JP4448933B2 - Organic waste treatment methods - Google Patents

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. The present invention relates to a method for treating organic waste to be decomposed and digested.

  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 of increasing the concentration of microorganisms in the digestion tank using a self-aggregated granule called UASB method has been studied and put into practical use (Patent Document 3). However, since this method cannot decompose solids so much, it is exclusively. 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.
Carbon felt is a highly durable material with high porosity and surface area. As a result of research on anaerobic degradation of cellulose using carbon felt as a fixed bed carrier material, an excellent fixing effect and a high decomposition rate have been obtained (Yang et al. 2004 Non-Patent Document 1). Various new and highly efficient reactor designs using carbon felt are conceivable.

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 YingnanYang, Kenichiro Tsukahara, Tatsuo Yagishita and Shigeki Sawayama: Performanceof a fixed-bed reactor packed with carbon felt during anaerobic digestion ofcellulose .Bioresource Technology, Volume 94, Issue 2, September 2004, Pages 197-201

An object of the present invention is to maintain anaerobic microorganisms efficiently in a digestion tank in a method for anaerobic treatment of an object to be treated consisting of organic waste in the presence of a carrier for immobilizing digestive microorganisms. An object is to provide a method of efficiently decomposing and gasifying methane by anaerobic digestion, increasing the production efficiency of methane and improving the digestion rate.
The present inventor studied the reactor design using carbon felt as a support material, and reached the present invention.
The anaerobic digestion characteristics of fixed bed reactor and fluidized bed reactor will be studied and a hybrid structure of fixed bed and fluidized bed will be developed. The fixed bed / fluidized bed hybrid reactor using carbon felt was operated continuously, the anaerobic digestion characteristics were examined, and the immobilized microorganisms were observed with an electron microscope to confirm the effect.

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.
The present invention relates to a method for directly anaerobically treating a liquid object containing organic waste in the presence of digestive microorganisms in an anaerobic digestion tank, and a fixed bed carrier whose surface is covered with carbon fibers and the surface Is a method for treating organic waste, characterized in that a fixed bed / fluidized bed hybrid reactor in which a fluidized bed carrier covered with carbon fiber is combined is used in an anaerobic digester.
In the present invention, a fluidized bed carrier whose surface is covered with carbon fibers is used in contact with both the gas phase and the liquid phase in the anaerobic digester.
Furthermore, the organic waste treatment method of the present invention is a method for directly digesting an object to be treated consisting of organic waste in the presence of a digestive microorganism-immobilized carrier in an anaerobic treatment, wherein (I) acid fermentability A step of anaerobically digesting the treated material in contact with a fixed bed carrier and a fluidized bed carrier in the presence of anaerobic digested sludge containing microorganisms and / or methane-fermenting microorganisms; (II) obtained in the digestion step A step of separating the digested product into a liquid phase portion and a solid phase portion, and (III) a step of recovering the solid phase portion obtained in the separation step.
In the present invention, the gas phase part containing methane generated in the step (I) can be used as fuel.
Further, in the present invention, the solid phase portion recovered in the recovery step (III) can be an organic fertilizer.
Furthermore, the present invention is an anaerobic digester that directly anaerobically treats a liquid object containing organic waste in the presence of digestive microorganisms in an anaerobic digestion tank, the surface of which is a carbon fiber. An anaerobic digester characterized in that a fixed bed / fluidized bed hybrid reactor in which a fixed bed carrier covered with carbon and a fluidized bed carrier covered with carbon fiber is combined is housed in an anaerobic digester .
Further, in the present invention, the fixed bed carrier may have a structure in which the surface of the molding resin is covered with carbon felt, and the fluid bed carrier may have a structure in which the foam molding resin is covered with carbon felt.

