Methanation treatment method and methanation treatment equipment

Abstract

To stir by heat convection by generating a convective flow in a methane fermentation liquid, without causing up-sizing of a heating device and a sharp rise of equipment cost and operation cost.SOLUTION: A methane fermentation processing method has, as organic wastes, first organic waste C1 and second organic waste C2, and involves a heating process to heat the second organic waste C2, a second supply process to supply the second organic waste C2 which has undergone the heating process to a lower side of the methane fermentation tank 31, and a first supply process to supply the first organic waste C1 which has not undergone the heating process to the methane fermentation tank 31 at a place different in a vertical direction from the second organic waste C2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation treatment, and a methane fermentation treatment facility.

Background Art

[0002] For example, in the disposal of organic waste such as sludge and biomass generated in wastewater treatment, methane fermentation (anaerobic fermentation) is widely carried out for the purpose of volume reduction and energy conversion. Methane fermentation is a technology in which organic waste is stored under anaerobic conditions for a certain period of time, and the organic waste is decomposed by the action of anaerobic microorganisms to generate biogas such as methane gas and carbon dioxide, and is widely adopted in domestic waste facilities and wastewater treatment facilities.

[0003] A methane fermentation facility for performing methane fermentation mainly includes a methane fermentation tank for storing organic waste and performing methane fermentation, a stirrer for stirring the methane fermentation liquid in the methane fermentation tank, and a heating device for heating the methane fermentation liquid.

[0004] As a method for stirring the methane fermentation liquid in the methane fermentation tank, there are stirring by an impeller type stirrer, stirring by a screw type stirrer, gas stirring for supplying a gas such as steam, and in addition, stirring by heat convection also exists (see, for example, Patent Document 1).

[0005] In Patent Document 1, a heating device is provided at the bottom of the methane fermentation tank, and the methane fermentation liquid is heated by the heating device to generate convection in the methane fermentation liquid and stir by heat convection.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In Patent Document 1, it is necessary to heat the entire anaerobic digestion liquid. As the anaerobic digestion tank becomes larger, it is necessary to install a large heating device corresponding to the volume of the anaerobic digestion liquid, which will lead to an increase in equipment costs and operating costs.

[0008] In addition, when a heating device is provided at the bottom of the anaerobic digestion tank, for example, when performing replacement work or maintenance work due to a failure of the device or the like, it is necessary to empty the anaerobic digestion tank once, which is a very laborious task.

[0009] In view of this actual situation, the main problem of the present invention is to provide an anaerobic digestion treatment method capable of generating convection in the anaerobic digestion liquid and stirring by heat convection without causing an increase in the size of the heating device, equipment costs, and operating costs, and an anaerobic digestion treatment facility.

Means for Solving the Problems

[0010] The first characteristic configuration of the present invention is in an anaerobic digestion treatment method for producing biogas by subjecting organic waste to anaerobic digestion in an anaerobic digestion tank, wherein the organic waste has a first organic waste and a second organic waste, a heating step of heating the second organic waste, a second supply step of supplying the second organic waste that has undergone the heating step to the lower side of the anaerobic digestion tank, and a first supply step of supplying the first organic waste that has not undergone the heating step to the anaerobic digestion tank at a location different from the second organic waste in the vertical direction.

[0011] According to this configuration, in the second supply step, since the second organic waste that has been heated through the heating step is supplied to the anaerobic digestion tank, the second organic waste can be heated and solubilized and then subjected to anaerobic digestion treatment in the anaerobic digestion tank, and the recovery efficiency of biogas can be increased.

[0012] When supplying the first organic waste and the second organic waste to the methane fermentation tank, in the second supply step, the second organic waste is supplied to the lower side of the methane fermentation tank, while in the first supply step, the first organic waste is supplied to a location in the methane fermentation tank that is different from the second organic waste in the vertical direction. As a result, in the methane fermentation tank, the second organic waste heated through the heating step exists on the lower side, and the first organic waste that has not been heated without going through the heating step exists at a location different from the lower side in the vertical direction. Therefore, a temperature distribution is generated in which the lower side is at a high temperature and other locations are at a low temperature in the vertical direction. Thus, since the movement of the methane fermentation liquid according to the temperature difference can occur, such as the high-temperature methane fermentation liquid moving from the lower side to the upper side, heat convection can be generated, and the methane fermentation liquid can be stirred by the heat convection.

