JP2005238200A - Method for treating organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently immobilizing microorganisms and improve gasification efficiency in an anaerobic digestion process intended for an organic waste or wastewater. <P>SOLUTION: In the method for directly subjecting a material to be treated which is composed of the organic waste to an anaerobic treatment in the presence of a digestive oganism immobilizing carrier, the immobilizing carrier composed of foamed polyurethane is used as the carrier. Also, the obtained gaseous phase is collected and is used as a fuel and the obtained solid phase is recovered and is used as an organic fertilizer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention enables organic waste and waste water discharged from households, restaurants, factories, sewage treatment plants, etc. to be anaerobically fermented directly using an anaerobic digestion tank, thereby quickly accelerating the organic matter in the waste. It relates to a method of decomposing and digesting.

  Anaerobic digestion is gaining attention as a method for treating organic waste such as garbage. However, the conventional anaerobic digestion method has a problem that the organic matter decomposition rate and the digestion gas generation rate are not sufficiently high, and therefore it is necessary to prepare a digester large to some extent. If the decomposition rate is increased, the digester can be made more compact, and the economic efficiency and energy balance can be improved.

In order to solve these problems, an excess portion of sludge generated by the activated sludge method is subjected to high-temperature anaerobic digestion, and the treatment liquid is circulated through a solid-liquid separation membrane, and water is extracted through the separation membrane. An organic sludge treatment method characterized by this is proposed (Patent Document 1), but this method is a conventional high-temperature anaerobic digestion method, and there is a problem that digestion efficiency does not sufficiently increase. .

In addition, a method of heat-treating a mixed liquid mainly composed of digested sludge from the anaerobic digestion reactor in the process of drawing and circulating / returning it has been proposed (Patent Document 2). In this method, digested sludge is treated at a high temperature. It is intended to destroy the structure of digested sludge physicochemically, and is not a method for improving the performance of the anaerobic digester itself, but the problem that digestion efficiency does not sufficiently increase remains.

An immobilization method has been studied in which an anaerobic digestion tank is provided with a carrier serving as a place where microorganisms reside, so that microorganisms involved in decomposition can be maintained in the tank at a high concentration and decomposition and gasification efficiency can be improved.
A method called UASB method that uses self-aggregated granules of microorganisms to increase the concentration of microorganisms in the digestion tank has been studied and put into practical use (Patent Document 3). It is used for the treatment of organic wastewater with a small amount of suspended solids, and is not suitable for anaerobic treatment of organic waste and wastewater containing solids.

An immobilized anaerobic digestion method using a porous ceramic granule carrier has been reported (Patent Document 4). However, since this method uses a ceramic granule with a through hole and is fixed in a rosary shape, the apparatus is complicated. The problem remains that the construction is difficult and the decomposition efficiency does not increase so much because the volume of the carrier in the tank is small.

  In addition, although a method using fluid 0.5 to 6 mm granular organic gel fine particles as a microorganism-immobilized carrier has been reported (Patent Document 5), producing fluid fine particles or maintaining them in a digestion tank. However, there are problems with economy and operability.

  Moreover, although the method of hydrophilizing a nonwoven fabric with an oxidizing agent and utilizing it as a microbial carrier has been reported (Patent Document 6), it is difficult to optimize the density and porosity because the nonwoven fabric uses fibers, There is a problem that it is not suitable as a carrier for microorganisms.

  In order to eliminate these drawbacks, the present inventors first performed anaerobic digestion treatment of organic wastewater and / or organic waste, and the resulting digested liquid is separated by a solid-liquid separation membrane. An anaerobic digestion treatment method for organic wastewater and / or organic waste, in which anaerobic digestion treatment is performed in the presence of an anaerobic digestive microorganism-immobilized carrier, has been proposed (Patent Document 7).

