JP3600566B2 - Method for treating organic waste and method for producing biogas - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating an organic waste containing a hardly decomposable component, and more specifically, an organic material having a high concentration of nitrogen and high chromaticity, such as human waste, septic tank sludge, livestock manure, food industry wastewater such as fishery processing. The present invention relates to a method for treating toxic waste and a method for producing biogas.
[0002]
[Prior art]
Sludges such as human waste sludge and sewage sludge in organic waste generally have a lower decomposition rate of organic substances than kitchen garbage or the like, and thus have a problem in that the amount of gas generated by methane fermentation is low. Therefore, as a treatment of organic waste, first, as shown in FIG. 4, the organic waste 1 is subjected to removal of impurities in a pretreatment step 10, and then an ozone generator 30 is used in an ozone oxidation step 30. A method has been proposed in which ozone is introduced from 32 to solubilize the organic waste 1 and further subjected to methane fermentation with anaerobic bacteria in the methane fermentation step 20 for treatment. Digested sludge 21 and biogas 31 are obtained by methane fermentation. In general, digested sludge 21 is separated into dehydrated sludge 51 and separated liquid 61 in solid-liquid separation step 40, and separated liquid 61 is further drained from biological treatment or the like. It is treated in the treatment step 50 and discharged as treated water 71. On the other hand, the biogas 31 is sent to the gas storage tank 22 or the like in order to use it for power generation or the like. Thus, the efficiency of methane fermentation can be improved by solubilizing the organic matter before the methane fermentation.
However, when ozone is blown in the preceding stage of methane fermentation as described above, a substance that easily decomposes reacts with ozone, so that there is a problem that a large amount of ozone is required to solubilize a hardly decomposable substance.
[0003]
[Problems to be solved by the invention]
In view of the above problems, the present invention can selectively solubilize hardly decomposable substances that are difficult to decompose in methane fermentation, thereby making it possible to economically increase the ozone addition rate in ozone oxidation. It is an object of the present invention to provide a method for treating organic waste and a method for producing biogas, which can improve the decomposition efficiency in methane fermentation and can also increase the rate of biogas generation.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, a method for treating organic waste according to the present invention includes a methane fermentation step of methane fermenting organic waste to obtain digested sludge and biogas, and oxidizing the digested sludge with ozone. An ozone oxidation step of obtaining solubilized sludge, and a solid-liquid separation step of solid-liquid separation of the solubilized sludge to obtain a dehydrated sludge and a separated liquid, wherein a part of the solubilized sludge is subjected to the methane fermentation step. It is characterized by being returned to. In this method, a part of the dewatered sludge can be returned to the methane fermentation step.
In this way, after methane fermentation of substances that are originally decomposable, solubilizing substances are solubilized by ozone oxidation, and methane fermentation is performed again. Thus, the solubilization can be selectively performed, the decomposition efficiency of methane fermentation can be improved, and the generation rate of biogas can be improved.
[0006]
Further, the method for treating organic waste according to the present invention includes a methane fermentation step of subjecting organic waste to methane fermentation to obtain digested sludge and biogas, and oxidizing the digested sludge with ozone to obtain a solubilized sludge. An ozone oxidation step, comprising a solid-liquid separation step of solid-liquid separation of the solubilized sludge to obtain a dehydrated sludge and a separated liquid, wherein a part of the dehydrated sludge is returned to the methane fermentation step. I do.
[0007]
The method for treating organic waste described above may further include a wastewater treatment step of treating the separated liquid with wastewater to obtain treated water.
The present invention is also a method for producing biogas, characterized by using the above-mentioned method for treating organic waste.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
First Embodiment FIG. 1 is a schematic view showing one embodiment of a method for treating organic waste according to the present invention. As shown in FIG. 1, the present embodiment has a pretreatment step 10 for removing impurities from the organic waste 1, a digestion sludge 2 and a biogas 3 by methane fermentation of the organic waste 1. Fermentation step 20 for obtaining liquefied sludge 4; ozone oxidation step 30 for oxidizing digested sludge 2 with ozone to obtain solubilized sludge 4; solid-liquid separation of solubilized sludge 4 to obtain dehydrated sludge 5 and separated liquid 6 The method includes a separation step 40 and a wastewater treatment step 50 of treating the separated liquid 6 with wastewater to obtain treated water 7. Then, a part of the solubilized sludge 4 is returned to the methane fermentation step 20 by a pump or the like.
