Method for operating an anaerobic treatment device, and an anaerobic treatment device.

Abstract

This technology provides an efficient way to defoam foam generated inside an anaerobic treatment tank. [Solution] An operating method for an anaerobic treatment apparatus 1 comprising an anaerobic treatment tank 1 for anaerobic fermentation treatment of organic waste, and stirring means for stirring the liquid L in the anaerobic treatment tank 1 and circulating the liquid L in the anaerobic treatment tank 1, comprising a heated defoaming liquid acquisition step for obtaining heated defoaming liquid containing a defoaming agent and water, and a defoaming liquid spraying step for spraying the heated defoaming liquid toward the liquid surface of the liquid L in the anaerobic treatment tank 1.

Description

Technical Field

[0001] The present invention relates to an operation method of an anaerobic treatment apparatus and an anaerobic treatment apparatus.

Background Art

[0002] Sludge and biomass used as raw materials for methane fermentation treatment may contain oil and fat components. Oil and fat components are hydrophobic and buoyant, and tend to accumulate near the liquid surface in the methane fermentation tank. In addition, oil and fat components are highly viscous and prone to foaming near the liquid surface, and the generated foam has the property of being difficult to disappear. Inside the methane fermentation tank, when biogas generated from the fermentation liquid moves to the upper gas phase part, an environment is formed where the oil and fat components accumulated near the liquid surface collide with the biogas and foam is likely to be generated. If foam continues to be generated in the methane fermentation tank, there is a problem that the foam enters the inside of the gas pipe that discharges biogas outside the methane fermentation tank, and has an adverse effect on the subsequent gas facilities.

[0003] Patent Document 1 describes that the gas phase part in the upper part of the methane fermentation tank is heated with hot water, or hot water is sprinkled on the liquid surface in the methane fermentation tank to defoam the foam generated on the liquid surface in the methane fermentation tank.

[0004] Patent Document 2 describes that when foaming of the fermentation liquid in the methane fermentation tank is detected, the temperature of the fermentation liquid is raised by a heat exchanger to defoam the foam generated on the liquid surface in the methane fermentation tank.

Prior Art Documents

Patent Documents

[0005] [[ID=3i]]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 describes using hot water to defoam foam generated in a methane fermentation tank. However, in practice, defoaming with hot water (heated water) alone is difficult (the defoaming efficiency is poor), and the use of an antifoaming agent is essential. On the other hand, because antifoaming agents are viscous, it is difficult to evenly distribute the antifoaming agent to the surface of the fermentation liquid in the methane fermentation tank.

[0007] It is desirable to be able to defoam the foam generated on the surface of the fermentation liquid in a methane fermentation tank in a cost-effective manner. However, the method described in Patent Document 2 raises the temperature of the entire fermentation liquid in the methane fermentation tank, not just near the surface, and requires a large amount of thermal energy to heat the fermentation liquid.

[0008] The objective of the present invention is to provide a technology that can efficiently defoam foam generated inside an anaerobic treatment tank. [Means for solving the problem]

[0009] (1) A method for operating an anaerobic treatment apparatus disclosed herein comprises an anaerobic treatment tank for anaerobic fermentation treatment of organic waste, and stirring means for stirring the liquid in the anaerobic treatment tank and circulating the liquid in the anaerobic treatment tank, comprising a heated defoaming liquid acquisition step for obtaining a heated defoaming liquid containing a defoaming agent and water, and a defoaming liquid spraying step for spraying the heated defoaming liquid toward the liquid surface in the anaerobic treatment tank.

[0010] According to the above configuration, heating the defoaming solution reduces its specific gravity. The defoaming solution with reduced specific gravity tends to remain on the surface of the liquid in the anaerobic treatment tank. Therefore, foam generated on the surface of the liquid in the anaerobic treatment tank can be efficiently defoamed. Furthermore, since only the defoaming agent, water, or defoaming solution (a mixture of defoaming agent and water) is heated, defoaming can be achieved efficiently with less thermal energy compared to methods that raise the temperature of all the liquids in the anaerobic treatment tank. In addition, since the defoaming agent is viscous, adding water to the defoaming agent and heating it reduces the viscosity of the defoaming agent, making it easier to spray the defoaming solution.

[0011] (2) In the operating method of (1) above, in the step of obtaining the heated defoaming liquid, the defoaming agent, the water, or a mixture of the defoaming agent and the water may be heated by the waste heat of a gas power generation that uses biogas generated in the anaerobic treatment tank as fuel.

[0012] This configuration allows for the efficient use of waste heat energy from gas power generation. Furthermore, it reduces the need for external energy input for heating.

[0013] (3) In the operating method of (1) or (2) above, the defoaming agent may be a defoaming agent that contains organic matter that can be decomposed by anaerobic treatment and has a specific gravity of less than 1 relative to water.

