Methane fermentation treatment method

Abstract

To provide an efficient methane fermentation treatment method by which a large amount of cereal plant residues generated in a field can be used as resources.SOLUTION: In the methane fermentation treatment method for subjecting a grain-based plant residue containing at least rice straw to methane fermentation treatment by charging the residue into a fermented sludge, the ammoniacal nitrogen concentration of the fermented sludge is adjusted to 10-400 mg / L, and the ammoniacal nitrogen concentration of the fermented sludge is maintained by adding a nitrogen source to the fermented sludge or diluting the fermented sludge with a low-nitrogen-concentration liquid or by at least one of these methods.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment method. [Background technology]

[0002] Traditionally, the large amounts of rice straw generated during rice harvesting have been plowed into the soil as organic fertilizer or incinerated on the field. However, the methane generated when the plowed-in rice straw decomposes in the soil in an anaerobic atmosphere is a greenhouse gas that has a significant impact on global warming. In addition, the soot and smoke generated when rice straw is incinerated on the field cause air pollution and odor problems. Therefore, how to dispose of large amounts of rice straw has been an issue. This issue is not limited to rice straw, but is also common to agricultural waste generated after the harvest of grains harvested on the field, including wheat straw (referred to as "cereal plant residues" in this specification).

[0003] Patent Document 1 discloses that straw from rice, barley, wheat, corn, and the like is lignocellulosic biomass containing cellulose, hemicellulose, and lignin, and that lignin, a persistent substance contained in lignocellulosic biomass, inhibits the biodegradation of cellulose and hemicellulose. Therefore, even if lignocellulosic biomass is directly subjected to methane fermentation, methane gas cannot be produced efficiently. In response to this problem, the patent document discloses methods of carrying out pretreatment such as steam explosion treatment and crushing treatment.

[0004] Incidentally, alkalinity is an indicator related to the stability of the methane fermentation process and is positioned as an indicator for maintaining the pH buffering capacity of fermented sludge. Non-Patent Document 1 states that when the input TS concentration is about 10%, the total alkalinity needs to be in the range of 5,000 to 10,000 mg / L, and Non-Patent Document 2 describes that in order for methane fermentation to proceed stably, it is preferable to maintain the pH at about 7.5, which is favorable for methanogens, and to set the alkalinity at 7,700 mg / L. Furthermore, it has been stated that a nitrogen source needs to be added to the fermented sludge for pH buffering and bacterial cell formation, and that the ammonia nitrogen concentration of the fermented sludge needs to be 500 mg / L or higher. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5567718 [Non-patent literature]

[0006] [Non-Patent Document 1] Ministry of the Environment, Minister's Secretariat, Waste Management Division, Waste and Recycling Department, Minister's Secretariat, Ministry of the Environment, Methane Gasification (Garbage Methane) Facility Development Manual [Non-patent document 2] Effect of retention time and load on high-temperature and high-concentration methane fermentation of food waste Journal of the Japan Society on Water Environment, Vol. 22, No. 12, 983-989, 1999 Summary of the Invention [Problem to be solved by the invention]

[0007] Various trial and error efforts are currently being made to find methods for efficiently fermenting grain residues, including rice straw, into methane, and a more effective methane fermentation method is desired.

[0008] An object of the present invention is to provide an efficient methane fermentation treatment method that can utilize the large amount of cereal plant residues generated in farm fields as a resource. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, a first characteristic feature of the methane fermentation treatment method according to the present invention is that it is a methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, and the ammoniacal nitrogen concentration of the fermented sludge is maintained at 10 to 400 mg / L.

[0010] As a result of extensive research and testing, the present inventors have discovered that when grain-based plant residues, including rice straw, are added to fermented sludge for methane fermentation, the conventionally required ammoniacal nitrogen concentration of 500 mg / L or more is not required. However, by adjusting the ammoniacal nitrogen concentration of the fermented sludge to 10-400 mg / L, continuous and successful methane fermentation can be achieved without adding an additional nitrogen source to the fermented sludge. Although the reason for this is unclear, it is presumed that the components derived from the grain-based plant residue exert a pH buffering effect.

[0011] The second characteristic configuration is, in addition to the first characteristic configuration described above, that the ammonia nitrogen concentration of the fermented sludge is adjusted by at least one of adding a nitrogen source to the fermented sludge or diluting the fermented sludge with a low-nitrogen concentration liquid.

