Wastewater treatment apparatus and wastewater treatment method

Abstract

To provide a wastewater treatment apparatus capable of maintaining the interface of a carrier at a proper position.SOLUTION: The wastewater treatment apparatus 1 for treating wastewater under an anaerobic condition includes a reaction tank 10 for storing a carrier 12 holding microorganisms. The reactor includes a draft tube 18 having an upper end opening and a lower end opening, an impeller device 20 that forms a downward flow in the draft tube 18 and forms an upward flow between the draft tube 18 and the inner surface of the reactor 10, a power control device 32 that controls the power of the impeller device 20, and a first detector 28a and a second detector 28b that are disposed at a predetermined interval in the vertical direction from the upper end A to the lower end B of the draft tube 18. The power controller 32 controls the power of the impeller device 20 so that the interface of the carrier 12 is positioned between the first detector 28a and the second detector 28b based on the detection results of the first detector 28a and the second detector 28b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a technique for a wastewater treatment device and a wastewater treatment method. [Background technology]

[0002] Examples of wastewater treatment methods that use carriers carrying microorganisms to treat wastewater under anaerobic conditions include denitrification of wastewater containing nitrate or nitrite, and methane fermentation of organic wastewater.

[0003] Patent Documents 1 and 2 propose a method for treating wastewater under anaerobic conditions by using an impeller device to form a downward flow in a draft tube arranged vertically in a tank and an upward flow between the draft tube and the inner wall surface of the tank, thereby causing the carrier to flow.

[0004] In particular, in Patent Document 2, in order to keep the interface of the carrier, which is the upper end of the region where the flowing carrier exists, below the upper end of the draft tube, a detection means capable of detecting the interface of the carrier is provided, and the output of the impeller device is controlled based on the signal from the detection means. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-288568 [Patent Document 2] Patent No. 2005-32859 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, Patent Document 2 does not disclose a specific detection means, but the inventors have studied and found that, in a detection means for detecting the carrier interface, for example, an instrument that irradiates ultrasound or a laser in the depth direction of a reaction vessel to detect the carrier interface located at a depth distance from the installation position of the detection means, it is difficult to detect the carrier interface due to the influence of air bubbles and the like that exist between the installation position of the detection means and the carrier interface. Furthermore, detection of the carrier interface is affected not only by the type (kind) of detection means but also by the installation position and the number of detection points, none of which are disclosed in Patent Document 2. Therefore, there is room for improvement in detecting the carrier interface and maintaining the carrier interface at an appropriate position based on the detection results.

[0007] Therefore, an object of the present disclosure is to provide a wastewater treatment device and a wastewater treatment method that can maintain the interface of the carrier at an appropriate position. [Means for solving the problem]

[0008] One aspect of the present disclosure is a wastewater treatment device that treats wastewater under anaerobic conditions, comprising: a reaction tank that stores carriers carrying microorganisms; a draft tube installed in the reaction tank and having an upper opening and a lower opening; an impeller device that creates a downward flow in the draft tube and an upward flow between the draft tube and the inner wall surface of the reaction tank; an output control device that controls the output of the impeller device; and a detection device that can detect the interface of the carrier when the interface of the carrier rises due to the upward flow caused by the impeller device reaches a detection device installation position, wherein the detection device has a first detection device and a second detection device installed at a predetermined interval in the vertical direction from the upper end to the lower end of the draft tube, and the output control device controls the output of the impeller device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is located between the first detection device and the second detection device.

[0009] In addition, in the above wastewater treatment device, it is preferable that the first detection device and the second detection device have a transmitter that emits a predetermined signal and a receiver that is arranged at a predetermined distance from the transmitter and receives the signal.

[0010] Furthermore, in the above wastewater treatment device, it is preferable that a third detection device is provided for detecting the carrier deposited at the bottom of the reaction tank, the third detection device being a vibration sensor installed at or near the bottom of the reaction tank, and the output control device controls the output of the impeller device based on the detection result of the third detection device.

[0011] In the wastewater treatment device, it is preferable that the output control device operates the impeller device continuously or intermittently.

