Wastewater treatment device and wastewater treatment method

Abstract

The present invention addresses the problem of providing a wastewater treatment device and a wastewater treatment method which are capable of continuously performing stable treatment by suppressing outflow of a carrier and clogging of a carrier layer in a wastewater treatment device and a wastewater treatment method using a treatment tank filled with a carrier. In order to solve the above problem, in wastewater treatment for anaerobic treatment of wastewater, a wastewater treatment device provided with a treatment tank filled with a carbonaceous carrier having a particle size of 0.7-2.0 mm and a wastewater treatment method are provided. The present invention is based on the insight found by the present inventors that when anaerobic treatment is performed using a treatment tank filled with a carbonaceous carrier, carrier outflow may occur depending on the particle size. According to the present invention, the floating of the carrier due to biogas generated in the anaerobic treatment can be suppressed, and the outflow of the carrier can be suppressed. Moreover, since the accumulation of solid components between the carriers is suppressed, clogging of the carrier layer can also be suppressed. As a result, stable processing can be continuously performed.

Description

Technical Field

[0001] The present invention relates to a wastewater treatment apparatus and a wastewater treatment method. In particular, it relates to a wastewater treatment apparatus and a wastewater treatment method for anaerobic treatment using a treatment tank filled with a carrier. Background Art

[0002] Generally, as a method for treating wastewater containing organic matter, a biological treatment method using various microorganisms is known. In particular, biological treatment in an anaerobic environment (hereinafter referred to as "anaerobic treatment") is notable for its advantages in terms of introduction, as it does not require aeration power and hardly generates excess sludge.

[0003] As such an anaerobic treatment, the upflow anaerobic sludge bed method (UASB) using a treatment tank filled with sludge or granules is known. Also known is a technique using a treatment tank filled with a carrier to increase the concentration of anaerobic microorganisms in the treatment tank.

[0004] Moreover, as the carrier used herein, resin carriers are well-known in terms of mechanical strength and durability.

[0005] For example, Patent Document 1 describes a technique of using ultra-high molecular weight polyethylene having an intrinsic viscosity within a specific range as a microbial immobilization carrier for an anaerobic fluidized bed. Also described in Patent Document 1 is a carrier made of this ultra-high molecular weight polyethylene, which is excellent in strength, heat resistance, and abrasion resistance and can be used as a carrier with long-term durability and long-term fluidization stability.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-202431 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] As a type of anaerobic treatment, methane fermentation treatment is known. Methane fermentation treatment is an anaerobic treatment in which organic matter in wastewater is decomposed into methane and carbon dioxide by the action of anaerobic microorganisms in an anaerobic environment, and it is widely used as an anaerobic treatment from the viewpoints of treatment cost and the effectiveness of the generated gas.

[0011] Here, when a carrier for increasing the microbial concentration is used in anaerobic treatment, in the case of using the resin carrier described in Patent Document 1, for a treatment accompanied by gas generation such as methane fermentation treatment, the generated gas causes the carrier to float and easily flow out of the tank (outside the system). Therefore, there is a problem that it is difficult to increase the anaerobic microbial concentration in the tank. In addition, hereinafter, the case where the carrier flows out of the tank (outside the system) will be simply referred to as "carrier outflow".

[0012] Moreover, in the description of Patent Document 1, a carrier with excellent strength and abrasion resistance can be used as a carrier for long-term fluidization stability. However, in the case of using a treatment tank filled with the carrier, as the treatment continues, the solid components contained in the water to be treated introduced into the treatment tank or the anaerobic microorganisms that proliferate over time accumulate in the carrier. As a result, the voids between the carriers decrease, leading to clogging of the carrier layer, and thus the treatment performance significantly decreases. In addition, this also causes an increase in the volume of the carrier layer, making it easier for carrier outflow to occur. Therefore, it is necessary to maintain long-term fluidization stability through carrier characteristics or treatment conditions other than strength and abrasion resistance.

[0013] An object of the present invention is to provide a wastewater treatment apparatus and a wastewater treatment method that can suppress carrier outflow and clogging of the carrier layer to continuously perform stable treatment in a wastewater treatment apparatus and a wastewater treatment method using a treatment tank filled with a carrier.

[0014] Means for Solving the Problem

[0015] The present inventors conducted in-depth research on the above problems, and as a result, found that in a wastewater treatment apparatus and a wastewater treatment method using a treatment tank filled with a carrier, by using a carbonaceous carrier having a specific particle size range, carrier outflow and clogging of the carrier layer can be suppressed, and thus stable treatment can be continuously performed, thereby completing the present invention.

[0016] That is, the present invention is the following wastewater treatment apparatus and wastewater treatment method.

[0017] In order to solve the above problems, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus for anaerobic treatment of wastewater, characterized in that it includes a treatment tank filled with a carbonaceous carrier having a particle size of 0.7 mm to 2.0 mm.

[0018] The present inventors found that when anaerobic treatment is performed using a treatment tank filled with a carbonaceous carrier, carrier outflow can occur due to the particle size.