The present invention relates to a method for directly anaerobically treating a liquid object containing organic waste in the presence of digestive microorganisms in an anaerobic digestion tank, and a fixed bed carrier whose surface is covered with carbon fibers and the surface By using a fixed bed / fluidized bed hybrid reactor combined with a fluidized bed carrier covered with carbon fiber in an anaerobic digestion tank, it is possible to efficiently digest and digest liquid processed materials containing organic waste. I can do it.
Since the microorganisms involved in the digestion are efficiently immobilized on the fixed bed carrier and the fluidized bed carrier, the microorganism concentration in the tank is high and the digestion proceeds efficiently. As a result, the decomposition rate of organic matter is high and methane gas is generated more rapidly. For example, when the organic load factor (OLR) was 6.34 g / l-reactor / d, the DOC removal rate reached 88% and the methane production rate reached 798 ml / l-reactor / d. After that, the fluidized bed of the fixed bed / fluidized bed hybrid reactor was taken out and the fermentation was continued only in the fixed bed. As a result, the organic loading rate was the same as above, the DOC removal rate was 62%, and the methane production rate was 638 ml / l-reactor / d Decreased to. More than the reduction of the support surface area, the hybrid reactor showed better results than the fixed bed reactor. Furthermore, no inhibition was observed even when the concentration of propionate added was 10000 mg / l.

The most important feature of the present invention is that the liquid material to be treated containing organic waste is directly anaerobically treated in the presence of digestive microorganisms in an anaerobic digestion tank. This is to use a fixed bed / fluidized bed hybrid reactor in which the bed carrier and the fluidized bed carrier whose surface is covered with carbon fiber are combined in the anaerobic digester.
Here, the fixed bed / fluidized bed hybrid reactor refers to a form in which a fluidized bed carrier is used in combination with a fixed bed carrier. Typically, as shown in FIG. 1, there is a fixed bed carrier in the liquid phase. In other words, the fluidized bed carrier is used in contact with both the gas phase and the liquid phase.
In addition, when the fluidized bed support is used in contact with both the gas phase and the liquid phase, the various fermentation microorganisms related to the decomposition of organic matter are immobilized and maintained by simultaneously contacting both the gas phase and the liquid phase in the anaerobic digester. It turns out that you can.
Since the immobilized microbial flora of the fixed bed carrier and the fluidized bed carrier are different, the biodiversity in the anaerobic digestion tank is increased, the microorganisms involved in decomposition digestion and gasification are diversified, and digestion is efficiently and stably promoted.

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.

  Moreover, the fixed bed carrier said in this specification means the method by which the fixed support | carrier is fix | immobilized in the anaerobic digester, and is a conventionally known method. The fluidized bed carrier means a method in which the carrier is not fixed in the anaerobic digestion tank and can be moved by stirring in the tank, and is a conventionally known method.

In addition, the acid-fermenting microorganism referred to in the present specification means a microorganism that generates 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 fixed bed carrier and a fluidized bed carrier are provided in the digester. It is desirable that the fluidized bed carrier is in contact with both the gas phase and the liquid phase in the anaerobic digester at the same time.
The material of the carrier may be anything such as an inorganic material or an organic material such as a resin, but the surface must be covered with carbon fibers. As an example of the carbon fiber referred to in the present invention, a carbon felt having a porosity of 92.2%, a specific surface area of 0.70 g / cm ³ and a specific gravity of 0.11 g / cm ³ can be used.

  The shape of the carrier is not limited, and can be formed into a cylindrical shape, a flat plate shape, a spherical shape, or a disk shape using an auxiliary material or the like.

  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 anaerobically digested using a fixed bed carrier and a fluidized bed carrier in which acid-fermentable microorganisms or methane-fermentable microorganisms are immobilized, the organic matter is decomposed and gasified, and anaerobic. Sexual digestion residue is obtained. 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 diagram for a typical case of implementing the present invention.
In FIG. 1, 1 is a waste storage tank, 2 is a raw material waste pipe, 3 is an anaerobic digester, 4 is a fixed bed carrier, 5 is a fluidized bed carrier, 6 is a stirring device, 7 is a digestion gas pipe, Digestion gas storage tank, 9 is treated product piping, 10 is a solid-liquid separator, 11 is treated solid matter piping, 12 is treated solid matter storage tank, 13 is treated liquid phase piping, and 14 is treated liquid phase storage tank. .

