JP2012016652A - Digestion system, grass-based biomass digestion tank, and grass-based biomass digestion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use wet biomass such as grass using existing equipment without excessively increasing the load on a sewage digestion tank.SOLUTION: This digestion system 1 includes the sewage digestion tank 100 for sewage treatment, a vegetation digestion tank 10 having an input port 11a of the wet biomass G10 in its upper part, a lower inflow pipe 14 for making digestive juice W100 in the sewage digestion tank 100 flow into the vegetation digestion tank 10, and a valve 14a for opening and closing the lower inflow pipe 14.

Description

  The present invention relates to a digestion system, a grass biomass digester, and a grass biomass digestion method.

  Conventionally, waste containing a large amount of cellulosic substrates such as grass generated by mowing roads or parks (hereinafter referred to as grass biomass) is generally incinerated and used as energy. It was rare. However, it is not possible to effectively use resources to incinerate grass-based biomass, which is wet biomass, without using it as energy. Thus, conventionally, grass-based biomass has been digested and disposed of together with other wet biomass such as food waste, sewage sludge, and livestock excrement by methane fermentation technology.

JP-A-2-268895 Japanese Patent Laid-Open No. 2-289482 JP 2001-114583 A JP 2003-94022 A JP 2006-305467 A Japanese Patent No. 3694744 Japanese Patent No. 4468123

  Here, when digesting and disposing of grass-based biomass together with other wet biomass, if these are mixed using an existing sewage digester, grass that could not be digested may be clogged in the pump. . Therefore, conventionally, it was necessary to separate and crush grass and the like before mixing them together in an existing sewage digester. However, it takes a lot of energy to separate and crush grass and the like. Therefore, this method could not be said to be an effective use of resources. This was the same for both wet and dry methane fermentation.

  Therefore, the present invention has been made in view of the above problems, and a digestion system, a grass biomass digester, and a grass biomass digestion capable of effectively utilizing wet biomass such as grass using existing equipment. It aims to provide a method.

  In order to achieve this object, a digestion system according to the present invention comprises a first digester for sewage treatment, a second digester equipped with a grass-based biomass inlet, and a digested liquid in the first digester. A first inflow pipe for flowing into the second digestion tank and a first inflow pipe valve for opening and closing the first inflow pipe are provided.

  The grassy biomass digestion tank according to the present invention includes an inlet for feeding grassy biomass, a first inflow pipe for allowing the digestive liquid in the sewage digester for sewage treatment to flow in, and the first inflow pipe. And a first inflow pipe valve that opens and closes.

  The grassy biomass digestion method according to the present invention is a grassy biomass digestion method in which grassy biomass is digested using a second digester disposed adjacent to a first digester for sewage treatment. The method includes an introduction step of introducing grass-based biomass into the digestion tank, and a digestion fluid inflow step of allowing the digestion fluid in the first digestion tank to flow into the second digestion tank.

  According to the present invention, it becomes possible to digest wet biomass such as grass using a digester in a digester for sewage digestion using a digester separate from a digester for sewage digestion. A digestion system, a grass biomass digester, and a grass biomass digestion method that can effectively utilize wet biomass such as grass using existing equipment without excessively increasing the burden on the sewage digester It can be realized.

FIG. 1 is a schematic diagram showing a schematic configuration of a digestion system according to Embodiment 1 of the present invention. FIG. 2 is a schematic diagram showing an example of a digestion system according to the present embodiment. FIG. 3 is a flowchart showing an outline of a method for digesting grass-based biomass according to the present embodiment. FIG. 4 is a flowchart showing an outline of the cleaning process shown in FIG. FIG. 5 is a schematic diagram showing a schematic configuration of a digestion system according to Embodiment 2 of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the following description, each drawing only schematically shows the shape, size, and positional relationship to the extent that the contents of the present invention can be understood. Therefore, the present invention is illustrated in each drawing. It is not limited to only the shape, size, and positional relationship. Moreover, in each figure, a part of hatching in a cross section is abbreviate | omitted for clarification of a structure. Furthermore, the numerical values exemplified below are merely preferred examples of the present invention, and therefore the present invention is not limited to the illustrated numerical values.