[0013] In this way, it is only necessary to adjust the supply positions of the first organic waste and the second organic waste to the methane fermentation tank, so there is no need to newly install a heating device or the like, and the methane fermentation liquid can be stirred without causing an increase in the size of the methane fermentation tank, equipment costs, and operating costs.

[0014] The second characteristic configuration of the present invention lies in that, in the second supply step, the second organic waste is supplied from a plurality of locations on the lower side of the methane fermentation tank.

[0015] According to this configuration, since the second organic waste is supplied from a plurality of locations on the lower side of the methane fermentation tank, the second organic waste supplied from each of the plurality of locations moves from the lower side to the upper side. Therefore, heat convection can be generated over a wide range, and the methane fermentation liquid can be efficiently stirred.

[0016] The third characteristic configuration of the present invention lies in that, in the second supply step, the second organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank.

[0017] According to this configuration, since the second organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank, heat convection can be generated throughout the methane fermentation tank by the swirling flow, and the stirring of the methane fermentation liquid can be performed efficiently and effectively.

[0018] The fourth characteristic configuration of the present invention lies in that, in the first supply step, the first organic waste is supplied from a plurality of locations above the methane fermentation tank.

[0019] According to this configuration, since the first organic waste is supplied from each of a plurality of locations above the methane fermentation tank, it is possible to make the first organic waste that has not been heated without going through the heating process exist as a whole above the methane fermentation tank. Since the second organic waste heated through the heating process exists on the lower side of the methane fermentation tank, a clear temperature distribution with a high temperature on the lower side and a low temperature on the upper side of the methane fermentation tank is generated, heat convection is appropriately generated, and the stirring of the methane fermentation liquid can be appropriately performed.

[0020] The fifth characteristic configuration of the present invention lies in that, in the first supply step, the first organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank.

[0021] According to this configuration, since the first organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank, heat convection can be generated throughout the methane fermentation tank by the swirling flow, and the stirring of the methane fermentation liquid can be performed efficiently and effectively.

[0022] The sixth characteristic configuration of the present invention is that a second supply pipe for supplying the second organic waste to the methane fermentation tank is provided. The second supply pipe has a rising portion that rises to a height above the liquid level of the methane fermentation liquid in the methane fermentation tank and a descending portion that descends from the rising portion to the lower side of the methane fermentation tank and is connected to the methane fermentation tank. In the second supply step, the second organic waste is supplied to the lower side of the methane fermentation tank through the rising portion and the descending portion of the second supply pipe.

[0023] Since the methane fermentation tank stores the methane fermentation liquid, when the second organic waste is supplied to the lower side of the methane fermentation tank, the hydraulic pressure of the methane fermentation liquid acts on the supply location of the second organic waste to the methane fermentation tank. Therefore, simply connecting the second supply pipe to the lower side of the methane fermentation tank and supplying the second organic waste from the second supply pipe to the methane fermentation tank may cause the second organic waste to flow backward from the methane fermentation tank to the second supply pipe due to the hydraulic pressure of the methane fermentation liquid.

[0024] Therefore, according to this configuration, the second organic waste is supplied to the lower side of the methane fermentation tank through the ascending part and the descending part of the second supply pipe. Thereby, by raising the second organic waste to a height above the liquid level of the methane fermentation liquid in the methane fermentation tank at the ascending part, it is possible to supply the methane fermentation tank in a state where a pressure equivalent to the hydraulic pressure of the methane fermentation liquid is generated in the second organic waste. Therefore, it is possible to appropriately supply the second organic waste to the methane fermentation tank while preventing the second organic waste from flowing backward from the methane fermentation tank to the second supply pipe.

[0025] Moreover, as a configuration for preventing backflow, it is only necessary to provide the second supply pipe with an ascending part and a descending part, and backflow can be prevented while simplifying the configuration and reducing costs.

[0026] The seventh characteristic configuration of the present invention is in a methane fermentation treatment facility that produces biogas by subjecting organic waste to methane fermentation treatment in a methane fermentation tank, wherein the organic waste includes a first organic waste and a second organic waste, a heating unit for heating the second organic waste, a second supply unit for supplying the second organic waste that has passed through the heating unit to the lower side of the methane fermentation tank, and a first supply unit for supplying the first organic waste that has not passed through the heating unit to the methane fermentation tank at a location different from the second organic waste in the vertical direction.