In order to carry out the present invention according to FIG. 1, anaerobic sludge containing microorganisms that cause methane fermentation is introduced from an organic waste storage tank 1 through an organic waste pipe 2, and a carbon felt fixed bed and Organic waste is supplied to the anaerobic digester 3 immobilized on the fluidized bed carrier.
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 fixed bed carrier and a fluidized bed carrier made of carbon fiber or the like installed therein to immobilize anaerobic microorganisms. The fluidized bed carrier 5 is preferably in contact with both the gas phase and the liquid phase in the anaerobic digester 3 at the same time. 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, since the immobilization method is a combination of a fixed bed and a fluidized bed, various methane-fermenting microorganisms are efficiently immobilized on each carrier, and the concentration and diversity of decomposing microorganisms in the tank are high. Compared with the conventional digestion method, the organic matter decomposition rate and digestion gasification rate are improved.

  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 8 through the digestion gas pipe 7. 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 10 through the treated product pipe 9. In the solid-liquid separation device 10, the liquid phase part (waste water) and the solid phase part (processed product) are separated, the solid phase part is stored in the solid phase part storage tank 12 through the process solid matter pipe 11, and the liquid phase The part is stored in the processing liquid phase storage tank 14 through the processing liquid phase piping 13.

  The solid-liquid separator 10 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.
[Method of Example 1]
As a fixed bed / fluidized bed hybrid reactor, a glass container having an inner diameter of 10 cm and a height of 15 cm was used. Carbon fiber was used as a carrier material for fixed bed and fluidized bed. The fixed floor portion is provided with carbon fibers having a height of 6.4 cm along the inner wall of the glass container, and the carrier volume is 200 cm ³ . As the fluidized bed carrier, five spherical carriers (one volume is 4 cm ³ ) wound with carbon fibers were introduced into the reactor while adjusting the buoyancy so as to float in the reactor.
The reactor was stirred with a stirrer in order to keep the reactor in a uniform state, and continuously operated at a medium temperature of 35 ° C. with a residence time of 5 days. Increase organic load to 0.11, 0.31 and 0.53 g / l-reactor / d, after fermentation for 40 days, organic load 1.07 g / l-reactor / d for 20 days, 3.17 g / l-reactor / d for 15 days, Then 6.34 g / l-reactor / d was operated for 13 days. Thereafter, the fluidized bed portion was removed from the reactor and the anaerobic digestion was continued. The organic substance load was operated with a fixed bed portion of 6.34 g / l-reactor / d for 20 days, 3.17 g / l-reactor / d for 15 days, and 1.07 g / l-reactor / d for 13 days.
The amount of gas produced from the reactor was measured, and the methane concentration was measured by gas chromatography. The dissolved total organic carbon concentration of the influent and effluent was measured, and the methane yield per added dissolved organic matter was examined. The immobilized microorganism was observed using an electron microscope.