[0019] The wastewater treatment device of the present invention is completed based on this insight. Based on this feature, it is possible to suppress the floating of the carrier caused by the biogas generated during anaerobic treatment, thereby suppressing the outflow of the carrier. And, since the specific gravity of the carbonaceous carrier tends to be greater than the specific gravity of the solid components contained in the wastewater, when the wastewater passes through the carrier layer as the water to be treated, the solid components are also more likely to pass through the carrier layer simultaneously. Therefore, the accumulation of solid components between the carriers can be suppressed, and thus the clogging of the carrier layer can also be suppressed. Thereby, stable treatment can be continuously performed.

[0020] Moreover, as an embodiment of the wastewater treatment device of the present invention, it is characterized in that the flow velocity in the treatment tank is controlled to be 1.0 to 2.0 times the minimum fluidization velocity of the carbonaceous carrier.

[0021] In the case of using a carrier with a relatively large particle size such as the carbonaceous carrier used in the present invention, since the possibility of carrier outflow is relatively high, it is particularly effective to appropriately control the flow velocity in the treatment tank.

[0022] Furthermore, according to this feature, it is possible to keep the carrier layer in a fluidized state at a flow velocity such that the carbonaceous carrier does not flow out of the tank. Thus, the formation of voids between the carriers becomes easier, and therefore substances (solid components in the wastewater or proliferated partial anaerobic microorganisms) that cause clogging of the carrier layer are more likely to pass through the carrier layer. That is, the carbonaceous carrier can be retained in the tank, and substances that cause clogging of the carrier layer can be efficiently discharged out of the tank (outside the system), thereby further suppressing carrier outflow and clogging of the carrier layer, and enabling stable treatment to be continuously performed.

[0023] Moreover, as an embodiment of the wastewater treatment device of the present invention, it is characterized in that it is provided with an internal circulation mechanism that recovers the treated water passing through the treatment tank and returns the recovered treated water to the treatment tank for circulation.

[0024] Generally, in a wastewater treatment device using a treatment tank filled with carriers, the flow velocity in the treatment tank related to the fluidization of the carrier layer in the treatment tank is controlled by controlling the flow rate (supply water volume) of the wastewater supplied from outside the treatment tank into the treatment tank. And, in this case, in order to supply (transport) the wastewater from outside the treatment tank into the treatment tank, a transport mechanism (such as a pump) equipped with a driving part is usually used. At this time, the force (energy) required for driving the transport mechanism depends on the pressure difference applied to the transport mechanism (the water pressure difference between the upstream side and the downstream side of the transport mechanism). That is, in the case of supplying wastewater to a treatment tank storing a certain amount of water (wastewater) from outside the treatment tank using a transport mechanism, as the required flow velocity in the treatment tank increases, the power for supplying wastewater from outside the treatment tank into the treatment tank (the driving energy of the transport mechanism) also increases.

[0025] On the other hand, according to this feature, when the wastewater (water to be treated) introduced into the treatment tank is discharged out of the system as treated water through the carrier layer, the treated water is recovered and returned to the treatment tank again for circulation. As a result, the upstream side and the downstream side of the conveying mechanism are within the same tank (treatment tank), so that the pressure difference applied to the conveying mechanism for conveying wastewater (circular movement) can be reduced. That is, even if the flow rate required in the treatment tank (the flow rate required to fluidize the carrier layer) increases, the increase in the power required to convey the wastewater (the driving energy of the conveying mechanism) can be suppressed, and thus the operating cost can be reduced.

[0026] The wastewater treatment method of the present invention for solving the above problems is a wastewater treatment method for anaerobic treatment of wastewater, characterized in that a treatment tank filled with carbonaceous carriers having a particle size of 0.7 mm to 2.0 mm is used.

[0027] The wastewater treatment method of the present invention is completed based on the above-mentioned insight regarding the relationship between carrier outflow and carrier particle size. Based on this feature, the floating of the carrier caused by the biogas generated during anaerobic treatment can be suppressed, thereby suppressing carrier outflow. And since the specific gravity of the carbonaceous carrier tends to be greater than the specific gravity of the solid components contained in the wastewater, when the wastewater passes through the carrier layer as the water to be treated, the solid components are also more likely to pass through the carrier layer simultaneously. Therefore, the accumulation of solid components between the carriers can be suppressed, and thus the clogging of the carrier layer can also be suppressed. Thereby, stable treatment can be continuously performed.

[0028] Moreover, as an embodiment of the wastewater treatment method of the present invention, it is characterized by including a flow rate control step: controlling the flow rate in the treatment tank to be 1.0 times to 2.0 times the minimum fluidization velocity of the carbonaceous carrier.

[0029] In the case of using a carrier with a relatively large particle size such as the carbonaceous carrier used in the present invention, since the possibility of carrier outflow is relatively high, it is particularly effective to appropriately control the flow rate in the treatment tank.

[0030] Furthermore, according to this feature, the carrier layer can be maintained in a fluidized state at a flow rate such that the carbonaceous carrier does not flow out of the tank. As a result, the formation of voids between the carriers becomes easier, so that substances causing clogging of the carrier layer (solid components in the wastewater or proliferated partial anaerobic microorganisms) can more easily pass through the carrier layer. That is, the carbonaceous carrier can be retained in the tank, and substances causing clogging of the carrier layer can be efficiently discharged out of the tank (out of the system), thereby further suppressing carrier outflow and clogging of the carrier layer, and enabling stable treatment to be continuously performed.

