JP4991832B2 - Methane fermentation method and methane fermentation apparatus - Google Patents

Description

  The present invention relates to a methane fermentation treatment and a methane fermentation apparatus capable of stably treating methane fermentation of organic waste over a long period of time.

  Methane fermentation treatment is an anaerobic treatment of organic waste with methane bacteria to convert the organic waste into methane gas. The organic waste is decomposed into biogas and water to greatly reduce the amount of waste. can do. In addition, there is a merit that methane gas generated as a by-product can be recovered as energy.

  If a large amount of methane bacteria can be stored in the methane fermentation tank, processing at higher speed becomes possible. As a means for storing a large amount of methane bacteria in the methane fermentation tank, there is a method of installing a filter bed for supporting microorganisms such as methane bacteria in the methane fermentation tank. However, there is a problem that not only the apparatus configuration becomes complicated, but also maintenance is troublesome and expensive because it is necessary to prevent clogging of the filter bed.

  Further, as a method not using a filter bed, there is a method in which a fermentation liquid taken out from a methane fermentation tank is subjected to solid-liquid separation, and the separated sludge separated into solid and liquid is returned to a methane fermentation tank or the like to perform methane fermentation.

  For example, in Patent Literature 1, organic waste is methane-fermented in a methane fermentation tank, and sludge from the methane fermentation tank is solid-liquid separated by solid-liquid separation means, and separated by solid-liquid separation by the solid-liquid separation means. A part of the sludge and a part of the separated liquid separated by the solid-liquid separating means are returned to be mixed with the organic waste, and the separated liquid separated by the solid-liquid separating means is further removed. A part is returned so as to be mixed with the sludge from the methane fermentation tank, and the remainder of the separated sludge solid-liquid separated by the solid-liquid separation means and the remainder of the separated liquid solid-liquid separated by the solid-liquid separation means A methane fermentation method is disclosed that discharges to the outside. Examples of the solid-liquid separation means include screw-type dehydrators, centrifugal dehydrators, filter press dehydrators, belt press dehydrators, multiple disk dehydrators, and other mechanical solid-liquid separation means, and precipitation-type solid-liquid separation means. It has been.

  Of the solid-liquid separation means disclosed in Cited Document 1, the precipitation-type solid-liquid separation means does not require power, so that the running cost is excellent.

  However, since many precipitation-type solid-liquid separation means do not have an internal structure that suppresses turbulence caused by inflow turbulence, mixing by wind, and generation of bubbles, the Reynolds number increases, The sedimentation property of sludge was impaired.

  Conventionally, the amount of sludge returned from the solid-liquid separation means to the methane fermentation tank and the amount of drainage from the solid-liquid separation means to the outside of the system are not particularly controlled and are kept constant. However, when the load of organic waste in the methane fermenter (depending on the input and concentration) increases, the viscosity of the fermented liquid in the methane fermenter increases and the sludge concentration in the fermented liquid extracted from the methane fermenter also increases. , Its viscosity also increases. Since the sedimentation rate of sludge in the precipitation-type solid-liquid separation means tends to become slower as the sludge concentration and the viscosity of the fermentation liquid increase, the load of organic waste in the methane fermentation tank fluctuates. Sedimentation time may not be sufficiently secured, and it may be difficult to return the sludge concentrated to the required concentration to the methane fermentation tank. Furthermore, the liquid property discharged from the precipitation-type solid-liquid separation means is deteriorated, and there is a problem that labor is required for wastewater treatment. For this reason, in the case of performing methane fermentation with a constant amount of sludge being returned from the precipitation-type solid-liquid separation means to the methane fermentation tank and the amount of drainage from the solid-liquid separation means to the outside of the system, Considering the load fluctuation of the organic waste, it is necessary to increase the safety factor and increase the tank volume of the precipitation type solid-liquid separation means.

JP 2006-255571 A

  The objective of this invention is providing the methane fermentation method and methane fermentation apparatus which can maintain a high decomposition rate in a short time, without taking a complicated apparatus structure.

In achieving the above object, the methane fermentation method of the present invention performs a methane fermentation treatment of organic waste in a methane fermentation tank, takes out a predetermined amount of the fermentation liquid from the methane fermentation tank, and the sludge concentration is reduced by gravity sedimentation means. A sludge sedimentation liquid that becomes higher as it goes downward is formed, and the sludge high-concentration liquid on the lower layer side of the sludge sedimentation liquid is directly or indirectly returned to the methane fermentation tank through a return line, and the sludge on the upper layer side of the sludge sedimentation liquid The low concentration liquid is discharged out of the system through the discharge line, and the total amount of the liquid amount returned through the return line and the liquid amount discharged through the discharge line is almost equal to the amount of the fermentation liquid taken out from the methane fermentation tank. In a methane fermentation process that controls to be equal,
Measuring the sludge concentration of the fermentation broth in the methane fermentation tank by the first sludge concentration measuring means;
Measuring a sludge concentration of a predetermined portion of the sludge sedimentation liquid formed by the gravity sedimentation means by a second sludge concentration measurement means;
Comparing the sludge concentration measured by the first sludge concentration measuring means with the sludge concentration measured by the second sludge concentration measuring means, the sludge concentration of the liquid discharged through the discharge line is the methane fermentation The sludge concentration of the fermentation liquor in the tank is lower than that, or the sludge concentration of the liquid returned to the methane fermentation tank through the return line is higher than the sludge concentration of the fermentation liquid in the methane fermentation tank. The amount of liquid discharged through the discharge line and the amount of liquid returned to the methane fermenter through the return line are controlled.

