JP2018187543A - Water treatment apparatus and water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for preventing a quality decline of treated water.SOLUTION: A water treatment apparatus (100) of the disclosure comprises a photoreaction tank (2), a separation tank (3), a light source (21), a filtration membrane (31), a supply channel (6), a transfer channel (7), a return channel (8), and a discharge channel (9). The supply channel (6) is a flow channel for supplying polluted water to the photoreaction tank (2). The transfer channel (7) is a flow channel for transferring slurry liquid from the photoreaction tank (2) to the separation tank (3). The return channel (8) is a flow channel for causing the slurry liquid to return from the separation tank (3) to the photoreaction tank (2). The discharge channel (9) is a flow channel for discharging treated water via the filtration membrane (31) to an outside. A concentration (n1) of photocatalytic particles in the photoreaction tank (2) is regulated by changing a ratio (v4/v3) of a flow rate (v4) of the treated water in the discharge channel (9) to a flow rate (v3) of the slurry liquid in the return channel (8).SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a water treatment apparatus and a water treatment method.

  In recent years, water treatment apparatuses using a photocatalyst have been proposed. In a conventional water treatment apparatus, photocatalyst particles such as titanium dioxide particles are suspended in water to be treated. The water is treated by passing the water containing the photocatalyst particles around the ultraviolet lamp.

  The water treatment apparatus described in Patent Document 1 includes a treatment tank and a separation tank. An ultraviolet lamp is arranged in the treatment tank. An ultrafiltration membrane is disposed in the separation tank. The purified water is transferred from the treatment tank to the separation tank. The titanium dioxide particles are separated from the water by the action of the ultrafiltration membrane. Thereby, the purified water is discharged to the outside.

  Patent Documents 2 to 4 also disclose a water treatment apparatus using a photocatalyst.

Japanese Patent No. 2125610 Japanese Patent No. 5111690 Japanese Patent Laid-Open No. 9-290165 JP 2000-271492 A

  In a conventional water treatment apparatus, the concentration of photocatalyst particles may fluctuate during operation and the quality of treated water may be reduced.

  The objective of this indication is to provide the technique for preventing the fall of the quality of treated water.

That is, this disclosure
A first tank for storing a slurry liquid containing photocatalyst particles and water;
A first flow path that is connected to the first tank and is a flow path for supplying contaminated water to the first tank;
A light source for irradiating the photocatalyst particles in the first tank with light;
A second tank connected to the first tank;
A filtration membrane disposed inside the second tank;
A second flow path that connects the first tank and the second tank, and is a flow path for transferring the slurry liquid from the first tank to the second tank;
A third flow path that connects the second tank and the first tank, and is a flow path for returning the slurry liquid from the second tank to the first tank;
A fourth channel that is connected to the second tank and is a channel for discharging treated water to the outside through the filtration membrane;
With
A water treatment device, wherein the concentration of the photocatalyst particles in the first tank is adjusted by changing a ratio of the flow rate of the treated water in the fourth flow channel to the flow rate of the slurry liquid in the third flow channel. provide.

  According to the technology of the present disclosure, it is possible to prevent deterioration of the quality of treated water.

FIG. 1 is a configuration diagram of a water treatment device according to an embodiment of the present disclosure. FIG. 2 is a block diagram of the controller. FIG. 3 is a graph showing the relationship between the concentration of titanium dioxide and the reaction rate. FIG. 4 is a diagram showing the balance of water in each of the photoreaction tank and the separation tank. FIG. 5 is a graph showing the relationship between the flow rate v3 of the slurry liquid in the return path and the concentration n1 of the photocatalyst particles in the photoreaction tank. FIG. 6 is a flowchart showing a process executed in the controller for operating the water treatment apparatus. FIG. 7A is a graph showing changes in the concentration of photocatalyst particles in each of the photoreaction tank and the separation tank when the operation of the water treatment apparatus is continued without adjusting the flow rate. FIG. 7B is a graph showing a change in the concentration of trivalent arsenic in the treated water when the operation of the water treatment apparatus is continued without adjusting the flow rate. FIG. 8A is a graph showing changes in the concentration of photocatalyst particles in each of the photoreaction tank and the separation tank of the water treatment apparatus of this embodiment. FIG. 8B is a graph showing a change in the concentration of atrazine in the treated water generated using the water treatment apparatus of the present embodiment. FIG. 9 is a configuration diagram of a water treatment device according to a modification.

(Knowledge that became the basis of this disclosure)
In a water treatment apparatus using a photocatalyst, the efficiency of water treatment decreases due to a plurality of factors. One factor is that the concentration of photocatalyst particles varies during operation. There is an optimum value for the concentration of the photocatalyst particles, and the treatment efficiency is lowered if the concentration is too low or too high. Even if the concentration of the photocatalyst particles is set to an optimum value before the operation of the water treatment apparatus, the concentration of the photocatalyst particles varies due to various phenomena. For example, the photocatalyst particles are deposited on the filtration membrane, so that the concentration of the photocatalyst particles is reduced. The concentration of the photocatalyst particles may be lowered by the precipitation and deposition of the photocatalyst particles at the bottom of the tank. The photocatalyst particles may peel off from the filtration membrane, and the concentration of the photocatalyst particles may increase. The photocatalyst particles are wound up from the bottom of the tank by the flow of water, and the concentration of the photocatalyst particles may increase.

  When the concentration of the photocatalyst particles fluctuates during operation, the treatment function of the water treatment device decreases. When the treatment function of the water treatment device is lowered, the contaminants cannot be sufficiently removed, and the quality of the treated water is lowered.

  In the conventional water treatment apparatus, the device for monitoring the concentration of the photocatalyst particles during operation and maintaining the concentration of the photocatalyst particles at an appropriate value has not been made.

