Methane fermentation processing method, and methane fermentation processor

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 and a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation treatment. [Background technology]

[0002] For example, methane fermentation (anaerobic fermentation) is widely used to reduce the volume of organic waste such as sludge and biomass generated during wastewater treatment and to convert it into energy. Methane fermentation is a technology in which organic waste is stored for a certain period of time under anaerobic conditions, whereby the organic waste is decomposed by the action of anaerobic microorganisms to produce biogas such as methane gas and carbon dioxide, and is widely used in wastewater treatment facilities and wastewater treatment facilities in Japan.

[0003] A methane fermentation facility that performs methane fermentation is primarily equipped with a methane fermentation tank in which organic waste is stored and methane fermented, an agitator that agitates the methane fermentation liquid in the methane fermentation tank, and a heating device that heats the methane fermentation liquid.

[0004] Methods for stirring the methane fermentation liquid in a methane fermenter include stirring with an impeller-type stirrer, stirring with a screw-type stirrer, and gas stirring by supplying a gas such as water vapor. In addition, stirring by thermal convection also exists (see, for example, Patent Document 1).

[0005] In Patent Document 1, a heating device is provided at the bottom of a methane fermentation tank, and the methane fermentation liquid is heated by the heating device, thereby generating convection in the methane fermentation liquid and stirring the liquid by the thermal convection. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-159295 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the entire methane fermentation liquid needs to be heated, and as the methane fermentation tank becomes larger, a heating device with a large capacity corresponding to the volume of the methane fermentation liquid needs to be installed, resulting in increased equipment costs and operating costs.

[0008] Furthermore, when a heating device is provided at the bottom of a methane fermentation tank, for example, when replacement or maintenance work is to be performed due to equipment failure, the methane fermentation tank must be emptied once, which is a very time-consuming task.

[0009] In view of this situation, the main object of the present invention is to provide a methane fermentation treatment method and a methane fermentation treatment facility that can generate convection in a methane fermentation liquid and stir it by thermal convection without increasing the size of the heating device or increasing the equipment and operating costs. [Means for solving the problem]

[0010] The first characteristic configuration of the present invention is a methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation treatment in a methane fermentation tank, The organic waste 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 been subjected to the heating step to a lower side of the methane fermentation tank; The first organic waste, which has not been subjected to a heating step, is supplied to the methane fermentation tank at a position vertically different from that of the second organic waste.

[0011] According to this configuration, in the second supply process, the second organic waste heated through the heating process is supplied to the methane fermentation tank. Therefore, the second organic waste can be heated and solubilized before undergoing methane fermentation processing in the methane fermentation tank, thereby improving the efficiency of biogas recovery.

[0012] When the first organic waste and the second organic waste are supplied 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, whereas in the first supply step, the first organic waste is supplied to a different location in the methane fermentation tank from the second organic waste in the vertical direction. As a result, in the methane fermentation tank, the second organic waste that has been heated through the heating step is present on the lower side, and the first organic waste that has not been heated through the heating step is present in a different location in the vertical direction from the lower side, resulting in a temperature distribution in which the lower side is high temperature and other locations are low temperature in the vertical direction. Therefore, the methane fermentation liquid can be moved in accordance with the temperature difference, such as the high-temperature methane fermentation liquid moving from the lower side to the upper side, and thermal convection can be generated, and the methane fermentation liquid can be stirred by the thermal convection.

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

[0014] A second characteristic configuration of the present invention is that in the second supplying 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, the second organic waste is supplied from a plurality of locations on the lower side of the methane fermentation tank, so that the second organic waste supplied from each of the plurality of locations moves from the lower side to the upper side. This allows thermal convection to occur over a wide area, and therefore allows the methane fermentation liquid to be stirred efficiently.

[0016] A third characteristic configuration of the present invention is that in the second supplying 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, the second organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank, so that the swirling flow can generate thermal convection throughout the entire methane fermentation tank, allowing the methane fermentation liquid to be stirred efficiently and effectively.

