JP4665693B2 - Method and apparatus for treating organic waste - Google Patents

Description

  The present invention relates to an organic waste processing method and an apparatus for methane fermentation of organic waste, and in particular, solid organic waste having a C / N ratio of 20 or less and a solid concentration of 30% by mass or more. The present invention relates to an object processing method and an apparatus.

  Conventionally, methane fermentation is known as a method of using organic waste as an energy source. In recent years, methane gas has attracted attention as a new energy source. Methane gas is obtained from solid organic waste such as plant residues such as pruned branches, rice straw, and rice husks, food waste, food processing residue, and livestock manure. The technology to extract is drawing attention.

  Here, methane fermentation is roughly classified into wet methane fermentation and dry methane fermentation according to the total solid (TS) concentration of the raw organic waste. In wet methane fermentation, methane sludge containing methane bacteria is retained in a fermenter in a state where it is suspended in a liquid or in a state of being accumulated in a granular form, and organic waste is a liquid having a TS concentration of about 4 to 10% by mass. Or it is introduced into the fermenter in a slurry state. In this way, wet methane fermentation targets liquefied organic waste, so when processing organic waste with a high solids concentration, such as garbage, organic waste prior to methane fermentation. A method for promoting solubilization of methane fermentation has been proposed (for example, Patent Document 1 and Patent Document 2).

  On the other hand, in the dry methane fermentation, the organic waste is introduced into the fermenter in a nearly solid state with a TS concentration of about 25 to 60% by weight, and the TS concentration is about 15 to 40% by mass in the fermenter. Solid methane sludge (dry methane sludge) is retained. As described above, according to dry methane fermentation, solid organic waste can be methane-fermented. Therefore, in recent years, dry methane fermentation has attracted attention as a technology for generating methane gas from solid organic waste as a raw material. Gathered.

  By the way, among solid organic waste, food waste, processed food residue, and livestock manure contain a large amount of protein, that is, organic nitrogen, and the C / N ratio (carbon / nitrogen mass ratio) is as low as 20 or less. . When organic waste with a low C / N ratio (hereinafter referred to as “low C / N organic waste”) is subjected to methane fermentation, organic matter is decomposed to produce methane gas, and organic nitrogen is decomposed at the same time. As a result, ammonia nitrogen is also produced.

The activity of methane bacteria is inhibited by a high concentration of free ammonia nitrogen, and when the ammonium (NH ₄ ⁺ ) concentration in methane sludge exceeds 2,500 mg / kg, the methane fermentation activity is significantly inhibited, and methane fermentation Is known to stop. Therefore, in the methane fermentation treatment of organic waste, prevention of inhibition of methane fermentation activity by free ammonia nitrogen (hereinafter abbreviated as “ammonia inhibition”) is an important technical issue. Various methods have been proposed to prevent inhibition.

As a method for preventing ammonia inhibition, a method of diluting organic waste with water, a method of volatilizing ammonia into the gas phase by passing a gas substantially free of oxygen and ammonia through a mixture in the fermenter, In addition, a method of insolubilizing ammonia by generating magnesium ammonium phosphate (hereinafter, “MAP”) has been proposed. There has also been proposed a method of changing the physicochemical properties of organic waste by mixing a plurality of types of organic waste. For example, in Patent Document 3, prior to methane fermentation, plant residues such as rice husk having a relatively high C / N ratio and tofu cake having a relatively low C / N ratio are mixed, and the resulting mixture is aerobic. A method of fermenting automatically has been proposed.
JP 2001-327998 A JP 2003-39096 A Japanese Patent Laid-Open No. 2002-154887

The problem of ammonia inhibition is a common problem when performing methane fermentation regardless of whether it is dry or wet, but ammonia inhibition is more likely to occur in dry methane fermentation than in wet methane fermentation. That is, in the wet methane fermentation, the organic load on the fermenter is about 2 to 8 kg-VS / m ³ / day, whereas in the dry methane fermentation, the organic load on the fermenter is about 8 to 18 kg-VS / m ³ / day. Therefore, in the first place, dry-type methane fermentation produces more ammonia nitrogen than wet-type methane fermentation.

  For example, when organic waste such as protein having an organic nitrogen concentration of 10,000 mg / kg (wet weight) is subjected to methane fermentation at an organic matter decomposition rate of 50%, 5,000 mg / kg (wet weight) of ammonia nitrogen is produced. appear. Part of the generated ammonia nitrogen is consumed by microorganisms, but as much as 4,000 mg / kg of ammonia nitrogen is present in the sludge during methane fermentation.

