JP2014161846A - Operation method of methane fermentation tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation method of a methane fermentation tank, capable of efficient removal of sediment depositing on the bottom of methane fermentation tank during continuous operation.SOLUTION: A methane fermentation tank having a screw-type or impeller-type agitator is normally operated and subjected to an operation for drawing out sediment when the sediment is deposited in the vicinity of the end part on the bottom. The sediment deposited in the vicinity of the end part on the bottom can be gathered to the center part of the bottom by counter-rotating the screw-type or impeller-type agitator. The gathered sediment is removed through a sediment drawing pipe arranged at the center part of the bottom.

Description

  The present invention is a method for operating a methane fermentation tank having a substantially horizontal bottom surface and a screw-type or impeller-type stirring device provided at the center of the tank, and can remove sediment deposited on the bottom surface. It relates to the driving method.

  An anaerobic digestion method is generally used as a method for treating wastewater containing organic substances such as sewage sludge for the purpose of stabilizing sludge and recovering methane gas. As anaerobic digestion method, wastewater containing organic substances is put into a methane fermentation tank (digestion tank) and fermented with methane bacteria under anaerobic conditions, so that the methane fermentation process that converts organic substances into methane gas is widely used. . Various treatment methods and methane fermenters have been proposed depending on the properties of the input materials and the operating conditions.

  When an organic substance is anaerobically biodegraded by methane bacteria under anaerobic conditions, it is decomposed into biogas and water. Such an anaerobic digestion method has the advantage that the organic matter contained in the wastewater can be greatly reduced and methane gas (biogas) produced as a by-product can be recovered as energy.

  In the wastewater, there are solids or fermentation unsuitables (sand, hair, vinyl pieces, etc.) that are hardly decomposable and have a high specific gravity, so these gradually accumulate in the methane fermentation tank. For this reason, it is necessary to periodically remove sediment deposited on the bottom surface of the methane fermentation tank. In Patent Document 1, a first fermenter and a second fermenter having a filter bed carrying anaerobic microorganisms mainly composed of methane bacteria are arranged in series to form a methane fermenter, and organic waste is disposed in the first fermenter. The slurry obtained by pulverizing the product is introduced, the liquid processing liquid after passing through the filter bed of the first fermenter and fermented with methane is sent to the second fermenter, and the processing liquid is again fermented with methane in the second fermenter. In the methane fermentation treatment method for recovering resources such as biogas and taking out fermentation waste liquid as digestive liquid, a gas stirring device is provided in the first fermentation tank until a predetermined time elapses after the slurry is charged During this time, the output of the gas agitator is stopped, or the output is weakened, and fermentation unsuitable substances in the slurry are settled and separated, and then the output of the gas agitator is increased to stir the slurry. It is characterized by fermenting while It discloses a methane fermentation treatment method of.

  The methane fermentation treatment method disclosed in Patent Document 1 uses, in the first fermenter, a component that can be subjected to fermentation treatment contained in the treatment liquid and an unsuitable fermentation material by utilizing the difference in sedimentation speed. Since it can be effectively separated, it becomes easy to treat fermentation inadequate materials, and it is possible to prevent such a situation that they are accumulated and clogged in the piping, and the methane fermentation treatment can be stably carried out for a long period of time. In the second fermenter, since a liquid processing liquid with a small amount of solids and an extremely small amount of unsuitable fermentation is sent, high-speed processing is possible in the second fermenter. Therefore, it is said that methane fermentation treatment with high speed and high volume load can be performed as a whole.

