1. An anaerobic treatment method ofcausing a raw material including harvest residues produced in an agricultural field to undergo methane fermentation to return fermentation residues produced from the methane fermentation to the agricultural field and to utilize biogas produced from the methane fermentation as an energy source, comprising: adjusting a cut lenglh of the harvest residues to be supplied to the methane fermentation based on information about demand for the fermentation residues or the biogas.

2. The anaerobic treatrnent method according to claim 1, further comprising adjusting a cut length or average cut length ofthe harvest residues to be supplied to the methane fermentation to be shortened in response to an increase in demand for the fermentation residues or the biogas.

3. The anaerobic treatrnent method according to claim I or 2, t'urther corlprising adjusting a cut length ofthe harvest residues using a previously determined relationship between a length ofthe harvest residues and a hydraulic retention time (HRT) required for the methane fermentation

4. The anaerobic trea[nent method according to any one ofclaims 1 to 3, further comprising storing the harvest residues separately in a plurality of cut lengths and, based on the information about demand for the fermentation residues or the biogas, selecting or mixing the harvest residues such that the harvest residues with a predetermined cut length are supplied to the methane fermentation.

FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. ANAEROBIC TREATMENT METHOD
2.
1. (A) KUBOTA CORPORATION
(B) Japan
(C) 1-2-47, Shikitsuhigashi, Naniwa-ku, Osaka-shi, Osaka 5568601, Japan
The following specification particularly describes the invention and the manner in which it is to be
performed.
2
Technical Field
[0001] The present invention relates to an anaerobic treatment method of causing a raw
material including harvest residues produced in an agricultural field to undergo methane
fermentation to utilize fermentation residues produced from the methane fermentation as a
compost or fertilizer and to utilize biogas produced from the methane fermentation as an
energy source.
Background Art
[0002] A large amount of rice straw produced from rice harvest operations has
conventionally been plowed back into the soil of an agricultural field as an organic fertilizer or
incinerated at the agricultural field. However, methane produced from the decomposition of
the plowed-back rice straw in the soil in an anaerobic atmosphere and carbon dioxide produced
from the incineration are greenhouse gases that have a large impact on global warming. As
such, there is a challenge in how to process the large amount of rice straw. Such a challenge
is not exclusive to rice straw, but is common to agricultural wastes (referred to herein as
“harvest residues”) produced after the harvest of grains harvested in agricultural fields,
including wheat straw and the like.
[0003] Patent Literature 1 proposes a methane fermentation method of causing straw crushed
into pieces of 10 mm to 100 mm to undergo methane fermentation in a fermentation liquid to
recover biogas and also recovering the straw after the fermentation from the digested solution
to utilize it as a bedding material.
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent No. 5567718
3
Summary of Invention
Technical Problem
[0005] The methane fermentation method disclosed in Patent Literature 1 is a very desirable
technique in terms of effective utilization of biomass resources, but there is room for further
innovations in terms of efficiently processing the large amount of harvest residues produced in
agricultural fields, including rice straw and wheat straw.
[0006] It is an object of the present invention to provide an anaerobic treatment method that
can efficiently utilize harvest residues produced in agricultural fields as resources.
Solution to Problem
[0007] To achieve the above object, an anaerobic treatment method is provided in accordance
with the present invention. As a first feature of the anaerobic treatment method, the method
causes a raw material including harvest residues produced in an agricultural field to undergo
methane fermentation to return fermentation residues produced from the methane fermentation
to the agricultural field and to utilize biogas produced from the methane fermentation as an
energy source, and comprises: adjusting a cut length of the harvest residues to be supplied to
the methane fermentation based on information about demand for the fermentation residues or
the biogas.
[0008] The time required for methane fermentation is important in terms of matching the
demand for the biogas or the fermentation residues. Hence, the cut length of the harvest
residues is adjusted according to the demand for the biogas or the fermentation residues. This
enables adjustment of the time required for methane fermentation, allowing for effective
utilization of the organic resources of the harvest residues.
[0009] In addition to the first feature above, the anaerobic treatment method has a second
feature that the method further comprises adjusting a cut length or average cut length of the
harvest residues to be supplied to the methane fermentation to be short in response to an
increase in demand for the fermentation residues or the biogas.