In addition, the methane fermentation apparatus of the present invention gravity settles sludge in a fermentation broth extracted from the methane fermentation tank for methane fermentation treatment of organic waste and the methane fermentation tank, and the sludge concentration increases toward the bottom. Gravity sedimentation means for forming sludge sedimentation liquid, return line for returning sludge high-concentration liquid on the lower side of the sludge sedimentation liquid directly or indirectly to the methane fermentation tank, and sludge low on the upper layer side of the sludge sedimentation liquid A fermentation liquid in which a total amount of a liquid amount returned through the return line and a liquid amount discharged through the discharge line is taken out from the methane fermentation tank. In a methane fermentation device controlled to be approximately equal to the amount of
First sludge concentration measuring means for measuring the sludge concentration of the fermentation broth in the methane fermenter;
A second sludge concentration measuring means for measuring a sludge concentration of a predetermined portion of the sludge sedimentation liquid formed by the gravity settling means;
The sludge of the liquid returned to the methane fermentation tank through the return line by comparing the sludge concentration measured by the first sludge concentration measuring means with the sludge concentration measured by the second sludge concentration measuring means. Through the discharge line, the concentration is higher than the sludge concentration of the fermentation liquid in the methane fermentation tank, and the sludge concentration of the liquid discharged through the discharge line is lower than the sludge concentration of the fermentation liquid in the methane fermentation tank. And a controller for controlling the amount of liquid to be discharged and the amount of liquid to be returned to the methane fermentation tank through the return line.

According to the present invention, according to the sludge concentration measured by the first sludge concentration measuring means and the sludge concentration measured by the second sludge concentration measuring means, the sludge concentration of the liquid discharged through the discharge line is methane fermentation. Make sure that each sludge concentration is lower than the sludge concentration in the fermentation broth in the tank, or higher than the sludge concentration in the fermentation broth in the methane fermentation tank. Adjust the amount.
When the sludge concentration of the liquid discharged through the discharge line is adjusted to be lower than the sludge concentration of the fermentation liquid in the methane fermentation tank, the sludge is drawn from the lower part of the gravity sedimentation means and returned to the methane fermentation tank through the return line. The sludge concentration in the liquid is relatively high. Similarly, if the sludge concentration in the liquid returned to the methane fermentation tank through the return line is adjusted to be higher than the sludge concentration in the fermentation liquid in the methane fermentation tank, the liquid discharged from the upper part of the gravity sedimentation means through the discharge line. The sludge concentration is relatively low.
For this reason, even if the properties of the organic waste supplied to the methane fermenter fluctuate and the sludge concentration in the fermentation liquid extracted from the methane fermenter fluctuates, the sludge concentration with reduced sludge concentration is reduced from the discharge line. Concentrated liquid can be discharged, and a sludge high-concentrated liquid concentrated to a concentration required for the methane fermentation tank can be returned from the return line. As a result, it is possible to perform methane fermentation while maintaining a high decomposition rate in a short period of time for treating the organic matter while keeping the methane bacteria in the fermentation tank for a long time without increasing the size of the gravity sedimentation means. .

In one aspect of the present invention, the second sludge concentration measuring means is disposed in the gravity settling means, above the discharge line and / or in the discharge line, and the first sludge concentration measurement. If the sludge concentration measured by the second sludge concentration measuring means is higher than the sludge concentration measured by the means, the amount of liquid discharged through the discharge line is reduced, and the first sludge concentration measurement is performed. If the sludge concentration measured by the second sludge concentration measuring means is lower than the sludge concentration measured by the means, the amount of liquid discharged through the discharge line is increased, and the methane fermentation through the return line The amount of liquid returned to the tank is controlled so as to be the amount obtained by subtracting the amount of liquid discharged through the discharge line from the amount of fermented liquid removed from the methane fermentation tank and introduced into the gravity sedimentation means. It is preferable to.
According to the said aspect, while being able to maintain the sludge density | concentration of the liquid discharged | emitted through a discharge line more stably and in a low state, making the sludge density | concentration of the liquid returned to a methane fermentation tank through a return line relatively high Can do.

In another aspect of the present invention, the second sludge concentration measuring means is disposed in the gravity settling means, below the discharge line and / or in the return line, and the first sludge concentration measurement. If the sludge concentration measured by the second sludge concentration measuring means is higher than the sludge concentration measured by the means, the amount of liquid returned to the methane fermentation tank through the return line is increased, When the sludge concentration measured by the second sludge concentration measuring means is lower than the sludge concentration measured by the sludge concentration measuring means, the amount of liquid returned to the methane fermentation tank through the return line is The amount of liquid that is reduced and discharged through the discharge line is returned to the methane fermenter through the return line from the amount of fermentation liquid that is removed from the methane fermenter and introduced into the gravity sedimentation means. Is preferably controlled such that the amount obtained by subtracting the amount of liquid.
According to the said aspect, while being able to maintain the sludge density | concentration of the liquid returned to a methane fermentation tank through a return line more stably and in a high state, making the sludge density | concentration of the liquid discharged | emitted through a discharge line relatively low Can do.