JP 2006-255545 A

  In order to allow the sediment deposited on the bottom surface to be discharged, as shown in Patent Document 1, the bottom surface of the methane fermentation tank has a convex shape downward, and a pipe is arranged to extract the sediment at the lowest position. It is common. In general, the methane fermentation tank installed in the sewage treatment plant for sewage sludge digestion is made of concrete and has an oval or turtle shell shape. In this case as well, the bottom of the methane fermentation tank protrudes downward. It has become. In many cases, a screw type or impeller type stirring device is provided in the methane fermenter to stir the liquid to be treated. However, even in the case of an oval shape, the bottom surface of the methane fermenter is convex downward. It is said that there is no dead space and the stirring efficiency of the liquid to be treated is high and preferable. When the screw type or impeller type stirring device is rotated, the flow of the liquid to be processed is in the direction shown in FIG.

  Anaerobic digestion is operated, for example, at a temperature of about 20 ° C. for a low temperature fermentation at a residence time of 30 to 60 days, for a medium temperature fermentation at a temperature of about 37 ° C. for a residence time of 20 to 30 days, and for a high temperature fermentation at a temperature of 55 ° C. It is operated at a residence time of around 7 to 20 days. For this reason, in such a methane fermentation tank, as shown in FIG. 5 (b), the deposit 14 accumulates on the convex portion at the lower part of the methane fermentation tank. Therefore, it is possible to extract the deposit 14 to some extent by installing the deposit extraction tube 16 on the convex portion. However, as shown in FIG. 6, the deposit 14 around the deposit extraction tube 16 can be removed, but the other deposits 14 are difficult to extract. As a result, there is a problem that the amount of deposit 14 in the lower part of the methane fermentation tank 11 gradually increases, and dead space increases in the methane fermentation tank 11.

  On the other hand, in recent years, as an alternative to a concrete methane fermentation tank, there has been an increasing demand for a steel plate methane fermentation tank that can be installed more easily. However, in a methane fermentation tank made of a steel plate, it is desired that the bottom surface is formed in a substantially flat shape without being convex downward from the viewpoint of ease of construction. In such a methane fermenter, when the methane fermenter 1 is continuously operated as shown in FIG. 1 (a), the deposit 4 moves down the side of the methane fermenter 1 as shown in FIG. 1 (b). It was found to be deposited in the center. In this case, even if the sediment extraction pipe 6 is installed at the center of the bottom surface 7 of the methane fermentation tank and the sediment 4 is extracted by the pump P, only the sediment around the extraction pipe 6 is extracted. Cannot be pulled out efficiently.

  Moreover, although the digestion liquid transfer pipe 8 is also provided in the lower part of the side surface of the methane fermenter 1, even if an attempt is made to pull out the deposit 4 from the digestion liquid transfer pipe 8 by a pump, the deposits around the digestive liquid transfer pipe 8. Only 4 is pulled out, and the deposit 4 cannot be pulled out efficiently.

  If the supply of the liquid to be processed is stopped and all the liquid 2 to be processed in the methane fermentation tank 1 is discharged, the deposit 4 can be discharged from the deposit extraction pipe 6 by washing the inside of the methane fermentation tank 1. It is. However, if the scale of the methane fermentation tank 1 is large, it takes time to discharge the liquid to be treated 2 and clean the inside of the methane fermentation tank 1, and the operation must be stopped for a long period of time. In addition, in a large-scale methane fermenter, it is not possible to provide a spare methane fermenter, and it takes time to start the fermentation process with microorganisms. For this reason, the washing | cleaning method which discharges the to-be-processed liquid 2 in the methane fermenter 1 is not realistic.

  Then, this invention aims at provision of the operating method of the methane fermenter which can remove the deposit deposited on the bottom face of a methane fermenter efficiently outside a methane fermenter, operating continuously.

  As a result of intensive studies, the inventors of the present invention, in a methane fermentation tank equipped with a screw-type or impeller-type stirrer, by rotating the stirrer in a reverse direction, As a result, the present invention has been completed.