[0027] According to this configuration, in the second supply unit, since the second organic waste heated through the heating unit is supplied to the methane fermentation tank, the second organic waste can be heated and solubilized and then subjected to methane fermentation treatment in the methane fermentation tank, and the recovery efficiency of biogas can be improved.

[0028] When supplying the first organic waste and the second organic waste to the methane fermentation tank, in the second supply unit, the second organic waste is supplied to the lower side of the methane fermentation tank, while in the first supply unit, the first organic waste is supplied to a location different from the second organic waste in the vertical direction in the methane fermentation tank. As a result, in the methane fermentation tank, the second organic waste heated through the heating unit exists on the lower side, and the first organic waste that has not been heated without passing through the heating unit exists at a location different from the lower side in the vertical direction. Therefore, a temperature distribution is generated in which the lower side is at a high temperature and other locations are at a low temperature in the vertical direction. Thus, the movement of the methane fermentation liquid according to the temperature difference, such as the high-temperature methane fermentation liquid moving from the lower side to the upper side, can be caused to generate heat convection, and the methane fermentation liquid can be stirred by the heat convection.

[0029] In this way, it is only necessary to adjust the supply positions of the first organic waste and the second organic waste to the methane fermentation tank, so there is no need to newly install a heating device or the like, and the methane fermentation liquid can be stirred without causing an increase in the size of the methane fermentation tank, equipment costs, and operating costs.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0031] Embodiments of the wastewater treatment facility to which the methane fermentation treatment method and the methane fermentation treatment facility according to the present invention are applied will be described with reference to the drawings.

[0032] 〔First Embodiment〕 This wastewater treatment facility 1 is a facility for treating organic wastewater such as sewage and drainage containing organic substances. As shown in FIG. 1, it is equipped with a sewage treatment system 2 and a sludge treatment system 3 (corresponding to a methane fermentation treatment facility) for methane fermentation treatment (anaerobic digestion treatment) of organic waste.

[0033] As shown in FIG. 1, the sewage treatment system 2 is equipped with a primary sedimentation tank 21, a biological treatment tank 22, and a final sedimentation tank 23 in the order of the flow direction of the raw water A1 of the organic wastewater. The raw water A1 first flows into the primary sedimentation tank 21, where floating substances and solids that are likely to precipitate are removed by sedimentation. Next, in the biological treatment tank 22, organic substances and other contaminants in the raw water A1 are decomposed and removed by the action of microorganisms. Finally, in the final sedimentation tank 23, activated sludge is sedimented, and the clarified supernatant water is discharged as treated water A2.

[0034] The raw sludge removed by sedimentation in the primary sedimentation tank 21 is sent as primary sedimentation sludge B1 to a first concentration device 24 (for example, a mechanical concentration device such as a screw concentrator, a centrifugal concentrator, or a flotation concentrator, or a gravity concentration device such as a gravity thickening tank) and concentrated to a solid concentration of about 2 to 10%. A part of the activated sludge removed by sedimentation in the final sedimentation tank 23 is returned to the biological treatment tank 22 as returned sludge B2, and the remaining excess sludge B3 is sent to a second concentration device 25 (for example, a mechanical concentration device such as a screw concentrator, a centrifugal concentrator, or a flotation concentrator) and concentrated to a solid concentration of about 2 to 10%.

[0035] The sludge treatment system 3 receives the organic wastes C1 and C2 from the sewage treatment system 2, and subjects the organic wastes C1 and C2 to methane fermentation treatment to produce methane gas. The organic wastes include a first organic waste C1 and a second organic waste C2 that is more difficult to decompose than the first organic waste C1. The sludge treatment system 3 receives the primary sedimentation sludge B1, which is the solid phase obtained by supplying the raw water A1 of the organic wastewater to the primary sedimentation tank 21 for solid-liquid separation, as the first organic waste C1, and receives a part of the excess sludge B3, which is the activated sludge obtained in the final sedimentation tank 23, as the second organic waste C2.

[0036] Thus, the organic waste from the sewage treatment system 2 is supplied to the sludge treatment system 3 in a state of being divided into the first organic waste C1 and the second organic waste C2. The volume ratio of the first organic waste C1 to the second organic waste C2 is not particularly limited and may be set as appropriate. For example, C1:C2 = 1.5:1, and it is preferable that the first organic waste C1 is more than the second organic waste C2.

