JPS61103599A - Method for recovering and returning methane fermentation accelerator - Google Patents

Abstract

PURPOSE:To maintain high fermentation performance by recovering a powdery fermentation accelerator from a fermenting liq. discharged from a methane fermenter, and returning the accelerator into the methane fermenter to maintain the concn. of the fermentation accelerator in the fermenting liq. in the methane fermenter. CONSTITUTION:A powdery fermentation accelerator having a dissociated radical on the surface is added into a methane fermenting liq. in a methane fermenter 5. The methane fermenting liq. after the completion of fermentation is introduced into a biological aeration vessel 6, and the fermenting liq. after biological aeration is introduced into a settling vessel 7. The fermentation accelerator, settled and separated in the settling vessel 7, is taken out, and returned into the fermenting liq. in the methane fermenter 5. Namely, the fermentation accelerator, added into the fermenting liq., can be efficiently recovered and returned, the concn. of the fermentation accelerator in the fermenting liq. is maintained, and high fermentation capacity can be kept.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for recovering a methane fermentation promoter from a fermentation liquid discharged from a methane fermentation tank and returning it to the methane fermentation tank.

Structure of conventional examples and their problems Methane fermentation is carried out under anaerobic conditions by the action of microorganisms.
This is a reaction that produces methane from organic matter. The container in which methane fermentation takes place is called a methane fermenter. This tank is a closed tank that maintains anaerobic conditions, and microorganisms live in the fermentation liquid that contains a large amount of sludge. Fermentation raw materials (organic substances) supplied from outside the tank mix with the fermentation liquid and undergo a reaction to generate methane.

Furthermore, although the volume of the fermentation liquor increases due to the supply of fermentation raw materials, the volume is discharged to the outside of the tank by that amount. The discharged fermentation liquid (this is called waste liquid) contains a large amount of BOD components and must be treated for environmental reasons. For this purpose, a biological aeration tank, which is an aerobic biological treatment device, is often connected after the fermenter. The general flow is shown in Figure 1. In the figure, 1 is a methane fermentation tank, 2 is a settling tank, and 3 is a biological aeration tank, which has an aeration agitation function. 4 is the final settling tank. Of these, sedimentation tank 2 is used for pre-treatment of aerobic biological treatment, and final sedimentation tank 4 is used for post-treatment of aerobic biological treatment, so sedimentation tank 2, biological treatment tank 3.
The final settling tank 4 is generally considered to be an aerobic biological treatment device. Furthermore, sludge is discharged from the settling tank 2 and the final settling tank 4, but these are normally disposed of by dewatering, incineration, or other methods. Also, the treated water is usually discharged into rivers, the sea, sewers, etc.

Now, for the purpose of improving the performance of the methane fermentation tank 1, sludge and water may be returned to the methane fermentation tank 1 from the aerobic biological treatment device. An example of this is the return of sludge discharged from the settling tank 2 to the methane fermentation tank 1. Microorganisms in the fermentation liquid tend to precipitate together with sludge particles, and the purpose is to collect the microorganisms along with the sludge and return them to the methane fermentation tank 1 to increase the concentration of microorganisms in the methane fermentation tank 1 and promote fermentation. .

Another example is one in which treated water flowing out of the final settling tank 4 is returned to the methane fermentation tank 1. One purpose is to dilute the raw material, and the other is to adjust the pH of the fermented liquid in the methane fermentation tank 1 by returning ammonium ions contained in the treated water. Alternatively, it supplies a source of nitrogen, which is one of the nutrients for microorganisms. .

On the other hand, the addition of a powder having a negative dissociative group on the surface into the fermentation solution has the effect of promoting fermentation, but the conventional return method described above collects and returns the powdered fermentation accelerator. It is inappropriate to do so. This is because if you try to collect the fermentation accelerator in the sedimentation tank 2, the sludge is also collected and returned. The sludge concentration increases, the fluidity of the fermentation liquid disappears, and contact between microorganisms and fermentation raw materials becomes difficult.
This is because if contact becomes difficult, fermentation will be delayed. Therefore, even if the fermentation accelerator can be recovered in the sedimentation tank 2, a large amount cannot be returned. Furthermore, the method of returning treated water cannot be a method of returning powdered fermentation accelerator.

Purpose of the Invention The present invention provides a method for recovering a powdered fermentation accelerator from the fermentation liquid discharged from a methane fermentation tank, returning it to the methane fermentation tank,
The present invention provides a method for maintaining high fermentation performance by maintaining the concentration of a fermentation promoter in a fermentation liquid in a methane fermentation tank.

It is known that fermentation can be promoted by adding powders such as clay minerals such as monomorionate kaolinite, silica gel, and cation exchange resins, which have negative charges on the surface, to the fermentation liquid.

In the present invention, this full-throttling accelerator is added to the fermentation liquor in the methane fermentation tank, and the concentration is maintained to maintain high fermentation ability.

The cause of the decrease in the concentration of the fermentation accelerator in the fermentation liquor is the outflow accompanying the discharge of the fermentation liquor, which has increased due to the supply of raw materials, out of the methane fermentation tank as waste liquor. In the present invention, the following method is used to collect the fermentation accelerator that has flowed out, return it to the methane fermentation tank, and maintain the concentration.