Specifically, the present invention
A method for operating a methane fermentation tank,
The methane fermenter is
A cylindrical shape having a bottom surface that is convex upward or downward, and an angle between a straight line connecting the end and the center with a horizontal line is greater than 0 degrees and less than 0.3 degrees,
In the center, a screw type or impeller type stirring device for stirring the liquid to be treated is provided,
At the center of the bottom is a sediment extraction tube,
The operation method is to perform a normal operation and a deposit extraction operation alternately,
During normal operation, by rotating the screw type or impeller type stirring device, a downward flow is generated at the center of the methane fermentation tank toward the bottom surface, and an upward flow is generated at the side of the methane fermentation tank toward the water surface. And
During the sediment extraction operation, the screw-type or impeller-type stirring device is rotated in the reverse direction to that during normal operation, so that an upward flow is generated toward the water surface in the center of the methane fermentation tank, and the bottom surface is directed toward the bottom surface. The present invention relates to an operation method characterized in that countercurrent is generated and deposits collected at the center of the bottom surface from the deposit extraction pipe are discharged out of the methane fermentation tank.

  In the specification of this application, “substantially horizontal” means that the bottom surface is horizontal (horizontal plane), as well as the bottom surface is slightly higher in the center than the end portion (circumferential portion) (the bottom surface is The case where it is convex upward) and the case where it is slightly lower (when the bottom surface is convex downward) are also included. When the central portion is higher or lower than the end portion (circumferential portion), the angle formed by the straight line connecting the end portion and the central portion with the horizontal line is preferably adjusted to 1 degree or less.

  It is preferable that a digestion juice extraction tube is connected to the lower side of the methane fermentation tank.

When the diameter of the bottom of the methane fermentation tank is T, the methane fermentation tank and the screw type or impeller type stirring device,
The blade diameter D of the stirring blade of the screw type or impeller type stirring device is 0.2 to 0.3 T,
The can height of the methane fermentation tank is 0.8 to 1.2 T,
The depth of the liquid to be treated in the methane fermentation tank is 0.8 to 1.0 T,
It is preferable that the upper end portion of the stirring blade of the screw type or impeller type stirring device is immersed 0.5D or more from the liquid surface of the liquid to be treated.

  According to the operation method of the methane fermentation tank of the present invention, it is possible to efficiently remove deposits while continuously operating the methane fermentation tank. Further, the flow of the liquid to be treated can be changed only by rotating the stirring device without adding new equipment and the like, and the deposits can be efficiently removed, so that the operating cost can be reduced.

It is a conceptual diagram illustrating the stirring of the liquid to be processed in the methane fermentation tank in the present invention, (a) shows the flow of the liquid to be processed during normal operation, (b) is a sediment deposition in the methane fermentation tank Indicates the position to perform. The deposit state in the case where the deposit is discharged from the deposit extraction pipe from the state shown in FIG. It is a conceptual diagram explaining stirring of the to-be-processed liquid in the methane fermentation tank in this invention, and shows the flow of the to-be-processed liquid at the time of reverse rotation of a stirring apparatus. It is a conceptual diagram explaining the state of the deposit in a methane fermenter, (a) shows the deposition state of the deposit after reverse rotation of a stirrer, (b) extracted the deposit from the deposit extraction pipe Indicates the state. It is a conceptual diagram explaining stirring of the to-be-processed liquid in the conventional methane fermenter, (a) shows the flow of the to-be-processed liquid during normal operation, (b) deposits deposits in the methane fermenter Indicates the position. FIG. 6 shows a deposit state when deposits are discharged from the deposit extraction pipe from the state shown in FIG.

  Embodiments of the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the following description.

  FIG. 1 is a conceptual diagram illustrating the stirring of the liquid 2 to be processed in the methane fermentation tank 1 according to the present invention. The methane fermentation tank 1 used in the present invention is a cylindrical body or a columnar body having a horizontal cross section of an octagon or more, and digests surplus sludge generated in a sewage treatment plant to take out digestion gas. It is configured as follows. The can body height of such a methane fermentation tank is 10 m or more and 30 m or less, and the diameter (when the horizontal cross section is polygonal, the diameter of the inscribed circle is 10 m or more and 30 m or less. The to-be-processed liquid 2 is maintained at 37 degreeC-40 degreeC suitable for medium temperature fermentation, for example with the heating apparatus like the heat exchanger which is not illustrated.