[0037] The sludge treatment system 3 includes a methane fermentation tank 31, a first supply unit 41 having a first supply pipe 42 for supplying the first organic waste C1 to the methane fermentation tank 31, and a second supply unit 51 having a second supply pipe 52 for supplying the second organic waste C2 to the methane fermentation tank 31.

[0038] The second organic waste C2 is more difficult to decompose than the first organic waste C1. The reason is that the excess sludge B3, which is the second organic waste C2, contains a large amount of microorganisms, and these microorganisms have strong cell walls, and the organic matter inside the cells is surrounded by the cell walls.

[0039] Therefore, the first supply unit 41 supplies the first organic waste C1 that has not passed through the heating unit to the methane fermentation tank 31 through the first supply pipe 42, while the second supply unit 51 supplies the second organic waste C2 that has passed through the heating unit 57 to the methane fermentation tank 31 through the second supply pipe 52. Thereby, in the second supply unit 51, the second organic waste C2 is preheated and warmed in the heating unit 57 during the supply to the methane fermentation tank 31, so that the cell wall is broken and the internal organic matter flows out, making gasification in the methane fermentation tank 31 easier.

[0040] The first supply pipe 42 in the first supply unit 41 is arranged in a state of connecting the first concentration device 24 and the methane fermentation tank 31. In the middle part of the first supply pipe 42, a first supply pump 43, which is a pump P for transporting the first organic waste C1 to the methane fermentation tank 31, is provided. The first supply pump 43 is arranged at the most upstream part in the flow direction of the first organic waste C1 in the first supply pipe 42.

[0041] The second supply pipe 52 in the second supply unit 51 is arranged in a state of connecting the second concentration device 25 and the methane fermentation tank 31. In the middle part of the second supply pipe 52, a second supply pump 53, a thermostat 54, and a third supply pump 55 are provided in order from the upstream side in the flow direction of the second organic waste C2. A heating pipe 56 for supplying the second organic waste C2 from the third supply pump 55 in the second supply pipe 52 to the thermostat 54 is provided, and a heating part 57 is arranged in the middle part of the heating pipe 56.

[0042] The second supply pump 53 is a pump P for transporting the second organic waste C2 to the methane fermentation tank 31, and the third supply pump 55 is a pump P for supplying the second organic waste C2 to the heating part 57. The heating part 57 is composed of a heat exchange part that exchanges heat between a heating medium supplied from a heat source (not shown) and the second organic waste C2 to heat the second organic waste C2. The heating part 57 may be any device that can heat the second organic waste C2, and is not limited to the heat exchange part.

[0043] The thermostat 54 maintains and retains the temperature of the second organic waste C2 heated by the heating part 57. Here, the target temperature when heating the second organic waste C2 by the heating part 57 may be set to a value between, for example, 65°C and 75°C, or may be set within a range without setting to a single point temperature so that it is between, for example, 70°C and 75°C. Preferably, it is set to 70°C. Also, regarding the residence time in the thermostat 54, it may be set to a value between 20 minutes and 40 minutes, or may be set within a range without setting to a single point time so that it is between, for example, 30 minutes and 40 minutes. Preferably, it is set to 30 minutes.

[0044] In the methane fermentation tank 31, the first organic waste C1 supplied through the first supply pipe 42 and the second organic waste C2 supplied through the second supply pipe 52 are received, and methane fermentation treatment (anaerobic digestion treatment) is performed by the action of anaerobic bacteria such as acid-producing bacteria and methane-producing bacteria.

[0045] The methane fermentation tank 31 is formed in a cylindrical shape with a circular cross-section, for example, as shown in Fig. 2(B). Regarding the shape of the methane fermentation tank 31, for example, it can also be formed in a cylindrical shape with a polygonal cross-section, and various shapes can be applied.

[0046] As shown in Fig. 2(A), the methane fermentation tank 31 is provided with a stirrer 61 for stirring the methane fermentation liquid 32 in the methane fermentation tank 31, a heating device 71 for heating the methane fermentation liquid 32 in the methane fermentation tank 31, and a drawing device 81 for drawing out deposits and the like deposited in the methane fermentation tank 31.

