Methane fermentation residue dewatering system

Abstract

This invention provides a methane fermentation residue dewatering system that can process methane fermentation residue without increasing the size of the equipment configuration beyond the storage tank, even when the properties of the fermentation liquid fluctuate significantly, leading to unstable water quality of the fermentation residue dewatered filtrate and unstable operation of the fermentation residue dewatering system. [Solution] The methane fermentation residue dewatering system A1 comprises a first solid-liquid separation unit 16 that separates the fermentation liquid containing fermentation residue discharged from a dry methane fermentation tank 14 into a first residue mainly consisting of solids and a first filtrate mainly consisting of liquids; a storage tank 18 that stores the first filtrate separated by the first solid-liquid separation unit 16; a circulating storage tank liquid solid-liquid separation unit 20 that separates the storage tank liquid a discharged from the storage tank 18 into a second residue mainly consisting of solids and a second filtrate mainly consisting of liquids; and a third solid-liquid separation unit 22 that separates the storage tank liquid b discharged from the storage tank 18 into a third residue mainly consisting of solids and a third filtrate mainly consisting of liquids.

Description

Technical Field

[0001] The present invention relates to a methane fermentation residue dehydration system in dry anaerobic digestion.

Background Art

[0002] When fermenting waste, before the fermentation treatment, it is sorted into organic waste (such as food waste) and fermentation-inappropriate substances that are not biodegradable (such as plastics, cloths, metals, etc.). The organic waste is used as a raw material for methane fermentation, and the fermentation-inappropriate substances can be treated by incineration or the like.

[0003] The methane obtained by methane fermentation treatment is used as fuel or the like as biogas. On the other hand, the methane fermentation residue generated by methane fermentation treatment is separated into sludge and drainage.

[0004] Generally, anaerobic digestion includes dry anaerobic digestion and wet anaerobic digestion. When treating general waste such as food waste, dry anaerobic digestion that is tolerant of the mixing of foreign substances is suitable. In dry anaerobic digestion, in the above sorting process, since fermentation-inappropriate substances cannot be completely removed, the dry anaerobic digestion residue also contains sludge mainly composed of organic substances and fermentation-inappropriate substances such as plastics.

[0005] Patent Document 1 discloses a methane fermentation device. This methane fermentation device maintains the fermentation tank in an appropriate state by circulating the fermentation liquid after methane fermentation containing fermentation-appropriate substances in the fermentation tank. Further, when the solid concentration of the fermentation liquid is high, the fermentation liquid is withdrawn to a rotary separator, and the separated liquid (filtrate) obtained by separating fermentation-inappropriate substances by a solid-liquid separation device (rotary concentration) is circulated in the fermentation tank to maintain the fermentation tank in an appropriate state.

[0006] Patent Document 2 discloses a methane fermentation residue dewatering system. This methane fermentation residue dewatering system is configured such that fermentation residue generated in a methane fermentation tank is supplied to a contaminant separation means, the sludge-containing liquid separated by the contaminant separation means is supplied to a concentration means, and the concentrated sludge concentrated by the concentration means is returned to the contaminant separation means by a concentrated sludge return means. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7298842 [Patent Document 2] Patent No. 5715350 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent Document 1 states that if the properties of the fermentation liquid (solids concentration, shape, and composition) fluctuate significantly, the water quality of the fermentation residue dewatering filtrate and the operation of the fermentation residue dewatering system may become unstable. Furthermore, since the equipment after the storage tank needs to be designed to accommodate large variations in the properties of the fermentation liquid (high solids concentration or a wide variety of solids), this may lead to an increase in the capacity of subsequent dewatering and separation equipment. For example, the storage tank (170), pump (P3), and dewatering equipment (180) in Patent Document 1 would need to be enlarged.

[0009] The present disclosure aims to provide a methane fermentation residue dewatering system that can process methane fermentation residue without increasing the size of the equipment configuration after the storage tank, even when the properties of the fermentation liquid (e.g., solid concentration, shape, size, and composition of solids) fluctuate greatly, and the water quality of the dewatered filtrate of the fermentation residue and the operation of the fermentation residue dewatering system become unstable. [Means for solving the problem]

[0010] The methane fermentation residue dewatering systems (A1, A2) described herein are: A first solid-liquid separation unit (16) separates the fermentation liquid containing fermentation residue discharged from the dry methane fermentation tank (14) into a first residue mainly consisting of solids and a first filtrate mainly consisting of liquids, A storage tank (18) for storing the first filtrate separated in the first solid-liquid separation unit (16), A circulating storage tank liquid solid-liquid separation unit (20) separates the storage tank liquid (a) discharged from the storage tank (18) into a second residue which is mainly solid and a second filtrate which is mainly liquid, A third solid-liquid separation unit (22) separates the storage liquid (b) discharged from the storage tank (18) into a third residue mainly consisting of solids and a third filtrate mainly consisting of liquids, It may also be equipped with.