In the present invention, a slurry adjustment tank for pre-treating organic waste into a slurry is disposed in front of the methane fermentation tank, and the return line is connected to the slurry adjustment tank and / or the methane fermentation tank. Is preferred.
According to the said aspect, the liquid which contains the sludge formed by the gravity sedimentation means in high concentration can be returned to a methane fermentation tank via a slurry adjustment tank, or can be directly returned to a methane fermentation tank. When returning a liquid containing sludge to a high concentration to the methane fermentation tank via the slurry adjustment tank, the slurry adjustment tank is solubilized, etc., so that the methane fermentation process is easily performed. The processing efficiency is improved, and higher decomposition efficiency is obtained.

  In the present invention, the sludge concentration measuring means is preferably at least one selected from a viscometer, a near infrared scattered light type concentration meter, an ultrasonic sludge interface meter, and a microwave concentration meter.

  According to the present invention, even if the properties of the organic waste supplied to the methane fermenter fluctuate and the sludge concentration of the fermentation liquor extracted from the methane fermenter fluctuates, the sludge concentration is reduced from the discharge line. The sludge low concentration liquid can be processed and discharged in a short time. Furthermore, from the return line, it is possible to return the high-concentrated sludge liquid concentrated to the concentration required for the methane fermentation tank, so that the methane bacteria in the fermenter can be secured and sufficient residence time of the methane bacteria can be taken. Become. As a result, organic waste can be methane-fermented in a short time and at a high decomposition rate without using a large-scale gravity sedimentation means.

It is a schematic block diagram showing 1st Embodiment of the methane fermentation apparatus of this invention. It is a control flowchart figure performed with the control apparatus of the methane fermentation apparatus. It is a schematic block diagram showing 2nd Embodiment of the methane fermentation apparatus of this invention. It is a control flowchart figure performed with the control apparatus of the methane fermentation apparatus.

1st Embodiment of the methane fermentation apparatus of this invention is described using FIG.
As shown in FIG. 1, the methane fermentation apparatus mainly includes a pretreatment tank 1, a methane fermentation tank 2, and a gravity sedimentation tank 3.

  The pretreatment tank 1 is a treatment tank that performs processing such as pulverization, crushing, and solubilization of organic waste sent from an organic waste supply source, and adjusts it into a slurry state, that is, a slurry adjustment tank. The pretreatment tank 1 also has a buffering function for stabilizing the inflow amount of organic waste adjusted to a slurry state into a methane fermentation tank 2 described later. In the pretreatment tank 1, a pipe L1 extending from an organic waste supply source and a pipe P1 extending from the bottom of the gravity settling tank 3 (may be connected to the lower part of the side surface) are provided. L2 (corresponding to “return line” in the present invention) is connected.

  A methane fermentation tank 2 is disposed at the subsequent stage of the pretreatment tank 1. The pretreatment tank 1 and the methane fermentation tank 2 are connected via a pipe L3 in which a pump P2 is interposed.

  The methane fermentation tank 2 is a treatment tank that anaerobically treats organic waste (slurry) supplied into the tank by the action of anaerobic microorganisms such as methane bacteria and decomposes it into biogas such as methane gas. The methane fermentation tank 2 is provided with a stirring device (not shown) for stirring the fermentation liquid in the tank and a first sludge concentration meter 10 for measuring the sludge concentration of the fermentation liquid in the tank. Further, from the upper part of the methane fermentation tank 2, a biogas extraction pipe L4 extends and is connected to a gas holder, a gas utilization facility, and the like.

  The stirring device is not particularly limited as long as it can stir the fermentation broth in the tank. For example, a stirrer equipped with a stirring blade may be used. In addition, a gas agitation that forms a path for circulating the fermented liquid in the tank and provides a mechanism for forming an upward flow or a downward flow in the fermented liquid in the tank, or circulates the generated biogas for bubbling. An apparatus may be provided.

  The first sludge concentration meter 10 is not particularly limited, and preferred examples include a viscometer, a near infrared scattered light type concentration meter, an ultrasonic sludge interface meter, a microwave concentration meter, and the like. Examples of the viscometer include “FMV80A” (trade name) marketed by Seconic. Moreover, as a near-infrared scattered light type | mold densitometer, "SG-200" (brand name) marketed, for example from Horiba Advanced Techno is mentioned. Moreover, as an ultrasonic sludge interface meter, for example, “SL-200” (trade name) marketed by HORIBA Advanced Techno is cited. Moreover, as a microwave densitometer, "LQ series" (brand name) marketed from Toshiba, for example can be used.

  A gravity sedimentation tank 3 is arranged at the subsequent stage of the methane fermentation tank 2. The methane fermentation tank 2 and the gravity sedimentation tank 3 are connected via a pipe L5 in which a pump P3 is interposed.

  The gravity sedimentation tank 3 is a treatment tank that gravity settles the sludge in the fermentation liquid taken out from the methane fermentation tank 2 to form a sludge sedimentation liquid whose sludge concentration increases downward. An example is a gravity sedimentation pond. Moreover, the sedimentation speed | rate of sludge can be raised more by arrange | positioning a water flow inclination board to the gravity sedimentation tank 3. FIG. As a gravity sedimentation tank provided with the water flow inclination board, what was described in Unexamined-Japanese-Patent No. 6-63321 etc. is mentioned, for example.