Although the capacity | capacitance of the methane fermenter 1 to which this invention is applied is not specifically limited, It is preferable that it is 750-6000m < ³ >. When the capacity of one methane fermentation tank is large and the area of the bottom surface 7 is large, a large amount of energy is required to collect the deposits near the center of the bottom surface by the reverse rotation of the stirring device 3.

  FIG. 2 shows the flow of the liquid 2 to be treated during normal operation. The methane fermentation tank 1 has a flat bottom surface 7 and is provided with a two-stage impeller blade connected to a motor 5 as a stirring device 3 at the center. Instead of the two-stage impeller blades, screw blades may be provided as the stirring device 3, and the impeller blades may be one stage or three or more stages.

  In the present invention, a propeller type, paddle type, flat paddle type, turbine type or cone type stirring device can be used as the impeller type stirring device. In the present invention, a ribbon type or screw type stirring device can be used as the screw type stirring device.

  The steel plate methane fermentation tank is generally installed on a concrete base, but the bottom of the methane fermentation tank is horizontal so that rainwater does not collect between the foundation and the methane fermentation tank. Alternatively, it is preferable to incline so as to be convex upward.

  The stirring device 3 is normally operated continuously, and the normal operation and the reverse rotation operation are continuously performed regularly by a timer or the like. Specifically, the reverse rotation operation is performed at a frequency of about once to four times a day, and the operation time is adjusted according to the amount of sludge that is input. When the blade diameter of the stirring blade is D and the diameter of the bottom surface of the methane fermentation tank is T, the ratio of the size of the methane fermentation tank 1 and the stirring blade is preferably D = 0.2T or more and 0.3T or less.

  As for the installation location of the stirring blade, it is preferable that the upper end of the stirring blade is immersed 0.5D or more from the liquid surface. When using a multistage stirring blade, it is preferable that the lowermost blade be installed 0.75D to 1.5D or more away from the bottom surface 7 of the methane fermentation tank 1.

  When a screw blade is provided as the stirring device 3, it is preferable to adjust the uppermost blade so that it is 50 cm or more and 200 cm or less from the liquid level in the methane fermentation tank 1. Moreover, when providing a screw blade, since a draft tube is normally installed, it is preferable to adjust so that the lowest part of a draft tube may be 2 m or more and 15 m or less from the bottom face 7 of the methane fermentation tank 1. FIG.

  A specific example of the liquid to be treated 2 is a liquid containing sludge generated at a sewage treatment plant or a biomass such as food waste, manure derived from livestock, etc., but contains an organic substance and has a negative effect on the growth of methane bacteria. As long as it does not contain, you may supply to the methane fermenter 1 as the to-be-processed liquid 2. FIG. In addition, it is preferable that the said sludge and food waste supplied to a methane fermenter are adjusted to solid content concentration 2-10% in advance.

  The flow direction of the liquid 2 to be treated shown in FIG. 1 (a) is the same as that in FIG. 5 (a), and descends toward the bottom surface 7 along the stirring device 3 (impeller blades) at the center of the methane fermentation tank 1. Current is generated. This downward flow strikes the bottom surface 7 and changes its direction in the side surface direction, and further rises toward the water surface by striking the side surface. And it becomes a downward flow again by the stirring apparatus 3. On the other hand, the generated biogas is taken out from a gas outlet provided in the upper part of the methane fermentation tank to a gas holder (not shown) installed outside.