[0012] To adjust the ammoniacal nitrogen concentration of the fermented sludge to the above-mentioned value, a nitrogen source may be added to the fermented sludge, or the fermented sludge may be diluted with a low-nitrogen concentration liquid.

[0013] The third characteristic feature of the present invention is that, in addition to the first characteristic feature described above, the methane fermentation treatment is a mesophilic methane fermentation treatment, and the ammonia nitrogen concentration of the fermented sludge is adjusted to 10 to 150 mg / L.

[0014] The fourth characteristic feature of the present invention is that, in addition to the first characteristic feature described above, the methane fermentation treatment is a high-temperature methane fermentation treatment, and the ammonia nitrogen concentration of the fermented sludge is adjusted to 150 to 400 mg / L.

[0015] The fifth characteristic feature of the method is a methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, and the amount of easily fermented methane material containing a nitrogen source added to the fermented sludge is adjusted based on collection / storage information of the cereal plant residue.

[0016] For example, the ease of fermentation of grain-based plant residues can be determined based on information about the collection and storage of the grain-based plant residues, such as the time elapsed since harvest and storage conditions, and by adjusting the amount of easily methane-fermented material added based on that condition, the amount of biogas produced in the methane fermentation process can be adjusted.

[0017] The sixth characteristic feature of the present invention is a methane fermentation treatment method in which cereal plant residues containing at least rice straw are added to fermented sludge and subjected to methane fermentation treatment, and the amount of easily methane-fermented material containing a nitrogen source added to the fermented sludge is adjusted based on biogas demand information.

[0018] By adjusting the amount of easily methane-fermented material added to the methane-fermentation sludge based on biogas demand information, the amount of biogas produced by the methane fermentation process can be adjusted to match demand.

[0019] The seventh characteristic feature of the present invention is a methane fermentation treatment method in which cereal plant residues containing at least rice straw are added to fermented sludge and subjected to methane fermentation treatment, and the amount of easily fermented methane material containing a nitrogen source added to the fermented sludge is adjusted based on the COD (chemical oxygen demand) of the digested sludge.

[0020] By adjusting the amount of easily methane fermented material added, the amount of undecomposed material remaining in the digested sludge can be reduced, the burden on wastewater treatment can be reduced, and discharge can be made easier. [Effects of the Invention]

[0021] As described above, according to the present invention, it is possible to provide an efficient methane fermentation treatment method that can utilize the large amount of grain plant residues generated in farm fields as a resource. [Brief explanation of the drawings]

[0022] [Figure 1] Diagram showing the methane fermentation system [Figure 2] An explanatory diagram showing the methane fermentation treatment method [Figure 3] Illustrative diagram of a reactor used in a methane fermentation treatment method [Figure 4] Illustration of basic parameters of the reactor [Figure 5] Graph showing mesophilic reactor test results [Figure 6] Graph showing the characteristics of the mesothermal reactor test results [Figure 7] A diagram showing the test results of a mesophilic reactor and explaining the characteristics of ammonia nitrogen concentration in 100% rice straw [Figure 8] Graph showing high temperature reactor test results [Figure 9] Graph showing the characteristics of high-temperature reactor test results [Figure 10] A diagram showing the test results of a high-temperature reactor and explaining the characteristics of ammonia nitrogen concentration in 100% rice straw DETAILED DESCRIPTION OF THE INVENTION

[0023] The methane fermentation treatment method of the present invention will be explained below using rice straw as an example of a large amount of cereal plant residue generated in farm fields. Note that the present invention is not limited to rice straw, and can also be applied to cereal plant residues such as barley, wheat, and corn.

[0024] [Methane fermentation system] FIG. 1 illustrates a methane fermentation system 1 in which the methane fermentation treatment method of the present invention is carried out. A methane fermentation system 1 is constructed for each community farming operation or for multiple neighboring community farming operations, and is equipped with multiple fields 2 where rice straw, which is grain-based plant residue 3, is produced, multiple storage locations 5 for storing the grain-based plant residue 3, and a methane fermentation apparatus 6 that mainly performs methane fermentation treatment on the grain-based plant residue 3. Although Fig. 1 shows a single methane fermentation apparatus 6, in practice, multiple series of methane fermentation apparatuses 6 may be installed in separate locations or all together in one place, depending on the scale of grain-based plant residue 3 to be received.

