JP7706302B2 - Organic matter treatment equipment - Google Patents

Description

The present invention relates to an organic matter treatment device that uses methane fermentation to treat organic matter.

Biogas obtained by methane fermentation of organic matter contains carbon dioxide and various other components in addition to methane. In recent years, so-called biomethanation technology has been developed to convert the carbon dioxide in biogas into methane using microorganisms, with the aim of using biogas as city gas. For example, Non-Patent Document 1 proposes a method in which hydrogen is blown into a liquid containing methanogens, and the carbon dioxide in the biogas is methanated by methanogens.

In the methane fermentation process, organic acids such as propionic acid are produced from organic matter via multiple substances, acetic acid is produced from these organic acids, and finally methane is produced from the acetic acid. When methane fermentation is carried out under conditions of high organic matter load (high organic acid production rate), blowing hydrogen into the methane fermentation liquid inhibits the production of acetic acid from the organic acids, increasing the organic acids in the methane fermentation liquid and lowering the pH of the solution. This reduces the activity of the bacteria involved in methane production from acetic acid, and there is a risk that methane fermentation will eventually stop.

Therefore, in order to avoid the halt of methane fermentation, the above-mentioned non-patent document 1 proposes adopting a two-tank system, generating biogas through methane fermentation in the first tank, and blowing in hydrogen in the second tank to methanate carbon dioxide.

Ilaria Bassani et al, “Biogas Upgrading via Hydrogenotrophic Methanogenesis in Two-Stage Continuous Stirred Tank Reactors at Mesophilic and Thermophilic Conditions”, Environ. Sci. Technol. 2015, 49, 12585-12593

However, when adopting a two-tank system as in the technology described in Non-Patent Document 1 above, the size of the device is unavoidable, and since equipment is required to steadily supply the methane fermentation liquid and biogas from the first tank to the second tank, the device also becomes complicated.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an organic matter treatment device that can achieve both methane fermentation of organic matter and methanation of carbon dioxide in biogas without adopting a two-tank system, while avoiding the occurrence of a situation in which methane fermentation stops.

The characteristic configuration of the organic matter treatment device according to the present invention for achieving the above object is as follows:
An organic matter treatment device comprising a methane fermentation tank to which organic matter is supplied,
a carrier impregnated with the methane fermentation liquid, the carrier being disposed in the methane fermentation tank in a state where a part of the carrier is immersed in the methane fermentation liquid in the methane fermentation tank and the remaining part is located in a space above the liquid level of the methane fermentation liquid, or in a state where the carrier is located in a space above the liquid level of the methane fermentation liquid;
and a hydrogen supply means for supplying hydrogen to the upper space.

According to the above characteristic configuration, the carrier is placed in a state where a part of it is immersed in the methane fermentation liquid in the methane fermentation tank and the remaining part is located in the space above the liquid level of the methane fermentation liquid, or in a state where it is located in the space above the liquid level of the methane fermentation liquid, and the carbon dioxide in the biogas present in the space above the liquid level can be methanated by the methanogens in the methane fermentation liquid impregnated in the carrier. In other words, according to the above characteristic configuration, methane fermentation can be performed in the methane fermentation liquid in the methane fermentation tank without blowing hydrogen into the methane fermentation liquid, and the carbon dioxide in the biogas generated by the methane fermentation can be methanated by the methanogens held in the carrier.

Therefore, according to the above characteristic configuration, it is possible to achieve both methane fermentation of organic matter and methanation of carbon dioxide in biogas in one methane fermentation tank without adopting a two-tank system, while avoiding the occurrence of a situation in which methane fermentation stops, and it is also possible to avoid making the equipment larger and more complicated.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
The present invention is characterized in that the carrier is provided with a fermentation liquid supplying means for constantly or intermittently supplying the methane fermentation liquid in the methane fermentation tank.