[Experimental results of Example 1 and discussion thereof]
The fixed-bed / fluidized-bed hybrid reactor was stabilized in a relatively short time after start-up from the continuous operation experiment. With an organic load (OLR) of 6.34 g / l-reactor / d, the DOC removal rate reached 88% and the methane production rate reached 798 ml / l-reactor / d. After that, when the fluidized bed of the hybrid reactor was taken out and fermentation was continued using only the fixed bed, the DOC removal rate was reduced to 62% and the methane production rate decreased to 638 ml / l-reactor / d with the same organic loading as described above. The fluidized bed carrier volume is 9% of the total carrier volume. Per carrier volume, the hybrid reactor outperformed the fixed bed only reactor. In particular, methane formation was observed at a high concentration of propionic acid (10000 mg / l). The hybrid reactor has a short startup and high organic matter removal rate.
In the observation of a fixed bed / fluidized bed hybrid reactor using an electron microscope, the microorganisms immobilized on the fluidized bed support are mainly spherical and bispherical Methanosarcina- like methane bacteria, long-spotted Methanobacterium- like methane bacteria, and slightly shorter gonococcal Methanosaeta- like methane. It was a fungus. On the other hand, the fixed bed carrier part was mainly fixed with spherical and bispherical Methanosarcina- like methanogens. It is considered that the diversity of methanogens fixed on fluidized bed carbon felt plays an important role in methanogenesis. From these experimental results, anaerobic microorganisms are efficiently immobilized and the organic waste decomposition rate and gasification rate are improved if a carbon felt hybridized with a fixed bed and fluidized bed is provided in the anaerobic digester. I understand.

[Fixed floor material]
The carbon felt used as a support material has a porosity of 92.2%, a specific surface area of 0.70 g / cm ³ and a specific gravity of 0.11 g / cm ³ . The structure of the carbon felt material was observed using an electron microscope. An electron micrograph of the immobilization material is shown in FIG.
[Semi-continuous operation]
A fixed bed reactor and a fluidized bed reactor (300 ml) having a carbon felt packing rate of 20% v / v were prepared. The other reactor was operated without a carrier and used as a control. All reactors were placed in a 35 ° C. incubator with stirring at 120 rpm. The generated biogas was collected with a syringe. The inoculum was 15% v / v of methanogenic sludge from Ibaraki Prefectural Sewage Treatment Plant, and supplied with a synthetic medium containing 5.0g TOC / l for one month at 35 ° C. . The reactor was operated for 42 days in a semi-continuous mode with a retention time (HRT) of 12 days. The liquid volume in the reactor is 150 ml. Reactor supplied with medium containing CH ₃ COONa (5 g / l), NH ₄ Cl (200 mg / l), KH ₂ PO ₄ (16 mg / l) and trace metal salt (200 mg / l) did.
[Continuous operation]
The structure of a fixed bed / fluidized bed hybrid (AFFH) reactor is shown in FIG. A glass container having an inner diameter of 10 cm and a height of 15 cm was used. The carbon felt described above was used as a carrier material for fixed beds and fluidized beds. The fixed floor part was a carbon felt with a height of 6.4 cm installed around the glass container, and the surface area was 200 cm ² . In the fluidized bed portion, five balls wrapped with carbon felt (one surface area of 4 cm ² and a total surface area of 20 cm ² ) were placed in the reactor.

The reactor was stirred with a stirrer to maintain a uniform state, and continuously operated at a medium temperature of 35 ° C. for 5 days with HRT. 16% w / w mesophilic anaerobic digested sludge and 84% w / w CH ₃ COONa (5 g / l), CH ₃ CH (OH) COONa (2.5 g / l), CH ₃ CH ₂ COONa (2.5 g / l), yeast extract (300 mg / l), NH ₄ Cl (200 mg / l), KH ₂ PO ₄ (16 mg / l) and trace metal solution were added to the reactor. Trace metal salt solutions are FeSO ₄・ 7H ₂ O (1.11 g / l), MgSO ₄・ 7H ₂ O (24.65 g / l), CaCl ₂・ 2H ₂ O (2.94 g / l), NaCl (23.4 g / l). l), MnSO ₄ · 4H ₂ O (111 mg / l), ZnSO ₄ · 7H ₂ O (28.8 mg / l), Co (NO3) ₂ · 6H ₂ O (29.2 mg / l), CuSO ₄ · 5H ₂ Contains O (25.2 mg / l), Na ₂ MoO ₄ · 2H ₂ O (24.2 mg / l), and H ₃ BO ₃ (31.0 mg / l). 5 N NaOH was added to adjust the pH of the synthetic medium to 7.2. 900 ml of fermentation broth mixed with 200 ml / l trace metal solution was put into the reactor and the operation was started. Increase organic load in the order of 0.11, 0.31, 0.53 g / l-reactor / d, ferment for 40 days, then organic load 1.07 g / l-reactor / d for 20 days, 3.17 g / l-reactor / d for 15 days Then, it was operated at 6.34 g / l-reactor / d for 13 days. Thereafter, the fluidized bed portion was removed from the reactor and the anaerobic digestion was continued. The organic load is 20 days at 6.34 g / l-reactor / d, 15 days at 3.17 g / l-reactor / d, then 13 days at 1.07 g / l-reactor / d Drove to 141 days.

