JP2005144262A - Methane fermentation method of solid organic waste containing foreign matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation method of a solid organic waste containing foreign matter, which method recovers a methane gas as desired while achieving the reduction of cost, such as initial cost and running cost, and the enlargement of an objective range. <P>SOLUTION: In this method, the TS (total) concentration in a methane fermentation vessel 2 into which a solid organic waste containing foreign matters is introduced is set at a prescribed TS concentration causing no separation/deposition of foreign matters from digested sludge; thus a prescribed effective fermentation-vessel volume is ensured and methane fermentation is performed under sufficient agitation in the vessel without enhancing the accuracy of separation/screening of the solid organic waste and the foreign matters at the former step and without selecting a solid organic waste having a low foreign matter content. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for recovering methane gas by subjecting solid organic waste containing impurities to methane fermentation treatment in a methane fermentation tank.

Conventionally, as a method of effectively using solid organic waste, the collected combustible waste is crushed by a crushing device, and the crushed combustible waste is separated by a separation / separation device to produce garbage (solid organic waste) and other impurities. There is known a method of separating and sorting into garbage, treating the separated and sorted garbage with methane fermentation in a methane fermentation tank, and collecting methane gas (see, for example, Patent Document 1).
JP 2002-166248 A

  However, in the separated and sorted garbage, in reality, foreign matters such as plastic pieces, which are contaminants, and solid organic substances having a low decomposition rate such as cork stoppers, chopsticks, and pruning branches remain at a predetermined ratio. For this reason, in the methane fermentation tank, even if the stirring strength is increased, foreign matters such as the above plastic pieces are separated from the digested sludge, and solid organic substances having a low decomposition rate such as corks, chopsticks and pruned branches Is separated from digested sludge in an undegraded state, and these contaminants accumulate on the liquid surface as scum or accumulate on the inner wall of the tank, resulting in a decrease in effective fermenter volume and insufficient agitation in the tank. Thus, there is a problem that methane gas cannot be recovered as desired.

  Here, in order to solve such a problem, it is conceivable to thoroughly separate and sort garbage and garbage by the separation and sorting device, but the initial cost and running cost become high. Further, in order to eliminate such an increase in initial cost and running cost, it is necessary to target garbage with a low contamination rate, and the target is limited.

  The present invention has been made to solve such a problem, and provides a method for recovering methane gas as desired while suppressing increase in costs such as initial cost and running cost and expanding the target range. For the purpose.

  The method of methane fermentation of solid organic waste containing impurities according to the present invention is a method of performing methane fermentation treatment of solid organic waste containing impurities in a methane fermenter and recovering methane gas. Solid: the total solid content) concentration is set to a predetermined TS concentration at which impurities do not separate and accumulate on the digested sludge.

  According to the method for methane fermentation of solid organic waste containing such impurities, the TS concentration of the methane fermenter is set to a predetermined TS concentration, whereby impurities are separated and deposited from the digested sludge. That is lost. Therefore, a certain effective fermenter volume can be secured without increasing the accuracy of separation and sorting of solid organic waste and contaminants in the previous stage and without selecting solid organic waste with a low contamination rate. At the same time, the inside of the tank is sufficiently stirred to perform methane fermentation.

  Here, as a specific method of setting the TS concentration of the methane fermenter to a predetermined TS concentration, solid organic waste containing impurities is mixed with moisture in the previous stage of the methane fermenter, and the mixture is put into the methane fermenter. There is a method of providing a mixing tank to be supplied and setting the amount of water supply to the mixing tank so that the TS concentration of the methane fermentation tank becomes a predetermined TS concentration.

  In addition, as another specific method for setting the TS concentration of the methane fermentation tank to a predetermined TS concentration, solid organic waste containing impurities is mixed with moisture in the previous stage of the methane fermentation tank, and the mixture is mixed with the methane fermentation tank. And a method of returning the digested sludge of the methane fermentation tank to the mixing tank.

  Here, according to experiments by the present inventors, when the predetermined TS concentration is 7 to 20%, separation of contaminants from digested sludge is effectively prevented.

  As described above, according to the method for methane fermentation of solid organic waste containing contaminants according to the present invention, the solid organic waste and contaminants can be solidified without increasing the accuracy of separation and sorting of the solid organic waste and contaminants. Without selecting organic waste, a certain effective fermenter volume is secured and the inside of the tank is sufficiently stirred to perform methane fermentation, so that the initial cost and running cost are prevented from increasing and the target range It is possible to recover methane gas as desired while expanding the range.

  Hereinafter, a preferred embodiment of a method for methane fermentation of solid organic waste containing impurities according to the present invention will be described with reference to FIG. FIG. 1 is a block configuration diagram showing a methane fermentation treatment system adopting a methane fermentation method for solid organic waste containing impurities according to an embodiment of the present invention.

  The system of this embodiment separates and sorts garbage, which is solid organic waste, from combustible waste carried from a garbage truck, and collects methane gas by subjecting this raw garbage to methane fermentation treatment, and pretreatment. The apparatus 1 and the methane fermentation tank 2 are provided.

  The pretreatment device 1 breaks the combustible waste that has been packed into the bag with the bag breaking device 1a, crushes the broken bag to a predetermined size or less with the crushing device 1b, and uses the crushed material as a separation and sorting device. For example, a garbage such as a trommel and a wind sorting device 1c are used to separate and sort the garbage into other garbage, and the separated and sorted food waste is introduced into the mixing tank 1d. The water and steam supplied through the supply water line L are stirred and mixed, and the food waste is acid-fermented and conditioned to a predetermined degree and precipitates and removes extraneous extraneous matter. Supply.