JP 07-148500 A Japanese Patent Laid-Open No. 10-085784 Japanese Patent Laid-Open No. 11-319782 JP 09-038686 A JP 2003-062594 A JP 2003-260446 A Japanese Patent Application No. 2002-339623

  The present invention is a further development of the method of Patent Document 7, and its object is to use a solid-liquid separation membrane for an object to be treated consisting of organic waste in the presence of a digestive microorganism-immobilized carrier. Without anaerobic treatment, the anaerobic microorganisms are efficiently maintained in the digestion tank, the organic waste is efficiently decomposed and gasified by anaerobic digestion, and the digestion rate is improved by increasing the production efficiency of methane. It is to provide a method of making it happen.

As a result of intensive studies to solve the above problems, the present inventor has completed the present invention.
That is, according to the present invention, the following inventions are provided.
(1) An organic property characterized in that an immobilized carrier made of foamed polyurethane is used as a carrier in a method for directly anaerobically treating an object to be treated made of organic waste in the presence of a carrier for immobilizing digestive microorganisms. Waste disposal method.
(2) The method for treating organic waste as described in (1) above, wherein the pores of the polyurethane foam are connected to each other.
(3) The method for treating organic waste as described in (1) above, wherein the number of pores of the foamed polyurethane is 20 or more per 25 mm.
(4) The organic waste treatment method according to (1) above, wherein the immobilization support is installed in a fixed bed type.
(5) In a method for directly anaerobically treating and digesting an object to be treated consisting of organic waste in the presence of a digestive microorganism-immobilized carrier, (I) containing acid-fermentable microorganisms and / or methane-fermentable microorganisms In the presence of anaerobic digested sludge, a process in which foamed polyurethane is used as a carrier of digestive microorganisms, and the treatment object is brought into contact with foamed polyurethane to digest anaerobically; (II) the digestion product obtained in the digestion process is liquid phase A method for treating organic waste, comprising: a step of separating the solid phase portion into a solid phase portion; and (III) a step of recovering the solid phase portion obtained in the separation step.
(6) The method for treating organic waste as described in (5) above, wherein the gas phase containing methane generated in the step (I) is used as fuel.
(7) The method for treating organic waste as described in (5) above, wherein the solid phase part recovered in the recovery step (III) is used as an organic fertilizer.
(8) An anaerobic digester equipped with a direct type anaerobic digester, wherein a digestive microorganism-immobilized carrier made of foamed polyurethane is accommodated in the anaerobic digester (1) ) To (7) An anaerobic digester used in the organic waste processing method according to any one of the above.

The present invention is configured as described above, and the organic waste and / or waste water is subjected to a decomposition digestion treatment of anaerobic microorganisms immobilized on the foamed polyurethane carrier. Since microorganisms involved in decomposing digestion are efficiently immobilized on polyurethane, the concentration of microorganisms in the tank is high, and decomposing digestion proceeds efficiently. As a result, the decomposition rate of organic matter is high and methane gas is generated more rapidly.

The greatest feature of the present invention is that it has an anaerobic digestion method directly in the presence of a normal fibrous digestible immobilization carrier without using a conventional solid-liquid separation membrane, and particularly anaerobic at the start of digester operation. In order to overcome the problem that it takes a long time for the break-in operation due to the slow immobilization rate of the sex microorganisms, a support made of polyurethane foam is selected as the support accommodated in the anaerobic digester.
In this way, when the foamed polyurethane carrier is used as the immobilization carrier, the number and density of the pores of the polyurethane are optimized, so that microorganisms involved in decomposition digestion and gasification efficiently enter the pores of the polyurethane. Because it is fixed at a high density, digestion is efficient.

In the present invention, anaerobic digestion is a method of generating methane and carbon dioxide from organic substances by the action of anaerobic microorganisms under anaerobic conditions without oxygen, and anaerobic digestion treatment is performed at 20 to 70 ° C., Preferably, both digestion methods of anaerobic digestion performed at 30 to 60 ° C are included. This anaerobic digestion treatment may be an intermediate temperature digestion method performed at 35 to 37 ° C or a high temperature digestion method performed at 55 ° C.
In the present invention, it is preferable to employ a wet digestion method in which digestion is performed using an immobilized microorganism and adjusting the water content of the raw material to 80% or more.