(Embodiment 1)
Hereinafter, a digestion system, a grassy biomass digestion tank, and a grassy biomass digestion method concerning Embodiment 1 of the present invention are explained in detail with reference to drawings. FIG. 1 is a schematic diagram showing a schematic configuration of a digestion system according to the first embodiment. As shown in FIG. 1, the digestion system 1 includes an existing sewage digester 100 and a plant digester 10 disposed adjacent to the sewage digester 100.

  Grass-based biomass G10 such as grass that has been transported by a transport vehicle 110 such as a dump truck or a garbage truck is input to the inside from an input port 11a provided above the plant digestion tank 10. The plant digestion tank 10 uses the water level difference D1 (= H100−H10) between the digestion solution W100 in the sewage digestion tank 100 and the digestion solution W10 in the plant digestion tank 10 for the digestion solution W100 in the sewage digestion tank 100. The digestive fluid W100 in the sewage digester 100 is caused to flow into the vegetation digester 10 using the upper inflow pipe 12 that flows into the digester 10 and the water level difference D1 between the digested fluid W100 and the digested fluid W10. A lower inflow pipe 14 is connected to a side discharge pipe 15 that wastes the digestive juice W10 in order to adjust the liquid level in the plant digestion tank 10. In addition, an outlet 11b for removing the residue G11 that could not be digested is provided at the bottom of the plant digestion tank 10. In this description, the digestive fluids W100 and W10 may each contain sludge.

  Here, the outlet of the upper inlet pipe 12 is located above the plant digestion tank 10. A shower head is provided at the outlet, and the digestive juice W100 is discharged in a shower shape. By releasing the digestive juice W100 from above into a shower shape, the surface of the grassy biomass G10 in the plant digestion tank 10 can be uniformly moistened with the digestive fluid W100. As a result, the fungus is activated to digest the grassy biomass. Can be promoted.

  The outlet of the lower inflow pipe 14 is located below the plant digestion tank 10. By flowing in the digestive juice W100 in the sewage digester 100 from below in the plant digester 10, the grass-based biomass G10 in the plant digester 100 is washed using the flow of the digested solution W100 and the like by this inflow. As a result, it becomes possible to activate the fungus and promote the digestion of grass-based biomass. However, it is also possible to use or use the release of the digestive fluid W100 from the upper inflow pipe 12 for washing the grassy biomass G10 in the vegetation digestion tank 10.

  The side discharge pipe 15 is branched into a plurality of branch pipes 15 </ b> A to 15 </ b> N on the upstream side (the plant digestion tank 10 side). The inflow ports of the branch pipes 15 </ b> A to 15 </ b> N are connected to different height positions on the side wall of the plant digestion tank 10. Thereby, it becomes possible to adjust easily the liquid level height of the digestive liquid W10 in the plant digestion tank 10 to the height where each branch pipe 15A-15N was connected. Moreover, it becomes easy to selectively discharge the supernatant portion of the digestive juice W10. In addition, the side part discharge pipe 15 after joining merges with the lower discharge pipe 13, for example.

  The inlet of the lower discharge pipe 13 is located near the bottom in the vegetation digestion tank 10 and discharges the digestive juice W10 near the bottom in the vegetation digestion tank 10. In addition, even if the digestive juice W10 discharged | emitted via the lower discharge pipe 13 (a part including the side part discharge pipe 15) returns to the sewage digestion tank 100, for example, it passes through a transport vehicle, a feed pipe, etc. May be sent to a sludge treatment facility such as a dehydrator (not shown). When returning the digested liquid W10 discharged to the lower discharge pipe 13 to the sewage digester tank 100, waste liquid or the like is not substantially generated from the plant digester tank 10, so that the grass-based biomass can be effectively used more efficiently. Here, the side discharge pipe 15 and the lower discharge pipe 13 after joining may be provided with a configuration such as a pump for promoting the discharge of the digestive fluid W10.