[0031] Advantages of the Invention

[0032] According to the present invention, it is possible to provide a wastewater treatment apparatus and a wastewater treatment method that can suppress the outflow of carriers and the clogging of the carrier layer in a wastewater treatment apparatus and a wastewater treatment method using a treatment tank filled with carriers, thereby enabling continuous and stable treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. 1 is a schematic explanatory view of a wastewater treatment apparatus according to a first embodiment of the present invention.

[0034] Figure 2 FIG. 2 is a graph showing the particle size limit of carbonaceous carriers flowing out of the tank in anaerobic treatment using a treatment tank filled with carbonaceous carriers.

[0035] Figure 3 FIG. 3 is a schematic explanatory view of another embodiment of the wastewater treatment apparatus according to the first embodiment of the present invention.

[0036] Figure 4 FIG. 4 is a schematic explanatory view of another embodiment of the wastewater treatment apparatus according to the first embodiment of the present invention.

[0037] Figure 5 FIG. 5 is a schematic explanatory view of another embodiment of the wastewater treatment apparatus according to the first embodiment of the present invention.

[0038] Figure 6 FIG. 6 is a schematic explanatory view of a wastewater treatment apparatus according to a second embodiment of the present invention.

[0039] Figure 7 FIG. 7 is a schematic explanatory view of another embodiment of the wastewater treatment apparatus according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The wastewater treatment apparatus and the wastewater treatment method of the present invention are suitable for use in the anaerobic treatment of wastewater containing organic matter.

[0041] Examples of the wastewater containing organic matter to be treated in the present invention include industrial wastewater discharged from various factories such as food factories, chemical factories, and pulp factories, as well as domestic sewage such as sewage. In addition, the wastewater containing organic matter is not limited to this, and any wastewater containing organic matter that can be biologically treated in an anaerobic environment can be used as the treatment object of the present invention. Examples of such wastewater include livestock manure and organic wastewater containing sludge (excess sludge).

[0042] Hereinafter, with reference to the drawings, embodiments of the wastewater treatment apparatus and the wastewater treatment method according to the present invention will be described in detail. Regarding the wastewater treatment method of the present invention, the operation description of the wastewater treatment apparatus according to the present invention will be used instead.

[0043] In addition, the wastewater treatment apparatus and the wastewater treatment method described in the embodiments are merely examples for explaining the wastewater treatment apparatus and the wastewater treatment method according to the present invention, and are not limited thereto.

[0044] [First Embodiment]

[0045] Figure 1 FIG. is a schematic explanatory view of the wastewater treatment apparatus according to the first embodiment of the present invention.

[0046] As Figure 1 shown, the wastewater treatment apparatus 1A in the present embodiment includes a treatment tank 2 filled with a carbonaceous carrier P therein and for introducing wastewater W0 for anaerobic treatment. And, there are provided a pipeline L1 as an introduction pipeline for introducing the wastewater W0 into the treatment tank 2 and a pipeline L2 as a discharge pipeline for discharging the treated water W1 discharged from the treatment tank 2 to the outside of the system. Moreover, as an internal circulation mechanism 3 for recovering the treated water W1 and returning it to the treatment tank 2 for circulation, there is provided a pipeline L3, a part of the treated water W1 discharged from the treatment tank 2 is introduced into the pipeline L3, and the pipeline L3 is connected to the pipeline L1 to form a circulation path of the treated water W1 to the treatment tank 2. In addition, Figure 1 the arrows in

[0047] FIG. indicate the flow direction of water. Figure 1 The treatment tank 2 is a reaction tank for anaerobic treatment of the wastewater W0. As

[0048] shown, the wastewater W0 is supplied to the treatment tank 2 via a pipeline L1 provided at the lower part of the treatment tank 2. In the treatment tank 2, the components contained in the wastewater W0 are decomposed by anaerobic microorganisms present therein. The treated water W1 after anaerobic treatment is discharged from the treatment tank 2 via a pipeline L2 provided at the upper part of the treatment tank 2. And, a part of the treated water W1 is recovered by the internal circulation mechanism 3 described later and introduced into the treatment tank 2 again. In addition, the treatment tank 2 is preferably set as a closed system to maintain an anaerobic environment.

[0049] The pipeline L1 for introducing the wastewater W0 into the treatment tank 2 may be connected to a distributor (dispersion pipe, dispersion plate, etc.) provided at the bottom of the treatment tank 2 for introducing the wastewater W0 into the treatment tank 2. Thereby, it is easy to control the flow rate of the wastewater W0 introduced into the treatment tank 2.

[0050] In addition, a pump may be provided on the pipeline L1 to form a stable upward flow (not shown) of the wastewater W0 in the treatment tank 2.

[0051] As the anaerobic microorganism in the present embodiment, any microorganism capable of anaerobically treating organic matter may be used, and there is no particular limitation on the specific type of microorganism. For example, in the case of performing methane fermentation treatment as the anaerobic treatment, acidogenic bacteria and methanogenic bacteria are used as the anaerobic microorganisms. As other anaerobic microorganisms, denitrifying bacteria used for denitrification treatment for nitrate and nitrite reduction or sulfate-reducing bacteria used for sulfate reduction treatment for sulfate reduction can be cited, etc.