[0012] In the wastewater treatment device, it is preferable that the output control device temporarily controls the output of the impeller device so that the interface of the carrier exceeds the upper end of the draft tube.

[0013] Another aspect of the present disclosure is a wastewater treatment method that uses the above-mentioned wastewater treatment device to treat wastewater under anaerobic conditions, characterized in that the output of the impeller device is controlled by the output control device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is positioned between the first detection device and the second detection device.

[0014] In addition, in the above wastewater treatment method, it is preferable that the first detection device and the second detection device have a transmitter that emits a predetermined signal, and a receiver that is arranged at a predetermined distance from the transmitter and receives the signal.

[0015] Furthermore, in the above wastewater treatment method, it is preferable that the wastewater treatment device has a third detection device that detects the carrier deposited on the bottom of the reaction tank, the third detection device being a vibration sensor installed on or near the bottom of the reaction tank, and the output of the impeller device is controlled by the output control device based on the detection result of the third detection device.

[0016] In the wastewater treatment method, it is preferable that the impeller device is operated continuously or intermittently by the output control device.

[0017] In the above wastewater treatment method, it is preferable that the output of the impeller device is controlled by the output control device so that the interface of the carrier temporarily exceeds the upper end of the draft tube. [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide a wastewater treatment device and a wastewater treatment method that can maintain the interface of the carrier at an appropriate position. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic cross-sectional view showing an example of a wastewater treatment device according to an embodiment of the present invention. [Figure 2] FIG. 2A is a schematic cross-sectional view showing an example of the configuration of a first detection device, and FIG. 2B is a schematic top view showing an example of the configuration of the first detection device. [Figure 3] FIG. 4 is a schematic cross-sectional view showing another example of the wastewater treatment device according to the present embodiment. [Figure 4] FIG. 1 is a schematic diagram showing an example of a submersible aerator. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present disclosure will be described below. The embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to the embodiment.

[0021] FIG. 1 is a schematic cross-sectional view showing an example of a wastewater treatment device according to this embodiment. FIG. 1 shows a state in which the wastewater treatment device is in operation and carriers, described below, are fluidized. The wastewater treatment device 1 shown in FIG. 1 includes a fluidized-bed reaction tank 10, in which carriers 12 carrying microorganisms are stored. A wastewater inlet line 14 is connected to the inlet of the reaction tank 10, and wastewater to be treated is supplied into the tank from the wastewater inlet line 14. A treated water discharge line 16 is connected to the outlet of the reaction tank 10, and treated water obtained by anaerobically treating the wastewater is discharged from the treated water discharge line 16 to the outside of the system. A screen is preferably installed near the outlet of the reaction tank 10. This prevents the carriers 12 from being discharged into the treated water discharge line 16.

[0022] The wastewater treatment device 1 also includes a draft tube 18 installed in the reaction tank 10 and having an upper end opening and a lower end opening. The draft tube 18 is installed vertically or approximately vertically. The wastewater treatment device 1 also includes an impeller device 20 that agitates the carriers 12 in the tank. The impeller device 20 shown in FIG. 1 includes a motor 22, an impeller (agitating blade) 24, and a shaft 26 connecting the motor 22 and the impeller 24, and the impeller 24 is disposed in the draft tube 18. By operating the impeller device 20, a downward flow is formed in the draft tube 18, and an upward flow is formed between the outer wall surface of the draft tube 18 and the inner wall surface of the reaction tank 10. This makes it possible to improve the fluidity of the carriers 12.

[0023] The wastewater treatment device 1 also includes a first detection device 28a and a second detection device 28b. The first detection device 28a and the second detection device 28b are detection devices that can detect, at their installation positions, the interface of the carrier 12 that rises due to the upward flow created by the operation of the impeller device 20. That is, the first detection device 28a and the second detection device 28b are detection devices that detect the interface of the carrier 12 when the interface of the carrier 12 reaches their respective installation positions. The interface of the carrier 12 means the upper end of the area where the flowing carrier 12 exists.

[0024] 1, the first detecting device 28a and the second detecting device 28b are installed between the upper end A and the lower end B of the draft tube 18, with a predetermined distance between them in the up-down direction from the upper end A to the lower end B. In FIG. 1, the first detecting device 28a is installed above the second detecting device 28b.

