JP2006224062A - Methane fermentation treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation method and equipment capable of efficiently performing methane fermentation of organic waste including bio-degradable plastic. <P>SOLUTION: Material to be treated comprising a mixture of the bio-degradable plastic and the organic waste is crushed by a crusher 1 and, thereafter, is fed to a mixing device 3 via a transfer device 2. Water vapor is supplied from a pipe 12 for water vapor in the transfer device 2, thereby, crushed material is quickly heated and the bio-degradable plastic in the crushed material is heat-melted. The crushed material to be treated including heat-melted bio-degradable plastic is introduced to the mixing device 3 and is mixed with methane-fermented sludge which is returned from a dry methane fermentation tank 5. The mixture in the mixing device 3 is fed into the dry methane fermentation tank 5 via a pump 4 and is subjected to methane fermentation. A part of bio-gas produced in the dry methane fermentation tank 5 is taken out of the upper part of the tank 5 through a pipe 9 as excess gas. The remaining part of the bio-gas is sent to a boiler 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for subjecting biodegradable plastics to methane fermentation treatment with organic waste such as garbage, food processing residue, surplus sludge such as activated sludge treatment.

  In the methane fermentation treatment of organic waste, the organic waste is pulverized and slurried, and then this slurry is put into a fermenter and fermented with methane bacteria under anaerobic conditions to convert the organic waste into biogas. It is a method of decomposing it into water, and has the merit that organic waste can be greatly reduced and methane gas produced as a by-product can be recovered as energy. In addition, since it is anaerobic and does not require aeration power, it is an energy-saving treatment method.

  Among the organic wastes described above, wastes that generate a strange odor such as garbage are generally collected in plastic bags or the like. However, since ordinary plastic does not have degradability, prior separation such as unpacking is required in the methane fermentation treatment. Since such separation is troublesome, it is considered that the plastic bag is biodegradable together with organic waste without sorting by using the above-mentioned plastic as a biodegradable plastic.

  However, the degradation rate of biodegradable plastics is slower than that of organic waste such as garbage, so when both are subjected to methane fermentation at the same time, undegraded plastic remains in the methane fermentation tank. End up.

As a method for efficiently fermenting a mixture of biodegradable plastic and organic waste as described above, JP-A-2001-269652 contains organic waste mixed with biodegradable plastic products. A biodegradable plastic product is mixed using an organic waste treatment apparatus comprising a treatment tank, a blower for sending air into the treatment tank, and a heating facility capable of heating the treatment tank. The disclosed organic waste is heated in the treatment tank at 60 to 100 ° C. for 1 to 48 hours to disintegrate the biodegradable plastic product, and then subjected to methane fermentation treatment.
JP 2001-269652 A

  However, in the methane fermentation treatment method described in JP-A-2001-269652, the decomposition process of the biodegradable plastic product requires a long time of 1 to 48 hours, and the treatment efficiency is not good. In addition, when such a high temperature treatment is performed for a long time, the activity of the bacteria in the organic waste is reduced, and the decomposition of the biodegradable plastic may be inhibited.

  In addition, in order to efficiently process organic waste by the methane fermentation method, a process of finely crushing organic waste is required, but plastic garbage collection bags, fish boxes, etc. The molded product is difficult to be miniaturized, and the organic waste is not sufficiently miniaturized, which may reduce the processing efficiency.

  The objective of this invention is providing the method and apparatus which can perform the methane fermentation process of the organic waste containing a biodegradable plastic efficiently.

  The method for methane fermentation treatment according to claim 1 is a method for methane fermentation treatment of a mixture of biodegradable plastic and organic waste, wherein the mixture is heated by bringing steam into contact with the mixture, and the biodegradable plastic in the mixture is heated. It has a melting step for melting at least a part, and then a methane fermentation treatment step for subjecting the mixture to a methane fermentation treatment.

  The methane fermentation treatment method according to claim 2 is characterized in that, in claim 1, a part of the methane fermentation treatment product from the methane fermentation treatment step is added to the mixture in the melting step.

