JP2006255571A - Methane fermentation system and methane fermentation process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform methane fermentation and to facilitate sterilization treatment etc., of a separated liquid. <P>SOLUTION: In addition to the conventional system of returning a part of separated sludge mingled with water so as to be mixed with organic waste on one side where the sludge is subjected to solid-liquid separation by a solid-liquid separation means 3, and in addition to the conventional system of returning a part of the separated liquid mingled with a solid so as to be mixed with the organic waste on the other side where the liquid is subjected to the solid-liquid separation, i.e. returning only a part of the separated sludge, the balance of the separated sludge and the separated liquid is discharged outside the system, thereby roughly discharging the undissolved solid, propagated methane bacteria, and introduced water to be the increased weight components within the system, controlling the inside of a methane fermenter 1 to specified conditions of a desired TS concentration and reducing the emission of the separated liquid to the outside of the system. Even more, further a part of the separated liquid is returned so as to be mixed with the sludge from the methane fermenter 1 to increase the TS concentration within the methane fermenter 1 to the desired TS concentration in the methane fermenter 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a methane fermentation system and a methane fermentation method.

Conventionally, organic waste is methane-fermented in a methane fermentation tank, the sludge of this methane fermentation tank is solid-liquid separated in a precipitation tank, and a part of the separated sludge separated into solid and liquid is returned to the methane fermentation tank, while being separated. An apparatus that discharges the remaining sludge and the separated liquid-solid separation liquid outside the system is known (for example, see Patent Document 1). In this apparatus, most of the solids in the organic waste are gasified and released by methane fermentation in the methane fermenter, while some of the solids in the organic waste are methane as undecomposed solids (residues). It remains in the fermenter, and part of it remains in the methane fermenter as proliferating methane bacteria (solid matter). Moreover, the water | moisture content in organic waste remains as it is in a methane fermentation tank. Therefore, this undecomposed solid matter, proliferating methane bacteria, and introduced water become an increase in the system.
JP 2002-301495 A

  Here, as described in the above publication, when a sludge from a methane fermentation tank is used as a solid-liquid separator, for example, when a mechanical one is used, water is contained in the separated sludge, and solid content is contained in the separated liquid. Are mixed, and the solids recovery rate varies depending on the concentration of sludge supplied and other conditions. Therefore, in the method of the above publication in which a part of the separated sludge is returned to the methane fermentation tank and the remainder of the separated sludge and the separated liquid are discharged out of the system, the above-described undecomposed solid matter, which is an increase in the system, and growth It is almost impossible to discharge methane bacteria and introduced water out of the system to make the inside of the methane fermentation tank have a desired high TS concentration and it is difficult to perform methane fermentation efficiently.

  In addition, the separation liquid discharged out of the system is subjected to, for example, sterilization processing in the subsequent stage, but the above-described conventional technique has a large amount of separation liquid discharged, and the sterilization processing in the subsequent stage is easy. Not.

  The present invention has been made to solve such problems. The inside of the methane fermenter is set to a constant condition of a desired high TS concentration, and methane fermentation is efficiently performed. It is an object of the present invention to provide a methane fermentation system and a methane fermentation method in which the amount of discharge to the waste water is reduced and the separation liquid in the subsequent stage can be easily sterilized, for example.

  The methane fermentation system according to the present invention includes a methane fermentation tank for methane fermentation of organic waste, a solid-liquid separation means for solid-liquid separation of sludge from the methane fermentation tank, and a separated sludge separated by solid-liquid separation by the solid-liquid separation means. A separation sludge return line that returns a part to be mixed with organic waste, and a part of the separated liquid that has been solid-liquid separated by solid-liquid separation means is returned to be mixed with organic waste. A separate liquid return line, a second separate liquid return line for returning a part of the separated liquid separated by the solid-liquid separation means so as to be mixed with the sludge from the methane fermentation tank, and the solid-liquid separation means A separation sludge discharge line that discharges the remainder of the separated sludge separated into solid and liquid at the outside of the system and a separation liquid discharge line that discharges the remainder of the separated liquid separated by the solid-liquid separation means to the outside of the system. It is characterized by.

  In the methane fermentation method according to the present invention, 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 solid-liquid separation is performed by solid-liquid separation means. A part of the separated 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 a part of the separated liquid separated by the solid-liquid separating means is further returned. Is mixed with sludge from the methane fermentation tank and the remainder of the separated sludge separated by solid-liquid separation by the solid-liquid separation means and the remainder of the separated liquid separated by solid-liquid separation by the solid-liquid separation means are discharged out of the system. It is characterized by.