[0025] FIG. 2(A) is a schematic cross-sectional view showing an example of the configuration of a first detection device, and FIG. 2(B) is a schematic top view showing an example of the configuration of a first detection device. The first detection device 28a shown in FIG. 2 includes a cylindrical body 34 with open top and bottom, and a transmitter 36a and a receiver 36b installed on the inner wall of the cylindrical body 34. The transmitter 36a emits a predetermined signal, such as ultrasonic waves, visible light, infrared rays, ultraviolet rays, or microwaves. The receiver 36b is disposed a predetermined distance from the transmitter 36a and receives the signal emitted from the transmitter 36a. Examples of the first detection device 28a equipped with such a transmitter 36a and receiver 36b include an ultrasonic level sensor, an optical level sensor, and a microwave level sensor. Although not shown in the figures, the second detection device 28b may have a similar configuration.

[0026] For example, when the interface of the carrier 12 has not reached the first detector 28a or the second detector 28b, there is no carrier inside the cylindrical body 34, so the signal transmitted from the transmitter 36a is hardly attenuated along the way, and the receiver 36b receives a signal of high intensity. On the other hand, when the interface of the carrier 12 has reached the first detector 28a or the second detector 28b, there is a carrier inside the cylindrical body 34, so the signal transmitted from the transmitter 36a is attenuated along the way, and the receiver 36b receives a signal of low intensity. The first detector 28a and the second detector 28b output the signal received by the receiver 36b as a detection signal.

[0027] The wastewater treatment device 1 includes an output control device 32 that has the function of controlling the output of the impeller device 20. The output control device 32 is configured, for example, by a microcomputer including a CPU that executes a predetermined program, and ROM and RAM that store the program, calculation results, etc., and an electronic circuit. The output control device 32 is electrically connected, for example, by wire or wirelessly, to the first detector 28a, the second detector 28b, and the motor 22 of the impeller device 20. Based on the detection results of the first detector 28a and the second detector 28b (i.e., the detection signals received by the receiver 36b), the output control device 32 controls the output of the motor 22 of the impeller device 20 so that the interface of the carrier 12 is located between the first detector 28a and the second detector 28b.

[0028] An example of the operation of the wastewater treatment device 1 shown in FIG. 1 will be described.

[0029] With the impeller device 20 stopped, wastewater is introduced into the reaction tank 10 through its inlet. In this state, the carriers 12 are deposited at the bottom of the reaction tank 10 and have not yet reached the second detection device 28a. In this state, the output control device 32 receives detection signals output from the first detection device 28a and the second detection device 28b and sets the detection signals as reference values. The output control device 32 then activates the motor 22 of the impeller device 20 to rotate the impeller 24. This creates a downward flow in the draft tube 18 and an upward flow between the outer wall surface of the draft tube 18 and the inner wall surface of the reaction tank 10, causing the carriers 12 carrying the microorganisms to flow and the interface of the carriers 12 to rise. The output control device 32 continually receives the detection signals output from the second detection device 28a and the first detection device 28a, compares them with the reference values, and determines whether the difference (absolute value) is greater than a preset threshold. If the difference between the detection signal output from the second detector 28b and the reference value is equal to or less than the threshold, it is determined that the interface of the carrier 12 has not reached the second detector 28b. For example, the output of the impeller device 20 may be increased (i.e., the output of the motor 22 may be increased) to increase the rotation speed of the impeller 24. If the difference between the detection signal output from the second detector 28b and the reference value is greater than the threshold, it is determined that the interface of the carrier 12 has reached the second detector 28b. At this stage, the output of the impeller device 20 may be further increased, maintained, or decreased (however, when decreasing the output, care must be taken to ensure that the interface of the carrier 12 does not fall below the installation position of the second detector 28b). In either case, the output control device 32 controls the output of the impeller device 20 according to a preset program. The output control device 32 also compares the detection signal output from the first detector 28a with the reference value to determine whether the difference (absolute value) is greater than a preset threshold. If the difference between the detection signal output from the first detection device 28a and the above-mentioned reference value is greater than the threshold value, the output control device 32 determines that the interface of the carrier 12 has reached the first detection device 28a, and reduces the output of the impeller device 20, slows down the rotation speed of the impeller 24, and lowers the interface of the carrier 12.If, as a result of reducing the output of the impeller device 20, the difference between the detection signal output from the second detector 28b and the reference value becomes larger than the threshold value, the output control device 32 determines that the interface of the carrier 12 has dropped to the level of the second detector 28b, and increases the output of the impeller device 20, increases the rotation speed of the impeller 24, and raises the interface of the carrier 12. In this way, the interface of the carrier 12 is controlled to be between the first detector 28a and the second detector 28b.