  A methane fermentation treatment method according to a third aspect is characterized in that, in the first or second aspect, the biodegradable plastic and the organic waste are crushed and then supplied to the melting step.

  A methane fermentation treatment method according to a fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein the temperature of the water vapor is 70 to 120 ° C, and the temperature of the object to be treated supplied to the methane fermentation process is the methane fermentation process. It is characterized by being higher than the temperature at.

  The methane fermentation treatment method according to claim 5 is characterized in that, in any one of claims 1 to 4, the melting treatment time in the melting step is 3 to 60 minutes.

  A methane fermentation treatment apparatus according to claim 6 is provided with a melting means for bringing water vapor into contact with a mixture of the biodegradable plastic and the organic waste to melt at least a part of the biodegradable plastic, A water vapor supply means for supplying water vapor and a methane fermentation tank for receiving a mixture from the melting means and performing a methane fermentation treatment are provided.

  According to a seventh aspect of the present invention, there is provided the methane fermentation treatment apparatus according to the sixth aspect, further comprising means for adding a part of the processed product of the methane fermentation tank to the melting means.

  The methane fermentation treatment apparatus according to claim 8 is provided with a crushing means for crushing the biodegradable plastic and the organic waste in claim 6 or 7, and supplying the crushed material in the crushing means to the melting means. It is characterized by comprising.

  According to the methane fermentation treatment method and apparatus of the present invention, a mixture of biodegradable plastic and organic waste is heated by bringing water vapor into contact with the mixture to melt the biodegradable plastic. The methane fermentation treatment can be performed efficiently. Moreover, since water vapor has a large latent heat, the mixture is heated and melted in a short time (for example, within 60 minutes), and the processing time is shortened. In addition, since the heating time is short in this way, even when a part of the processed methane fermentation tank is added to the mixture, the decrease in the activity of methane bacteria is suppressed.

  Prior to the melting of the mixture, the biodegradable plastic and the organic waste are crushed to improve the melting treatment efficiency and the methane fermentation treatment efficiency.

  When performing steam heating of this mixture, by adding a part of the processed methane fermentation tank, methane fermentation bacteria are uniformly added to the object to be processed and the methane fermentation treatment efficiency is further improved.

  When the temperature of the water vapor is increased to 70 ° C. or higher, the temperature of the object to be treated supplied to the methane fermentation process becomes higher than the temperature of the methane fermentation process. By mixing with the return sludge in the mixing process, methane fermentation The temperature can be reduced to a temperature suitable for.

  According to the present invention, organic waste such as garbage disposed in a biodegradable plastic bag can be efficiently subjected to methane fermentation without using a bag opener.

  Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a system diagram showing a methane fermentation treatment method and apparatus according to an embodiment.

  Raw materials in a biodegradable plastic bag, or a biodegradable plastic fish box, food box, etc., made of a mixture of biodegradable plastic and organic waste, are processed by a crusher 1. After being crushed, it is sent to the mixing device 3 via a screw-type transfer device 2 in which a screw is arranged in the pipe. By supplying water vapor from the water vapor pipe 12 in the transfer device 2, the crushed material is rapidly heated, and at least a part, preferably more than half, of the biodegradable plastic in the crushed material is thermally melted. The to-be-processed crushed material containing the biodegradable plastics thus melted is introduced into the mixing device 3 and mixed with the methane fermentation sludge returned from the dry methane fermentation tank 5. The melted biodegradable plastic is finely dispersed in the mixture and reduced in temperature to 60 ° C. or less by mixing in the mixing device 3.

  In addition, as will be described later, the amount of sludge returned is as large as about 3 to 50 times the amount of crushed material introduced from the transfer device 2. Since the temperature of methane fermentation sludge is normally about 50-55 degreeC, the temperature of the mixture sent out from the mixing apparatus 3 to the methane fermentation tank 5 is 55-57 degreeC by supplying water vapor | steam from the piping 13 with respect to the mixing apparatus 3. FIG. It is preferable that the temperature is slightly higher than the temperature in the methane fermentation tank 5. Thereby, the temperature in the methane fermentation tank 5 is raised, and methane fermentation efficiency improves.