[0011] The aforementioned methane fermentation residue dewatering systems (A1, A2) are: A wastewater treatment unit (24) that performs wastewater treatment (e.g., biological treatment, physical treatment) on the third filtrate separated in the third solid-liquid separation unit (22), It may also be equipped with.

[0012] The aforementioned methane fermentation residue dewatering systems (A1, A2) are: A fermentation liquid discharge path (L14) sends the fermentation liquid discharged from the dry methane fermentation tank (14) to the first solid-liquid separation unit (16), A first filtrate path (L16) sends the first filtrate separated in the first solid-liquid separation unit (16) to the storage tank (18), A storage liquid extraction path (L18a) sends the storage liquid (a) from the storage tank (18) to the circulating storage liquid solid-liquid separation unit (20), A storage tank liquid circulation path (L20) returns the second filtrate separated in the circulating storage tank liquid solid-liquid separation section (20) to the storage tank (18), A storage liquid path (L18b) sends the storage liquid (b) from the storage tank (18) to the third solid-liquid separation unit (22), A third filtrate path (L22) sends the third filtrate separated in the third solid-liquid separation unit (22) to the wastewater treatment unit (24), It may also be equipped with.

[0013] The methane fermentation system (A) to which the methane fermentation residue dehydration system (A1, A2) is applied is a dry methane fermentation tank (14) for methane-fermenting a methane fermentation raw material, and a raw material mixing section (12) for mixing a raw material for methane fermentation and water, and further includes the substrate processed in the raw material mixing section (12) may be sent to the dry methane fermentation tank (14) as a methane fermentation raw material.

[0014] The methane fermentation system (A) has a raw material input path (L12) for sending the substrate from the raw material mixing section (12) to the dry methane fermentation tank (14), and a fermentation liquid circulation path (L142) for returning the fermentation liquid branched from the fermentation liquid derivation path (L14) to the dry methane fermentation tank (14) again, and may be provided with.

[0015] The methane fermentation residue dehydration system (A1, A2) may be provided with a first mixing water path (L1) for introducing the water into the raw material mixing section (12), or a second mixing water path (L181, L221, L241) through which one or more of the storage tank liquid (b), the third residue (sludge), and the treated water after wastewater treatment are introduced in addition to or instead of the water.

[0016] Each path (L12, L14, L142, L18a, L18b, L20, L22, L181, L221, L241) may be provided with a partition valve, a flow rate regulating valve, a liquid feed pump (P1 to P5), a flow meter, and the like.

[0017] The methane fermentation residue dehydration system (A1, A2) may be provided with a storage tank liquid measurement section (184) for measuring the liquid level (liquid height from the bottom surface) or the liquid volume of the storage tank liquid in the storage tank (18).

[0018] The methane fermentation residue dehydration system (A1, A2) It may also include a first property analysis unit (26) for analyzing the properties of the liquid in the storage tank (18) (e.g., solid concentration, shape, size, composition of the solids, etc.).

[0019] The methane fermentation residue dewatering system (A1, A2) It may also include a second property analysis unit (27) for analyzing the properties of the fermentation broth sent to the first solid-liquid separation unit (16) (e.g., solid concentration, shape, size, composition of the solids).

[0020] The first property analysis unit (26) and the second property analysis unit (27) may be equipped with means for manually or automatically obtaining analysis sample liquids (storage tank liquid and fermentation broth). In the case of manual operation, it may be configured to manually take out the analysis sample liquid from a sample liquid extraction tube that extracts the analysis sample liquid from the storage tank (18) or a path (e.g., L14, L16, L18a, L20, etc.). In the case of automatic operation, it may be composed of means for sucking the analysis sample liquid from this sample liquid extraction tube.

[0021] The methane fermentation residue dewatering system (A1, A2) When the variation in properties exceeds a threshold or a predetermined range in the analysis results of the first property analysis unit (26) or the second property analysis unit (27), it may further include a control unit (28) for controlling (such as a liquid transfer pump P4, valve, etc.) to send the storage tank liquid (a) from the storage tank (18) to the circulating storage tank liquid solid-liquid separation unit (20).

[0022] The control unit (28) may control (such as a liquid transfer pump P4, valve, etc.) to intermittently or continuously send the storage tank liquid (a) from the storage tank (18) to the solid-liquid separation unit (20).