  Furthermore, in wet methane fermentation, since methane fermentation is performed in a liquid system, ammonia nitrogen produced in the methane fermentation process is diluted with many liquids. On the other hand, in dry methane fermentation, since the TS concentration of the raw material organic matter is high, it is considered that ammonia nitrogen produced in the process of methane fermentation is dissolved and concentrated in a small amount of water. For this reason, in dry methane fermentation, ammonia inhibition is more likely to occur than in wet methane fermentation, and in particular, when organic waste having a C / N ratio of 20 or less is used as an object to be treated, the problem of ammonia inhibition is likely to occur.

  However, even ammonia prevention methods effective in wet methane fermentation are often not applicable to dry methane fermentation. For example, when organic waste is diluted with water, the TS concentration in the fermenter may be reduced and dry methane fermentation may not be possible. Moreover, when the moisture content of the organic waste put into a fermenter becomes high, the water | moisture content contained in the fermentation residue discharged | emitted from a fermenter will increase, and the cost of processing of a fermentation residue and wastewater treatment will be caused.

  Furthermore, dry methane fermentation is a method in which almost solid dry methane sludge and organic waste are subjected to methane fermentation in a solid phase, and most of the ammonia nitrogen produced by methane fermentation is included in the solid matter. It is in a state dissolved in a small amount of water. For this reason, in dry methane fermentation, it is not easy to volatilize ammonia by injecting gas from which ammonia has been removed, and the balance of nitrogen, phosphorus, and magnesium concentrations in organic waste to be methane-fermented is suitable for MAP production. It is also difficult to generate the MAP while maintaining the above range.

  This invention is made | formed in view of the said subject, and it aims at preventing ammonia inhibition at the time of dry-type methane fermentation of a solid low C / N organic waste. In addition, the present invention makes it possible to perform high-temperature dry methane fermentation at 45 to 60 ° C. without heating the organic waste by steam blowing or the like, and can suppress an increase in the processing cost of the fermentation residue. It aims at providing the processing method of a thing.

  Prior to the methane fermentation process in which dry methane fermentation is performed, the present inventors aerobically ferment organic waste under aerobic conditions, and organic nitrogen contained in organic waste is contained in the cells of aerobic bacteria. The present inventors have found that ammonia inhibition can be prevented by fixing to the present invention, thereby completing the present invention. Specifically, the present invention provides the following.

(1) A part of the organic waste is subjected to aerobic microorganisms by subjecting the organic waste having a C / N ratio of 20 or less and a total solid concentration of 30% by mass or more to aerobic fermentation under aerobic conditions. An aerobic treatment step for obtaining an aerobic fermentation intermediate converted to methane, and a methane fermentation step for mixing the aerobic fermentation intermediate and dry methane sludge having a total solid concentration of 15% by mass or more to dry dry methane fermentation And a method for treating organic waste.

  (2) In the aerobic treatment step, the organic waste is decomposed under aerobic conditions until the organic matter contained in the organic waste becomes 70% by mass or more and 90% by mass or less. Of organic waste.

(3) In the aerobic treatment step, the organic waste is aerobically fermented until the microorganism concentration per dry weight of the aerobic fermentation intermediate is in the range of 10 ⁵ / g to 10 ⁹ / g. The processing method of the organic waste as described in (1) or (2).

(4) The organic waste treatment method according to any one of (1) to (3), wherein high-temperature dry methane fermentation is performed at 45 to 60 ° C. in the methane fermentation step.

(5) An oxygen-containing gas in which solid organic waste having a C / N ratio of 20 or less and a total solid concentration of 30% by mass or more is introduced, and the organic waste is subjected to aerobic fermentation under aerobic conditions. An aerobic fermentation tank having a supply means and an aerobic fermentation intermediate taken out from the aerobic fermentation tank are introduced, and the aerobic fermentation intermediate and dry methane sludge having a total solid concentration of 15% by mass or more are mixed. A methane fermenter in which dry methane fermentation is performed in a state where the organic waste is contained in the organic aerobic fermenter until the organic matter contained in the organic waste becomes 70% by mass or more and 90% by mass or less. Organic waste processing equipment that has the capacity to decompose organic waste.

  The present invention is a method for treating a solid or mud-like organic waste having a total solid concentration of 30% or more, particularly about 35 to 55% by mass (collectively referred to as “solid”). In the present invention, among solid organic wastes, the mass ratio of carbon (C) / nitrogen (N) is 20 or less, preferably 18 or less, particularly preferably about 3 to 12, and the nitrogen content is A large amount of solid organic waste (solid low C / N organic waste) is a suitable treatment target. Specific examples of solid low C / N organic waste include garbage, livestock manure, and food processing residue (hereinafter referred to as “food processing residue”) discharged from establishments such as households and restaurants. Simply referred to as “food residue”). Further, organic sludge dehydrated matter (hereinafter referred to as “dehydrated cake”) generated in connection with sewage and sewage treatment or the like may be the subject of the present invention.