[0030] The first and second detectors 28a and 28b used in the wastewater treatment device 1 shown in FIG. 1 are devices capable of detecting the interface of the carrier 12 when the interface reaches their respective installation positions. This allows for accurate detection of the interface of the carrier 12, with minimal interference from noise, such as suspended sludge and air bubbles, during detection. The first and second detectors 28a and 28b are installed at a predetermined vertical distance from the upper end A to the lower end B of the draft tube 18. Based on the detection results of these detectors, the output of the impeller device 20 is controlled to position the interface of the carrier 12 between the first and second detectors 28a and 28b. In this way, maintaining the interface of the carrier 12 between the first and second detectors 28a and 28b reduces the influence of oxygen dissolution from the liquid surface. Furthermore, the carrier 12 is prevented from being drawn into the draft tube 18, and the shear force of the impeller 24 prevents wear on the carrier 12 and the detachment of microorganisms attached to the carrier 12. It also prevents the non-fluidized carriers 12 from accumulating on the bottom of the reaction tank 10. These factors lead to an improvement in the efficiency of wastewater treatment.

[0031] FIG. 3 is a schematic cross-sectional view showing another example of a wastewater treatment device according to this embodiment. In the wastewater treatment device 2 shown in FIG. 3, components similar to those in the wastewater treatment device 1 shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The wastewater treatment device 2 shown in FIG. 3 includes a third detection device 28c that detects the carriers 12 deposited on the bottom of the reaction tank 10. The third detection device 28c is a vibration sensor, such as a tuning fork sensor. The vibration sensor 28c is installed on or near the bottom of the reaction tank 10. When there is little carrier 12 deposited on the bottom of the reaction tank 10, the vibration of the vibration unit of the vibration sensor 28c is not impeded, and a strong signal is detected. On the other hand, when there is a sufficient amount of carrier 12 deposited on the bottom of the reaction tank 10, the vibration of the vibration unit of the vibration sensor 28c is impeded by the carriers 12 deposited on the bottom of the reaction tank 10, and a weak signal is detected. The vibration sensor 28c is electrically connected to the output control device 32, for example, wirelessly or by wire, and outputs a detected signal (detection result) to the output control device 32.

[0032] An example of the operation of the wastewater treatment device 2 shown in FIG. 3 will be described.

[0033] As described above, the output of the impeller device 20 is controlled based on the detection results of the first detector 28a and the second detector 28b so that the interface of the carrier 12 is located between the first detector 28a and the second detector 28b. The output control device 32 also receives a signal output from the vibration sensor 28c and compares the signal with a preset threshold. If the signal output from the vibration sensor 28c is equal to or greater than the threshold, the output control device 32 determines that the amount of carrier 12 deposited on the bottom of the reaction vessel 10 is small, and controls the output of the impeller device 20 based on the detection results of the first detector 28a and the second detector 28b. On the other hand, if the signal output from the vibration sensor 28c is less than the threshold, the output control device 32 determines that the amount of carrier 12 deposited on the bottom of the reaction vessel 10 is large, and further increases the output of the impeller device 20. For example, the output control device 32 increases the output of the impeller device 20 until the signal output from the vibration sensor 28c is equal to or greater than the threshold. However, as a result of increasing the output of the impeller device 20 based on the signal output from the vibration sensor 28c, if the difference between the detection signal output from the first detection device 28a and the reference value becomes greater than the threshold value, as described above, the output control device 32 determines that the interface of the carrier 12 has reached the first detection device 28a and reduces the output of the impeller device 20.