  From the side of the gravity settling tank 3, a pipe L6 (corresponding to the “discharge line” in the present invention) for discharging the sludge low concentration liquid on the upper layer side (hereinafter also referred to as “sludge separation liquid”) to the outside of the system is connected. ing. A pump P4 is interposed in the pipe L6. Further, a pipe L2 connected to the pretreatment tank 1 extends from the lower part (bottom part in the present embodiment) of the gravity settling tank 3, and is also referred to as a sludge high-concentration liquid sludge (hereinafter referred to as "sludge concentrate") on the lower layer side. ) At least a part thereof can be returned to the pretreatment tank 1. The second sludge concentration meter 20 is disposed in the gravity settling tank 3 above the position where the pipe L6 is connected to the gravity settling tank 3. The second sludge concentration meter 20 in the present embodiment is installed so that the concentration of the sludge separation liquid in the upper layer portion of the sludge sedimentation liquid can be measured even if the upper surface position of the sludge sedimentation liquid in the gravity sedimentation tank 3 fluctuates. The second sludge concentration meter 20 is the same as the first sludge concentration meter 10 described above. Moreover, it is preferable that the 2nd sludge concentration meter 20 is installed in the connection part vicinity with the piping L6.

  The control device 100 controls the operation of the pumps P1 and P4 according to a flowchart shown in FIG.

  Next, the operation of the first embodiment of the methane fermentation method of the present invention will be described using the case of using this methane fermentation apparatus as an example.

  Organic waste is supplied to the pretreatment tank 1 from the pipe L1 and the pipe L2, and is subjected to processing such as pulverization and crushing, solubilization processing, and the like, and is adjusted to a slurry state. The organic waste pretreatment method can be appropriately changed depending on the type and properties of the organic waste used for the treatment. For example, in the case of organic waste such as dust, garbage, livestock manure, sewage sludge, it is preferable to mix with clean water and perform processing such as crushing and crushing. In the case of an organic waste containing a large amount of fats and oils, such as fat and oil drainage, stearic acid, palmitic acid, etc., it is preferably heated to 65 to 80 ° C. and solubilized.

  The organic waste pretreated in a slurry state is supplied into the methane fermentation tank 2 via the pipe L3 by the pump P2.

  In the methane fermentation tank 2, stirring is performed continuously or intermittently by a stirring means (not shown) so that the sludge concentration and temperature of the fermentation liquid in the tank are substantially uniform. The sludge concentration of the fermentation broth in the tank is measured by the first sludge concentration meter 10 and the measurement result is input to the control device 100.

  The organic waste (slurry) supplied to the methane fermentation tank 2 is methane-fermented by the action of anaerobic microorganisms such as methane bacteria by staying in the methane fermentation tank 2 for a predetermined period. Then, the same amount of fermentation liquid in the methane fermentation tank 2 as the organic waste (slurry) supplied to the methane fermentation tank 2 is drawn out from the pipe L5 by the pump P3 and supplied to the gravity sedimentation tank 3. In addition, biogas such as methane gas generated when methane fermentation of organic waste is taken out of the tank from the pipe L4 and stored in a biogas holder (not shown) or the like.

  In the gravity sedimentation tank 3, the sludge in the fermentation liquid taken out from the methane fermentation tank 2 is gravity settled to form a sludge sedimentation liquid in which the sludge concentration increases downward, and at least a part of the sludge sedimentation liquid is pumped through the pipe L6. While discharging by P4, the remainder is returned to the pretreatment tank 1 by the pump P1 through the pipe L2. Further, the second sludge concentration meter 20 measures the sludge concentration in a predetermined portion of the sludge sedimentation liquid. In the methane fermentation apparatus of this embodiment, the second sludge concentration meter 20 is disposed in the gravity sedimentation tank 3 and above the connection position of the pipe L6 to the gravity sedimentation tank 3, so that the second sludge The densitometer 20 measures the sludge concentration of the sludge separation liquid. Then, the measurement result of the second sludge concentration meter 20 is input to the control device 100.

  When the measurement results of the first sludge densitometer 10 and the second sludge densitometer 20 are input to the control device 100, the second sludge concentration from the control device 100 is higher than the measurement value of the first sludge densitometer 10. An output signal is transmitted to the pumps P1 and P4 so that the measured value of the total 20 becomes smaller, and the amount of liquid returned to the pretreatment tank 1 through the pipe L2 (hereinafter referred to as “return amount of sludge concentrate”) And the amount of liquid discharged through the pipe L6 (hereinafter also referred to as “sludge separation liquid discharge amount”).

  That is, as shown in FIG. 2, when the measurement results of the first sludge concentration meter 10 and the second sludge concentration meter 20 are input (step S1), the measured value C1 of the first sludge concentration meter 10 and the second Comparison with the measured value C2 of the sludge concentration meter 20 is performed (step S2).