  According to such a methane fermentation system and methane fermentation method, in addition to the conventional method of returning a part of the separated sludge mixed with water on one side of the solid-liquid separation to be mixed with the organic waste, Return the part of the separated liquid mixed with solids to the organic waste and return another part of the separated liquid to the sludge from the methane fermentation tank. In other words, in addition to the conventional method of returning only a part of the separated sludge after solid-liquid separation, a part of the separated liquid separated by solid-liquid separation is also returned, and the separated sludge and the remaining liquid are discharged out of the system. Therefore, undegraded solid matter, proliferating methane bacteria, and introduced water that are increased in the system can be discharged out of the system, and the inside of the methane fermenter can be set to a constant condition of the desired TS concentration. And the separation liquid out of the system Is it possible to reduce emissions. Moreover, since a part of the separated liquid is returned to be mixed with the sludge from the methane fermentation tank, the TS concentration in the methane fermentation tank can be increased as desired.

  Here, specific examples of the solid-liquid separation means in which water is mixed in the separated sludge after solid-liquid separation and the solid content is mixed in the separated liquid-solid separation liquid include mechanical or precipitation type solid-liquid separation means. .

  As described above, according to the present invention, the inside of the methane fermentation tank can be set to a constant condition with a desired high TS concentration, so that methane fermentation can be performed efficiently and the system of the separated liquid Since it is possible to reduce the discharge amount to the outside, it is possible to facilitate, for example, sterilization of the separated liquid in the subsequent stage.

  Hereinafter, preferred embodiments of a methane fermentation system and a methane fermentation method according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a methane fermentation system according to an embodiment of the present invention, which is employed in, for example, a waste treatment facility.

  As shown in FIG. 1, the methane fermentation system 100 includes a methane fermentation tank 1, a mixing tank 2, and a solid-liquid separation unit 3 connected in this order, and a separated sludge discharge side of the solid-liquid separation unit 3 and a methane fermentation tank. 1 connected to the methane fermentation tank 1 and the separated sludge discharge line L4 branched in the middle of the separated sludge return line L1, the separated liquid discharge side of the solid-liquid separation means 3, and the methane fermentation tank 1. The separated liquid return line L2, the second separated liquid return line L3 connecting the separation liquid discharge side of the solid-liquid separation means 3 and the mixing tank 2, and the separation branched in the middle of these separated liquid return lines L2 and L3. A liquid discharge line L5 is provided, and the introduced organic waste is subjected to a predetermined methane fermentation treatment. And here, water-containing solids (such as household waste) such as food residues are introduced as organic waste as high-concentration organic waste.

  The methane fermentation tank 1 is composed of the organic waste to be introduced, a part of the separated sludge returned via the separated sludge return line L1, and the separated liquid returned via the first separated liquid return line L2. A portion of the mixture is stirred with a stirrer and methane-fermented to produce biogas mainly composed of methane and carbon dioxide. The biogas produced in the methane fermentation tank 1 is used as a fuel for generators and boilers such as gas engines and fuel cells, for example. Further, methane in biogas is used as an automobile fuel or the like by concentrating it by, for example, a gas separation membrane method, a PSA method, or a pressurized water absorption method.

  The mixing tank 2 connected to the methane fermentation tank 1 mixes the sludge from the methane fermentation tank 1 and a further part of the separated liquid returned via the second separated liquid return line L3 by stirring with a stirrer. And uniform properties.

  The solid-liquid separation means 3 connected to the mixing tank 2 is for separating the sludge from the mixing tank 2 into a solid and a liquid, and separates it into a separated sludge and a separated liquid. Examples of the solid-liquid separation means 3 include mechanical solid-liquid separation means such as a screw press dehydrator, a centrifugal dehydrator, a filter press dehydrator, a belt press dehydrator, a multi-disc dehydrator, or a precipitation type ( A solid-liquid separation means (precipitation tank) of a sedimentation separation type) is used.

  A separation sludge return line L1 connecting the separated sludge discharge side of the solid-liquid separation means 3 and the methane fermentation tank 1 returns a part of the separated sludge from the solid-liquid separation means 3 to the methane fermentation tank 1. On the other hand, the first separation sludge return line L2 connecting the separation liquid discharge side of the solid-liquid separation means 3 and the methane fermentation tank 1 returns a part of the separation liquid from the solid-liquid separation means 3 to the methane fermentation tank 1. To do. The second separation sludge return line L3 connecting the separation liquid discharge side of the solid-liquid separation means 3 and the mixing tank 2 returns a further part of the separation liquid from the solid-liquid separation means 3 to the mixing tank 2. .