  In addition, each of the branch pipes 15A to 15N of the upper inlet pipe 12, the lower inlet pipe 14, the side outlet pipe 15 and the lower outlet pipe 13 is provided with valves 12a, 14a, 15a to 15n that are manually opened or closed. , And 13a are provided, and the respective flow paths are opened and closed as necessary.

  Further, in the upper part of the vegetation digestion tank 10, a lower discharge pipe 13 for discharging the digestive fluid W10 in the vegetation digestion tank 10, an air pipe 16 for introducing / exhausting air into the vegetation digestion tank 10, and a vegetation digestion A gas exhaust pipe 17 for exhausting a gas such as methane generated in the tank 10 is connected. The air pipe 16 and the gas exhaust pipe 17 are respectively provided with valves 16a and 17a that are manually or automatically opened and closed, and the respective flow paths are opened and closed as necessary.

  The air exhaust pipe 16 is used to extract air from the sewage digester 10 when the digestive fluid W100 is allowed to flow from the sewage digester 100 into the sealed vegetation digester 10 by closing the inlet 11a and the outlet 11b. It is piping. The air exhaust pipe 16 is also a pipe for introducing air into the plant digestion tank 10 when the digestive fluid W10 is discharged from the plant digestion tank 10.

  The gas exhaust pipe 17 is a pipe for discharging the gas in the plant digestion tank 10 after completion of the digestion process or digestion process. In addition, the gas exhaust pipe 17 joins the gas exhaust pipe 120 connected to the sewage digester 100, for example. The gas exhaust pipe 120 is provided with a valve 120a that opens and closes manually or automatically, and the flow path is opened and closed as necessary. The gas exhausted from the sewage digester 100 or the plant digester 10 is, for example, via a gas exhaust pipe 120 (partly including the gas exhaust pipe 17), for example, a gas purification apparatus (for example, the gas purification apparatus 200 shown in FIG. 2). The gas is purified to biogas and stored in a gas tank (for example, see gas tank 210 shown in FIG. 2).

  In the first embodiment, for example, as shown in FIG. 2, a plurality of plant digesters 10-1 to 10-n may be installed adjacent to one sewage digester 100. FIG. 2 is a schematic diagram illustrating an example of a digestion system according to the first embodiment. In this case, as shown in FIG. 2, the gas exhaust pipes 17-1 to 17-n of the vegetation digesters 10-1 to 10-n are joined together to the gas exhaust pipe 120 of the sewage digester 100. Also good.

  Subsequently, the method for digesting grass biomass according to the first embodiment will be described in detail with reference to the drawings. FIG. 3 is a flowchart showing an outline of the grass-based biomass digestion method according to the first embodiment. As shown in FIG. 3, in this digestion method, first, the inlet 11a of the plant digestion tank 10 is opened, and grass-based biomass G10 such as grass that has been transported by the transport vehicle 110 or the like from this slot 11a is removed. 10 (step S101). Subsequently, it is determined whether or not the grass-based biomass G10 has reached a predetermined amount set in advance as a guide (step S102). If the predetermined amount has not been reached (No in step S102), the next grass-based biomass is determined. Wait for G10 input. On the other hand, if it is equal to or greater than the predetermined amount (Yes in Step S102), first, the inlet 11a of the plant digestion tank 10 is closed (Step S103), and then the valve 16a of the air pipe 16 is opened (Step S104). Subsequently, by opening the valve 14a of the lower inflow pipe 14 (step S105), the digestive fluid W100 in the sewage digester 100 is introduced into the plant digester 10 while the air in the plant digester 10 is being evacuated. At this time, the upper inflow pipe 12 may be used in combination. Note that the predetermined amount may be, for example, a weight or a bag. Further, a predetermined collection period or the like may be used instead of the predetermined amount.

