JP2014200755A - Water treatment method and water treatment apparatus - Google Patents

Abstract

Provided is a water treatment method capable of removing not only organic substances by decomposition but also impurities other than organic substances such as heavy metals and radioactive substances at a high removal rate at the same time. A plurality of electrodes 20 are arranged at a tip portion with a predetermined interval in a treatment tank 10 into which water to be treated is introduced. The processing target water is introduced so that the tip of the electrode 20 is immersed in the processing tank 10, and the working gas is introduced and injected into the introduced processing target water through the gas introduction path 13, thereby causing bubbles of the working gas. And a bubble jet which is a gas-liquid two-phase flow consisting of water to be treated. By introducing this bubble jet into the tip of the electrode 20 to which an AC voltage is applied, a plasma arc discharge is generated between the electrodes 20 to oxidize and decompose organic matter and to ionize and dissolve in the water to be treated. Generates an active substance that solidifies it into a removable state by oxidizing heavy metal, etc. [Selection] Figure 1

Description

  The present invention relates to a water treatment method and a water treatment apparatus. More specifically, the present invention is intended for treating conductive water containing impurities, solidifying and removing heavy metal impurities contained in the water by ionization, and removing organic substances. The present invention relates to a water treatment method for performing gasification, disinfection, cleaning, activation, and the like by decomposition, and a water treatment apparatus used for carrying out the water treatment method.

  Water treatment technology that includes impurities such as metals and organic substances is widely used in water and sewage water treatment, factory wastewater treatment, etc., and continues to develop.

  As such water treatment technology, ozone treatment, electrocoagulation method, advanced oxidation method (Advanced Oxidation Technologies: AOT's), etc. are known, and organic compounds that cannot be decomposed / removed by the accelerated oxidation method are decomposed / removed. For this purpose, a water treatment technique for performing plasma discharge on water to be treated has also been proposed (see Patent Document 1).

[Ozone treatment]
Among the above conventional water treatment methods, ozone treatment is a treatment method widely used for treatment of water and sewage, etc., and by adding ozone to the water to be treated, sterilization using the strong oxidizing action of ozone, Deodorizing, decolorizing, etc.

  In this method, ozone is generated by performing an electrical discharge (glow discharge, dielectric barrier discharge, corona discharge) in the air or oxygen with an ozone generator, and the ozone thus obtained is oxidized into the contaminated water. Introduce as.

  However, in this method, since there are many substances that do not react with ozone, they cannot be used for the treatment of pollutants containing these substances as impurities.

  In addition, by using ozone as the oxidant and using chloride (chlor) as the oxidant, ozonides and organochlorine compounds (trihalomethane, etc.) that are generated as secondary compounds can be removed from impurities before treatment. Also has the disadvantage of becoming a highly toxic substance.

[Electrocoagulation method]
Among the water treatment technologies mentioned above, the electrocoagulation method is a method for removing impurities by coagulating and precipitating impurities in the contaminated water by flowing contaminated water between the electrodes arranged in the treatment tank.

  In this method, at least the anode of the electrodes is made of iron or aluminum, and when the voltage is applied between the electrodes, the electrode is ionized to elute the electrode in the contaminated water, thereby using the eluted electrode as a flocculant.

  That is, the aluminum or iron hydroxide produced when the electrode elutes in the contaminated water reacts with the impurities dissolved in the contaminated water to form an insoluble compound, and the compound thus produced By aggregating and precipitating, it becomes easy to remove.

  This electrocoagulation method can remove emulsified and dispersed impurities such as heavy metal ions, petroleum products, polymers, fats and oils contained in water.

[Promoted oxidation method]
Accelerated oxidation (Advanced Oxidation Technologies, AOT's) is a combination of two or more oxidants such as ozone, ultraviolet light, and hydrogen peroxide. By generating radicals, organic substances that are pollutants are removed by an oxidative decomposition reaction.

  In this method, ozone, ultraviolet rays, and hydrogen peroxide used as oxidizing agents become oxygen and water after decomposition of pollutants, so there is no generation of secondary waste, and OH radicals have very strong oxidizing power. Organic substances can be completely decomposed, OH radicals have low selectivity, and are extremely effective in decomposing and removing highly toxic organic substances such as dioxins, environmental hormones, and agricultural chemicals. There is an advantage that effects such as deodorization and COD reduction can be enjoyed simultaneously.

[Treatment with plasma (Patent Document 1)]
It cannot be decomposed by using strong oxidants such as chlorine, ozone, and OH radicals, and OH radicals are generated by combining ozone, hydrogen peroxide, and ultraviolet irradiation by the above-mentioned accelerated oxidation method. In a gas-liquid two-phase flow device that bubbles gas into a liquid containing a hardly decomposable organic substance for the purpose of decomposing an organic fluorine compound that does not decompose at all, it is a discharge plasma in the bubbled gas. A gas-liquid two-phase flow plasma processing apparatus having a high-voltage power source for generating a gas has also been proposed (see Patent Document 1). According to this apparatus, the discharge plasma causes a hardly decomposable organic substance such as an organic fluorine compound. Is also described that it can be directly decomposed (Patent Document 1 [0029] column).

JP 2011-56451 A

  Among the conventional technologies described above, the accelerated oxidation method uses OH radicals generated by the combined application of ozone, hydrogen peroxide, and ultraviolet irradiation to decompose and remove impurities. Compared with the case where these oxidizing agents are used alone, OH radicals can be generated more efficiently, and as a result, high processing efficiency can be obtained.

