JP7202074B2 - How to start up methane fermentation - Google Patents

Description

The present invention relates to a method for starting up methane fermentation in which methanogenic bacteria are cultured to generate methane gas.

In general, when starting up and operating a methane fermentation plant, methanogens need to obtain digestive fluid (seed sludge) from the already operating plant.

For example, in Japanese Patent Application Laid-Open No. 2005-46788 (Patent Document 1), at the start of methane fermentation, at the time of restart, etc., a fungal concentrate obtained by concentrating fungal cells in seed sludge or fermentation liquid is applied to the object to be treated. It is disclosed to add

JP-A-2005-46788

In order to efficiently start up the methane fermentation process, it is desirable to obtain seed sludge from existing plants. However, it may be difficult to find a methane fermentation facility with the same conditions as the plant to be launched. Further, in the methane fermentation treatment method of Patent Document 1, it is necessary to obtain seed sludge from an existing plant when starting up the plant.

The present invention was made to solve the above problems, and its object is to provide a method for starting up methane fermentation capable of generating methane gas without using seed sludge or the like. aim.

A method for starting up methane fermentation according to an aspect of the present invention is a method for starting up methane fermentation in which methanogens are cultured to generate methane gas, and cattle dung containing methanogens and feed are prepared. a step of charging cow dung and feed into a fermenter in a predetermined ratio of cow dung and feed; and a step of culturing methanogenic bacteria in the fermenter to generate methane gas.

Preferably, the feed input on a dry matter basis is 0.1-20% of the cow dung input.

Preferably, when the temperature in the fermenter is 36° C., the feed input on a dry matter basis is 0.5-10% of the cow dung input.

Preferably, when the temperature in the fermenter is 42° C., the feed input on a dry matter basis is 0.1-2.5% of the cow dung input.

Preferably, the temperature in the fermenter is gradually raised from 36°C to 42°C after the cow dung and feed are put into the fermenter.

Preferably, the feed input on a dry matter basis is 0.5-10% of the cow dung input.

Preferably, the combined weight of cow dung and feed solids relative to the total weight charged into the fermenter is between 10% and 15%.

Preferably, a biomass raw material different from cow dung is introduced into the fermenter in addition to the cow dung after the methanogen culture in the cow dung is stabilized in the fermenter.

ADVANTAGE OF THE INVENTION According to this invention, the start-up method of methane fermentation which can generate methane gas without using seed sludge etc. can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows the whole flow of the methane fermentation method which concerns on embodiment of this invention. Fig. 4 is a schematic graph showing changes in the amount of biogas generated by the methane fermentation method according to the embodiment of the present invention; It is a flow chart which shows the start-up process (STEP1) of methane fermentation. It is a graph which shows transition of the temperature, pH, ORP, and methane concentration in each process. 4 is a flow chart showing a step (STEP 2) of stepwise charging of biomass raw materials and a step (STEP 3) of continuously charging a plurality of types of biomass raw materials. It is a typical graph which shows the procedure which inject|throws-in a biomass raw material. FIG. 4 is a schematic diagram showing the state of decomposing bacteria in a fermenter in a step (STEP 2) of stepwise introduction of biomass raw materials. It is a flowchart for determining whether to switch to a recovery step (STEP4). It is a flow chart which shows a recovery process (STEP4).

An embodiment of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

The overall flow of the methane fermentation method according to the embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 is a flow chart showing the overall flow of the methane fermentation method. FIG. 2 is a line graph showing an image of changes in the amount of biogas generated by the methane fermentation method, in which the vertical axis indicates the amount of biogas and the horizontal axis indicates the number of processing days.

In the overall flow of the methane fermentation method according to the present embodiment, after the methane fermentation start-up step (STEP 1), a step of stepwise introducing a plurality of types of biomass raw materials into the fermenter (STEP 2) is performed, and then A step (STEP 3) of continuously charging a plurality of types of biomass raw materials into the fermenter is performed.