  Organic waste may contain about 1-30 mass% inorganic substance other than organic substance. In this specification, “organic matter” refers to a carbon compound that can be reduced in ignition at 600 ° C., and may be abbreviated as “VS” hereinafter.

  Organic waste is mixed with aerobic fermentation sludge containing aerobic microorganisms, particularly thermophilic aerobic bacteria, and aerobically biotreated while supplying oxygen-containing gas such as air in an aerobic fermenter. In the present invention, in the aerobic treatment step of aerobically fermenting organic waste, the aerobic treatment is terminated in a state where a part of the organic waste is decomposed by the aerobic fermentation sludge, and during the aerobic fermentation The organic waste (aerobic fermentation intermediate) is sent to the methane fermentation process.

  In the aerobic treatment step, it is preferable to maintain the oxygen concentration of the gas discharged outside the tank to be 10% by volume or more by supplying an oxygen-containing gas such as air to the aerobic fermentation tank. Moreover, by adjusting the supply amount of the oxygen-containing gas to the aerobic fermenter, the temperature in the aerobic fermenter is maintained at 60 to 80 ° C., particularly about 65 to 70 ° C. preferable.

  The timing to end the aerobic treatment is an index of any one or more of the weight of organic waste introduced into the aerobic fermenter, the concentration of bacterial cells, and the amount of ammonia generated by the aerobic treatment of organic waste. Can be determined as In addition, the processing time of organic waste necessary until the predetermined amount of organic matter is decomposed, that is, the residence time in the aerobic fermentation tank is obtained by preliminary experiments, and the aerobic treatment is performed when the predetermined residence time has elapsed. May be terminated. By treating in this way, an aerobic fermentation intermediate having a total solid concentration of 30% by mass or more can be obtained.

  If the time for continuing the aerobic treatment is too long, the aerobic fermentation of the organic waste proceeds excessively, and the amount of organic matter to be methane-fermented in the subsequent methane fermentation process is insufficient, resulting in a decrease in the yield of methane gas. On the other hand, if the time for continuing the aerobic treatment is too short, there is a possibility that ammonia inhibition may occur in the methane fermentation process because the amount of organic waste subjected to aerobic fermentation is too small. That is, in the aerobic treatment step, an amount of organic waste that can prevent ammonia inhibition is subjected to aerobic fermentation, and a predetermined amount, for example, at least half of the organic waste is removed from the aerobic fermentation tank without being decomposed. To.

Specifically, as described in (2), when the organic matter contained in the organic waste introduced into the aerobic fermenter is decomposed to 70 to 90% by mass before the aerobic treatment. The aerobic treatment process is terminated. Further, (3) as described in, aerobic fermentation cell concentration of the discharged aerobic fermentation intermediate from tank 10 ⁵ / g or more 10 ⁹ / g they become less aerobic treatment step May be terminated. Alternatively, the amount of ammonia gas generated in the aerobic treatment step is the amount of ammonia gas generated by decomposition of about 1/3 to 2/3 of the organic nitrogen contained in the organic waste. You may make it complete | finish an aerobic treatment process at the time.

Thus, in this invention, the organic waste (aerobic intermediate) in the middle of aerobic fermentation is sent to a methane fermentation tank. In the methane fermentation tank, a methane fermentation process is performed in which the TS concentration is about 15 to 40% by mass, and a dry methane sludge in the form of a mass and an aerobic fermentation intermediate are mixed to perform methane fermentation. Dry methane sludge contains about 10 ^7-9 N / g (dry weight) of methane bacteria as colony forming bacteria count (CFU), compared with wet methane sludge with a TS concentration of about 4-10 mass%. And methane fermentation with high organic load.

The treatment conditions in the methane fermentation process are not particularly limited, and for example, an organic load of 8 to 18 kg-VS / m ³ / day, a temperature of 20 to 60 ° C., a pH of 7 to 9 in the tank in the methane fermentation tank, and residence The time may be about 8 to 15 days. The aerobic fermentation intermediate may be mixed with dry methane sludge inside the methane fermentation tank, but the fermentation residue that is extracted from the methane fermentation tank and returned to the methane fermentation tank as return sludge is removed outside the methane fermentation tank. It is preferable to mix with an aerobic fermentation intermediate.

  In the present invention, the organic waste is aerobically fermented in the aerobic treatment step, so that the aerobic fermentation intermediate taken out from the aerobic fermentation tank is about 60 to 80 ° C. For this reason, in this invention, the inside of the tank of a methane fermentation tank can be maintained at 45-60 degreeC, without heating a methane fermentation raw material, and high temperature methane fermentation can be performed as described in (4). When performing high temperature methane fermentation, since the fermentation residue withdrawn from the methane fermentation tank is about 50 ° C., the aerobic fermentation intermediate and the fermentation residue are mixed at a mass ratio of 1: 2 to 20 to perform methane fermentation. It is preferable.

