Methane fermentation processing method, and methane fermentation processor

Abstract

To prevent blockage of a piping by removing components that causes blockage in the piping for supplying organic wastes into a methane fermentation tank, without causing complexity of equipment constitution and cost increase.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 first supply process to supply the first organic waste C1 which has not undergone the heating process to the methane fermentation tank 31, a second supply process to supply the second organic waste C2 which has undergone the heating process to the methane fermentation tank 31, and a third supply process to supply the second organic waste C2 which has undergone the heating process into the first supply piping 42 that supplies the first organic waste C1 to the methane fermentation tank 31.SELECTED DRAWING: Figure 1

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] For example, when primary sludge from sewage sludge is subjected to methane fermentation, components that cause blockages in the pipes, such as calcium stearate, may accumulate in the pipes that supply the primary sludge to the methane fermentation tank, causing blockages in the pipes. Therefore, a method for cleaning the inside of the pipes when blockages occur has been known (see, for example, Patent Documents 1 and 2).

[0005] In Patent Document 1, the inside of the pipe is cleaned by supplying a cleaning liquid such as a strong acid such as hydrochloric acid or a solvent mixed with methanol and chloroform into the pipe. In Patent Document 2, a coagulation settling device is provided that separates the water to be treated into sludge and treated water, and the inside of the pipe is cleaned by extracting the fluid from the coagulation settling device and supplying the extracted fluid as cleaning water to the pipe through which the sludge flows. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-213990 A [Patent Document 2] JP 2019-063764 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the cleaning liquid is supplied into the piping by providing a storage and supply facility such as a cleaning liquid storage section, a cleaning liquid supply line, a delivery pump, and a valve body, and therefore the storage and supply facility must be provided, which leads to a complication of the facility configuration and an increase in costs. In addition, when the cleaning liquid is a strong acid, it is necessary to take measures to prevent it from having a negative impact on the environment, which may also lead to a complication of the facility configuration and an increase in costs.

[0008] In Patent Document 2, the water to be treated is limited to water that has good separation properties for decomposing into sludge and treated water, and it may not be applicable to the case where primary settling sludge is subjected to methane fermentation treatment. Also, when the temperature of the fluid extracted from the coagulation settling device is, for example, around room temperature, simply supplying the fluid into the piping may not remove the components that cause blockage.

[0009] In view of this situation, a main object of the present invention is to provide a methane fermentation treatment method and a methane fermentation treatment facility that can remove components that cause blockages in the piping that supplies organic waste to a methane fermentation tank, thereby preventing blockage of the piping, without complicating the equipment configuration or increasing costs. [Means for solving the problem]

[0010] A 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, comprising: The organic waste includes a first organic waste and a second organic waste, a heating step of heating the second organic waste; a first supply step of supplying the first organic waste that has not been subjected to a heating step to the methane fermentation tank; a second supply step of supplying the second organic waste that has been subjected to the heating step to the methane fermentation tank; The second organic waste that has been subjected to the heating step is supplied into a first supply pipe that supplies the first organic waste to the methane fermentation tank.

[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] In the third supply process, the first supply piping is originally supplied with the second organic waste to be supplied to the methane fermentation tank, so there is no need to newly install storage and supply equipment, such as a cleaning liquid, for storing a cleaning liquid and supplying it to the first supply piping, and the first supply piping can be cleaned without complicating the equipment configuration or increasing costs.

[0013] Moreover, in the third supply step, the second organic waste heated in the heating step is supplied into the first supply pipe, so that the components that cause clogging can be melted by the heated second organic waste. Therefore, the components that cause clogging can be appropriately removed, and clogging of the first supply pipe can be prevented.

[0014] A second characteristic configuration of the present invention is that in the third supply process, the second organic waste is supplied to the first supply piping in a form in which the second organic waste is circulated in the flow direction of the first organic waste in the first supply piping.

[0015] According to this configuration, the second organic waste is circulated in the same direction as the first organic waste in the first supply pipe, so that the second organic waste only needs to be circulated in the first supply pipe in the same manner as the first organic waste. Therefore, the equipment for circulating the first organic waste can be used as is, and the equipment configuration can be simplified and costs can be reduced.