  When the measurement value C2 of the second sludge concentration meter 20 is larger than the measurement value C1 of the first sludge concentration meter 10, it means that the sludge concentration of the sludge separation liquid discharged through the pipe L6 is high. The output of P4 is reduced, and the discharge amount of the sludge separation liquid discharged through the pipe L6 is reduced. At the same time, the output of the pump P1 is that the return amount of the sludge concentrate returned through the pipe L2 is the discharge of the sludge separation liquid from the amount of the fermentation liquid taken out from the methane fermentation tank 2 and charged into the gravity sedimentation tank 3. Control so that the amount is reduced. Specifically, by reducing the output of the pump P4 and reducing the discharge amount of the sludge separation liquid, it is necessary to increase the return amount of the sludge concentrate, and therefore the output of the pump P1 is increased ( Step S3). Thereby, it can prevent that the sludge separation liquid with a high sludge density | concentration will be discharged | emitted, and a methane microbe can be made to stay in the methane fermentation tank 2 for a long period of time.

  On the other hand, when the measurement value C2 of the second sludge concentration meter 20 is smaller than the measurement value C1 of the first sludge concentration meter 10, it means that the sludge concentration of the sludge separation liquid discharged through the pipe L6 is low. The output of the pump P4 is increased to increase the discharge amount of the sludge separation liquid discharged through the pipe L6. At the same time, the output of the pump P1 is that the return amount of the sludge concentrate returned through the pipe L2 is the discharge of the sludge separation liquid from the amount of the fermentation liquid taken out from the methane fermentation tank 2 and charged into the gravity sedimentation tank 3. Control so that the amount is reduced. Specifically, by increasing the output of the pump P4 and increasing the discharge amount of the sludge separation liquid, it is necessary to reduce the return amount of the sludge concentrate, so the output of the pump P1 is reduced ( Step S4). Thereby, the discharge rate of the fermented liquid thrown into the gravity sedimentation tank 3 can be increased as much as possible, and processing efficiency can be improved.

  And since it can prevent that sludge separation liquid with a high sludge density | concentration will be discharged | emitted from piping L6 by such operation, the sludge density | concentration of the sludge concentrate returned relatively via piping L2 is compared. It is possible to maintain the amount of microorganisms necessary for methane fermentation at all times by returning microorganisms in the sludge into the methane fermentation tank 2.

  In the conventional method, the return amount from the gravity sedimentation tank 3 to the methane fermentation tank 2 and the discharge amount outside the system through the pipe L6 are made constant. As described above, since the sludge sedimentation rate in the gravity sedimentation means tends to become slower as the sludge concentration increases, the sludge concentrate with a sufficiently concentrated sludge concentration is returned to the methane fermentation tank. To operate so that the sludge separation liquid with sufficiently reduced sludge concentration can be discharged, it is necessary to increase the tank volume by taking into account the load fluctuation of organic waste and increasing the tank volume. There was a problem that became complicated.

  On the other hand, according to the present invention, the pumps P1 and P4 are driven so that the measurement value of the second sludge concentration meter 20 is smaller than the measurement value of the first sludge concentration meter 10 as described above. By controlling, even if the load of the organic waste in the methane fermentation tank 2 fluctuates with the tank volume of the gravity sedimentation tank 3 being relatively small, the sludge concentration of the sludge separation liquid discharged from the pipe L6 is low. While being able to maintain in a state, the sludge density | concentration of the sludge concentrated semen liquid returned to the methane fermentation tank 2 can be maintained in a high state. Thereby, organic waste can be methane-fermented efficiently and at a high decomposition rate.

  In this embodiment, the sludge concentrate is returned from the gravity settling tank 3 to the pretreatment tank 1, and the sludge concentrate is indirectly returned to the methane fermentation tank 2, but the pipe L2 is connected to the methane fermentation tank. 2 may be connected directly to the methane fermentation tank 2. However, when the sludge concentrate is returned to the pretreatment tank 1, the solubilization process is performed and the methane fermentation process is easily performed, so that the treatment efficiency in the methane fermentation tank 2 is improved and higher decomposition efficiency is obtained. This is preferable.

  Moreover, although the 2nd sludge concentration meter 20 was installed above the piping L6 in the gravity sedimentation tank 3, it installs in the piping L6, and the sludge density | concentration of the liquid (sludge separation liquid) which passes the piping L6 is directly set. You may measure.

  Next, 2nd Embodiment of the methane fermentation apparatus of this invention is described using FIG. In addition, the same code | symbol is attached | subjected to the location substantially the same as 1st Embodiment, and the description is abbreviate | omitted.

  In this embodiment, the second sludge densitometer 21 is different from the first embodiment in that the second sludge concentration meter 21 is arranged in the gravity settling tank 3 and below the connection position of the pipe L6 of the gravity settling tank 3. To do.

  That is, in this embodiment, the second sludge concentration meter 21 measures the sludge concentration of the sludge high concentration liquid (sludge concentrate) on the lower layer side of the sludge sedimentation liquid. The second sludge concentration meter 21 is preferably disposed at the bottom of the gravity sedimentation tank 3, and more preferably disposed in the vicinity of the connection portion with the pipe L2.

  In this embodiment, when the measurement results of the first sludge densitometer 10 and the second sludge densitometer 21 are respectively input to the control device 101, the control device 101 is more than the measured value of the first sludge densitometer 10. The output signal is transmitted to the pumps P1 and P4 so that the measured value of the second sludge concentration meter 20 becomes larger, and the return amount of the sludge concentrate and the discharge amount of the sludge separation liquid are controlled.