The water treatment device according to the first aspect of the present disclosure is:
A first tank for storing a slurry liquid containing photocatalyst particles and water;
A first flow path that is connected to the first tank and is a flow path for supplying contaminated water to the first tank;
A light source for irradiating the photocatalyst particles in the first tank with light;
A second tank connected to the first tank;
A filtration membrane disposed inside the second tank;
A second flow path that connects the first tank and the second tank, and is a flow path for transferring the slurry liquid from the first tank to the second tank;
A third flow path that connects the second tank and the first tank, and is a flow path for returning the slurry liquid from the second tank to the first tank;
A fourth channel that is connected to the second tank and is a channel for discharging treated water to the outside through the filtration membrane;
With
The concentration of the photocatalyst particles in the first tank is adjusted by changing the ratio of the flow rate of the treated water in the fourth flow channel to the flow rate of the slurry liquid in the third flow channel.

  According to the first aspect, since the concentration of the photocatalyst particles in the first tank (photoreaction tank) is appropriately adjusted, efficient water treatment is performed in the first tank. Therefore, high quality treated water can continue to be generated.

  In the second aspect of the present disclosure, for example, the water treatment apparatus according to the first aspect includes a pump disposed in the second flow path or the third flow path between the first tank and the second tank. Is further provided. By the action of this pump, the slurry liquid can be transferred from the first tank (photoreaction tank) to the second tank (separation tank).

  In the third aspect of the present disclosure, for example, the water treatment apparatus according to the first or second aspect further includes a pump disposed in the fourth flow path. With this pump, the treated water can be taken out of the water treatment apparatus.

  In the fourth aspect of the present disclosure, for example, in the water treatment device according to any one of the first to third aspects, the concentration of the photocatalyst particles in the first tank is increased by decreasing the ratio. According to the fourth aspect, the concentration of the photocatalyst particles in the first tank (photoreaction tank) is adjusted to an appropriate range.

  In the fifth aspect of the present disclosure, for example, in the water treatment device according to any one of the first to fourth aspects, the concentration of the photocatalyst particles in the first tank is decreased by increasing the ratio. According to the fifth aspect, the concentration of the photocatalyst particles in the first tank (photoreaction tank) is adjusted to an appropriate range.

  In the sixth aspect of the present disclosure, for example, a water treatment device according to any one of the first to fifth aspects is attached to the first tank, and a concentration for measuring the concentration of the photocatalyst particles in the first tank. A measuring device is further provided. According to the sixth aspect, the concentration of the photocatalyst particles in the first tank (photoreaction tank) can be accurately measured during the operation of the water treatment apparatus.

  In the seventh aspect of the present disclosure, for example, in the water treatment device according to the sixth aspect, the ratio is adjusted such that the concentration of the photocatalyst particles measured by the concentration measuring device falls within a threshold range. According to the seventh aspect, since the concentration of the photocatalyst particles is appropriately adjusted, efficient water treatment is performed in the first tank (photoreaction tank). Therefore, high quality treated water can continue to be generated.

The water treatment method according to the eighth aspect of the present disclosure includes:
Supplying contaminated water to the first tank storing the slurry liquid containing photocatalyst particles and water;
Irradiating the photocatalyst particles in the first tank with light;
Transferring the slurry liquid from the first tank to the second tank;
Returning the slurry liquid from the second tank to the first tank;
Discharging the treated water to the outside through the filtration membrane disposed in the second tank;
The photocatalyst in the first tank is changed by changing the ratio of the flow rate of the treated water discharged from the second tank to the outside to the flow rate of the slurry liquid returned from the second tank to the first tank. Adjusting the concentration of the particles;
Is included.

  According to the eighth aspect, since the concentration of the photocatalyst particles in the first tank (photoreaction tank) is appropriately adjusted, efficient water treatment is performed in the first tank. Therefore, high quality treated water can continue to be generated.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

  As shown in FIG. 1, the water treatment apparatus 100 of this embodiment includes a photoreaction tank 2, a separation tank 3, a supply path 6, a transfer path 7, a return path 8, and a discharge path 9. The supply path 6 is connected to the photoreaction tank 2. The photoreaction tank 2 and the separation tank 3 are connected to each other by the transfer path 7 and the return path 8. The discharge path 9 is connected to the separation tank 3. Contaminated water is supplied to the photoreaction tank 2 from the outside of the water treatment apparatus 100 through the supply path 6. The treated water is discharged from the separation tank 3 to the outside of the water treatment apparatus 100 through the discharge path 9.

  The water treatment device 100 further includes a concentration measuring device 4, a pressure gauge 5, an introduction pump 11, an introduction flow meter 12, a controller 13, a compressor 19, a light source 21, a water level meter 22, a filtration membrane 31, a circulation pump 71, a circulation A flow meter 72, a filtration pump 81, and a filtration flow meter 82 are provided.

<Photoreaction tank 2>
The photoreaction tank 2 has a contaminated water inlet 23, a first outlet 24 and a first inlet 25. A supply path 6 is connected to the contaminated water inlet 23. The transfer path 7 is connected to the first discharge port 24. The return path 8 is connected to the first introduction port 25. The photoreaction tank 2 is made of a corrosion resistant material such as metal or resin. A light source 21 and a water level gauge 22 are attached to the photoreaction tank 2. The photoreaction tank 2 is also referred to as “first tank”.

  The photoreaction tank 2 stores a slurry liquid containing photocatalyst particles and water. When the introduction pump 11 is operated, the contaminated water containing impurities is introduced into the photoreaction tank 2 through the contaminated water inlet 23. “Impurity” means a substance harmful to humans. Impurities are, for example, arsenic such as trivalent arsenic, metals containing chromium such as hexavalent chromium, halides such as bromic acid, organic substances contained in pharmaceuticals, organic substances contained in agricultural chemicals, or substances containing microorganisms. The contaminated water is a slurry liquid in which impurities are dissolved.

  The photocatalyst particles receive light from the light source 21 and process impurities contained in the contaminated water. The contaminated water is changed to the first treated water. The first treated water is a slurry liquid containing photocatalyst particles, treated impurities and water, and is discharged to the transfer path 7 through the first discharge port 24. The treated impurities include ions generated by the oxidation-reduction reaction and decomposition products. Removing the impurities contained in the contaminated water includes detoxifying the impurities by a redox reaction. In the case where the impurity is an organic substance, the generation of an aqueous solution containing the detoxified impurity by decomposing the impurity is also included in removing the impurity contained in the contaminated water.