[0052] In addition, as the anaerobic microorganism of the present embodiment, either isolated microorganisms or inoculated sludge from other wastewater treatment facilities or the like can be used. Moreover, the anaerobic microorganisms contained in the wastewater W0 can be utilized.

[0053] The carbonaceous carrier P of the present embodiment refers to a substance composed of an inorganic material mainly composed of carbon. Specifically, carbon black, graphite, coke, activated carbon, etc. can be cited. In addition, as the carbonaceous carrier P of the present embodiment, there is no particular limitation on the presence or absence of micropores. However, from the viewpoint of being able to adsorb components that hinder the anaerobic treatment using anaerobic microorganisms in addition to retaining anaerobic microorganisms, it is preferably provided with micropores. Specifically, activated carbon is preferably used.

[0054] Moreover, as the carbonaceous carrier P of the present embodiment, a carbonaceous carrier having a specific particle size range is used.

[0055] The present inventors have obtained the following technical insight: When performing anaerobic treatment using a treatment tank filled with a carbonaceous carrier, the loss of the carbonaceous carrier to the outside of the tank (outside the system) occurs depending on its particle size.

[0056] Herein, the relationship between the outflow of the carbonaceous carrier to the outside of the tank (outside the system) and the particle size of the carbonaceous carrier will be described based on examples.

[0057] First, two types of activated carbon with different particle sizes (activated carbon P1 and activated carbon P2) were used as the carbonaceous carrier, and each activated carbon was filled into a treatment tank with an effective volume of 1.8 liters. Moreover, wastewater containing organic matter was introduced into the treatment tank, and anaerobic treatment (methane fermentation) was performed. Then, in the treatment tank, the phenomenon that the generated biogas bubbles adhered to the activated carbon occurred. Moreover, in the treatment tank filled with activated carbon P1, the activated carbon floated in the treatment tank and flowed out to the outside of the tank (outside the system). On the other hand, in the treatment tank filled with activated carbon P2, the activated carbon remained in the treatment tank as it was.

[0058] At this time, the particle sizes of the activated carbon (activated carbon P1) that flowed out of the tank and the activated carbon (activated carbon P2) that remained in the tank were measured respectively.

[0059] The particle size measurement was carried out in accordance with JIS Z 8815:1994 "General Rules for Sieving Test Methods", using sieves with mesh sizes (mm) of 0.30, 0.425, 0.50, 0.60, 0.71, 0.85, 1.00, 1.18, and 1.40.

[0060] In addition, the packing density (measurement value based on JIS K 1474) of the activated carbon in this example is as follows: for activated carbon P1, it is 0.43 - 0.53 g / mL; for activated carbon P2, it is 0.47 - 0.55 g / mL.

[0061] The results are shown in Figure 2 .

[0062] Figure 2 It is a chart showing the results of measuring the particle sizes of the activated carbon (activated carbon P1) flowing out of the tank and the activated carbon (activated carbon P2) remaining in the tank in the above-mentioned example.

[0063] Figure 2 In the chart in

[0064] here, since there is almost no difference in the packing density between activated carbon P1 and activated carbon P2, Figure 2 the chart related to activated carbon P1 in

[0065] shows the particle size distribution of the carbonaceous carriers that will flow out with the biogas generated during anaerobic treatment when filled in the treatment tank, and the chart related to activated carbon P2 shows the particle size distribution of the carbonaceous carriers that will not cause carrier outflow. Figure 2 That is, the chart in

[0066] shows the particle size limit of the carbonaceous carriers flowing out of the tank during anaerobic treatment using a treatment tank filled with carbonaceous carriers. Figure 2 It can be understood from

[0067] that by setting the lower limit of the particle size of the carbonaceous carriers to 0.7 mm or more, more than 90% of the carbonaceous carriers can be prevented from flowing out and retained in the treatment tank.

[0068] The carbonaceous carrier P in the present embodiment tends to have a specific gravity greater than that of the solid components (mainly organic substances) contained in the wastewater W0. Therefore, as the wastewater W0 passes through the carrier layer in the treatment tank 2 as the water to be treated, the solid components will also pass through the carrier layer simultaneously. That is, the accumulation of solid components in the wastewater between the carbonaceous carriers P is suppressed. Thereby, the decline in the function of the carbonaceous carrier P and the clogging of the carrier layer are suppressed.

[0069] Moreover, if wastewater is continuously supplied to the closed carrier layer, the volume of the carrier layer will increase, so it is easy to cause the carrier to flow out. On the other hand, by using the carbonaceous carrier P of the present embodiment, the clogging of the carrier layer can be suppressed, so the outflow of the carrier caused by the increase in the volume of the carrier layer can also be suppressed.

[0070] Therefore, the wastewater treatment apparatus 1A of the present embodiment can suppress the outflow of the carrier and the clogging of the carrier layer by limiting the particle size of the carbonaceous carrier P filled in the treatment tank 2 to a specific range, thereby enabling stable treatment to be continuously carried out.