When operating an organic matter treatment device continuously, it may be necessary to supply methane fermentation liquid to the carrier if the methane fermentation liquid impregnated in the carrier falls off or if the activity of the methane bacteria in the methane fermentation liquid decreases due to some factor. According to the above characteristic configuration, methane fermentation liquid can be supplied to the carrier when the activity of the methane bacteria in the methane fermentation liquid impregnated in the carrier decreases or whenever a certain amount of time has passed since the start of treatment. Therefore, continuous operation of the organic matter treatment device is possible without the need to remove the carrier from the methane fermentation tank and impregnate it with methane fermentation liquid.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
The present invention is characterized in that a washing means for washing the carrier is provided.

When the carrier is repeatedly impregnated with the methane fermentation liquid or the methane fermentation liquid is repeatedly supplied by the fermentation liquid supply means, dirt accumulates on the carrier surface, preventing the flow of gas (hydrogen and carbon dioxide) into the carrier, making it difficult for the methanation of carbon dioxide by the methanogens in the methane fermentation liquid impregnated in the carrier to occur. However, with the above characteristic configuration, the carrier can be washed, so that the accumulation of dirt on the carrier surface can be suppressed, and the occurrence of a situation in which the methanation of carbon dioxide by the methanogens is difficult can be suppressed. This enables stable continuous operation of the organic matter treatment device.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
In the methane fermentation tank, methane fermentation treatment is carried out with an organic matter load of 3 g CODcr/L/day or more.

When the methane fermentation process is a process with a particularly high organic matter load (large amount of methane generated), the situation where methane fermentation stops is easily caused by blowing hydrogen into the methane fermentation liquid. With the above characteristic configuration, when performing a methane fermentation process with a high organic matter load as described above, it is possible to methanate the carbon dioxide in the biogas while avoiding the occurrence of the situation where methane fermentation stops.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
The organic matter is food waste.

The above characteristic configuration makes it possible to methanate the carbon dioxide in the biogas while avoiding the occurrence of a situation in which methane fermentation stops when processing food waste, which tends to have a relatively high organic matter load.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
A recovery means for recovering gas from the upper space in the methane fermentation tank;
The gas recovered by the recovery means is supplied to the upper space together with hydrogen supplied by the hydrogen supply means.

According to the above characteristic configuration, the hydrogen supplied to the methane fermentation tank that is not used for methanation can be recovered from the upper space together with the biogas and supplied to the upper space again, making it possible to effectively utilize unused hydrogen.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
The carrier is a fiber carrier.

The inventors of the present application have experimentally confirmed that by using a fiber carrier as a carrier and impregnating the carrier with a methane fermentation liquid, methanation of carbon dioxide occurs in the presence of hydrogen and carbon dioxide.

Further characteristic configurations of the organic matter treatment device according to the present invention are as follows:
The fiber support is a carbon fiber support.

The inventors of the present application have experimentally confirmed that the methanation of carbon dioxide occurs sufficiently by using a carbon fiber support as the fiber support.

1 is a diagram showing a schematic configuration of an organic matter treatment apparatus according to an embodiment; 13 is a graph showing experimental results. 13 is a graph showing experimental results. FIG. 13 is a diagram showing a schematic configuration of an organic matter treatment apparatus according to another embodiment.

The following describes an organic matter treatment device according to one embodiment of the present invention with reference to the drawings. Note that the following description will be given using an example in which the organic matter to be treated is food waste.

Figure 1 is a diagram showing the schematic configuration of an organic matter treatment device according to one embodiment. As shown in Figure 1, the organic matter treatment device includes a methane fermentation tank 10 to which food waste is supplied, a hydrogen supply unit 20 (hydrogen supply means) that supplies hydrogen into the methane fermentation tank 10, and a biogas recovery unit 30 (recovery means) that recovers biogas from within the methane fermentation tank 10.

[Methane fermentation tank]
As shown in Fig. 1, the methane fermentation tank 10 is configured with a housing and is configured to form a methane fermentation space 11 in which food waste supplied from outside the housing is biodegraded by methane fermentation using methane bacteria. The methane fermentation space 11 is provided with a heat exchanger (not shown) for maintaining the methane fermentation liquid in the methane fermentation space 11 at a temperature suitable for performing methane fermentation well (e.g., 30 to 37°C or 50 to 65°C). In this embodiment, a food waste supply port 15 for supplying food waste is provided on one of two opposing inner walls of the housing in the methane fermentation space 11, facing the methane fermentation space 11. In addition, a treated water discharge port 16 for discharging treated water to the outside is provided on the other of the two inner walls, facing the methane fermentation space 11.