  If the normal operation is continued, the soil, sand, or hard-to-decompose solids such as metal pieces contained in the liquid to be treated 2 in the methane fermentation tank 1, or unsuitable masses of fermentation such as hair or plastic pieces Gradually build up. In the case of the methane fermenter 1 having a shape as shown in FIG. 1 (a), the deposit 4 is deposited so as to be closer to the side surface on the bottom surface 7 and lower toward the center as shown in FIG. 1 (b). To do. In this case, the deposit 4 cannot be removed efficiently by the digestive juice transfer pipe 8 provided below the side surface of the methane fermentation tank 1. That is, when the liquid to be treated 2 (digested liquid) is pulled out from the digestive liquid transfer pipe 8, the deposit 4 around the digestive liquid transfer pipe 8 is removed through the digestive liquid transfer pipe 8, but most other deposits. 4 is a state where it is not removed and is directly deposited on the bottom surface 7 of the methane fermentation tank 1.

  Therefore, it is conceivable to open the sediment extraction pipe 6 disposed on the bottom surface 7 of the methane fermentation tank 1 and discharge the sediment 4. In this case, as shown in FIG. 2, the sediment extraction pipe 6 is used. Only the surrounding deposit 4 is removed. On the other hand, it is conceivable to provide a large number of deposit extraction pipes 6 (for example, about 10), but the extraction efficiency is low, which is not practical. In addition, in order to remove the deposit 4, it is conceivable to drain all the liquid 2 to be treated, empty the inside of the methane fermentation tank 1, and wash the bottom surface 7. It is not realistic considering the number of days outage.

  However, in the present invention, the normal operation is continued for a certain period, and when the deposit 4 is deposited near the end of the bottom surface 7, the rotation direction of the motor 5 is reversed and the agitator 3 is rotated reversely to the normal operation. A deposit extraction process is performed. At this time, the flow direction of the liquid 2 to be processed is as shown in FIG. At this time, since a flow toward the center is generated in the vicinity of the bottom surface 7, a horizontal flow is added to the deposit 4 at the end, and the deposit 4 is extracted as shown in FIG. It is moved to the center where the tube 6 is installed.

  In the state shown in FIG. 4 (a), by operating the pump P provided in the sediment extraction pipe 6, the sediment collected to the center can be efficiently extracted from the sediment extraction pipe 6. It becomes possible.

  The rotation speed and direction of the motor 5 are controlled by a control device (not shown). The rotation speed of the agitator 3 is 10 to 20 r / min in the case of normal rotation, and is operated at a rotation speed of 40 to 100% of the normal rotation in the case of reverse rotation.

  The time for reversely rotating the stirring device 3 may be proportional to the amount of the deposit 4 or may be periodically operated for a predetermined time. Usually, the reverse rotation is performed about 1 to 4 times per day, about 5 to 30 minutes per time. However, when there are many deposits 4, the number and time of the reverse rotation operation may be increased.

  In addition to periodically rotating in the reverse direction as described above, the stirring device 3 may detect the presence or absence of deposits with a sensor, and may perform a reverse rotation operation when deposits are detected. In this case, the reverse rotation operation may be performed several times a day after detection. However, in order to reliably discharge the deposit, 1 day a day for several days (for example, 2 to 4 days) after sensor detection. Up to 4 reverse rotation operations may be performed.

  When detecting the presence or absence of deposits, the presence or absence of deposits may be directly measured using a temperature sensor or ultrasonic sensor, etc., and by measuring the amount of biogas containing methane, It is also possible to predict the decrease in the effective volume of the material and indirectly measure the presence or absence of deposits.

  When detecting the presence or absence of deposits using a sensor and carrying out the deposit removal step, the specific judgment criteria are, for example, deposition up to a height of 3 to 5% of the can height It is a case where it is determined that the deposit has been deposited, or a case where it is determined that the deposit has been deposited up to a volume of 3 to 5% with respect to the volume of the digester.

  If the flow rate of the liquid 2 to be processed is too low, the deposit 4 cannot be moved. Conversely, if the flow rate of the liquid 2 to be processed is too high, the deposit 4 is wound up by the stirring device 3. For this reason, in the deposit extraction process, it is preferable to adjust the flow rate of the liquid 2 to be processed to 10 cm / second or more and 50 cm / second or less. The flow rate of the liquid 2 to be treated is controlled by adjusting the output of the motor 5.