[0014] With this configuration, the defoaming agent contains organic matter that can be decomposed in anaerobic treatment, so it can be decomposed in the anaerobic treatment tank and does not inhibit the anaerobic treatment reaction. Furthermore, when mixed with water to form a defoaming solution, its specific gravity becomes less than 1, and it remains on the surface of the liquid in the anaerobic treatment tank along with the foam, which also has a specific gravity of less than 1, allowing for more efficient defoaming.

[0015] (4) In any of the operating methods described in (1) to (3) above, in the defoaming liquid spraying step, after stopping the stirring means or after reducing the intensity of the stirring means, the heated defoaming liquid may be sprayed toward the liquid surface in the anaerobic treatment tank.

[0016] This configuration suppresses the flow of the liquid in the anaerobic treatment tank, causing oil and grease to accumulate at the liquid surface due to the difference in specific gravity and promoting foaming. Then, by spraying the defoaming solution onto the liquid surface in the anaerobic treatment tank, intermittent defoaming becomes possible, reducing the amount of defoaming agent used. In addition, the reduction in the defoaming effect due to stirring and mixing of the defoaming solution is suppressed, improving the duration of the defoaming effect.

[0017] (5) In any of the operating methods described in (1) to (4) above, in the defoaming liquid spraying step, the heated defoaming liquid may be sprayed toward the liquid surface in the anaerobic treatment tank after the foam height level in the anaerobic treatment tank has reached a predetermined value or higher.

[0018] With this configuration, after a certain amount of foam is generated, an antifoaming solution is sprayed onto the liquid surface in the anaerobic treatment tank, enabling more appropriate intermittent operation and further reducing the amount of antifoaming agent used.

[0019] (6) In any of the operating methods described in (1) to (5) above, a liquid discharge step may be further provided after the defoaming liquid spraying step, in which the liquid near the liquid surface in the anaerobic treatment tank is discharged to the outside of the anaerobic treatment tank.

[0020] With this configuration, after spraying the defoaming solution, the oily substances that have accumulated near the liquid surface in the anaerobic treatment tank can be discharged outside the tank, thus removing the remaining oily substances after defoaming, which are the root cause of foaming.

[0021] (7) The anaerobic treatment apparatus disclosed herein comprises an anaerobic treatment tank for anaerobic fermentation treatment of organic waste, and stirring means for stirring the liquid in the anaerobic treatment tank and circulating the liquid in the anaerobic treatment tank, and further comprises heated defoaming liquid acquisition means for obtaining heated defoaming liquid containing a defoaming agent and water, and a control device for controlling the spraying of the heated defoaming liquid toward the liquid surface in the anaerobic treatment tank.

[0022] According to the above configuration, heating the defoaming solution reduces its specific gravity. The defoaming solution with reduced specific gravity tends to remain on the surface of the liquid in the anaerobic treatment tank. Therefore, foam generated on the surface of the liquid in the anaerobic treatment tank can be efficiently defoamed. Furthermore, since only the defoaming agent, water, or defoaming solution (a mixture of defoaming agent and water) is heated, defoaming can be achieved efficiently with less thermal energy compared to methods that raise the temperature of all the liquids in the anaerobic treatment tank. In addition, since the defoaming agent is viscous, adding water to the defoaming agent and heating it reduces the viscosity of the defoaming agent, making it easier to spray the defoaming solution.

[0023] (8) In the anaerobic treatment apparatus of (7) above, the heating defoaming liquid acquisition means may include a gas generator that uses the biogas generated in the anaerobic treatment tank as fuel, and a heat exchanger that heats the defoaming agent, the water, or a mixture of the defoaming agent and the water by the waste heat generated by the gas generator.

[0024] According to this configuration, the waste heat energy of gas power generation can be efficiently utilized. In addition, the external energy input for heating can be reduced.

Effect of the Invention

[0025] According to the present invention, the bubbles generated inside the anaerobic treatment tank can be efficiently defoamed.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram showing a methane fermentation treatment apparatus as an anaerobic treatment apparatus according to the first embodiment of the present invention. [Figure 2] It is an injection pattern of the defoaming liquid in the methane fermentation treatment apparatus as an anaerobic treatment apparatus according to the first embodiment of the present invention. [Figure 3] It is a flowchart showing a part of the control process in the methane fermentation treatment apparatus as an anaerobic treatment apparatus according to the first embodiment of the present invention. [Figure 4] It is a diagram showing a methane fermentation treatment apparatus as an anaerobic treatment apparatus according to the second embodiment of the present invention. [Figure 5] It is a diagram showing a methane fermentation treatment apparatus as an anaerobic treatment apparatus according to the third embodiment of the present invention.

Modes for Carrying Out the Invention

[0027] Hereinafter, modes for carrying out the present invention will be described with reference to the drawings.

[0028] In the present invention, organic waste supplied to the anaerobic treatment device includes sewage sludge, human waste sludge, agricultural community wastewater sludge, septic tank sludge, food waste such as kitchen waste (food-derived biomass), lignocellulosic waste such as recycled paper and waste paper, agricultural residues, and livestock manure. These organic wastes may be treated individually or in combination. Below, sewage sludge will be used as an example of organic waste supplied to the methane fermentation tank, and its treatment will be described. In this embodiment, a digester 1 in which methane fermentation is performed is shown as the anaerobic treatment tank, but the anaerobic treatment tank may be a hydrogen fermentation tank in which hydrogen fermentation is performed.