  That is, as shown in FIG. 4, when the measurement results of the first sludge concentration meter 10 and the second sludge concentration meter 21 are input (step S11), the measured value C1 of the first sludge concentration meter 10 and the second Comparison with the measured value C2 ′ of the sludge concentration meter 21 is performed (step S12).

  When the measurement value C2 ′ of the second sludge concentration meter 21 is larger than the measurement value C1 of the first sludge concentration meter 10, it means that the sludge concentration of the sludge concentrate returned through the pipe L2 is high. The output of the pump P1 is increased to increase the amount of sludge concentrate returned through the pipe L2. At the same time, the output of the pump P4 is that the amount of sludge separation liquid discharged through the pipe L6 is returned from the amount of fermentation liquid taken out from the methane fermentation tank 2 and introduced into the gravity settling tank 3 through the pipe L2. Control to reduce the amount of concentrate. Specifically, by increasing the output of the pump P1 and increasing the return amount of the sludge concentrate, it is necessary to reduce the discharge amount of the sludge separation liquid, so the output of the pump P4 is decreased ( Step S13). As a result, the sludge can be efficiently returned to the methane fermentation tank 2 to ensure the amount of microorganisms necessary for fermentation and the residence time.

  On the other hand, when the measured value C2 ′ of the second sludge concentration meter 21 is smaller than the measured value C1 of the first sludge concentration meter 10, it means that the sludge concentration of the sludge concentrate returned through the pipe L2 is low. Therefore, the output of the pump P1 is reduced and the amount of the sludge concentrate returned through the pipe L2 is reduced. At the same time, the output of the pump P4 is that the amount of sludge separation liquid discharged through the pipe L6 is returned from the amount of fermentation liquid taken out from the methane fermentation tank 2 and introduced into the gravity settling tank 3 through the pipe L2. Control to reduce the amount of concentrate. Specifically, by reducing the output of the pump P1 and reducing the return amount of the sludge concentrate, the discharge amount of the sludge separation liquid needs to be increased conversely, so the output of the pump P4 is increased ( Step S14). As a result, it is possible to prevent a liquid having a low sludge concentration from being returned to the methane fermentation tank 2 and a decrease in the microorganism concentration in the methane fermentation tank 2.

  And since sludge is efficiently returned to the methane fermentation tank 2 by such operation, the sludge density | concentration of the sludge separation liquid discharged | emitted from the piping L6 will be maintained in a comparatively low state from now on, The waste water treatment can be facilitated.

  According to this embodiment, since the return amount of the concentrated sludge is controlled while measuring the sludge concentration of the sludge concentrate, the desired sludge concentration, preferably the sludge concentration of the fermentation liquor in the methane fermentation tank 2 is more reliably determined. The sludge concentrate concentrated to 1.5 to 3 times, more preferably 2 to 3 times, can be directly or indirectly returned to the methane fermentation tank 2.

  In this embodiment, the second sludge concentration meter 21 is disposed at the bottom of the gravity sedimentation tank 3, but is installed in the pipe L1 to directly determine the sludge concentration of the liquid (sludge concentrate) that passes through the pipe L1. You may measure.

  Moreover, operation which takes out fermentation liquid from the methane fermenter 2 and throws it into the gravity sedimentation tank 3 may be performed continuously, and may be performed intermittently for every predetermined time. In the case where the fermentation liquid is intermittently charged into the gravity sedimentation tank 3, the total amount of the sludge concentrate return and the sludge separation liquid discharged is charged from the methane fermentation tank 2 to the gravity sedimentation tank 3. When the amount of the fermented liquid is reached, the driving of the pumps P1 and P4 may be stopped and the fermented liquid may be charged again from the methane fermenter 2 to the gravity settling tank 3.

  Moreover, in the methane fermentation tank 2 and the gravity sedimentation tank 3, a level meter for measuring the liquid level in the tank is installed, and the pumps P2 and P3 are set so that the liquid level in each tank is within a predetermined range. The drive may be controlled. For example, when the liquid level in the methane fermentation tank 2 exceeds a predetermined value, the driving of the pump P2 is stopped or reduced, and the driving of the pump P3 is increased. Further, when the liquid level in the methane fermentation tank 2 falls below a predetermined value, the driving of the pump P3 is stopped or reduced, and the driving of the pump P2 is increased. When the liquid level in the gravity sedimentation tank 3 exceeds a predetermined value, the driving of the pump P3 is stopped or reduced. Further, when the liquid level in the gravity settling tank 3 falls below a predetermined value, the drive of the pump P3 is increased.