[0018] A fourth characteristic configuration of the present invention is that in the first supplying step, the first organic waste is supplied from a plurality of locations on the upper side of the methane fermentation tank.

[0019] According to this configuration, the first organic waste is supplied from each of a plurality of locations on the upper side of the methane fermentation tank, so that the first organic waste that has not been heated through a heating process can be present entirely on the upper side of the methane fermentation tank. The second organic waste that has been heated through a heating process is present on the lower side of the methane fermentation tank, so that a clear temperature distribution is generated in which the lower side of the methane fermentation tank is high temperature and the upper side is low temperature, so that thermal convection is appropriately generated and the methane fermentation liquid can be appropriately stirred.

[0020] A fifth characteristic configuration of the present invention is that in the first supplying 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, the first organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank, so that the swirling flow can generate thermal convection throughout the entire methane fermentation tank, allowing the methane fermentation liquid to be stirred efficiently and effectively.

[0022] A sixth characteristic configuration of the present invention is a methane fermentation tank comprising a second supply pipe for supplying the second organic waste to the methane fermentation tank, the second supply pipe has an ascending portion that ascends to a height equal to or higher than the liquid level of the methane fermentation liquid in the methane fermentation tank, and a descending portion that descends from the ascending portion to a lower side of the methane fermentation tank and is connected to the methane fermentation tank, The second supply step is a step of supplying the second organic waste to a lower side of the methane fermentation tank through an ascending portion and a descending portion of the second supply pipe.

[0023] Since the methane fermentation tank stores a methane fermentation liquid, when the second organic waste is supplied to the lower side of the methane fermentation tank, the head pressure of the methane fermentation liquid is applied to the supply point 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 back from the methane fermentation tank to the second supply pipe due to the head 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 portion and the descending portion of the second supply pipe. As a result, the second organic waste is raised in the ascending portion to a height equal to or higher than the liquid level of the methane fermentation liquid in the methane fermentation tank, so that the second organic waste can be supplied to the methane fermentation tank in a state in which a pressure equivalent to the head pressure of the methane fermentation liquid is generated in the second organic waste. Therefore, the second organic waste can be appropriately supplied to the methane fermentation tank while preventing the second organic waste from flowing back from the methane fermentation tank to the second supply pipe.

[0025] Moreover, the configuration for preventing backflow only requires providing the second supply pipe with an ascending portion and a descending portion, which makes it possible to prevent backflow while simplifying the configuration and reducing costs.

[0026] A seventh characteristic configuration of the present invention is a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation treatment in a methane fermentation tank, The organic waste 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 a lower side of the methane fermentation tank; The methane fermentation tank further includes a first supply unit that supplies the first organic waste, which has not passed through a heating unit, to the methane fermentation tank at a position vertically different from that of the second organic waste.

[0027] According to this configuration, the second supply section supplies the second organic waste that has been heated through the heating section to the methane fermentation tank, so that the second organic waste can be heated and solubilized before undergoing methane fermentation processing in the methane fermentation tank, thereby improving the efficiency of biogas recovery.

[0028] When the first organic waste and the second organic waste are supplied to the methane fermentation tank, the second supply unit supplies the second organic waste to the lower side of the methane fermentation tank, whereas the first supply unit supplies the first organic waste to a different location in the methane fermentation tank 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 unit is present on the lower side, and the first organic waste not heated through the heating unit is present in a different location in the vertical direction from the lower side, resulting in a temperature distribution in which the lower side is high temperature and other locations are low temperature in the vertical direction. Therefore, the methane fermentation liquid can be moved in accordance with the temperature difference, such as the high-temperature methane fermentation liquid moving from the lower side to the upper side, and thermal convection can be generated, and the methane fermentation liquid can be stirred by the thermal convection.