[Chemical analysis]
The digestive juice was sampled twice a week. The sample was centrifuged at 10,000 rpm for 10 minutes to precipitate microorganisms, and the supernatant was measured as DOC with a TOC analyzer. Biogas production and pH in the reactor were measured daily. The biogas concentration was measured using a gas chromatograph.
[Observation with electron microscope]
The morphology of the cells attached to the carrier material was observed with a scanning electron microscope. After the experiment was completed, the carrier was taken out, and the immobilized microorganism was first washed with a buffer solution (pH 7.0). The sample was fixed in a 10% glutaraldehyde solution soaked overnight. The fixed sample was desalted with pure water and frozen at −20 ° C. for 3 hours. Furthermore, the frozen sample was dried with a freeze dryer. These samples were coated with gold powder before microscopic observation.
[Results and discussion]
FIG. 4 shows changes in the amount of methane gas accumulated in a fixed bed, a fluidized bed reactor, and a reactor without a carrier. As a result, the cumulative amount of methane gas decreased in the order of fixed bed, fluidized bed, and no carrier. FIG. 5 shows the results of average methane yield in each anaerobic digester. The fixed bed reactor showed the highest methane yield of about 217 ml CH ₄ / g-DOC _added . The methane yield also decreased in the order of fixed bed, fluidized bed, and no support. From these results, it became clear that the fixed reactor has better digestion efficiency than the fluidized reactor. The methane concentration of each reactor is shown in FIG. A similar methane concentration was seen in the reactor with the carrier, but the methane concentration in the reactor without the carrier was low.
The change in the DOC removal rate is shown in FIG. In the reactor with two carriers, a removal rate of 98% was obtained. The fastest DOC removal is in the fixed bed reactor. A 90% removal rate was obtained 14 days after the start of fermentation. In comparison, a fluidized bed reactor required 27 days to achieve the same removal rate. In the reactor without support, the removal rate after 42 days was 55%. From these results, it can be seen that the fixed bed reactor exhibits superior anaerobic digestion characteristics compared to the fluidized bed reactor.

As a result of continuous operation of AFFH reactor The methane concentration in biogas gradually increased from start-up and reached 91.6% on the 7th day, and was maintained at that concentration until the end of operation (Fig. 8). Since the digestive fluid has a relatively high pH, it is considered that the carbon dioxide in the biogas produced in the reactor was dissolved in the digestive fluid and the methane concentration increased. Good start-up was achieved by immobilizing a large amount of microorganisms using high porosity carbon felt.
As shown in Fig. 8, the average methane yield is 340 ml / l-reactor / d, from 61 to 76 when the organic load is 1.07 g / l-reactor / d for 20 days from 40 to 60 days. When operating for 15 days with an organic load of 3.17 g / l-reactor / d, the average methane yield is 673 ml / l-reactor / d, with an organic load of 6.34 g / l-reactor / d from 77 to 90 days. When operated for 13 days, the average methane yield is 798 ml / l-reactor / d.
After operating in a fixed bed / fluidized bed hybrid (AFFH) reactor for 90 days, the fluidized bed part was taken out from the AFFH reactor and the anaerobic digestion was continued only with the fixed bed. The organic load was 6.34 g / l-reactor / d for 20 days, 3.17 g / l-reactor / d for 15 days, and 1.07 g / l-reactor / d for 141 days. As shown in FIG. 8, the average methane yield when operating for 20 days at an organic load of 6.34 g / l-reactor / d from 91 to 111 days is 638 ml / l-reactor / d, from 112 to 127. The average methane yield when operating for 15 days with an organic load of 3.17 g / l-reactor / d is 537 ml / l-reactor / d, from 128 to 141 days, with an organic load of 1.07 g / l-reactor / d The average methane yield when operated for 13 days is 272 ml / l -reactor / d. If methane production is kept constant for more than double HRT, it can be said to be stable. The methane yield of this system suggests that the fixed bed / fluidized bed hybrid (AFFH) reactor is a stable and excellent anaerobic digestion reactor system.
It has been reported that propionic acid concentrations of 1500 mg / l to 2220 mg / l affect methanogens. Regarding the toxicity of propionic acid to methanogens, it has been reported that there was a limit in methane production when the propionic acid concentration reached 5000 mg / l. In contrast, the methanogens in this system were able to adapt to high propionic acid concentrations. Even when the propionic acid concentration reached 10000 mg / l, there was no effect on methanogenesis.