In STEP 1, a methane fermentation start-up step, methanogens are cultured in a fermenter to proliferate the methanogens. In STEP 2, in which the biomass raw materials are introduced step by step, the types of biomass raw materials to be introduced are increased one by one and introduced into the fermenter. In STEP 3, a step of continuously charging multiple types of biomass raw materials, all of the multiple types of biomass raw materials charged in STEP 2 are mixed and charged into a fermenter. In addition, when methane gas is not normally generated in STEP 1, or when the amount of biogas generated decreases during STEP 3, a recovery step (STEP 4) is performed.

As shown in FIG. 2, the amount of biogas in the fermenter increases as STEP 1, STEP 2, and STEP 3 are shifted to. Biogas is a gas generated by decomposition of biomass raw materials in a fermenter, and is a gas containing, for example, methane, carbon dioxide, and trace amounts of hydrogen sulfide. Conditions for switching from STEP1 to STEP2 and from STEP2 to STEP3 will be described later.

Each STEP will be described in detail below.

<Methane fermentation start-up process (STEP 1)>
FIG. 3 is a flow chart showing the start-up process (STEP 1) of methane fermentation. The start-up step (STEP 1) of methane fermentation will be described with reference to FIG. The start-up process of methane fermentation is a process of generating methane gas using methanogenic bacteria. The methane fermentation start-up step (STEP 1) includes a step S11 of preparing cow dung and feed, a first raw material input step S12, and a first methanogen culture step S13.

Cow dung is cow dung and contains methanogens. The feed is typically cattle feed, but may be feed for livestock such as pigs, chickens, and horses. Feed for cattle is typically silage, but compound feed, green cut feed crops (not lactic acid fermented), and the like may also be used. Examples of silage include pasture silage mainly composed of grasses and corn silage of maize. A compound feed is a feed in which various raw materials such as wheat and corn are blended to adjust nutrients. The compound feed may be, for example, a compound feed containing silage.

The first raw material charging step S12 is a step of charging the cow dung and the feed into the fermenter with a predetermined ratio of the cow dung and the feed. The input amount of feed in dry matter weight ratio is 0.1 to 20%, preferably 0.1 to 10%, more preferably 0.5 to 10% of the input amount of cow dung. In addition, the total weight of cow dung and feed solids relative to the total weight put into the fermenter is, for example, 5% to 20%, preferably 10% to 15%. In addition to the cow dung and feed, the fermenter contains, for example, solids and water.

The first methanogen culturing step S13 is a step of generating methane gas while culturing methanogens in the fermenter. After the cow dung and feed are put into the fermenter, the fermentation temperature inside the fermenter is gradually raised from 36°C to 42°C. It is preferable to raise the temperature, for example, at a pace of 1° C. per day. The final fermentation temperature in the fermenter is 42°C and it is preferred to maintain the temperature in the fermenter at 42°C. By maintaining the fermentation temperature at 42°C, the processing time can be shortened and the volume of the fermenter can be reduced compared to methane fermentation at 36°C.

Generally, when starting up a new methane fermentation process, it is desirable to obtain digestive fluid (seed sludge) from an operating plant under the same conditions (same temperature) as the process. However, in some cases, seed sludge cannot be obtained because an operating plant with the same conditions as the new process cannot be found. At present, there is no operating plant with a fermentation temperature of 42°C in Japan, so it is difficult to obtain seed sludge with a fermentation temperature of 42°C. However, by using the process of the present embodiment, it is not necessary to obtain seed sludge from other operating plants, and methane fermentation can be started up from scratch. Furthermore, by setting the feed input amount to 0.1 to 20% of the cow dung input amount in terms of dry matter weight ratio, it is possible to culture methanogenic bacteria in a short time and start methane fermentation early. can. In addition, when the fermentation temperature is gradually raised from 36 ° C. to 42 ° C., the amount of feed input in terms of dry matter weight ratio is 0.5 to 10% of the input amount of cow dung. can be cultured.