  The organic waste processing method according to the present invention can be carried out using an organic waste processing apparatus including an aerobic fermentation tank provided with oxygen-containing gas supply means and a methane fermentation tank capable of maintaining anaerobic conditions. . In the present invention, in particular, the aerobic fermenter is configured so that the entire amount of decomposable organic waste is taken out of the tank before being aerobically fermented.

  That is, the organic waste stay days (fermentation days) in the aerobic fermenter is about 3 to 40 days depending on the aerobic fermenter volume, the type of organic waste, and the like. Since only a part of the organic waste is decomposed aerobically, it is shorter than the case where almost all the organic waste is decomposed aerobically. Therefore, in the aerobic fermenter, only a part of the organic waste is aerobically decomposed as described in (5), and the remaining part, for example, more than half of the organic waste is discharged without being decomposed. It is preferable to design to have a capacity.

  In this invention, before carrying out methane fermentation of organic waste, the ammonia inhibition in a methane fermentation process is prevented by aerobically decomposing a part of organic waste. The details of this mechanism of action are not clear, but by aerobically decomposing only a portion of the organic waste, a portion of the organic nitrogen contained in the organic waste is taken up by the aerobic microorganism. It is presumed that ammonia inhibition during methane fermentation can be prevented by fixing to aerobic microorganisms.

  That is, in the aerobic treatment process, a part of the organic waste introduced into the aerobic fermenter is mineralized by the metabolic activity of aerobic microorganisms to generate carbon dioxide, water, ammonia gas, and the like. Aerobic microorganisms grow. Aerobic microorganisms have a C / N ratio of about 4 to 5 and a high nitrogen content ratio. Particularly, a large amount of glutamate dehydrogenase (GDH) is contained in the cytoplasm of thermophilic bacteria. Since such microorganisms have cell walls that are difficult to biodegrade, such as chitin, nitrogen incorporated in the microorganisms is difficult to be decomposed in the methane fermentation process. For this reason, a part of the organic waste, for example, about 30% by mass is aerobically decomposed in the aerobic treatment process, so that a part of the organic nitrogen contained in the organic waste is retained in the microbial cells, and methane This is thought to reduce the amount of ammonia produced in the fermentation process.

  Thus, according to this invention, ammonia inhibition in a methane fermentation process can be suppressed by converting a part of organic waste into a microbial cell by aerobic fermentation. In addition, since the temperature of organic waste rises by aerobic fermentation of organic waste in the aerobic treatment process, high-temperature methane is not heated by blowing steam into the fermentation raw material to be put into the methane fermentation tank. Can be fermented. For this reason, the equipment for heating a fermentation raw material and an operating cost can be reduced. Furthermore, conventionally, since the moisture content of the fermentation raw material is increased by about 10% by blowing steam for heating, there is a problem in that the solid content in the methane fermentation tank is decreased and the moisture content of the fermentation residue is increased. However, according to the present invention, such a problem can be avoided. In addition, according to the present invention, solid low C / N organic waste can be fermented with methane without being mixed with other organic waste having a high C / N ratio. Can be avoided.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of an organic waste processing apparatus 11 according to an embodiment of the present invention. The processing apparatus 11 includes an aerobic fermentation tank 21, a mixing apparatus 23, and a methane fermentation tank 25.

  The aerobic fermenter 21 includes an aeration fan 22 that is an oxygen-containing gas supply unit that blows in air as an oxygen-containing gas, and a deodorizing device 24 that processes exhaust gas containing ammonia. The aerobic fermentation tank 21 is connected to the mixing device 23 via the transfer path 31. The mixing device 23 is connected to the methane fermentation tank 25 via the introduction path 33 and the sludge return path 36, and a part of the fermentation residue discharged from the methane fermentation tank 25 is mixed as return sludge containing dry methane sludge. Sent to the device 23. In the mixing device 23, the aerobic fermentation intermediate sent from the aerobic fermentation tank 21 via the transfer path 31 and the return sludge returned from the methane fermentation tank 25 via the sludge return path 36 are mixed, and the mixture is mixed. Is introduced into the methane fermentation tank 25 via the introduction path 33.