  However, this method requires not only an expensive ozone generator, but also the addition of hydrogen peroxide to the contaminated water or the provision of a UV lamp to irradiate ultraviolet rays, which makes the apparatus configuration large. Therefore, a large initial investment is required.

  In addition, the treatment capacity of contaminated water depends greatly on the generation efficiency of ozone and hydrogen peroxide and the light emission efficiency of the UV lamp. Therefore, if the high treatment capacity is maintained, the power consumption increases and the running cost is also large. It will be something.

  On the other hand, in the water treatment method introduced as the above-mentioned Patent Document 1, plasma is generated in bubbles by introducing contaminated water as gas-liquid two-phase fluid by introducing oxygen in the form of bubbles between the electrodes. However, by directly decomposing impurities with the active substance generated in the bubbles by this plasma, it is possible to decompose even the hardly decomposable organic substances that could not be decomposed by the conventional water treatment method.

  However, in the water treatment apparatus described in Patent Document 1, since the discharge is performed with a dielectric interposed between the cathode and the anode, the electric charge does not flow into the electrode due to the presence of this insulator, so the discharge is It does not become an arc, does not cause a temperature rise, does not generate a powerful flash or noise, and performs a discharge called “dielectric barrier discharge” or “silent discharge” (Patent Document 1 [0024] column) However, there is still room for improvement in processing capacity.

  In other words, the flash light during plasma discharge contains ultraviolet light, which not only kills microorganisms and algae in contaminated water, but also contributes to the generation of ozone and OH radicals by causing a dissociation reaction with oxygen. To do. In addition, shock waves and heat generated by stuttering generated with flash light contribute to the killing of microorganisms and algae and decomposition of organic matter. Further improvement can be expected.

  Therefore, the present invention has been made to solve the above-mentioned drawbacks of the prior art, and water treatment using plasma discharge can be performed more economically and efficiently, and further, by decomposition of organic matter. To provide a water treatment method capable of removing not only removal but also impurities other than organic substances such as heavy metals and radioactive substances at the same time with a high removal rate, and a water treatment apparatus used for carrying out the water treatment method. Objective.

  Hereinafter, means for solving the problem will be described together with reference numerals used in the embodiment for carrying out the invention. This code is used to clarify the correspondence between the description of the scope of claims and the description of the mode for carrying out the invention. Needless to say, this code is limited to the interpretation of the technical scope of the present invention. Not used.

In order to achieve the above object, the water treatment method of the present invention accommodates a plurality of rod-like electrodes 20 arranged between the tip portions with a predetermined interval, and each of the electrodes 20 and the water to be treated. A treatment tank 10 for storing or passing is provided,
The treatment target water is introduced so that at least the tip of each electrode 20 is immersed in the treatment tank 10, a working gas is injected into the introduced treatment target water, and the bubbles of the working gas and the liquid A bubble jet that is a gas-liquid two-phase flow composed of
A plasma arc discharge is generated between the electrodes 20 by introducing the bubble jet into the tip of the electrode 20 to which an AC voltage is applied (Claim 1).

  In the present invention, the electrode 20 includes a rod formed in a predetermined length and a long wire wound in a coil shape.

  In the water treatment method, the electrode 20 may be fed into the treatment tank 10 in the longitudinal direction at a predetermined speed, and the interval between the tip portions of the electrode 20 may be maintained at the predetermined interval. Item 2).

  Further, iron or aluminum may be used as the electrode 20 described above. However, iron or aluminum dissolves quickly by plasma arc discharge and cannot be used for a long time. Therefore, it is preferably formed of a hafnium alloy. (Claim 3).

  Further, the above-described gas injection is performed at a supersonic speed of Mach 1.0 to 1.5, and the gas flow injected into the water to be treated is dispersed to form minute bubbles in the water to be treated. (Claim 4).

  It is preferable that the bubbles are dispersed in this manner so that the diameter of the bubbles after dispersion is 1 to 2 mm.

  Furthermore, the plasma arc discharge occurs when the discharge start voltage is in the range of 40 to 70% of the peak voltage of the AC voltage applied to the electrode 20, and no discharge occurs when the discharge start voltage is less than the discharge start voltage. Then, the contact area of the electrode 20 with respect to the water to be treated is adjusted so that the current density at which the inter-electrode current flows is obtained (Claim 6).

  Further, the flow velocity of the bubble jet described above is preferably in the range of 10 to 50 m / second in the injection axis direction.

  Furthermore, it is preferable that the operation gas injection is performed so that the gas content of the water to be treated is 30 to 90% in volume ratio.

Moreover, the water treatment apparatus 1 of the present invention used in the above-described water treatment method fixes a plurality of electrodes 20 in the treatment tank 10 in which the water to be treated is placed so that the tip portions are close to each other. A plurality of electrode insertion holes 15 for providing
A working gas is injected into the water to be treated introduced into the treatment tank 10 toward the tip end side of the electrode 20, and a gas-liquid two-phase flow constituted by the bubbles of the working gas and the water to be treated While providing a gas introduction path 13 for generating a bubble jet,
A voltage source (not shown) for applying an AC voltage necessary for generating a plasma arc discharge between the tip portions of the electrode 20 under generation of the bubble jet is provided. 9).