The timing for switching from STEP 1 to STEP 2 is when the culture of methanogenic bacteria in cow dung and feed becomes stable. That is, when the pH, ORP (oxidation-reduction potential) and methane concentration in the fermenter are within the preferred range. Further, when the above measurement results in the fermenter are within the suitable range, specifically, the pH in the fermenter is 6.5 or more, preferably 6.5 or more and 8 or less, and the ORP is -350 mV. or less, and the methane concentration is 50% or more, preferably 50% to 60%.

FIG. 4 is a graph showing changes in temperature, pH, ORP, and methane concentration from the top. The vertical axis indicates temperature (°C), pH, ORP (mV), and methane concentration (%), respectively, and the horizontal axis indicates the number of treatment days. As shown in FIG. 4, at the boundary between STEP 1 and STEP 2, the temperature is about 42° C., the pH is about 6.8, the ORP is about −350 mV, and the methane concentration is about 50%. Almost satisfy the above conditions. Thus, when the culture of methanogenic bacteria in cow manure and feed in the fermenter is stabilized, it is time to switch from STEP1 to STEP2.

As described above, the input amount of feed in terms of dry matter weight ratio is 0.1 to 20%, preferably 0.1 to 10%, more preferably 0.5 to 10% of the input amount of cow dung. . This input amount was found as a result of the inventor's earnest research. The contents of the research will be described with reference to Tables 1 to 4 below.

Tables 1 and 2 are tables showing changes in methane concentration when the fermentation temperature is set to 36 ° C., Table 1 shows the case where silage is used as feed, and Table 2 shows the case where mixed feed is used as feed. indicate the case. Tables 3 and 4 are tables showing changes in methane concentration when the fermentation temperature is set to 42 ° C., Table 3 shows the case where silage is used as feed, and Table 4 shows the case where mixed feed is used as feed. indicate the case. The vertical column indicates the ratio of silage or compound feed to cow dung, and the horizontal column indicates the number of days treated and the number of days reached. Here, the number of days to reach indicates the number of days required for the methane concentration to reach 50% or more at each compounding ratio. A methane concentration of 50% or more means that the culture of methanogens has stabilized, so it means that it is time to switch from STEP1 to STEP2. In the following table, the mixing ratio of cow dung without silage or mixed feed, that is, with only cow dung in the fermenter, is indicated as 0%. The shaded parts in Tables 1 to 4 have a higher methane concentration than the one in which only cow dung was put into the fermenter (0% feed mixture ratio), or the methane concentration exceeds 50%. It requires a short number of days.

Before explaining Tables 1 to 4, these test methods will be explained. First, cow dung and feed (silage, compound feed) are prepared and mixed. 5 ml of the mixed cow dung and feed is placed in a 10 ml vial, sealed with a butyl rubber stopper and an aluminum cap, and kept warm in an incubator set at 36°C or 42°C. Additionally, the vials are shaken periodically to culture the methanogens. On the 3rd, 5th, 7th, 10th, 14th and 21st days from the start date, 100 μl of biogas is withdrawn from the vial and the methane concentration is measured by gas chromatography analysis (GC analysis).

First, the case where the fermentation temperature is set to 36° C. will be described. As shown in Table 1, when the blending ratio of silage is in the range of 0.5 to 10%, the methane concentration is higher than when the blending ratio of silage is 0%. A high methane concentration can be read as efficient methane fermentation, that is, efficient cultivation of methanogenic bacteria. That is, when the blending ratio of silage is 0.5 to 10%, methane fermentation starts up better than when only cow dung is added.

In addition, when the silage blending ratio is in the range of 0.5 to 20%, the number of days until the methane concentration reaches 50% or more is shorter than when the silage blending ratio is 0%. . A short number of days until the methane concentration reaches 50% or more means that the period until the methane concentration reaches 50% is short, and STEP 2 can be started early. When the silage blending ratio is 20%, the methane concentration is lower than when silage is not blended within 14 days, but the number of days when the methane concentration is 50% or more is the same as when only cow dung is fed. Since it is shorter than , it is favorable in that it is possible to shift to STEP 2 at an early stage.