[0047] As shown in Fig. 2(A), the stirrer 61 is disposed at the center of the methane fermentation tank 31 in a plan view. The stirrer 61 includes blades 62 rotatable around a vertical axis and a rotation drive device 63 such as a motor for rotationally driving the blades 62. Incidentally, the stirrer 61 shown in Fig. 2(A) is merely an example, and various other stirrers 61 can be applied.

[0048] As shown in Fig. 2(A), the heating device 71 includes a circulation path 72 for taking out the methane fermentation liquid 32 in the methane fermentation tank 31 to the outside and circulating it, a circulation pump 73 for circulating the methane fermentation liquid 32 in the circulation path 72, and a heat exchange section 74 for heat-exchanging the methane fermentation liquid 32 in the circulation path 72 with a heating medium. The heating device 71 circulates the methane fermentation liquid 32 through the circulation path 72 in a form of heating the methane fermentation liquid 32 in the heat exchange section 74 by operating the circulation pump 73, thereby heating the methane fermentation liquid 32.

[0049] In the methane fermentation tank 31, since it is generally considered that the temperature of the methane fermentation liquid 32 may decrease due to heat dissipation or the like, the temperature of the methane fermentation liquid 32 is maintained within a predetermined range of the appropriate temperature for methane fermentation by heating the methane fermentation liquid 32 with the heating device 71. The heating device 71 may be operated constantly, but it may also be operated as needed to heat the methane fermentation liquid 32 only when the temperature of the methane fermentation liquid 32 drops with respect to the predetermined range of the appropriate temperature.

[0050] As shown in Fig. 2(A), the extraction device 81 includes an extraction pipe 82 for extracting deposits and the like deposited in the methane fermentation tank 31, and an extraction pump 83 for extracting deposits and the like through the extraction pipe 82. The extraction pipe 82 is arranged such that a suction portion 84 for sucking deposits and the like deposited in the methane fermentation tank 31 is located near the bottom of the methane fermentation tank 31.

[0051] The extraction pipe 82 has a rising portion 82a that rises to a height above the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31, and a descending portion 82b that descends from the rising portion 82a to the lower side of the methane fermentation tank 31. The extraction pump 83 is arranged at a downstream portion of the extraction pipe 82 with respect to the descending portion 82b. A seal pot 85 for storing deposits and the like to be extracted is arranged at a portion having a height above the liquid level 33 of the methane fermentation liquid 32 between the rising portion 82a and the descending portion 82b in the extraction pipe 82 or at a portion straddling the height of the liquid level 33. Note that the extraction pump 83 is not an essential component, and the methane fermentation liquid 32, deposits, etc. may be discharged by extrusion through the seal pot 85 from the extraction pipe 82 generated by the supply of the first organic waste C1 and the second organic waste C2 to the methane fermentation tank 31 without installing the extraction pump 83.

[0052] In the methane fermentation tank 31, as shown in Fig. 2(A), the methane fermentation liquid 32 is stirred by providing a stirrer 61. In addition to the stirrer 61, a heat convection type stirring device 91 for stirring the methane fermentation liquid 32 by heat convection is provided. This heat convection type stirring device 91 adjusts the supply positions of the first organic waste C1 and the second organic waste C2 to the methane fermentation tank 31 to generate heat convection in the methane fermentation liquid 32 in the methane fermentation tank 31 and stir the methane fermentation liquid 32.

[0053] As shown in Fig. 2(A), in the first supply section 41, at the connection point between the first supply pipe 42 and the methane fermentation tank 31, a first ejection section 92 for ejecting the first organic waste C1 from the first supply pipe 42 into the methane fermentation tank 31 is provided. In the second supply section 51, at the connection point between the second supply pipe 52 and the methane fermentation tank 31, a second ejection section 93 for ejecting the second organic waste C2 from the second supply pipe 52 into the methane fermentation tank 31 is provided.

[0054] As shown in Fig. 2(A), the heat convection type stirring device 91 disposes the first ejection section 92 on the upper side of the methane fermentation tank 31 and supplies the first organic waste C1 to the upper side of the methane fermentation tank 31 at the first supply section 41, while disposing the second ejection section 93 on the lower side of the methane fermentation tank 31 and supplying the second organic waste C2 to the lower side of the methane fermentation tank 31 at the second supply section 51.