  The mixture in the mixing device 3 is sent to the dry methane fermentation tank 5 via the pump 4 and subjected to methane fermentation treatment. Although illustration is omitted, in the methane fermentation tank 5, there is a relatively high concentration of sludge having a sludge concentration of 15 to 40% by weight, and the material to be treated is sufficiently mixed with the methane fermentation bacteria by mixing with the returned sludge. Since it is supplied to the methane fermenter in a state where the methane is fermented, the methane fermentation proceeds sufficiently without stirring the inside of the methane fermenter.

  Moreover, when the sludge concentration is high, the residence time in the tank may be as long as about 90 days, but the load of methane fermentation does not change, and biogas can be recovered with a constant efficiency. The fermentation temperature in the methane fermentation tank 5 is preferably about 50 to 55 ° C., particularly about 50 to 53 ° C., and the residence time in the tank is preferably about 18 to 90 days.

  A part of the methane fermentation sludge generated by the fermentation reaction is discharged as a residue from the bottom of the tank 5 through the screw-type transfer device 6, and the remainder of the sludge is mixed via the screw-type transfer device 7 as described above. Supplied to the device 3. A part of the biogas produced in the dry methane fermentation tank 5 is taken out from the pipe 9 as surplus gas from the upper part of the tank 5. The remainder of the biogas is sent to the boiler 10. Water vapor generated in the boiler 10 is supplied from the pipe 11 to the transfer device 2 through the pipe 12 and supplied to the mixing device 3 through the pipe 13.

In this biodegradable plastic and organic waste treatment system, the temperature of water vapor supplied from the pipes 12 and 13 to the transfer device 2 and the mixing device 3 is 70 to 120 ° C, preferably 100 to 120 ° C, and the pressure is 0. 3 kg / cm ² or more and preferably 1.2~2.0kg / cm ² approximately. By supplying this high-temperature steam from the pipe 12 into the transfer device 2, the crushed material in the transfer device 2 is rapidly heated. A normal biodegradable plastic has a glass transition temperature of around 60 ° C., and supplies water vapor of 70 ° C. or more from the pipe 12 to the transfer device 2 to heat the object to be processed to 70 to 120 ° C., preferably 100 to 120 ° C. By doing so, the biodegradable plastic is melted in a short time of about 3 to 60 minutes, for example, about 5 to 20 minutes, and this biodegradable plastic is finely dispersed in the mixture in the mixing device 3.

  If the water vapor temperature is 120 ° C. or higher, the temperature of the material to be treated becomes higher than 60 ° C. when transferred to the methane fermentation tank even if the temperature is neutralized by mixing with the return sludge in the mixing step. Is unfavorable because of lowering.

  Moreover, although high energy is required for the production | generation of high temperature steam, since this embodiment is an energy self-supporting type using the energy (biogas) collect | recovered by methane fermentation, it produces | generates high temperature steam efficiently. Can do.

Ratio B of methane fermentation sludge amount B (kg) returned to mixing device 3 per unit time and total amount A (kg) of new feed biodegradable plastic and organic waste introduced into mixing device 3 / A is preferably about 3-50, particularly about 5-15. By increasing the amount of sludge returned in this way, even if some methane bacteria are damaged by contact with high-temperature steam in the mixing device 3, the mixture sent from the mixing device 3 to the dry methane fermentation tank 5 A large amount of methane bacteria remain in the methane fermenter, and the methane fermentation process is efficiently performed in the dry methane fermentation tank 5. According to the present invention, it is possible to set the decomposition rate of organic matter by methane fermentation in the tank 5 to about 1 to 10 kgVS / m ³ · day.

  Although it does not specifically limit as organic waste which is a candidate for treatment of the present invention, such as food waste discharged from restaurants and general households, food processing residue discharged from food factories, manure, activated sludge treatment, etc. Excess sludge etc. can be illustrated.