[0016] A third characteristic configuration of the present invention is that in the third supply process, the second organic waste is supplied to the first supply piping in a form in which the second organic waste is circulated in a direction opposite to the flow direction of the first organic waste in the first supply piping.

[0017] According to this configuration, the second organic waste is circulated in the opposite direction to the flow direction of the first organic waste in the first supply piping. Therefore, even if a component that causes blockage is generated in the upstream portion of the first supply piping, the second organic waste can be circulated to the location where the component is generated, and the component can be appropriately removed.

[0018] In a fourth characteristic configuration of the present invention, in the first supply step, the water to be treated is supplied to a first settling tank, and the first organic waste, which is a solid phase obtained by performing solid-liquid separation, is supplied to the methane fermentation tank; The third supply step is a step of supplying the second organic waste that has circulated through the first supply pipe to the primary sedimentation tank.

[0019] According to this configuration, since a primary settling basin is provided to supply the first organic waste to the methane fermentation tank, the second organic waste that has circulated through the first supply pipe is supplied to the primary settling basin that is originally provided. This eliminates the need to provide new equipment for disposing of the second organic waste that has circulated through the first supply pipe, making it possible to simplify the equipment configuration and reduce costs, and also making it possible to use the second organic waste supplied to the primary settling basin as a raw material for methane fermentation.

[0020] A fifth characteristic configuration of the present invention lies in that the third supplying step is executed every time a set time elapses.

[0021] According to this configuration, the third supply process is executed every time the set time elapses, so that the first supply piping is repeatedly cleaned to prevent accumulation of components that cause blockage, thereby making it possible to appropriately prevent blockage of the first supply piping.

[0022] A sixth characteristic configuration of the present invention is a first supply device for supplying the first organic waste to the methane fermentation tank, The third supply process execution timing determination process is performed to determine the execution timing of the third supply process based on the operating state of the first supply device, the flow rate of the first organic waste in the first supply piping, or the pressure inside the piping.

[0023] If a small amount of clogging occurs during the process of supplying the first organic waste to the methane fermentation tank, the operating state of the first supply device will change, the flow rate of the first organic waste will decrease, and the pressure in the first supply piping will increase, resulting in changes in the flow rate and pressure in the piping.

[0024] Therefore, according to this configuration, in the third supply step execution timing determination step, the execution timing for executing the third supply step is determined based on the operating state of the first supply device, the flow rate of the first organic waste in the first supply piping, or the internal pressure of the first supply piping. This allows the third supply step to be executed at an appropriate timing, so that the third supply step is not executed unnecessarily and clogging of the first supply piping can be appropriately prevented.

[0025] 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 first supply unit having at least a first supply pipe for supplying the first organic waste that has not passed through a heating unit to the methane fermentation tank; A second supply unit having at least a second supply pipe that supplies the second organic waste that has passed through the heating unit to the methane fermentation tank; and a third supply unit having at least a third supply pipe that supplies the second organic waste that has passed through the heating unit from inside the second supply pipe to inside the first supply pipe.

[0026] 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.

[0027] In the third supply section, the first supply piping is originally supplied with the second organic waste to be supplied to the methane fermentation tank, so there is no need to newly install storage and supply equipment, such as a cleaning liquid, for storing a cleaning liquid and supplying it to the first supply piping, and the first supply piping can be cleaned without complicating the equipment configuration or increasing costs.

[0028] Moreover, since the third supply section supplies the second organic waste heated through the heating section into the first supply pipe, the components that cause blockages can be melted by the heated second organic waste, making it possible to properly remove the components that cause blockages and prevent blockages in the first supply pipe. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a wastewater treatment facility according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing a schematic configuration of a wastewater treatment facility according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] 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.

[0031] [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).

[0032] The wastewater treatment system 2 is equipped with, in the order of the flow direction of raw organic wastewater water A1, a primary sedimentation basin 21, a biological treatment tank 22, and a final sedimentation basin 23. 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.