[0023] (Function and effect) (1) The sorted waste obtained by crushing and sorting the raw materials (including fermentation-inappropriate substances) is mixed and treated with water or the filtrate or treated water processed at a later stage than the storage tank, and the substrate with the adjusted solid concentration is put into the dry methane fermentation tank, and the dry methane fermentation tank can be maintained in an appropriate state. (2) In order to maintain an appropriate volume in the fermentation tank, the fermentation liquid containing the fermentation residue is periodically discharged from the fermentation tank and dehydrated and separated in the first solid-liquid separation unit. The filtrate after dehydration and separation is stored in a storage tank, and an appropriate amount is drawn from the storage tank to a small circulating storage tank liquid solid-liquid separation unit according to the solid content for solid-liquid separation. The second filtrate, after solid-liquid separation, is returned to the storage tank. This allows for solid-liquid separation in accordance with fluctuations in the solid-liquid concentration in the storage tank. By adjusting the amount drawn from the storage tank to the circulating storage tank liquid solid-liquid separation unit, the solid content in the storage tank can be leveled. The solid load (TS amount; the load is determined by the amount of filtrate × concentration) in the third solid-liquid separation unit and the wastewater treatment unit can be leveled. (3) The liquid stored in the storage tank is further dehydrated and separated in the third solid-liquid separation section. Depending on the purpose of reusing the filtrate, the wastewater is further treated. (4) Even if the properties of the fermentation liquid change significantly due to the raw materials and the solid content increases, the solids resulting from the property changes can be processed in the small-scale circulating storage liquid solid-liquid separation unit. This stabilizes the water quality of the fermentation residue dewatered filtrate and the operation of the entire fermentation residue dewatering system. (5) By leveling the solid load introduced into the third solid-liquid separation section downstream of the storage tank, it becomes possible to suppress the need to increase the capacity of the equipment (including wastewater treatment equipment) from the third solid-liquid separation section downstream of the storage tank. [Brief explanation of the drawing]

[0024] [Figure 1] This is a diagram showing the methane fermentation residue dewatering system A1 of Embodiment 1. [Figure 2] This figure shows the methane fermentation residue dewatering system A2 of Embodiment 2. [Modes for carrying out the invention]

[0025] Some embodiments of the present invention are described below. The embodiments described below illustrate just one example of the present invention. The present invention is not limited in any way to the embodiments described below, and includes various modifications that are implemented without changing the gist of the present invention.

[0026] (Embodiment 1) Figure 1 shows an example of the configuration of methane fermentation residue dewatering system A1. Methane fermentation system A, which includes fermentation residue dewatering system A1, comprises a raw material sorting device 10, a raw material mixing unit 12, and a dry methane fermentation tank 14. Fermentation residue dewatering system A1 comprises a first solid-liquid separation unit 16, a storage tank 18, a circulating storage tank liquid-solid-liquid separation unit 20, a third solid-liquid separation unit 22, and a wastewater treatment unit 24.

[0027] The raw materials consist of a mixture of materials suitable and unsuitable for methane fermentation, such as food waste and household waste. The raw material sorting device 10 separates materials suitable for methane fermentation from materials unsuitable for methane fermentation. The raw material sorting device 10 may also be a crushing and sorting unit that crushes the raw material and separates materials unsuitable for fermentation from materials suitable for fermentation. The crushing and sorting unit may include a magnetic separator that separates metals from nonmetals from the crushed material by magnetic force, and a sorting device that separates non-combustible materials from combustible materials from the non-metallic crushed material sorted by the magnetic separator.

[0028] The raw material mixing section 12 mixes the raw materials for methane fermentation with water. The raw material mixing section 12 can be, for example, a spiral mixer, a single-screw mixing device, or a twin-screw mixing device. Water is introduced into the raw material mixing section 12 from, for example, the first mixing water route L1. The first mixing water route L1 is equipped with a gate valve, a liquid transfer pump, and a flow meter, and the amount of water introduced corresponds to the amount of raw materials being input. The raw material input route L12 is a piping route that sends the substrate from the raw material mixing section 12 to the dry methane fermentation tank 14. Route L12 is equipped with a gate valve, a liquid transfer pump P1, and a flow meter to adjust the amount of substrate being supplied.