[0029] In this way, since it is only necessary to adjust the supply positions of the first organic waste and the second organic waste to the methane fermentation tank, there is no need to install a new heating device or the like, and the methane fermentation liquid can be stirred without increasing the size of the methane fermentation tank or incurring high equipment costs or operating costs. [Brief description of the drawings]

[0030] [Figure 1] A diagram showing the overall configuration of a wastewater treatment facility. [Diagram 2] (A) is a side view showing the schematic configuration of a methane fermentation tank, and (B) is a plan view of the methane fermentation tank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wastewater treatment facility to which the methane fermentation treatment method and the methane fermentation treatment equipment 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 that treats organic wastewater such as sewage and wastewater containing organic matter, and as shown in Figure 1, it is equipped with a wastewater treatment system 2 and a sludge treatment system 3 (equivalent to a methane fermentation treatment facility) that subjects organic waste to methane fermentation treatment (anaerobic digestion treatment).

[0033] As shown in Figure 1, the wastewater treatment system 2 is equipped with a primary sedimentation basin 21, a biological treatment tank 22, and a final sedimentation basin 23 in the flow direction of raw organic wastewater water A1. The raw water A1 first flows into the primary sedimentation basin 21, where suspended matter and solids that tend to settle are settled and removed. Next, in the biological treatment tank 22, organic matter and other contaminants in the raw water A1 are decomposed and removed by the action of microorganisms. Finally, activated sludge is settled in the final sedimentation basin 23, and the clean supernatant water is discharged as treated water A2.

[0034] The raw sludge that has been settled and removed in the primary settling basin 21 is sent as primary settling sludge B1 to a first thickener 24 (e.g., a mechanical thickener such as a screw thickener, centrifugal thickener or flotation thickener, or a gravity thickener such as a gravity thickener tank) and is thickened, for example, to a solid concentration of about 2 to 10%. A portion of the activated sludge that has been settled and removed in the final settling basin 23 is returned to the biological treatment tank 22 as returned sludge B2, and the remaining excess sludge B3 is sent to a second thickener 25 (e.g., a mechanical thickener such as a screw thickener, centrifugal thickener or flotation thickener) and is thickened, for example, to a solid concentration of about 2 to 10%.

[0035] The sludge treatment system 3 receives the organic wastes C1 and C2 from the wastewater treatment system 2 and produces methane gas by subjecting the organic wastes C1 and C2 to methane fermentation. 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 first settling sludge B1, which is a solid phase obtained by supplying the raw organic wastewater A1 to a first settling basin 21 and performing solid-liquid separation, as the first organic waste C1, and receives excess sludge B3, which is a part of the activated sludge obtained in the final settling basin 23, as the second organic waste C2.

[0036] In this way, the organic waste from the wastewater treatment system 2 is supplied to the sludge treatment system 3 in a state in which it is separated 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 appropriately, but it is preferable to set it to, for example, C1:C2=1.5:1, so that the first organic waste C1 is greater than the second organic waste C2.

[0037] The sludge treatment system 3 includes a methane fermentation tank 31, a first supply section 41 having a first supply piping 42 that supplies the first organic waste C1 to the methane fermentation tank 31, and a second supply section 51 having a second supply piping 52 that supplies 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. This is because the excess sludge B3, which is the second organic waste C2, contains many microorganisms, and these microorganisms have strong cell walls, which surround the organic matter inside the cells.

[0039] Thus, 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, whereas 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. As a result, in the second supply unit 51, the second organic waste C2 is preheated in the heating unit 57 on the way to the methane fermentation tank 31, thereby destroying the cell walls and causing the organic matter inside to flow out, facilitating gasification in the methane fermentation tank 31.

[0040] The first supply pipe 42 in the first supply section 41 is disposed in a state in which it connects the first concentrator 24 and the methane fermentation tank 31. A first supply pump 43, which is a pump P that transports the first organic waste C1 to the methane fermentation tank 31, is provided at a midpoint of the first supply pipe 42. The first supply pump 43 is disposed at the most upstream position of the first supply pipe 42 in the flow direction of the first organic waste C1.