The space above the methane fermentation space 11 (the space above the liquid level of the methane fermentation liquid in the methane fermentation tank 10) constitutes a biogas collection space 12 that collects biogas such as methane and carbon dioxide produced in the methane fermentation space 11.

In the biogas collection space 12, a mesh-like support member S is placed between the two opposing inner walls of the housing. A carrier T impregnated with methane fermentation liquid is placed on this support member S. The carrier T is not in contact with the liquid surface of the methane fermentation liquid in the methane fermentation space 11, but there is no problem if it does come into contact. In this embodiment, the carrier T is a fiber carrier made of carbon fiber, but is not particularly limited as long as it can hold the methane fermentation liquid. For example, polyester, PVA, and acrylic resin can be used. Note that the higher the bulk density of the carrier T, the higher the methanation rate of carbon dioxide (in other words, carbon dioxide can be converted to methane efficiently), so it is preferable to use a carrier with a large bulk density within the range in which the methane fermentation liquid can be impregnated.

In addition, a first shower 40 (fermentation liquid supply means) that sprays the methane fermentation liquid pumped up from the methane fermentation space 11 onto the carrier T, and a second shower 45 (cleaning means) that sprays a cleaning liquid (e.g., water) onto the carrier T to clean the carrier T, are installed on the ceiling of the housing that constitutes the methane fermentation tank 10 (above the biogas collection space 12).

The first shower 40 is configured to pump up the methane fermentation liquid from the methane fermentation space 11 via the fermentation liquid supply passage 41, which is provided with an on-off valve, a flow rate control valve, and the like (not shown). In this embodiment, the operation of these on-off valves and flow rate control valves can be controlled by a control device (not shown), and the amount of methane fermentation liquid sprayed from the first shower 40 and the timing of spraying can be adjusted. Therefore, the first shower 40 can supply the methane fermentation liquid in the methane fermentation space 11 to the carrier T constantly or intermittently. The supply of methane fermentation liquid to the carrier T by the first shower 40 may be performed every time a predetermined time has elapsed since the start of operation of the organic matter treatment device, or may be performed throughout the operation.

The second shower 45 is configured to receive cleaning liquid from a cleaning liquid supply unit 47 via a cleaning liquid supply path 46. An on-off valve and a flow rate control valve (not shown) are provided in the cleaning liquid supply path 46. In this embodiment, the operation of these on-off valves and flow rate control valves can be controlled by a control device (not shown), and the amount of cleaning liquid sprayed from the second shower 45 and the timing of spraying can be adjusted. It is preferable to wash the carrier T with the second shower 45 when the organic matter treatment device is not operating. The frequency of washing depends on the susceptibility of the carrier T to soiling, etc., but is preferably about once a week, for example.

If the microorganisms on the carrier T require trace elements to maintain activity, the first shower 40 can supply methane fermentation liquid as trace elements, or a cleaning liquid containing trace elements such as iron, nickel, and cobalt can be supplied from the second shower 45.

In this embodiment, in the biogas collection space 12, a hydrogen supply port 23 for supplying hydrogen from the hydrogen supply unit 20 is provided on one of the two opposing inner walls of the housing, facing the biogas collection space 12. In addition, a biogas outlet 33 for extracting biogas to the biogas recovery unit 30 is provided on the other of the two inner walls, also facing the biogas collection space 12.

In this embodiment, the hydrogen supply unit 20 is made up of a hydrogen cylinder 21 in which hydrogen is stored, a hydrogen supply path 22, a hydrogen supply port 23, and the like, and hydrogen in the hydrogen cylinder 21 is supplied into the biogas collection space 12 via the hydrogen supply path 22 and the hydrogen supply port 23. In this embodiment, the operation of the opening and closing valve provided in the hydrogen cylinder 21 can be controlled by a control device (not shown). Therefore, the hydrogen supply unit 20 can supply hydrogen into the biogas collection space 12 at any supply amount and any timing. The hydrogen supply unit 20 is not particularly limited as long as it is configured to be able to supply hydrogen into the biogas collection space 12. For example, a hydrogen production device may be used instead of the hydrogen cylinder 21.