[0071] As described above, among the reasons for the carbonaceous carrier P in the treatment tank 2 to flow out of the tank (outside the system), it is greatly affected by the floating caused by the attachment of biogas. Therefore, not only the specific gravity (density) of the carbonaceous carrier P, but also the particle size of the carbonaceous carrier P related to the area where biogas can attach (the surface area of the carbonaceous carrier P) has a greater influence on the outflow of the carrier. And the flow rate in the treatment tank 2 has a smaller influence on the outflow of the carrier compared to the floating caused by the attachment of biogas.

[0072] On the other hand, the clogging of the carrier layer occurs due to the accumulation of substances that cause the clogging of the carrier layer (solid components in the wastewater or proliferated partial anaerobic microorganisms) on the carbonaceous carrier P. Therefore, in the wastewater treatment apparatus 1A of the present embodiment, in addition to separating according to the specific gravity difference between the carbonaceous carrier P and the substances that cause the clogging of the carrier layer, it is also preferably provided with a mechanism capable of efficiently separating the substances that cause the clogging of the carrier layer from the carbonaceous carrier P.

[0073] In the case of using a carrier with a relatively large particle size such as the carbonaceous carrier P used in the present embodiment, since the possibility of the carrier flowing out is high, it is particularly effective to appropriately control the flow rate in the treatment tank 2.

[0074] Therefore, as an example of the wastewater treatment apparatus 1A of the present embodiment having a mechanism capable of efficiently separating the substances that cause the clogging of the carrier layer from the carbonaceous carrier P, the following method can be cited: while setting the particle size of the carbonaceous carrier P filled in the treatment tank 2 to a specific range, the flow rate in the treatment tank 2 is controlled to a specified multiple of the minimum fluidization velocity of the carbonaceous carrier P.

[0075] Here, the minimum fluidization velocity (Umf) is a value that depends on the particle size, particle shape, or specific gravity (density) of the target particles (carbonaceous carrier P), and can be calculated based on the relationship between the flow velocity and pressure loss.

[0076] Specifically, a pressure sensor can be set in the treatment tank 2, and the relationship between the flow velocity and pressure (pressure loss) of the fluid flowing in the treatment tank 2 can be obtained. The pressure loss derived from the measurement results of the pressure sensor increases with the increase in the flow velocity, but tends to be constant after a certain point. Moreover, the flow velocity at which the pressure loss starts to remain constant varies depending on the particles, and this flow velocity is the minimum fluidization velocity Umf of each particle.

[0077] At this time, as the installation position of the pressure sensor installed in the treatment tank 2, the bottom of the tank is preferably used. Thereby, the pressure change of the entire treatment tank 2 can be detected. And, regarding the pressure sensor installed in the treatment tank 2, it is preferable to install multiple sensors in the vertical direction of the tank. In the treatment tank 2 filled with the carrier, the hydrostatic pressure caused by the stored water (wastewater W0) is larger than the pressure loss caused by the particles (carbonaceous carrier P). Therefore, by installing multiple pressure sensors and using the pressure difference between them, the pressure loss can be derived with higher accuracy.

[0078] And, regarding the minimum fluidization velocity, in addition to calculating based on the above-mentioned relationship between the flow velocity and pressure loss, it can also be calculated by using known experimental formulas or arithmetic expressions based on various experiments. For example, in addition to using the Ergun equation and its modified forms, the Wen-Yu equation etc. can be cited.

[0079] More specifically, it can be cited: controlling the flow velocity in the treatment tank 2 to be 1.0 to 2.0 times the minimum fluidization velocity of the filled carbonaceous carrier P. By setting the flow velocity in the treatment tank 2 to be 1.0 times or more, more preferably 1.1 times or more, the fluidized state of the carrier layer can be reliably formed and maintained. On the other hand, if the flow velocity in the treatment tank 2 is increased, the fluidized state of the carrier layer can be maintained, but there may be a risk of the carrier flowing out. And, with the control of the flow velocity, the driving energy of the conveying mechanism (such as a pump) also increases. Therefore, by setting the flow velocity in the treatment tank 2 to be 2.0 times or less, more preferably 1.5 times or less, of the minimum fluidization velocity of the filled carbonaceous carrier P, the carbonaceous carrier P can be prevented from being discharged out of the tank while reducing the operating cost related to maintaining the fluidized state of the carrier layer. That is, by controlling the flow velocity in the treatment tank 2 within a specified multiple of the minimum fluidization velocity of the filled carbonaceous carrier P, the carrier layer can be appropriately maintained in a fluidized state at a flow velocity at which the carbonaceous carrier P does not flow out of the tank.

[0080] At this time, the formation of voids between the carbonaceous carriers P becomes easier. Although part of the substances that cause the clogging of the carrier layer are captured by the carbonaceous carriers P, most of them are discharged through the carrier layer. That is, the carbonaceous carriers P are retained in the treatment tank 2. On the other hand, the substances that cause the clogging of the carrier layer can be efficiently discharged outside the tank (outside the system), so that the outflow of the carriers and the clogging of the carrier layer can be further suppressed, and stable treatment can be continuously performed.

[0081] Moreover, at this time, as the mechanism for controlling the flow velocity in the treatment tank 2 in the wastewater treatment apparatus 1A of the present embodiment, it is only necessary to be able to control the flow velocity in the treatment tank 2 so as to satisfy a specified value based on the minimum fluidization velocity of the above-mentioned carbonaceous carriers P.