[0025] The facility is also equipped with a biogas power generation plant 8 that generates electricity using the methane gas (biogas) produced in the methane fermentation plant 6 as fuel. The electricity generated by the biogas power generation plant 8 is consumed as electrical energy in the area, and the waste heat from combustion produced in the biogas power generation plant 8 is used as a heat source for the methane fermentation plant 6 and the greenhouse, among other purposes.

[0026] The methane fermentation device 6 comprises a methane fermentation tank containing fermented sludge, a feeding device that feeds grain-based plant residue 3 into the methane fermentation tank, a stirring mechanism that stirs the fermented sludge to which the grain-based plant residue 3 has been fed, and a heating mechanism that adjusts the fermentation temperature. A portion of the exhaust heat from combustion generated during power generation is supplied to the heating mechanism, where it is heated to approximately 55°C, which is suitable for high-temperature fermentation, and the organic matter is digested under anaerobic conditions to produce biogas such as methane gas and carbon dioxide. Note that the methane fermentation tank may also be heated by the heating mechanism to approximately 35°C, which is suitable for mesophilic fermentation.

[0027] A fermentation residue storage device 7 that stores the fermentation residue produced in the methane fermentation device 6 is provided near the methane fermentation device 6, and the fermentation residue stored in the fermentation residue storage device 7 is returned to the farm field 2 as compost or fertilizer.

[0028] When the rice harvest season arrives, the large amount of rice straw remaining in the post-harvest field 2, in other words, grain plant residue 3, is collected in cylindrical packs using a roll baler, for example. It is physically difficult, including the cost of equipment, to accumulate such a large amount of grain plant residue in one place and subject it to methane fermentation all at once, and even if a large amount of biogas is produced temporarily, it may not be able to be used effectively, so a separate biogas storage facility is required.

[0029] Therefore, multiple storage locations 5 are provided in a dispersed manner throughout the farming areas that make up the community-based farming, and the grain plant residues 3 collected in each field 2 are cut into pieces of a predetermined size using a crushing device that can cut the residue into pieces as needed, such as a chipper shredder, used as a pre-treatment device 4, and then accumulated in the nearest storage location 5. "As needed" means that the storage location 5 is adjusted to correspond to the HRT (hydraulic retention time) during methane fermentation, which is adjusted according to various demand forecasts by the management device 20, which will be described later.

[0030] The storage locations 5 are provided in various forms, such as storage locations with roofs and storage locations without roofs where waste is stored in the open. An appropriate number of methane fermentation devices 6 are provided depending on the layout and number of storage locations 5.

[0031] A management device 20 consisting of a cloud-based server equipped with a storage device 21 is provided for each community farming operation or for each of multiple neighboring community farming operations to manage the grain plant residue 3. The management device 20 manages information such as the storage location and storage format, as well as the start date of storage (rice harvesting time), cutting length, variety, and grower. The manager of the methane fermentation apparatus 6 and the manager of the gasification apparatus 9 are configured to be able to grasp the management status of the grain plant residue 3 via a terminal device capable of communicating with the management device 20.

[0032] The management device 20 creates a storage plan and utilization plan for the grain plant residue 3 based on a forecast of demand for the year until the next year's harvest, and based on this plan, the grain plant residue 3 is dispersed, stored in different crushed states, and utilized in multiple storage locations 5. Uncrushed grain plant residue 3 is piled up in cylindrical packaging, and grain plant residue 3 crushed to a predetermined size is stored in flexible container bags or the like.

[0033] The utilization plan by the management device 20 and information on the distributed storage of grain plant residues 3 in storage locations 5 based on the utilization plan are notified to workers including the manager via a terminal device, so that the workers including the manager can appropriately process the grain plant residues 3 based on the utilization plan.

[0034] The demand forecast includes a predicted value of the amount of electricity required for each specified period by the biogas power generation plant 8, a predicted value of the amount of heat required for a specified period when using the waste heat from combustion generated by the combustor provided in the biogas power generation plant 8, and a predicted value of the amount required for a specified period when using the fermentation residue from the methane fermentation plant 6 as compost or fertilizer.