[DOC removal rate of AFFH reactor]
FIG. 9 shows the relationship between the change in organic load and the DOC removal rate during operation of the AFFH reactor. On the 22nd day after startup, the DOC removal rate was 95.7%. The DOC removal rate was 88.0-99.7% when the organic load was relatively high. From the 91st day, the DOC removal rate was 62.0 to 80.0% when only the fixed bed was loaded with the same organic load. FIG. 10 shows the change in DOC removal rate at different organic loadings. The DOC removal rate decreased with increasing organic loading. After removing the fluidized bed (carbon felt area decreased by 1/11), the DOC removal rate decreased by 24% with the same organic loading. The decrease in DOC removal rate was greater than the decrease in carrier area.
When the organic load is 6.34 g / l-reactor / d, the AFFH reactor has a DOC removal rate of 88% or more, so the AFFH system can be said to be a highly efficient reactor system. With increasing organic loading, the DOC removal rate decreased somewhat, but the system can operate at relatively high loads. The use of carbon felt in the hybrid and the immobilization of various microorganisms may have contributed to higher efficiency of the AFFH system.
[Observation of immobilized microorganisms with a microscope]
After 90 days of continuous operation of the reactor, the fluidized bed carrier was taken out and observed with a microscope (FIG. 11). According to these micrographs, it was found that the attached microorganisms were mainly composed of spherical and bispherical Methanosarcina- like methane bacteria, long-spotted Methanobacterium methane bacteria, and slightly shorter gonococcal Methanosaeta- like methane bacteria.
On the 141st day after the end of continuous operation, the fixed bed carrier was taken out and observed with a microscope (FIG. 12). It was observed that spherical and bispherical Methanosarcina- like methanogens were immobilized on the carrier. It was revealed that the microorganisms attached to the fluidized bed carrier of the AFFH reactor were more diverse than the fixed bed carrier part. It is considered that the diversity of methanogens attached to the carbon felt in the fluidized bed plays an important role in methanogenesis.

[Summary]
As a result of the semi-continuous experiment, it was found that the fixed bed had better methane fermentation characteristics than the fluidized bed. From the continuous operation of the AFFH reactor, this system has shown satisfactory results at relatively high organic loads. In particular, methane formation was observed even under conditions of high concentration of propionic acid (10000 mg / l). The AFFH reactor has a short start-up and a high organic matter removal rate. Under the same operating conditions, the fixed bed / fluidized bed hybrid (AFFH) reactor achieved better results than the reduction of the carrier area than the fixed bed only reactor.
In the observation of the fixed bed / fluidized bed hybrid reactor using an electron microscope, the microorganisms immobilized on the fluidized bed support are mainly spherical or bispherical Methanosarcina- like methane bacteria, long-spotted Methanobacterium- like methane bacteria, and slightly shorter gonococcal Methanosaeta- like. It was a methane bacterium. On the other hand, in the fixed bed carrier part, mainly spherical and bispherical Methanosarcina- like methanogens were fixed. The diversity of methanogens immobilized on fluidized bed carbon felt may play an important role in methane production.