  The slurry liquid is returned from the separation tank 3 to the photoreaction tank 2 through the return path 8 and the first introduction port 25. This slurry liquid is a slurry liquid generated by separating the second treated water from the first treated water, and contains photocatalyst particles and water.

  The photocatalyst particles are, for example, titanium dioxide particles, zinc oxide particles, tungsten oxide particles, or iron oxide particles. One or more selected from these can be used for the water treatment apparatus 100. These photocatalyst particles may be supported on a support such as zeolite particles. The photocatalyst particles remove impurities contained in the contaminated water by a photocatalytic reaction.

  The photocatalytic reaction of the photocatalyst particles will be described in detail. For example, when titanium dioxide is irradiated with light having an ultraviolet wavelength range, excited electrons and holes are generated. When holes react with water molecules, OH radicals (active oxygen) having strong oxidizing power are generated. Excited electrons or active oxygen causes an oxidation-reduction reaction of impurities. Thereby, organic substances contained in pharmaceuticals, organic substances contained in agricultural chemicals, harmful substances such as microorganisms are decomposed. Alternatively, the state changes to a state where harmful metals are easily removed. For example, active oxygen changes trivalent arsenic to pentavalent arsenic. Pentavalent arsenic is easily adsorbed by the adsorbent. Excited electrons change hexavalent chromium to trivalent chromium. Trivalent chromium is easily removed by precipitation. Impurities are treated by a photocatalytic reaction that occurs when the photocatalyst particles are irradiated with light. The harmful metal is removed in another process such as an adsorption process or a precipitation process after changing to a state where it is easily removed.

  The photocatalyst particles are not limited to the above example. Other known photocatalyst particles can be used as long as they can flow inside the water treatment apparatus 100 and can treat impurities by a photocatalytic reaction.

<Light source 21>
The light source 21 is, for example, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an excimer lamp, a xenon lamp, sunlight, black light, or an LED. In the present embodiment, the light source 21 is disposed inside the photoreaction tank 2. The light source 21 has a cylindrical shape extending from the upper surface to the lower surface of the photoreaction vessel 2. The light source 21 irradiates the photocatalyst particles in the photoreaction tank 2 with ultraviolet rays. The wavelength range of ultraviolet rays is, for example, 200 to 400 nm. The light source 21 may output monochromatic light or continuous light.

  When the material of the photocatalyst particles is titanium dioxide, the light source 21 generates OH radicals by irradiating the photocatalyst particles with light having an ultraviolet wavelength range. The OH radical reacts with the removal target to remove impurities from the contaminated water.

  The light source 21 may be disposed outside the photoreaction tank 2. In this case, the light emitted from the light source 21 passes through the photoreaction vessel 2 and is irradiated toward the photocatalyst particles in the photoreaction vessel 2. When the photoreaction vessel 2 is made of a material having ultraviolet transparency, this configuration can be adopted. Alternatively, the light emitted from the light source 21 is irradiated from above the photoreaction tank 2 toward the photocatalyst particles in the photoreaction tank 2. When the upper part of the photoreaction tank 2 is opened, this configuration can be adopted.

<Separation tank 3>
The separation tank 3 has a first chamber 3a, a second chamber 3b, a second introduction port 32, a second discharge port 33, and a treated water discharge port 34. A filtration membrane 31 is disposed inside the separation tank 3. The first chamber 3 a is a space surrounded by the filtration membrane 31. The second chamber 3 b is a space that is not surrounded by the filtration membrane 31. The transfer path 7 is connected to the second introduction port 32. The return path 8 is connected to the second discharge port 33. A discharge path 9 is connected to the treated water discharge port 34. Through the transfer path 7, the slurry liquid (first treated water) is introduced from the photoreaction tank 2 to the separation tank 3. The slurry liquid is stored in the second chamber 3 b of the separation tank 3. The separation tank 3 is also made of a corrosion resistant material such as metal or resin. The separation tank 3 is also referred to as “second tank”.

  The filtration membrane 31 is, for example, a hollow fiber membrane or a flat membrane, and has a plurality of holes having a diameter smaller than that of the photocatalyst particles. By the filtration membrane 31, the internal space of the separation tank 3 is divided into a first chamber 3a and a second chamber 3b.

  The first chamber 3 a is a part of the internal space of the separation tank 3 and is a space surrounded by the filtration membrane 31. The treated water discharge port 34 opens toward the first chamber 3a. The second chamber 3 b is a part of the internal space of the separation tank 3 and is not surrounded by the filtration membrane 31. The second introduction port 32 and the second discharge port 33 are opened toward the second chamber 3b.

  When the filtration pump 81 is operated, the first chamber 3a is depressurized. The filtration membrane 31 filters the first treated water stored in the second chamber 3b and separates it into photocatalyst particles and second treated water. The second treated water is treated water that has passed through the filtration membrane 31 and does not contain photocatalyst particles. Photocatalyst particles remain in the second chamber 3b by the action of the filtration membrane 31. The second treated water that has passed through the filtration membrane 31 is stored in the first chamber 3a. The second treated water is discharged as treated water to the outside of the water treatment apparatus 100 through the treated water discharge port 34 and the discharge path 9.

  Photocatalyst particles remain in the second chamber 3b. Specifically, the slurry liquid containing the photocatalyst particles is stored in the second chamber 3b. This slurry liquid is generated by separating the second treated water from the first treated water, and contains the photocatalyst particles at a high concentration. The slurry liquid is discharged from the separation tank 3 to the return path 8 through the second discharge port 33.

  In the separation tank 3, filtration using the filtration membrane 31 is performed. Thereby, the 2nd treated water is taken out from the 1st treated water. When the filtration pump 81 is operated with the filter membrane 31 immersed in the first treated water and the first chamber 3a is decompressed, the second treated water is sucked into the first chamber 3a. Since the particle diameter of the photocatalyst particles contained in the first treated water is larger than the diameter of the pores of the filtration membrane 31, the photocatalyst particles cannot pass through the filtration membrane 31 and remain in the second chamber 3b.