  The treatment tank 10 is provided with a water supply port 11 for continuously introducing the water to be treated and a drain port 12 for continuously discharging the treated water so that the water treatment apparatus 1 can perform continuous water treatment. (Claim 10). In this case, the flow rate of water in the treatment tank is preferably 0.5 seconds or less of the residence time outside the discharge range and 15 seconds or less in all steps. The drain temperature of the drain port 12 is preferably 60 ° C. or lower.

  Further, the electrode insertion hole 15 described above is provided through the wall surface of the processing tank 10, and the electrode 20 is fed into the processing tank 10 at a predetermined speed in the longitudinal direction through the electrode insertion hole 15. The apparatus 30 may be provided (claim 11).

  In addition, a gas flow distributor 14 formed of a porous body, for example, a cylindrical mesh or the like, that disperses the injected gas in the water to be treated is provided at the tip of the gas introduction path 13 (claim 12).

  According to the configuration of the present invention described above, according to the water treatment method and the water treatment apparatus 1 of the present invention, the following remarkable effects can be obtained.

  Plasma is generated in the treated water by injecting an operating gas into the treatment target water to form a bubble jet, and applying an alternating voltage between the electrodes 20 in contact with the treatment target water to generate dielectric breakdown under the generation of the bubble jet. Arc discharge could be generated.

  The occurrence of this plasma arc discharge generates highly active molecules and radicals directly in the bubbles, thereby generating heavy metals that are ionized and dissolved in the water to be treated without generating harmful secondary products. Can be solidified and organic substances in the water to be treated can be decomposed at the same time.

  In addition, when water treatment is performed by the method of the present invention, it is not necessary to use an ozone generator, hydrogen peroxide, a UV lamp, or the like as in the accelerated oxidation method described as the prior art. In comparison, economically high-efficiency water treatment could be performed without the use of chemicals and without generation of secondary products.

  In particular, in the present invention, since plasma arc discharge is generated, unlike the method described in Patent Document 1 in which dielectric barrier discharge (silent discharge) is performed, the discharge is accompanied by heat generation, intense flashing, and noise. ing.

  As a result, it is possible to enjoy combined effects such as the destruction of microorganisms and algae in the water to be treated and the decomposition of organic and inorganic impurities due to the generation of shock waves due to heat generation, intense ultraviolet irradiation, and noise. The generation of OH radicals and the like could be further promoted by the powerful ultraviolet irradiation accompanied by the generation of water, and the energy generated by the plasma arc discharge could be used comprehensively for water treatment.

  In addition, when using a hafnium alloy electrode as an electrode, not only is it possible to simultaneously solidify heavy metals that are ionized and dissolve and decompose organic substances, but it is also difficult to dissolve the electrodes due to the occurrence of plasma arc discharge. Since processing can be performed continuously and stably, it is advantageous in terms of cost.

  On the other hand, when a soluble electrode such as iron or aluminum is used, although the electrode is dissolved by plasma arc discharge, the electrode components are eluted in the water to be treated, and the eluted electrode components are dissolved in the water to be treated. By acting as a flocculant for impurities, the removal rate of impurities other than organic substances such as heavy metals and radioactive materials could be improved by agglomeration and precipitation even when centrifugation and filtration were not performed. .

  When using an electrode made of a hafnium alloy, the heavy metal is solidified by passing through the water treatment device of the present invention, and then solidified by removing solidified impurities by centrifugation or filtration. Compared to waiting for the natural precipitation of impurities, the processing speed can be greatly improved. Even when using electrodes made of iron or aluminum, centrifugation and filtration are performed after the impurities are aggregated. The processing time can be further shortened by removing the agglomerated impurities.

  Here, even in the “electrocoagulation method” described as the prior art, impurities dissolved in the liquid can be aggregated by the eluted electrode components. However, in the method of the present invention, iron or aluminum is used. Unlike the electrocoagulation method, each electrode becomes a liquid by electrolysis when it becomes an anode during the half cycle of the voltage, unlike the electrocoagulation method. In addition to elution into the liquid, it also evaporates with the plasma arc discharge and dissolves in the liquid in large quantities when it becomes the cathode in another half cycle of the voltage. High processing efficiency can be realized.

  Furthermore, when the electrode feeding device 30 is provided and the electrode 20 is fed into the processing tank 10 at a predetermined speed in the longitudinal direction, the electrode 20 can be used even when a soluble electrode is used. Was fed into the treatment tank 10 at a predetermined speed, so that the distance between the tip portions of the electrodes 20 could be maintained at a constant distance, and plasma arc discharge could be stably performed. As a result, it was possible to provide a water treatment method and a water treatment apparatus 1 with stable treatment capacity.

  In the present invention, the electrode feeding device 30 is not necessarily provided, and the electrode 20 may be attached in a fixed position. In this case, the electrode 20 can withstand long-time use by using a hafnium alloy. Further, when an electrode made of iron or aluminum is used, the electrode voltage may be changed by changing the interelectrode distance due to elution or evaporation.

  The operating gas is injected at a supersonic speed of Mach 1.0 to 1.5 and dispersed by the gas flow distributor 14 so that the bubble jet can be stably maintained over a long distance. Water to be treated in which various bubbles were formed could be introduced.

  By making the bubble diameter as small as 1-2 mm, the surface area of the bubble and the water to be treated can be increased, and the active substance generated in the bubble by the plasma arc discharge diffuses into the water to be treated. Water treatment efficiency can be further improved.