  Examples of the biodegradable plastic include a packaging bag for storing the above organic waste. In addition, molded products such as fish boxes and tableware made of biodegradable plastics can be decomposed according to the present invention.

  The biodegradable plastic is not particularly limited, and examples thereof include microbial production systems such as polyhydroxybutyrate (polyhydroxybutyrate), polylactic acid (polylactide), poly-ε-caprolactone, polybutylene succinate, polyethylene succinate, polyethylene Chemical synthesis systems such as terephthalate modified type, starch systems such as modified starch and cellulose acetate can be treated.

  Hereinafter, experimental examples and examples will be described.

Experimental example 1
A 0.02 kg bag made of polylactic acid as a biodegradable plastic is melted by bringing water vapor at a temperature of 110 ° C. and a pressure of 1.5 kg / cm ² into contact for 15 minutes and then supplying it to a batch-type methane fermenter with an internal volume of 3 L. Then, methane fermentation treatment was performed at a temperature of 55 ° C. for 7 days. The cumulative amount of biomass generated at this time is shown in FIG. As shown in FIG. 2, it was found that almost all of the biodegradable plastic could be decomposed by the treatment for about 7 days.

Example 1
The following input raw materials were processed under the following conditions by the methane fermentation treatment apparatus shown in FIG.
The biodegradable plastic is a polylactic acid bag, and a bag containing household garbage and wrapping paper in this bag was used as an object to be processed. The volume of the methane fermentation tank 5 is 700L.
[Processed object]
Biodegradable plastic 1kg / day Moisture content 0%; Loss on ignition: 99%
Household garbage 5 kg / day, moisture content 80%; loss on ignition: 90%
Wrapping paper 2kg / day, moisture content 10%; loss on ignition: 95%
Methane fermenter return sludge 3.6kg / day [injected steam volume and temperature]
Injection steam volume: 1.0 kg / day from piping 12
From pipe 13 0.5 kg / day Steam pressure: 1.5 kg / cm ²
As a result, biogas was produced at a biogas generation amount of 2.9 Nm ³ / day (methane concentration 60%), and the water content of the methane fermentation sludge was 81%.

It is a flowchart which shows the methane fermentation processing method which concerns on embodiment. It is a graph which shows the result of an example of an experiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crusher 2 Crushed material transfer device 3 Mixing device 4 Pump 5 Dry methane fermentation tank 10 Boiler 11, 12, 13 Pipe for steam

Claims (8)

In a method for methane fermentation treatment of a mixture of biodegradable plastic and organic waste,
A melting step of melting at least a portion of the biodegradable plastic in the mixture by heating the mixture in contact with water vapor;
Next, a methane fermentation treatment process for treating the mixture with methane fermentation,
A methane fermentation treatment method characterized by comprising:   2. The methane fermentation treatment method according to claim 1, wherein a part of the methane fermentation treatment product from the methane fermentation treatment step is added to the mixture in the melting step.   3. The methane fermentation treatment method according to claim 1, wherein the biodegradable plastic and the organic waste are crushed and then supplied to the melting step. In any 1 item | term of the Claims 1 thru | or 3, the temperature of the said water vapor | steam is 70-120 degreeC,
A method for methane fermentation treatment, characterized in that the temperature of the object to be treated supplied to the methane fermentation process is higher than the temperature in the methane fermentation process.   The methane fermentation treatment method according to any one of claims 1 to 4, wherein a melting time in the melting step is 3 to 60 minutes. Melting means for bringing the mixture of the biodegradable plastic and the organic waste into contact with water vapor to melt at least a part of the biodegradable plastic;
Water vapor supply means for supplying water vapor to the melting means;
A methane fermentation treatment apparatus comprising a methane fermentation tank that receives a mixture from the melting means and performs methane fermentation treatment.   The methane fermentation treatment apparatus according to claim 6, further comprising means for adding a part of the processed product of the methane fermentation tank to the melting means.   The methane fermentation according to claim 6 or 7, further comprising a crushing means for crushing the biodegradable plastic and the organic waste, and configured to supply the crushed material in the crushing means to the melting means. Processing equipment.

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