  Thereafter, it is determined whether or not the liquid level of the digestive liquid W10 in the plant digestion tank 10 has reached a predetermined height (step S106), and waiting for it to reach (No in step S106). Thereafter, when the predetermined height is reached (Yes in step S106), the valves 14a and 16a of the lower inflow pipe 14 and the air pipe 16 are closed (step S107). In addition, the method of arrange | positioning a liquid level sensor etc. in the predetermined | prescribed height in the vegetation digestion tank 10 detects whether the liquid level of the digestive liquid W10 in the vegetation digestion tank 10 reached | attained the predetermined height, for example. Various modifications such as a method based on whether a predetermined time has passed or not can be made.

  Next, while waiting for a predetermined number of days (here, 60 days) from the introduction of the digestive fluid W100, the valve 12a of the upper inflow pipe 12 is opened at a predetermined interval (for example, every day) for a predetermined time (for example, 1 hour) ( In step S108), the upper layer of the grassy biomass G10 is prevented from being dried in the plant digestion tank 10 by taking a shower of the digestive fluid W100 in the plant digestion tank 10.

  In addition, as a treatment for improving the digestion efficiency of the grass-based biomass G10 once or twice or more after the predetermined number of days (60 days) from the introduction of the digestive liquid W100, the grass in the plant digestion tank 10 is used. A cleaning process for cleaning the system biomass G10 is executed (No in Step S109 and Step S110). This cleaning process may be performed, for example, every predetermined number of days (for example, 14 days or 30 days). Details of the cleaning process will be described later. It should be noted that until the predetermined number of days (60 days) has passed since the introduction of the digestive juice W100, for example, even after the cleaning process is performed once, the process of step S108 may be continued.

  Next, when the remaining days of the predetermined number of days (60 days) have elapsed (Yes in step S110), the valves 17a and 14a of the gas exhaust pipe 17 and the lower inflow pipe 14 are opened (step S111), whereby grass-based biomass. A gas such as methane generated in the plant digestion tank 10 by digestion of G10 is sent out to the gas exhaust pipe 17 with the pressure of the digestive liquid W100 flowing from the sewage digestion tank 100. The gas sent out to the gas exhaust pipe 17 is then sent to, for example, the gas purification device 200 (see FIG. 2) and purified, and then stored in the gas tank 210 (see FIG. 2).

  Then, it waits until the exhaust of the gas in the plant digestion tank 10 is completed (No in Step S112), and when completed (Yes in Step S112), the valves 17a and 14a of the gas exhaust pipe 17 and the lower inflow pipe 14 are closed ( Then, the digestion liquid W10 in the plant digestion tank 10 is discharged by opening the valves 16a and 13a of the air pipe 16 and the lower discharge pipe 13 (step S114). In addition, the digestive liquid W10 discharged | emitted from the plant digestion tank 10 may be returned to the sewage digestion tank 100, for example, and may be sent to sludge treatment facilities, such as a dehydrator.

  Thereafter, when the discharge of the digestive juice W10 is completed (Yes in step S115), the valves 16a and 13a of the air pipe 16 and the lower discharge pipe 13 are closed (step S116), and the operation is ended.

  With the configuration and operation as described above, in the first embodiment, the digestive juice W100 in the sewage digester 100 is used by using a plant digester 10 different from the sewage digester 100 for sewage digestion. It is possible to digest the grass-based biomass G10. Accordingly, a grass-based biomass digester, a digestion system, and a grass-based biomass digestion method capable of effectively utilizing grass-based biomass using existing facilities without excessively increasing the burden on the sewage digester 100 Can be realized.