As shown in Table 2, when the compounding ratio of compounded feed is in the range of 0.1 to 2.5%, methane fermentation starts up better than when only cow dung is added. I understand. Further, when the mixing ratio of the mixed feed is in the range of 0.1 to 1.0%, STEP 2 can be started earlier than when only cow dung is added.

Next, the case where the fermentation temperature is set to 42° C. will be described. As shown in Table 3, when the blending ratio of silage is 0.1 to 2.5%, methane fermentation starts up better than when only cow dung is added, and only cow dung is added. Compared to the case where the

As shown in Table 4, when the blending ratio of the compound feed is 0.1 to 1.0%, compared to the case where only cow dung is added, the start-up of methane fermentation is better, and only cow dung is added. Compared to the case of throwing in, it is possible to shift to STEP2 earlier.

As shown in Table 1, the mixing ratio of silage is 30% or more. As shown in Table 2, the mixing ratio of mixed feed is 1.5% or more. As shown in Table 3, the mixing ratio of silage is 5.0% or more. As shown in Table 4, when the mixing ratio of the mixed feed is 1.5% or more, the methane concentration is lower than when only cow dung is added. In other words, in order to start up methane fermentation early, in addition to putting cow dung and feed into the fermenter, the ratio of cow dung and feed is also important. In the above description, silage and mixed feed were used as feed, but the type of feed is not limited to these.

As described above, as shown in Tables 1 to 4, when the input amount of feed in terms of dry matter weight ratio is 0.1 to 20% of the input amount of cow dung, methane fermentation can be started up early, STEP 2. early transition to Preferably, when the fermentation temperature is 36° C., the methane fermentation can be started up early when the input amount of feed in dry matter weight ratio is 0.5 to 10% of the input amount of cow dung. , STEP 2 can be started early. Further, when the fermentation temperature is 42° C., methane fermentation can be started up early when the input amount of feed in dry matter weight ratio is 0.1 to 2.5% of the input amount of cow dung. , STEP 2 can be started early.

In STEP 2, in addition to cow dung, a biomass raw material different from cow dung is put into the fermenter. Biomass raw materials different from cow dung include, for example, pig manure, chicken manure, food residue as so-called garbage, and grease trap sludge. Next, STEP2 will be described in detail.

<Process of stepwise introduction of biomass raw material (STEP 2)>
With reference to FIGS. 2 and 4 to 7, the step (STEP 2) of stepwise introduction of biomass raw material in the methane fermentation method according to the embodiment of the present invention will be described. STEP 2 is a process in which a plurality of types of biomass raw materials are not mixed and fed all at once, but are stepwise fed while increasing the types of biomass raw materials one by one.

As shown in FIG. 5, the step (STEP2) of introducing biomass raw materials in stages includes a first mixed raw material introduction step S21 and a second mixed raw material introduction step S22. The first mixed raw material input step S21 is a step performed after the culture of methanogenic bacteria in cow dung and feed in STEP1 is stabilized.

FIG. 6 is a schematic graph showing a procedure for charging biomass raw material. The vertical axis indicates the wet weight of the biomass raw material in the fermenter, and the horizontal axis indicates the number of processing days. The first mixed raw material input step S21 is a step of charging a first mixed raw material containing a first biomass raw material and a second biomass raw material different from the first biomass raw material into a fermenter. As shown in FIG. 6, in the present embodiment, the first biomass material is cow dung, and the second biomass material is pig dung. In the first mixed raw material introduction step S21, a first mixed raw material containing cow manure and pig manure is introduced into the fermenter.