[0029] The dry methane fermentation tank 14 is a device that performs methane fermentation on the substrate processed in the raw material mixing section 12. The dry methane fermentation tank 14 is not particularly limited and any known device can be used. The first fermentation liquid outlet route L14 is a piping route that sends the fermentation liquid containing fermentation residue, which is discharged from the dry methane fermentation tank 14, to the first solid-liquid separation unit 16. Route L14 is equipped with a gate valve, a liquid transfer pump P3, and a flow meter to adjust the amount of fermentation liquid supplied. The fermentation liquid circulation route L142 is a piping route that returns the fermentation liquid branched off from the first fermentation liquid outlet route L14 back to the dry methane fermentation tank 14. Route L142 is equipped with a gate valve, a liquid transfer pump P2, and a flow meter to adjust the circulation rate of the fermentation liquid.

[0030] The first solid-liquid separation unit 16 separates the fermentation liquid containing the fermentation residue discharged from the dry methane fermentation tank 14 into a first residue, which is mainly solid, and a first filtrate, which is mainly liquid. However, the solid-liquid separation is not complete, and solid matter is also present in the first filtrate, causing fluctuations in the concentration of this solid matter. The first solid-liquid separation unit 16 is not particularly limited, but a known solid-liquid separation device can be used. The first filtrate path L16 is a piping path that sends the first filtrate separated in the first solid-liquid separation unit 16 to the storage tank 18. The path L16 may be equipped with a gate valve, a liquid transfer pump, and a flow meter to adjust the amount of first filtrate supplied. The first solid residue separated in the first solid-liquid separation unit 16 may be incinerated.

[0031] The storage tank 18 stores the first filtrate separated in the first solid-liquid separation unit 16. The storage tank 18 is not particularly limited, and a known storage tank can be used. The storage tank 18 may be equipped with a stirring device to agitate the storage liquid intermittently or continuously. The storage tank liquid extraction route L18a is a piping route that sends the storage tank liquid a from the storage tank 18 to the circulating storage tank liquid solid-liquid separation unit 20. Route L18a is equipped with a gate valve, a liquid transfer pump P4, and a flow meter to adjust the amount of storage tank liquid a drawn out. The adjustment of the drawing out amount will be described later.

[0032] The circulating storage liquid solid-liquid separation unit 20 separates the storage liquid a discharged from the storage tank 18 into a second residue, which is mainly solid, and a second filtrate, which is mainly liquid. Solid-liquid separation can be performed when the solid content concentration in the storage liquid fluctuates significantly. The circulating storage tank liquid solid-liquid separation unit 20 is not particularly limited, and known solid-liquid separation devices can be used, such as small drum-type screens or centrifugal separators. However, complete solid-liquid separation is not achieved, and solid matter is still present in the second filtrate. Nevertheless, by returning the second filtrate, which has a lower solid matter concentration, to the storage tank 18, the solid matter concentration in the storage tank liquid in the storage tank 18 can be reduced. The storage tank liquid circulation route L20 is a piping route that returns the second filtrate separated in the circulating storage tank liquid solid-liquid separation unit 20 to the storage tank 18. Route L20 may be equipped with a gate valve, a liquid transfer pump, and a flow meter to adjust the amount of second filtrate supplied. The second solid residue separated in the circulating storage tank liquid-solid-liquid separation unit 20 may be incinerated. The storage tank liquid route L18b is a piping route that sends the storage tank liquid b from the storage tank 18 to the third solid-liquid separation unit 22. Route L18b may be equipped with a gate valve, a liquid transfer pump, and a flow meter to adjust the amount of storage tank liquid b sent in.

[0033] The third solid-liquid separation unit 22 separates the storage liquid b discharged from the storage tank 18 into a third residue, which is mainly solid, and a third filtrate, which is mainly liquid. The third solid-liquid separation unit 22 is not particularly limited, but a known solid-liquid separation device can be used, and since the solid content concentration of the storage liquid b sent from the storage tank 18 can be kept relatively constant with little fluctuation, it can be constructed as a small device. The third filtrate path L22 is a piping path that sends the third filtrate separated in the third solid-liquid separation unit 22 to the wastewater treatment unit 24.

[0034] The wastewater treatment unit 24 treats the third filtrate separated in the third solid-liquid separation unit 22 as wastewater. The wastewater treatment unit 24 may be, for example, a device that performs biological treatment or physical treatment.

[0035] The storage tank liquid measuring unit 184 measures the liquid level (liquid height from the bottom) or liquid volume of the storage tank 18. The storage tank liquid measuring unit 184 is not particularly limited, and known devices can be used. Depending on the liquid volume of the storage tank liquid, the timing and amount of the first filtrate supplied from the first solid-liquid separation unit 16 may be controlled.