  Next, the cleaning process shown in step S109 of FIG. 3 will be described in detail with reference to the drawings. FIG. 4 is a flowchart showing an outline of the cleaning process shown in FIG. As shown in FIG. 4, in the cleaning process, it is determined whether or not a predetermined number of days (for example, 14 days) has elapsed since the introduction of the digestive fluid W100 or the previous cleaning process (step S120). If it has not elapsed (No in step S120), the process returns to the operation shown in FIG. On the other hand, when the predetermined number of days have passed (Yes in step S120), first, the valve 16a of the air pipe 16 is opened and the valve 13a of the lower discharge pipe 13 is opened (step S121), so that the digestion in the plant digestion tank 10 is performed. The liquid W10 is discharged. Thereby, what inhibits digestion of grass-based biomass G10 (hereinafter simply referred to as digestion residue of fungi) such as digestion residue of bacteria attached to grass-based biomass G10 in plant digestion tank 10 is caused by the flow of digestive fluid W10. Washed away. At this time, the digestive juice W10 may be discharged by using the side discharge pipe 15 together. In this case, as a procedure for opening the valves 15a to 15n of the plurality of branch pipes 15A to 15N branched from the side discharge pipe 15, for example, the valve 15a of the uppermost branch pipe 15A is opened, and then in the plant digestion tank 10 When the liquid level drops to the position of the inlet of the discharge pipe where the valve is opened, a procedure of opening the valve of the next discharge pipe to the lowest branch pipe 15N can be adopted.

  Thereafter, when the liquid level in the vegetation digestion tank 10 is lowered to a predetermined height (for example, a height at which half or more of the grass-based biomass G10 is exposed from the digestive liquid W10) (Yes in step S122), then the air The valves 16a and 13a of the pipe 16 and the side discharge pipe 13 are closed (step S123), and then the valves 17a and 12a of the gas exhaust pipe 17 and the upper inflow pipe 12 are opened (step S124), thereby the sewage digester 100. The digestive liquid W100 is showered from above in the plant digestion tank 10. As a result, the fungus discharge remaining on the surface of the grass-based biomass G10 is washed away by the shower effect, and the plant digestion tank 10 is filled with the digestive fluid W100 in the sewage digestion tank 100, so that the grass-based biomass G10 is obtained. New bacteria adhere. As a result, the digestion efficiency of the grass-based biomass G10 is improved and digestion is promoted. However, at this time, the lower inflow pipe 14 may be used together, or the lower inflow pipe 14 may be used instead of the upper inflow pipe 12. Even in this case, since the flow of the digestive fluid W10 can be generated in the plant digestion tank 10, the digestion residue of the fungi remaining on the surface of the grass biomass G10 can be washed away, and the plant digestion tank 10 The inside is filled with the digestive liquid W100 in the sewage digestion tank 100, and new bacteria adhere to the grassy biomass G10.

  Thereafter, it is determined whether or not the liquid level in the plant digestion tank 10 has reached a predetermined height for operation (step S125), and if it has reached (Yes in step S125), the gas exhaust pipe 17 and the upper inflow pipe 12 are reached. The valves 17a and 12a are closed (step S126), and then the operation returns to the operation shown in FIG.

  By operating in this way, in the first embodiment, the digestive residue W100 in the sewage digester 100 is used for the digestion residue of the bacteria attached to the grass biomass G10 in the plant digester 10 for the grass biomass. Therefore, digestion can be promoted by improving the digestion efficiency of the grass-based biomass G10. For this reason, compared with the case where grass-based biomass is digested in the sewage digester 100, the grass-based biomass is effectively utilized using existing facilities without excessively increasing the burden on the sewage digester 100. Is possible. Further, in the grass-based biomass cleaning method according to the first embodiment, since it is not necessary to physically move grass-based biomass such as grass, for example, grass-based biomass can be obtained by moving the grass-based biomass and stirring the digestion liquid. Compared with a method of removing digestion residues such as attached bacteria, it is possible to easily and easily wash grass biomass and promote digestion.