[0035] For example, when the waste heat from combustion generated from a combustor provided in the biogas power generation system 8 is used as a heat source for a greenhouse, predicted values ​​of the required amount of heat and the required time are stored in storage device 21. Also, when the fermentation residue is to be returned to a field as fertilizer based on the amount of fertilizer components in the fermentation residue analyzed in advance, predicted values ​​of the time to apply fertilizer as base fertilizer, the amount of fertilizer components required, and the amount of fertilizer returned from the fermentation residue, and predicted values ​​of the time to apply fertilizer as top-dressing, the amount of fertilizer components required, and the amount of fertilizer returned from the fermentation residue are stored in storage device 21. In the case of rice cultivation, base fertilizer needs to be applied mainly during plowing from April to May, and top-dressing needs to be applied mainly around July. The amount of fertilizer needed to apply just the right amount during such periods is stored in storage device 21 as a predicted value of demand.

[0036] [Methane fermentation treatment method] The methane fermentation treatment method of the present invention is carried out using the methane fermentation apparatus 6 described above. Specifically, rice straw, which is essentially 100% grain-based plant residue 3, is added via an input device to methane fermentation sludge filled in a methane fermentation tank. The ammoniacal nitrogen concentration in the fermented sludge is then maintained at 10 to 400 mg / L. To maintain the ammoniacal nitrogen concentration at 10 to 400 mg / L, at least one of the following methods is implemented: adding a nitrogen source to the fermented sludge or diluting the fermented sludge with a low-nitrogen-concentration liquid. Examples of nitrogen sources that can be used include food waste, food waste generated in food factories, and even livestock manure. If the ammoniacal nitrogen concentration falls within the range of 10 to 400 mg / L due solely to the nitrogen content of the grain-based plant residue 3 itself, there is no need to implement any of the above methods.

[0037] When high-temperature methane fermentation treatment is performed at approximately 55°C as the methane fermentation treatment, it is preferable to adjust the ammoniacal nitrogen concentration of the fermented sludge to 150 to 400 mg / L, and when mesophilic methane fermentation treatment is performed at approximately 35°C as the methane fermentation treatment, it is preferable to adjust the ammoniacal nitrogen concentration of the fermented sludge to 10 to 150 mg / L.

[0038] As a result of experimental research by the inventors of the present application, when grain plant residues including rice straw are added to fermented sludge and subjected to methane fermentation treatment, it is not necessary to ensure an ammoniacal nitrogen concentration of 500 mg / L or more, as was previously required. As long as the ammoniacal nitrogen concentration of the fermented sludge is maintained at 10 to 400 mg / L, this methane fermentation treatment method is based on the new finding that good methane fermentation can be achieved without adding a separate nitrogen source to the fermented sludge.

[0039] 2 shows a methane fermentation management method operated in a methane fermentation system 1. The system is configured to carry out a grain plant residue collection step (SA1) of collecting grain plant residue 3 generated in a farm field 2, a demand forecasting step (SA2) of predicting the annual demand for recyclable resources using grain plant residue, a raw material storage step (SA3) of storing the grain plant residue 3 in multiple storage locations 5 based on the demand forecast, a methane fermentation treatment step (SA5) of supplying some of the stored grain plant residue 3 to a methane fermentation device 6 for methane fermentation based on the demand situation (SA4), and a reduction step (SA8) of returning the fermentation residue generated in the methane fermentation treatment step to the farm field 2 as compost or fertilizer.

[0040] By fermenting the waste in a methane fermentation process (SA5), and then recovering the generated methane gas and using it as fuel for biogas power generation (SA6), the energy recovered from the grain plant residues 3 can be effectively utilized.Furthermore, the fermentation residue can be recovered (SA7) and returned to the field 2 as compost or fertilizer (SA8), thereby achieving a circular utilization of resources and reducing farming costs.

[0041] Furthermore, when a large amount of grain residue 3 is collected from the field 2 due to overlapping harvest seasons, the grain residue 3 can be temporarily stored in a storage facility in the raw material storage process of step SA3, and if necessary (SA4), a portion of the grain residue 3 can be supplied to the methane fermentation treatment process of step SA5, thereby enabling the grain residue 3 to be used efficiently until, for example, a time outside the harvest season. Note that the grain residue 3 collected in the field 2 may also be supplied directly to the methane fermentation treatment process of step SA5 without going through a storage facility provided in the storage location 5.