  Thus, if it is set as the structure which mixes dry-type methane sludge and organic waste outside the methane fermentation tank 25, even if it is a solid substance whose TS density | concentration is about 30-70 mass%, without adding dilution water. Can be mixed with dry methane sludge. Moreover, since it is not necessary to stir the inside of the methane fermentation tank 25, it becomes easy to maintain the inside of the methane fermentation tank 25 under anaerobic conditions. However, the present invention does not exclude a method of mixing dry methane sludge with fermentation raw materials inside the methane fermentation tank 25 by providing a stirring means inside the methane fermentation tank 25. Also, one end edge of the sludge return path 36 may be connected between the mixing device 23 and the methane fermentation tank 25.

  The methane fermentation tank 25 is further connected to a waste mud passage 35 and a gas passage 37, and the contents in the tank subjected to methane fermentation in the methane fermentation tank 25 (a methane fermentation product of dry methane sludge and an aerobic fermentation intermediate) ) Is taken out from the mud passage 35 as a fermentation residue. A sludge return path 36 is connected in the middle of the waste mud path 35, and a part of the fermentation residue is returned as return sludge. The fermentation residue that is not used as return sludge may be used as a raw material for producing compost, carbide, etc. In such a case, the waste mud passage 35 may be connected to one or both of a composting device and a carbonizing device. .

  The gas path 37 is connected to a gas purification device 27 that purifies methane gas. The gas purifier 27 is connected to the gas tank G, and the purified methane gas is stored in the gas tank G.

  In addition, although the processing apparatus 11 is comprised as an apparatus which performs 45-60 degreeC high temperature methane fermentation, the mixing apparatus 23 is not provided with the heating means. In the present invention, since the aerobic fermentation intermediate that has been aerobically fermented in the aerobic fermenter 21 and heated to about 60 to 80 ° C. is used as a fermentation raw material of the methane fermenter 25, This is because heating is unnecessary.

  That is, conventionally, about 10% by mass of steam is blown into the organic waste introduced into the methane fermentation tank 25 for heating, which causes a decrease in the TS concentration. Since heating is not required, it is possible to improve the yield of methane gas by preventing a decrease in TS concentration in the 25 methane fermentation tanks. Moreover, since the moisture content of the fermentation residue discharged | emitted from the methane fermenter 25 can be reduced, the generation amount of a fermentation residue is reduced and the moisture of a fermentation residue is evaporated when using a fermentation residue as raw materials, such as compost. It is also possible to reduce the amount of energy required to make it happen.

  Next, the organic waste processing method using the processing apparatus 11 will be described. In the present invention, a solid low C / N organic waste having a C / N ratio of 20 or less and a TS concentration of 30% by mass or more is used as a raw material.

  First, prior to the methane fermentation process, organic waste is introduced into the aerobic fermentation tank 21 and processed in the aerobic treatment process. In the aerobic treatment process, for example, the mass of the organic waste is 10 to 30% by mass until the part of the organic waste is aerobically decomposed while supplying air from the ventilation fan 22 to the aerobic fermenter 21. Biodegradation under aerobic conditions until dry weight decreases. The exhaust gas discharged from the aerobic fermentation tank 21 as air is blown is preferably processed by the deodorizing device 24 as in the present embodiment. Moreover, it is preferable to provide a stirrer (not shown) or the like in the aerobic fermentation tank 21 as necessary, and to make the entire aerobic fermentation tank 21 an aerobic condition.

  The inside of the aerobic fermentation tank 21 is preferably maintained at 60 to 80 ° C., and it is preferable to adjust the amount of ventilation from the ventilation fan 22 as necessary to prevent a temperature drop. Moreover, in order to prevent the yield reduction of the methane gas generated in the methane fermentation process provided in the latter stage of the aerobic treatment process, the aerobic fermentation tank 21 before the organic waste is excessively aerobically decomposed in the aerobic treatment process. The product in the tank is taken out and supplied from the transfer path 31 to the mixing device 23.

  In the mixing apparatus 23, the returned sludge of about 50 ° C. returned from the methane fermentation tank 25 and the aerobic fermentation intermediate supplied from the aerobic fermentation tank 21 are mixed, and this mixture is used as a methane fermentation raw material to produce methane fermentation. Supply to tank 25.

  The methane fermentation tank 25 holds dry methane obtained by acclimatizing methane sludge of an existing apparatus as seed sludge through a startup process or the like in advance, and the mixture is subjected to methane fermentation as anaerobic conditions. In the present invention, since the aerobic fermentation intermediate heated in the process of aerobic fermentation in the aerobic treatment step is used as a methane fermentation raw material, in the methane fermentation tank 25 without providing the mixing device 23 with a heating means. High-temperature methane fermentation can be performed at a tank temperature of about 45-60 ° C. The mixture introduced into the methane fermentation tank 25 is moved to the lower part of the methane fermentation tank 25 with the introduction of a new mixture while being decomposed by the action of the dry methane sludge, and is taken out from the mud passage 35 as a fermentation residue.