  The dielectric breakdown is related to the current density, and the current density is related to the contact area between the water to be treated and the electrode 20, so that plasma arc discharge can be achieved by appropriately adjusting the contact area between the electrode 20 and the water to be treated. Can be suitably set within a voltage range of 40 to 70% with respect to the peak value of the AC voltage.

  When the moving speed of the bubble jet is set in the range of 10 to 50 m / sec, the bubble jet is surely contained in the area between the electrodes 20 where plasma arc discharge due to dielectric breakdown occurs and includes fine bubbles. It is possible to introduce.

  Moreover, it is possible to exhibit the high resolution | decomposability of the organic substance at the time of water treatment by making the gas content rate of process target water into the range of 30 to 90% by volume ratio.

Front sectional drawing of the water treatment apparatus (apparatus structure 1) of this invention. Front sectional drawing of the water treatment apparatus (apparatus structure 2) of this invention. III-III sectional view taken on the line of FIG. Front sectional drawing of the water treatment apparatus (apparatus structure 3) of this invention. Front sectional drawing of the water treatment apparatus (apparatus structure 4) of this invention. FIG. 6 is a sectional view taken along line VI-VI in FIG. 5. The graph which shows the pressure change in the injection direction of a gas jet. Drawing substitute photograph showing oscilloscope waveform of interelectrode voltage and interelectrode current. Drawing substitute photograph showing oscilloscope waveform of interelectrode voltage and interelectrode current. The correlation between electrode distance, electrical conductivity of water to be treated, and electrode voltage. Explanatory drawing which showed the relationship between a current density and a dielectric breakdown state. The correlation figure of the gas content rate of a process target water, and a dielectric breakdown voltage. The graph which shows the decoloring test result of process target water.

  Next, embodiments of the present invention will be described below with reference to the accompanying drawings.

[Configuration of water treatment equipment]
Device configuration 1 (see FIG. 1)
Reference numeral 1 in FIG. 1 indicates a water treatment apparatus of the present invention. In the illustrated embodiment, the water treatment apparatus 1 can continuously perform treatment on flowing target water. For example, the water treatment apparatus 1 of the present invention may be configured as a batch type.

  The water treatment apparatus 1 includes a treatment tank 10 into which water to be treated is introduced, an electrode feeding apparatus 30 for feeding a rod-shaped electrode 20 having a sharp or conical tip in the treatment tank 10, and , And an AC voltage source (not shown) that applies an AC voltage to the electrode 20.

  In the illustrated embodiment, the above-described processing tank 10 is configured by a cylindrical body whose both ends are closed, and on one end side (the lower side of the paper in FIG. 1) of the cylindrical processing tank 10, A water supply port 11 for introducing the water to be treated is provided, and water treated through the treatment tank 10 is reacted with the other end of the treatment tank 10 (upper side in FIG. 1). A drain port 12 is provided for discharging together with the aggregates and bubbles generated by the water, and the water to be treated is continuously supplied into the treatment tank 10 and drained, whereby the inside of the treatment tank 10 is treated in the axial direction. Water is supposed to pass through.

  A pair of gas introduction paths 13 and 13 are provided at the end of the treatment tank 10 on the side where the water supply opening 11 is provided at symmetrical positions with respect to the water supply opening 11. For example, air, carbon dioxide gas, or a mixed gas thereof is blown into the water to be treated in the treatment tank 10 as the working gas via 13, thereby being constituted by water in the treatment tank 10 and bubbles of the working gas. In addition, it is configured to generate a bubble jet that is a gas-liquid two-phase flow.

  A gas flow distributor 14 composed of a porous material, for example, a cylindrical mesh, is attached to the tip of the gas introduction path 13, and the gas injected into the processing tank 10 through the gas introduction path 13 is The gas flow disperser 14 is crushed into fine bubbles and can be dispersed in the treated water.

  An electrode insertion hole 15 formed through the side wall of the processing tank 10 is opened in front of the gas injection direction by the gas introduction path 13, and the electrode insertion hole 15 extends from the outside of the processing tank 10. By inserting the electrode 20 toward the inside, the tip of the electrode 20 can be protruded into the space in the processing tank 10.

  As an example, the electrode 20 is disposed with an angle θ with respect to the central axis of the processing tank 10 of 30 ° to 90 °, preferably 45 ° to 90 °, and in the illustrated embodiment, the processing tank 10 It is inserted so that the tip is upward with an inclination of about 70 ° with respect to the central axis.

  The electrode insertion hole 15 is preferably provided immediately above the formation position of the gas introduction path in plan view. Therefore, in the illustrated embodiment in which the electrode insertion holes 15 are provided at two positions at the target position, the gas introduction hole 15 is provided. The passage 13 is also provided at two locations, and is configured so that two bubble jets are generated in the treatment tank 10.

  Reference numeral 30 in FIG. 1 denotes an electrode feeding device that feeds the electrode 20 into the processing tank 10 at a predetermined speed. The electrode feeding apparatus 30 is connected to the outside of the processing tank 10 to each electrode. It is provided corresponding to the position where the insertion hole 15 is formed.

  In the illustrated example, the electrode 20 is sandwiched between the pair of rollers 31 and 32, and at this time, at least one of the rollers 31 and 32 is rotationally driven by a motor or the like (not shown) to drive the rollers 31 and 32. By controlling the rotation speed of the motor, the electrode 20 can be quantitatively fed into the processing tank 10 at a desired speed.

  In the example shown in the figure, the electrode 20 described above is shown as a cylindrical rod formed in a certain length. However, instead of this configuration, for example, a long wire electrode wound in a coil shape is used. It is good also as what feeds in the processing tank 10, pulling out.