In this embodiment, the biogas recovery unit 30 is composed of a tank 31 connected to a pump (not shown), a biogas extraction path 32, a biogas outlet 33, a circulation supply path 34, and the like, and biogas is sucked from the biogas collection space 12 through the biogas outlet 33 and the biogas extraction path 32 to store the biogas in the tank 31. The biogas recovery unit 30 is also configured to supply the biogas recovered in the tank 31 together with hydrogen to the biogas collection space 12 through the circulation supply path 34 that connects the tank 31 and the hydrogen supply path 22. In this embodiment, the biogas extraction path 32 and the circulation supply path 34 are each provided with an opening/closing valve and a flow rate adjustment valve that can be operated and controlled by a control device (not shown). Therefore, according to the biogas recovery unit 30, biogas can be recovered from the biogas collection space 12 at any extraction amount and any timing, and biogas can be supplied to the biogas collection space 12 at any supply amount and any timing through the circulation supply path 34. The biogas recovery unit 30 is not particularly limited as long as it is configured to recover biogas from the biogas collection space 12.

In the methane fermentation tank 10 having the above configuration, biogas is generated by performing methane fermentation in the methane fermentation space 11, and the generated biogas is collected in the biogas collection space 12. Then, using the hydrogen supplied into the biogas collection space 12, the carbon dioxide in the biogas in the biogas collection space 12 (the space above the liquid level of the methane fermentation liquid) is methanized by the methane bacteria in the methane fermentation liquid impregnated in the carrier T. In other words, in this embodiment, without blowing hydrogen into the methane fermentation liquid in the methane fermentation space 11, methane fermentation is performed in the methane fermentation liquid in the methane fermentation space 11, and the carbon dioxide in the biogas generated by the methane fermentation can be methanized by the methane bacteria held in the carrier T. In one methane fermentation tank 10, the carbon dioxide in the biogas can be methanized while avoiding the occurrence of a situation in which methane fermentation stops, and the size and complication of the device can be avoided.

In this embodiment, the methane fermentation tank 10 performs a methane fermentation process to treat food waste, and this type of methane fermentation process is a process with a high organic load (high methane generation). In a methane fermentation process with a high organic load, blowing hydrogen into the methane fermentation liquid can easily cause the methane fermentation to stop. In other words, the organic treatment device according to this embodiment can be particularly suitably used when a methane fermentation process with a high organic load (more specifically, a methane fermentation process with an organic load of 3 g CODcr/L/day or more, preferably 5 g CODcr/L/day or more, more preferably 10 g CODcr/L/day or more) is performed in the methane fermentation tank 10.

[Processing flow]
The process of treating food waste using the organic matter treatment apparatus having the above-mentioned configuration will be described below.

First, food waste is supplied to the methane fermentation tank 10, where it is fermented to produce biogas, which is then collected in the biogas collection space 12.

Here, hydrogen is supplied from the hydrogen supply unit 20 into the biogas collection space 12. Therefore, the hydrogen supplied into the biogas collection space 12 is used by the methane bacteria in the methane fermentation liquid impregnated into the carrier T to methanate the carbon dioxide in the biogas in the biogas collection space 12.

Meanwhile, the treated water produced by methane fermentation is discharged to the outside through the treated water outlet 16.

As described above, the organic matter treatment device according to this embodiment can perform methane fermentation in the methane fermentation liquid and methanation of the carbon dioxide in the biogas generated by methane fermentation without blowing hydrogen into the methane fermentation liquid in the methane fermentation space. Therefore, without adopting a two-tank system, it is possible to achieve both methane fermentation of organic matter and methanation of the carbon dioxide in the biogas while avoiding the occurrence of a situation in which methane fermentation stops in a single methane fermentation tank, and it is also possible to avoid making the device larger and more complicated.

The following are examples and comparative examples.