[0033] 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%.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 (corresponding to a first supply device), 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 treatment (anaerobic digestion treatment) by the action of anaerobic bacteria such as acid-producing bacteria and methanogens. Although not shown, the methane fermentation tank 31 is equipped with a heating device that heats the methane fermentation liquid in the methane fermentation tank 31, an agitator that agitates the methane fermentation liquid in the methane fermentation tank 31, and the like. A heat insulating material or the like can be provided on the outer wall portion of the methane fermentation tank 31 to prevent a drop in the temperature of the methane fermentation liquid in the methane fermentation tank 31.

[0044] Regarding the predetermined optimum temperature range for methane fermentation processing in the methane fermentation tank 31, when performing methane fermentation processing at a medium temperature, the predetermined optimum temperature range can be set, for example, to a temperature range of 30°C to 45°C, and when performing methane fermentation processing at a high temperature, the predetermined optimum temperature range can be set, for example, to a temperature range of 50°C to 60°C.

[0045] In the methane fermentation treatment method, the first organic waste C1 is supplied to the methane fermentation tank 31 without undergoing a heating process in the first supply unit 41. In contrast, the second organic waste C2 is supplied to the methane fermentation tank 31 in the second supply unit 51. The second organic waste C2 is preheated to break the cell walls and allow the organic matter inside to flow out, solubilizing the second organic waste C2. Therefore, the second organic waste C2, which is more difficult to decompose than the first organic waste C1, can be solubilized and then subjected to methane fermentation treatment in the methane fermentation tank 31, improving the efficiency of biogas recovery.

[0046] The primary sludge B1, which is the first organic waste C1, contains components such as calcium stearate that can cause blockages in pipes. Therefore, in the first supply pipe 42 that supplies the first organic waste C1 to the methane fermentation tank 31, components such as calcium stearate may accumulate, causing blockages in the pipes.

[0047] Therefore, a cleaning configuration is provided for cleaning the first supply pipe 42. This cleaning configuration will be described below.

[0048] As shown in FIG. 1, the second organic waste C2 that has passed through the heating section 57 is not only supplied to the methane fermentation tank 31 via the second supply piping 52, but a third supply section 61 is also provided which has a first direction third supply piping 62 (corresponding to the third supply piping) that supplies the second organic waste C2 that has passed through the heating section 57 from inside the second supply piping 52 to inside the first supply piping 42.

[0049] The first-direction third supply piping 62 is disposed so as to connect a portion of the second supply piping 52 between the third supply pump 55 and the methane fermentation tank 31 and a portion of the first supply piping 42 corresponding to the upstream end, such as near the first supply pump 43. A first on-off valve 63 is disposed in a midway portion of the first-direction third supply piping 62, for interrupting the flow of the second organic waste C2 through the first-direction third supply piping 62.

[0050] As shown in FIG. 1(A), by performing the first supply step, heating step, and second supply step with the first on-off valve 63 in a closed state, the first organic waste C1 is supplied to the methane fermentation tank 31 via the first supply piping 42, and the second organic waste C2 is supplied to the methane fermentation tank 31 via the second supply piping 52, as shown by the thick lines in FIG. 1(A), and methane fermentation processing is carried out in the methane fermentation tank 31.

[0051] 1(B), the heating step is continued, the first on-off valve 63 is opened, and a third supply step is performed in which the second organic waste C2 heated through the heating step is supplied from the second supply pipe 52 to the first supply pipe 42 in the first-direction third supply pipe 62 of the third supply unit 61. In this third supply step, the second organic waste C2 is supplied to the first supply pipe 42 in the first-direction third supply pipe 62 to a portion corresponding to the upstream end of the first supply pipe 42, so that the second organic waste C2 is supplied to the first supply pipe 42 in a form in which the flow direction of the first organic waste C1 in the first supply pipe 42 is defined as a first direction and the second organic waste C2 flows in the first direction.

[0052] By carrying out this third supply step, even if components that cause clogging remain in the first supply pipe 42, the second organic waste C2 heated by the heating unit 57 can be supplied from the second supply pipe 52 to the first supply pipe 42 as shown by the thick line in Fig. 1 (B), and the components that cause clogging can be melted and removed in the heated second organic waste C2. Since the connection point of the first direction third supply pipe 62 in the first supply pipe 42 corresponds to the upstream end, the second organic waste C2 supplied to the upstream end is passed to the methane fermentation tank 31 in the same manner as the first organic waste C1. Therefore, the components that cause clogging can be removed over substantially the entire length of the first supply pipe 42, and clogging of the pipe can be prevented.