  The deposit 4 that has moved to the center of the bottom surface 7 is removed out of the methane fermentation tank 1 by a pump P provided in the deposit extraction pipe 6. The deposit is extracted at least once during the reverse rotation operation, and the discharge time is adjusted to about 3 to 5 minutes each time. After completion of the deposit extraction process, the deposit extraction pipe 6 is closed, and the extraction of the deposit 4 is stopped. When the deposit extraction process is repeated, the deposit extraction pipe 6 is opened again and the pump 4 is operated, whereby the deposit 4 is extracted. Thereafter, when the reverse rotation operation time reaches a predetermined time, the stirring device 3 is switched to the normal rotation, and the normal operation of the methane fermentation tank 1 is resumed.

  The stirring device 3 is normally stopped for about 5 minutes at the time of the first switching when the motor 5 is switched from the normal rotation to the reverse rotation or at the second switching when the motor 5 is switched from the reverse rotation to the normal rotation. While the stirring device 3 is stopped, the pump P may be operated to discharge the deposits. After the deposit is discharged, the deposit extraction pipe 6 is closed, and the extraction of the deposit 4 is stopped.

  By pulling out the deposit when the stirring device 3 is stopped, the solid matter can be discharged before the solid matter floating by the stirring of the liquid 2 to be treated becomes agglomerated and difficult to transfer.

  In addition, since the methane fermentation tank 1 is normally operated with a residence time of 20 to 30 days in the case of medium temperature fermentation, the liquid to be processed is supplied when the object to be processed is supplied to the methane fermentation tank 1. In accordance with the increased amount of 2, the liquid 2 to be treated in the methane fermentation tank 1 is drawn out by natural suction using a pump or a water level difference. For this reason, in the present invention, the sludge extraction operation may be synchronized with the input timing of the workpiece, or may be performed regardless of the input of the workpiece.

  The liquid to be treated or the sediment drawn from the digestion fluid transfer pipe 8 or the sediment withdrawal pipe 6 is appropriately supplied to a biological treatment tank such as a secondary methane fermentation tank to further biologically decompose the remaining organic matter. It may be dehydrated by a dehydrator or the like. When dehydrated, the dehydrated filtrate may be separately subjected to water treatment, and the dehydrated product may be incinerated or discarded.

  It is also possible to use the deposit extraction pipe 6 as a digestion liquid transfer pipe without providing the digestion liquid transfer pipe 8. In the case where the digestive juice transfer pipe 8 is provided independently, mixing the digestive juice and the deposit can be suppressed by adjusting the height at which the digestive juice transfer pipe 8 is installed. On the other hand, by installing the digestive fluid transfer pipe 8 in the vicinity of the bottom surface, it is also possible to extract a part of the deposit from the digestive fluid transfer pipe 8.

  The methane fermentation tank 1 may be provided with a heating device (not shown) for adjusting the temperature of the digested liquid 2 to a temperature range suitable for methane fermentation. In addition, a circulation line (not shown) for circulating the digested liquid transferred from the sediment extraction pipe 6 or the digested liquid transfer pipe 8 to the methane fermentation tank is provided, and the liquid temperature is adjusted in this return path. A heating device may be provided, and the liquid to be treated after heating may be returned to the methane fermentation tank 1.

[Example]
The experiment was performed using a cylindrical steel plate digestion tank with a diameter of 10 m and a height of 11 m. The digester is turned the object to be processed of 750 meters ^3, the interior of the digester is provided two-stage stirring blades of the impeller type with a diameter of about 2m (height of each from the digester bottom, 2m and 8m), 15 rpm The agitating blade was rotated. The sludge to be subjected to methane fermentation was supplied at 30 m ³ / day, and methane fermentation was performed with a residence time of 25 days.