[0042] The raw material storage step of step SA3 is preferably configured to store the grain plant residue 3 collected in the grain plant residue collection step of step SA1 under different storage conditions corresponding to the storage location 5. When the grain plant residue 3 is distributed and stored in a plurality of storage locations 5, by varying the storage conditions of the grain plant residue 3 according to the storage location 5, even large amounts of grain plant residue 3 can be processed flexibly in accordance with expected future demand for resources.

[0043] Possible storage conditions include, for example, the cutting length and storage amount of the grain plant residue 3. For example, if it is necessary to proceed with the methane fermentation treatment early, the HRT can be shortened by using grain plant residue with a short cutting length, and as a result, the amount of methane fermentation treatment can be increased. In this way, as a pretreatment, by adjusting the storage amount and cutting length of the grain plant residue and storing it in different storage locations, it is possible to respond to changes in the timing and processing amount of the methane fermentation treatment. When storing for a long period of time, by storing the grain plant residue 3 in a long state without cutting it, it is possible to use the storage period to properly compost it under anaerobic conditions to facilitate methane fermentation.

[0044] As shown in step SA4, when the management device 20 determines, based on the demand forecast stored in the memory device 21 or the actual demand, that a large amount of top dressing will be required in the near future, such as one month from now, the grain plant residue stored in the storage area 5 where short-cut grain plant residue is accumulated is supplied to the nearest methane fermentation device 6, and the device is operated with a short HRT set, thereby adjusting the amount of processing that can be performed by methane fermentation, and management can be performed so that a fermentation residue with a high soluble content suitable for top dressing can be obtained in a short period of time.

[0045] Furthermore, if the management device 20 determines, based on the demand forecast stored in the memory device 21 or actual demand, that a large amount of base fertilizer will be required in the distant future, such as several months from now, the grain plant residues 3 in the storage area 5 where long cut lengths of grain plant residues 3 are accumulated can be supplied to the nearest methane fermentation device 6 in advance from a time when sufficient HRT can be secured, thereby managing the fermentation residues containing a large amount of organic matter suitable for base fertilizer so that the required amount can be secured until the time when they are needed.

[0046] Since the grain residue 3 contains organic matter such as lignin, which is anaerobic and difficult to decompose, and fertilizer components such as silica, it can be returned to the field as compost or fertilizer to effectively restore soil fertility. However, the grain residue 3 is low in nitrogen and phosphorus, resulting in an imbalance in the nutrients required for compost or fertilizer. Therefore, in the methane fermentation treatment of step SA5, it is preferable to adjust the components to produce a balanced compost or fertilizer by supplementing the methane fermentation apparatus 6 with livestock manure or other materials and then performing methane fermentation.

[0047] The management device 20 described above manages storage information, including the storage location 5 for storing the grain plant residue 3 and storage conditions, in the raw material storage process of step SA3, and manages the timing and / or amount of supplying at least a portion of the grain plant residue to the methane fermentation treatment process of step SA5 based on the storage information. At this time, it is preferable to adjust the amount of easy-to-methane-ferment material added to the fermentation sludge. Suitable easy-to-methane-ferment material to be used is nitrogen sources such as food waste and food waste generated in food processing plants.

[0048] By adjusting the amount of nitrogen sources such as kitchen waste and food waste added, it is possible to control the methane fermentation processing speed and the amount of biogas generated, as well as the COD decomposition rate. Therefore, by adjusting the amount of kitchen waste and other materials added in conjunction with storage information in response to demand forecasts, it becomes possible to adjust the processing speed over a wider range.

[0049] The management device 20 notifies the manager or worker in advance to store the waste in different storage locations under different storage conditions depending on the time when methane fermentation processing is required and the amount of processing required at that time, making it easier to manage the timing and amount of processing of subsequent methane fermentation processing.

[0050] It is preferable that the method further comprises a fermentation residue storage step of storing in a fermentation residue storage device 7 the fermentation residue generated in the methane fermentation treatment step of step SA5 and recovered in the fermentation residue recovery step of step SA7, and that at least a portion of the fermentation residue stored in the fermentation residue storage step is returned to the field 2 in a reduction step of step SA8. It is preferable to adjust the amount of easy methane fermentation additive in the methane fermentation treatment step based on the COD of the digested sludge, which is the fermentation residue, and this reduces the amount of undecomposed matter remaining in the digested sludge, reduces the load on wastewater treatment, and makes discharge easier.