[0053] In the sludge treatment system 3, normally, the first supply process, the heating process, and the second supply process are carried out with the first on-off valve 63 in a closed state, as shown in Figure 1 (A), and at a timing when it is preferable to clean the first supply piping 42, the first on-off valve 63 is switched to an open state, as shown in Figure 1 (B), to carry out the third supply process.

[0054] For example, the third supply step is executed every time the set time elapses, for example, once a day, once every two days, etc. In this case, the set time can be set not only to a fixed time, but also to different times according to various conditions. For example, since the flow rate of the first organic waste C1, which is the primary settling sludge B1, varies depending on the inflow amount of the raw organic wastewater A1 flowing into the primary settling tank 21 of the wastewater treatment system 2, the set time can be changed and set depending on the inflow amount of the raw organic wastewater A1. For example, the set time can be changed and set sequentially, such as 2 hours, 8 hours, 2 hours, 12 hours, etc., in a form in which the set time is shortened as the inflow amount of the raw organic wastewater A1 increases.

[0055] Furthermore, in winter and the like, the temperature of the first organic waste C1 also drops with the drop in the outside air temperature, making it easier for components that cause blockage to remain. Therefore, the set time can be changed according to the season, for example, by setting the set time shorter in winter and longer in summer and the like. Since it is considered that the drop in temperature of the first organic waste C1 makes the piping more likely to become clogged, for example, by providing a heat insulating material around the first supply piping 42, the drop in temperature of the first organic waste C1 can be suppressed.

[0056] Furthermore, a third step execution timing determination step can be performed to determine the execution timing for the third supply step based on various conditions, rather than using time. If some clogging occurs during the process of supplying the first organic waste C1 to the methane fermentation tank 31, the discharge pressure of the first supply pump 43 will decrease and the operating state will change, and the flow rate of the first organic waste C1 will decrease and the pressure inside the first supply piping 42 will increase, causing changes in the flow rate and pressure inside the piping.

[0057] Therefore, in the third supply process execution timing determination process, the execution timing for executing the third supply process is determined based on the operating state of the first supply pump 43, the flow rate of the first organic waste C1 in the first supply piping 42, or the internal pressure of the first supply piping 42.

[0058] The operating state of the first supply pump 43 can be acquired, for example, by a management device or a control device of the sludge treatment system 3 or the like acquiring various information from the first supply pump 43. For example, when the management device or the control device detects a predetermined change state, such as a decrease in the discharge pressure, based on the acquired operating state of the first supply pump 43, it can determine that it is time to execute the third supply process.

[0059] Here, the first supply pump 43 can be omitted, and an automatic valve (corresponding to a first supply device) can be provided upstream of the first supply piping 42, and the opening of the automatic valve can be adjusted using the conveying force of a pump attached to the primary settling tank 21 or the like, thereby supplying the first organic waste C1 to the methane fermentation tank 31 through the first supply piping 42. In this case, the opening state of the automatic valve changes depending on the degree of clogging during the process of supplying the first organic waste C1 to the methane fermentation tank 31. Therefore, in the third supply step execution timing determination step, the opening state of the automatic valve is acquired instead of the operating state of the first supply pump 43, thereby making it possible to determine the execution timing for the third supply step.

[0060] The flow rate of the first organic waste C1 in the first supply pipe 42 can be acquired by, for example, installing a flow meter or the like in the first supply pipe 42 and having a management device or control device acquire detection information from the flow meter, thereby acquiring the flow rate of the first organic waste C1. For example, when the acquired flow rate of the first organic waste C1 by the management device or control device falls below a set flow rate, it can be determined that it is time to execute the third supply process. For example, the set flow rate can be set to 0.8 times that of normal operation, and normal operation is defined as a state in which there is no excessive or insufficient inflow of the material to be treated and the supply device is operating at a rated rate. In this case, the stop condition for the third supply process can be set to a state in which the flow rate of the first organic waste C1 is equivalent to that of normal operation.