Example 1
A 3 ^cm3 carbon fiber carrier ("Dona Carbo Felt" manufactured by Osaka Gas Chemical Co., Ltd.) impregnated with methane fermentation liquid for 24 hours was placed in a 120 ml vial that simulated the space above the liquid level of the methane fermentation liquid in a methane fermentation tank (hereinafter also referred to as the gas phase space). Next, the gas in the vial was replaced with biogas generated from a separate methane fermentation test device for food waste, and then 100 ml of hydrogen gas was added and heated at 55°C. When the amount of gas in the vial was measured after 24 hours, 13.5 ml of hydrogen had been consumed. This corresponds to the amount required to methanate 3.4 ml of carbon dioxide.
From this, it was confirmed that by placing a carrier impregnated with methane fermentation liquid in the gas phase space, methanation of carbon dioxide occurs in the gas phase space.
The carbon dioxide consumption rate per carrier volume was calculated to be 0.047 ml/ ^cm3 /hour. The typical biogas generation rate from food waste processing equipment is 2 ml/ml/day, and since 40% of the biogas is carbon dioxide, the carbon dioxide generation rate is 0.033 ml/ml/hour. In other words, it was found that by installing a carrier with a volume equivalent to the methane fermentation liquid in the methane fermentation tank and impregnating the carrier with the methane fermentation liquid, most of the carbon dioxide in the biogas generated by methane fermentation can be methanated.

Example 2
A 24 ^cm3 carbon fiber carrier impregnated with the methane fermentation liquid for 24 hours was placed in a vial of the same type as that used in Example 1. Next, the gas in the vial was replaced with the above biogas, and then 100 ml of hydrogen gas was added and heated at 55° C. The hourly methane production rate in the vial, which increased over a 6-hour period from 18 hours to 24 hours after the start of heating, was 1.8 ml/hour.
On the other hand, when the gas in the vial was completely replaced with new biogas after 24 hours and 100 ml of hydrogen was added and the same test was performed, the methane production rate per hour was 4.6 ml. From this, it is presumed that the methanogens once immobilized on the carrier can be reused repeatedly and that the ability of the methanogens on the carrier was improved by self-propagation while undergoing methanation reactions on the carrier.

Example 3
When the carbon fiber carrier was impregnated with the methane fermentation liquid for 10 minutes and 2 hours, the amount of methane generated did not increase between the impregnation times of 10 minutes and 2 hours. The amount of methane fermentation liquid attached to the carrier was 0.5 times that of the impregnation time of 24 hours for 10 minutes and 0.6 times that of the impregnation time of 24 hours. In both cases, the amount of methane generated decreased despite the attachment of a certain amount of methane fermentation liquid. Therefore, it is considered that it is important for methane bacteria to settle on the carrier for the methanation of carbon dioxide. As can be seen from Example 2, once the methane bacteria settle on the carrier, the activity of the methane bacteria can be maintained and expanded thereafter, so there is no need to constantly supply the methane fermentation liquid to the carrier.

Example 4
A test was carried out in the same manner as in Example 2 using four types of carbon fiber supports (bulk density: 9.5, 63, 100 kg/m ³ ). The relationship between the amount of liquid retained on the support and the rate of increase in methane gas is shown in FIG.
As can be seen from FIG. 2, methane generation was confirmed for all carriers, but no correlation was observed between the carrier retention liquid volume and the methane increase rate.
FIG. 3 shows the relationship between bulk density and methane increase rate.
As can be seen from FIG. 3, the higher the bulk density of the carrier, the faster the methane increase rate. This confirms that the weight per volume is important for effectively methanating carbon dioxide.

Comparative Example 1
After replacing the gas in a vial of the same type as that used in Example 1 with the biogas, 100 ml of hydrogen gas was added and heated at 55° C. When the amount of gas in the vial was measured after 24 hours, no consumption of hydrogen was confirmed. This confirmed that methanation of carbon dioxide does not occur in the gas phase space in the absence of a carrier impregnated with a methane fermentation liquid.

Comparative Example 2
A certain amount of methane fermentation liquid was placed in a vial of the same type as that used in Example 1, and after replacing the gas with biogas, 100 ml of hydrogen gas was added and heated at 55° C. When the amount of gas in the vial was measured after 24 hours, no consumption of hydrogen in the gas phase space was confirmed. From this, it was confirmed that a carrier impregnated with methane fermentation liquid is necessary to cause methanation of carbon dioxide in the gas phase space.