  In addition, when digesting and disposing of grass-based biomass in addition to wet biomass such as food waste, sewage sludge, and livestock excrement that should be treated in the past, the load on one sewage digester is increased. However, according to the present embodiment 1, since the digester for plants and plants is used separately from the sewage digester, It is possible to efficiently digest grass-based biomass without excessively increasing the load on the sewage digester.

  Furthermore, grass biomass produced by mowing roads and parks is not stable throughout the year. Therefore, the digester that digests grass-based biomass exclusively will be a facility with a stop depending on the season. Introducing such a facility with a start and stop requires a great burden on the processing facility in terms of introduction cost, facility area, and the like. On the other hand, in this Embodiment 1, since it becomes possible to digest vegetation biomass using the existing sewage digester, it can avoid that a processing facility requires a big burden.

(Embodiment 2)
Next, a digestion system, a grass biomass digester, and a grass biomass digestion method according to Embodiment 2 of the present invention will be described in detail with reference to the drawings. However, in the following description, the same configurations and operations as those of the first embodiment described above are denoted by the same reference numerals, and redundant description thereof is omitted.

  FIG. 5 is a schematic diagram illustrating a schematic configuration of the digestion system according to the second embodiment. As is clear from comparison between FIG. 1 and FIG. 5, the digestion system 4 according to the second embodiment has a configuration similar to the plant digestion tank 10 in the digestion system 1 shown in FIG. 1 and 10-2 are provided in two stages. Other configurations are the same as those of the digestion system 1.

  In the example shown in FIG. 5, the digestive juice W100 is sent from the sewage digester 100 into the upper plant digester 10-1 via the lower inflow pipe 14-1. Moreover, the digestive liquid W100 in the sewage digester 100 is showered in the plant digester 10-1 through the upper inflow pipe 12-1. The air in the plant digestion tank 10-1 is appropriately exhausted through an air pipe 16-1 that merges with an air pipe 16-2 described later, and the gas in the plant digestion tank 10-1 is appropriately gas. Exhaust is performed through a gas exhaust pipe 17-1 that joins the exhaust pipe 120.

  Moreover, the digestive liquid W10 in the plant digestion tank 10-1 is suitably discharged | emitted via the lower discharge pipe 13-1. The discharged digestion liquid W10 is introduced into the lower plant digestion tank 10-2. In addition, the supernatant of the digestive juice W10 in the plant digestion tank 10-2 is appropriately placed in the lower plant digestion tank 10-2 via any one of the branch pipes 15A-1 to 15N-1 and the side discharge pipe 15-1. Showered inside. The air in the plant digestion tank 10-2 is appropriately exhausted through an air pipe 16-2, which will be described later, and the gas in the plant digestion tank 10-2 is appropriately supplied via a gas pipe 17-1. The gas is exhausted through a gas exhaust pipe 17-2 that joins the exhaust pipe 120.

  In addition, the digestive liquid W10 in the plant digestion tank 10-2 is suitably discharged | emitted via the lower discharge pipe 13-2. Further, the supernatant of the digestive juice W10 in the plant digestion tank 10-2 is appropriately sent to the lower discharge pipe 13-2 via one of the branch pipes 15A-2 to 15N-2 and the side discharge pipe 15-2. It is done. For example, the digestive juice W10 that has flowed into the lower discharge pipe 13-2 is sent to a lower vegetation digester tank (not shown) or returned to the sewage digester tank 100, via a transport vehicle, a feed pipe, or the like. May be sent to a sludge treatment facility such as a dehydrator (not shown).

  Thus, in this Embodiment 2, the digestive liquid W10 of the vegetation digestion tank 10-1 located in an upper stage is cooperated with the vegetation digestion tanks 10-1 and 10-2 arranged in a plurality of stages. On the other hand, it can be effectively utilized in the plant digestion tank 10-2 located in the lower stage. As a result, a digestion system, a grass-based biomass digester, and a grass-based biomass digestion method capable of effectively utilizing grass-based biomass using existing facilities while further reducing the burden on the sewage digester 100 are realized. It becomes possible.