The second mixed raw material input step S22 is performed after the first mixed raw material input step S21 and after the culture of the methanogenic bacteria of the first mixed raw material in the fermenter is stabilized, the first biomass raw material, the second biomass raw material, It is a step of charging a second mixed raw material containing a first biomass raw material and a third biomass raw material different from the second biomass raw material into a fermenter. As shown in FIG. 6, in the present embodiment, the second mixed raw material introduction step S22 includes three steps. S22a, a 4-type mixed raw material input step S22b in which 4 types of raw materials mixed with cow dung, pig dung, chicken dung, and food residue are added, and 5 types mixed with cow dung, pig dung, chicken dung, food residue, and grease trap sludge. It also includes a step S22c of feeding a five-kind mixed raw material for feeding raw materials. In this way, the second mixed raw material charging step S22 may include a plurality of steps of stepwise charging a plurality of mixed raw materials.

The timing of introducing the mixed raw material, specifically, the timing of transitioning from the first mixed raw material introduction step S21 to the three mixed raw material introduction step S22a, the timing of shifting from the three mixed raw material introduction step S22a to the four mixed raw material introduction step S22b. The timing of shifting from the 4-mixed raw material input step S22b to the 5-mixed raw material input step S22c is when the culture of the methanogenic bacteria of the mixed raw material in the fermenter becomes stable. That is, when the pH, ORP (oxidation-reduction potential) and methane concentration in the fermenter are within the preferred range. Further, when the above measurement results in the fermenter are within the suitable range, specifically, the pH in the fermenter is 6.5 or more, preferably 6.5 or more and 8 or less, and the ORP is -350 mV. or less, and the methane concentration is 50% or more, preferably 50% to 60%. The timing of charging the mixed raw material into the fermenter may be, for example, every few hours, but preferably every few days.

As shown in FIG. 4, the pH, ORP, and methane concentration fluctuate at the timing of charging the mixed raw material, but the temperature is about 42° C., and the pH is between about 6.8 and pH 7. , and the ORP is between about −350 mV and −500 mV, and the methane concentration is between about 50% and 60%, which substantially satisfies the above conditions.

Preferably, the second biomass material has a higher fermentation load than the first biomass material, and the third biomass material has a higher fermentation load than the second biomass material. That is, in the present embodiment, the fermentation load increases in the order of cow manure, pig manure, chicken manure, food residue, and grease trap sludge, with cow manure having the lowest fermentation load and grease trap sludge having the highest fermentation load. Here, the fermentation load refers to the load required for methane fermentation. is low. In other words, when the fermentation load is high, the fermentation is difficult, and when the fermentation load is excessive, the fermentation tends to be inhibited, whereas when the fermentation load is low, the fermentation is easy. Therefore, in the present embodiment, cow dung with a low fermentation load is first introduced, and grease trap sludge with a high fermentation load is added last.

FIG. 7 is a schematic diagram showing the state of decomposing bacteria in the fermenter in the step (STEP 2) of stepwise introduction of the biomass raw material. Degrading bacteria (hydrolyzing bacteria, acid-producing bacteria) differ depending on the type of biomass raw material. As shown in FIG. 7, when methane fermentation is started with cow dung and feed, bacteria that decompose cow dung grow in the fermenter. When a biomass raw material different from cow dung (pig dung in FIG. 7) is added to the fermenter in which cow dung degrading bacteria have grown, only the degrading bacteria corresponding to the pig dung grow and the cow dung degrading bacteria decrease. There is a possibility of doing so. Therefore, in order to grow cow dung-degrading bacteria and pig dung-degrading bacteria in a well-balanced manner in the fermenter, pig manure is not added alone, but pig manure is added based on cow dung. As a result, degrading bacteria for pig manure and degrading bacteria for cow manure grow in a well-balanced manner in the fermenter.