[0041] The second supply pipe 52 in the second supply section 51 is disposed in a state in which it connects the second concentrator 25 and the methane fermentation tank 31. A second supply pump 53, a thermostatic tank 54, and a third supply pump 55 are provided in this order from the upstream side in the flow direction of the second organic waste C2 at a midpoint of the second supply pipe 52. A heating pipe 56 is provided for supplying the second organic waste C2 from the third supply pump 55 of the second supply pipe 52 to the thermostatic tank 54, and a heating section 57 is disposed at a midpoint of the heating pipe 56.

[0042] The second supply pump 53 is a pump P that transports the second organic waste C2 to the methane fermentation tank 31, and the third supply pump 55 is a pump P that supplies the second organic waste C2 to a heating section 57. The heating section 57 is composed of a heat exchange section that heats the second organic waste C2 by exchanging heat between a heating medium supplied from a heat source not shown and the second organic waste C2. The heating section 57 is not limited to a heat exchange section as long as it can heat the second organic waste C2.

[0043] The thermostatic chamber 54 maintains the temperature of the second organic waste C2 heated by the heating unit 57 and retains it therein. The target temperature for heating the second organic waste C2 by the heating unit 57 may be set to a value between 65°C and 75°C, for example, or may be set within a range rather than a single point temperature, for example between 70°C and 75°C. Preferably, it is set to 70°C. The retention time in the thermostatic chamber 54 may be set to a value between 20 minutes and 40 minutes, or may be set within a range rather than a single point time, for example between 30 minutes and 40 minutes. Preferably, it is set to 30 minutes.

[0044] The methane fermentation tank 31 receives 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, and performs methane fermentation processing (anaerobic digestion processing) through the action of anaerobic bacteria such as acid-producing bacteria and methanogenic bacteria.

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

[0046] As shown in FIG. 2(A), the methane fermentation tank 31 is equipped with an agitator 61 for agitating 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 an extraction device 81 for extracting sediments and the like accumulated in the methane fermentation tank 31.

[0047] As shown in Fig. 2(A), the agitator 61 is disposed in the center of the methane fermentation tank 31 in plan view. The agitator 61 is equipped with blades 62 that can freely rotate about a vertical axis, and a rotation drive device 63 such as a motor that rotates the blades 62. Incidentally, the agitator 61 shown in Fig. 2(A) is merely an example, and various other types of agitators 61 can be applied.

[0048] 2(A), the heating device 71 is equipped with a circulation path 72 that takes out and circulates the methane fermentation liquid 32 in the methane fermentation tank 31 to the outside, a circulation pump 73 that circulates the methane fermentation liquid 32 in the circulation path 72, and a heat exchanger 74 that exchanges heat between the methane fermentation liquid 32 in the circulation path 72 and a heating medium. By operating the circulation pump 73, the heating device 71 circulates the methane fermentation liquid 32 through the circulation path 72 in a form in which the methane fermentation liquid 32 is heated in the heat exchanger 74, thereby heating the methane fermentation liquid 32.

[0049] In the methane fermentation tank 31, it is considered that the temperature of the methane fermentation liquid 32 will normally drop due to heat radiation, etc., so the temperature of the methane fermentation liquid 32 is maintained within a predetermined temperature range suitable for methane fermentation by heating the methane fermentation liquid 32 with a heating device 71. The heating device 71 may be operated at all times, but may also be operated as necessary to heat the methane fermentation liquid 32 only when the temperature of the methane fermentation liquid 32 drops below the predetermined suitable temperature range.

[0050] 2(A), the extraction device 81 is equipped with an extraction pipe 82 for extracting sediments and the like accumulated in the methane fermentation tank 31, and an extraction pump 83 for extracting the sediments and the like through the extraction pipe 82. The extraction pipe 82 is disposed so that a suction part 84 for sucking in the sediments and the like accumulated in the methane fermentation tank 31 is located near the bottom of the methane fermentation tank 31.