(Measurement of sediment)
The height of the sediment was measured from the top using a probe every 1 m from the center of the tank to the outer wall. Contour lines were drawn on the assumption that the same amount of sediment was deposited in the same distance from the center. The volume of the deposit was obtained from the height of the deposit in the digestion tank, and the volume ratio of the deposit to the digestion tank (deposit volume / volume of the digestion tank) was calculated.

  The probe has a weight attached to the tip of the string, and if there is a deposit, the weight stops to the middle of the digestion tank without sinking, so by measuring the depth at which the weight sinks, It becomes possible to measure the height of the deposit.

(Implementation of reverse rotation)
After the start of the digestion operation, the sediment began to gradually accumulate, and after about 4 months, it was judged that the volume ratio of the sediment to the digestion tank (deposit volume / digestion tank volume) was about 3.5%. Therefore, in addition to the normal operation, the agitator was reversely rotated (15 rpm, several minutes, 4 to 5 times / day), and the digestive juice was extracted in accordance with the reverse rotation of the agitator.

  The normal operation of methane fermentation was combined with the sediment discharge operation by reverse rotation operation for 10 days, and the deposit status of the deposit in the digestion tank was confirmed using a probe. It was confirmed that the volume fraction of the deposit was reduced to 2.5%. After that, the operation was continued for 4 months, but it was confirmed that the deposit status could be reduced to about 2.5% by performing the reverse rotation operation similar to the above.

  The operation method of the methane fermenter of the present invention is useful in the fields of wastewater treatment and energy.

1, 11: Methane fermentation tank 2, 12: Liquid to be treated (digested liquid)
3, 13: Stirrer 4, 14: Sediment 5, 15: Motor 6, 16: Sediment extraction tube 7, 17: Bottom surface 8: Digestion fluid transfer tube P: Pump

Claims (4)

A method for operating a methane fermentation tank,
The methane fermenter is
A cylindrical shape having a bottom surface that is convex upward or downward, and an angle between a straight line connecting the end and the center with a horizontal line is greater than 0 degrees and less than 0.3 degrees,
In the center, a screw type or impeller type stirring device for stirring the liquid to be treated is provided,
At the center of the bottom is a sediment extraction tube,
The operation method is to perform a normal operation and a deposit extraction operation alternately,
During normal operation, by rotating the screw type or impeller type stirring device, a downward flow is generated at the center of the methane fermentation tank toward the bottom surface, and an upward flow is generated at the side of the methane fermentation tank toward the water surface. And
During the sediment extraction operation, the screw-type or impeller-type stirring device is rotated in the reverse direction to that during normal operation, so that an upward flow is generated toward the water surface in the center of the methane fermentation tank, and the bottom surface is directed toward the bottom surface. A counter flow is generated, and the deposit collected in the center of the bottom from the deposit extraction pipe is discharged out of the methane fermentation tank.   The operation method of the methane fermentation tank of Claim 1 with which the digestive-solution transfer pipe is connected to the side lower side of the said methane fermentation tank. When the diameter of the bottom of the methane fermentation tank is T, the methane fermentation tank and the screw type or impeller type stirring device,
The blade diameter D of the stirring blade of the screw type or impeller type stirring device is 0.2 to 0.3 T,
The can height of the methane fermentation tank is 0.8 to 1.2 T,
The depth of the liquid to be treated in the methane fermentation tank is 0.8 to 1.0 T,
The operation method of the methane fermenter of Claim 1 or 2 with which the upper end part of the stirring blade of the said screw type or impeller type stirring apparatus is immersed 0.5D or more from the liquid level of a to-be-processed liquid. The rotational speed of the stirring device during the normal operation is 10 to 20 r / min,
The methane fermenter according to any one of claims 1 to 3, wherein a rotational speed of the stirring device during the sediment extraction operation is 40 to 100% of a rotational speed of the stirring device during the normal operation. Driving method.

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