to be treated which flows into the reaction tank (10).

The electrode 30 is made of tungsten, and the outside of the electrode 30 is covered with an insulator 35 made of a ceramic material. The distance between the two electrodes 30 is preferably about 0.2 to 0.5 mm.

When electric power is supplied to the electrode 30 through the power supply 20, plasma is generated in water by electric discharge. In order to prevent the temperature of the treatment object from rising when the plasma is generated by the electric discharge, the treatment object water is introduced into the cooling part 40 by using the circulation pump 50 to raise the temperature of the treatment object water to 15 to 25 캜 . The reactor 10 and the cooling unit 40 are connected to the first inlet pipe 55 and the second outlet pipe 45. The water to be treated which has been cooled to a predetermined temperature in the cooling section 40 flows into the reaction tank 10 through the first inlet pipe 55.

A dissolving tank 67 as an oxygen dissolving means for dissolving oxygen in the water to be treated and an oxygen tank 69 connected to the dissolving tank 67 to supply oxygen into the dissolving tank. The dissolving tank 67 and the cooling unit 40 are connected to the second inlet pipe 61 and the second outlet pipe 65. A part of the water to be treated passing through the cooling section 40 flows into the dissolution tank 67 through the second inflow pipe 61. The water to be treated whose dissolved oxygen concentration is adjusted in the dissolution tank 67 flows into the cooling unit 40 through the second outflow pipe 65. A pump for circulating the water to be treated is provided in the melting tank.

The water treatment method using an underwater plasma reaction according to an embodiment of the present invention includes a first step of dissolving oxygen in a treatment object water to adjust a dissolved oxygen concentration in the treatment target water, And a third step of supplying power to the electrode 30 to generate plasma in the water to be treated which flows into the reaction tank 10 to decompose contaminants. Each step will be examined in detail.

1. Step 1

First, dissolved oxygen is dissolved in the treatment target water to adjust the dissolved oxygen concentration in the treatment target water.

The number of objects to be treated means the number of objects to be treated. Wastewater, sewage, heavy water, ground water, intermediate treatment water generated in the ordinary water treatment process, etc. may be included as the target water to be treated.

The present invention dissolves oxygen in the water to be treated before the plasma reaction to adjust the dissolved oxygen concentration. By increasing the dissolved oxygen concentration in the water to be treated, it is possible to greatly increase the generation of oxidizing species such as OH radicals in the plasma reaction in water.

Preferably, the dissolved oxygen concentration in the water to be treated is adjusted to 30 to 70 ppm. If the dissolved oxygen concentration is less than 30 ppm, the rate of decomposition of contaminants is low. When the dissolved oxygen concentration exceeds 70 ppm, too much OH radical is generated in the water, and thus hydrogen peroxide (H ₂ O ₂ ) is generated by the recombination of the OH radicals. Therefore, the decomposition rate of the pollutant does not increase, Lower. This is because the oxidizing power of H ₂ O ₂ (1.78 V) is lower than that of OH radicals.

Various methods may be used to dissolve oxygen in the water to be treated. For example, the oxygen dissolving means 60 as shown in Fig. 1 is used. In the illustrated example, a dissolution tank 67 into which water to be treated flows into the dissolution tank is connected to the dissolution tank 67 and an oxygen tank 69 which supplies oxygen into the dissolution tank. Oxygen supplied from the oxygen tank to the inside of the dissolution tank comes into contact with the water to be treated which flows into the dissolution tank and is dissolved in the water to be treated. In order to increase the dissolution efficiency upon dissolution, the pressure of the dissolution tank may be increased or the temperature of the water to be treated may be lowered.

As described above, the present invention enhances the water treatment efficiency by dissolving oxygen in the water to be treated and raising the dissolved oxygen, rather than aerating air or oxygen into the water to be treated.

2. Phase 2

Next, the water to be treated whose dissolved oxygen concentration is adjusted is introduced into the reaction tank 10.

The water to be treated flowing out of the reaction tank (10) has a circulation structure that flows into the reaction tank (10) again via the cooling part (40). This is to prevent the temperature rise of the water to be treated by electric discharge. The cooling unit 40 cools the temperature of the water to be treated which flows into the reaction tank 10 to 15 to 25 占 폚. A conventional constant temperature regulator may be used as the cooling section 40.