[0051] The withdrawal pipe 82 has an ascending portion 82a for ascending to a height equal to or higher than the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31, and a descending portion 82b for descending from the ascending portion 82a to the lower side of the methane fermentation tank 31. The withdrawal pump 83 is disposed in the withdrawal pipe 82 at a portion downstream of the descending portion 82b. A seal pot 85 for storing sediments and the like to be extracted is disposed in the withdrawal pipe 82 at a portion between the ascending portion 82a and the descending portion 82b that is equal to or higher than the liquid level 33 of the methane fermentation liquid 32 or at a portion that spans the height of the liquid level 33. The withdrawal pump 83 is not an essential component, and the methane fermentation liquid 32, sediments, and the like generated by supplying the first organic waste C1 and the second organic waste C2 to the methane fermentation tank 31 may be discharged by extrusion discharge from the withdrawal pipe 82 through the seal pot 85 without providing the withdrawal pump 83.

[0052] 2(A), the methane fermentation tank 31 is provided with an agitator 61 for agitating the methane fermentation liquid 32, but in addition to the agitator 61, a thermal convection type agitator 91 is provided for agitating the methane fermentation liquid 32 by thermal convection. This thermal convection type agitator 91 adjusts the supply positions of the first organic waste C1 and the second organic waste C2 relative to the methane fermentation tank 31 to generate thermal convection in the methane fermentation liquid 32 in the methane fermentation tank 31, thereby agitating the methane fermentation liquid 32.

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

[0054] As shown in Figure 2 (A), the thermal convection type mixing device 91 has a first jetting section 92 disposed above the methane fermentation tank 31 and supplies first organic waste C1 to the upper side of the methane fermentation tank 31 via a first supply section 41, while a second jetting section 93 is disposed below the methane fermentation tank 31 and supplies second organic waste C2 to the lower side of the methane fermentation tank 31 via a 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 is present on the lower side, and the unheated first organic waste C1 is present on the upper side, resulting in a temperature distribution in which the lower side is hotter and the upper side is colder in the vertical direction. Therefore, the methane fermentation liquid 32 moves in accordance with the temperature difference, such as when the high-temperature methane fermentation liquid 32 moves from the lower side to the upper side, generating thermal convection and stirring the methane fermentation liquid 32.

[0056] 2(A), the second ejection part 93 can be disposed within a range of a predetermined height from the bottom of the methane fermentation tank 31, which is defined as the lower side of the methane fermentation tank 31. The predetermined height can be changed as appropriate, but the lower side of the methane fermentation tank 31 can be defined as a range at least below the center of the methane fermentation tank 31 in the vertical direction. The predetermined height from the bottom of the methane fermentation tank 31 can be within a range of H / 2 to H / 10, preferably H / 4 to H / 10, where H is the height of the methane fermentation tank 31.

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

[0058] In Figure 2 (A), the vertical ejection direction of the first organic waste C1 from the second ejection section 93 is a direction facing diagonally upward, but it can also be a horizontal direction, for example, and the ejection direction can be changed as appropriate.

[0059] As shown in Fig. 2(B), a plurality of second jetting parts 93 are provided at intervals in the circumferential direction of the methane fermentation tank 31, and the second supplying part 51 supplies the second organic waste C2 from each of the plurality of second jetting parts 93 into the methane fermentation tank 31. Incidentally, Fig. 2(A) shows only some of the second jetting parts 93, and Fig. 2(B) omits the agitator 61 and the like in order to show the plurality of second jetting parts 93 at the center. Each of the plurality of second jetting parts 93 is set so that the jetting direction in a plan view faces the circumferential direction of the methane fermentation tank 31. As a result, the second supplying part 51 supplies the second organic waste C2 from each of the plurality of second jetting parts 93 in a form that forms a swirling flow in the methane fermentation tank 31.