Device configuration 2 (see Figs. 2 and 3)
In the water treatment apparatus 1 shown in FIG. 1, the gas introduction path 13, the electrode insertion hole 15, and the electrode feeding apparatus 30 are respectively provided at equal intervals of 180 ° in the circumferential direction of the treatment tank 10. However, as shown in FIG. 2 and FIG. 3, for example, three of these members are provided at equal intervals of 120 ° to form a triple bubble jet in the processing tank 10. In addition, a three-phase AC voltage may be applied to the electrode inserted into the electrode insertion hole 15, and although not shown, three or more of these members may be provided. If a single-layer AC power supply is used, each part is provided as a multiple of 2, and if a three-phase AC power supply is used, it is provided as a multiple of 3.

Device configuration 3 (see FIG. 4)
As described above, in the configuration example of the water treatment apparatus 1 described with reference to FIGS. 1 to 3, the configuration example in which the electrode 20 is inserted from the side surface of the treatment tank 10 toward the central axis of the treatment tank 10 is described. However, instead of this configuration, as shown in FIG. 4, the electrode 20 may be inserted in the longitudinal direction of the processing bath 10 from one end and the other end of the processing bath 10.

  In the example shown in FIG. 4, a water supply port 11 is provided at the lower end of the treatment tank 10, a drainage port 12 is provided at the upper end, a gas introduction path 13 is provided at the lower end side of the treatment tank, and this gas introduction path 13 is connected to the tip of the electrode 20. It arrange | positions toward the drain outlet 12 through the space.

Device configuration 4 (see FIGS. 5 and 6)
In the water treatment apparatus 1 described with reference to FIG. 4, a single gas introduction path 13 is provided only on the lower end side of the treatment tank 10. As shown in FIG. 6, it is good also as what each provides the gas introduction path 13 in the upper and lower ends of a processing tank.

  In the configuration shown in FIG. 4, the water to be treated is introduced from the lower end side of the treatment tank 10 and discharged from the upper end side. However, in the embodiment shown in FIGS. In addition, a water supply port 11 is provided respectively, and a drainage port 12 for discharging the treated water is formed outside the processing tank 10 from the side wall at the center position in the longitudinal direction of the processing tank 10.

  In the embodiment shown in FIGS. 5 and 6, a groove 16 that is continuous in the circumferential direction is formed in the inner wall of the treatment tank 10 at an intermediate position in the longitudinal direction of the treatment tank 10, and the above-described drain outlet is formed in the groove 16. 12 is communicated.

[Water treatment method]
The water treatment method of the present invention can be carried out using the water treatment apparatus 1 of the present invention described above. In addition, in the following description, when there is no description in particular, the water treatment apparatus 1 demonstrates on the assumption that the thing of the structure shown in FIG. 1 is used.

  The processing target water is introduced into the processing tank 10 through the water supply port 11 provided on the lower end side of the processing tank 10 to fill the processing tank 10 with the processing target water, and with respect to the processing target water in the processing tank 10. The working gas (for example, air, carbon dioxide gas or a mixed gas thereof) is jetted and supplied from the gas introduction path 13 provided on the lower end side of the processing tank 10 through the gas flow distributor 14.

  The operating gas is injected such that the gas content in the water to be treated is 30 to 90% by volume, and the gas flow velocity in the gas introduction path 13 before reaching the gas flow distributor 14 is It is performed so that Mach is 1.0 to 1.5.

  In this way, when the working gas is injected into the water to be processed in the processing tank 10, the gas formed by the processing target water in the processing tank 10 and the bubbles of the injected gas is formed in front of the gas flow distributor 14. A bubble jet which is a liquid two-phase flow is generated, and the flow of the bubble jet rises along the inner wall of the processing tank 10 and becomes a flow toward the tip of the electrode 20.

  The velocity in the jet axis direction of the bubble jet directed toward the electrode 20 is preferably 10 to 50 m / second, and the bubble jet is introduced into the interval between the tips of the electrode 20 while cooling the electrode 20.

  At this time, the air bubbles are evenly dispersed in the water to be treated in the treatment tank 10, continuously pass through the discharge area formed between the electrodes 20, and the drain port provided on the upper end side of the treatment tank 10. It flows to 12 and is discharged out of the processing tank.

  Bubbles in the water to be treated are combined and enlarged before reaching the drain 12 and change into a random shape.

  In the method of the present invention, the physical effect and the motion condition are stabilized by combining various treatments, thereby improving the economics and treatment capacity in water treatment. As an example, the working gas is dispersed in a supersonic gas jet.

  In this way, the working gas is blown into the water to be treated at supersonic speed to form a gas-liquid integrated jet, and the shaped jet is pulverized by reducing the moving speed of the working gas and perturbing the liquid. (FIG. 7).

  When the speed of the working gas flowing into the water to be treated is high, the movement of the water to be treated in the gas inflow region becomes intense, and a two-phase flow in which gas-liquid mixing occurs due to the gas jet crushing (the water to be treated contains particulate impurities). If included, gas-liquid-solid three-phase flow) occurs. The standard size of the bubbles formed immediately before the gas flow distributor 14 is proportional to the diameter of the gas introduction passage 13 located in the gas flow distributor 14 and opening in the shape of a nozzle. In order to suppress the occurrence of a large turbulent flow that occurs at the boundary portion, a cylindrical mesh serving as the gas flow distributor 14 is attached to the tip of the gas introduction path 13.