Example 1
Methane fermentation was performed using the methane fermentation apparatus shown in FIG. As the methane fermentation tank 2, a tank having a volume of 5 L was used. Moreover, the gravity precipitation tank 3 used the tank of the volume 0.5L. Further, as the sludge concentration meters 10 and 20, a vibration viscometer “VM-10A” (trade name, manufactured by Seconic) was used. Moreover, as organic waste, solid sludge concentration of about 30,000 mg / L, non-volatile organic matter (VS) concentration of about 25,000 mg / L, mixed sludge in the sewage treatment plant (primary sludge TS concentration: surplus sludge TS Concentration = 6: 4) was used.
The TS concentration (evaporation residue) was measured according to the sewage test method-2.2.9. That is, the amount of solid matter remaining after evaporation of the sample solution at 110 ° C. was divided by the sample solution volume. Further, the VS concentration was determined from the TS concentration (the value obtained by dividing the fermentation liquid (mg / l) by evaporating to dryness at 110 ° C. and dividing the mass of the remaining solid material by the sample liquid volume). It was determined by subtracting the ash concentration obtained by dividing the mass of the remaining solid heated at ± 25 ° C. by the sample volume.
From the preconditioning tank 1 to the methane fermentation tank 2, slurry is charged into four parts a day via the pump P 2, and methane fermentation is performed with a load of 10 days (mixed sludge amount to be charged a day 500 mL). It was. Moreover, the fermented liquor was discharged | emitted from the methane fermentation tank 2 to the gravity precipitation tank 3 by the 4 divisions per day via the pump P3. The flow of operation | movement extracted the fermentation liquid from the methane fermenter 2, and then supplied the slurry.
During the methane fermentation, the driving of the pumps P1 and P4 is controlled by the flowchart shown in FIG. 2 so that the measured value by the first sludge concentration meter 10 becomes larger than the measured value by the second sludge concentration meter 20. The amount of liquid returned to the pretreatment tank 1 through the pipe L2 and the amount of liquid discharged through the pipe L6 were controlled. The amount of liquid returned to the pretreatment tank 1 through the pipe L2 was an amount obtained by subtracting the amount of liquid discharged through the pipe L6 from the amount of fermentation liquid charged into the gravity precipitation tank 3.
When the VS concentration of the fermentation broth after 30 days had elapsed after the residence time of 10 days was measured, it was 10,500 mg / L and the VS decomposition rate was 58.0%.

(Example 2)
Using the methane fermentation apparatus shown in FIG. 3, during the methane fermentation, the pumps P <b> 1 and P <b> 4 are driven so that the measured value by the first sludge concentration meter 10 becomes smaller than the measured value by the second sludge concentration meter 21. Control was performed according to the flowchart shown in FIG. 4, and methane was used in the same manner as in Example 1 except that the amount of liquid returned to the pretreatment tank 1 through the pipe L2 and the amount of liquid discharged through the pipe L6 were controlled. Fermentation was performed. The amount of liquid discharged through the pipe L6 was an amount obtained by subtracting the amount of liquid returned to the pretreatment tank 1 through the pipe L2 from the amount of fermentation liquid charged into the gravity settling tank 3.
When the VS concentration of the fermentation broth after 30 days had elapsed after the residence time of 10 days was measured, it was 10,100 mg / L and the VS decomposition rate was 59.6%.

(Comparative Example 1)
In Example 1, methane fermentation was performed in the same manner as in Example 1 except that methane fermentation was performed by discharging the entire amount of the liquid in the gravity sedimentation tank 3 through the pipe L6.
When the VS concentration of the fermented liquid after 30 days had elapsed after the residence time in the methane fermenter 2 of the organic waste charged into the methane fermenter 2 became 10 days (500 mL added daily), The VS decomposition rate was 53.6%.

(Comparative Example 2)
In Example 1, the amount of liquid returned from the gravity settling tank 3 through the pipe L2 to the pretreatment tank 1 was 50 mL, and the amount of liquid discharged through the pipe L6 was 500 mL. Methane fermentation was performed.
It was 11,300 mg / L when the VS density | concentration of the fermented liquid after 30 days passed since the residence time in the methane fermenter 2 of the organic waste thrown into the methane fermenter 2 became 10 days. The VS decomposition rate was 54.8%.

1: Pretreatment tank 2: Methane fermentation tank 3: Gravity sedimentation tank 10: First sludge concentration meter 20, 21: Second sludge concentration meter 100, 101: Controllers L1-L6: Piping P1-P4: Pump

Claims (9)