[0082] Furthermore, as the treatment in the treatment tank 2 continues, microorganisms will adhere to the carbonaceous carriers P, which will cause a change in the specific gravity of the carbonaceous carriers P, and thus the fluidity or the minimum fluidization velocity of the carbonaceous carriers P will change. Therefore, when controlling the flow velocity in the treatment tank 2, it is preferable to provide a pressure sensor in the treatment tank 2 and detect the change in the minimum fluidization velocity by continuously or periodically deriving the pressure loss. Thereby, the flow velocity can be controlled according to the state (minimum fluidization velocity) of the carbonaceous carriers P in the treatment tank 2, and more stable treatment can be further performed.

[0083] Here, in a conventional wastewater treatment apparatus using a treatment tank filled with carriers, generally, the flow velocity control related to the fluidization of the inside of the treatment tank and the carrier layer is performed by controlling the flow rate (supply water volume) of the wastewater supplied from outside the treatment tank into the treatment tank. And, in order to supply (transport) the wastewater from outside the treatment tank 2 into the treatment tank 2, a transport mechanism (such as a pump) having a driving part is also used. At this time, the force (energy) required to drive the transport mechanism depends on the pressure difference applied to the transport mechanism (the water pressure difference between the upstream side and the downstream side of the transport mechanism). That is, in the case of supplying the wastewater W0 to the treatment tank 2 storing a certain amount of water (wastewater W0) from outside the treatment tank 2 using a transport mechanism, as the required flow velocity in the treatment tank 2 increases, the power for supplying the wastewater W0 from outside the treatment tank 2 into the treatment tank 2 (the driving energy of the transport mechanism) also increases. In particular, in the case of using carriers with a relatively large particle size such as the carbonaceous carriers P used in the present embodiment, the absolute value of the flow velocity (minimum fluidization velocity) required to fluidize the carrier layer tends to be large, resulting in an increase in the operating cost of the wastewater treatment apparatus 1.

[0084] Therefore, in the wastewater treatment apparatus 1A of the present embodiment, for example, as Figure 1As shown in the figure, an internal circulation mechanism 3 can be provided. This internal circulation mechanism 3 recovers the treated water W1 that has passed through the treatment tank 2 and returns the recovered treated water W1 to the treatment tank 2 for circulation, thereby controlling the flow rate inside the treatment tank 2. More specifically, when the wastewater W0 introduced into the treatment tank 2 passes through the carrier layer and is discharged as treated water W1 outside the tank (outside the system), a part of the treated water W1 is recovered, and the recovered treated water W1 is returned to the treatment tank 2 for circulation again. As a result, the upstream side and the downstream side of the conveying mechanism are within the same tank (treatment tank 2), so that the pressure difference of the conveying mechanism for conveying the treated water W1 (circular movement) can be reduced. That is, even if the required flow rate inside the treatment tank 2 increases, the increase in the power required to convey the treated water W1 (the driving energy of the conveying mechanism) can be suppressed, thereby reducing the operating cost.

[0085] There are no particular limitations on the specific structure and mechanism of the internal circulation mechanism 3.

[0086] As an example of the internal circulation mechanism 3, for example, as Figure 1 shown, the following example can be cited: a pipeline L3 is provided for recovering and conveying the wastewater W0 (treated water W1) that has passed through the carrier layer from the upper part of the treatment tank 2, and this pipeline L3 is connected to the pipeline L1 to form a circulation path for the internal circulation of the treated water W1 to the treatment tank 2. And, in order to efficiently convey the treated water W1 in the circulation path and easily control the flow rate, it is preferable to provide a conveying mechanism (such as a pump, not shown) with a driving part on the pipeline 3. At this time, a component (such as a sieve) for suppressing the outflow of the carrier can also be provided at the connection part (water intake part) between the pipeline L3 and the treatment tank 2.

[0087] And, as another mode of the internal circulation mechanism 3, for example, it can be cited that a drainage pipe is provided inside the treatment tank 2, and by reversing the flow direction of the treated water W1 inside and outside the drainage pipe, the internal circulation of the treated water W1 can be carried out inside the treatment tank 2.

[0088] Moreover, as another mode of the internal circulation mechanism 3, it can be cited that in the recovery of the treated water W1, an overflow component recovery mechanism is provided for recovering the overflow component of the treated water W1 that exceeds the specified water level inside the treatment tank 2, and the treated water W1 recovered by this overflow component recovery mechanism is circulated internally via the pipeline L3. By using the overflow component inside the treatment tank 2 as the object treated water W1 for recovery and circulation, it is easy to carry out the internal circulation of the treated water W1 to the treatment tank 2 while maintaining the total water volume inside the treatment tank 2.

[0089] Hereinafter, as an example related to the internal circulation mechanism 3 in the wastewater treatment device 1A, an example of setting an overflow component recovery mechanism will be described according to Figure 3 the figure.

[0090] Figure 3 It is a schematic explanatory diagram showing another mode of the wastewater treatment apparatus 1A of the present embodiment.

[0091] As Figure 3 shown, as the wastewater treatment apparatus 1A in the present embodiment, an overflow weir 31 can be cited as an overflow component recovery mechanism in the internal circulation mechanism 3. In addition, in Figure 3 , the illustration of the pipe line L2 for discharging the treated water W1 to the outside of the system is omitted.