[0051] By storing the excess fermentation residue generated in the methane fermentation treatment process in step SA5 in the fermentation residue storage device 7, it can be returned as compost or fertilizer to the required field 2 at the required time. The fermentation residue containing a mixture of solid and liquid components may be stored in that state, or the solid and liquid components may be separated and stored separately.

[0052] It is preferable that the methane fermentation processing method is configured to adjust the amount of grain-based plant residue supplied to the gasification processing step of step SA9 based on storage information of the grain-based plant residue 3 stored in the raw material storage step of step SA3.

[0053] The time required for methane fermentation is important from the perspective of matching the demand for methane gas and fermentation residues. Therefore, by adjusting the cutting length of the grain-based plant residue 3 to match the predicted demand for methane gas and fermentation residues, it becomes possible to adjust the HRT, which is the time required for methane fermentation, and to make effective use of the organic resource that is the grain-based plant residue 3.

[0054] Specifically, when the demand for compost or the like or energy source increases, it is preferable to adjust the cut length or average cut length of the grain plant residue 3 to be supplied to methane fermentation so as to be shorter.

[0055] It is preferable to adjust the amount of the material that can be easily fermented by methane based on biogas demand information, instead of or in addition to adjusting the cutting length of the grain plant residue 3. As the material that can be easily fermented by methane, as described above, food waste and food waste generated in food processing factories can be suitably used.

[0056] The methane fermentation process is controlled by operating conditions such as temperature, HRT, organic matter load, etc. By adjusting the chopping length or average chopping length of the grain-based plant residues fed to methane fermentation to be shorter, the HRT can be shortened, which allows for appropriate response to increased demand for compost, etc. or energy sources.

[0057] If the relationship between the length of the grain residue 3 and the HRT required for methane fermentation is understood in advance, it becomes possible to appropriately adjust the cutting length of the grain residue 3 based on this relationship to a value consistent with the target HRT. The shorter the length of the rice straw, the shorter the HRT, and as the length of the rice straw increases, the HRT gradually saturates. For example, if the rice straw is a few millimeters long, the HRT can be adjusted to about 20 days, and if the length of the rice straw is a dozen or so millimeters, the HRT can be adjusted to about 40 days.

[0058] The grain plant residue 3 is stored in separate cutting lengths, and based on demand information for compost or energy sources, the cutting lengths of the grain plant residue to be supplied to methane fermentation are selected or blended to a predetermined length.

[0059] If the grain plant residue 3 is stored in advance in separate cutting lengths, it is possible to select or mix the grain plant residue so that the cutting length is a specified length, thereby adjusting the HRT to match the demand information for compost, etc. or energy sources.

[0060] In the above example, a portion of the grain plant residue 3 collected in cylindrical packaging using a roll baler or the like is crushed in advance by a crushing device and stored in the storage area 5, but it is also possible to crush or cut the residue to the required size using a crushing device when subjecting it to methane fermentation processing. [Example]

[0061] Figure 3 shows the configuration of a continuous stirred tank reactor used to confirm the fermentation efficiency of rice straw, which was used as a fermentation substrate. A stirring blade is immersed in a cylindrical reaction tank sealed with a lid, and a heater is installed around the reaction tank, allowing it to maintain a temperature of 55°C, which is suitable for high-temperature fermentation, or 35°C, which is suitable for mesophilic fermentation. The substrate is fed into an inlet in the lid, and biogas such as methane gas and carbon dioxide are extracted from an outlet in the lid. A motor that drives the stirring blade is installed in the lid.

[0062] Figure 4 shows the basic parameters of a continuous stirred tank reactor. Digested sludge from an existing wastewater treatment plant is used as the seed sludge, and the HRT is set to 60 days. A mixture of food waste and rice straw is used as the substrate. The substrate is divided into four phases, Phase 1 to Phase 4, with food waste and rice straw mixture ratios adjusted to 40%, 60%, 80%, and 100%, and is continuously added over a period of approximately 500 days. Phase 1 uses a 40% mixture ratio substrate, Phase 2 a 60% mixture ratio substrate, Phase 3 an 80% mixture ratio substrate, and Phase 4 a 100% mixture ratio substrate, i.e., rice straw only.