In addition, the acid-fermenting microorganism referred to in the present specification means a microorganism that produces an organic acid or the like in anaerobic digestion, and examples thereof include Bacteroides sp., Clostridium sp., Bacillus sp., Lactobacillus sp. Methane-fermenting microorganisms mean microorganisms that produce methane in anaerobic digestion, such as Methanobacterium sp., Methanothermobacter sp., Methanosarcina sp., Methanosaeta sp. Both are well known in the art.

  The organic waste subject to treatment of the present invention includes food residues and wastewater discharged from households, restaurants, food factories, etc., and fermentation residues and wastewater discharged from fermentation plants, etc., sewage treatment plants, food factories, and septic tanks. It means organic sludge discharged after wastewater treatment, etc., plant biomass such as fallen leaves and pruned branches, and waste paper.

  To carry out the method of the present invention, anaerobic digested sludge and raw organic waste are mixed in a digestion tank, adjusted to a moisture content of 75-99.9%, preferably 85-98%, and crushed as necessary. And an anaerobic digestion treatment at 20 ° C. or higher, desirably 30 to 60 ° C., more preferably 35 or 55 ° C.

In this case, in the present invention, a foamed polyurethane fixed carrier is provided in the digestion tank.
The polyurethane referred to in the present invention is a general term for a polymer having a urethane bond, and the urethane bond refers to a product formed by an addition reaction between an isocyanate group and a compound having an active hydrogen such as a hydroxyl group. The body is used as an immobilization carrier. With foamed polyurethane, the density and the number of pores can be arbitrarily adjusted.
As a method for containing the immobilization carrier, either a fixed bed, a fluidized bed, or a combination thereof may be used. However, the immobilization carrier is fixed in the anaerobic digestion tank and does not move, and digestion proceeds with the digest moving. A fixed bed is preferably used.

The shape of the foamed polyurethane as the carrier is not limited, and can be molded into a cylindrical shape, a flat plate shape, a spherical shape, or a disk shape using an auxiliary material. The thickness of the polyurethane foam is 5 to 200 mm preferably 10 to 50 mm, the density of the polyurethane is 5 to 100 kg / m ³ preferably 20~40kg / m ^3, the polyurethane is, the pores are interconnected It is desirable to have an open cell structure. Further, the number of pores is 10/25 mm or more, desirably 20-50 / 25 mm.

  As anaerobic digested sludge used for immobilization, normal anaerobic digested sludge used for anaerobic digestion of sewage sludge containing acid-fermenting microorganisms and methane-fermenting microorganisms or existing anaerobic digested sludges are separately cultured. Can be used.

As described above, when organic waste is digested anaerobically using a foamed polyurethane carrier to which acid-fermenting microorganisms and methane-fermenting microorganisms are immobilized, the organic matter is decomposed and gasified, and anaerobic digestion residue is produced. can get. The anaerobic digestion residue generated at that time contains a large amount of fertilizer components such as nitrogen and phosphorus, and can be used as an organic fertilizer because fermentation is progressing.
In addition, the salt content in organic fertilizer produced by the aerobic compost method may be a problem. In this method, the fermentation residue is solid-liquid separated and the solid phase becomes organic fertilizer. Since it is contained in many parts, the organic fertilizer obtained by this method has the advantage that the salt concentration is lower than the organic fertilizer by the compost method.

  Also, methane generated during digestion can be used as fuel for boiler fuel, digestion gas power generation, micro gas turbines and fuel cells after reforming to hydrogen.

Next, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a flow sheet for carrying out the present invention.
In FIG. 1, 1 is a waste storage tank, 2 is a raw material waste pipe, 3 is an anaerobic digestion tank, 4 is a foamed polyurethane carrier, 5 is a stirring device, 6 is a digestion gas pipe, 7 is a digestion gas storage tank, 8 Is a processing liquid pipe, 9 is a solid-liquid separator, 10 is a processing solid pipe, 11 is a processing solid storage tank, 12 is a processing liquid phase piping, and 13 is a processing liquid phase storage tank.