  At this time, if the inflow speed of the working gas is less than Mach 1.0, the speed at the inflow portion of the gas jet decreases, and the formation distance of the bubble jet decreases rapidly. When the Mach number exceeds 1.5, a large turbulence occurs due to an increase in wave motion in the area where the gas jet is initially introduced. In this case as well, the formation distance of the bubble jet is drastically reduced. Is preferably Mach 1.0 to 1.5.

  In this way, by taking measures to prevent the formation distance of the bubble jet from decreasing, the space between the electrodes 20 in the treatment tank 10 can be filled uniformly with bubbles having a diameter of about 1 to 2 mm.

  The bubble jet formed by the gas flow distributor 14 flows toward the electrode 20 so as to spread along the wall surface in the processing tank 10 (however, since bubbles do not collect around the inner wall surface of the processing tank 10, The frequency of bubbles passing through the wall surface is substantially zero).

  Due to the characteristics of the jet (Coanda effect), the water to be treated flows along the inner wall surface of the treatment tank 10, hits the electrode 20 protruding from the wall surface, and flows along the surface of the electrode 20. As a result, bubbles in the water to be treated flow between the tips of the electrodes 20, and the bubbles uniformly fill the water to be treated.

  In the method of the present invention, the water to be treated comes into contact with the surface of the electrode 20 and the presence of bubbles between the tips of the electrode 20 allows the water to be continuously transferred from the liquid without destroying the molecular structure of the water. Current can be generated in a non-discharged state by ionization. This makes it possible to prepare the preconditions that cause dielectric breakdown.

  It is preferable to set the flow velocity in the jet axis direction of the bubble jet toward the electrode portion to be in the range of 10 to 50 m / sec. The reason is that arc discharge due to dielectric breakdown is performed within this flow velocity range. This is because a bubble jet containing bubbles can be reliably introduced into the region between the electrodes.

  By appropriately setting the interval between the tips of the electrodes 20 protruding into the processing tank 10, plasma arc discharge can be controlled and stably generated. In addition, when a soluble electrode such as iron or aluminum is used as the electrode, when the electrode 20 acts as an anode in a half cycle of the AC voltage, the electrode material is not only eluted evenly in the liquid, but also a further half. Even when acting as a cathode in the cycle, the electrode material evaporates and elutes into the liquid as the plasma arc discharge occurs. As a result, the electrode material eluted in the liquid in this way acts as an aggregating agent for aggregating and precipitating impurities dissolved in the liquid, and in the method of the present invention, heavy metals dissolved in the liquid and In addition to solidifying inorganic impurities such as radioactive substances, it is possible to remove them by agglomeration and precipitation.

  When the voltage exceeds 40% to 70% of the discharge start voltage with respect to the peak value of the AC voltage, dielectric breakdown occurs and arc discharge occurs every half cycle of the applied AC voltage, and is less than the discharge start pressure. It is an important feature of the present invention to ensure the generation of the inter-electrode current without discharge in the state of the voltage.

  It has been confirmed by experiment using a frequency of 50-5000-30000 Hz that this condition is not related to the frequency of the applied voltage.

  The conductivity of the water to be treated is 30 to 500 mS / m, and the voltage setting and the distance between the electrodes change in relation to the conductivity of the water to be treated. The area of the electrode that comes into contact with the water to be treated is set in relation to the current density that is the premise of dielectric breakdown.

  8 and 9 show the oscilloscope waveforms of voltage and current in the water treatment apparatus 1 with a power supply frequency of 50 Hz.

  It can be confirmed from the current waveforms in FIGS. 8 and 9 that diffusion discharge after dielectric breakdown has occurred. This discharge is characterized in that the current becomes a high pulse and contains a high frequency component. The reason is that many arcs with arc discharge time of 0.00001 to 0.000001 seconds are generated and disappeared on the bubble surface. By such ultra-fast local heating and cooling of the bubble surface, excitons with a concentration much higher than the average concentration are generated. (Propagating through a deformable lattice in which the molecule is vibrating) and free radicals are generated.

  8 and 9, it can be seen that the discharge start voltage is about 60% of the peak value of the AC voltage in the illustrated example.

  FIG. 10 shows a correlation diagram between the electrode distance, the conductivity of the water to be treated, and the electrode voltage. From FIG. 10, the electrode voltage increases as the distance between the electrodes increases, and the electrode voltage decreases as the conductivity of the water to be treated increases.

  Therefore, the water treatment can be performed efficiently and economically by adjusting the interelectrode distance and the voltage value according to the relative relationship with the conductivity of the liquid to be treated.

  As an example, in the example shown in FIG. 10, when the liquid conductivity is 150 mS / m, the voltage is 1800 V, and the interelectrode distance corresponding to this voltage 1800 V is 25 mm.

  In addition, when the electrode 20 is fixed without providing the electrode feeding device 30, the distance between the electrodes may be fixed by using an electrode made of a hafnium alloy, When a soluble electrode made of aluminum or aluminum is used in a fixed manner, the electrode voltage is increased in accordance with the increase in the inter-electrode distance associated with the evaporation of the electrode 20 in accordance with the above correspondence.

  FIG. 11 is a correlation diagram between a current density and a dielectric breakdown state generated between electrodes in a liquid.

  The state of dielectric breakdown was confirmed visually, and each parameter was obtained from the oscilloscope display for calculation.