[0029] <First Embodiment> The first embodiment of the present invention will be described below. Figure 1 is a diagram showing a methane fermentation treatment apparatus 101 as an anaerobic treatment apparatus according to the first embodiment of the present invention. As shown in Figure 1, the methane fermentation treatment apparatus 101 comprises a digester 1 as a methane fermentation tank, a gas generator 2, and a controller 10.

[0030] (digestion tank) Digestor 1 is a tank for anaerobic fermentation treatment of sewage sludge (organic waste). The total solids (TS) of the raw sludge supplied to digester 1 are preferably, for example, 3.0 to 10.0%. Digestor 1 is operated at 30 to 45°C for a residence time of about 15 to 30 days in medium-temperature fermentation treatment, and at 50 to 60°C for a residence time of about 7 to 20 days in high-temperature fermentation treatment. When sewage sludge is fermented in digester 1, the solids concentration of the digested sludge (methane fermentation liquid) is reduced to about half of the solids concentration of the supplied raw sludge due to the decomposition action of methane fermentation bacteria. Digestor 1 may be a tank made of steel plate or a tank made of concrete.

[0031] (stirring means) The digester 1 is equipped with a stirrer 5 and a circulation pump 6 as means of agitating the sewage sludge introduced into the digester 1 and circulating the digested sludge (methane fermentation liquid) within the digester 1. The stirrer 5 is a means of agitating the sewage sludge introduced into the digester 1 and the digested sludge (methane fermentation liquid) within the digester 1. The circulation pump 6 is a means of circulating the digested sludge (methane fermentation liquid) within the digester 1. Figure 1 shows the stirrer 5, which agitates the sludge with multiple stages of blades 5a (impellers) that rotate horizontally. The drive source for the stirrer 5 is, for example, an electric motor 5b. The stirrer 5 is generally located in the center of the digester 1 in a plan view. As indicated by arrow D, during normal operation, the rotation of the blades 5a generates a downward flow in the center of the digester 1. This downward flow spreads out at the bottom of the digester 1, reverses, and becomes an upward flow. The agitator 5 (blade 5a) may also be rotated in reverse. When the agitator 5 is rotated in reverse, the sludge flow in the digester tank 1 will be the opposite of that during normal operation. That is, an upward flow will be generated in the center of the digester tank 1, and this upward flow will spread out and reverse at the top of the digester tank 1 to become a downward flow. In addition, other types of agitators, such as screw-type or draft-tube agitators, may be used instead of the impeller-type agitator 5 as in this embodiment.

[0032] Figure 1 also shows a circulation pump 6 that draws digested sludge (methane fermentation liquid) from a draw pipe 6a located in the lower part of the digester tank 1 and supplies the drawn-out digested sludge (methane fermentation liquid) from the upper part of the digester tank 1 via a return pipe 6b located in the upper part of the digester tank 1. The circulation pump 6 is installed in the draw pipe 6a, and the discharge pressure of the circulation pump 6 draws the digested sludge (methane fermentation liquid) out of the digester tank 1, and the digested sludge (methane fermentation liquid) is supplied into the digester tank 1 from the upper part via the return pipe 6b. Furthermore, although not shown in the figure, a heating device (e.g., a heat exchanger) may be provided in the draw pipe 6a or the return pipe 6b to heat the digested sludge (methane fermentation liquid) to maintain a predetermined temperature. In addition, a submersible pump may be used instead of the circulation pump 6 installed in the draw pipe 6a outside the tank as in this embodiment.

[0033] Anaerobic fermentation of sewage sludge generates digester gas in digester tank 1. Digester gas is a biogas consisting of approximately 50-60% methane and 40-50% carbon dioxide by volume. The generated digester gas is removed from digester tank 1 and stored in a gas tank (not shown). The digester gas is used as fuel to heat the defoaming solution. It is also used as fuel to heat digester tank 1 or as fuel for the gas generator 2. In other words, by treating sewage sludge with methane fermentation, the energy contained in the sewage sludge can be recovered as digester gas (gas energy). Digester gas is generated continuously in digester tank 1, in principle.

[0034] (Gas generator) The gas generator 2 is a gas generator that generates electricity using digester gas as fuel. The digester gas is supplied from the digester tank 1 to the gas generator 2. The gas generator 2 comprises a gas engine 7, a generator (not shown) connected to the gas engine 7, and a heat exchanger 8.

[0035] The gas engine 7 may be a gas engine that uses only digester gas as fuel, or it may be a gas engine that co-fires digester gas with city gas, heavy oil, or LP gas.