[0009]
In the pretreatment step 10, a means combining a foreign matter removing device such as a screen or a centrifugal separator with a dehydrating device such as a screw press can be used to remove foreign matter.
As the methane fermentation step 20, an organic substance can be CO ₂ reduced and acetic acid decomposed by an anaerobic methane-producing bacterium to use a methane fermentation tank that produces methane. Further, a gas storage tank 22 for temporarily storing the biogas 3 containing the generated methane is provided.
As the ozone oxidation step 30, an ozone reaction tank into which ozone generated by the ozone generator 32 is introduced from the bottom can be used. Ozone can be efficiently brought into contact with the digested sludge 2 by introducing it as bubbles using a diffuser plate or a diffuser tube. An oxidizing agent such as hydrogen peroxide (H ₂ O ₂ ) can be added to promote solubilization.
The solid-liquid separation step 40 includes mechanical separation such as centrifugation, membrane separation such as ultrafiltration (UF) and microfiltration (MF), and the accumulation of colloids and ultrafine particles on a porous support. For example, a dynamic filtration utilizing the above method can be used.
As the wastewater treatment step 50, biological denitrification treatment for removing BOD, nitrogen, COD, phosphorus, chromaticity, and the like can be used.
[0010]
According to such a configuration, first, the organic waste 1 is introduced into the methane fermentation step after impurities are removed in the pretreatment step 10. In the methane fermentation step 20, the organic waste 1 is mixed with a solubilized sludge 4, which will be described later, returned from the ozone oxidation step 30, and the methane-producing bacteria perform the methane fermentation treatment. The digested sludge 2 containing the hardly decomposable substance is sent to the ozone oxidation step 30, while the biogas 3 containing methane generated by methane fermentation is sent to the gas storage tank 22.
Here, if an aeration tank is installed between the methane fermentation step 20 and the ozone oxidation step 30, the BOD in the digested sludge 2 will decrease, leading to a reduction in the amount of biogas 2 obtained as a result. Therefore, it is not preferable. Further, the installation of the aeration tank is not preferable because it requires an increase in equipment and aeration power.
[0011]
In the ozone oxidation step 30, the hardly decomposable substance in the digested sludge 2 that has not been decomposed by the methane fermentation treatment is oxidatively decomposed by contact with ozone, and is reformed to be easily biodegradable. At this time, the supply amount of ozone is about 3 to 7 mg / kgts, which can sufficiently solubilize the hardly decomposable substance, and particularly preferably about 5 mg / kgts. The solubilized sludge 4 obtained by this ozone oxidation is returned to the methane fermentation step 20 again, and the biodegradable substance is digested and decomposed by methane fermentation.
[0012]
As described above, by providing the methane fermentation step 20 before the ozone oxidation step 30, since the biodegradable substance is digested and decomposed in advance, the hardly decomposable substance can be selectively solubilized, and the ozone addition rate can be increased. Can be economical. In addition, by returning the solubilized sludge 4 obtained in the ozone oxidation step 30 to the methane fermentation step 20, it becomes possible to digest and decompose the hardly decomposable substances in the organic waste 1, and to generate the biogas 3 And the gas generation rate can be improved. That is, the recycling of the organic waste 1 can be promoted. Further, the ozone oxidation step 30 enables the decomposition of the chromaticity component contained in the organic waste 1 which is difficult to decompose, so that the load of the post-process wastewater treatment step 50 can be reduced. Usually, a part of the solubilized sludge 4 is returned to the methane fermentation step 20. Thereby, the hardly decomposable substance in the waste can be efficiently digested and decomposed in the methane fermentation step 20.
[0013]
A part of the solubilized sludge 4 is sent to a solid-liquid separation step 40. In the solid-liquid separation step 40, the dewatered sludge 5 and the separated liquid 6 are separated, and the dewatered sludge 5 is appropriately treated by incineration or composting. Further, the separated liquid 6 is sent to a wastewater treatment step 50, subjected to a denitrification treatment, and then discharged as treated water 7.