[0055] As a result, in the methane fermentation tank 31, the second organic waste C2 heated by the heating section 57 exists on the lower side, and the unheated first organic waste C1 exists on the upper side. Therefore, a temperature distribution is generated in the vertical direction where the lower side is at a high temperature and the upper side is at a low temperature. Thus, the movement of the methane fermentation liquid 32 according to the temperature difference, such as the high-temperature methane fermentation liquid 32 moving from the lower side to the upper side, generates heat convection and stirs the methane fermentation liquid 32.

[0056] Regarding the location where the second ejection part 93 is disposed, as shown in Fig. 2(A), for example, a range of a predetermined height from the bottom of the methane fermentation tank 31 can be defined as the lower side of the methane fermentation tank 31, and the second ejection part 93 can be disposed within this range. Regarding the predetermined height, it can be changed as appropriate, but at least the range below the central part of the methane fermentation tank 31 in the vertical direction can be defined as the lower side of the methane fermentation tank 31. The predetermined height from the bottom of the methane fermentation tank 31 can be, for example, in the range of H / 2 to H / 10, preferably H / 4 to H / 10, when the height of the methane fermentation tank 31 is H.

[0057] The second ejection part 93 is disposed below the blades 62 of the stirrer 61. As shown by the dotted line in Fig. 2(A), the second ejection part 93 is disposed above the suction part 84 of the extraction pipe 82 and the connection point of the circulation path 72, preventing the second organic waste C2 ejected from the second ejection part 93 from being directly drawn into the extraction pipe 82 from the suction part 84 or directly supplied to the circulation path 72.

[0058] In Fig. 2(A), the ejection direction of the first organic waste C1 in the vertical direction in the second ejection part 93 is set to be obliquely upward, but it can also be, for example, the horizontal direction, and the ejection direction can be changed as appropriate.

[0059] As shown in Fig. 2(B), a plurality of second ejection parts 93 are provided at intervals in the circumferential direction of the methane fermentation tank 31, and the second supply part 51 supplies the second organic waste C2 from each of the plurality of second ejection parts 93 into the methane fermentation tank 31. Incidentally, in Fig. 2(A), only some of the second ejection parts 93 are shown, and in Fig. 2(B), the stirrer 61 etc. are omitted to show the plurality of second ejection parts 93 at the center. The ejection direction in plan view of each of the plurality of second ejection parts 93 is set to be in the direction towards the circumferential direction of the methane fermentation tank 31. Thereby, the second supply part 51 supplies the second organic waste C2 from each of the plurality of second ejection parts 93 in a form that forms a swirling flow in the methane fermentation tank 31.

[0060] The timing of ejecting the second organic waste C2 from each of the plurality of second ejection parts 93 may be such that the ejection is simultaneous for all the second ejection parts 93, or the ejection may be at different timings. When ejecting at different timings, for example, the second organic waste C2 can be ejected one by one in order in the circumferential direction of the methane fermentation tank 31.

[0061] In this way, since the ejection direction in each of the plurality of second ejection parts 93 is a direction facing obliquely upward in the vertical direction and a direction facing the circumferential direction of the methane fermentation tank 31 in plan view, a spiral vortex flowing from the lower side to the upper side can be formed, heat convection can be generated throughout the methane fermentation tank 31, and the methane fermentation liquid 32 can be stirred efficiently and effectively.

[0062] Since the second supply pipe 52 supplies the second organic waste C2 to the lower side of the methane fermentation tank 31, as shown in Fig. 2(A), it has a rising part 52a that rises to a height above the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31, a descending part 52b that descends from the rising part 52a to the lower side of the methane fermentation tank 31 and is connected to the methane fermentation tank 31, and a connecting part 52c that connects the rising part 52a and the descending part 52b at a height above the liquid level 33 of the methane fermentation liquid 32.

[0063] Thereby, by raising the second organic waste C2 to a height above the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31 at the rising part 52a, it is possible to supply the second organic waste C2 to the methane fermentation tank 31 in a state where a pressure equivalent to the head pressure of the methane fermentation liquid 32 is generated in the second organic waste C2. Therefore, while preventing the second organic waste C2 from flowing backward from the methane fermentation tank 31 into the second supply pipe 52, the second organic waste C2 can be appropriately supplied to the methane fermentation tank 31.