[0036] The heat exchanger 8 may be a cooling water heat exchanger that recovers thermal energy (heat) from cooling water that has become hot after cooling the gas engine 7, or it may be an exhaust gas heat exchanger that recovers thermal energy (heat) from the exhaust gas of the gas engine 7. This thermal energy is the waste heat from power generation obtained by the gas generator 2. The cooling water heat exchanger is a water-water heat exchanger. When the heat exchanger 8 is a cooling water heat exchanger, the hot water obtained from the cooling water that has become hot after cooling the gas engine 7 is supplied from the cooling water heat exchanger to the heat exchanger 9 described below. As described above, in addition to using a cooling water heat exchanger, an exhaust gas heat exchanger may also be used as the heat exchanger 8. The exhaust gas heat exchanger is an exhaust gas-heat transfer oil heat exchanger. In the exhaust gas heat exchanger, the heat transfer oil obtained from the exhaust gas is used for heating the defoaming liquid.

[0037] (Means for obtaining heated defoaming liquid, and process for obtaining heated defoaming liquid) The heated defoaming liquid acquisition device 3 (heated defoaming liquid acquisition means) is a device for heating the defoaming liquid using waste heat from power generation. The heated defoaming liquid acquisition process is a process of heating the defoaming liquid using waste heat from power generation. The heated defoaming liquid acquisition device 3 has a gas generator 2 that uses digester gas generated in the digester tank 1 as fuel, and a heat exchanger 9 that acts as a heater to heat the mixture of defoaming agent and water (defoaming liquid) using waste heat from power generation of the gas generator 2. When hot water containing waste heat from power generation recovered in the heat exchanger 8 is supplied to the heat exchanger 9, heat is transferred from the hot water to the defoaming liquid, and the defoaming liquid is heated. The heat exchanger 9 is an indirect heat exchanger. In this way, the defoaming liquid is heated in the heat exchanger 9 using waste heat from power generation obtained from the gas generator 2.

[0038] Furthermore, the heat transfer medium for heating the defoaming solution is not limited to hot water. In addition to hot water, steam and heat transfer oil (oil) can also be used as heat transfer mediums for heating the defoaming solution.

[0039] Figure 1 shows an example in which the defoaming solution is heated by supplying hot water from heat exchanger 8 to heat exchanger 9. However, the defoaming solution may also be heated directly using only the heat exchanger 8 of the gas generator 2 without installing heat exchanger 9. In this case, instead of hot water, the defoaming solution is supplied to heat exchanger 8, and the defoaming solution is heated in heat exchanger 8 by the waste heat generated by the gas generator 2.

[0040] (Means for spraying defoaming solution, and process for spraying defoaming solution) The defoaming liquid spraying device 4 (defoaming liquid spraying means) is a device that sprays heated defoaming liquid toward the liquid surface in the digester tank 1. The defoaming liquid spraying device 4 has a defoaming liquid supply pipe 4a and an injection nozzle 4b. The defoaming liquid spraying process is a process of spraying heated defoaming liquid toward the liquid surface in the digester tank 1. The defoaming liquid, heated by the waste heat from power generation obtained from the gas generator 2, is sprayed toward the liquid surface in the digester tank 1 via the defoaming liquid supply pipe 4a. Here, "liquid" means methane fermentation liquid if it is in the digester tank 1 where methane fermentation is performed, and hydrogen fermentation liquid if it is in the hydrogen fermentation tank where hydrogen fermentation is performed.

[0041] An injection nozzle 4b is positioned at the tip of the defoaming liquid supply pipe 4a or similar location so that the defoaming agent can be uniformly sprayed over the entire liquid surface in the digestion tank 1. The form of spraying the defoaming liquid is not particularly limited, but for example, as shown in Figure 1, the defoaming liquid may be supplied into the tank in a mist form from the injection nozzle 4b, and then descend while floating in the gaseous phase to come into contact with the foam B. Although not shown in the figure, the defoaming liquid may also be sprayed towards the liquid surface as a stream of water. Furthermore, the defoaming liquid may be sprayed towards the liquid surface periodically even if foam B is not generated. Alternatively, instead of arranging the injection nozzle 4b, holes may be provided in the defoaming liquid supply pipe 4a (pipe), and the defoaming liquid may be sprayed from these holes. There may be one or more holes.

[0042] As shown in Figure 1, when an impeller-type agitator 5 is used as the stirring means, the defoaming liquid tends to flow downward from near the center (axis) of the tank. Therefore, the amount of defoaming liquid sprayed may be increased from near the center (axis) of the tank towards the outer circumference, or the defoaming liquid may not be sprayed near the center (axis) of the tank, but rather sprayed in a ring shape near the outer circumference of the digestion tank 1.

[0043] It is preferable that the defoaming liquid sprayed onto the liquid surface by the defoaming liquid spraying device 4 remains on the entire liquid surface for several minutes. Figure 2 shows the spray pattern of the defoaming liquid sprayed onto the liquid surface in the digestion tank 1. The area enclosed by the dashed line in Figure 2 is the area where the defoaming liquid was sprayed. As shown in Figure 2, it is preferable that the defoaming liquid is sprayed over an area of ​​80% or more of the liquid surface.