  The separated sludge discharge line L4 branched from the separated sludge return line L1 discharges the remainder of the separated sludge outside the system, and the separated liquid discharge line branched from the first and second separated liquid return lines L2 and L3. L5 is subjected to a subsequent sterilization treatment to discharge the remainder of the separation liquid out of the system and discharge it to a river or the like.

  Next, the effect | action of the methane fermentation system 100 comprised in this way is demonstrated. The introduced organic waste is a part of the separated sludge returned from the solid-liquid separation means 3 via the separated sludge return line L1 and the first separated liquid return from the solid-liquid separation means 3 in the methane fermentation tank 1. It is mixed with a part of the separated liquid returned via the line L2, and is subjected to methane fermentation in the methane fermentation tank 1 having a desired high TS concentration by returning the separated sludge and the separated liquid.

  By the methane fermentation in the methane fermenter 1, most of the solids in the organic waste are gasified and released as biogas, and are used as they are, and some of them are methane fermentation as undecomposed solids (residues). It remains in the tank 1, and a part further remains in the methane fermenter 1 as proliferating methane bacteria (solid matter). On the other hand, the water in the organic waste remains in the methane fermentation tank 1 (a part of the water is gasified and a very small amount of water is generated by the reaction).

  This undecomposed solid matter, proliferating methane bacteria, and introduced water become an increased amount in the methane fermentation tank 1, and there is no increase or decrease in the liquid level in the methane fermentation tank 1 within the methane fermentation tank 1 under a certain condition of a desired TS concentration. In order to make the TS concentration constant), this increased amount needs to be discharged out of the system, which will be described later.

  The sludge in the methane fermentation tank 1 is mixed with a part of the separated liquid returned from the solid-liquid separation means 3 through the second separated liquid return line L3 in the mixing tank 2, and the sludge in the mixing tank 2 is Solid-liquid separation is performed by the solid-liquid separation means 3 into separated sludge and separated liquid.

  Here, as the solid-liquid separation means 3, as described above, since a mechanical type or a precipitation type is used, moisture is contained in the separated sludge after solid-liquid separation, and solid content is contained in the separated liquid-solid separated liquid. As they are mixed, the solids recovery rate varies depending on the supplied sludge concentration and other conditions. Therefore, in the conventional method in which a part of the separated sludge is returned to the methane fermentation tank and the remainder of the separated sludge and the whole of the separated liquid are discharged out of the system, undecomposed solid matter that increases in the system, growth It is almost impossible to discharge the methane bacteria and the introduced water out of the system to make the inside of the methane fermentation tank have a desired high TS concentration constant condition.

  However, in this embodiment, a part of the separated sludge of the solid-liquid separation means 3 is returned to the methane fermentation tank 1 by the separated sludge return line L1, and a part of the separated liquid is sent by the first separated liquid return line L2. It is returned to the methane fermentation tank 1, and a part of the separated liquid is returned to the mixing tank 2 through the second separated liquid return line L3, while the remaining separated sludge is discharged out of the system through the separated sludge discharge line L4. At the same time, the remainder of the separation liquid is discharged out of the system through the separation liquid discharge line L5.

  As described above, in this embodiment, in addition to the conventional method in which a part of the separated sludge mixed with water and mixed with the organic waste is returned on one side of the solid-liquid separation, the other side subjected to the solid-liquid separation. And a part of the separated liquid mixed with the solid matter is returned to be mixed with the organic waste, and a part of the separated liquid is returned to be mixed with the sludge from the methane fermentation tank 1, that is, the solid liquid In addition to the conventional method in which only a part of the separated sludge is returned, a part of the separated liquid that has been solid-liquid separated is also returned, and the separated sludge and the remaining liquid are discharged outside the system. The amount of undegraded solids, proliferating methane bacteria, and introduced water that are to be increased in the system can be discharged out of the system, and the inside of the methane fermenter 1 can be set to a constant condition of a desired TS concentration. At the same time, it is possible to reduce the amount of separation liquid discharged outside the system. It is a function. Moreover, since a part of the separated liquid is returned so as to be mixed with the sludge from the methane fermentation tank 1, the TS concentration in the methane fermentation tank 1 can be increased as desired. As a result, it is possible to efficiently perform methane fermentation and facilitate sterilization of the separated liquid in the subsequent stage. In this embodiment, it is not necessary to add seed sludge and add water.