[0010] The methane fermentation process is controlled by operating conditions such as the
4
temperature, hydraulic retention time (HRT), and organic load. By adjusting the cut length or
average cut length of the harvest residues to be supplied to the methane fermentation to be
short, the HRT can be shortened, which can consequently increase the amount to be treated of
the anaerobic treatment. This allows for properly responding to an increase in demand for the
biogas or the fermentation residues.
[0011] In addition to the first or second feature above, the anaerobic treatment method has a
third feature that the method further comprises adjusting a cut length of the harvest residues
using a previously determined relationship between a length of the harvest residues and a
hydraulic retention time (HRT) required for the methane fermentation.
[0012] By knowing the relationship between the length of the harvest residues and the HRT
required for methane fermentation in advance, the cut length of the harvest residues can be
properly adjusted to a value consistent with the target HRT, consequently allowing for
adjustment of the amount to be treated of the anaerobic treatment.
[0013] In addition to any one of the first to third features above, the anaerobic treatment
method has a fourth feature that the method further comprises storing the harvest residues
separately in a plurality of cut lengths and, based on the information about demand for the
fermentation residues or the biogas, selecting or loading the harvest residues such that the
harvest residues with a predetermined cut length are supplied to the methane fermentation.
[0014] By pre-storing the harvest residues separately in multiple cut lengths, those with a
predetermined cut length can be selected or loaded from them. This allows the HRT to be
adjusted to be consistent with the information about demand for the biogas or the fermentation
residues, consequently allowing for adjustment of the amount to be treated of the anaerobic
treatment.
Advantageous Effects of Invention
[0015] As described above, the present invention can provide an anaerobic treatment method
that can efficiently utilize harvest residues produced in agricultural fields as resources.
Brief Description of Drawings
5
[0016] FIG. 1 illustrates a method for processing harvest residues produced in agricultural
fields.
FIG. 2 illustrates a resource recycling method for harvest residues produced in
agricultural fields.
FIG. 3 is a characteristic diagram illustrating correlation between a length L of the
harvest residues (rice straw), a hydraulic retention time (HRT), and an amount to be treated.
Description of Embodiments
[0017] An anaerobic treatment method, a resource recycling method incorporating the
anaerobic treatment method, and a resource recycling management method of the present
invention are described below, by way of example with respect to rice straw, which is rice
harvest residues produced in agricultural fields.
[0018]
[Resource Recycling System]
FIG. 1 illustrates a resource recycling system 1 implementing the resource recycling
method of the present invention.
The resource recycling system 1 is constructed for each community farm or for
multiple community farms in the neighborhood. The resource recycling system 1 includes
multiple agricultural fields 2 where rice straw, or harvest residues 3, is produced, multiple
storage locations 5 for storing the harvest residues 3, a methane fermentation apparatus 6 for
conducting methane fermentation treatment mainly for the harvest residues 3, and a gasifier 9
for generating a synthesis gas from the harvest residues 3. FIG. 1 shows a single methane
fermentation apparatus 6 and a single gasifier 9; however, in practice, multiple lines of
methane fermentation apparatuses 6 and/or multiple lines of gasifiers 9 may be dispersed or be
consolidated in one location, depending on the size of the harvest residues 3 to be received.
[0019] The resource recycling system 1 also includes a biogas power generator 8 for
generating electricity using methane gas (biogas) generated in the methane fermentation
apparatus 6 as a fuel. The electricity generated by the biogas power generator 8 is consumed
6
as electrical energy for the relevant area, and combustion waste heat produced in the biogas
power generator 8 is used as a heat source for the methane fermentation apparatus 6 and for
greenhouses. Carbon dioxide produced in the biogas power generator 8 is supplied to
greenhouses as a raw material gas for photosynthesis.
[0020] The methane fermentation apparatus 6 includes, among others, a methane
fermentation tank containing a fermentation liquid, a feeder for feeding the harvest residues 3
into the methane fermentation tank, a mixing mechanism for mixing the harvest residues 3 and
the fermentation liquid, and a heating mechanism for adjusting the fermentation temperature.
A portion of the combustion waste heat produced during power generation is supplied to the
heating mechanism to heat the methane fermentation tank to about 55°C suitable for a
thermophilic methane fermentation method, and organic substances are digested under
anaerobic conditions to generate the biogas such as methane gas and carbon dioxide.