Here, when the digested sludge 2 after the methane fermentation step 20 is to be treated in the wastewater treatment step 50, the carbon content (C) in the liquid tends to be insufficient, and the denitrification treatment does not proceed well or is unstable. Easy to be. Therefore, in some cases, it was necessary to supply a C component such as methanol. In the present embodiment, by introducing the solubilized sludge 4 after the ozone oxidation step 30 to the wastewater treatment step 50, the denitrification treatment can be performed in a state where the C / N ratio is well balanced. The C / N ratio is also important, but generally has about 3 or more.
[0014]
Reference Embodiment FIG. 2 is a schematic view showing one reference embodiment of a method for treating organic waste . The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 2, this embodiment includes a pretreatment step 10, a methane fermentation step 20, an ozone oxidation step 30, a solid-liquid separation step 40, and a wastewater treatment step 50, as in FIG. Become. However, all the solubilized sludge 4 is returned to the methane fermentation step 20, and a part of the digested sludge 2 is introduced to the solid-liquid separation step 20.
[0015]
According to such a configuration, first, the organic waste 1 is introduced into the methane fermentation step after impurities are removed in the pretreatment step 10. In the methane fermentation step 20, the organic waste 1 and the solubilized sludge 4 returned from the ozone oxidation step 30 are mixed, and the methane-producing bacteria perform the methane fermentation treatment. Then, the digested sludge 2 containing the hardly decomposable substance is sent to the ozone oxidation step 30, and the biogas 3 containing methane generated by methane fermentation is sent to the gas storage tank 22.
In the ozone oxidation step 30, the hardly decomposable substance in the digested sludge 2 that has not been decomposed by the methane fermentation treatment is oxidatively decomposed by contact with ozone, and is reformed to be easily biodegradable. All the solubilized sludge 4 obtained by this ozone oxidation is returned to the methane fermentation step 20 again, and the biodegradable substance is digested and decomposed by methane fermentation. A part of the digested sludge 2 is sent to a solid-liquid separation step 40. Usually, the digested sludge 2 is sent to the solid-liquid separation step 40. Thereby, the sludge sufficiently digested and decomposed by the circulation of the methane fermentation step 20 and the ozone oxidation step 30 is sent to the solid-liquid separation step 40. In the solid-liquid separation step 40, the dewatered sludge 5 and the separated liquid 6 are separated, and the dewatered sludge 5 is appropriately treated by incineration or composting. Further, the separated liquid 6 is sent to a wastewater treatment step 50, subjected to a denitrification treatment, and then discharged as treated water 7.
[0016]
As described above, also in this embodiment , the biodegradable substance is digested and decomposed in advance, as described above, so that the hardly decomposable substance can be selectively solubilized in the ozone oxidation step 30, and the ozone addition rate can be reduced. Can be economical. In addition, by returning the solubilized sludge 4 obtained in the ozone oxidation step 30 to the methane fermentation step 40, it becomes possible to digest and decompose hardly decomposable substances in the organic waste 1, and to generate the biogas 3 Can also be improved. Further, the ozone oxidation step 30 enables the decomposition of the chromaticity component contained in the organic waste 1 which is difficult to decompose, so that the load of the post-process wastewater treatment step 50 can be reduced.
[0017]
Here, the dewatered sludge 5 can be returned to the methane fermentation step 20. Thereby, the solid matter concentration in the methane fermentation tank can be kept high, and the generation rate of biogas 3 in methane fermentation can be improved.
[0018]
Second Embodiment FIG. 3 is a schematic view showing one embodiment of a method for treating organic waste according to the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 3, in the present embodiment, as in FIG. 1, a pretreatment step 10, a methane fermentation step 20, an ozone oxidation step 30, a solid-liquid separation step 40, and a wastewater treatment step 50 are performed. Comprising. However, it is configured that only a part of the dewatered sludge 5 is returned to the methane fermentation step 20.
[0019]
According to such a configuration, first, the organic waste 1 is introduced into the methane fermentation step after impurities are removed in the pretreatment step 10. In the methane fermentation step 20, the organic waste 1 and the dewatered sludge 5 returned from the solid-liquid separation step 40 are mixed, and the methane-producing bacteria perform methane fermentation. Then, the digested sludge 2 containing the hardly decomposable substance is sent to the ozone oxidation step 30, and the biogas 3 containing methane generated by methane fermentation is sent to the gas storage tank 22.