  The extraction amount of the fermentation residue from the methane fermentation tank 25 per day is preferably 0.1 to 1 times, particularly 0.2 to 0.5 times that in the tank. Moreover, it is preferable to circulate a part of the extracted fermentation residue to the methane fermentation tank 25 via the sludge return path 36 so that the circulation ratio is 1 to 6 times / week. The returned sludge may be directly circulated to the methane fermentation tank 25 without being mixed with the fermentation raw material. However, by mixing the returned sludge and the fermentation raw material outside the methane fermentation tank 25, methane bacteria can be easily dispersed in the fermentation raw material having a high TS concentration, and the methane fermentation conditions in the methane fermentation tank 25 can be reduced. Since disturbance can be prevented, the returned sludge is preferably returned to the mixing device 23.

  Of the fermentation residue taken out from the methane fermenter 25, the surplus excluding the return sludge is supplied from the mud passage 35 to a composting device or the like, and can be used as a raw material for compost or the like. Further, methane gas generated by methane fermentation of organic waste in the methane fermentation tank 25 can be taken out from the gas passage 37 to the outside of the methane fermentation tank 25 and used as an energy source.

[Example 1]
As Example 1, chicken manure was treated as a solid low C / N organic waste using the treatment apparatus 11 shown in FIG. Chicken manure has a moisture content of 70% by weight, organic matter concentration of 78% by weight (dry weight), total nitrogen (TN) concentration of 28,000 mg / kg (wet weight), ammonia concentration of 4,000 mg / kg (wet weight), C The / N ratio was 4.2.

  The chicken manure was subjected to aerobic treatment in the aerobic fermentation tank 21, and the obtained aerobic fermentation intermediate was taken out from the aerobic fermentation tank 21. The conditions of the aerobic treatment in the aerobic fermenter 21 are as follows, and 13,607 kg / day (wet weight) of the aerobic fermentation intermediate is obtained in this aerobic treatment step, and 84.15 kg / day of ammonia. Volatilized into the gas phase.

[Aerobic treatment conditions]
Tank volume; 312m ³
Aerobic treatment days: 10-day organic matter (VS) decomposition rate: 24% by mass
Organic waste input amount: 25,000 kg / day

  The aerobic fermentation intermediate obtained in the aerobic treatment step described above has a water content of 51.8% by mass, an organic substance concentration of 62.1% by mass (dry weight), and a TN concentration of 22,000 mg / kg (wet weight). The ammonia concentration was 1,500 mg / kg (wet weight), the C / N ratio was 68, and the temperature was 65 ° C.

  The aerobic fermentation intermediate is sent to the mixing device 23 through the transfer path 31 and mixed with the return sludge (dry methane sludge) returned from the methane fermentation tank 25 by the mixing apparatus 23 and then into the methane fermentation tank 25. Feed and ferment methane. The conditions of methane fermentation in the methane fermentation tank 25 are shown below.

[Methane fermentation conditions]
Tank volume; 462 m ³
Methane fermentation days: 34 days organic matter (VS) decomposition rate: 45% by mass
Aerobic fermentation intermediate input amount; 13,607 kg / day return sludge amount; 130,000 kg / day temperature in tank; 50-55 ° C.

The amount of methane gas obtained by methane fermentation under the above conditions was 1,780 Nm ³ , and 11,800 kg / day of fermentation residue was taken out from the methane fermentation tank 25. Fermentation residue is 60% by mass water content, ammonium (NH ₄ ⁺ ) concentration of 2,000 mg / kg (wet weight), temperature of 52 ° C., solid low C / N organic waste in treatment using treatment device 11 The overall weight loss rate was 52.8% by mass. Moreover, in Example 1, since the blowing of the steam to the methane fermentation raw material thrown into the methane fermentation tank 25 and the drying of the fermentation residue taken out from the methane fermentation tank 25 were unnecessary, the methane gas taken out from the methane fermentation tank 25 Was stored in the gas tank G. In Example 1, ammonia inhibition did not occur during the treatment period of 90 days.

[Comparative Example 1]
As Comparative Example 1, an experiment using the processing apparatus 12 according to the conventional flow shown in FIG. The processing device 12 is different from the processing device 11 in the following points. First, the processing apparatus 12 does not include an aerobic fermentation tank, and is configured such that steam is blown into the mixing apparatus 23 by connecting a steam generator 26 to the methane fermentation tank 25. Further, the processing device 12 is provided with a drying means 28 for reducing the moisture content of the fermentation residue discharged from the methane fermentation tank 25, and a composting device 29A for fermenting the fermentation residue aerobically and composting. Hereinafter, the process of the solid low C / N organic waste (chicken manure) by the processing apparatus 12 will be described.