<Supply path 6 and discharge path 9>
The supply path 6 and the discharge path 9 are connected to the photoreaction tank 2 and the separation tank 3, respectively. An introduction pump 11 and an introduction flow meter 12 are arranged in the supply path 6. The supply path 6 is a flow path for supplying contaminated water to the photoreaction tank 2. A filtration pump 81 and a filtration flow meter 82 are disposed in the discharge path 9. The discharge path 9 is a flow path for discharging treated water (second treated water) to the outside through the filtration membrane 31. Each of the supply path 6 and the discharge path 9 is constituted by at least one pipe.

<Transfer path 7 and return path 8>
The transfer path 7 connects the first discharge port 24 of the photoreaction tank 2 and the second introduction port 32 of the separation tank 3. The transfer path 7 is a flow path for transferring the slurry liquid (first treated water) from the photoreaction tank 2 to the separation tank 3. A circulation pump 71 and a circulation flow meter 72 are arranged in the transfer path 7. When the circulation pump 71 is operated, the first treated water is transferred from the first discharge port 24 of the photoreaction tank 2 to the second introduction port 32 of the separation tank 3 through the transfer path 7. The transfer path 7 is composed of at least one pipe.

  The return path 8 connects the first inlet 25 of the photoreaction tank 2 and the second outlet 33 of the separation tank 3. The return path 8 is a flow path for returning the slurry liquid from the separation tank 3 to the photoreaction tank 2. The water level of the separation tank 3 is adjusted to exceed the water level of the photoreaction tank 2. Through the return path 8, the slurry liquid is returned from the second discharge port 33 of the separation tank 3 to the first introduction port 25 of the photoreaction tank 2. The return path 8 may be configured by at least one pipe, or may have a hole provided in a wall separating the photoreaction tank 2 and the separation tank 3.

  The supply path 6 is also referred to as “first flow path”. The transfer path 7 is also referred to as “second flow path”. The return path 8 is also referred to as “third flow path”. The discharge path 9 is also referred to as “fourth flow path”.

<Introduction pump 11>
The introduction pump 11 is disposed in the supply path 6. The contaminated water is introduced into the photoreaction tank 2 through the contaminated water inlet 23 by the function of the introduction pump 11. The introduction pump 11 can be a pump that can change the flow rate (unit: liter / min) of the contaminated water in the supply path 6. The introduction pump 11 is, for example, a tube pump. The tube pump includes a tube having elasticity and a roller that deforms the tube. By changing the rotation speed (rpm) of the roller, the flow rate of the liquid pushed out from the tube can be adjusted.

<Circulating pump 71>
The circulation pump 71 is disposed in the transfer path 7. By the action of the circulation pump 71, the first treated water is discharged from the photoreaction tank 2 through the first discharge port 24 and is introduced into the separation tank 3 through the second introduction port 32. The circulation pump 71 can be a pump that can change the flow rate (unit: liter / min) of the first treated water in the transfer path 7. A tube pump having the same structure as the introduction pump 11 can be used as the circulation pump 71. The flow rate of the first treated water in the transfer path 7 can be adjusted by the circulation pump 71.

<Filtration pump 81>
The filtration pump 81 is disposed in the discharge path 9. The filtration pump 81 is, for example, a tube pump. For example, the filtration pump 81 is controlled so that the flow rate of the treated water (second treated water) in the discharge passage 9 is constant. As the filtration pump 81, a tube pump having the same structure as the introduction pump 11 can be used. The treated water can be taken out of the water treatment apparatus 100 by the filtration pump 81.

  When the filtration pump 81 is operated, the pressure in the first chamber 3a decreases. When the pressure in the first chamber 3a falls below the pressure in the second chamber 3b, the water contained in the first treated water passes through the filtration membrane 31 as the second treated water. The photocatalyst particles contained in the first treated water remain in the second chamber 3b. That is, the filtration pump 81 sucks the second treated water into the first chamber 3a. When the filtration pump 81 continues to depressurize the first chamber 3a, the second treated water is discharged to the outside of the water treatment apparatus 100 through the treated water discharge port 34 and the discharge path 9.

  The size of the pores of the filtration membrane 31 is not particularly limited as long as it does not allow the photocatalyst particles to pass through. If the pore size (average pore size) of the filtration membrane 31 is too large, the photocatalyst particles pass through the filtration membrane 31. If the pore size of the filtration membrane 31 is too small, a large suction pressure is required during filtration, and the filtration pump 81 is loaded more than necessary. Considering these, the size of the pores of the filtration membrane 31 is, for example, in the range of 10 to 200 nm. The average pore diameter of the filtration membrane 31 is measured by, for example, the bubble point method.

<Compressor 19>
The compressor 19 supplies air bubbles to the photoreaction tank 2 and the separation tank 3 during the operation of the water treatment apparatus 100. The air bubbles stir the slurry liquid stored in the photoreaction tank 2 and the separation tank 3 to prevent the photocatalyst particles from precipitating or supply the oxygen necessary for the photocatalyst to generate hydroxy radicals. . The compressor 19 can supply air bubbles toward the filtration membrane 31 of the separation tank 3. The photocatalyst particles are removed from the surface of the filtration membrane 31 by air bubbles.

<Pressure gauge 5>
The pressure gauge 5 is disposed in the discharge path 9 between the filtration membrane 31 and the filtration pump 81. The filtration pressure is monitored by the pressure gauge 5. “Filtration pressure” is the pressure of the treated water in the discharge passage 9. It can be detected that a problem such as clogging has occurred in the filtration membrane 31 due to the filtration pressure. For example, when clogging occurs in the filtration membrane 31, the filtration pressure increases significantly to maintain the flow rate.