[0021] A fermentation residue tank 7 is provided near the methane fermentation apparatus 6
to store fermentation residues produced in the methane fermentation apparatus 6, and the
fermentation residues stored in the fermentation residue tank 7 are returned to the agricultural
fields 2 as a compost or fertilizer.
[0022] The gasifier 9 includes a reaction tower into which the cut harvest residues 3 are fed.
The harvest residues 3 are fluidized and mixed with high-temperature steam and oxygen gas
inside the reaction tower to cause a water gas reaction and a water gas shift reaction, thereby
generating a synthesis gas containing hydrogen and carbon monoxide. Biochar consisting of
silica-containing carbon components is also generated as ash discharged with the synthesis gas.
[0023] The water gas reaction refers to an endothermic reaction in which carbon monoxide
CO and hydrogen H2 are generated from solid carbon C contained in the harvest residues 3 and
steam H2O in a high temperature environment at or above 500℃, as shown in the following
formula:
C + H2O → CO + H2
[0024] The water gas shift reaction refers to an exothermic reaction in which carbon dioxide
CO2 and hydrogen H2 are generated from carbon monoxide CO and steam H2O in a high
7
temperature environment at or above 800℃, as shown in the following formula:
CO + H2O → CO2 + H2
[0025] The synthesis gas generated in the gasifier 9 is purified by a gas purifier 10, and the
biochar containing carbon components removed from the synthesis gas is returned to the
agricultural fields 2 as a compost or fertilizer together with the fermentation residues described
above.
[0026] The resource recycling system 1 includes a synthesis gas power generator 11 that uses
the synthesis gas generated in the gasifier 9 as a fuel to generate electricity. The generated
electricity is supplied as electrical energy for the relevant area, and the combustion waste heat
produced in the synthesis gas power generator 11 is used as a heat source for the methane
fermentation apparatus 6 and for greenhouses. Carbon dioxide produced in the synthesis gas
power generator 11 is supplied to greenhouses as a raw material for photosynthesis.
[0027] Instead of the synthesis gas power generator 11, the resource recycling system 1 may
include an FT synthesis apparatus that uses a synthesis gas consisting of carbon monoxide and
hydrogen as a raw material to synthesize liquid hydrocarbon as a fuel through a catalytic
reaction. The FT synthesis, which is an abbreviation for the Fischer-Tropsch synthesis, refers
to a series of synthesis reaction processes for synthesizing liquid hydrocarbon from carbon
monoxide and hydrogen through a catalytic reaction.
[0028] At the time of rice harvest, a large amount of rice straw remaining in the agricultural
fields 2 after the harvest, or the harvest residues 3, is, for example, packed into a cylindrical
shape and collected by a roll baler or the like. Accumulating such a large amount of harvest
residues in one location and conducting methane fermentation treatment on it at one time is
physically difficult, including the cost of equipment, so even if a large amount of biogas is
temporarily obtained, it may not be effectively utilized. Accordingly, separate biogas storage
facilities are required.
[0029] Thus, multiple storage locations 5 are dispersed throughout the farming areas
constituting the community farm. The harvest residues 3 collected in each agricultural field 2
are, if necessary, cut by a chipper shredder or any other crusher that is used as a pre-treatment
8
apparatus 4 and capable of cutting the residues into a predetermined size, before being
accumulated in a nearest storage location 5. The above phrase “if necessary” means that such
cutting is performed to correspond to the hydraulic retention time (HRT) during methane
fermentation, which is adjusted according to various demand forecasts by a management
device 20 (described below).
[0030] Various forms of storages are provided in the storage location 5, including a roofed
storage and an unroofed storage where the residues are stored open-air. The appropriate
number of methane fermentation apparatuses 6 and/or gasifiers 9 are provided according to the
layout and number of storage locations 5.
[0031] A management device 20, which is implemented by a cloud-based server equipped
with a memory device 21, is provided to manage the harvest residues 3 for each community
farm or for multiple community farms in the neighborhood. In addition to the storage
locations and types of storage, the management device 20 manages information such as the
start of storage (rice harvest time), cut lengths, varieties, and growers. The resource recycling
system 1 is configured such that a manager of the methane fermentation apparatus 6 and a
manager of the gasifier 9 can identify the management condition of the harvest residues 3 via
respective terminals that can communicate with the management device 20.