The organic waste treatment method of the present invention can efficiently decompose and digest a liquid material containing organic waste by using a fixed bed / fluidized bed hybrid reactor in an anaerobic digester. Since microorganisms involved in digestion are efficiently immobilized on the fixed bed carrier and fluidized bed carrier, the concentration of microorganisms in the tank is high, and digestion digestion proceeds efficiently. As a result, the decomposition rate of organic matter is high, and methane gas Can be generated more quickly, and can be expected to be used not only for the treatment of organic waste but also for a fuel supply device.

Explanatory drawing of the anaerobic digester of the organic waste which concerns on this invention. Electron micrograph of immobilization material Schematic of fixed bed / fluidized bed hybrid (AFFH) reactor Change chart of methane gas amount Results chart of average methane yield in anaerobic digesters Methane concentration chart of each reactor Change of DOC removal rate Changes in methane concentration and methane production rate in biogas during AFFH reactor operation Relationship between organic substance load change and DOC removal rate during AFFH reactor operation Changes in DOC removal rate under organic loading Electron micrograph of the surface of the fluidized bed support after 90 days of continuous operation of the reactor. Electron micrograph of the surface of the fixed bed carrier after 141 days of continuous operation

Explanation of symbols

1. Waste storage tank 2. 2. Raw material waste piping Anaerobic digester 4. Fixed bed carrier 5. Fluidized bed carrier6. 6. Stirring device Digestion gas piping8. 8. Digestion gas storage tank Process piping 10. Solid-liquid separator 11. Processing solid piping,
12 Processed solids storage tank 13. Treatment liquid phase piping 14. Treatment liquid storage tank

Claims (6)

In a method for directly anaerobically treating a liquid material containing organic waste in the presence of digestive microorganisms in an anaerobic digestion tank, a fixed bed carrier whose surface is covered with carbon fiber and a surface made of carbon fiber. A method for treating organic waste, characterized in that a fixed bed / fluidized bed hybrid reactor combined with a fluidized bed carrier in contact with both gas phase and liquid phase in an anaerobic digester is used in the anaerobic digester. . In a method of directly anaerobically treating and digesting an object to be treated made of organic waste in the presence of a carrier for immobilizing a digestive microorganism placed in an anaerobic digestion tank , (I) acid-fermenting microorganisms and / or methane In the presence of anaerobic digested sludge containing fermentable microorganisms, the process object is contacted with a fixed bed carrier and a fluidized bed carrier in contact with both the gas phase and the liquid phase in the anaerobic digester to digest anaerobically (II) separating the digested product obtained in the digestion step into a liquid phase part and a solid phase part, and (III) recovering the solid phase part obtained in the separation step. A characteristic method for treating organic waste. The method for treating organic waste according to claim 2 , wherein the gas phase portion containing methane generated in the step (I) is used as fuel. The method for treating organic waste according to claim 2 , wherein the solid phase portion recovered in the recovery step (III) is an organic fertilizer. An anaerobic digester that directly anaerobically treats liquid waste containing organic waste in the presence of digestive microorganisms in an anaerobic digestion tank, and a fixed-bed carrier whose surface is covered with carbon fiber; A fixed bed / fluidized bed hybrid reactor that is combined with a fluidized bed carrier that is covered with carbon fiber and in contact with both the gas phase and the liquid phase in the anaerobic digester is housed in the anaerobic digester. Anaerobic digester to do. The anaerobic digester according to claim 5 , wherein the fixed bed carrier has a structure in which the surface of the molding resin is covered with carbon felt, and the fluidized bed carrier has a structure in which the foam molding resin is covered with carbon felt.