<Flow meters 12, 72 and 82>
The introduction flow meter 12 is disposed in the supply path 6. In the present embodiment, the introduction flow meter 12 is located between the introduction pump 11 and the contaminated water introduction port 23. The flow rate of contaminated water in the supply path 6 is detected by the introduction flow meter 12. The circulation flow meter 72 is disposed in the transfer path 7. In the present embodiment, the circulation flow meter 72 is located between the circulation pump 71 and the second introduction port 32. The flow rate of the slurry liquid (first treated water) in the transfer path 7 is detected by the circulation flow meter 72. The filtration flow meter 82 is disposed in the discharge path 9. In the present embodiment, a filtration flow meter 82 is located between the filtration pump 81 and the outside of the water treatment apparatus 100. The flow rate of treated water (second treated water) in the discharge passage 9 is detected by the filtration flow meter 82. The types of the flow meters 12, 72 and 82 are not particularly limited. As the flow meters 12, 72 and 82, known flow meters such as an electromagnetic flow meter, a Karman vortex flow meter, an impeller flow meter, and an ultrasonic flow meter can be used.

<Water level gauge 22>
The water level meter 22 is disposed inside the photoreaction tank 2 and detects the water level of the slurry liquid in the photoreaction tank 2. The type of the water level gauge 22 is not particularly limited. The water level gauge 22 may be a contact type water level gauge or a non-contact type water level gauge. Examples of the contact type water level meter include a float type water level meter and a capacitance type water level meter. As a non-contact type water level gauge, an ultrasonic water level gauge can be mentioned.

<Density measuring device 4>
The concentration measuring device 4 is attached to the photoreaction tank 2 and measures the concentration of photocatalyst particles in the photoreaction tank 2. According to the concentration measuring device 4, the concentration of the photocatalyst particles in the photoreaction tank 2 can be accurately measured during the operation of the water treatment device 100.

  The concentration measuring device 4 includes a cell 40, a light source 41, an illuminance meter 42, and a control circuit 43. The cell 40 communicates with the photoreaction tank 2, and the slurry liquid flows into the cell 40. The light source 41 and the illuminance meter 42 are attached to the cell 40 and face each other via the slurry liquid in the cell 40. Light is emitted from the light source 41 toward the illuminance meter 42, and the illuminance meter 42 detects the intensity I of transmitted light. The control circuit 43 calculates the concentration of the photocatalyst particles based on the intensity I of the transmitted light.

According to Lambert-Beer's law, transmitted light intensity I is expressed by the following formula (1) using incident light intensity I ₀ , molar extinction coefficient ε, medium molar concentration c, and medium length L. . By measuring the intensity I of the transmitted light, the molar concentration c of the medium can be calculated.

I = I ₀ · exp (−εcL) (Formula 1)

The control circuit 43 is constituted by, for example, a microcomputer including a processor, a memory, an input / output interface, and the like. The control circuit 43 refers to a predetermined concentration determination standard and calculates the concentration of the photocatalyst particles in the photoreaction tank 2 using the intensity I of the transmitted light detected by the illuminometer 42. An example of the predetermined concentration determination standard is a relational expression that expresses the relationship between absorbance and concentration, or a reference table that describes the relationship between absorbance and concentration. Absorbance is calculated using transmitted light intensity I and incident light intensity I ₀ . The control circuit 43 calculates the concentration corresponding to the absorbance using a relational expression or a reference table. Another example of the predetermined density determination standard is a relational expression representing the relationship between the intensity and density of transmitted light, or a reference table in which the relationship between the intensity and density of transmitted light is described.

  The calculated molar concentration c may be treated as it is as the concentration of the photocatalyst particles in the photoreaction tank 2. Alternatively, the molar concentration c (mol / liter) may be converted into the concentration (mg / liter) of other units.

  The functions of the control circuit 43 may be integrated into the controller 13. Furthermore, the control circuit 43 may take part of the function of the controller 13.

<Controller 13>
As illustrated in FIG. 2, the controller 13 includes an arithmetic circuit 50, a determination circuit 51, a storage circuit 52, and a transmission / reception circuit 53. The controller 13 controls devices such as the introduction pump 11, the light source 21, the compressor 19, the circulation pump 71, and the filtration pump 81. The controller 13 is electrically connected to the introduction flow meter 12, the circulation flow meter 72, and the filtration flow meter 82. Detection signals from the flow meters 12, 72 and 82 are input to the controller 13. Based on the detection signal, the controller 13 specifies the flow rate in the supply path 6, the flow rate in the transfer path 7, and the flow rate in the discharge path 9.

  The controller 13 is, for example, a microcomputer configured with a semiconductor integrated circuit. The arithmetic circuit 50 and the determination circuit 51 are, for example, a processor unit 60 of a microcomputer.

  The arithmetic circuit 50 executes a program for operating the water treatment apparatus 100. The storage circuit 52 includes, for example, a volatile memory, a nonvolatile memory, and a large capacity storage. An example of a volatile memory is a random access memory used as a work area for a program. An example of the nonvolatile memory is a read-only memory in which a program is stored. An example of mass storage is a hard disk drive or flash memory.

  The transmission / reception circuit 53 is a circuit used for transmission / reception of data between the controller 13 and the concentration measuring device 4. The concentration measuring device 4 measures the concentration of the photocatalyst particles in the photoreaction tank 2 and transmits it to the controller 13. The transmission / reception circuit 53 is a circuit for outputting a control signal to a device such as a pump, and is a circuit for acquiring a detection signal from a device such as a flow meter.

  The determination circuit 51 determines whether the concentration of the photocatalyst particles in the photoreaction tank 2 is within the threshold range. The threshold range is a range defined by the first threshold and the second threshold. The first threshold defines the lower limit value of the concentration of the photocatalyst particles in the photoreaction tank 2. The second threshold defines an upper limit value of the concentration of photocatalyst particles in the photoreaction tank 2. The first threshold value and the second threshold value are described in a program for operating the water treatment apparatus 100 and are stored in the storage circuit 52.