[0044] (antifoaming liquid) The defoaming solution contains an antifoaming agent and water. The type of antifoaming agent is not particularly limited, but an alcohol-based antifoaming agent is preferable because its high hydrophilicity makes it easily soluble when mixed with water. Furthermore, since alcohol-based antifoaming agents contain organic matter that can be decomposed by anaerobic treatment and have a specific gravity of less than 1 relative to water, the defoaming solution containing the alcohol-based antifoaming agent tends to remain on the surface of the liquid in the digester 1. Therefore, foam generated on the surface of the liquid in the anaerobic treatment tank can be efficiently defoamed. The temperature of the defoaming solution is preferably higher than the temperature of the methane fermentation liquid in the digester 1, for example, 60 to 80°C. Alternatively, the temperature may be the temperature of the methane fermentation liquid plus a predetermined value. For example, if the predetermined value is 20°C, the temperature will be 55 to 60°C for mesothermal methane fermentation (35 to 40°C) and 70 to 75°C for high-temperature methane fermentation (50 to 55°C). The defoaming solution may be prepared by heating the defoaming agent and water after mixing, or by heating either the defoaming agent or the water separately before mixing. The mixing ratio of the defoaming agent to the water is not particularly limited, but it is preferable to have a mass ratio of defoaming agent:water = 1:10 to 1:20. For example, 6 kg of alcohol-based defoaming agent (product name Senka Co., Ltd. Anti-Home HA-07) may be mixed with 90 to 100 kg of water. Note that silicone-based defoaming agents have a specific gravity greater than 1, so there is a risk of them settling. Furthermore, siloxanes may be generated and, if mixed into the digester gas, may cause malfunctions in the biogas equipment. Therefore, although the use of silicone-based defoaming agents as a temporary defoaming measure is not ruled out, it is not considered a preferred type of defoaming agent to be used in this invention.

[0045] (Foam detection sensor) The presence of foam in the digester tank 1 may be detected using a foam detection sensor 11 or by visual inspection. The installation location of the foam detection sensor 11 is not particularly limited, but it may be located lower than the intake port of the digester gas pipe 14 within the digester tank 1 and at the height between the intake port of the digester gas pipe 14 and the liquid surface. As shown in Figure 1, only one foam detection sensor 11 may be installed on the inner surface of the digester tank 1, but multiple foam detection sensors 11 may be installed to prevent false detections. Since false detections are likely to occur on the inner surface of the digester tank 1 due to changes in the liquid level, dirt, and water droplet formation, the foam detection sensor 11 may be installed in the upper part of the digester tank 1. Multiple sensors may be installed at the same height or at different heights. Since the interface between the foam and the gas phase is not always at the same height (there are irregularities depending on the location), if it is detected that the foam height level at at least one location exceeds a predetermined value, defoaming liquid may be sprayed. When multiple sensors are installed at different heights, the defoaming process can be adjusted so that the foam interface is at the height between the sensors. For example, two sensors may be used to control the on / off spraying of the defoaming solution.

[0046] (Liquid discharge route and liquid discharge process) The liquid discharge path 12 is a path for discharging the liquid near the liquid surface in the digester tank 1 to the outside of the digester tank 1 after the defoaming liquid spraying treatment. The liquid discharge process is a process of discharging the liquid near the liquid surface in the digester tank 1 to the outside of the digester tank 1 after the defoaming liquid spraying process. The method of discharging the liquid near the liquid surface after the defoaming liquid spraying treatment is not particularly limited, and may be used to cause overflow by supplying raw materials or treated water, to cause overflow by flowing methane fermentation liquid, treated water, or inert gas near the liquid surface, or to extract it with the discharge pump 13. The liquid near the liquid surface may be discharged immediately after the defoaming liquid spraying treatment, or it may be done after a predetermined time (for example, 5 to 30 minutes) has elapsed.

[0047] (controller) Controller 10 is a control device that controls each component of the methane fermentation treatment apparatus. Signals from various instruments installed in each component of the methane fermentation treatment apparatus are input to Controller 10.

[0048] The controller 10 is configured to perform the following controls. Note that the controls performed by the controller 10 described below may also be performed manually by a person. That is, a person may manually spray the defoaming solution.

[0049] As shown in Figure 3, when control by the controller 10 is initiated and foaming is detected near the liquid surface in the digester tank 1 by the foaming detection sensor 11 (S1), the controller 10 stops the agitator or reduces the intensity of the agitator. Specifically, it stops the rotation of the impeller 5a of the agitator 5 or reduces the rotation speed of the impeller 5a, and stops the operation of the circulation pump 6 to stop the circulation of the liquid in the digester tank 1 (S2). After a predetermined time (e.g., 0 to 30 minutes) has elapsed since the agitator 5 and circulation pump 6 stopped operating, heated defoaming liquid is sprayed from the defoaming liquid sprayer 4 toward the liquid surface in the digester tank 1 (S3). If foaming is still detected by the foaming detection sensor 11 after a predetermined time (e.g., 5 to 30 minutes) has elapsed since the spraying of the defoaming liquid (YES in S4), heated defoaming liquid is sprayed from the defoaming liquid sprayer 4 toward the liquid surface in the digester tank 1 (S3). If, after a predetermined time (e.g., 5 to 30 minutes) has elapsed since the defoaming solution was sprayed, the foaming detection sensor 11 does not detect foaming (NO in S4), then the spraying of the defoaming agent is stopped (S5), and the operation of the agitator 5 and circulation pump 6 is restarted (S6). S3 may be performed before S2.