  FIG. 2 is a diagram showing an example of the material balance of the methane fermentation system 100 of FIG. 1, and is when the TS recovery rate of the separated sludge of the solid-liquid separation means 3 is 70%. Here, 25 kg of food waste (moisture 18.75 kg, TS (solid matter) 6.25 kg; TS concentration 25%) is introduced as organic waste. This organic waste is methane-fermented in a methane fermenter 1 having a TS concentration of 4%, and 4.4 kg of biogas is released. On the other hand, 1.85 kg of undecomposed solid matter and proliferating methane bacteria and water of 18.75 kg The mixture (TS concentration 8.98%) remains as an increase in the system.

  Here, in order to maintain the balance in the system by setting the TS concentration in the methane fermenter 1 to 4%, as shown in FIG. 2, 1.54 kg (moisture 1.39 kg, TS 0.15 kg) of the separated sludge is methane. While returning to the fermenter 1, a part of 27.86 kg of the separated liquid may be returned to the methane fermenter 1, and a further part of 164 kg of the separated liquid may be returned to the mixing tank 2. As a result, the TS concentration in the methane fermentation tank 1 is maintained at 4%, and the remaining 12.5 kg of separated sludge (moisture 11.2 kg, TS 1.25 kg) and the remaining liquid 7.6 kg (moisture 7.54 kg, TS0.02 kg) is discharged out of the system, and undecomposed solid matter, proliferating methane bacteria, and introduced water that are increased in the system are generally discharged out of the system.

  As mentioned above, although this invention was concretely demonstrated based on the embodiment, this invention is not limited to the said embodiment. For example, in the above embodiment, a part of the separated sludge is returned to the methane fermentation tank 1 by the separated sludge return line L1, and a part of the separated liquid is returned to the methane fermentation tank 1 by the first separated liquid return line L2. The organic waste may be returned to the line for transferring the organic waste to the methane fermentation tank 1, and when an acid generation tank is provided, for example, where the organic waste flows into the preceding stage of the methane fermentation tank 1, it is returned to the acid generation tank In short, it suffices if it can be returned to be mixed with organic waste.

  Moreover, in the said embodiment, although a part of separation liquid is returned to the mixing tank 2 by the 2nd separated liquid return line L3, the line which transfers the sludge of the methane fermentation tank 1 to the mixing tank 2 You may return it to Further, the mixing tank 2 may be omitted, and in this case, the sludge from the methane fermentation tank 1 may be returned to the line for transferring to the solid-liquid separation means 3. I just need to be able to return it.

  Further, in the above-described embodiment, water solids such as food residues are targeted as high-concentration organic wastes as being particularly suitable, but high-concentration liquid organic wastes may be used. Is applicable to all organic waste.

It is a schematic structure figure showing a methane fermentation system concerning an embodiment of the present invention. It is a figure which shows an example of the material balance of the methane fermentation system of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Methane fermentation tank, 2 ... Mixing tank, 3 ... Solid-liquid separation means, 100 ... Methane fermentation system, L1 ... Separation sludge return line, L2 ... First separation liquid return line, L3 ... Second separation liquid return line , L4 ... separation sludge discharge line, L5 ... separation liquid discharge line.

Claims (3)

A methane fermentation tank for methane fermentation of organic waste,
Solid-liquid separation means for solid-liquid separation of the sludge from the methane fermentation tank;
A separated sludge return line for returning a part of the separated sludge separated by solid-liquid separation by the solid-liquid separation means to be mixed with the organic waste,
A first separated liquid return line for returning a part of the separated liquid separated by the solid-liquid separation means so as to be mixed with the organic waste;
A second separated liquid return line for returning a further part of the separated liquid separated by the solid-liquid separation means so as to be mixed with the sludge from the methane fermentation tank;
A separation sludge discharge line for discharging the remaining sludge separated by the solid-liquid separation means out of the system;
A methane fermentation system comprising: a separation liquid discharge line for discharging the remainder of the separation liquid solid-liquid separated by the solid-liquid separation means to the outside of the system.   The methane fermentation system according to claim 1, wherein the solid-liquid separation means is a mechanical type or a precipitation type. Organic waste is methane fermented in a methane fermenter,
The sludge from this methane fermentation tank is solid-liquid separated by solid-liquid separation means,
A part of the separated sludge separated by solid-liquid separation by the solid-liquid separation means and a part of the separated liquid separated by solid-liquid separation means are returned so as to be mixed with the organic waste, and the solid-liquid Return a further part of the separated liquid separated by the separation means to be mixed with the sludge from the methane fermentation tank,
A methane fermentation method characterized by discharging 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 to the outside of the system.

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