[0032] The resource recycling system 1 is configured such that the management device 20
creates a storage plan and a utilization plan for the harvest residues 3 based on annual demand
forecasts until the following year’s harvest, and based on the plans, the harvest residues 3 are
stored dispersedly in the multiple storage locations 5 in different crushed conditions and
utilized. Uncrushed harvest residues 3 are stacked in cylindrical packages, and harvest
residues 3 crushed into a predetermined size are stored in containers such as flexible container
bags.
[0033] The resource recycling system 1 is configured such that the utilization plan created by
the management device 20 and information about the dispersed storage of the harvest residues
3 in the storage locations 5 based on the utilization plan are reported to operators including the
managers via respective terminals, and the operators including the managers can properly
9
process the harvest residues 3 based on the utilization plan.
[0034] The demand forecasts include a forecast of the amount of electricity required to be
generated by the biogas power generator 8 or the synthesis gas power generator 11 for each
predetermined period, a forecast of the amount of heat required for a predetermined period
when the combustion waste heat produced from the combustor in the biogas power generator 8
or the synthesis gas power generator 11 is used, and a forecast of the amount of fermentation
residues required for a predetermined period when the fermentation residues from the methane
fermentation apparatus 6 are used as a compost or fertilizer.
[0035] For example, when the combustion waste heat produced from the combustor in the
biogas power generator 8 or the synthesis gas power generator 11 is used as a heat source for
greenhouses, forecasts of the amount and timing of heat required are stored in the memory
device 21. Also, for example, when the fermentation residues are returned to the agricultural
fields as a fertilizer based on the amount of fertilizer components in the fermentation residues
that is analyzed in advance, forecasts of when the fertilizer is to be applied as a base fertilizer,
the amount of fertilizer components required, and the amount of fermentation residues
returned, as well as forecasts of when the fertilizer is to be applied as an additional fertilizer,
the amount of fertilizer components required, and the amount of fermentation residues returned
are stored in the memory device 21. In the case of rice cultivation, it is necessary to apply the
base fertilizer mainly during soil puddling conducted in April and May and to apply the
additional fertilizer mainly around July. The just enough amount of fertilizer required to be
applied at such times is stored as a demand forecast in the memory device 21.
[0036]
[Resource Recycling Method]
As shown in FIG. 2, the resource recycling method operated by the resource recycling
system 1 is configured to execute, among others: a harvest residue collection step (SA1) of
collecting the harvest residues 3 produced in the agricultural fields 2; a demand forecasting
step (SA2) of forecasting the annual demand for recycled resources using the harvest residues;
a raw material storage step (SA3) of storing the harvest residues 3 dispersedly in multiple
10
storage locations 5 based on the forecast demand; an anaerobic treatment step (SA5) of
supplying a portion of the stored harvest residues 3 to the methane fermentation apparatus 6 to
cause them to undergo methane fermentation based on the demand situation (SA4); and a
returning step (SA8) of returning the fermentation residues produced in the anaerobic
treatment step to the agricultural fields 2 as a compost or fertilizer.
[0037] The harvest residues 3 are caused to undergo methane fermentation in the anaerobic
treatment step (SA5), and the produced methane gas is recovered and used as a fuel for biogas
power generation (SA6), thus effectively utilizing the energy recovered from the harvest
residues 3. The fermentation residues are also recovered (SA7) and returned to the
agricultural fields 2 as a compost or fertilizer (SA8). This recycling and utilization of
resources can reduce the farming cost.
[0038] When a large amount of harvest residues 3 is collected from the agricultural fields 2
due to overlapping harvest periods, the harvest residues 3 can be temporarily stored in the
storages in the raw material storage step SA3, and if necessary (SA4), a portion of the harvest
residues 3 can be supplied to the anaerobic treatment step SA5. This allows for, for example,
effective utilization of the harvest residues 3 even outside the harvest periods. The harvest
residues 3 collected from the agricultural fields 2 may be supplied directly to the anaerobic
treatment step SA5 without going through storages provided in the storage locations 5.