[0061] The internal pressure of the first supply pipe 42 can be acquired by installing a pressure gauge or the like in the first supply pipe 42 and having a management device or control device acquire information detected by the pressure gauge. For example, when the acquired internal pressure of the first supply pipe 42 rises to or above a set pressure, the management device or control device can determine that it is time to execute the third supply process. For example, the set pressure can be set to 1.3 times the pressure during normal operation. In this case, the stop condition for the third supply process can be set to the pressure during normal operation being equal to the pressure during normal operation in the first supply pipe 42.

[0062] In this way, by performing the third supply process execution timing determination process, when it is determined that it is the timing to execute the third supply process, the management device or control device can switch the first opening / closing valve 63 to an open state to automatically perform the third supply process.

[0063] Regarding the third supply process, when the stop condition is satisfied, the third supply process is stopped, and the first opening / closing valve 63 is switched to a closed state as shown in FIG. 1(A), so that the first supply process, the heating process, and the second supply process can be performed.

[0064] The stop condition can be set, for example, based on the elapsed time from the start of the third supply step. The stop condition can also be set such that the operating state of the first supply pump 43 is free from a state in which the discharge pressure drops, the flow rate of the first organic waste C1 in the first supply pipe 42 is restored to a flow rate higher than the set flow rate, the internal pressure of the first supply pipe 42 is restored to a pressure lower than the set pressure, etc. In this way, various conditions that can be used to determine that the blockage of the first supply pipe 42 has been cleared can be set as the stop condition.

[0065] In Fig. 1(B), the first on-off valve 63 is provided only on the first-direction third supply pipe 62, and no on-off valve is provided on the second supply pipe 52 at a location downstream of the connection point of the first-direction third supply pipe 62. Thus, a portion of the second organic waste C2 in the second supply pipe 52 is supplied to the first supply pipe 42 by the first-direction third supply pipe 62, and although the thick line is omitted in Fig. 1(B), the remaining portion of the second organic waste C2 flows directly through the second supply pipe 52 and is supplied to the methane fermentation tank 31.

[0066] In FIG. 1(B), an on-off valve is also provided in the second supply pipe 52 at a downstream side of the connection point of the third supply pipe 62 for the first direction, and in the third supply step, the on-off valve is closed, so that the entire amount of the second organic waste C2 in the second supply pipe 52 can be supplied to the first supply pipe 42 via the third supply pipe 62 for the first direction.

[0067] 1(B) shows a case where the third supply step is performed by stopping the operation of the first supply pump 43 to stop the first supply step and then performing the third supply step. However, the third supply step can also be performed while continuing the operation of the first supply pump 43 to continue the first supply step. In this case, the first organic waste C1 and the second organic waste C2 are mixed in the first supply piping 42, and the mixture is supplied to the methane fermentation tank 31.

[0068] Second Embodiment This second embodiment is an embodiment in which the flow direction of the second organic waste C2 in the third supply step is different from that of the first embodiment. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted.

[0069] In the first embodiment, as shown by the thick line in Figure 1 (B), in the third supply process, the second organic waste C2 is supplied to a portion of the first direction third supply pipe 62 corresponding to the upstream end of the first supply pipe 42, so that the flow direction of the first organic waste C1 in the first supply pipe 42 is defined as the first direction, and the second organic waste C2 is supplied to the first supply pipe 42 in a form in which the second organic waste C2 flows in the first direction.

[0070] In contrast, in the second embodiment, as shown by the thick line in Figure 2 (B), in the third supply process, the second organic waste C2 is supplied to a portion corresponding to the downstream end of the first supply pipe 42 via a third supply pipe 64 for the second direction (corresponding to the third supply pipe), so that the second organic waste C2 is supplied to the first supply pipe 42 in a form in which the second direction is opposite to the flow direction of the first organic waste C1 in the first supply pipe 42 and the second organic waste C2 flows in the second direction.

[0071] 2, the second-direction third supply pipe 64 in the second embodiment replaces the first-direction third supply pipe 62 in the first embodiment, and is disposed so as to connect a portion of the second supply pipe 52 between the third supply pump 55 and the methane fermenter 31 and a portion corresponding to the downstream end of the first supply pipe 42. A second on-off valve 65 for interrupting the flow of the second organic waste C2 through the second-direction third supply pipe 64 is disposed in a midway portion of the second-direction third supply pipe 64.