The organic waste is subjected to methane fermentation treatment in a methane fermentation tank, and a predetermined amount of the fermentation liquid is taken out from the methane fermentation tank to form a sludge sedimentation liquid in which the sludge concentration increases downward by gravity sedimentation means. The sludge high-concentration liquid on the lower layer side is directly or indirectly returned to the methane fermentation tank through a return line, and the sludge low-concentration liquid on the upper layer side of the sludge sedimentation liquid is discharged out of the system through the discharge line, In the methane fermentation method for controlling the total amount of liquid to be returned through the return line and the amount of liquid to be discharged through the discharge line to be substantially equal to the amount of the fermentation liquid to be taken out from the methane fermentation tank,
Measuring the sludge concentration of the fermentation broth in the methane fermentation tank by the first sludge concentration measuring means;
Measuring a sludge concentration of a predetermined portion of the sludge sedimentation liquid formed by the gravity sedimentation means by a second sludge concentration measurement means;
Comparing the sludge concentration measured by the first sludge concentration measuring means with the sludge concentration measured by the second sludge concentration measuring means, the sludge concentration of the liquid discharged through the discharge line is the methane fermentation The sludge concentration of the fermentation liquor in the tank is lower than that, or the sludge concentration of the liquid returned to the methane fermentation tank through the return line is higher than the sludge concentration of the fermentation liquid in the methane fermentation tank. Controlling the amount of liquid discharged through the discharge line and the amount of liquid returned to the methane fermentation tank through the return line.   The second sludge concentration measuring means is disposed in the gravity settling means and above the discharge line and / or in the discharge line, and from the sludge concentration measured by the first sludge concentration measuring means. However, if the sludge concentration measured by the second sludge concentration measuring means is higher, the amount of liquid discharged through the discharge line is reduced, and the sludge concentration measured by the first sludge concentration measuring means is reduced. However, if the sludge concentration measured by the second sludge concentration measuring means is lower, the amount of liquid discharged through the discharge line is increased, and the amount of liquid returned to the methane fermentation tank through the return line is: It controls so that it may become the quantity which reduced the liquid quantity discharged | emitted through the said discharge line from the quantity of the fermented liquid taken out from the said methane fermenter and thrown into a gravity sedimentation means. Tan fermentation process.   The second sludge concentration measuring means is disposed in the gravity settling means and below the discharge line and / or in the return line, and from the sludge concentration measured by the first sludge concentration measuring means. However, if the sludge concentration measured by the second sludge concentration measuring means is higher, the amount of liquid returned to the methane fermenter through the return line is increased and measured by the first sludge concentration measuring means. If the sludge concentration measured by the second sludge concentration measuring means is lower than the measured sludge concentration, the amount of liquid returned to the methane fermentation tank is reduced through the return line and discharged through the discharge line. The amount of liquid to be obtained is the amount obtained by subtracting the amount of liquid returned to the methane fermenter through the return line from the amount of fermented liquid taken out from the methane fermenter and introduced into the gravity sedimentation means. Controlled to so that methane fermentation method according to claim 1.   The slurry adjustment tank which pre-processes organic waste in the front | former stage of the said methane fermentation tank is arrange | positioned, The said return line is connected to the said slurry adjustment tank and / or the said methane fermentation tank, The Claims 1-3 The methane fermentation method according to any one of the above. A methane fermentation tank for subjecting organic waste to methane fermentation, and gravity sedimentation means for gravity-settling the sludge in the fermentation liquor taken out of the methane fermentation tank to form a sludge sedimentation liquid whose sludge concentration increases downward. A return line for returning the sludge high concentration liquid on the lower layer side of the sludge sedimentation liquid directly or indirectly to the methane fermentation tank, and a discharge line for discharging the sludge low concentration liquid on the upper layer side of the sludge sedimentation liquid to the outside of the system The total amount of the liquid returned through the return line and the liquid discharged through the discharge line is controlled so as to be substantially equal to the amount of the fermentation liquid taken out from the methane fermentation tank. In methane fermentation equipment,
First sludge concentration measuring means for measuring the sludge concentration of the fermentation broth in the methane fermenter;
A second sludge concentration measuring means for measuring a sludge concentration of a predetermined portion of the sludge sedimentation liquid formed by the gravity settling means;
The sludge of the liquid returned to the methane fermentation tank through the return line by comparing the sludge concentration measured by the first sludge concentration measuring means with the sludge concentration measured by the second sludge concentration measuring means. Through the discharge line, the concentration is higher than the sludge concentration of the fermentation liquid in the methane fermentation tank, and the sludge concentration of the liquid discharged through the discharge line is lower than the sludge concentration of the fermentation liquid in the methane fermentation tank. A methane fermentation apparatus, comprising: a controller for controlling the amount of liquid discharged and the amount of liquid returned to the methane fermentation tank through the return line.   The second sludge concentration measuring means is disposed in the gravity settling means and above the discharge line and / or in the discharge line, and the control device is configured to provide the first sludge concentration measuring means. When the sludge concentration measured by the second sludge concentration measuring means is higher than the sludge concentration measured by the above, the amount of liquid discharged through the discharge line is reduced, and the first sludge concentration measuring means When the sludge concentration measured by the second sludge concentration measuring means is lower than the sludge concentration measured by the above, the amount of liquid discharged through the discharge line is increased, and the methane fermenter is passed through the return line. The amount of liquid returned to the tank is controlled so that the amount of fermentation liquid taken out from the methane fermentation tank and introduced into the gravity sedimentation means is subtracted from the amount discharged through the discharge line. To methane fermentation apparatus according to claim 5.   The second sludge concentration measuring means is disposed in the gravity settling means and below the discharge line and / or in the return line, and the control device is configured to provide the first sludge concentration measuring means. When the sludge concentration measured by the second sludge concentration measuring means is higher than the sludge concentration measured by the above, the amount of liquid returned to the methane fermentation tank through the return line is increased, and the first sludge concentration is measured. If the sludge concentration measured by the second sludge concentration measuring means is lower than the sludge concentration measured by the sludge concentration measuring means, the amount of liquid returned to the methane fermentation tank through the return line is reduced. The amount of liquid discharged through the discharge line is taken into the methane fermenter through the return line from the amount of fermentation liquid taken out from the methane fermenter and introduced into the gravity sedimentation means. It is controlled to be an amount obtained by subtracting the amount of liquid feed, methane fermentation apparatus according to claim 5.   The slurry adjustment tank which pre-processes organic waste in the front | former stage of the said methane fermentation tank is arrange | positioned, The said return line is connected to the said slurry adjustment tank and / or the said methane fermentation tank. The methane fermentation apparatus of any one of -7.   The said sludge density | concentration measuring means is 1 or more types chosen from a viscometer, a near-infrared scattered light type | formula densitometer, an ultrasonic sludge interface meter, and a microwave densitometer, The any one of Claims 5-8. Methane fermentation equipment.