  The current density was calculated by dividing the current value displayed on the oscilloscope by the surface area of the electrode exposed in the water to be treated.

  The dielectric breakdown conditions that occur between the electrodes and in the vicinity of the electrode surface are different, and the dielectric breakdown between the electrodes occurs on the inner surface of the bubble gas bubble, and then spreads while being connected to the liquid through the inner surface of the bubble.

  Since bubbles are bounced back on the electrode surface, dielectric breakdown also occurs in the boundary layer near the electrode. The dielectric breakdown in the vicinity of the electrode is important, and this feature is included in the features of the present invention.

The results shown in FIG. 11 show that a steel wire having a diameter of 2.5 mm was used as an electrode, and in the operation mode of the apparatus, voltage: 1500 to 2500 V, current: 4 А, liquid electrical conductivity: 150 mS / m, electrode spacing: 35 mm Gas volume content in the liquid: 75%, the electrode is placed in parallel with the bubble gas jet, and the exposed length of the electrode in the liquid is varied from 1 mm to 40 mm (surface area from 7.85 mm ² to 314 mm ² ). The current density was changed from 0.51 А / mm ² to 0.0127 А / mm ² , and the dielectric breakdown state was visually confirmed.

  FIG. 12 shows a correlation diagram between the gas content of the liquid and the breakdown voltage. From FIG. 12, it was confirmed that the dielectric breakdown voltage hardly changed in the range of the gas content rate in which the experiment was performed.

  In the water treatment method of the present invention, a large amount of highly active substance exceeding the saturation state is generated in the bubbles, thereby diffusing the highly active substance into the liquid from the bubble surface, thereby ionizing into the liquid to be treated. In addition to solidifying the dissolved impurities, the impurities can be easily removed and gasification, sterilization, bleaching, and the like by decomposition of the organic compound can be suitably performed.

  In particular, by using iron or aluminum as an electrode and dissolving the electrode in a large amount as a coagulant in the water to be treated by plasma arc discharge, the liquid is treated by a complex action that also involves aggregation and precipitation of impurities. be able to.

  As a result, in the method of the present invention, the processing capability is remarkably improved as compared with the conventional processing process. Therefore, the method of the present invention is a versatile method as a liquid electrochemical process.

  In addition, the water treatment according to the method of the present invention is characterized in that no by-products (secondary products that cause environmental pollution) are generated. According to the discharge operating conditions of the present invention, the ozone concentration in the gas phase and aqueous solution phase drops to 3%, which is a very important value in commercialization.

  Ozone is generated in bubbles and enters water from bubbles, but it is short-lived for 1 second or less, and in order to generate OH radicals, discharge must be generated near the surface of bubbles in aqueous solution. .

  According to the diffusion plasma arc discharge used in the method of the present invention, an ozonation / hydration mixture having a lifetime of 1 second or less is generated. Therefore, the residence time of the liquid in the treatment tank may be 1 second or more, and the amount of active substance generated in the liquid affects the economics and treatment capacity of the water treatment of the present invention. Improving the amount of substances generated is an important issue.

  Here, active substances generated by plasma arc discharge include substances that oxidize or reduce substances that diffuse from bubbles into the water to be treated and dissolve in the water to be treated. Some of them disappear naturally without being oxidized.

  Therefore, the water treatment according to the present invention can be achieved by reducing the amount of the active substance that naturally disappears in the gas bubbles and increasing the amount of the active substance that diffuses from the bubbles into the liquid and oxidizes impurities. Can be performed more economically and efficiently.

  FIG. 13 shows the results of measuring how the decomposition time of the organic matter dissolved in the liquid changes by changing the gas content of the water to be treated based on the above idea.

The water to be treated in this experiment is water in which an orange colorant is dissolved (C ₁₆ H ₁₂ O ₄ N ₂ S aqueous solution having a concentration of 0.5% or less), and the gas content of the water to be treated is changed. It was measured how the decolorization time of the aqueous solution changed.

  From the result of FIG. 13, when the gas content is gradually increased from the state in which the operating gas is not injected into the water to be treated, the decolorization time is gradually decreased, and thus the organic matter resolution is improved. Confirmed to do.

  This decrease in decolorization time peaked when the gas content reached about 60%, and it was confirmed that if the gas content was increased thereafter, the decolorization time gradually increased and the resolution of organic matter decreased. It was.

  The above results show that when the gas content is significantly lower than 60%, the concentration of the active substance in the bubbles becomes too high, and the spontaneous extinction rate of the active substance is increased, so that the impurities in the liquid are decomposed or solidified. As a result, the processing capacity decreases as a result of an increase in the amount of active substances that do not contribute to the removal, but when the gas content is significantly higher than the gas content of 60%, the concentration of the active substance generated in each bubble is low. This is considered to be because the amount of the active substance that diffuses and enters the liquid from the bubbles is reduced, and the action of oxidizing the substance dissolved in the liquid is reduced.

  Therefore, as the gas content in the liquid approaches 60%, it is possible to obtain a high effect, and the preferred range of the gas concentration is 30 to 90. % Is preferable.

  Here, as can be seen from the gas content of the liquid described above, it is important to diffuse more active substance generated in the gas bubbles into the liquid in order to improve the processing efficiency of the liquid. I know that there is.

  Such diffusion of the active substance is affected by the surface area of the boundary between the bubble and the liquid, and the larger the boundary surface area, the easier the active substance diffuses into the liquid.