[0072] As shown in FIG. 2(A), by performing the first supply step, heating step, and second supply step with the second on-off valve 65 in a closed state, the first organic waste C1 is supplied to the methane fermentation tank 31 via the first supply piping 42, and the second organic waste C2 is supplied to the methane fermentation tank 31 via the second supply piping 52, as shown by the thick lines in FIG. 2(A), and methane fermentation processing is carried out in the methane fermentation tank 31.

[0073] 2(B), the heating step is continued, the second on-off valve 65 is opened, and a third supply step is performed in which the second organic waste C2 heated through the heating step in the second-direction third supply pipe 64 of the third supply unit 61 is supplied from inside the second supply pipe 52 to the first supply pipe 42. In this third supply step, the second organic waste C2 is supplied to the first supply pipe 42 in the second-direction third supply pipe 64 to a portion corresponding to the downstream end of the first supply pipe 42, so that the second organic waste C2 is supplied to the first supply pipe 42 in a form in which the second direction is opposite to the flow direction of the first organic waste C1 in the first supply pipe 42 and the second organic waste C2 flows in the second direction.

[0074] Since the connection point of the first supply pipe 42 to the second-direction third supply pipe 64 corresponds to the downstream end, the second organic waste C2 supplied to the downstream end is circulated in the second direction over substantially the entire length of the first supply pipe 42. Therefore, components that cause clogging can be removed over substantially the entire length of the first supply pipe 42, making it possible to prevent clogging of the pipe.

[0075] In this way, the second organic waste C2 is circulated in the second direction in the first supply pipe 42. For example, by arranging a discharge section 66 in the second direction near the front of the first supply pump 43, as shown in FIG. 2(B), the removed components that cause blockage can be discharged to the outside of the first supply pipe 42 together with the second organic waste C2.

[0076] 2(B), a return pipe 67 is provided which branches off from the first supply pipe 42 in the second direction from near the front of the first supply pump 43, and the return pipe 67 is connected to the primary settling basin 21 and the first thickener 24. A third on-off valve 68 is provided midway along the return pipe 67 to interrupt the flow of the second organic waste C2 in the return pipe 67. As a result, in the third supply step, the third on-off valve 68 is opened, and the second organic waste C2 supplied to the first supply pipe 42 can be supplied to the primary settling basin 21 and the first thickener 24.

[0077] Incidentally, by providing on-off valves at the connection point of the return pipe 67 to the primary settling basin 21 and at the connection point of the return pipe 67 to the first thickener 24, it is possible to select whether the second organic waste C2 supplied to the first supply pipe 42 is supplied to the primary settling basin 21 or to the first thickener 24. Furthermore, since the first thickener 24 can be omitted, in the case where the first thickener 24 is omitted, the third on-off valve 68 can be opened to supply the second organic waste C2 supplied to the first supply pipe 42 to the primary settling basin 21.

[0078] In the second embodiment, as in the first embodiment, the first supply step, the heating step, and the second supply step are usually performed with the second on-off valve 65 in a closed state as shown in Fig. 2(A), and at a timing when it is preferable to clean the first supply pipe 42, the second on-off valve 65 is switched to an open state as shown in Fig. 2(B) to perform the third supply step. The timing of performing the third supply step is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0079] Third Embodiment In the third embodiment, as in the second embodiment, the flow direction of the second organic waste C2 in the third supply step is different, but the flow direction of the second organic waste C2 is not fixed, but can be freely switched between the first direction and the second direction. Other configurations are the same as those in the first embodiment, so the same reference numerals are used and the description thereof is omitted.