[0050] In step S2 above, when stopping the operation of the agitator 5, the rotation of the impeller 5a may be stopped immediately, or the rotation speed of the impeller 5a may be reduced in multiple stages before stopping. Also, when reducing the rotation speed of the agitator 5, the rotation of the impeller 5a may be reduced all at once to a predetermined rotation speed, or the rotation speed of the impeller 5a may be reduced in multiple stages. Also, when stopping the operation of the circulation pump 6 to stop the circulation of liquid in the digester tank 1, the circulation of liquid may be stopped immediately, or the circulation of liquid may be reduced all at once to a predetermined circulation volume before stopping, or the circulation volume of liquid may be reduced in multiple stages before stopping. Furthermore, it is preferable to stop both the agitator 5 and the circulation pump 6 before spraying the defoaming liquid, but stopping only one of them is also acceptable.

[0051] In step S3 described above, the heated defoaming solution may be sprayed toward the liquid surface in the digester tank 1 at the same time as the operation of the agitator 5 is stopped or the operation of the circulation pump 6 is stopped.

[0052] <Second Embodiment> Next, a second embodiment of the present invention will be described. Figure 4 shows an anaerobic treatment apparatus (methane fermentation treatment apparatus 102) according to an embodiment of the present invention. The difference from the methane fermentation treatment apparatus 101 of the first embodiment is that in this embodiment, an antifoaming agent heated by waste heat from power generation is mixed with water, and the resulting antifoaming liquid is uniformly sprayed over the entire liquid surface in the digester tank 1. Equipment common to the methane fermentation treatment apparatus 101 of the first embodiment and the methane fermentation treatment apparatus 102 of the second embodiment is denoted by the same reference numerals.

[0053] Figure 4 shows an example in which the defoaming agent is heated by supplying hot water from heat exchanger 8 to heat exchanger 9. However, the defoaming agent may also be heated directly using only the heat exchanger 8 of the gas generator 2 without installing heat exchanger 9. In this case, instead of hot water, the defoaming agent is supplied to heat exchanger 8, and the defoaming agent is heated in heat exchanger 8 by the waste heat generated by the gas generator 2.

[0054] <Third Embodiment> Next, a third embodiment of the present invention will be described. Figure 5 shows an anaerobic treatment apparatus (methane fermentation treatment apparatus 103) according to an embodiment of the present invention. The difference from the methane fermentation treatment apparatus 101 of the first embodiment is that in this embodiment, water heated by waste heat from power generation is mixed with an antifoaming agent, and the resulting antifoaming liquid is uniformly sprayed onto the entire liquid surface in the digester tank 1. Equipment common to the methane fermentation treatment apparatus 101 of the first embodiment and the methane fermentation treatment apparatus 103 of the third embodiment is denoted by the same reference numerals.

[0055] Figure 5 shows an example in which water for mixing with the defoaming agent is heated by supplying hot water from heat exchanger 8 to heat exchanger 9. However, the water for mixing with the defoaming agent may be heated directly using only the heat exchanger 8 of the gas generator 2 without installing heat exchanger 9. In this case, instead of hot water, water for mixing with the defoaming agent is supplied to heat exchanger 8, and the water is heated in heat exchanger 8 by the waste heat generated by the gas generator 2.

[0056] (effect) The method for operating the anaerobic treatment apparatus of this embodiment is a method for operating an anaerobic treatment apparatus (methane fermentation treatment apparatus 101, 102, 103) comprising an anaerobic treatment tank (digestion tank 1) for anaerobic fermentation treatment of organic waste, and stirring means (stirrer 5, circulation pump 6) for stirring the liquid in the anaerobic treatment tank (digestion tank 1) and circulating the liquid in the anaerobic treatment tank (digestion tank 1), comprising a heated defoaming liquid acquisition step for obtaining heated defoaming liquid containing a defoaming agent and water, and a defoaming liquid spraying step for spraying the heated defoaming liquid toward the liquid surface in the anaerobic treatment tank (digestion tank 1).

[0057] According to the above driving method, the following effects can be obtained.