In order to implement the present invention according to FIG. 1, anaerobic sludge containing microorganisms causing methane fermentation is introduced from an organic waste storage tank 1 through an organic waste pipe 2 and fixed to a foamed polyurethane carrier. Organic waste is supplied to the converted anaerobic digester 3.
As described above, as the anaerobic sludge containing microorganisms that cause methane fermentation, anaerobic digested sludge or the like of sewage sludge in a sewage treatment plant may be used. In this case, the anaerobic digester 3 has a cylindrical or flat foamed polyurethane carrier 4 inside thereof, and immobilizes anaerobic microorganisms. Usually, for immobilizing microorganisms, a method is used in which anaerobic digested sludge is introduced into the tank at the start-up of the digestion tank, followed by operation for 2 to 3 weeks without adding the raw material, and then gradually adding the raw material.

  In the anaerobic digestion tank 3, the waste is subjected to digestion while receiving the action of decomposing the immobilized microorganisms. By this digestion treatment, organic matter in the waste is decomposed and digested more rapidly and stably than methane in comparison with conventional anaerobic digestion. In the case of the present invention, the methane-fermenting microorganisms are efficiently immobilized on the foamed polyurethane carrier with optimized density and number of pores, and the concentration of decomposing microorganisms in the tank is high. An increase in speed and digestion gasification rate is achieved. In particular, the rate of immobilization of anaerobic microorganisms at the start of digester operation is fast, and the break-in operation can be shortened.

  The anaerobic digestion tank according to the present invention is desirably provided with a stirring device in order to stir sludge in the tank and promote the fermentation reaction. Moreover, you may implement | achieve stirring by removing the sludge in a tank and throwing in again.

Further, the digestion gas containing methane generated in the anaerobic digestion tank 3 is stored in the digestion gas storage tank 7 through the digestion gas pipe 6. Digester gas in this case is usually CH _4: 50 to 100 mol%, CO _2: 0 to 50 mol%, H _2: containing 0-10 mol%.

  On the other hand, the digest obtained in the anaerobic digester 3 is introduced into the solid-liquid separator 9 through the treated product pipe 8. In the solid-liquid separation device 9, the liquid phase part (waste water) and the solid phase part (processed product) are separated, and the solid phase part is stored in the solid phase part storage tank 11 through the process solids pipe 10, and the liquid phase The part is stored in the processing liquid phase storage tank 13 through the processing liquid phase piping 12.

  The solid-liquid separation device 9 includes a filter, a centrifuge, a sedimentation tank, and the like. The digest is separated into a liquid phase part and a solid phase part by this solid-liquid separation device. This solid phase portion contains a large amount of fertilizer components such as nitrogen and phosphorus, and can be used as an organic fertilizer because fermentation is progressing. The liquid phase part (waste water) is usually one having a low concentration of dissolved organic matter or dissolved inorganic matter, and is discharged after waste water treatment as necessary.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
To a 300 ml reactor, 150 ml of a mixture of digested sludge and acetic acid medium was added. Polyurethane foam (number of pores 20/25 mm) is fixed in a 20% (v / v, 30 ml) digestive fluid reactor to form a fixed bed. After sealing, the gas inside is replaced with nitrogen and the reactor is filled with nitrogen. Made anaerobic. The amount of gas produced from the plastic bottle was measured with a syringe, and the methane concentration was measured with gas chromatography. The cells were cultured for 42 days in a semi-continuous system in which an acetic acid medium was supplied once a week to a 35 ° C. vibration incubator (120 rpm). The dissolved total organic carbon concentration of the influent and effluent was measured, and the methane yield per added dissolved organic matter was examined.

Reference example 1
A foamed polyurethane having 13 pores / 25 mm was used as a fixed bed, and the same experiment as in Example 1 was performed to measure each data.