In the ozone oxidation step 30, the hardly decomposable substance in the digested sludge 2 that has not been decomposed by the methane fermentation treatment is oxidatively decomposed by contacting with ozone, and is reformed to be easily biodegradable. All the solubilized sludge 4 obtained by the ozone oxidation is sent to the solid-liquid separation step 40. In the solid-liquid separation step 40, the dewatered sludge 5 and the separated liquid 6 are separated, and a part of the dewatered sludge 5 is returned to the methane fermentation step 20. A part of the dewatered sludge 5 is appropriately treated by incineration or composting. On the other hand, the separated liquid 6 is sent to a wastewater treatment step 50, subjected to a denitrification treatment, and discharged as treated water 7.
[0020]
Thus, also in this embodiment, since the biodegradable substance is digested and decomposed in advance, the hardly decomposable substance can be selectively solubilized in the ozone oxidation step 30, and the ozone addition rate can be reduced economically. can do. In addition, the solubilized sludge 4 obtained in the ozone oxidation step 30 returns only the dehydrated sludge 5 that has passed through the solid-liquid separation step 40 to the methane fermentation step 40, so that the insoluble substances in the organic waste 1 can be reduced. Digestion and decomposition can be performed, and the solid matter concentration in the methane fermentation tank can be maintained at a high concentration. Therefore, the generation rate of biogas 3 can be improved. Furthermore, the ozone oxidation step 30 also enables the decomposition of chromaticity components contained in the organic waste 1 that are difficult to decompose, so that the load of the wastewater treatment step 50 in the subsequent step can be reduced.
[0021]
Further, as another embodiment, the configurations shown in FIGS. 1 and 3 can be provided simultaneously. By returning the solubilized sludge 4 after the ozone oxidation step 30 and the dehydrated sludge 5 after the solid-liquid separation step 40 to the methane fermentation step 20, the amount of biogas 3 generated in the methane fermentation can be increased, The gas generation rate can be improved.
[0022]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to selectively solubilize hardly decomposable substances that are hardly decomposed in methane fermentation, thereby economically reducing the ozone addition rate in ozone oxidation. The present invention can provide a method for treating organic waste and a method for producing biogas, which can improve the decomposition efficiency in methane fermentation and can also increase the generation rate of biogas.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of a method for treating organic waste according to the present invention.
FIG. 2 is a schematic view showing one embodiment of a method for treating organic waste .
FIG. 3 is a schematic diagram showing an embodiment of a method for treating organic waste according to the present invention.
FIG. 4 is a schematic diagram showing a conventional method for treating organic waste.
[Explanation of symbols]
Reference Signs List 1 organic waste 2 digested sludge 3 biogas 4 solubilized sludge 5 dehydrated sludge 6 separated solution 7 treated water 10 pretreatment step 20 methane fermentation step 22 gas storage tank 30 ozone oxidation step 32 ozone generator 40 solid-liquid separation step 50 Wastewater treatment process

Claims (5)

Methane fermentation of organic waste to obtain digested sludge and biogas by methane fermentation; ozone oxidation step of oxidizing the digested sludge with ozone to obtain solubilized sludge; and solid-liquid separation of the solubilized sludge. A method for treating organic waste, comprising a dewatered sludge and a solid-liquid separation step of obtaining a separated liquid, wherein a part of the solubilized sludge is returned to the methane fermentation step. Processing method according to claim 1 organic waste, wherein the return portions of the dewatered sludge in the methane fermentation step. Methane fermentation of organic waste to obtain digested sludge and biogas by methane fermentation; ozone oxidation step of oxidizing the digested sludge with ozone to obtain solubilized sludge; and solid-liquid separation of the solubilized sludge. A method for treating organic waste, comprising a dewatered sludge and a solid-liquid separation step of obtaining a separated liquid, wherein a part of the dewatered sludge is returned to the methane fermentation step. The method for treating organic waste according to any one of claims 1 to 3 , further comprising a wastewater treatment step of treating the separated liquid with wastewater to obtain treated water. Method for producing biogas, characterized in that it uses a method of processing organic waste according to any one of claims 1-3.

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