[0063] Figure 5 shows the time series of biogas production rate, gas composition, pH, ammonia nitrogen, and alkalinity during mesophilic fermentation, corresponding to phases 1 to 4, and Figure 6 shows the average values ​​for each phase.

[0064] As the proportion of rice straw increases, the biogas production rate gradually decreases due to the increase in the amount of refractory substances in the substrate. In particular, when the rice straw content increases to 60%, the concentrations of ammonia nitrogen and alkalinity gradually decrease due to the low nitrogen content in the substrate.

[0065] However, even when the rice straw content was 100%, the biogas production rate was approximately 0.473 L / L / d, indicating that methane fermentation was progressing. Figure 7 shows the measurement dates and measurement data for ammonia nitrogen in Phase 4. It was found that in mesophilic methane fermentation treatment with a rice straw content of 100%, stable methane fermentation could be carried out with the ammonia nitrogen concentration in the fermented sludge maintained at 10-150 mg / L.

[0066] Figure 8 shows the time series of the biogas production rate, gas composition, pH, ammonia nitrogen, and alkalinity characteristics during high-temperature fermentation, corresponding to phases 1 to 4, and Figure 9 shows the average values ​​for each phase.

[0067] The same trends as in mesophilic fermentation were observed. When the rice straw ratio increased to 80%, the thermophilic reactor also showed a decreasing trend in ammonia nitrogen and alkalinity, but these concentrations were higher than those in the mesophilic reactor.

[0068] Even when the rice straw content was 100%, the biogas production rate was approximately 0.81 L / L / d, indicating that methane fermentation was progressing. Figure 10 shows the measurement dates and measurement values ​​for ammonia nitrogen in Phase 4. It was found that in high-temperature methane fermentation treatment with a rice straw content of 100%, stable methane fermentation could be carried out with the ammonia nitrogen concentration in the fermented sludge maintained at 150-400 mg / L.

[0069] That is, the methane fermentation treatment method according to the present invention can achieve stable methane fermentation treatment by maintaining the ammoniacal nitrogen concentration of the fermentation sludge at 10 to 400 mg / L.

[0070] The various embodiments described above are examples of the present invention, and the scope of the present invention is not limited by the description. It goes without saying that the present invention can be appropriately modified and designed within the scope in which the effects of each invention are achieved. [Explanation of symbols]

[0071] 1: Methane fermentation system 2: Field 3: Grain-based plant residues (rice straw) 4: Pre-treatment device 5: Storage location 6: Methane fermentation equipment 7: Fermentation residue storage device 8: Biogas power generation equipment 20: Management device 21: Storage device

Claims

1. A methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, A methane fermentation treatment method characterized by maintaining the ammoniacal nitrogen concentration of the fermented sludge at 10 to 400 mg / L.

2. 2. The methane fermentation treatment method according to claim 1, wherein the ammoniacal nitrogen concentration of the fermented sludge is adjusted by at least one of adding a nitrogen source to the fermented sludge and diluting the fermented sludge with a low-nitrogen concentration liquid.

3. The methane fermentation treatment is a mesophilic methane fermentation treatment, 2. The methane fermentation treatment method according to claim 1, wherein the ammonia nitrogen concentration of the fermented sludge is adjusted to 10 to 150 mg / L.

4. The methane fermentation treatment is a high-temperature methane fermentation treatment, 2. The methane fermentation treatment method according to claim 1, wherein the ammonia nitrogen concentration of the fermented sludge is adjusted to 150 to 400 mg / L.

5. A methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, A methane fermentation treatment method, characterized in that the amount of easily methane-fermented material containing a nitrogen source to be added to the fermented sludge is adjusted based on collection / storage information of the cereal plant residue.

6. A methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, A methane fermentation treatment method, characterized in that the amount of easily fermented methane material containing a nitrogen source added to the fermented sludge is adjusted based on biogas demand information.

7. A methane fermentation treatment method in which cereal plant residue containing at least rice straw is added to fermented sludge and subjected to methane fermentation treatment, A methane fermentation treatment method, characterized in that the amount of easily fermented methane containing a nitrogen source to be added to the fermented sludge is adjusted based on the COD of the digested sludge.

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