[0034] The output control device 32 may operate continuously or intermittently the impeller device 20. That is, the output control device 32 may operate the impeller device 20 continuously or intermittently so that the interface of the carrier 12 is located between the first detection device 28a and the second detection device 28b.

[0035] The output control device 32 may also control the output of the impeller device 20 so that the interface of the carrier 12 temporarily exceeds the upper end A of the draft tube 18. If the output of the impeller device 20 is controlled and normal operation is continued with the interface of the carrier 12 positioned between the first detection device 28a and the second detection device 28b, excessive microorganisms may adhere to the carrier 12, resulting in a decrease in the fluidity of the carrier 12. However, by increasing the output of the impeller device 20 and performing strong stirring operation with the interface of the carrier 12 exceeding the upper end A of the draft tube 18, the microorganisms adhering to the carrier 12 are detached by the shear force of the impeller 24 when the carrier enters the draft tube 18, thereby restoring the fluidity of the carrier 12. The normal operation time is not particularly limited, but may be, for example, in the range of 10 to 300 minutes. The strong stirring operation time is also not particularly limited, but may be, for example, in the range of 1 to 30 minutes.

[0036] First detection device 28a and second detection device 28b may be installed at a predetermined interval in the vertical direction from upper end A to lower end B of draft tube 18, but when the distance from upper end A to lower end B of draft tube 18 is taken as 100% (upper end A is 0%), first detection device 28a is preferably installed at a position between 0% and 20%, more preferably between 5% and 15%, and second detection device 28b is preferably installed at a position between 40% and 60%, more preferably between 45% and 55%.

[0037] The first detecting device 28a and the second detecting device 28b are not limited to the ultrasonic level sensor, optical level sensor, or microwave level sensor described above, and may be, for example, an imaging device that captures an image of the inside of the reaction vessel 10. For example, the output control device 32 performs image analysis on the image output from the imaging device to determine whether the interface of the carrier 12 has reached the installation position of the imaging device.

[0038] The third detector 28c is preferably installed at a position between 5% and 10% of the distance from the bottom of the reaction vessel 10 to the liquid surface, where the distance is 100% (the bottom is 0%).

[0039] The carrier 12 used in this embodiment may be a carrier used in conventional anaerobic biological treatment, such as a porous material made of cellulose, polyethylene, polypropylene, polyurethane, or the like, or a gel-like material made of polyvinyl alcohol, polyethylene glycol, or the like.

[0040] The shape of the carrier 12 is not particularly limited, but is preferably a sphere, cube, rectangular parallelepiped, or cylindrical shape with a diameter of about 0.5 mm to 20 mm. To create a fluidized state of the carrier 12 inside the reaction vessel 10, for example, the specific gravity of the carrier 12 is preferably at least greater than 1.0, with a true specific gravity of 1.1 or greater or an apparent specific gravity of 1.01 or greater. The amount of carrier 12 introduced into the reaction vessel 10 is preferably in the range of 5 to 50% of the volume of the reaction vessel 10.

[0041] The shape of the reaction tank 10 may be rectangular or cylindrical, and is not particularly limited. To prevent deposition at the corners of the tank bottom, the corners of the tank bottom are preferably tapered, and a taper of 45 degrees or more is particularly preferred. In addition, to minimize oxygen dissolution from the liquid surface, a lid is preferably installed on the top of the tank.

[0042] The shape of the draft tube 18 may be rectangular or cylindrical and is not particularly limited, but a cylindrical shape is preferred because it is easier to make the downward flow velocity inside uniform. In order to prevent the carrier 12 from remaining on the liquid surface, it is preferable that the cross-sectional area of ​​the draft tube 18 is set so that the average downward flow velocity inside the draft tube 18 is 20 cm / s or more.

[0043] The draft tube 18 is preferably installed diagonally if the reaction tank 10 is a rectangular tank, or at the center if the reaction tank 10 is a cylindrical tank. The number of draft tubes 18 installed per tank does not necessarily have to be one, and multiple draft tubes 18 may be installed depending on the shape of the tank.