  In the processing device 12, the chicken manure is sent to the mixing device 23 from the storage tank 20 that temporarily stores it. Steam is supplied from the steam generator 26 to the mixing device 23, and the chicken manure heated by the blowing of steam is sent to the methane fermentation tank 25 as a solid low C / N organic waste. In order to generate steam to be supplied to the mixing device 23, a steam generator 26 is connected to the methane fermentation tank 25. The steam generator 26 generates steam using methane gas extracted from the methane fermentation tank 25 as an energy source. Furthermore, drying means 28 for generating warm air using methane gas as an energy source and blowing this warm air into the fermentation residue is connected to the composting device 29A.

  Using this processing apparatus 12, chicken feces having the same properties as those used in Example 1 were processed. The processing conditions of the methane fermentation tank 25 were as follows.

[Methane fermentation conditions]
Tank volume; 593m ³
Methane fermentation days: 24 days organic matter (VS) decomposition rate: 45% by mass
Organic waste input amount; 25,000 kg / day return sludge amount; 250,000 kg / day temperature in tank; 52 ° C.

The amount of methane gas obtained by methane fermentation under the above conditions was 2,300 Nm ³ , and 25,100 kg / day of fermentation residue was taken out from the methane fermentation tank 25. The fermentation residue had a moisture content of 79.4% by mass, and the ammonium (NH ₄ ⁺ ) concentration exceeded 2,500 mg / kg (wet weight) 20 days after the start of the treatment, and the treatment could not be continued due to ammonia inhibition.

  During the experiment period until the treatment was stopped, the fermentation residue was composted by aerobic fermentation using the composting device 29A except for the portion returned to the mixing device 23 as return sludge. The processing conditions for composting are shown below.

[Composting conditions]
Tank volume; 542 m ³
Aerobic treatment days: 14 days organic matter (VS) decomposition rate: 10% by mass
Fermentation residue input; 25,100 kg / day temperature; 60 ° C

The compost obtained by the composting treatment under the above conditions has a moisture content of 60% by mass, and the amount of compost obtained is 14,164 kg / day, which is a solid low C / N in the treatment using the treatment device 12 The weight loss rate of the whole organic waste was 43.3% by mass. Further, yield of methane gas that is removed from the methane fermentation tank 25 was the 2,300Nm ^3, these, 460 nm ³ is used for steam generation in the steam generator 26, 1,172Nm ³ is dried fermentation residue It was used to generate warm air for As a result, the amount of methane gas stored in the gas tank G was 668 Nm ³ .

[Comparative Example 2]
As the comparative example 2, the processing apparatus 12 of FIG. 2 was used, and the mixture which mixed the paper with the chicken manure used in Example 1 was processed. The paper had a water content of 15% by mass, an organic substance concentration of 25.2% by mass (dry weight), a TN concentration of 1,900 mg / kg (wet weight), and an ammonia concentration of 0 mg / kg (wet weight). Chicken manure was mixed so as to be treated at a throughput of 25,000 kg / day and paper was treated at a throughput of 50,000 kg / day, and the mixture of paper and chicken manure was further diluted with 60,000 kg / day of diluted water.

Dilution of the mixture of chicken manure and paper (methane fermentation raw material) supplied from the mixing device 23 to the methane fermentation tank 25 has a moisture content of 66 mass% after heating by steam blowing, and an organic matter concentration of 86 mass% ( Dry weight), TN concentration 6,800 mg / kg (wet weight), ammonium (NH ₄ ⁺ ) concentration 700 mg / kg (wet weight), C / N ratio 26, and temperature 55 ° C. The methane fermentation treatment conditions in Comparative Example 2 are shown below.

[Methane fermentation conditions]
Tank volume; 4,958m ³
Methane fermentation days: 36 days organic matter (VS) decomposition rate: 48% by mass
Input amount of organic waste; 135,000 kg / day return sludge amount; 810,000 kg / day temperature in tank; 52 ° C.

The amount of methane gas obtained by methane fermentation under the above conditions was 19,300 Nm ³ , and 128,000 kg / day of fermentation residue was taken out from the methane fermentation tank 25. The fermentation residue had a moisture content of 76.2% by mass, an ammonium (NH ₄ ⁺ ) concentration of 2,000 mg / kg, and no ammonia inhibition occurred during the 14-day treatment period.

  During the experiment period, the fermentation residue was composted by aerobic fermentation using the composting device 29A except for the portion returned to the mixing device 23 as return sludge. The processing conditions for composting are shown below.