  Since other configurations and operations are the same as those in the first embodiment, detailed description thereof is omitted here.

  In addition, the above-described embodiment and its modifications are merely examples for carrying out the present invention, and the present invention is not limited to these, and various modifications according to specifications and the like are within the scope of the present invention. Furthermore, it is obvious from the above description that various other embodiments are possible within the scope of the present invention. For example, it is needless to say that the modification examples illustrated as appropriate for each embodiment can be applied to other embodiments.

1, 4 Digestion system 10, 10-1 to 10-n Plant digestion tank 11a Input port 11b Outlet port 12, 12-1, 12-2 Upper inflow tube 13, 13-1, 13-2 Lower discharge tube 14, 14 -1 Lower inlet pipe 15, 15-1, 15-2 Side outlet pipe 15A-15N, 15A-1-15N-1, 15A-2-15N-2 Branch pipe 12a, 13a, 14a, 15a-15n, 16a , 17a, 120a Valve 16, 16-1, 16-2 Air piping 17, 17-1 to 17-n Gas exhaust pipe 100 Sewage digestion tank 110 Transport vehicle 120 Gas exhaust pipe 200 Gas purification device 210 Gas tank D1 Water level difference G10 Grass Biomass G11 residue W10, W100 digestive juice

Claims (9)

A first digester for sewage treatment;
A second digester with an inlet for grass-based biomass;
A first inflow pipe for allowing the digestive juice in the first digestion tank to flow into the second digestion tank;
A first inlet pipe valve for opening and closing the first inlet pipe;
A digestion system comprising: The one or more second digesters are disposed adjacent to one or more sides or obliquely below the first digesters,
The first inflow pipe causes the digestive fluid to flow into the second digestion tank based on a water level difference between the liquid level in the first digestion tank and the liquid level in the second digestion tank. The digestion system according to claim 1.   The digestion system according to claim 1, further comprising a second inflow pipe that discharges the digestive liquid in the first digestion tank in a shower shape from above in the second digestion tank.   The digestion system according to any one of claims 1 to 3, wherein the second digestion tank includes an outlet for taking out the residue in a lower part. A third digester with a plant biomass inlet;
A third inflow pipe for allowing the digestive juice in the second digestion tank to flow into the third digestion tank;
A third inlet pipe valve for opening and closing the third inlet pipe;
The digestive system according to claim 1, further comprising: An inlet for introducing grass-based biomass;
A first inflow pipe through which a digestion liquid in a sewage digester for sewage treatment flows,
A first inlet pipe valve for opening and closing the first inlet pipe;
A grass-based biomass digester characterized by comprising. A grass-based biomass digestion method for digesting grass-based biomass using a second digester disposed adjacent to a first digester for sewage treatment,
A charging step of charging grass biomass into the second digestion tank;
A digestion fluid inflow step for allowing the digestion fluid in the first digestion tank to flow into the second digestion tank;
A grass-based biomass digestion method characterized by comprising:   The grass-based biomass digestion method according to claim 7, further comprising a discharge step of discharging the digestion liquid in the first digestion tank in a shower shape from above in the second digestion tank. A grass biomass digestion method for digesting grass biomass using a second digester and a third digester disposed adjacent to a first digester for sewage treatment,
A first charging step of charging grass-based biomass into the second digestion tank;
A first digestive fluid inflow step for causing the digestive fluid in the first digestive fluid to flow into the second digestive fluid;
A second charging step of charging grass biomass into the third digester;
A second digestive fluid inflow step for allowing the digestive fluid in the second digestive fluid to flow into the third digestive fluid;
A grass-based biomass digestion method characterized by comprising:

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