3. Stage 3

Next, electric power is supplied to the electrode (30) provided in the reaction tank (10), and plasma is generated in the water to be treated which flows into the reaction tank (10) to decompose contaminants.

When electrical energy is applied to the water to discharge it, the flow of ions and electrons generates plasma. Since the basic liquid is water, the main generating elements of the plasma are hydrogen and oxygen. As the amount of electric energy applied increases, the flow of ions and electrons increases and the intensity of the plasma increases.

A strong electric field by a water discharge (electrical field), a strong ultraviolet light (ultraviolet radiation), along with over-pressure shock waves (overpressure shock wave), ozone OH ·, H ·, O · , 1 O 2, HO 2, O - 2, H ₂ O ₂ And the like are known to generate free radicals. These unstable products oxidize with pollutants and decompose organic pollutants. Among the free radicals, O, OH, ¹ O ₂ , HO ₂ , O ^- ₂ , H ₂ O ₂ Oxidative species are more oxidative than other radicals.

In particular, dissolved oxygen and free radicals in the water to be treated react secondary to form peroxide or a new type of radical, thereby proceeding a chain oxidative decomposition reaction, thereby increasing the decomposition rate of the organic matter.

It is preferable to supply pulses (pulse width 1 to 5)) rather than supplying power continuously to the electrode 30 at the time of power supply. When a power source is supplied as a pulse, a stable plasma discharge state can be maintained and the electrode can be inhibited from melting.

The power supply condition supplied to the electrode for generating the plasma is 220 to 300 V, the pulse width is 1 to 5 ㎲, and the frequency is 25 to 35 KHz.

Hereinafter, the water treatment method of the present invention will be described by way of examples. However, the following experimental examples are intended to illustrate the present invention in detail, and the scope of the present invention is not limited to the following experimental examples.

&Lt; Experiment of underwater plasma reaction &

1. Experimental Method

(1) Underwater plasma reactor

The underwater plasma reactor used in the experiment was the one shown in Fig.

A high frequency bipolar pulse power supply (Nano technology, NTI-500W) was used as the power supply. The operating condition of the power supply was 240V, frequency 25kHz, pulse width 4μs.

The applied power was supplied to the tungsten electrode installed in the reaction tank. Tungsten electrodes (2 mm, 99.95% purity, T.TM Korea Co.) were installed in both insulators and the distance between the electrodes was maintained at 0.3 mm.

During the reaction, the temperature of the water to be treated was kept at 20 ° C by using a constant temperature regulator and a roller pump to prevent the temperature rise due to the plasma. The circulation rate of the water to be treated via the reaction tank and the constant temperature regulator and the circulation rate of the water to be treated via the constant temperature regulator and the dissolution tank were kept at 500 mL / min.

A DO generator (Oxylife Co., korea) was used as an oxygen dissolution means. The DO generator dissolves oxygen in the liquid, and the dissolved oxygen concentration (DO concentration) can be controlled within the range of 30 to 70 ppm by controlling the flow rate and the friction coefficient.

(2) Optical Emission Spectrum (OES) experiments

The spectrum of the light source generated in the plasma was measured in the range of 200 nm to 1000 nm using Optical Emission Spectroscopy (AvaSpec - 3648, Avantes) to analyze the type and intensity of the light emitting material in the plasma generation.

For the luminescence analysis, distilled water with a DO concentration of 7 ppm was used as the treatment target water. In order to compare this, the DO generator was operated to adjust the DO concentration to 30, 50, and 70 ppm.

(3) Methylene blue decomposition experiment

Methylene blue was used as a decomposition substance using an underwater plasma reactor. Methylene blue is available from Daejung Chemical & Metals Co., Ltd. Ltd. The maximum absorption wavelength λ _max is 665 nm. To investigate the decomposition reaction of methylene blue, 3,000 mL of methylene blue aqueous solution was prepared. The initial concentration of methylene blue in the methylene blue aqueous solution was 1.4695 × 10 ^-2 mM.

Before the plasma reaction was induced, the circulation was maintained for 30 minutes before the reaction to make the concentration of the methylene blue aqueous solution uniform. The methylene blue aqueous solution was measured at the maximum absorption wavelength using a UV-Vis spectrophotometer (Libra S-12, Biochrom Co. Ltd.). The methylene blue concentration was determined by the calibration curve.