The graph of FIG. 3 shows the relationship between the titanium dioxide concentration (mg / liter) and the reaction rate k (min ⁻¹ ). As can be understood from the graph of FIG. 3, a high reaction rate (k> 0.9) is achieved when the concentration of the photocatalyst particles is within the first threshold value T1 and the second threshold value T2. The first threshold T1 is a lower limit concentration at which high purification performance cannot be obtained. The second threshold T2 is an upper limit concentration at which high purification performance cannot be obtained. The first threshold value T1 and the second threshold value T2 should be appropriately determined according to the type of photocatalyst, the type of contaminant contained in water, the temperature of water, and the like. The concentration n1 of the photocatalyst particles in the photoreaction tank 2 is adjusted to a range of 0.1 g / liter to 4 g / liter, for example. In this case, the first threshold value T1 is 0.1 g / liter, and the second threshold value T2 is 4 g / liter.

  Next, a method for adjusting the concentration of the photocatalyst particles in the photoreaction tank 2 will be described.

  As shown in FIG. 4, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 includes the flow rate v1 of the contaminated water in the supply path 6, the flow rate v2 of the slurry liquid in the transfer path 7, the flow rate v3 of the slurry liquid in the return path 8. The flow rate v4 of the treated water in the path 9, the volume M1 of the photoreaction tank 2, the volume M2 of the separation tank 3, and the average concentration α of the photocatalyst particles are expressed by the following formula (2). “Average concentration α” means a concentration when it is assumed that the photocatalyst particles are dispersed in the photoreaction tank 2 and the separation tank 3 on the average. The average concentration α is obtained by dividing the total weight (unit: g) of the photocatalyst particles by the total (unit: liter) of the volume M1 of the photoreaction tank 2 and the volume M2 of the separation tank 3.

  n1 = α (M1 + M2) / (M1 + ((v4 / v3) +1) M2) (2)

  In the formula (2), the volumes M1 and M2 are constants. If the flow rate ratio (v4 / v3) changes, the concentration n1 of the photocatalyst particles in the photoreactor 2 also changes. By changing the ratio (v4 / v3) of the flow rate v4 of the treated water in the discharge path 9 to the flow rate v3 of the slurry liquid in the return path 8, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 can be adjusted.

  The graph of FIG. 5 shows the calculation result of Expression (2), and shows the relationship between the flow rate v3 of the slurry liquid in the return path 8 and the concentration n1 of the photocatalyst particles. The horizontal axis of the graph represents the flow rate v3. The vertical axis of the graph represents the density n1. The following conditions were used in the calculation of the process of obtaining the graph of FIG. However, the present disclosure is not limited to these selected values.

M1: 6 liters M2: 8 liters v4: 1 liter / min
α: 2 g / liter

  As can be understood from the graph of FIG. 5, when the flow rate v3 increases, that is, when the ratio (v4 / v3) decreases, the concentration n1 increases. When the flow rate v3 decreases, that is, the ratio (v4 / v3) increases, the concentration n1 decreases.

  In the present embodiment, the ratio (v4 / v3) is decreased when the concentration n1 is lower than the first threshold T1, and the ratio (v4 / v3) is increased when the concentration n1 is higher than the second threshold T2. The ratio (v4 / v3) is adjusted so that the concentration n1 of the photocatalyst particles measured by the concentration measuring device 4 falls within the threshold range. Since the concentration n1 of the photocatalyst particles is appropriately adjusted, efficient water treatment is performed in the photoreaction tank 2. Therefore, high quality treated water can continue to be generated.

  In the water treatment apparatus 100, the relationship of v3 + v4 = v2 is established. Therefore, Expression (2) can be expressed by two flow rates selected from the flow rates v2, v3, and v4.

  Next, the operation of the water treatment apparatus 100 will be described.

  The flowchart of FIG. 6 shows a process executed in the controller 13 in order to operate the water treatment apparatus 100. The photoreaction tank 2 and the separation tank 3 of the water treatment apparatus 100 are prefilled with a predetermined amount of slurry liquid containing photocatalyst particles.

  In step S1, various devices are started. Specifically, the compressor 19 is started, air is sent to the photoreaction tank 2 and the separation tank 3, and the slurry liquid is stirred. The circulation pump 71 is started and the slurry liquid is circulated inside the photoreaction tank 2 and the separation tank 3. When the light source 21 is turned on and contaminated water is introduced into the photoreaction tank 2, preparation is made so that a redox reaction by the photocatalyst occurs immediately.

  Next, in step S <b> 2, the introduction pump 11 is started to introduce contaminated water into the photoreaction tank 2. The contaminated water is introduced into the photoreaction tank 2 from an external container, for example. Since the ultraviolet light is irradiated from the light source 21 toward the slurry liquid in the photoreaction tank 2, the contaminated water is immediately treated. Impurities contained in the contaminated water are decomposed by the photocatalytic reaction of the photocatalyst particles, and the contaminated water is changed to the first treated water.

  Next, the filtration pump 81 is started in step S3. The first treated water is sent to the separation tank 3 by the circulation pump 71. When the filtration pump 81 is started, the first chamber 3a of the separation tank 3 is decompressed. When the first chamber 3a is depressurized, water passes through the filtration membrane 31 and moves to the first chamber 3a, and the photocatalyst particles cannot pass through the filtration membrane 31 and remain in the second chamber 3b. The treated water is sucked into the filtration pump 81 and discharged to the outside of the water treatment device 100 through the discharge path 9. In the second chamber 3b of the separation tank 3, the slurry liquid (concentrated water) containing the photocatalyst particles at a high concentration remains. The slurry liquid is returned from the second chamber 3 b of the separation tank 3 to the photoreaction tank 2 through the return path 8.

  In the present embodiment, the flow rate v1 of the contaminated water in the supply path 6 is equal to the flow rate v4 of the treated water in the discharge path 9. In this case, the ratio (v4 / v3) can be changed only by changing the flow rate v3. Further, during the operation of the water treatment apparatus 100, the flow rate v1 of the contaminated water and the flow rate v4 of the treated water are constant. When the adjustment of the flow rates v1 and v4 is not essential, the configuration of the supply path 6 and the discharge path 9 can be simplified.

  Next, in step S4, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 is measured. The current concentration n1 is measured by the concentration measuring device 4 and transmitted to the controller 13.