First, without separating the sludge and fermentation accelerator in the waste liquid discharged from the methane fermentation tank, the waste liquid is led to a biological aeration tank, and the waste liquid with reduced sludge after biological aeration treatment is led to the next settling tank. The fermentation accelerator that is sedimented and separated is extracted and returned to the fermentation liquid in the methane fermentation tank.

In addition, what is referred to here as a biological aeration tank has the function of sending air into the tank to stir the liquid in the tank, such as the activated sludge method or fixed bed aeration method, as well as supplying oxygen. Organic matter is oxidized and decomposed by the action of aerobic microorganisms to eliminate it.

Description of examples An embodiment of the present invention will be described with reference to the flowchart of FIG.

In the figure, 5 is a methane fermentation tank, and 6 is a biological aeration tank, which has an aeration agitation function. 7 is a sedimentation tank, 8 is a pump connected to the sedimentation tank 7, 9 is a return pipe connecting the sedimentation tank 7 and the methane fermentation tank 6, and the pump 8 is disposed in the middle.

The raw material is supplied to the methane fermenter 1. In addition, a powdered fermentation accelerator having a negative dissociative group on the surface is added to the methane fermentation liquid. Now, since the amount of fermentation liquid in the methane fermentation tank 1 increases due to the raw material, the fermentation liquid is discharged from the methane fermentation tank 1 as waste liquid by that amount. This waste liquid is led to a biological aeration tank 6, where it is subjected to biological oxidation, and then led to a settling tank 7, where solid matter is sedimented and separated, and the supernatant liquid is discharged. The solid matter is extracted by a pump 8 and returned to the methane fermentation tank 1. The fermentation accelerator mentioned above is Montmorionato, which has a negative charge on the surface.
Clay minerals such as kaolinite, silica gel.

Powder such as cation exchange resin.

The waste liquid discharged from the methane fermentation tank 5 is a liquid substance containing sludge, a powdered fermentation accelerator, and non-fermentable substances contaminated in the raw material. This non-fermented material may cause later mechanical failures such as blockage of pipes, and a screen may be installed between the methane fermentation tank 6 and the biological aeration tank 6 in order to remove this non-fermented material. Further, in the embodiment, it is considered that the difference in height of the water surface is used to cause the water to naturally overflow, but if the difference in height of the water surface cannot be taken care of, a pump bit and a pump may be installed to pump the liquid.

Next, the waste liquid flows into the biological aeration tank 6 and is subjected to biological oxidation, which has the following two main purposes. First, biological oxidation reduces sludge. The sludge in the methane fermentation waste liquid mainly consists of organic matter such as microorganisms and dead microorganisms, and decomposition and digestion have already progressed in the methane fermentation tank ε, but in the methane fermentation tank 5 it is anaerobic. Because only reactions proceed, organic matter that is difficult to decompose and digest anaerobically remains. This is decomposed aerobically to reduce the amount of sludge.

Next, the redox potential of the waste liquid immediately after being discharged from the methane fermentation tank 1 is low at -200 to -400 mV, and is in a strongly anaerobic state, but by aerating it with air and making it an aerobic state. The sedimentation properties of the fermentation accelerator are improved, and subsequent recovery in the sedimentation tank 7 becomes easier. Further, since aerobic microorganisms grow naturally in the aeration tank 6, there is no need to perform seeding from outside.

In addition, the biological aeration tank 6 must be such that the fermentation accelerator does not settle and accumulate therein, but for this purpose, the aeration tank of the activated sludge method that is commonly used can be used as is, and a normal aeration tank can be used. It can be used.

In the settling tank 7, the solid content in the waste liquid treated in the biological aeration tank 6 settles, and the organic matter in this solid content settles in the biological aeration tank 6.
As the sedimentation properties have been improved,
The fermentation accelerator is recovered efficiently and concentrated to a small volume.

Next, the pump 8 removes the solid matter precipitated in the settling tank γ.
1 and returned to the methane fermentation tank 5. Therefore, the concentration of the fermentation promoter in the fermentation liquid in the methane fermentation tank ε is maintained. Furthermore, since the sludge with a reduced amount is returned, the sludge in the methane fermentation tank 5 does not increase in volume significantly, and contact between the fermentation raw material and microorganisms in the fermentation liquid is not inhibited. Furthermore, since the volume to be returned is small, an increase in the amount of fermented liquid due to return does not lead to further discharge of waste liquid.

Effects of the Invention The present invention makes it possible to efficiently recover and return the fermentation accelerator added to the fermentation liquid. Therefore, it is possible to maintain the concentration of the fermentation promoter in the fermentation liquid and maintain high fermentation ability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the flow of a conventional methane fermentation apparatus, and FIG. 2 is a block diagram showing the flow of an embodiment of the present invention. 5... Methane fermentation tank, 6... Biological aeration tank, 7... Sedimentation tank, 8... Pump, 9
...Return piping.

Claims (1)

[Claims] A powdered fermentation accelerator with a negative dissociative group on the surface is added to the methane fermentation liquid, the methane fermentation liquid after fermentation is led to a biological aeration tank, and the fermented liquid after biological aeration is led to a settling tank, where precipitation A methane fermentation accelerator recovery and return method in which the fermentation accelerator that settles and separates in the tank is extracted and returned to the fermentation liquid in the methane fermentation tank.