2. Experimental results

(1) Luminescence analysis results

The spectrum of light emitted from the plasma provides information about the chemical and physical processes that take place in the plasma. Emission of light occurs in the process of electron collision excitation and dissociation of atoms.

The optical emission spectra (OES) results of the plasma generated by varying the DO concentration of distilled water are shown in FIG. In FIG. 2, the condition that the DO concentration is 7 ppm is a condition that DO generator is not used. DO concentration in general water is about 7ppm. In FIG. 2, the DO concentration is 50 ppm. The DO concentration of the distilled water is increased to 50 ppm using a DO generator.

Referring to FIG. 2, emission spectra of OH radicals (283 and 309 nm), Hα (656 nm), Hβ (486 nm) and O _Ⅰ (777 and 844 nm) were confirmed at a DO concentration of 50 ppm. On the other hand, no OH radica of 283 nm was observed at the DO concentration of 7 ppm. In addition, OH radicals (283 and 309 nm) at 309 nm were found to have larger peaks at a DO concentration of 50 ppm than at 7 ppm.

And the amounts of radicals generated when the DO concentrations were 7 ppm, 30 ppm, 50 ppm, and 70 ppm were measured and shown in FIG. The OH radicals (283 and 309 nm) increased with increasing DO concentration and decreased at 70 ppm. Hβ (486 nm) and O _Ⅰ (777 and 844 nm) are the lowest when the DO concentration is 50 ppm.

(2) Methylene blue decomposition test result

The rate of decomposition of methylene blue using plasma at different DO concentrations is shown in FIG.

The rate of decomposition reaction was higher under the condition of increasing the DO concentration by using the DO generator compared to the case of not using the DO generator (7 ppm). Especially, the decomposition reaction rate is the highest at 50 ppm. When the DO concentration of 70 ppm reason showing a lower decomposition rate constant relative to 50 ppm is if too many OH radical is generated in water the OH radical to and make a H ₂ O ₂ to each other recombination as the following equation, the H ₂ This is because the oxidizing power (1.78 V) of O ₂ is lower than that of OH radical.

OH + OH - > H ₂ O ₂

FIG. 5 shows changes in the concentration of methylene blue depending on the presence or absence of the plasma reaction and the DO concentration.

5 shows the change in the concentration of methylene blue in the methylene blue aqueous solution having a dissolved oxygen concentration of 7 ppm under the condition of using only the DO generator without plasma generation and the LPP is the condition in which the plasma was generated in the methylene blue aqueous solution having the dissolved oxygen concentration of 7 ppm The concentration of methylene blue in DO Ge. + L.P.P. is a change in the concentration of methylene blue under the condition that the plasma is generated in a methylene blue aqueous solution in which the dissolved oxygen concentration is increased to 50 ppm.

Referring to FIG. 5, there was no change in the concentration of methylene blue in the condition using the DO generator alone (DO Ge.), Indicating that decomposition did not occur. The rate of decomposition of methylene blue was increased about 3 times under the condition of dissolved oxygen concentration of 50 ppm (DO Ge. + L.P.P.) compared with the condition of LPC of 7 ppm in the plasma reaction.

From the above-described experimental results, it was confirmed that the present invention can effectively decompose organic pollutants in the water to be treated by using an underwater plasma reaction. In particular, it was shown that increasing the dissolved oxygen concentration in the treated water can increase the decomposition rate. The dissolved oxygen concentration of the appropriate water to be treated is 30 to 70 ppm.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

10: Reactor 20: Power supply
30: electrode 40: cooling section
60: Oxygen dissolution means

Claims

A first step of dissolving oxygen in the water to be treated to adjust the concentration of dissolved oxygen in the water to be treated;
A second step of introducing the object water to a reaction tank provided with a pair of electrodes;
And a third step of supplying power to the electrode to generate plasma in the water to be treated which flows into the reaction tank to decompose contaminants.

The method according to claim 1, wherein the second step comprises circulating the object to be treated through the reaction vessel, and cooling the object water to be introduced into the reaction vessel to 15 to 25 캜. Water treatment method.

The water treatment method according to claim 1, wherein the power supplied to the electrode is 220 to 300 V, a pulse width is 1 to 5 mu s, and a frequency is 25 to 35 KHz.

The water treatment method according to any one of claims 1 to 3, wherein the first step is to adjust the dissolved oxygen concentration to 30 to 70 ppm.