[Another embodiment]
[1] In the above embodiment, the carrier T is disposed on the support member S, and the carrier T is positioned in the biogas collection space 12 above the methane fermentation space 11, but the present invention is not limited to this. For example, as shown in FIG. 4, the carrier T may be disposed so that a part of the carrier T is immersed in the methane fermentation liquid in the methane fermentation space 11 and the remaining part is positioned in a space above the liquid level of the methane fermentation liquid. Even in this case, since a part of the carrier T is positioned above the liquid level of the methane fermentation liquid, methane fermentation can be performed in the methane fermentation liquid in the methane fermentation space 11 without blowing hydrogen into the methane fermentation liquid in the methane fermentation space 11, and the carbon dioxide in the biogas in the biogas collection space 12 generated by the methane fermentation can be methanized by the methanogens held in the carrier T. Therefore, without adopting a two-tank system, it is possible to achieve both methane fermentation of organic matter and methanation of carbon dioxide in the biogas in one methane fermentation tank while avoiding the occurrence of a situation in which methane fermentation stops, and it is also possible to avoid an increase in size and a complication of the device.

[2] In the above embodiment, the first shower 40 is provided as a fermentation liquid supply means, but this is not limited thereto, and the embodiment may not include a fermentation liquid supply means.

[3] In the above embodiment, the second shower 45 is provided as a cleaning means, but this is not limited thereto, and the cleaning means may not be provided.

[4] In the above embodiment, the organic matter to be treated is food waste, but this is not limited thereto, and the organic matter to be treated may be other organic matter. In addition, the organic matter may be subjected to pretreatment such as crushing or solubilization.

[5] In the above embodiment, a biogas recovery unit 30 is provided as a recovery means, and the biogas recovered from the biogas collection space 12 is supplied back to the biogas collection space 12 to circulate the biogas, but this is not limited to the above. For example, the biogas recovered by the biogas recovery unit 30 may be stored in a tank without being circulated.

The configurations disclosed in the above embodiments (including other embodiments) can be applied in combination with configurations disclosed in other embodiments, provided no contradictions arise. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited thereto, and can be modified as appropriate within the scope of the purpose of the present invention.

The present invention can be used in organic matter treatment devices that use methane fermentation to treat organic matter.

1: organic matter treatment device 10: methane fermentation tank 12: biogas collection space (space above the liquid level of the methane fermentation liquid)
20: Hydrogen supply unit (hydrogen supply means)
30: Biogas recovery section (recovery means)
40: First shower (fermentation liquid supply means)
45: Second shower (cleaning means)
T: Carrier

Claims (8)

An organic matter treatment device comprising a methane fermentation tank to which organic matter is supplied,
a carrier impregnated with the methane fermentation liquid, the carrier being disposed in the methane fermentation tank in a state where a part of the carrier is immersed in the methane fermentation liquid in the methane fermentation tank and the remaining part is located in a space above the liquid level of the methane fermentation liquid, or in a state where the carrier is located in a space above the liquid level of the methane fermentation liquid;
and a hydrogen supplying means for supplying hydrogen to the upper space. The organic matter treatment device according to claim 1, further comprising a fermentation liquid supply means for constantly or intermittently supplying the methane fermentation liquid in the methane fermentation tank to the carrier. The organic matter treatment device according to claim 1 or 2, further comprising a cleaning means for cleaning the carrier. The organic matter treatment device according to any one of claims 1 to 3, wherein the methane fermentation tank performs methane fermentation treatment with an organic matter load of 3 g CODcr/L/day or more. The organic matter treatment device according to any one of claims 1 to 4, wherein the organic matter is food waste. A recovery means for recovering gas from the upper space in the methane fermentation tank;
6. The organic matter treatment apparatus according to claim 1, wherein the gas recovered by said recovery means is supplied to said upper space together with hydrogen supplied by said hydrogen supply means. An organic matter treatment device according to any one of claims 1 to 6, wherein the carrier is a fibrous carrier. The organic matter treatment device according to claim 7, wherein the fiber carrier is a carbon fiber carrier.

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