Considering these principles, it is preferable to put cow dung into the base as follows. That is, as shown in FIG. 6, if the wet weight ratio of cow manure and pig manure in the first mixed raw material introduction step S21 is set to a:b, the three kinds of mixed raw material introduction step S22a in the second mixed raw material introduction step S22 The wet weight ratio of cow dung, pig dung, and chicken dung is a:b:c, and the wet weight ratio of the cow dung, pig dung, chicken dung, and food residue in the step S22b of adding four mixed raw materials is a:b:c:d. The wet weight ratio of cow dung, pig dung, chicken dung, food residue, and grease trap sludge in the five-kind mixed raw material input step S22c is a:b:c:d:e.

That is, the wet weight ratio of cow manure and pig manure in the initial pig manure charging step (S21) is constant even in the subsequent mixed raw material charging steps (S22a, S22b, S22c, STEP3). The same applies to the wet weight ratio with other biomass raw materials in the chicken manure initial input step (S22a), food residue initial input step (S22b), and grease trap sludge initial input step (S22c). That is, the wet weight ratio of the biomass raw materials to be fed in the first and second mixed raw material feeding steps S21, S22a, S22b, and S22c is always the same in the subsequent feeding steps. As a result, new biomass raw materials are added to the previous biomass raw materials, so that the decomposing bacteria corresponding to each biomass raw material can be grown in a well-balanced manner in the fermenter.

After step S22c of introducing five kinds of raw materials (cow manure, pig manure, poultry manure, food residue, grease trap sludge), which are the raw materials finally introduced in STEP2, the process is switched to the next STEP3.

The timing of switching from STEP 2 to STEP 3 is when the culture of the methanogenic bacteria of the five raw materials is stabilized. That is, when the pH, ORP (oxidation-reduction potential) and methane concentration in the fermenter are within the preferred range. Further, when the above measurement results in the fermenter are within the suitable range, specifically, the pH in the fermenter is 6.5 or more, preferably 6.5 or more and 8 or less, and the ORP is -350 mV. or less, and the methane concentration is 50% or more, preferably 50% to 60%.

As shown in FIG. 4, at the boundary between STEP 2 and STEP 3, the temperature is about 42° C., the pH is about 7.4, the ORP is about −450 mV, and the methane concentration is about 60%. Satisfy the above conditions. In this way, when the culture of the methanogenic bacteria as the biomass raw material in the fermenter is stabilized, the process is switched from STEP2 to STEP3. The timing for switching from STEP2 to STEP3 is the same condition as the timing for switching from STEP1 to STEP2 described above.

STEP 3 is a step of continuously charging a plurality of types of biomass raw materials. Next, STEP3 will be described in detail.

<Step of continuously inputting multiple types of biomass raw materials (STEP 3)>
2, 5 and 6, the step (STEP 3) of continuously charging a plurality of types of biomass raw materials will be described.

STEP 3 is a continuous raw material mixture input step (S30) in which the second raw material mixture is added after the culture of the methanogenic bacteria of the second raw material mixture is stabilized in the fermenter. As shown in FIG. 6, in the present embodiment, for example, when there are five types of planned raw materials, five types of cow manure, pig manure, chicken manure, food residue and grease trap sludge introduced in the five types of mixed raw material introduction step S22c A mixed raw material is put into a fermenter. After that, the digestive liquid (fermented liquid) in the fermenter is withdrawn until the amount of fermented liquid in the fermenter returns to the specified amount. When the biomass raw material in the fermenter is large, the five kinds of mixed raw materials are put into the fermenter after extracting the digestive juice from the fermenter. The wet weight ratio of cow dung, pig dung, chicken dung, food residue, and grease trap sludge to be fed into the fermentation tank is a:b:c:d:e, which is the wet weight ratio of the previous step (five mixed raw material feeding step S22c). is identical to Further, the timing of continuously adding these five kinds of mixed raw materials may be, for example, every few days, but it is preferably every several hours.