[0044] The distance (bottom of the liquid) from the liquid surface to the upper end of the draft tube 18 is preferably, for example, about 300 to 1000 mm. Also, a structure that allows the height of the draft tube 18 to be adjusted may be provided.

[0045] The impeller device 20 is not limited to a configuration including a motor 22, a shaft 26, and an impeller 24 installed in the draft tube 18 as shown in Fig. 1, and may be, for example, a submerged throw-in type. An example of a submerged throw-in type is the "SJ type" submerged aerator manufactured by ShinMaywa Industries, Ltd. Specifically, as shown in Fig. 4, a submerged aerator 20a is installed near the bottom of the reaction vessel 10, and the draft tube 18 is installed in line with the suction surface of the submerged aerator 20a.

[0046] The clearance between the impeller 24 of the impeller device 20 and the surrounding wall surface is preferably within a range of 1.2 times or more and 10 times or less the longer side of the carrier 12, for example.

[0047] The pH of the wastewater is preferably in the range of 6.0 to 8.0, and more preferably in the range of 7.0 to 8.0. The pH of the wastewater can be adjusted, for example, by adding a pH adjuster to the wastewater. The pH adjuster is not particularly limited and may be an acidic agent such as hydrochloric acid, an alkaline agent such as sodium hydroxide, or the like. The pH adjuster may also be, for example, sodium bicarbonate, a phosphate buffer solution, or the like, which has a buffering effect.

[0048] In this embodiment, when starting up the apparatus, digested sludge, anaerobic granules, etc. may be charged into the reaction tank 10 together with the carrier 12. The amount of sludge charged into the reaction tank 10 may be, for example, 1,000 to 10,000 mg / L.

[0049] Furthermore, if necessary, a hydrogen donor such as methanol may be added to the reaction vessel 10. Furthermore, in order to maintain good decomposition activity of the microorganisms, for example, nutrients may be added to the reaction vessel 10. Examples of nutrients include carbon sources, nitrogen sources, and other inorganic salts (Ni, Co, Fe, etc.).

[0050] The water temperature in the reaction tank 10 is preferably 20° C. or higher. The method for adjusting the water temperature in the reaction tank 10 is not particularly limited, but for example, a heating device such as a heater may be installed in the reaction tank 10 and the water temperature in the reaction tank 10 may be adjusted by heat from the heater or the like.

[0051] The wastewater to be treated in this embodiment is, for example, organic wastewater containing biodegradable organic matter, such as wastewater from food processing factories, chemical factories, semiconductor factories, machinery factories, sewage, and human waste. [Example]

[0052] Hereinafter, the present disclosure will be described more specifically and in detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0053] Example 1 A denitrification test was conducted using the wastewater treatment device shown in Figure 3. The test conditions were as follows: Reactor volume: 0.74m 3 Carrier: Polyvinyl alcohol gel carrier Carrier filling rate: 20% (bulk volume / tank volume) ·Test wastewater: NO3-N 50mgN / L, PO4-P 2mg / L Amount of hydrogen donor added: Methanol was added in an amount three times the influent NO3-N load. First and second detection devices: ultrasonic level sensors (sensors having a transmitter and a receiver spaced a predetermined distance apart, manufactured by Shibaura Semtech Co., Ltd.) Third detection device: Vibration sensor (manufactured by Yamamoto Electric Industry Co., Ltd.) When the distance from the bottom of the reaction tank to the liquid surface is taken as 100%, the second detection device is installed at the 50% position, the first detection device is installed at the 70% position, and the third detection device is installed at the 5% position. When the distance from the bottom of the reactor to the liquid surface is taken as 100%, the bottom end of the draft tube is located at 10% and the top end of the draft tube is located at 80%. Controlling the output of the impeller device: Based on the detection results of the third detection device, the output of the impeller device was controlled so that the carrier would not deposit at the bottom of the reaction tank, and based on the detection results of the first detection device and the second detection device, the output of the impeller device was controlled so that the interface of the carrier would be located between the first detection device and the second detection device.