[0039] Preferably, the raw material storage step SA3 is configured to store the harvest
residues 3 collected in the harvest residue collection step SA1 under different storage
conditions corresponding to the storage locations 5. This is because by varying the storage
conditions for the harvest residues 3 according to the storage locations 5 when storing the
harvest residues 3 dispersedly in the multiple storage locations 5, even a large amount of
harvest residues 3 can be processed flexibly to meet anticipated future resource demands.
[0040] Assumable storage conditions include, for example, the cut length of the harvest
residues 3 and the amount of storage. For example, when the anaerobic treatment needs to be
done early, harvest residues with a shorter cut length can be used to shorten the HRT, which
can consequently increase the amount to be treated of the anaerobic treatment. Adjusting the
11
amount of storage and cut length of the harvest residues in this manner as a preprocess before
storing them in different storage locations can accommodate changes in when and how much
the anaerobic treatment is to be done. When the harvest residues 3 are stored over a long
period of time, they can be stored in a long state without being cut, which, taking advantage of
the storage period, allows them to property mature under anaerobic conditions to facilitate
methane fermentation.
[0041] As shown in step SA4, if the management device 20 determines, based on the forecast
demand stored in the memory device 21 or an actual demand, that a large amount of additional
fertilizer will be needed in the near future, such as one month ahead, the harvest residues may
be managed such that those in the storage location 5 where the harvest residues with a shorter
cut length are accumulated are supplied to the nearest methane fermentation apparatus 6, and it
may be operated with a shorter HRT setting. The amount to be treated of the anaerobic
treatment can be thus adjusted, making it possible to obtain fermentation residues with high
dissolved content suitable for additional fertilizers in a short period of time.
[0042] If the management device 20 determines, based on the forecast demand stored in the
memory device 21 or an actual demand, that a large amount of base fertilizer will be needed in
a more distant future, such as several months ahead, the harvest residues may be managed such
that those in the storage location 5 where the harvest residues 3 with a longer cut length are
accumulated are supplied to the nearest methane fermentation apparatus 6 in advance, starting
from a time when there is enough time to ensure a sufficient HRT. Thus, the required amount
of fermentation residues with high organic content suitable for base fertilizers can be secured
until the time when they are needed.
[0043] Since the harvest residues 3 contain organic substances such as lignin, which is
difficult to decompose in anaerobic condition, and fertilizer ingredients such as silica
components, returning the harvest residues 3 to agricultural fields as a compost or fertilizer can
effectively restore the soil fertility. The harvest residues 3 have a high C/N ratio and lack
elements necessary for methane fermentation, which may make stable methane fermentation
impossible. In addition, the harvest residues 3 have small nitrogen and phosphorus
12
components, so that there is an imbalance in nutrients necessary for a compost or fertilizer.
Accordingly, the anaerobic treatment in step SA5 preferably involves feeding deficient
components, such as copper, iron, nickel, and cobalt, needed by methane fermentation bacteria,
as well as nitrogen and phosphorus components recovered from livestock manure and the like
to the methane fermentation apparatus 6 to cause methane fermentation, thereby adjusting the
components of the harvest residues 3 to make them a well-balanced compost or fertilizer.
[0044] As described above, the resource recycling method is configured to execute a
management step of managing storage information including the storage locations 5 and the
storage conditions to store the harvest residues 3 in the raw material storage step SA3, and
managing, based on the storage information, the timing and/or amount of supply of at least a
portion of the harvest residues to the anaerobic treatment step SA5.
[0045] The management step is executed by the above-described management device 20,
which informs the managers and operators in advance to pre-store the harvest residues in
different storage locations under different storage conditions depending on the timing when the
anaerobic treatment will be required and the amount to be treated required at that time. This
facilitates the management of the timing and amount to be treated of the subsequent anaerobic
treatment.
[0046] The resource recycling method preferably further includes a fermentation residue
storage step of storing, in the fermentation residue tank 7, the fermentation residues produced
in the anaerobic treatment step SA5 and recovered in the fermentation residue recovery step
SA7, and the method is preferably configured to return at least a portion of the fermentation
residues stored in the fermentation residue storage step to the agricultural fields 2 in the
returning step SA8.
[0047] Excess fermentation residues produced in the anaerobic treatment step SA5 are stored
in the fermentation residue tank 7, so that they can be returned as a compost or fertilizer to the
agricultural field 2 in need, when needed. The fermentation residues with mixed solid and
liquid components may be stored in that state, or the fermentation residues may undergo
solid-liquid separation to store solid and liquid components separately.