[0060] The second organic waste C2 may be ejected from each of the multiple second ejection parts 93 simultaneously or at different times. When ejecting at different times, the second organic waste C2 may be ejected one by one in sequence around the circumference of the methane fermentation tank 31, for example.

[0061] In this way, the spray direction of each of the multiple second spray sections 93 is directed diagonally upward in the vertical direction and toward the circumferential direction of the methane fermentation tank 31 in a planar view, thereby forming a spiral vortex flow from the bottom to the top, generating thermal convection throughout the entire methane fermentation tank 31, and allowing the methane fermentation liquid 32 to be stirred efficiently and effectively.

[0062] The second supply pipe 52 supplies the second organic waste C2 to the lower side of the methane fermentation tank 31, and is provided with an ascending section 52a for ascending the waste to a height equal to or higher than the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31, a descending section 52b for descending from the ascending section 52a to the lower side of the methane fermentation tank 31 and connecting to the methane fermentation tank 31, and a connecting section 52c for connecting the ascending section 52a and the descending section 52b at a height equal to or higher than the liquid level 33 of the methane fermentation liquid 32, as shown in FIG. 2(A).

[0063] As a result, the second organic waste C2 is raised at the rising portion 52a to a height equal to or higher than the liquid level 33 of the methane fermentation liquid 32 in the methane fermentation tank 31, so that the second organic waste C2 can be supplied to the methane fermentation tank 31 while generating a pressure in the second organic waste C2 equivalent to the head pressure of the methane fermentation liquid 32. Therefore, the second organic waste C2 can be appropriately supplied to the methane fermentation tank 31 while preventing the second organic waste C2 from flowing back from the methane fermentation tank 31 to the second supply piping 52.

[0064] If the second supply pipe 52 is full and the check valve or the like is not functioning, there is a possibility that the second organic waste C2 will flow back due to the siphon effect, so it is preferable to provide a siphon breaker in a location along the second supply pipe 52. Also, a check valve or the like can be additionally provided in a location along the second supply pipe 52.

[0065] 2(A), the location of the first jetting part 92 may be, for example, a range a predetermined distance from the upper end of the methane fermentation tank 31 as the upper side of the methane fermentation tank 31, and the first jetting part 92 may be disposed in that range. The predetermined distance may be changed as appropriate, but the upper side of the methane fermentation tank 31 may be at least a range above the center of the methane fermentation tank 31 in the vertical direction.

[0066] In FIG. 2(A), the first jetting section 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 jetting section 92 can also be disposed above the liquid level 33 of the methane fermentation liquid 32.

[0067] In Figure 2 (A), the vertical ejection direction of the first organic waste C1 from the first ejection section 92 is a direction facing diagonally downward, but it can also be a horizontal direction, for example, and the ejection direction can be changed as appropriate.

[0068] As shown in Fig. 2(B), the first jetting parts 92 are provided in a plurality of locations spaced apart from each other in the circumferential direction of the methane fermentation tank 31, similar to the second jetting parts 93, and the first supplying part 41 supplies the first organic waste C1 from each of the plurality of first jetting parts 92 into the methane fermentation tank 31. In Fig. 2(B), the first jetting parts 92 are shown in parentheses because they are arranged in the same manner as the second jetting parts 93. Each of the plurality of first jetting parts 92 is set so that the jetting direction in a plan view is directed toward the circumferential direction of the methane fermentation tank 31. As a result, the first supplying part 41 supplies the first organic waste C1 from each of the plurality of first jetting parts 92 in a form that forms a swirling flow in the methane fermentation tank 31.

[0069] The first organic waste C1 may be ejected from each of the multiple first ejection parts 92 simultaneously or at different times. When the first organic waste C1 is ejected at different times, for example, the first organic waste C1 may be ejected one by one in sequence in the circumferential direction of the methane fermentation tank 31.

[0070] The first and second jetting parts 92 and 93 may be disposed at the same or different positions in the circumferential direction of the methane fermentation tank 31. The first and second jetting parts 92 and 93 may be set in the same circumferential direction of the methane fermentation tank 31 in terms of the jetting direction in a plan view, or may be set in opposite directions in the circumferential direction of the methane fermentation tank 31.