By taking step-by-step steps such as STEP 2, the degrading bacteria corresponding to each biomass raw material grow in a well-balanced manner, so even if multiple types of biomass raw materials are mixed and put in at once in STEP 3, stable methane fermentation can be achieved. It can be performed. Also, by making the dry matter ratio of the biomass raw material in STEP 3 the same as the dry matter ratio of the biomass raw material in STEP 2, it is possible to maintain a balance of decomposing bacteria corresponding to each biomass raw material. Furthermore, since methane fermentation can be performed using a plurality of types of biomass raw materials, a larger amount of methane gas can be expected compared to the conventional case of using a single biomass raw material.

In the present embodiment, livestock manure such as cow manure, pig manure, and chicken manure, food residue, and food waste such as grease trap sludge were used as a plurality of types of biomass raw materials. , resource crops such as herbs may be used.

Further, in the present embodiment, the step (STEP 2) of stepwise introduction of the biomass raw material includes the first mixed raw material introduction step S21 and the second mixed raw material introduction step S22, but at least the first mixed raw material It suffices if only the input step S21 is provided. That is, when the biomass raw materials to be input are cow dung and chicken dung, the methane fermentation method only needs to include a step of inputting the first mixed raw material, which is a mixture of cow dung and chicken dung. It is not necessary that five raw materials be used.

In addition, even if the number of types of raw materials to be finally put into the fermenter is five or more, the types of raw materials to be put into the fermenter are gradually increased so that the number of types of raw materials to be finally put into the fermenter is increased. After all the types of raw materials to be put in and the culture of methanogenic bacteria in the fermenter are stabilized, all the types of raw materials to be finally put into the fermenter may be put into the fermenter.

Through STEP 3 described above, stable operation of methane fermentation using multiple types of biomass raw materials is possible. However, since methane fermentation is a reaction performed by microorganisms, fermentation inhibition may occur due to various factors such as internal and external factors, resulting in a decrease in the amount of biogas or cessation of methane fermentation. There is In such cases, the following steps are performed.

<Recovery process (STEP4)>
The recovery step (STEP4) will be described with reference to FIGS. The recovery step (STEP 4) is a step to restore the biogas generation amount to a normal state, for example, when the methane fermentation is in a bad condition such as fermentation inhibition.

FIG. 8 is a flowchart for determining whether to switch to the recovery step (STEP4). As shown in FIG. 8, first, the methane concentration in the fermenter is measured (S31). If the methane concentration in the fermenter is not less than 50%, that is, if the methane concentration is 50% or more, STEP 3, the step of continuously supplying mixed raw materials, is continued (S30). Specifically, five kinds of mixed raw materials are put in, for example, after waiting for several hours to several days to culture methanogenic bacteria, the methane concentration in the fermenter is measured again (S31). This process is a process when methane fermentation is performed normally.

On the other hand, if the methane concentration in the fermenter is less than 50%, the mode is switched to the recovery process (S34). This is because a methane concentration of less than 50% means that methane fermentation is not efficiently performed. When measuring the methane concentration in the fermenter, it is preferable to measure the pH, ORP and biogas amount of the fermenter. Preferred ranges for these values are a fermentor pH of 6.5 to 8 and an ORP of -350 mV or less. The amount of biogas is an arbitrary value determined by the biogas raw material to be fed.

FIG. 9 is a flow chart showing the recovery process (STEP4). As shown in FIG. 9, the ammonia concentration and organic acid concentration in the fermenter are measured (S41), and the dilution ratio of the fermentation liquid in the fermenter is adjusted according to the measurement results of the ammonia concentration and organic acid concentration. Specifically, when at least one of the ammonia concentration and the organic acid concentration in the fermenter exceeds a predetermined threshold value, the dilution ratio is calculated so as to obtain a desired dilution ratio (S43), and the diluent is put into the fermentation tank and diluted (S44). This is because ammonia and organic acids are substances that inhibit the growth of methanogens, and therefore if they exceed a predetermined threshold, the culture of methanogens is inhibited and methane fermentation is not performed normally. It is preferable to withdraw the digestive fluid from the fermenter before adding the diluent.