  In step S5, it is determined whether the density n1 is greater than or equal to the first threshold value T1. When the concentration n1 is smaller than the first threshold value T1, the flow rate v3 of the slurry liquid in the return path 8 is increased in step S6. Specifically, the rotational speed of the circulation pump 71 is increased. When the rotational speed of the circulation pump 71 is increased, the flow rate v2 of the slurry liquid in the transfer path 7 is increased. Since the flow rate v2 of the slurry liquid in the transfer path 7 is equal to the flow rate v3 of the slurry liquid in the return path 8, the flow rate v3 increases as the flow rate v2 increases. As described with reference to FIG. 5, when the flow rate v3 increases, the ratio (v4 / v3) decreases and the concentration n1 increases. Thereby, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 is adjusted to an appropriate range.

  If the density n1 is greater than or equal to the first threshold T1 in step S5, it is determined in step S7 whether or not the density n1 is less than or equal to the second threshold T2. When the concentration n1 is larger than the second threshold value T2, the flow rate v3 of the slurry liquid in the return path 8 is decreased in step S8. Specifically, the rotational speed of the circulation pump 71 is decreased. When the rotational speed of the circulation pump 71 is decreased, the flow rate v2 of the slurry liquid in the transfer path 7 is decreased. Since the flow rate v2 of the slurry liquid in the transfer path 7 is equal to the flow rate v3 of the slurry liquid in the return path 8, when the flow rate v2 decreases, the flow rate v3 also decreases. As described with reference to FIG. 5, when the flow rate v3 decreases, the ratio (v4 / v3) increases and the concentration n1 decreases. Thereby, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 is adjusted to an appropriate range.

  Next, in step S9, it is determined whether or not to continue the operation of the water treatment apparatus 100. For example, when the operation switch of the water treatment apparatus 100 is turned off, various devices are stopped and the operation of the water treatment apparatus 100 is stopped in step S10. In other cases, the processes in steps S4 to S8 are repeatedly executed. A continuous water treatment is performed by continuing the process (function recovery process) of steps S4 to S9.

  By adjusting the rotation speed of the circulation pump 71, the concentration n1 of the photocatalyst particles in the photoreaction tank 2 is maintained in a range between the first threshold value T1 and the second threshold value T2. Since the concentration n1 of the photocatalyst particles is appropriately adjusted, efficient water treatment is performed in the photoreaction tank 2. Therefore, high quality treated water can continue to be generated. The concentration of contaminants in treated water is always below the reference value.

  According to the present embodiment, the excitation light (ultraviolet light) is irradiated to the photocatalyst particles dispersed in the liquid (slurry liquid) in the photoreaction tank 2. This method can achieve a reaction efficiency that is 10 times higher than the method in which the photocatalyst particles fixed to the inner wall of the photoreaction tank are irradiated with excitation light. If the concentration n1 of the photocatalyst particles is too low, the number of photocatalytic reactions occurring is reduced and the reaction efficiency is lowered. If the concentration n1 of the photocatalyst particles is too high, the light transmittance of the slurry liquid is lowered and the reaction efficiency is lowered. The concentration n1 of the photocatalyst particles in the photoreaction tank 2 is desirably in the range of 0.1 g / liter to 4 g / liter.

  According to the water treatment apparatus 100 of the present embodiment, the quality of treated water can be maintained at a high level in water treatment using photocatalyst particles. If water treatment is continued with an inappropriate concentration, the concentration of contaminants in the treated water may exceed the reference concentration.

  The graph of FIG. 7A shows changes in the concentration of photocatalyst particles in each of the photoreaction tank and the separation tank when the operation of the water treatment apparatus is continued without adjusting the flow rate. In the graph of FIG. 7A, the horizontal axis represents the elapsed time from the start of operation. The vertical axis represents the concentration of photocatalyst particles. As understood from the graph of FIG. 7A, when the flow rate was not adjusted, the concentration of the photocatalyst particles in each of the photoreaction tank and the separation tank gradually decreased.

  The graph of FIG. 7B shows a change in the concentration of trivalent arsenic in the treated water when the operation of the water treatment apparatus is continued without adjusting the flow rate. In the graph of FIG. 7B, the horizontal axis represents the elapsed time from the start of operation. The vertical axis represents the concentration of trivalent arsenic. As can be understood from the graph of FIG. 7B, the concentration of trivalent arsenic was not more than the reference value at the time when the operation was started. As the operation continued, the concentration of trivalent arsenic gradually increased and exceeded the standard value set for tap water (the upper limit of the tap water standard value). It is considered that the trivalent arsenic treatment capacity (contaminant removal capacity) decreased with decreasing photocatalyst particle concentration. Contaminants other than trivalent arsenic are expected to show the same trend.

  On the other hand, the graph of FIG. 8A shows changes in the concentration of the photocatalyst particles in each of the photoreaction tank and the separation tank of the water treatment apparatus of this embodiment. As can be understood from the graph of FIG. 8A, the concentration of the photocatalyst particles in each of the photoreaction tank and the separation tank was kept constant by adjusting the ratio (v4 / v3).

  The graph of FIG. 8B has shown the change of the concentration of atrazine (agrochemical component) in the treated water produced | generated using the water treatment apparatus of this embodiment. As can be understood from the graph of FIG. 8B, the concentration of atrazine in the treated water was also maintained at a substantially constant value.

  According to the water treatment apparatus 100 of the present embodiment, treated water that satisfies the tap water reference value can be continuously produced.

(Modification)
The concentration of the photocatalyst particles in the photoreaction tank 2 may be adjusted so as to converge to a predetermined optimum concentration P. As shown in FIG. 3, the optimum concentration P is the concentration at which the highest reaction rate k is achieved. Instead of step S5 to step S8 in the flowchart of FIG. 6, the following processing may be executed. That is, when the current concentration n1 is smaller than the optimum concentration P, the flow rate v3 of the slurry liquid in the return path 8 is increased. When the flow rate v3 increases, the ratio (v4 / v3) decreases and the concentration n1 increases. When the current concentration n1 is larger than the optimum concentration P, the flow rate v3 of the slurry liquid in the return path 8 is decreased. When the flow rate v3 decreases, the ratio (v4 / v3) increases and the concentration n1 decreases. Thereby, the density n1 is always kept close to the optimum density P.