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

[0072] In the first supply step, the first organic waste C1 is ejected from each of the multiple first ejection parts 92 into the methane fermentation tank 31, forming a swirling flow in the methane fermentation liquid 32. In the second supply step, the second organic waste C2 is ejected from each of the multiple second ejection parts 93 into the methane fermentation tank 31, forming a swirling flow in the methane fermentation liquid 32. In this way, in both the first supply step and the second supply step, a swirling flow is formed in the methane fermentation liquid 32, generating thermal convection throughout the entire methane fermentation tank 31, and efficiently stirring the methane fermentation liquid 32.

[0073] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied alone, but may also be applied in combination with the configurations of other embodiments.

[0074] (1) In the above embodiment, the first organic waste C1 is the primary settling sludge B1, and the second organic waste C2, which is more difficult to decompose than the first organic waste C1, is the excess sludge B3. However, the first organic waste and the second organic waste can be changed as appropriate. For example, the first organic waste can be food waste such as deli scraps, and the second organic waste can be oxidation ditch sludge or woody or plant biomass such as thinning materials or rice straw.

[0075] (2) In the above embodiment, the heating pipe 56 is connected to the second supply pipe 52, and the heating unit 57 is disposed in a portion of the heating pipe 56, but, for example, the heating pipe 56 may be omitted, and the heating unit 57 and the thermostatic bath 54 may be disposed in this order from the upstream side in the flow direction of the second organic waste C2 in a portion of the second supply pipe 52. In this way, the heating unit 57 may be any unit capable of heating the second organic waste C2 flowing through the second supply pipe 52, and its location may be changed as appropriate.

[0076] (3) In the above embodiment, the first supply unit 41 supplies the first organic waste C1 to the upper side of the methane fermentation tank 31 by the first jetting unit 92, but it is sufficient if the first organic waste C1 is supplied to a location different in the vertical direction from the second organic waste C2 supplied to the lower side of the methane fermentation tank 31. For example, the first organic waste C1 can be supplied to the middle part of the methane fermentation tank 31. [Explanation of symbols]

[0077] 3 Sludge treatment system (methane fermentation treatment facility) 31 Methane fermentation tank 32 Methane fermentation liquid 33 Liquid level 41 1st supply section 51 2nd supply section 52 2nd supply piping 52a Ascending section 52b Descending part 57 Heating section C1 First organic waste C2 Secondary organic waste

Claims

1. A methane fermentation method for producing biogas by subjecting organic waste to methane fermentation in a methane fermenter, comprising the steps of: The organic waste 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 been subjected to the heating step to a lower side of the methane fermentation tank; a first supplying step of supplying the first organic waste, which has not been subjected to a heating step, to the methane fermentation tank at a position vertically different from that of the second organic waste.

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

3. 3. The methane fermentation treatment method according to claim 2, wherein in the second supplying step, the second organic waste is supplied in a form that forms a swirling flow in the methane fermentation tank.

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

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

6. A second supply pipe is provided to supply the second organic waste to the methane fermentation tank; the second supply pipe has an ascending portion that ascends to a height equal to or higher than the liquid level of the methane fermentation liquid in the methane fermentation tank, and a descending portion that descends from the ascending portion to a lower side of the methane fermentation tank and is connected to the methane fermentation tank, 2. The methane fermentation treatment method according to claim 1, wherein in the second supply step, the second organic waste is supplied to a lower side of the methane fermentation tank through an ascending portion and a descending portion of the second supply pipe.

7. In a methane fermentation treatment facility that produces 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, 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 a lower side of the methane fermentation tank; a first supply section that supplies the first organic waste, which has not passed through a heating section, to the methane fermentation tank at a different position in the vertical direction from that of the second organic waste, said methane fermentation treatment equipment comprising:

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