[0064] When the second supply pipe 52 is full of liquid and the check valve or the like is not functioning, backflow of the second organic waste C2 may occur due to the siphon phenomenon. Therefore, it is preferable to provide a siphon breaker at an intermediate portion of the second supply pipe 52. Further, a check valve or the like can be additionally provided at an intermediate portion of the second supply pipe 52.

[0065] Regarding the location where the first ejection part 92 is disposed, as shown in Fig. 2(A), for example, a range at a predetermined distance from the upper end of the methane fermentation tank 31 can be defined as the upper side of the methane fermentation tank 31, and the first ejection part 92 can be disposed within that range. The predetermined distance can be changed as appropriate, but in the vertical direction, at least a range above the central part of the methane fermentation tank 31 can be defined as the upper side of the methane fermentation tank 31.

[0066] In Fig. 2(A), the first ejection part 92 is disposed below the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31. However, for example, as shown by the dotted line, the first ejection part 92 can also be disposed above the liquid level 33 of the methane fermentation liquid 32.

[0067] In Fig. 2(A), the ejection direction of the first organic waste C1 in the vertical direction at the first ejection part 92 is set to be in the diagonally downward direction. However, for example, it can also be in the horizontal direction, and the ejection direction can be changed as appropriate.

[0068] Similar to the second ejection part 93, as shown in Fig. 2(B), a plurality of first ejection parts 92 are provided at intervals in the circumferential direction of the methane fermentation tank 31, and the first supply part 41 supplies the first organic waste C1 from each of the plurality of first ejection parts 92 into the methane fermentation tank 31. In Fig. 2(B), since it is arranged in the same way as the second ejection part 93, the first ejection part 92 is shown in parentheses. The ejection direction of each of the plurality of first ejection parts 92 in plan view is set to be in the direction toward the circumferential direction of the methane fermentation tank 31. Thereby, the first supply part 41 supplies the first organic waste C1 from each of the plurality of first ejection parts 92 in a form that forms a swirling flow in the methane fermentation tank 31.

[0069] The timing of ejecting the first organic waste C1 from each of the plurality of first ejection parts 92 may be such that ejection is performed simultaneously at all the first ejection parts 92, or ejection may be performed at different timings. When ejecting at different timings, for example, the first organic waste C1 can be ejected one by one in order in the circumferential direction of the methane fermentation tank 31.

[0070] Regarding the relationship of the arrangement positions of the first ejection part 92 and the second ejection part 93, they can be arranged at the same position or at different positions in the circumferential direction of the methane fermentation tank 31. The first ejection part 92 and the second ejection part 93 can be set in the same direction in the circumferential direction of the methane fermentation tank 31 regarding the ejection direction in plan view, or conversely, they can be set in opposite directions in the circumferential direction of the methane fermentation tank 31.

[0071] As described above, in this embodiment, as a methane fermentation treatment method, in order to generate and stir heat convection in the methane fermentation liquid 32, the second organic waste C2 that has undergone the heating process in the heating part 57 is supplied to the lower side of the methane fermentation tank 31 in the second supply process, and the first organic waste C1 that has not undergone the heating process is supplied to the methane fermentation tank 31 at an upper position of the methane fermentation tank 31 that is different from the second organic waste C2 in the vertical direction in the first supply process.

[0072] In the first supply process, the first organic waste C1 is ejected from each of the plurality of first ejection parts 92 into the methane fermentation tank 31 to form a swirling flow in the methane fermentation liquid 32. Also in the second supply process, the second organic waste C2 is ejected from each of the plurality of second ejection parts 93 into the methane fermentation tank 31 to form a swirling flow in the methane fermentation liquid 32. In this way, in both the first supply process and the second supply process, a swirling flow is formed in the methane fermentation liquid 32 to generate heat convection throughout the methane fermentation tank 31, and the stirring of the methane fermentation liquid 32 is efficiently performed.

[0073] 〔Alternative Embodiment〕 Another embodiment of the present invention will be described. Note that the configurations of the embodiments described below are not limited to being applied individually, and can also be applied in combination with the configurations of other embodiments.

[0074] (1) In the above embodiment, the first organic waste C1 is used as the primary sludge B1, and the second organic waste C2, which is more difficult to decompose than the first organic waste C1, is used as the excess sludge B3. However, what the first organic waste and the second organic waste are can be changed as appropriate. For example, the first organic waste can be food waste such as vegetable scraps, and the second organic waste can be oxidation ditch sludge, woody and plant-based biomass such as thinned wood and rice straw.