  The methane fermentation tank 2 is a liquid which circulates the mixture from the mixing tank 1d, for example, mechanical stirring, or gas stirring by installing a draft pipe in the center of the tank and supplying gas to the draft pipe. The mixture is stirred with a predetermined stirring force for a predetermined period by stirring or the like, and is subjected to methane fermentation.

  And the digested sludge of this methane fermentation tank 2 is extracted from the bottom part of the said methane fermentation tank 2, and is used for a predetermined sludge process or a predetermined sludge utilization equipment, On the other hand, the biogas discharged | emitted from the upper part of the methane fermentation tank 2 The (methane gas and carbon dioxide mixed gas) is separated and purified at a later stage and used as, for example, a fuel for a natural gas vehicle.

  By the way, the garbage separated and sorted by the separation and sorting apparatus 1c is actually contaminated with foreign matters such as plastic pieces and solid organic substances with low decomposition rate such as corks, chopsticks and pruned branches at a predetermined ratio. Remaining. Therefore, garbage containing foreign substances and solid organic matter having a low decomposition rate are introduced into the methane fermentation tank 2.

  Therefore, in the present embodiment, the TS (Total Solid) concentration of the methane fermentation tank 2 is a predetermined TS concentration at which impurities introduced into the methane fermentation tank 2 are not separated and deposited on the digested sludge. Is set to This predetermined TS concentration is set to 7 to 20% in this embodiment. Specifically, the TS concentration of the methane fermentation tank 2 is set to the predetermined TS concentration by adjusting the amount of water supplied from the supply water line L to the mixing tank 1d. Various other methods for setting the TS concentration of the methane fermentation tank 2 to a predetermined TS concentration are conceivable. For example, there is a method of returning the digested sludge of the methane fermentation tank 2 to the mixing tank 1d.

  In this embodiment, since the TS concentration of the methane fermenter 2 is set to the predetermined TS concentration, in the methane fermenter 2, impurities (plastic pieces) Such as foreign substances such as cork stoppers, disposable chopsticks, pruned branches, etc.) are separated and deposited. This is thought to be because, by setting the TS concentration of the methane fermentation tank 2 to the above-mentioned predetermined TS concentration, the viscosity of the sludge increases and the solid content is entrained, making it difficult to separate.

  Therefore, it is possible to select the garbage with a low contamination rate without increasing the accuracy of separating and sorting the garbage and foreign substances in the previous stage (without making the separation and sorting device 1c an apparatus with higher sorting ability). Without allowing (mixing the foreign matter and solid organic matter having a low decomposition rate into the garbage), a predetermined effective fermenter volume is secured and the inside of the tank is sufficiently stirred to perform methane fermentation. As a result, it is possible to recover methane gas as desired while suppressing increase in costs such as initial cost and running cost and expanding the target range.

  According to the experiments by the present inventors, it was confirmed that separation of impurities from digested sludge can be effectively prevented by setting the predetermined TS concentration to 7 to 20% as described above. Incidentally, the TS concentration of the conventional methane fermenter is generally about 3 to 5%, and at such a low TS concentration, foreign matters such as plastic pieces are separated from the digested sludge. The solid organic matter with a low decomposition rate such as pruned branches is separated from the digested sludge in an undecomposed state, and these contaminants accumulate on the liquid surface as scum or ring along the inner peripheral wall of the tank. Will be deposited.

  As described above, the present invention has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment. For example, in the above embodiment, the food waste is acid-fermented and conditioned in a predetermined manner. In addition, in order to precipitate and remove heavy foreign substances, garbage containing foreign substances is introduced into the mixing tank 1d. However, it is also possible to directly supply the methane fermentation tank 2 without passing through the mixing tank 1d. . In this case, for example, water may be supplied to the methane fermentation tank 2 to adjust the amount of supplied water so that the TS concentration of the methane fermentation tank 2 becomes the predetermined TS concentration.

  Moreover, in the said embodiment, although it is effective, solid organic waste is made into garbage, However For example, it is applicable also to solid organic waste, such as a sewage sludge.

It is a block block diagram which shows the methane fermentation processing system which employ | adopted the methane fermentation method of the solid organic waste containing impurities based on embodiment of this invention.

Explanation of symbols

  2 ... Methane fermenter, L ... Supply water line.

Claims (4)

In a method of recovering methane gas by subjecting solid organic waste containing impurities to methane fermentation treatment in a methane fermentation tank,
A method for methane fermentation of solid organic waste containing contaminants, wherein the TS concentration of the methane fermentation tank is set to a predetermined TS concentration at which the contaminants are not separated and deposited with respect to digested sludge. In the front stage of the methane fermentation tank, a mixing tank is provided that mixes solid organic waste containing the impurities with moisture and supplies the mixture to the methane fermentation tank.
The methane fermentation of solid organic waste containing impurities according to claim 1, wherein the amount of water supply to the mixing tank is set so that the TS concentration of the methane fermentation tank becomes the predetermined TS concentration. Method. In the front stage of the methane fermentation tank, a mixing tank is provided that mixes solid organic waste containing the impurities with moisture and supplies the mixture to the methane fermentation tank.
The method for methane fermentation of solid organic waste containing impurities according to claim 1, wherein the digested sludge of the methane fermentation tank is returned to the mixing tank.   The said predetermined | prescribed TS density | concentration was 7 to 20%, The methane fermentation method of the solid organic waste containing the contaminant as described in any one of Claims 1-3 characterized by the above-mentioned.

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