[Composting conditions]
Tank volume; 2,286 m ³
Aerobic treatment days: 14 days organic matter (VS) decomposition rate: 10% by mass
Fermentation residue input amount: 810,000 kg / day temperature in the tank; 60 ° C

The compost obtained by the composting treatment under the above conditions had a moisture content of 60% by mass, and the amount of compost obtained was 124,811 kg / day. In Comparative Example 2, since the paper with a high C / N ratio was added to the chicken dung, which is a solid low C / N organic waste, and processed, the fermentation residue was composted and reduced in weight, but was still put into the processing device 12. The amount of compost exceeded the amount of chicken manure. As a result, the weight loss rate of only the solid low C / N organic waste was -66.4% by mass. The yield of methane gas taken out from the methane fermentation tank 25 was 19,300 Nm ³ , of which 2,390 Nm ³ was used for steam generation in the steam generator 26 and 5,443 Nm ³ was fermentation residue. It was used to generate hot air to dry the water. As a result, the amount of methane gas stored in the gas tank G was 11,467 Nm ³ .

  In Table 1, with respect to Example 1, Comparative Example 1 and Comparative Example 2, the amount of methane gas taken out from the methane fermentation tank 25, the amount of methane gas stored in the gas tank G, and the weight loss rate of solid low C / N organic waste (Wet weight) and the total volume of the processing tank of the entire processing apparatus are shown.

  In Comparative Example 1 in which solid low C / N organic waste was treated, ammonia inhibition occurred as a result of not performing aerobic fermentation prior to methane fermentation. In Comparative Example 2, the solid low C / N organic waste was mixed with paper having a high C / N ratio, and further diluted water was added, so that ammonia inhibition could be prevented, but the fermentation supplied to the methane fermentation tank 25. The TS concentration of the raw material decreased, and the moisture content of the fermentation residue increased. Moreover, in the comparative example 2, other organic wastes, such as paper added to a solid low C / N organic waste, are required, and the enlargement of the processing apparatus was caused.

  On the other hand, in Example 1 in which solid low C / N organic waste was treated alone as in Comparative Example 1, ammonia inhibition was prevented by performing aerobic fermentation at a decomposition rate of 24% by mass prior to methane fermentation. did it. Further, since steam for heating the methane fermentation raw material supplied to the methane fermentation tank and hot air for drying the fermentation residue are unnecessary, it is possible to operate with energy saving. Furthermore, since it is not necessary to mix paper or the like with solid low C / N organic waste, it is not necessary to secure organic waste for adjusting the C / N ratio, and the processing apparatus can be downsized.

  The present invention can be used to produce methane gas using organic waste as a raw material.

It is a schematic diagram which shows the processing apparatus of the organic waste which concerns on one Embodiment of this invention. It is a schematic diagram which shows the processing apparatus of the organic waste which concerns on a prior art.

Explanation of symbols

11, 12 Treatment device 21 Aerobic fermenter 22 Ventilation fan (oxygen-containing gas supply means)
23 Mixing device 24 Deodorizing device 25 Methane fermentation tank 27 Gas purification device 31 Transfer path 33 Introduction path 35 Drainage path 36 Sludge return path G Gas tank

Claims (5)

By aerobically fermenting organic waste with a C / N ratio of 20 or less and a total solid concentration of 30% by mass or more under aerobic conditions, a part of the organic waste is converted into aerobic microorganisms. An aerobic treatment step for obtaining an aerobic fermentation intermediate;
A method for treating organic waste, comprising: a methane fermentation step in which the aerobic fermentation intermediate and dry methane sludge having a total solid concentration of 15% by mass or more are mixed and subjected to dry methane fermentation. The organic matter according to claim 1, wherein in the aerobic treatment step, the organic waste is decomposed under aerobic conditions until the organic matter contained in the organic waste becomes 70 mass% or more and 90 mass% or less. Waste disposal method. In the aerobic treatment step, the organic waste is subjected to aerobic fermentation until the microorganism concentration per dry weight of the aerobic fermentation intermediate is in the range of 105 / g to 109 / g. 2. The method for treating organic waste according to 2. The processing method of the organic waste in any one of Claim 1 to 3 which performs high temperature dry methane fermentation at 45-60 degreeC in the said methane fermentation process. An oxygen-containing gas supply means for introducing a solid organic waste having a C / N ratio of 20 or less and a total solids concentration of 30% by mass or more and aerobically fermenting the organic waste under aerobic conditions An aerobic fermenter, and
The aerobic fermentation intermediate taken out from the aerobic fermentation tank is introduced, and dry methane fermentation is performed in a state where the aerobic fermentation intermediate and dry methane sludge having a total solid concentration of 15% by mass or more are mixed. A methane fermentation tank,
The aerobic fermenter is an organic waste processing apparatus having a capacity for decomposing the organic waste until the organic waste contained in the organic waste reaches 70% by mass or more and 90% by mass or less.

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