  The filtration pump 81 may have a filtration pump controller. The filtration pump controller is arranged in the drainage channel 9 and acquires information on the flow rate v4 from the filtration flow meter 82. The rotation speed of the filtration pump 81 can be controlled by the filtration pump controller so that the flow rate v4 is kept constant.

  As shown in FIG. 9, a circulation pump 71 may be disposed in the return path 8 instead of the transfer path 7. The circulation flow meter 72 may also be disposed in the return path 8. As shown in FIG. 9, the water treatment device 102 according to the modified example further includes a water level gauge 62 attached to the separation tank 3 in addition to the configuration of the water treatment device 100. The water level meter 62 is disposed inside the separation tank 3 and detects the water level of the slurry liquid in the separation tank 3. As the water level gauge 62, the same type as the water level gauge 22 can be used. In the water treatment apparatus 102, the pump 11 and the pump 81 are controlled according to the detection results of the water level gauges 22 and 62 in order to keep the water level in the photoreaction tank 2 and the water level in the separation tank 3 constant.

  The method for adjusting the flow rate v3 is not limited to adjusting the rotational speed of the circulation pump 71. The water treatment apparatus 100 may include, for example, a flow rate adjustment valve arranged in at least one selected from the transfer path 7 and the return path 8. Even if the circulation pump 71 is not a pump that can change the number of revolutions, the flow rate v3 can be changed by changing the opening of the flow rate adjustment valve. That is, the water treatment apparatus 100 may be a mechanism arranged in at least one selected from the transfer path 7 and the return path 8 and may have a mechanism for adjusting the flow rate v3. Examples of the mechanism for adjusting the flow rate v3 include a circulation pump 71, a flow rate adjustment valve, and the like.

  In this embodiment, the photoreaction tank 2 is a single tank. However, the photoreaction tank 2 may be composed of a plurality of tanks. The plurality of tanks are connected to each other by at least one flow path.

  The controller 13 may be constituted by a semiconductor circuit integrated on one chip, or may be constituted by a combination of a plurality of chips. It is not essential that all of the processes shown in FIG. 7 be realized by software, and a part thereof may be realized by a dedicated hardware circuit.

  The concentration measuring device 4 may be attached to the separation tank 3. In this case, the concentration of the photocatalyst particles in the separation tank 3 can be measured by the concentration measuring device 4. The concentration measuring device 4 may be attached to both the photoreaction tank 2 and the separation tank 3. However, since the photocatalytic reaction occurs in the photoreaction vessel 2, it is desirable to directly measure the concentration of the photocatalyst particles in the photoreaction vessel 2.

  The technology disclosed in this specification is useful for a water treatment method using a photocatalyst and a water treatment apparatus using a photocatalyst. The technology disclosed in this specification is particularly useful for domestic water purification facilities or public water purification facilities. According to the technology of the present disclosure, impurities contained in water such as drinking water, waste water, inland river water, and lake water can be continuously removed in a practical time.

2 Photoreaction tank 3 Separation tank 4 Concentration measuring device 6 Supply path 7 Transfer path 8 Return path 9 Discharge path 10 Introduction pump 12 Introduction flow meter 13 Controller 21 Light source 22 Water level gauge 23 Contaminated water introduction port 24 First discharge port 25 1 introduction port 31 filtration membrane 32 2nd introduction port 33 2nd discharge port 34 treated water discharge port 62 water level meter 71 circulation pump 72 circulation flow meter 81 filtration pump 82 filtration flow meter 100 water treatment device

Claims (8)

A first tank for storing a slurry liquid containing photocatalyst particles and water;
A first flow path that is connected to the first tank and is a flow path for supplying contaminated water to the first tank;
A light source for irradiating the photocatalyst particles in the first tank with light;
A second tank connected to the first tank;
A filtration membrane disposed inside the second tank;
A second flow path that connects the first tank and the second tank, and is a flow path for transferring the slurry liquid from the first tank to the second tank;
A third flow path that connects the second tank and the first tank, and is a flow path for returning the slurry liquid from the second tank to the first tank;
A fourth channel that is connected to the second tank and is a channel for discharging treated water to the outside through the filtration membrane;
With
The water treatment device, wherein the concentration of the photocatalyst particles in the first tank is adjusted by changing a ratio of the flow rate of the treated water in the fourth flow channel to the flow rate of the slurry liquid in the third flow channel.   The water treatment apparatus according to claim 1, further comprising a pump disposed in the second flow path or the third flow path.   The water treatment apparatus according to claim 1, further comprising a pump disposed in the fourth flow path.   The water treatment apparatus according to any one of claims 1 to 3, wherein the concentration of the photocatalyst particles in the first tank is increased by decreasing the ratio.   The water treatment apparatus according to claim 1, wherein the concentration of the photocatalyst particles in the first tank is decreased by increasing the ratio.   The water treatment apparatus according to any one of claims 1 to 5, further comprising a concentration measuring device attached to the first tank and measuring the concentration of the photocatalyst particles in the first tank.   The water treatment device according to claim 6, wherein the ratio is adjusted so that the concentration of the photocatalyst particles measured by the concentration measurement device falls within a threshold range. Supplying contaminated water to the first tank storing the slurry liquid containing photocatalyst particles and water;
Irradiating the photocatalyst particles in the first tank with light;
Transferring the slurry liquid from the first tank to the second tank;
Returning the slurry liquid from the second tank to the first tank;
Discharging the treated water to the outside through the filtration membrane disposed in the second tank;
The photocatalyst in the first tank is changed by changing the ratio of the flow rate of the treated water discharged from the second tank to the outside to the flow rate of the slurry liquid returned from the second tank to the first tank. Adjusting the concentration of the particles;
Including a water treatment method.

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