Reference example 2
A foamed polyurethane having 20 pores / 25 mm was used as a fluidized bed, and the same experiment as in Example 1 was performed to measure each data.

[Experimental Results and Discussion of Example 1 and Reference Example 1]
In Comparative Example 1 in which polyurethane foam with 13 pores / 25 mm was used as a fixed bed, the cumulative amount of methane gas produced after 42 days of culture was 413 ml, whereas the fixed bed method with 20 pores / 25 mm was used. The amount of accumulated methane gas produced in Example 1 was 1073 ml. Further, in Reference Example 1, there was a methane yield of 208 ml / g-added dissolved total organic carbon, while in Example 1, the methane yield of 590 ml / g-added dissolved total organic carbon. It is considered that more methane bacteria were immobilized in the reactor using fixed polyurethane foam with a pore number of 20/25 mm, and digestion gas production was improved compared to a foamed polyurethane reactor with a pore number of 13/25 mm.

[Experimental results and discussion of Example 1 and Reference Example 2]
In Reference Example 2 in which foamed polyurethane is a fluidized bed having a pore number of 20/25 mm, the cumulative amount of methane gas produced after 42 days of culture was 631 ml, whereas the cumulative amount of methane gas produced in Example 1 was 1073.
ml. Further, under the same experimental conditions, the methane yield of 307 ml / g-added dissolved total organic carbon in Reference Example 2 was 590 ml / g-added dissolved total organic carbon in Example 1, and the methane yield of Reference Example 2 was 590 ml / g-added dissolved total organic carbon. It is believed that the reactor with the fixed bed was more stable than the fluidized bed, and more digestion gas was produced.

From these experimental results, anaerobic microorganisms are efficiently immobilized and organic waste decomposition rate and gasification when equipped with a fixed-bed foamed polyurethane carrier with 20 pores / 25mm in an anaerobic digester. It can be seen that the speed is improved.

It is explanatory drawing of the anaerobic digester of the organic waste which concerns on this invention.

Explanation of symbols

1. Waste storage tank 2. 2. Raw material waste piping Anaerobic digester 4. 4. Foamed polyurethane carrier 5. Stirrer 6. Digestion gas piping Digestion gas storage tank8. Process pipe 9. Solid-liquid separator 10. Processing solid piping,
11. Processed solids storage tank 12. Treatment liquid phase piping 13. Treatment liquid storage tank

Claims (8)

In a method for anaerobically treating an object to be treated consisting of organic waste directly in the presence of a digestive microorganism-immobilized carrier, an immobilized carrier made of polyurethane foam is used as the carrier. Processing method. The method for treating organic waste according to claim 1, wherein the pores of the polyurethane foam are connected to each other. The method for treating organic waste according to claim 1, wherein the number of pores of the foamed polyurethane is 20 or more per 25 mm. 2. The method for treating organic waste according to claim 1, wherein the fixed carrier is installed in a fixed bed type. (I) Anaerobic digestion containing acid-fermentable microorganisms and / or methane-fermentable microorganisms in a method of directly anaerobically treating and digesting an object to be treated consisting of organic waste in the presence of a digestive microorganism-immobilized carrier. In the presence of sludge, a process in which foamed polyurethane is used as a carrier for digestive microorganisms and the treatment object is brought into contact with foamed polyurethane to digest anaerobically; (II) the digested product obtained in the digestion process is mixed with the liquid phase part and solid phase A method for treating organic waste, comprising: a step of separating into a phase part; and (III) a step of recovering the solid phase part obtained in the separation step. 6. The method for treating organic waste according to claim 5, wherein the gas phase portion containing methane generated in the step (I) is used as fuel. 6. The method for treating organic waste according to claim 5, wherein the solid phase portion recovered in the recovery step (III) is an organic fertilizer. An anaerobic digester equipped with a direct type anaerobic digester, wherein a digestive microorganism-immobilized carrier made of foamed polyurethane is accommodated in the anaerobic digester. 7. An anaerobic digester used in the organic waste processing method according to any one of 7 above.

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