[0054] Example 2 Using the wastewater treatment device shown in Figure 1, a denitrification test was conducted under the same conditions as in Example 1, except that the output of the impeller device was controlled based on the detection results of the first and second detectors so that the interface of the carrier was located between the first and second detectors.

[0055] (Comparative Example) No detection device was installed, and the output of the impeller device was controlled so that the carriers flowed and spread throughout the reaction vessel. That is, in the comparative example, the interface of the carriers exceeded the top end of the draft tube and reached the liquid surface.

[0056] As a result of the denitrification test, the maximum allowable load was 2.0 kgN / (m 3 ·d), and Example 2 is 1.7 kgN / (m 3 ·d), and the comparative example is 0.9 kgN / (m 3 d). In the comparative example, the carriers flowed and spread throughout the reaction vessel and were subjected to shear forces from the impeller, which is thought to have resulted in a decrease in the amount of microorganisms adhering to the carriers and the dissolution of oxygen from the water surface, resulting in a decrease in treatment performance. On the other hand, in Examples 1 and 2, the carrier interface was maintained at an appropriate position, neither exceeding the upper end of the draft tube nor falling below the lower end of the draft tube, which prevented the carriers from being subjected to shear forces from the impeller or from depositing at the bottom of the reaction vessel, and as a result, it is thought that treatment performance was improved.

[0057] The following test was carried out as a reference example. Reference Example 1: Tests were conducted under the same conditions as in Example 1, except that a vibration sensor was used as the second detection device. However, the vibration sensor was unable to detect the interface of the flowing carrier. In other words, the vibration sensor was unsuitable as a detection device capable of detecting the interface of the carrier when it reached the installation position of the detection device. Reference Example 2: A test was conducted under the same conditions as in Example 1, except that an ultrasonic level sensor was used as the third detection device. However, the ultrasonic level sensor detected not only the carriers deposited at the bottom of the reaction tank but also the carriers that were flowing, and was therefore unsuitable as the third detection device. Reference Example 3: A test was conducted under the same conditions as in Example 1, except that an ultrasonic concentration meter was installed at a shallower water depth instead of the first detection device. A Honda Electronics ultrasonic concentration meter was used. This ultrasonic concentration meter is an instrument that irradiates ultrasonic waves in the depth direction of the reaction tank and detects the interface of sludge, etc., that exists at a position distant in the depth direction from the installation position of the ultrasonic concentration meter. With this type of instrument, noise is generated by suspended sludge and tiny air bubbles, and it was not possible to detect the interface of the flowing carrier.

[0058] [Note] The present disclosure has the following configuration. (1) A wastewater treatment device that treats wastewater under anaerobic conditions, a reaction tank for storing carriers holding microorganisms; a draft tube installed in the reaction vessel and having an upper end opening and a lower end opening; an impeller device that forms a downward flow in the draft tube and forms an upward flow between the draft tube and an inner wall surface of the reaction vessel; an output control device that controls the output of the impeller device; a detection device that can detect the interface of the carrier when the interface of the carrier that rises due to the upward flow caused by the impeller device reaches a detection device installation position, the detection device includes a first detection device and a second detection device installed at a predetermined interval in the up-down direction from the upper end to the lower end of the draft tube, The output control device controls the output of the impeller device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is positioned between the first detection device and the second detection device. (2) The wastewater treatment device described in (1) above is characterized in that the first detection device and the second detection device have a transmitting unit that transmits a predetermined signal and a receiving unit that is arranged at a predetermined distance from the transmitting unit and receives the signal. (3) a third detection device that detects the carriers deposited on the bottom of the reaction vessel, the third detection device being a vibration sensor installed on or near the bottom of the reaction vessel; The wastewater treatment device according to (1) or (2) above, wherein the output control device controls the output of the impeller device based on the detection result of the third detection device. (4) The wastewater treatment device according to any one of (1) to (3) above, wherein the output control device operates the impeller device continuously or intermittently. (5) The wastewater treatment device according to any one of (1) to (4) above, wherein the output control device temporarily controls the output of the impeller device so that the interface of the carrier exceeds the upper end of the draft tube. (6) A wastewater treatment method for treating wastewater under anaerobic conditions using the wastewater treatment device described in (1) above, A wastewater treatment method, characterized in that the output of the impeller device is controlled by the output control device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is located between the first detection device and the second detection device. (7) The wastewater treatment method described in (6) above, characterized in that the first detection device and the second detection device have a transmitter that emits a predetermined signal and a receiver that is arranged at a predetermined distance from the transmitter and receives the signal. (8) the wastewater treatment device has a third detection device that detects the carrier deposited on the bottom of the reaction tank, the third detection device being a vibration sensor installed on or near the bottom of the reaction tank; The wastewater treatment method according to (6) or (7) above, wherein the output of the impeller device is controlled by the output control device based on the detection result of the third detection device. (9) The wastewater treatment method according to any one of (6) to (8) above, wherein the impeller device is operated continuously or intermittently by the output control device. (10) The wastewater treatment method according to any one of (6) to (9) above, wherein the output of the impeller device is controlled by the output control device so that the interface of the carrier temporarily exceeds the upper end of the draft tube. [Explanation of symbols]