[0058] By heating the defoaming solution, its specific gravity decreases. The defoaming solution with a lower specific gravity tends to remain on the surface of the liquid in the anaerobic treatment tank (digestion tank 1). Therefore, foam generated on the surface of the liquid in the anaerobic treatment tank (digestion tank 1) can be efficiently defoamed. Furthermore, since only the defoaming agent, water, or the defoaming solution (a mixture of defoaming agent and water) is heated, defoaming can be achieved efficiently with less thermal energy compared to methods that raise the temperature of all the liquid in the anaerobic treatment tank (digestion tank 1). In addition, since the defoaming agent is viscous, adding water to the defoaming agent and heating it reduces the viscosity of the defoaming agent, making it easier to spray the defoaming solution.

[0059] Furthermore, in the heated defoaming liquid acquisition process, the defoaming agent, the water, or a mixture of the defoaming agent and the water may be heated using the waste heat from a gas power generation system that uses biogas generated in the anaerobic treatment tank (digestion tank 1) as fuel. This allows for efficient utilization of the waste heat energy from the gas power generation system and reduces the external energy input required for heating.

[0060] Furthermore, the defoaming agent may contain organic matter that can be decomposed by anaerobic treatment and have a specific gravity of less than 1 relative to water. In this case, since the defoaming agent contains organic matter that can be decomposed by anaerobic treatment, it can be decomposed in the anaerobic treatment tank (digestion tank 1) and does not inhibit the anaerobic treatment reaction. Also, when mixed with water to form a defoaming solution, the specific gravity becomes less than 1, and together with foam, which also has a specific gravity of less than 1, it remains on the surface of the liquid in the anaerobic treatment tank (digestion tank 1), allowing for more efficient defoaming.

[0061] In the defoaming liquid spraying step, after stopping the stirring means (stirrer 5, circulation pump 6) or reducing the intensity of the stirring means (stirrer 5, circulation pump 6), the heated defoaming liquid may be sprayed toward the liquid surface in the anaerobic treatment tank (digestion tank 1). This suppresses the flow of the liquid in the anaerobic treatment tank (digestion tank 1), collects the oil and grease at the liquid surface due to the difference in specific gravity to promote foaming, and then sprays the defoaming liquid toward the liquid surface in the anaerobic treatment tank (digestion tank 1) to enable intermittent defoaming, thereby reducing the amount of defoaming agent used. In addition, the reduction in the defoaming effect due to stirring and mixing of the defoaming liquid is suppressed, and the duration of the defoaming effect is improved.

[0062] In the defoaming solution spraying step, the heated defoaming solution may be sprayed toward the liquid surface in the anaerobic treatment tank (digestion tank 1) after the foam height level in the anaerobic treatment tank (digestion tank 1) reaches a predetermined value or higher. This allows for more appropriate intermittent operation by spraying the defoaming solution toward the liquid surface in the anaerobic treatment tank (digestion tank 1) after a certain amount of foam has been generated, further reducing the amount of defoaming agent used.

[0063] The process may further include a liquid discharge step after the defoaming liquid spraying step, in which the liquid near the liquid surface in the anaerobic treatment tank (digestion tank 1) is discharged to the outside of the anaerobic treatment tank. This allows the oil and grease that have accumulated near the liquid surface in the anaerobic treatment tank after the defoaming liquid spraying step to be discharged to the outside of the anaerobic treatment tank (digestion tank 1), thereby removing the remaining oil and grease that is the root cause of foaming after defoaming. The discharge of the liquid near the liquid surface may be performed immediately after the defoaming liquid spraying step, or it may be performed after a predetermined time (for example, 5 to 30 minutes) has elapsed.

[0064] The present invention is not limited to the embodiments described above. The components of the above embodiments can be combined as appropriate, and various modifications can be made to the above embodiments. For example, the above embodiments can be modified as follows.

[0065] In the above description of the embodiment, an example was shown where the anaerobic treatment tank is a digester 1 (methane fermentation tank) that contributes to the generation of digester gas. However, the anaerobic treatment may also be a hydrogen fermentation tank that contributes to the generation of biohydrogen. For example, a two-stage hydrogen-methane fermentation may be performed in a single tank, where hydrogen fermentation is carried out as the first stage, followed by methane fermentation as the second stage. In hydrogen fermentation, biohydrogen gas and carbon dioxide are produced in a ratio of approximately 1:1, and organic acids such as acetic acid, which are raw materials for methane fermentation, are produced in the fermentation liquid. Alternatively, the process may be divided into a hydrogen fermentation tank and a methane fermentation tank, with hydrogen fermentation and methane fermentation carried out in separate tanks.

[0066] Hydrogen fermentation is carried out at 30-60°C, more preferably 50-60°C, and even more preferably 55°C. Furthermore, hydrogen fermentation is carried out at a pH of 4.0-6.5, more preferably 4.0-5.0. In the case of a two-stage hydrogen-methane fermentation, hydrogen fermentation takes 1-2 days and methane fermentation takes 7-10 days, thus shortening the fermentation period compared to methane fermentation alone.

[0067] The gas generator 2 may be a gas generator that generates electricity using biohydrogen gas produced by hydrogen fermentation as fuel. The biohydrogen gas is supplied from the hydrogen fermentation tank to the gas generator 2.