[0092] The overflow weir 31 only needs to be provided above the treatment tank 2 and can recover the treated water W1 overflowing from a specified position of the treatment tank 2. And there is no particular limitation on the structure of the overflow weir 31. As Figure 3 shown in (A) of Figure 3 , it can be provided along the inner circumference of the treatment tank 2. As Figure 3 shown in (C) of Figure 3 , it can also be provided along the outer circumference of the treatment tank 2. And in order to improve the suppression effect of the carrier outflow, as Figure 3 shown in (B) of Figure 3 , a screen 32 can be provided so that the treated water W1 overflows to the overflow weir 31 side via the screen 32. At this time, there is no particular limitation on the position where the screen 32 is provided, but examples include: as Figure 3 shown in (B) of Figure 3 , provided directly in front of the overflow weir 31, or as

[0093] shown in (D) of

[0094] , provided on the entire upper surface of the treatment tank 2, etc.

[0095] Moreover, as another mode of the overflow weir 31, a trough-shaped member can be cited as being provided at the center of the treatment tank 2. At this time, a screen 32 can be provided around the trough-shaped member to improve the suppression effect of the carrier outflow.

[0096] Generally, in a treatment tank equipped with such a separation device, if the flow rate in treatment tank 2 is increased, the separation efficiency of the separation device will decrease, making it difficult to continuously perform stable treatment. On the other hand, in the wastewater treatment device 1A of the present embodiment, in the case where an overflow component recovery mechanism is provided, the separation device is not necessary. Therefore, even if the flow rate in treatment tank 2 is increased to maintain the fluidization of the carrier layer, stable treatment can be continuously performed.

[0097] Moreover, as the internal circulation mechanism 3, a treated water recovery mechanism for efficiently recovering only the liquid component in the treated water W1 can be provided instead of the overflow component recovery mechanism.

[0098] Figure 4 and Figure 5 is a schematic explanatory diagram showing another mode of the wastewater treatment device 1A of the present embodiment.

[0099] As the wastewater treatment device 1A in the present embodiment, as the treated water recovery mechanism in the internal circulation mechanism 3, a device provided with the Figure 4 shown settler 33, or a device provided with the Figure 5 shown rectifying member 34 can be cited. Additionally, in Figure 4 and Figure 5 the illustration of the pipeline L2 for discharging the treated water W1 to the outside of the system is omitted.

[0100] When the settler 33 is provided as the treated water recovery mechanism, as shown in (A) in Figure 4 and (B) in Figure 4 the pipeline L3 is connected above the settler 33. Thereby, the clarified treated water W1 from which the biogas and solid components have been separated can be recovered and introduced into the pipeline L3 for internal circulation. In this case, since the solid components contained in the treated water W1 undergoing internal circulation are significantly reduced, clogging of the carrier layer can be further suppressed.

[0101] Moreover, as shown in (B) in Figure 4 a screen 32 can also be provided at the connection between the pipeline L3 and the treatment tank 2 to enhance the effect of suppressing the outflow of the carrier.

[0102] In addition, the structure of the settler 33 is not particularly limited and may not have a left - right symmetric structure. For example, it can be provided only near the connection between the pipeline L3 and the treatment tank 2 (water intake part). Thereby, the number of components related to the wastewater treatment device 1A can be reduced.

[0103] Moreover, as the treated water recovery mechanism, it can also be as shown in Figure 5As shown, a rectifying member 34 is provided in place of the settler 33. The rectifying member 34 only needs to be able to form the flow direction of the treated water W1 above the treatment tank 2, and in particular, it can be cited that it is arranged focusing on the moving direction of the biogas in the treated water W1. For example, it can be cited that: as Figure 5 shown in (A) of Figure 5 , the rectifying member 34 is arranged so that the biogas in the treated water W1 moves in a direction away from the connection part (water intake part) of the pipeline L3 and the treatment tank 2; as Figure 5 shown in (B) of Figure 5 , the rectifying member 34 is arranged so that the biogas in the treated water W1 can wash the screen 32 provided at the connection part (water intake part) of the pipeline L3 and the treatment tank 2.

[0104] In addition, in the wastewater treatment device 1A of the present embodiment, when separating the biogas in the treated water W1 by providing a treated water recovery mechanism or the like, the biogas can also be recovered and returned to the treatment tank 2. Thus, while controlling the flow rate through the internal circulation of the treated water W1, the flow rate can also be controlled through the internal circulation of the biogas. Thus, even when using a carbonaceous carrier P with a relatively large minimum fluidization velocity, it is easy to control the flow rate required to form a fluidized bed layer in the treatment tank 2.

[0105] In addition, various auxiliary devices can also be provided in the treatment tank 2 of the present embodiment. For example, the treatment tank 2 can also be equipped with an internal water temperature adjustment mechanism, a pH regulator dosing mechanism, and a mechanism for adding the necessary nutrients (such as metals such as nitrogen, phosphorus, cobalt, and nickel) for microorganisms. In particular, when performing methane fermentation based on acidogenic bacteria and methanogenic bacteria as anaerobic treatment, as an auxiliary device of the treatment tank 2, a mechanism for recovering, purifying, and storing methane gas is preferably provided.