[0075] (2) In the above embodiment, the heating pipe 56 is connected to the second supply pipe 52, and the heating part 57 is disposed at an intermediate part of the heating pipe 56. However, for example, the heating pipe 56 can be omitted, and at an intermediate part of the second supply pipe 52, the heating part 57 and the constant temperature bath 54 can be disposed in this order from the upstream side in the flow direction of the second organic waste C2. In this way, the heating part 57 only needs to be able to heat the second organic waste C2 flowing through the second supply pipe 52, and the installation location thereof can be changed as appropriate.

[0076] (3) In the above embodiment, the first supply part 41 supplies the first organic waste C1 above the methane fermentation tank 31 by the first ejection part 92. However, in the vertical direction, it only needs to be a location different from the second organic waste C2 supplied below the methane fermentation tank 31. For example, the first organic waste C1 can also be supplied to an intermediate part of the methane fermentation tank 31.

Explanation of Reference Numerals

[0077] 3 Sludge treatment system (methane fermentation treatment facility) 31 Methane fermentation tank 32 Methane fermentation liquid 33 Liquid level 41 First supply part 51 Second supply part 52 Second supply pipe 52a Rising part 52b descending part 57 heating part C1 first organic waste C2 second organic waste

Claims

1. In a methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, the organic waste includes a first organic waste and a second organic waste that is more difficult to decompose than the first organic waste, a heating step of heating the second organic waste, a second supply step of supplying the second organic waste that has undergone the heating step to the lower side of the methane fermentation tank, and a first supply step of supplying the first organic waste that has not undergone the heating step to the methane fermentation tank at a location different from the second organic waste in the vertical direction. A methane fermentation treatment method.

2. In a methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, the organic waste (excluding the organic waste after methane fermentation treatment that has been put into the methane fermentation tank and subjected to methane fermentation treatment) includes a first organic waste and a second organic waste, a heating step of heating the second organic waste, a second supply step of supplying the second organic waste that has undergone the heating step to the lower side of the methane fermentation tank, and a first supply step of supplying the first organic waste that has not undergone the heating step to the methane fermentation tank at a location different from the second organic waste in the vertical direction. A methane fermentation treatment method.

3. The methane fermentation treatment method according to claim 1 or 2, wherein in the second supply step, the second organic waste is supplied from a plurality of locations on the lower side of the methane fermentation tank.

4. The methane fermentation treatment method according to claim 3, wherein in the second supply step, the second organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank.

5. The methane fermentation treatment method according to claim 1 or 2, wherein in the first supply step, the first organic waste is supplied from a plurality of locations on the upper side of the methane fermentation tank.

6. The methane fermentation treatment method according to claim 5, wherein in the first supply step, the first organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank.

7. A second supply pipe for supplying the second organic waste to the methane fermentation tank is provided, the second supply pipe has a rising portion that rises to a height above the liquid level of the methane fermentation liquid in the methane fermentation tank, and a descending portion that descends from the rising portion to the lower side of the methane fermentation tank and is connected to the methane fermentation tank. The methane fermentation treatment method according to claim 1 or 2, wherein in the second supply step, the second organic waste is supplied to the lower side of the methane fermentation tank through the rising portion and the falling portion of the second supply pipe.

8. In a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, the organic waste includes a first organic waste and a second organic waste that is more difficult to decompose than the first organic waste, a heating unit that heats the second organic waste, a second supply unit that supplies the second organic waste that has passed through the heating unit to the lower side of the methane fermentation tank, a methane fermentation treatment facility including a first supply unit that supplies the first organic waste that has not passed through the heating unit to the methane fermentation tank at a location different from the second organic waste in the vertical direction.

9. In a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, the organic waste (excluding the organic waste after methane fermentation treatment that has been introduced into the methane fermentation tank and subjected to methane fermentation treatment) includes a first organic waste and a second organic waste, a heating unit that heats the second organic waste, a second supply unit that supplies the second organic waste that has passed through the heating unit to the lower side of the methane fermentation tank, a methane fermentation treatment facility including a first supply unit that supplies the first organic waste that has not passed through the heating unit to the methane fermentation tank at a location different from the second organic waste in the vertical direction.

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