[0068] In the above description of the embodiment, the defoaming agent, the water, or a mixture of the defoaming agent and water is heated by the waste heat from the gas generator 2, which uses biogas generated in the digester 1 as fuel. However, the defoaming agent, the water, or a mixture of the defoaming agent and water (defoaming liquid) may be heated by hot water from a hot water boiler or heat transfer oil from a heat transfer oil boiler, without using the waste heat from the gas generator 2. The fuel for the hot water boiler or heat transfer oil boiler may be digester gas only, a mixture of digester gas and city gas, heavy oil, or LP gas, or city gas, heavy oil, or LP gas only.

[0069] In the above description of the embodiment, an example was shown in which there is no heating device for heating the liquid in the digester tank 1, but a heating device for heating the liquid in the digester tank 1 may be provided. The liquid in the digester tank 1 may be heated by the waste heat from the gas generator 2, or by boiler heat, etc. [Industrial applicability]

[0070] The operating method of the anaerobic treatment apparatus of the present invention, and the anaerobic treatment apparatus itself, can be used to decompose various organic wastes such as sewage sludge, human waste sludge, agricultural village wastewater sludge, septic tank sludge, food waste (food-based biomass) such as food scraps, lignocellulose waste such as construction waste and waste paper, agricultural residues, and livestock manure, and to produce methane and hydrogen using the decomposed materials as raw materials. [Explanation of symbols]

[0071] 1: Digestion tanks (methane fermentation tanks, anaerobic treatment tanks) 2: Gas generator 3: Heating antifoaming liquid acquisition device 4: Antifoaming liquid spraying device 4a: Defoaming liquid supply pipe 4b: Spray nozzle 5: Stirrer 5a: Blades (impeller) 5b: Electric motor 6: Circulation pump 6a: Extracted tube 6b: Return tube 7: Gas engine 8, 9: Heat exchanger 10: Controller 11: Foam detection sensor 12: Liquid drainage pathway 13: Discharge pump 14: Digestive gas (methane gas) supply route 101, 102, 103: Methane fermentation treatment equipment (anaerobic treatment equipment) L:Liquid B: Foam

Claims

1. An anaerobic treatment tank for anaerobic fermentation treatment of organic waste, A stirring means for stirring the liquid in the anaerobic treatment tank and circulating the liquid in the anaerobic treatment tank, A method for operating an anaerobic treatment device, comprising: A heated defoaming liquid acquisition process to obtain a heated defoaming liquid containing a defoaming agent and water, A defoaming liquid spraying step in which the heated defoaming liquid is sprayed toward the liquid surface in the anaerobic treatment tank, A method for operating an anaerobic treatment device, comprising the following features.

2. In the method for operating the anaerobic treatment apparatus described in claim 1, In the process of obtaining the heated defoaming liquid, the defoaming agent, the water, or a mixture of the defoaming agent and the water is heated by the waste heat from a gas power generation that uses biogas generated in the anaerobic treatment tank as fuel. Operating method for an anaerobic treatment system.

3. In the method for operating the anaerobic treatment apparatus according to claim 1 or 2, The aforementioned defoaming agent contains organic matter that can be decomposed by anaerobic treatment and has a specific gravity of less than 1 relative to water. Operating method for an anaerobic treatment system.

4. In the method for operating the anaerobic treatment apparatus according to claim 1 or 2, In the defoaming liquid spraying step, after stopping the stirring means or reducing the intensity of the stirring means, the heated defoaming liquid is sprayed toward the liquid surface in the anaerobic treatment tank. Operating method for an anaerobic treatment system.

5. In the method for operating the anaerobic treatment apparatus according to claim 1 or 2, In the defoaming solution spraying step, after the foam height level in the anaerobic treatment tank reaches a predetermined value or higher, the heated defoaming solution is sprayed toward the liquid surface in the anaerobic treatment tank. Operating method for an anaerobic treatment system.

6. In the method for operating the anaerobic treatment apparatus according to claim 1 or 2, The process further includes a liquid discharge step, after the defoaming liquid spraying step, in which the liquid near the liquid surface in the anaerobic treatment tank is discharged to the outside of the anaerobic treatment tank. Operating method for an anaerobic treatment system.

7. An anaerobic treatment tank for anaerobic fermentation treatment of organic waste, A stirring means for stirring the liquid in the anaerobic treatment tank and circulating the liquid in the anaerobic treatment tank, An anaerobic treatment apparatus comprising, A means for obtaining a heated defoaming liquid containing an defoaming agent and water, A control device that controls the dispensing of the heated defoaming solution toward the liquid surface in the anaerobic treatment tank, An anaerobic treatment device equipped with the following features.

8. In the anaerobic treatment apparatus according to claim 7, The means for obtaining the heated defoaming liquid is, A gas generator that uses biogas generated in the aforementioned anaerobic treatment tank as fuel, A heat exchanger that heats the defoaming agent, the water, or a mixture of the defoaming agent and the water using the waste heat from the gas generator, An anaerobic treatment apparatus having

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