[0080] In the third embodiment, as shown in Fig. 1, in addition to the third supply pipe 62 for the first direction, a third supply pipe 64 for the second direction is provided as shown by a dotted line in Fig. 1. In the third supply step, by opening the first on-off valve 63 of the third supply pipe 62 for the first direction, the flow direction of the first organic waste C1 in the first supply pipe 42 can be set as a first direction, and the second organic waste C2 can be flowed in the first direction. Conversely, by opening the second on-off valve 65 of the third supply pipe 64 for the second direction, the opposite direction to the flow direction of the first organic waste C1 in the first supply pipe 42 can be set as a second direction, and the second organic waste C2 can be flowed in the second direction. Therefore, by switching between a state in which the first on-off valve 63 is open and a state in which the second on-off valve 65 is open, the flow direction of the second organic waste C2 in the first supply pipe 42 can be switched between the first direction and the second direction in the third supply step.

[0081] For example, in a third supply process performed at a certain timing, the first on-off valve 63 is opened and the flow direction of the second organic waste C2 in the first supply pipe 42 is set to the first direction, and in a third supply process performed at the next timing, the second on-off valve 65 is opened and the flow direction of the second organic waste C2 in the first supply pipe 42 is set to the second direction, so that the flow direction of the second organic waste C2 in the first supply pipe 42 can be switched between the first direction and the second direction each time the third supply process is performed.

[0082] Also, at the beginning of the third supply step, the first on-off valve 63 is opened to set the flow direction of the second organic waste C2 in the first supply pipe 42 to the first direction, and during the third supply step, the second on-off valve 65 is opened to switch the flow direction of the second organic waste C2 in the first supply pipe 42 to the second direction. Conversely, at the beginning of the third supply step, the flow direction of the second organic waste C2 in the first supply pipe 42 is the second direction, and during the third supply step, the flow direction of the second organic waste C2 in the first supply pipe 42 can be switched to the first direction. In this way, the flow direction of the second organic waste C2 in the first supply pipe 42 can be switched between the first direction and the second direction during the execution of the third supply step.

[0083] [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.

[0084] (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.

[0085] (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. [Explanation of symbols]

[0086] 3 Sludge treatment system (methane fermentation treatment facility) 21 First settling pond 31 Methane fermentation tank 41 1st supply section 42 1st supply piping 53 First supply pump (first supply device) 51 2nd supply section 52 2nd supply piping 57 Heating section 61 Third supply section 62 3rd supply piping for 1st direction (3rd supply piping) 64 3rd supply piping for 2nd direction (3rd supply piping) 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 first supply step of supplying the first organic waste that has not been subjected to a heating step to the methane fermentation tank; a second supply step of supplying the second organic waste that has been subjected to the heating step to the methane fermentation tank; a third supply step of supplying the second organic waste that has been subjected to the heating step into a first supply pipe that supplies the first organic waste to the methane fermentation tank.

2. 2. The methane fermentation treatment method according to claim 1, wherein in the third supply step, the second organic waste is supplied to the first supply pipe in a form in which the second organic waste is circulated in the flow direction of the first organic waste in the first supply pipe.

3. 2. The methane fermentation treatment method according to claim 1, wherein in the third supply step, the second organic waste is supplied to the first supply pipe in a form in which the second organic waste is circulated in a direction opposite to a flow direction of the first organic waste in the first supply pipe.

4. In the first supply step, the first organic waste, which is a solid phase obtained by supplying the water to be treated to a first settling tank and performing solid-liquid separation, is supplied to the methane fermentation tank; 4. The methane fermentation treatment method according to claim 3, wherein in the third supply step, the second organic waste that has circulated through the first supply pipe is supplied to the primary sedimentation tank.

5. The methane fermentation treatment method according to claim 1 , wherein the third supply step is performed every time a set time elapses.

6. a first supply device for supplying the first organic waste to the methane fermentation tank; 2. The methane fermentation treatment method according to claim 1, further comprising a third supply step execution timing determination step for determining the execution timing of the third supply step based on the operating state of the first supply device, the flow rate of the first organic waste in the first supply pipe, or the pressure inside the 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 first supply unit having at least a first supply pipe for supplying the first organic waste that has not passed through a heating unit to the methane fermentation tank; A second supply unit having at least a second supply pipe that supplies the second organic waste that has passed through the heating unit to the methane fermentation tank; a third supply section having at least a third supply pipe that supplies the second organic waste that has passed through the heating section from the second supply pipe to the first supply pipe, the third supply section being provided in a methane fermentation treatment facility.

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