13
[0048] The resource recycling method further includes a gasification treatment step of
gasifying the harvest residues 3 collected in the harvest residue collection step SA1 in the
gasifier 9 (SA9), and the method is configured to adjust the amount of harvest residues
supplied to the gasification treatment step based on the information about demand for
fermentation residues determined in step SA4.
[0049] A required amount of harvest residues is supplied to the anaerobic treatment step SA5
to yield fermentation residues in an amount that is required in the returning step SA8 based on
the information about demand for fermentation residues determined in step SA4, and excess
harvest residues 3 are supplied to the gasification treatment step SA9 to generate a synthesis
gas. The generated synthesis gas is supplied to the synthesis gas power generator 11 to
generate electricity (SA10).
[0050] The resource recycling method is preferably configured to adjust the amount of
harvest residues supplied to the gasification treatment step SA9 based on the storage
information about the harvest residues 3 stored in the raw material storage step SA3.
[0051] A large amount of harvest residues 3 collected in the same period is temporarily
stored in the raw material storage step SA3, and if necessary, a portion of them is supplied to
the anaerobic treatment step SA5 while another portion of them is supplied to the gasification
treatment step SA9. This allows for effective utilization of the harvest residues 3 as recycled
resources.
[0052] For the gasification treatment step SA9, the harvest residues 3 as the raw material
need to be cut into small pieces. Accordingly, the management device 20 is configured to
manage the harvest residues 3 such that those to be supplied to the gasification treatment step
are cut into a predetermined size by the pre-treatment apparatus 4 in step SA3 in advance
before they are accumulated in a predetermined storage location 5.
[0053] The resource recycling method is configured to recover biochar (SA11), which is a
by-product from the gasification treatment step SA9 based on carbon separated in the gas
purifier 10, and return it to the agricultural fields 2 together with a compost or fertilizer, which
is the fermentation residues (SA8). This allows for efficient recycling and utilization of
14
resources.
[0054]
[Resource Recycling Management Method]
The resource recycling management method according to the present invention is
configured to execute: a harvest residue collection step (SA1) of collecting the harvest residues
3 produced in the agricultural fields 2; an anaerobic treatment step (SA5) of causing the
harvest residues collected in the harvest residue collection step to undergo methane
fermentation; a returning step (SA8) of returning at least a portion of fermentation residues
produced in the anaerobic treatment step to the agricultural fields; and a resource recycling
management step (SA4) of adjusting the amount to be treated in the anaerobic treatment step
based on the amount and timing of the harvest residues 3 obtained in the harvest residue
collection step (SA1) and the return amount required in the returning step (SA8).
[0055] The resource recycling management method further includes a raw material storage
step (SA3) of storing the harvest residues 3. The resource recycling management step (SA4)
is configured to adjust the storage locations and storage conditions for the raw material in the
raw material storage step (SA3) based on the amount and timing of the harvest residues
obtained in the harvest residue collection step (SA1) and the return amount required in the
returning step (SA8). The resource recycling management step (SA4) is executed by the
above-described management device 20 and memory device 21.
[0056]
[Anaerobic Treatment Method]
The above-described resource recycling method incorporates an anaerobic treatment
method of the present invention. That is, the anaerobic treatment method is configured to
cause the raw material including the harvest residues 3 produced in the agricultural fields 2 to
undergo methane fermentation to utilize fermentation residues produced from the methane
fermentation as a compost or fertilizer and to utilize biogas produced from the methane
fermentation as an energy source. The anaerobic treatment method is also configured to
adjust the cut length of the harvest residues 3 to be supplied to the methane fermentation
15
apparatus 6 based on the information about demand for the compost etc. or the energy source
managed by the management device 20.
[0057] As already explained above, the time required for methane fermentation is important
in terms of matching the demand for methane gas and fermentation residues. Hence, the cut
length of the harvest residues 3 is adjusted according to the forecast demand for methane gas
and fermentation residues. This enables adjustment of the HTR, which is the time required
for methane fermentation, allowing for effective utilization of the organic resources of the
harvest residues 3.
[0058] Specifically, it is preferable that the cut length or average cut length of the harvest
residues 3 to be supplied to the methane fermentation is adjusted to be short in response to an
increase in demand for the compost etc. or the energy source.