[0059] 1, 2 wastewater treatment device, 10 reaction tank, 12 carrier, 14 wastewater inlet line, 16 treated water discharge line, 18 draft tube, 20 impeller device, 20a submersible aerator, 22 motor, 24 impeller (agitating blade), 26 shaft, 28a first detection device, 28b second detection device, 28c vibration sensor, 32 output control device, 34 cylindrical body, 36a transmitter, 36b receiver.

Claims

1. A wastewater treatment device that treats wastewater under anaerobic conditions, a reaction tank for storing carriers holding microorganisms; a draft tube installed in the reaction vessel and having an upper end opening and a lower end opening; an impeller device that forms a downward flow in the draft tube and forms an upward flow between the draft tube and an inner wall surface of the reaction vessel; an output control device that controls the output of the impeller device; a detection device that can detect the interface of the carrier when the interface of the carrier that rises due to the upward flow caused by the impeller device reaches a detection device installation position, the detection device includes a first detection device and a second detection device installed at a predetermined interval in the up-down direction from the upper end to the lower end of the draft tube, The output control device controls the output of the impeller device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is positioned between the first detection device and the second detection device.

2. The wastewater treatment device according to claim 1, characterized in that the first detection device and the second detection device have a transmitter that transmits a predetermined signal and a receiver that is arranged at a predetermined distance from the transmitter and receives the signal.

3. a third detection device that detects the carriers deposited on the bottom of the reaction vessel, the third detection device being a vibration sensor installed on or near the bottom of the reaction vessel; The wastewater treatment device according to claim 1 or 2, wherein the output control device controls the output of the impeller device based on the detection result of the third detection device.

4. The wastewater treatment device according to claim 1 or 2, wherein the output control device operates the impeller device continuously or intermittently.

5. 3. The wastewater treatment device according to claim 1, wherein the output control device controls the output of the impeller device so that the interface of the carrier temporarily exceeds the upper end of the draft tube.

6. A wastewater treatment method for treating wastewater under anaerobic conditions using the wastewater treatment device according to claim 1, A wastewater treatment method, characterized in that the output of the impeller device is controlled by the output control device based on the detection results of the first detection device and the second detection device so that the interface of the carrier is positioned between the first detection device and the second detection device.

7. The wastewater treatment method according to claim 6, characterized in that the first detection device and the second detection device each have a transmitter that transmits a predetermined signal, and a receiver that is arranged at a predetermined distance from the transmitter and receives the signal.

8. the wastewater treatment device includes a third detection device that detects the carrier deposited on the bottom of the reaction tank, the third detection device being a vibration sensor installed on or near the bottom of the reaction tank; 8. The wastewater treatment method according to claim 6, wherein the output of the impeller device is controlled by the output control device based on the detection result of the third detection device.

9. 8. The wastewater treatment method according to claim 6, wherein the output control device operates the impeller device continuously or intermittently.

10. 8. The wastewater treatment method according to claim 6, wherein the output of the impeller device is controlled by the output control device so that the interface of the carrier temporarily exceeds the upper end of the draft tube.

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