  Therefore, in the water treatment apparatus of the present invention, the surface area of the gas-liquid interface is increased by reducing the size of the gas bubbles, and such fine bubbles can be generated. In order to make it possible, gas gas dispersers 14 made of a cylindrical mesh or the like are arranged in front of the gas injection port, etc., so that the gas bubbles in the discharge area and the liquid flow in the treatment tank 10 In order to minimize the size, the device configuration is devised to reduce the amount of active substances that disappear without contributing to liquid processing, thereby improving processing efficiency.

  In addition, pulverization of bubbles caused by turbulent flow in the treatment tank 10, reduction of surface tension due to thermal expansion of bubbles caused by plasma arc discharge, increase in pressure inside the bubbles, and the like, pulverization of bubbles is activated, and active substances in the liquid Can be promoted.

  In the water treatment method of the present invention, as described above, not only the organic substance is decomposed using the active substance generated in the bubbles by the plasma arc discharge, but also impurities such as heavy metals and radioactive substances dissolved in the liquid. It has already been described that one of the features is that it can be solidified and removed.

  Thus, in order to confirm that the water treatment method of the present invention has the ability to remove heavy metals and radioactive substances, the heavy metal salt dissolved in the water to be treated (Table 1) using the water treatment device of the present invention. And a removal test for radioactive substances (Tables 2 to 4).

Removal test of heavy metal Table 1 shows the results of treating the water containing heavy metal through the water treatment device of the present invention. In this test example, a water treatment device equipped with an electrode made of hafnium alloy was used, and the water to be treated after passing through the water treatment device was filtered with a filter medium (made of cotton) to solidify heavy metal. Removed.

  From the above results, it was confirmed that when water treatment is performed using the water treatment apparatus of the present invention, heavy metals dissolved in the liquid can be suitably removed with an extremely high removal rate.

Radioactive substance removal test Tables 2-4 show the results of measurement of the residual state of radioactive substances after treatment with water containing radioactive substances and solidification and removal of impurities through the water treatment device of the present invention. .

  As a result, it was confirmed that according to the water treatment method of the present invention, the removal of radioactive substances contained in the liquid can be suitably performed.

DESCRIPTION OF SYMBOLS 1 Water treatment apparatus 10 Treatment tank 11 Water supply port 12 Drainage port 13 Gas introduction path 14 Gas flow dispersion device 15 Electrode insertion hole 16 Groove 20 Electrode 30 Electrode feeding device 31, 32 Roller

Claims (12)

Provided with a plurality of electrodes disposed between the tip portions with a predetermined interval, and a treatment tank for storing or passing the treatment target water while accommodating each of the electrodes,
The treatment target water is introduced so that at least the tip portion of each electrode is immersed in the treatment tank, and a working gas is injected into the introduced treatment target water, and configured by bubbles of the working gas and the liquid A bubble jet, which is a gas-liquid two-phase flow,
A water treatment method, wherein a plasma arc discharge is generated between the electrodes by introducing the bubble jet into a tip portion of the electrodes to which an alternating voltage is applied.   2. The water treatment method according to claim 1, wherein the electrode is fed into the treatment tank at a predetermined speed in a longitudinal direction, and an interval between tip portions of the electrode is maintained at the predetermined interval.   The water treatment method according to claim 1, wherein the electrode is formed of a hafnium alloy.   Injecting the working gas at a supersonic speed of Mach 1.0 to 1.5 and dispersing the gas flow injected into the water to be treated to form the fine bubbles in the water to be treated. The water treatment method according to any one of claims 1 to 3, wherein the water treatment method is characterized.   The water treatment method according to claim 4, wherein the diameter of the dispersed bubbles is 1 to 2 mm.   The plasma arc discharge occurs when the discharge start voltage is in the range of 40 to 70% with respect to the peak voltage of the AC voltage applied to the electrodes, and when the discharge start voltage is less than the discharge start voltage, no discharge occurs between the electrodes. The water treatment method according to claim 1, wherein the contact area of the electrode with respect to the water to be treated is adjusted so as to obtain a current density at which a current flows.   The water treatment method according to any one of claims 1 to 6, wherein a flow velocity of the bubble jet flow in the injection axis direction is set in a range of 10 to 50 m / sec.   The water treatment method according to any one of claims 1 to 7, wherein the gas is injected so that a gas content of the treatment target water is 30 to 90% in a volume ratio. In the treatment tank into which the water to be treated is placed, a plurality of electrode insertion holes for fixing a plurality of electrodes in the treatment tank so that the tip portions are brought close to each other are provided,
A bubble that is a gas-liquid two-phase flow composed of bubbles of the working gas and the water to be treated by injecting a working gas into the water to be treated introduced into the treatment tank toward the tip end side of the electrode In addition to providing a gas introduction path that generates a jet,
A water treatment apparatus comprising: a voltage source that applies an AC voltage necessary for generating a plasma arc discharge between tip portions of the electrodes under generation of the bubble jet.   The water treatment apparatus according to claim 9, wherein a water supply port for introducing treatment target water into the treatment tank and a drainage port for discharging treated water are provided.   The electrode insertion hole is provided through the wall of the processing tank, and an electrode feeding device is provided for feeding the electrode into the processing tank at a predetermined speed in the longitudinal direction through the electrode insertion hole. The water treatment apparatus according to claim 9 or 10.   The water treatment device according to any one of claims 9 to 11, wherein a gas air flow disperser for dispersing the injection gas in the water to be treated is provided at a tip of the gas introduction path.

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