[0059] The methane fermentation process is controlled by operating conditions such as the
temperature, hydraulic retention time (HRT), and organic load. By adjusting the cut length or
average cut length of the harvest residues to be supplied to the methane fermentation to be
short, the HRT can be shortened, which allows for properly responding to an increase in
demand for the compost etc. or the energy source.
[0060] By knowing the relationship between the length of the harvest residues 3 and the HRT
required for methane fermentation in advance, the cut length of the harvest residues 3 can be
properly adjusted to a value consistent with the target HRT based on this relationship. FIG. 3
shows the relationship between the length L of the rice straw as the harvest residues 3 and the
HRT. As a characteristic of the relationship, the shorter the length L of the rice straw, the
shorter the HRT, and the HRT gradually saturates as the length L of the rice straw increases.
For example, if the length L of the rice straw is a few millimeters, the HRT can be adjusted to
about 20 days, and if the length L of the rice straw is a dozen millimeters, the HRT can be
adjusted to about 40 days.
[0061] The anaerobic treatment method is configured to store the harvest residues 3
separately in multiple cut lengths and, based on the information about the demand for the
compost etc. or the energy source, select or load the harvest residues 3 such that those with a
16
predetermined cut length are supplied to the methane fermentation.
[0062] By storing the harvest residues 3 separately in multiple cut lengths, those with a
predetermined cut length can be selected or loaded from them. This allows the HRT to be
adjusted to be consistent with the information about demand for the compost etc. or the energy
source.
[0063] In the above example, a portion of the harvest residues 3 packed into a cylindrical
shape and collected by a roll baler or the like is pulverized by a pulverizer in advance before
being stored in the storage location 5. However, they may be crushed or cut into a required
size using a crusher when they are subjected to the methane fermentation treatment.
[0064] In the above embodiment, a portion of the harvest residues is supplied to the gasifier
9. However, they may be supplied to any other apparatus capable of supplying waste heat
and/or electricity and/or returning the products to the agricultural fields, and such apparatuses
may include, for example, an apparatus that processes the harvest residues by heating, such as
an incinerator, a pyrolysis furnace, and a carbonization furnace.
[0065] While the rice straw has been discussed as an example of the harvest residues 3, any
agricultural waste produced after the harvest of grains harvested in agricultural fields may be
used. As such, the rice straw may contain rice hulls, and wheat straw, cornstalks, etc. may
also be used.
[0066] It will be appreciated that any of the above-described embodiments is only an
example of the present invention. The above descriptions are not limiting the present
invention, and the embodiments may be varied as suited, as long as such variations provide the
functions and effects of the present invention as well.
Reference Signs List
[0067] 1: Resource recycling system
2: Agricultural field
3: Harvest residue (rice straw)
4: Pre-treatment apparatus
17
5: Storage location
6: Methane fermentation apparatus
7: Fermentation residue tank
8: Biogas power generator
9: Gasifier
10: Gas purifier
11: Synthesis gas power generator
20: Management device
21: Memory device

WE CLAIM:

1. An anaerobic treatment method ofcausing a raw material including harvest residues
produced in an agricultural field to undergo methane fermentation to return fermentation
residues produced from the methane fermentation to the agricultural field and to utilize biogas
produced from the methane fermentation as an energy source, comprising:
adjusting a cut lenglh of the harvest residues to be supplied to the methane
fermentation based on information about demand for the fermentation residues or the biogas.

2. The anaerobic treatrnent method according to claim 1, further comprising adjusting a
cut length or average cut length ofthe harvest residues to be supplied to the methane
fermentation to be shortened in response to an increase in demand for the fermentation
residues or the biogas.

3. The anaerobic treatrnent method according to claim I or 2, t'urther corlprising
adjusting a cut length ofthe harvest residues using a previously determined relationship
between a length ofthe harvest residues and a hydraulic retention time (HRT) required for the
methane fermentation

4. The anaerobic trea[nent method according to any one ofclaims 1 to 3, further
comprising storing the harvest residues separately in a plurality of cut lengths and, based on
the information about demand for the fermentation residues or the biogas, selecting or mixing
the harvest residues such that the harvest residues with a predetermined cut length are supplied
to the methane fermentation.