[0036] (Control of the amount of liquid (a) withdrawn from the storage tank) The first property analysis unit 26 analyzes the properties of the stored liquid in the storage tank 18 (for example, the concentration of solids and the shape and size of the solids). The first property analysis unit 26 measures the amounts of liquid and solid components separated from the solid-liquid mixture and calculates the solid concentration. The first property analysis unit 26 may be equipped with means for obtaining analytical sample liquid (storage liquid and fermentation liquid) manually or automatically. In the manual case, the analytical sample liquid may be manually extracted from a sample liquid extraction tube that extracts the analytical sample liquid from the storage tank 18 or a pathway (L14, L16, L18a, L20, etc.). In the automatic case, the unit may be equipped with means for aspirating the analytical sample liquid from this sample liquid extraction tube.

[0037] The control unit 28 controls the liquid transfer pump P4 to send the storage liquid a from the storage tank 18 to the second solid-liquid separation unit 20 when the variation in properties in the analysis results of the first property analysis unit 26 exceeds a threshold or a predetermined range. For example, when the variation in solid concentration becomes large, the timing and amount of the storage liquid a can be controlled. Changes in properties include, for example, the change in solid concentration per unit time (e.g., from 1 minute to 1 hour), the change in the shape of the solid, and the change in the size of the solid.

[0038] The control unit 28 can control the liquid transfer pump P4 to intermittently or continuously send the storage liquid a from the storage tank 18 to the second solid-liquid separation unit 20.

[0039] The control unit 28 may be implemented through the cooperation of one or more processors, memory, and a program indicating the procedure, or it may be implemented by one or more types of dedicated circuits, PLCs (Programmable Logic Controllers), computers, etc.

[0040] (Another embodiment) A second property analysis unit 27 may be provided instead of, or in addition to, the first property analysis unit 26. The second property analysis unit 27 analyzes the properties of the fermentation liquid sent to the first solid-liquid separation unit 16 (for example, the concentration of solids, the shape and size of the solids). The control unit 28 controls the liquid transfer pump P4 to send the storage liquid a from the tank 18 to the second solid-liquid separation unit 20 when the variation in properties in the analysis results of the second property analysis unit 27 exceeds a threshold or a predetermined range. For example, when the variation in solid concentration becomes large, the timing and amount of the storage liquid a can be controlled.

[0041] (Embodiment 2) The methane fermentation residue dewatering system A2 of Embodiment 2 has the same configuration as the methane fermentation residue dewatering system A1 of Embodiment 1, and the same reference numerals have the same function, so their explanation will be omitted.

[0042] The methane fermentation residue dewatering system A2 of Embodiment 2 includes second mixing water channels L181, L221, and L241 into which one or more of the following are introduced: storage liquid b, third residue (sludge), and treated wastewater. The second mixing water channels L181, L221, and L241 are equipped with gate valves, liquid transfer pumps, and flow meters. The timing and amount of storage liquid b, third residue (sludge), and treated wastewater are introduced are set in accordance with the amount of raw material input. [Explanation of symbols]

[0043] A Methane fermentation system A1, A2 Methane Fermentation Residue Dehydration System 12 Raw material mixing section 14 Dry methane fermentation tank 16 First solid-liquid separation section 18 Storage tank 20 Circulating storage tank liquid-solid-liquid separation section 22 Third solid-liquid separation section 24. Drainage Treatment Section 26 First Property Analysis Department 27 Second property analysis department 28 Control Unit

Claims

1. A first solid-liquid separation unit separates the fermentation liquid containing fermentation residue discharged from a dry methane fermentation tank into a first residue mainly consisting of solids and a first filtrate mainly consisting of liquids. A storage tank for storing the first filtrate separated in the first solid-liquid separation section, A circulating storage tank liquid-solid-liquid separation unit separates the storage liquid discharged from the storage tank into a second residue which is mainly solid and a second filtrate which is mainly liquid, A third solid-liquid separation unit separates the storage liquid discharged from the storage tank into a third residue mainly consisting of solids and a third filtrate mainly consisting of liquids. Equipped with, Methane fermentation residue dewatering system.

2. The system further includes a control unit that controls the intermittent or continuous feeding of the storage liquid from the storage tank to the circulating storage liquid solid-liquid separation unit. The methane fermentation residue dewatering system according to claim 1.

3. The system further includes a control unit that controls the flow of the stored liquid from the storage tank to the circulating storage liquid solid-liquid separation unit when the variation in properties exceeds a threshold or a predetermined range. The methane fermentation residue dewatering system according to claim 1.

4. A dry methane fermentation tank for methane fermentation of methane fermentation raw materials, A methane fermentation system comprising a methane fermentation residue dewatering system according to any one of claims 1 to 3.

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