The dilution rate of the diluent is a numerical value determined in consideration of the ammonia concentration in the fermenter and the organic substance concentration in the fermenter, and the dilution rate is 10 times or less. Here, the threshold range of ammonia concentration (C _NH4+ ) in the fermenter is less than 4000 mg/l. The threshold range for organic acid concentration (C _VFA ) in the fermenter is less than 3000 mg/l. The organic acid concentration is the potential organic acid concentration (C _VFA2 ) calculated from the organic matter concentration (C _TOC ) as the total organic carbon concentration (TOC) in the fermenter, and the organic acid concentration in the fermenter (C _VFA1 ) is C _VFA1 +C _VFA2 . Note that the potential organic acid concentration is the organic acid concentration that may be generated from undigested organic matter in the fermenter. The dilution rate of the diluent is determined so that the ammonia concentration (C _NH4+ ) is less than 4000 mg/l, the organic acid concentration (C _VFA1 +C _VFA2 ) is less than 3000 mg/l, and the dilution rate is less than 10. When measuring the concentration of ammonia in the fermenter and the concentration of organic matter in the fermenter, the concentration of methane bacteria in the fermenter may be measured. When the methanogen concentration is less than 10 ⁷ cells/ml, seed sludge and a biomass feedstock such as cow dung containing methanogens are introduced into the fermenter. This is because a methanogen concentration of less than 10 ⁷ cells/ml and a low methane concentration (less than 50%) means that the number of methanogens is small and methane fermentation is reduced.

After that, in order to allow the methanogenic bacteria to grow, for example, it waits for several minutes to several hours (S45), and measures the methane concentration in the fermenter (S46). When measuring the methane concentration in the fermenter, it is preferable to measure the pH, ORP and biogas amount of the fermenter. Preferred ranges for these values are a fermentor pH of 6.5 to 8 and an ORP of -350 mV or less. The amount of biogas is an arbitrary value determined by the biogas raw material to be fed. If the methane concentration is 50% or more (S46), the mode is switched to the normal mode of STEP 3 (S47). If the methane concentration is less than 50%, then again consider steps S42-S46 above.

Conventionally, when the amount of biogas in the fermenter decreased or fermentation stopped, it was necessary to rely on the experience of the operator or to start the methane fermentation start-up process from scratch. The recovery process (STEP 4) according to the present embodiment makes it possible to clarify the management items and operation methods when methane fermentation is not performed normally, providing a recovery means for methane fermentation that does not rely on the experience of the operator. can do.

The recovery process can also be performed when the methane fermentation start-up process (STEP 1) fails, that is, when the methane concentration in the fermenter does not reach 50% or more.

Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiment within the same scope as the present invention or within an equivalent scope.

INDUSTRIAL APPLICABILITY The methane fermentation method of the present invention is effectively utilized in a methane fermentation method for performing methane fermentation using a biomass raw material.

Claims (4)

A method for starting up methane fermentation in which methanogenic bacteria are cultured to generate methane gas without using seed sludge,
preparing cattle dung containing methanogens and feed as silage or compound feed ;
A step of charging the cow dung and the feed into a fermenter at a predetermined ratio of the cow dung and the feed;
Culturing methanogenic bacteria in the fermenter to generate methane gas ,
The silage input in dry matter weight ratio is 0.5-2.5% of the cow dung input, or the compound feed input in dry matter weight ratio is 0.5% of the cow dung input. 1 to 1.0%, a method for starting up methane fermentation. The method for starting up methane fermentation according to claim 1, wherein the temperature in the fermenter is gradually increased from 36°C to 42°C after the cow dung and the feed are put into the fermenter. The method for starting up methane fermentation according to claim 1 or 2 , wherein the total weight of solid content of said cow dung and said feed with respect to the total weight put into said fermenter is 10% to 15%. 4. Any one of claims 1 to 3 , wherein a biomass raw material different from the cow dung is introduced into the fermenter in addition to the cow dung after the culture of the methanogenic bacteria in the cow dung is stabilized in the fermenter. A method for starting up the described methane fermentation.

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