[0106] [Second Embodiment]

[0107] Figure 6 and Figure 7 are schematic explanatory views of the wastewater treatment device 1B of the second embodiment of the present invention.

[0108] The wastewater treatment device 1B according to the present embodiment, as Figure 6 and Figure 7 shown, is based on the wastewater treatment device 1A in the first embodiment and is provided with a carrier recovery unit 4 for recovering the carbonaceous carrier P flowing out of the treatment tank 2.

[0109] In addition, in the structure of the wastewater treatment device 1B in the present embodiment, the parts having the same structure as those of the wastewater treatment device 1A in the first embodiment are omitted from description.

[0110] In the wastewater treatment apparatus 1B of the present embodiment, by providing a carrier recovery unit 4 on the circulation path of the internal circulation mechanism 3, the carbonaceous carrier P flowing out of the treatment tank 2 together with the treated water W1 is recovered and returned to the treatment tank 2. Thereby, the outflow of the carbonaceous carrier P can be suppressed, and the concentration of anaerobic microorganisms in the treatment tank 2 can be maintained, so that efficient anaerobic treatment and stable treatment can be continuously performed.

[0111] The carrier recovery unit 4 in the present embodiment is not particularly limited as long as it can recover the carbonaceous carrier P flowing out from the treatment tank 2 to the side of the internal circulation mechanism 3 and return it to the treatment tank 2 via the internal circulation mechanism 3.

[0112] As an example of the carrier recovery unit 4, for example, as Figure 6 shown, a separation tank 41 can be provided on the circulation path (pipe line L3) of the internal circulation mechanism 3. The separation tank 41 can be: a separation tank that introduces the treated water W1 via the pipe line L3 and can recover the carbonaceous carrier P contained in the treated water W1 by sedimentation separation. Moreover, the carbonaceous carrier P recovered by the separation tank 41 is returned to the treatment tank 2 together with the treated water W1 via the pipe line L3 again. On the other hand, a part of the treated water W1 from which the carbonaceous carrier P has been removed is discharged to the outside of the system via the pipe line L4.

[0113] In addition, as another mode of the carrier recovery unit 4, for example, as Figure 7 shown in (A), a separation tank 41 is provided on the circulation path (pipe line L3) of the internal circulation mechanism 3, and a screen 42 is further provided inside the separation tank 41; or as Figure 7 shown in (B), a cyclone 43 is provided on the circulation path (pipe line L3) of the internal circulation mechanism 3, etc.

[0114] In any of the carrier recovery units 4, the treated water W1 containing the recovered carbonaceous carrier P is returned to the treatment tank 2 via the pipe line L3, and a part of the treated water W1 from which the carbonaceous carrier P has been removed is discharged to the outside of the system via the pipe line L4.

[0115] In addition, the above embodiment shows an example of a wastewater treatment apparatus and a wastewater treatment method. The wastewater treatment apparatus and the wastewater treatment method according to the present invention are not limited to the above embodiment, and can be modified within the scope not changing the gist described in the technical solution for the wastewater treatment apparatus and the wastewater treatment method according to the above embodiment.

[0116] For example, in the wastewater treatment apparatus and the wastewater treatment method of the present embodiment, in order to continuously perform stable treatment, it is preferable to perform anti-corrosion (anti-electro-corrosion) treatment of the treatment tank. More specifically, examples include: using concrete or resin (FRP) as the material of the treatment tank; or processing the inner surface of the treatment tank (lining, coating, painting, etc.).

[0117] Industrial Applicability

[0118] The wastewater treatment apparatus and the wastewater treatment method of the present invention can be used for anaerobic treatment of wastewater containing organic matter. In particular, the wastewater treatment apparatus and the wastewater treatment method of the present invention are suitable for use in anaerobic treatment accompanied by the generation of biogas.

[0119] Symbol Explanation

[0120] 1A, 1B - wastewater treatment apparatus, 2 - treatment tank, 3 - internal circulation mechanism, 31 - overflow weir, 32 - screen, 33 - settler, 34 - rectifying member, 4 - carrier recovery section, 41 - separation tank, 42 - screen, 43 - cyclone, L1 to L4 - pipelines, P - carbonaceous carrier, W0 - wastewater, W1 - treated water.

Claims

1. A wastewater treatment device for anaerobic treatment of wastewater, characterized in that the wastewater treatment device is provided with a treatment tank filled with a carbonaceous carrier having a particle size of 0.7 mm to 2.0 mm.

2. The wastewater treatment device according to claim 1, characterized in that the flow rate in the treatment tank is controlled to be 1.0 to 2.0 times the minimum fluidization velocity of the carbonaceous carrier.

3. The wastewater treatment device according to claim 1 or 2, characterized in that it is provided with an internal circulation mechanism that recovers the treated water passing through the treatment tank and returns the recovered treated water to the treatment tank for circulation.

4. A wastewater treatment method for anaerobic treatment of wastewater, characterized in that a treatment tank filled with a carbonaceous carrier having a particle size of 0.7 mm to 2.0 mm is used.

5. The wastewater treatment method according to claim 4, characterized in that it includes a flow rate control step that controls the flow rate in the treatment tank to be 1.0 to 2.0 times the minimum fluidization velocity of the carbonaceous carrier.

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